Surface charging and points of zero charge

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2009 by Taylor and Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number: 978-1-4200-5188-9 (Hardback) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright. com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Kosmulski, Marek, 1956Surface charging and points of zero charge / Marek Kosmulski. p. cm. -- (Surfactant science series ; 145) Includes bibliographical references and index. ISBN 978-1-4200-5188-9 (hard back : alk. paper) 1. Points of zero charge. 2. Surface energy. 3. Volumetric analysis. I. Title. II. Series. QD571.K787 2009 541’. 335 --dc22 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

2009012179

To my wife

Contents Preface ......................................................................................................... xxiii Acknowledgments ..................................................................................... xxvii Chapter 1

Introduction ................................................................................. 1 1.1 1.2 1.3 1.4 1.5

Nomenclature .................................................................... 8 Scope ............................................................................... 10 Inert Electrolytes ............................................................. 12 The Significance of Parks’ Review ................................. 15 Structure of Adsorbents .................................................. 17 1.5.1 Alumina ........................................................... 17 1.5.2 Iron (Hydr)oxides ............................................. 19 1.5.3 Magnanese Oxides ........................................... 20 1.5.4 Silica ................................................................ 20 1.5.5 Titania .............................................................. 20 1.5.6 Clay Minerals .................................................. 20 1.5.7 Nitrides ............................................................ 21 1.6 Solubility ......................................................................... 21 1.6.1 Simple (Hydr)oxides ........................................ 21 1.6.2 Other Materials ................................................ 23 1.7 Solid Phase Transformation at Room Temperature in Contact with Solution ................................................. 24 1.7.1 Alumina ........................................................... 25 1.7.2 CdO .................................................................. 25 1.7.3 CuO .................................................................. 25 1.7.4 Iron (Hydr)oxides ............................................. 25 1.7.5 Other Systems .................................................. 25 1.8 Solid Phase Transformation on Heating ......................... 26 1.9 Kinetics ........................................................................... 26 1.9.1 Proton Adsorption ............................................ 27 1.9.2 Isotope Exchange ............................................. 28 1.9.3 Dissolution ....................................................... 29 1.10 Solution Chemistry—pH Scale ....................................... 30 1.10.1 Problem 1: Concentration versus Activity ....... 32 1.10.2 Problem 2: Experiments at Constant Ionic Strengths ................................................. 32 xiii

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1.10.3 Problem 3: Buffered versus Unbuffered System ... 1.10.4 Problem 4: Sodium Effect ................................ 1.10.5 Problem 5: Suspension Effect .......................... 1.10.6 Problem 6: Different pH Scales ....................... 1.10.7 Problem 7: Electrolysis .................................... 1.11 Very Dilute Solutions ...................................................... 1.12 Speciation in Solution ..................................................... Chapter 2

33 33 33 34 34 34 36

Methods ..................................................................................... 39 2.1

2.2 2.3

2.4

2.5

2.6

Experimental Setup in Electrokinetic Measurements ...... 2.1.1 Electrophoresis ................................................ 2.1.2 Electro-Osmosis ............................................... 2.1.3 Streaming Potential ......................................... 2.1.4 Sedimentation Potential ................................... 2.1.5 Electroacoustic Methods .................................. Experimental Conditions in Electrokinetic Measurements ................................................................. CO2 and Silica Problem .................................................. 2.3.1 The CO2 Problem ............................................. 2.3.2 The Silica Problem .......................................... Experimental Results: z Potential ................................... 2.4.1 Shapes of Individual Electrokinetic Curves .............................................................. 2.4.2 Position of IEP ................................................. 2.4.3 Aging and Hysteresis ....................................... 2.4.4 Effect of Ionic Strength on the Numerical Value of the z Potential .................................... 2.4.5 Effect of the Nature of the Salt on the Numerical Values of the z Potential ................ Experimental Conditions: Titration ................................ 2.5.1 The Choice of an Inert Electrolyte and the Range of Ionic Strengths ........................... 2.5.2 Solid-to-Liquid Ratio ....................................... 2.5.3 Other Titration Parameters .............................. Results: Titration ............................................................. 2.6.1 Presence or Absence of CIP ............................ 2.6.2 Reproducibility and Reversibility .................... 2.6.3 Shape of Charging Curves and Typical Values of s0 ...................................................... 2.6.4 Effect of Ionic Strength on Charging Curves .............................................................. 2.6.5 Effect of the Nature of the Salt on Numerical Values of s0 .................................... 2.6.6 Surface Charging of Materials Other than Metal Oxides ...........................................

41 41 46 47 48 48 51 55 55 57 59 60 61 61 62 65 66 71 72 72 74 74 76 77 79 79 80

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2.7 2.8

2.9

Chapter 3

Relation of Results Obtained by Different Methods .......................................................................... Other Methods ................................................................ 2.8.1 Methods Involving Nonaqueous Solvents ....... 2.8.2 Electrical Methods ........................................... 2.8.3 Sum Frequency Generation and SecondHarmonic Generation ...................................... 2.8.4 Methods Equivalent to Titration ...................... 2.8.5 Force between Particles ................................... 2.8.6 Nonstandard Methods ...................................... Adsorption Models .......................................................... 2.9.1 Density of Protonable Surface Groups ............ 2.9.2 Electrostatic Models ........................................ 2.9.3 Surface Acidity ................................................

80 81 81 81 82 82 87 88 89 89 92 96

Compilation of PZCs/IEPs ....................................................... 101 3.1

Simple Oxides ................................................................ 3.1.1 Aluminum (Hydr)oxides ................................. 3.1.2 Beryllium (Hydr)oxides ................................. 3.1.3 Bi2O3 .............................................................. 3.1.4 Ca(OH)2 ......................................................... 3.1.5 Cadmium (Hydr)oxides ................................. 3.1.6 Cerium (Hydr)oxides ..................................... 3.1.7 Cobalt (Hydr)oxides ....................................... 3.1.8 Chromium (Hydr)oxides ................................ 3.1.9 Copper (Hydr)oxides ....................................... 3.1.10 Dy2O3 ............................................................. 3.1.11 Er2O3 .............................................................. 3.1.12 Iron (Hydr)oxides ........................................... 3.1.13 GeO2 .............................................................. 3.1.14 Ga2O3 ............................................................. 3.1.15 HfO2 ............................................................... 3.1.16 HgO ................................................................ 3.1.17 Indium (Hydr)oxides ...................................... 3.1.18 IrO2 ................................................................ 3.1.19 Hydroxides of Lanthanides ............................ 3.1.20 La2O3 .............................................................. 3.1.21 Magnesium (Hydr)oxides .............................. 3.1.22 Manganese (Hydr)oxides ............................... 3.1.23 Niobium (Hydr)oxides ................................... 3.1.24 Neodymium (Hydr)oxides ............................. 3.1.25 Nickel (Hydr)oxides ....................................... 3.1.26 Lead (Hydr)oxides ......................................... 3.1.27 PdO ................................................................ 3.1.28 Praseodymium (Hydr)oxides .........................

101 101 193 194 195 195 197 202 207 216 221 221 221 321 321 322 323 323 326 327 328 329 333 353 356 357 364 367 367

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3.2

3.1.29 PtO2 ................................................................ 3.1.30 PuO2 ............................................................... 3.1.31 Ruthenium (Hydr)oxides ................................ 3.1.32 Sb2O5 .............................................................. 3.1.33 Sc2O3 .............................................................. 3.1.34 Samarium (Hydr)oxides ................................. 3.1.35 Silica .............................................................. 3.1.36 Tin (Hydr)oxides ............................................. 3.1.37 Tantalum (Hydr)oxides .................................. 3.1.38 Thorium (Hydr)oxides ................................... 3.1.39 Titanium (Hydr)oxides ................................... 3.1.40 Tl2O3 .............................................................. 3.1.41 Uranium (Hydr)oxides ................................... 3.1.42 Vanadium (Hydr)oxides ................................. 3.1.43 Tungsten (Hydr)oxides ................................... 3.1.44 Y2O3 ............................................................... 3.1.45 Yb2O3 .............................................................. 3.1.46 Zinc (Hydr)oxides ........................................... 3.1.47 Zirconium (Hydr)oxides ................................ Aluminosilicates, Phyllosilicates, Clays, and Clay Minerals ................................................................ 3.2.1 Adularia ......................................................... 3.2.2 Amelia Albite from Wards ............................ 3.2.3 (Ca,Fe)2(Ln,Al,Fe)3Si3O12OH, Allanite (orthite) from Kabuland, Norway .................. 3.2.4 Amphiboles .................................................... 3.2.5 Andalusite ...................................................... 3.2.6 Andesine ........................................................ 3.2.7 Anorthite ........................................................ 3.2.8 Anorthoclase .................................................. 3.2.9 Anthophyllite ................................................. 3.2.10 Augite, (Al,Ca,Fe,Mg,Ti)2(Al,Si)2O6 .............. 3.2.11 Beidellite, SBCa-1 .......................................... 3.2.12 Bentonite ........................................................ 3.2.13 Be3Al2Si6O18 Beryl from Hoggar, Algeria ..... 3.2.14 Biotite K(Mg,Fe,Mn)3(OH,F)2 (Al,Fe,Ti)Si3O10 .............................................. 3.2.15 Blazer from Huber Na2O · Al2O3 · 2.8 SiO2 · 7 H2O .............................................. 3.2.16 Bronzite from Kraubath .................................. 3.2.17 Bytownite ........................................................ 3.2.18 Chlorite (Mg,Al,Fe)12(Al,Si)8O20(OH)16 .......... 3.2.19 Cleavelandite .................................................. 3.2.20 Clinochlore ....................................................

368 369 369 373 373 373 374 431 440 443 445 502 503 506 507 508 513 514 524 548 548 548 548 548 549 549 549 549 549 549 550 550 550 550 551 551 551 551 552 552

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3.2.21 3.2.22 3.2.23 3.2.24 3.2.25 3.2.26 3.2.27 3.2.28 3.2.29 3.2.30 3.2.31 3.2.32 3.2.33 3.2.34 3.2.35 3.2.36 3.2.37 3.2.38 3.2.39 3.2.40 3.2.41 3.2.42 3.2.43 3.2.44 3.2.45 3.2.46 3.2.47 3.2.48 3.2.49 3.2.50 3.2.51 3.2.52 3.2.53 3.2.54 3.2.55

Clinoptilolite, Zeolite, Unit Cell: Na6(AlO2)6(SiO2)30 · 24H2O ........................... Clinozoisite from Kirchham .......................... Cordierite 2MgO · 2Al2O3 · 5SiO2 ................. Ca2(Fe,Al)Al2[O/OH/SiO4/Si2O7] Epidote from Knappenwand .......................... Feldspar .......................................................... Garnets ........................................................... Halloysite-7Å ................................................. Hornblende ..................................................... Illite ................................................................ Kaolinite and Kaolin Si2Al2O5(OH)4 ............. Labradorite ..................................................... Laponite Na0.8Mg5.4Li0.4Si8O20(OH)4 from Laporte .................................................. Mica ............................................................... Microcline ...................................................... Montmorillonite ............................................. Montmorillonite–Alumina Composite .......... Mordenite (Synthetic Zeolite) from Huber NaAlSi5O12 · 3H2O ......................................... Muscovite ....................................................... Na3K(AlSiO4)4 Nephelin from Skudesundskjaer ............................................ Oligoclase ...................................................... Olivine from Dreis ......................................... Orthoclase ...................................................... Palygorskite (Mg,Al)2Si4O10(OH) · 4(H2O) from Tunisia ................................................... Perlite from Cumaovasi, Turkey (or from Izmir) ............................................... Pyrophyllite Al2(OH)2Si4O10 .......................... Rhomboporphyr ............................................. Ripidolite ....................................................... Sanidine ......................................................... Saponite ......................................................... Sapphirine ...................................................... Serpentine ...................................................... Smectite ......................................................... Tremolite ........................................................ Turmaline (drawite) NaMg3Al6B3Si6O27 (OH,F)4 .......................................................... Vermiculite from Clay Minerals Society Repository ......................................................

552 553 553 553 554 554 555 555 555 559 572 572 572 574 575 583 584 584 584 584 585 585 585 585 586 586 586 587 587 587 587 588 588 589 589

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3.3

3.4

3.2.56 Vesuvian from Solberg .................................. 3.2.57 Zeolites .......................................................... 3.2.58 Zinnwaldite ................................................... Mixed Oxides ................................................................ 3.3.1 Materials Containing Aluminum .................. 3.3.2 Bi–Th Mixed Oxides ...................................... 3.3.3 Materials Containing Ce ................................. 3.3.4 Materials Containing Co ................................ 3.3.5 Materials Containing Cr ................................. 3.3.6 Materials Containing Fe ................................. 3.3.7 In–Sn Mixed Oxides ...................................... 3.3.8 Mixed Oxides Containing Mg ....................... 3.3.9 Material Containing Nb ................................. 3.3.10 Materials Containing Ni ................................ 3.3.11 Materials Containing Pb ................................ 3.3.12 Materials Containing Ru ............................... 3.3.13 Silicates .......................................................... 3.3.14 Materials Containing SnO2 ............................ 3.3.15 Materials Containing TiO2 ............................ 3.3.16 Materials Containing WO3 ............................ 3.3.17 Materials Containing Zn ................................ 3.3.18 Materials Containing Zirconia ...................... Salts ............................................................................... 3.4.1 Aluminates and Haloaluminates ................... 3.4.2 Borides and Borates ....................................... 3.4.3 Carbides, Carbonates, and Salts of Organic Acids ................................................ 3.4.4 Chlorides ........................................................ 3.4.5 Chromates ...................................................... 3.4.6 LiCoO2 ........................................................... 3.4.7 Fluorides ........................................................ 3.4.8 Ba Ferrite from Aldrich ................................. 3.4.9 AgI ................................................................. 3.4.10 Manganates .................................................... 3.4.11 Molybdates ..................................................... 3.4.12 Sr1-xNbO3-d .................................................... 3.4.13 Nitrides .......................................................... 3.4.14 Niobates ......................................................... 3.4.15 Phosphates and Apatites ................................ 3.4.16 Silicates .......................................................... 3.4.17 Sulfides and Sulfates ...................................... 3.4.18 Titanates ......................................................... 3.4.19 Tungstates and Tungstophosphates ................ 3.4.20 BaZrO3 ...........................................................

590 590 591 591 592 610 611 611 612 613 624 625 626 627 628 628 630 647 648 654 655 656 665 665 666 666 696 697 698 698 701 701 701 707 708 709 720 720 739 740 769 774 775

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3.5

3.6

3.7

3.8

3.9

Glasses .......................................................................... 3.5.1 Commercial ................................................... 3.5.2 Other .............................................................. Carbon and Carbon-Rich Materials .............................. 3.6.1 Diamond ........................................................ 3.6.2 Graphite ......................................................... 3.6.3 Fullerene C60 .................................................. 3.6.4 Carbon Black, Activated Carbons, and Related Products ..................................... 3.6.5 Activated Carbon Cloths and Fibers .............. 3.6.6 Composite Material ........................................ Other Inorganic Materials .............................................. 3.7.1 Silicon, >99.6% HQ Silgrain from Elkem Materials .............................................. 3.7.2 Sulfur .............................................................. 3.7.3 Ice .................................................................. 3.7.4 D2O Ice .......................................................... 3.7.5 Gas Bubbles ................................................... 3.7.6 Natural Inorganic Materials .......................... Coatings ......................................................................... 3.8.1 Alumina Coatings ........................................... 3.8.2 Hydrous Chromia on Hematite ...................... 3.8.3 Co Oxide on Stober Silica ............................. 3.8.4 Iron (Hydr)oxide Coatings ............................. 3.8.5 Germania on Silica ........................................ 3.8.6 IrO2 on Stober Silica ...................................... 3.8.7 Mn Compounds on Hematite ......................... 3.8.8 Nickel (Hydr)oxide Coatings ......................... 3.8.9 RuO2 on Silica ................................................ 3.8.10 Silica Coatings ............................................... 3.8.11 Sn(OH)4 on Hematite ..................................... 3.8.12 Titania Coatings ............................................. 3.8.13 Yttria on Hematite ......................................... 3.8.14 Zr (Hydr)oxide Coatings ................................ 3.8.15 Passive Layer on Ti6Al4V Alloy ................... 3.8.16 Passive Films on Stainless Steels .................. 3.8.17 NiCO3 · Ni(OH)2 · H2O on MnCO3 .................. 3.8.18 YOHCO3 Coatings ......................................... 3.8.19 Zr2O2(OH)2CO3 and Zr2 (OH)6 SO4 on Polystyrene ................................................ Well-Defined Low-Molecular-Weight Organic Compounds ................................................................... 3.9.1 Hydrocarbons ................................................. 3.9.2 Bromododecane from Sigma-Aldrich ...........

776 776 779 781 781 781 781 782 807 811 811 811 811 812 812 812 813 814 814 820 820 821 823 824 824 824 825 826 828 829 833 834 835 835 835 835 836 837 837 839

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3.10

3.11

3.12

3.13

3.9.3 Fullerol ........................................................... 3.9.4 Acids .............................................................. 3.9.5 Cholesterol, 99+%, Alfa Aesar ...................... Polymers (Macroscopic Specimens) ............................. 3.10.1 Polyamides ..................................................... 3.10.2 Polycarbonates ............................................... 3.10.3 Polyetheretherketone, Victrex, Lite K, from Lipp-Terler ............................................. 3.10.4 Polyetherimide, Molecular Mass 89 100, from Lipp-Terler ............................................. 3.10.5 Polyethylene ................................................... 3.10.6 Poly(ethylene imine) from Polysciences ................................................... 3.10.7 PMMA ........................................................... 3.10.8 Polypropylene from E-Plas ............................ 3.10.9 Polystyrene ..................................................... 3.10.10 PTFE .............................................................. 3.10.11 Polyurethane .................................................. 3.10.12 Polymers, Fibers ............................................ 3.10.13 Polymers, Powders ......................................... Latexes .......................................................................... 3.11.1 Commercial ................................................... 3.11.2 Synthetic ........................................................ 3.11.3 Origin Unknown ............................................ Natural High-Molecular-Weight Organic Substances ..... 3.12.1 Humic and Fulvic Acid .................................. 3.12.2 Marine Colloidal Organic Matter .................. 3.12.3 Suspended Particulate Matter from River Mersey in NW England ....................... 3.12.4 Cellulose ........................................................ 3.12.5 Dextrin ........................................................... 3.12.6 b-Casein ........................................................ 3.12.7 Lysozyme ....................................................... 3.12.8 Chitosan ......................................................... 3.12.9 Chitosan–Polymethacrylic Acid Composites ..................................................... 3.12.10 Asphaltene ..................................................... Microorganisms ............................................................ 3.13.1 Bacterium Bacillus subtilis ............................ 3.13.2 Bacterium Corynebacterium xerosis ............. 3.13.3 Cell Walls of Bacterium Rhodococcus erythropolis .................................................... 3.13.4 Bacterium Rhodococcus opacus from Fundacao Tropical de Pesquisas e Tecnologia Andre Tosello, Sao Paulo ............

839 839 841 841 841 842 842 842 843 843 843 843 844 844 844 845 845 845 845 848 851 852 852 855 856 856 857 857 857 858 858 858 859 859 859 860

860

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3.14 3.15

3.16 3.17 3.18 3.19 3.20 3.21

3.22. Chapter 4

3.13.5 Bacterium Shewanella putrefaciens .............. 3.13.6 MS2 Bacteriophages ...................................... Metals ............................................................................ Literature Intentionally Ignored .................................... 3.15.1 PZCs/IEPs Not Reported or Not Found ........ 3.15.2 Secondary Sources ........................................ 3.15.3 The Electrolyte Is Not Inert ........................... 3.15.4 Mechanical Mixtures and Complex and Ill-Defined Materials ..................................... 3.15.5 Nonstandard, Incorrect, or Undefined Method, and Nonstandard Terminology ........ 3.15.6 Wrong Citations ............................................. Temperature Effect ....................................................... Pressure Effect .............................................................. Compilations of PZC of Various Materials .................. Correlations ................................................................... Mixed Water–Organic Solvents .................................... Nonaqueous Solvents .................................................... 3.21.1 Allegedly Pure Solvents ................................. 3.21.2 Effect of Water ............................................... 3.21.3 Effect of Inorganic Electrolytes ..................... 3.21.4 Effect of pH ................................................... Conclusion .....................................................................

860 860 861 861 861 861 862 863 864 866 866 868 869 870 873 874 875 875 876 876 876

Ion Specificity .......................................................................... 879 4.1

Affinity Series ............................................................... 4.1.1 Aluminas ........................................................ 4.1.2 Iron (Hydr)oxides ........................................... 4.1.3 MnO2 .............................................................. 4.1.4 Hydrous Niobia .............................................. 4.1.5 Silica .............................................................. 4.1.6 SnO2 ............................................................... 4.1.7 Thoria ............................................................. 4.1.8 Titania ............................................................ 4.1.9 UO2 ................................................................ 4.1.10 WO3 ................................................................ 4.1.11 Zirconia .......................................................... 4.1.12 Mica ............................................................... 4.1.13 Na-Montmorillonite ....................................... 4.1.14 Red Mud ........................................................ 4.1.15 Alkali Metal-Substituted Manganese Oxides .... 4.1.16 d-MnO2 .......................................................... 4.1.17 Si3N4 ............................................................... 4.1.18 Chrisotile .......................................................

879 880 880 881 881 881 882 883 883 883 883 883 884 884 884 884 884 884 884

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4.2

4.3

4.1.19 Controlled Pore Glasses ................................. 4.1.20 Diamond ........................................................ Uptake of 1-1 Electrolyte Ions at or Near the PZC ....... 4.2.1 Alumina ......................................................... 4.2.2 Gibbsite .......................................................... 4.2.3 CdO ................................................................ 4.2.4 Co3O4 ............................................................. 4.2.5 Magnetite (containing 2.4% of Silica) ........... 4.2.6 Hematite ......................................................... 4.2.7 Goethite ......................................................... 4.2.8 HfO2 ............................................................... 4.2.9 Niobia ............................................................. 4.2.10 Silica .............................................................. 4.2.11 Hydrous Tin Oxide ........................................ 4.2.12 ThO2 ............................................................... 4.2.13 Titania ............................................................ 4.2.14 Zirconia .......................................................... 4.2.15 Alumina–Silica Mixed Oxides ...................... 4.2.16 Silica–Titania and Alumina–Silica– Titania Mixed Oxides .................................... 4.2.17 Titania–Zirconia Mixed Oxides .................... 4.2.18 d-MnO2 .......................................................... 4.2.19 Porous Glasses ............................................... High Ionic Strength ....................................................... 4.3.1 Ions in Solution .............................................. 4.3.2 Experimental Methods .................................. 4.3.3 Electroacoustic Method .................................

884 884 884 885 886 886 886 886 886 886 886 887 887 887 887 887 888 888 888 888 888 889 889 889 890 891

Appendix ....................................................................................................

893

References ..................................................................................................

911

Index ........................................................................................................... 1057

Preface In 1995, I came to the Forschungszentrum Karlsruhe, Germany as an Alexander von Humboldt fellow. The Forschungszentrum (Research Center) had just been renamed from Kernforschungszentrum (Nuclear Research Center), reflecting the change in its research profile from nuclear technology to more general research in natural sciences. I was one of very few experienced surface chemists among numerous non-surface chemists who started new projects more or less related to surface phenomena. Not surprisingly, several colleagues approached me with questions, one being about the points of zero charge (PZCs) of various materials. In the beginning, I advised my colleagues to use the review by Parks [1]. Indeed, [1] used to be the most complete review on PZCs of oxides, and authors who reported their own measurements usually compared their results with those reported by Parks. The popularity of Parks’ review is reflected by the number of citations. Yet my colleagues were not entirely satisfied. Parks reports data only for a limited number of materials. Moreover, my colleagues were concerned about the significance of expressions such as “titania has a PZC at pH 6.” Should we expect the same PZC for all titanias, no matter what method is used and what batch of material is used? Is the scatter of results reported in the literature due to real differences in properties between particular samples or to a real difference between the isoelectric point on the one hand and the PZC obtained by titration on the other? Both approaches are equally attractive, and the truth is probably somewhere in between. Probably the differences in PZC obtained for different samples of a material having the same chemical formula are due to a combination of real differences in properties and experimental errors (e.g., insufficient purity), and it is very difficult to completely exclude either of these factors or to assess their contributions to the observed effect. Yet the question about the existence/nonexistence of a common PZC for all titanias (or other groups of materials with a common chemical formula) cannot be avoided in a review of PZCs. In my previous review [2], all PZCs of materials with a common chemical formula were grouped and analyzed together. The entries were sorted only by chemical formula. In the present review, a completely different approach is adopted. PZC data on well-defined specimens of materials are sorted by trade name and manufacturer (for commercial materials), location (for natural materials), or specific recipe (for synthetic materials). This approach emphasizes the comparison between particular results obtained for different samples of apparently the same or at least very similar material. The classification of materials according to the above criteria was more difficult than originally expected. Detailed sample information is often missing or xxiii

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incomplete in scientific publications. Often, literature references are given instead of specific data. Spelling errors in trade and manufacturers’ names are common. Even complete trade name and manufacturer information is not sufficient for correct classification. The results reported in this book were taken from papers published over a few decades. In the meantime, manufacturers, distributors, and other enterprises have merged, split, or changed their names. The same product might have been offered under various brand names. Thus, the number of classes distinguished in this book is probably much larger than the number of significantly different products. On the other hand, it may very well be that the recipe for a commercial product may have been modified without its trade name being changed. The present author does not possess this knowledge. Calcination and washing are other factors that make comparison of results from different sources obtained for apparently the same material more difficult. Original commercial materials often undergo calcination and/or washing before their surface charging is studied. Calcination removes organic impurities from the surface, but it also removes surface hydroxyl groups, which are responsible for the surface charging. Calcination at high temperatures also induces diffusion of impurities from the bulk solid onto the surface. The conditioning of the sample after calcination may strongly affect its surface charging properties. Numerous studies have been devoted solely to the effect of different calcination–rehydration sequences on surface charging. In fact, a new material is produced when the original sample is calcined at sufficiently high temperature. The goal of washing is to remove impurities, which are usually concentrated on the surface. The effect of washing on the isoelectric point (IEP) of titania was systematically studied in [3]. In fact, washing also modifies the surface by leaching the components of the sample, changing the degree of hydration, and replacing substances originally present in the sample by other substances originating from the washing solution. The idea of a washing procedure that removes only impurities is an example of wishful thinking. A description of washing procedures in the literature is often incomplete or missing, but even with detailed information, it is difficult to assess the nature of the changes induced by washing. In the present book, all results obtained for the same original commercial material—uncalcined and calcined, unwashed and washed in different ways— have been analyzed as one group. Many groups consist of a single sample; that is, only one study reporting PZCs/IEPs for certain commercial materials could be found. A few commercial materials have become very popular, and numerous studies reporting PZCs/IEPs could be found. A similar approach applies to home-synthesized materials. Again, certain recipes have frequently been used to synthesize materials for surface charging studies, and numerous studies reporting PZCs/IEPs of such materials could be found, while other recipes have been used only in single studies. A few studies of surface charging of home-synthesized materials reported original recipes. In other studies, the recipes were taken from the literature. When possible in this book, a recipe is reported for each synthetic material, which makes it possible to synthesize similar material. However, certain obvious details are omitted. For

Preface

xxv

instance, the use of distilled water (rather than tap water) to prepare solutions and to wash precipitates is standard. Also, details regarding the equipment (glassware and filters) and the chemicals (manufacturer and purity) are usually omitted. For several specimens, a literature reference is given instead of a specific recipe. Several recipes are reported only in theses, internal reports, and other difficult-toaccess sources. Usually, the original papers reporting synthetic recipes analyze a broad spectrum of experimental conditions. A literature reference is then not sufficient to identify a specific recipe. Problems with identification of specific recipes are explicitly stated in this book when appropriate. Most studies reporting PZCs/ IEPs of home-synthesized materials refer to a specific recipe. Similar recipes are grouped together here; that is, recipes for home-synthesized materials that belong to one group are not necessarily identical. Results obtained for natural materials from the same geographic location (mine or a specific country, etc.) are grouped together. Of course, specimens collected at the same site do not necessarily have identical properties, in contrast with series of commercial materials sold under the same trade names or series of home-synthesized materials prepared according to the same recipe. Finally, results of surface charging studies of materials of unknown (or unreported) origin are also given. These materials very likely belong to one of the groups of commercial, home-synthesized, or natural materials, but as their origin is unknown, each of these materials is treated as a single-member group. For each type of material (commercial, home-synthesized, natural, or “origin unknown”) the physical properties related to surface charging properties are reported when available. As many sources as possible (not limited to the papers reporting surface charging studies) have been used to obtain these data. The results from different sources are often scattered. In this respect, the present book presents more detailed data than previous compilations of PZCs/IEPs. The style of organization and presentation of the PZC/IEP data here follows the style of my previous book [2]. The present compilation of PZC/IEP is critical and selective; that is, numerous studies reporting PZC/IEP data or cited as sources of such data have deliberately been rejected. Many other studies relevant to the present compilation might have been overlooked or were unavailable. A reader may be interested in a certain study apparently reporting PZC/IEP data on materials of interest even when it is not used in the present book. To this end, the references deliberately omitted in this book are listed, together with a short explanation of the nature of the results presented there. A few papers cited as references allegedly containing PZC/IEP information are also mentioned, even if inspection of the original papers indicates absence of such information. Marek Kosmulski

Acknowledgments The collection of publications cited in the present compilation is based on the anonymous work of numerous librarians. Several scientists replied to my requests and sent me reprints of their publications. I take this opportunity to express my gratitude to them. The technical assistance of Piotr Próchniak and Teresa Chlebik from the Department of Electrochemistry, Lublin University of Technology is gratefully acknowledged as are grants from Lublin University of Technology and from the Alexander von Humboldt Foundation. Parts of this book were written at Åbo Akademi (Finland) and the European Institute of Transuranium Elements (Karlsruhe, Germany). Professors Jarl B. Rosenholm and Thomas Fanghänel are acknowledged for their hospitality. Marek Kosmulski

xxvii

1

Introduction

Introductory descriptions of surface charging and the electrical double layer can be found in numerous handbooks of surface and colloid chemistry (e.g., [4–7]), in other books (e.g., [8–10]), and in review articles (e.g., [11]). The reader of the present book is assumed to be familiar with these phenomena and with basic ideas and methods of analytical chemistry. Figures 1.1 and 1.2 show the idealized picture as presented in the handbooks. The s0(pH) curves obtained at different concentrations c1 < c2 < c3 of an inert 1-1 electrolyte shown in Figure 1.1 have a common intersection point (CIP) at s0 = 0. The absolute value of s0 at constant pH increases as the ionic strength increases on the both sides of the point of zero charge (PZC). s0 at constant ionic strength steadily decreases as pH increases. Many examples of such sets of three or more charging curves are reported in the literature. The number of charging curves shown in Figure 1.1 is limited to three for clarity. Differences between c1, c2, and c3 by an order of magnitude are necessary to obtain a clear difference in the absolute value of s0 and a clear CIP. When the differences between the concentrations are smaller, the charging curves obtained at various ionic strengths are likely to overlap rather than intersect. The z(pH) curves obtained at different concentrations c1 < c2 < c3 of an inert 1-1 electrolyte shown in Figure 1.2 show a common IEP. The absolute value of z at constant pH decreases as the ionic strength increases on both sides of the IEP. z at constant ionic strength steadily decreases as pH increases. Studies reporting electrokinetic data for numerous ionic strengths are rare. Electrokinetic data obtained at one ionic strength are sufficient to determine the IEP. Differences between c1, c2, and c3 by an order of magnitude produce a clear difference in the z potential. When the differences between the concentrations are smaller, the electrokinetic curves obtained at various ionic strengths are likely to overlap, as observed in [12] (anatase in 0.001 and 0.0025 M KCl). On the other hand, an increase in KCl concentration from 0.01 to 0.045 M induced a decrease in electroacoustic signal by a factor of about 3 on both sides of the IEP [438]. The following figures illustrate problems that occur in real systems. Let us consider a quantity XYZ (e.g., s0 or z potential) that reverses its sign at pH0. Here, pH0 represents electroneutral conditions without specifying precisely what quantity is meant and how it was measured, and the PZC and IEP are examples of pH0. The line in Figure 1.3 represents an idealized situation: XYZ depends only on pH, and many high-precision data points are available on both sides of pH0. A line drawn 1

2

s0

Surface Charging and Points of Zero Charge

PZC

0 c1 c2 c3 pH

FIGURE 1.1 Expected course of s0(pH) curves. c1, c2, and c3 are different concentrations of an inert 1-1 electrolyte, with c1 < c2 < c3.

z

through these points gives pH0. Actual systems are more complicated. Figures 1.4 through 1.12 show typical problems that make determination of pH0 difficult. Only one problem is illustrated in each figure, but in fact combinations of two or more problems often occur. Figure 1.4 illustrates the effect of quantities other than pH on XYZ. These quantities, such as temperature and the nature and concentration of the 1-1 electrolyte and of impurities present in the system, are usually controlled, although in fact they cannot be set exactly constant, but vary over a limited range. Varying degrees of attention have been paid to controlling these quantities, and the level of control claimed in a scientific paper (e.g., the temperature limits) is not necessarily realistic. Different measurable quantities, for example s0 from titration and z potential from electrokinetic measurements, represent the state of the charged surface. In principle, each of these quantities can reverse

IEP

0 c3 c2 c1 pH

FIGURE 1.2 Expected course of z(pH) curves. c1, c2, and c3 are different concentrations of an inert 1-1 electrolyte, with c1 < c2 < c3.

3 XYZ

Introduction

pH0

0

pH

FIGURE 1.3 Idealized situation as found in handbooks: pH0 depends only on pH. XYZ represents a quantity that reverses its sign at pH0.

XYZ

sign at different pH values, thus producing different pH0 values (Figure 1.5). In the presence of inert electrolytes, the CIP and IEP of the same sample of pure metal oxide often match, but in a few studies they have been substantially different. It is an open question whether the discrepancies between the CIP and IEP of the same sample of metal oxide reported in the literature are only due to experimental errors and impurities or whether they may also occur in properly conducted experiments with very pure materials. Different specimens represented by the same chemical formula often produce different pH0 values (Figure 1.6). This is an experimental fact, and the reason for these discrepancies is not clear. Substantial discrepancies in the pH0 of particular

pH0 (T2) pH0 (T3)

pH0 (T1)

0 T1 T2 T3

pH

FIGURE 1.4 Real situation: pH0 depends on quantities other than pH. Temperature and the nature and concentration of a 1-1 electrolyte and of impurities present in the system are examples of such quantities.

4 X, Y, or Z (scaled)

Surface Charging and Points of Zero Charge

pH0 (Z) pH0 (Y )

pH0 (X)

0 X Y Z

pH

FIGURE 1.5 Real situation: different quantities that represent the sign of the electric charge at the surface produce different pH0 values. An example is s0 from titration compared with z potential.

XYZ

specimens (>1 pH unit) are due to impurities. In principle, different crystallographic structures and different morphologies of crystals (exposure of different faces) of the same chemical structure can also produce different pH0 values, and, for example, numerous studies of the effect of interatomic distances on the acidity of surface oxygen atoms have been published. The discrepancies in pH0 in a series of clean samples that differ only in structure and/or morphology do not exceed 1 pH unit. Figures 1.3 through 1.6 illustrate an idealized picture, in which the measurements produce exact values. Real XYZ measurements produce ranges (average values with limits of uncertainty represented by error bars) rather than

pH0 (specimen 3) pH0 (specimen 2)

pH0 (specimen 1)

0 Specimen 1 Specimen 2 Specimen 3

pH

FIGURE 1.6 Real situation: different specimens produce different pH0 values, although they represent the same chemical formula. Possible reasons include impurities and the effect of interatomic distances on the acidity of surface oxygen atoms.

5 XYZ

Introduction

0

Possible range of pH0

pH

FIGURE 1.7 Real situation: the XYZ measurement produces a range (represented by an error bar) rather than a single quantity (represented by a point). The sign of XYZ is uncertain over a range of pH, which depends on the error in XYZ.

XYZ

single quantities (represented by points). Figure 1.7 shows that the sign of XYZ is uncertain over a particular pH range, which depends on the error in XYZ. Even with very low error in XYZ (Figure 1.8, error bars not shown), the error in the pH measurements (represented by error bars) makes pH0 uncertain in unbuffered systems. In microelectrophoresis, errors in pH measurements are the main source of uncertainity. Section 1.10 discusses pH measurements in more detail. In real measurements, both pH and XYZ values are uncertain.

0

Possible range of pH0

pH

FIGURE 1.8 Even with very low error in XYZ (error bars not shown), the error in pH measurements (represented by error bars) makes pH0 uncertain in unbuffered systems. In microelectrophoresis, errors in pH measurements are the main source of uncertainty.

6

Slow titration

XYZ

XYZ

Surface Charging and Points of Zero Charge

Fast titration pH

0 pH0 (base titration)

pH0 (acid titration) Base titration Acid titration pH

FIGURE 1.9 Real situation: hysteresis. The loop narrows as the titration rate decreases, but it is often difficult to avoid, even with very slow titration.

In Figures 1.1 through 1.8, a tacit assumption was made that the system is in adsorption equilibrium. Real measurements (Figure 1.9) are often carried out in titration mode. Reversibility of titration (acid titration vs. base titration) is not guaranteed, but this is seldom examined; that is, titration in only one direction is reported in most studies. The system tends to “remember” its state from the past: this phenomenon is called hysteresis. The XYZ obtained in base titration starting at low pH is more positive than XYZ at the same pH obtained in acid titration starting at high pH. Therefore, base titration gives a higher pH0 than acid titration, and the actual pH0 is in between, but not necessarily half way. The hysteresis loop narrows as the titration rate decreases (two small loops in the right upper corner of Figure 1.9), but it is often difficult to avoid, even at very low titration rates. Silicate and carbonate anions are omnipresent: they occur as impurities in metal oxides and in other adsorbents, and in water and in other reagents used to prepare solutions, and they are absorbed from air and leached out from parts of the apparatus. Their sorption leads to an increase in negative charge and to a shift in pH0 to low pH (Figure 1.10). The binding mechanism of silicates and carbonates is complex; for example, metal silicates and carbonates are often more stable (in terms of G 0 of pure solid phases) and less soluble than the corresponding oxides. In typical surface charging experiments, the concentrations of silicates and carbonates are reduced by using an inert gas atmosphere and plastic ware rather than glassware, but such attempts do not guarantee the absolute absence of silicates and carbonates. Often, data points very close to pH0 are not available or are scattered, and pH0 is determined by interpolation. This is a typical situation in electrophoresis, because dispersions are unstable near the IEP. IEPs determined by interpolation are usually based on an arbitrary curve connecting the data points (represented by circles in Figure 1.11). The two curves in Figure 1.11 represent two interpolations. Both interpolations look “reasonable,” but they produce very different pH0 values.

7 XYZ

Introduction

pH0 (CO2/SiO2 removed)

0 pH0 (CO2/SiO2 present) CO2/SiO2 removed CO2/SiO2 present pH

FIGURE 1.10 Real situation: adsorption of silicate and carbonate leads to a shift in pH0.

XYZ

Numerous pH0 values reported in the literature, especially at very low or very high pH, were obtained by extrapolation. Extrapolation is used when only data points on one side of the IEP are available or when the data points in the vicinity of the IEP are scattered. For example, in [14], a PZC of MoO3 at pH -0.5 is claimed, which certainly could not have been obtained by direct measurement. pH0 values determined by extrapolation are usually based on an arbitrary curve connecting the data points (represented by circles in Figure 1.12). The two curves in Figure 1.12 represent two extrapolations. Both extrapolations look “reasonable,” but they produce very different pH0 values. When the pH0 falls beyond the range of data points, it is safer to report a limit (e.g., “pH0 < 2 if any”) rather than a specific value of pH0.

pH0 (interpolation 2)

0 pH0 (interpolation 1) Data points

pH

FIGURE 1.11 Data points in the close neighborhood of pH0 are not available (this is often the case in electrophoresis), and the pH0 is determined by interpolation. Circles represent data points. Curves represent two arbitrary interpolations.

8

Surface Charging and Points of Zero Charge pH0 (extrapolation 2) XYZ

0 pH0 (extrapolation 1)

Data points

pH

FIGURE 1.12 pH0 falls outside the range of data points, and is determined by extrapolation. Circles represent data points. Curves represent two arbitrary extrapolations. Numerous pH0 values reported in the literature, especially in ranges of very low or of very high pH, have been obtained by extrapolation.

1.1 NOMENCLATURE The terms “point of zero charge” and “isoelectric point” and the corresponding abbreviations PZC and IEP are used in the present book according to IUPAC recommendations [15,16]. The PZC is defined as the conditions at which the surface charge density equals zero; for metal oxides and related materials, it is determined by potentiometric titration or by related methods as the point at which the apparent surface charge density determined in the presence of an inert electrolyte is independent of ionic strength. Zero net surface charge density does not imply the absence of any charges, but rather the presence of equal amounts of positive and negative charge. The IEP is defined as the conditions at which the electrokinetic charge density and thus the electrokinetic (z) potential equals zero; it is determined by electrokinetic methods (see [17] for measurement and interpretation of electrokinetic phenomena). Different versions of these abbreviations—lower- and upper-case, with or without periods—are used in the literature. The same abbreviations also appear in the form of subscripts, for example, pHIEP. This notation emphasizes that there are species other than protons that may produce a reversal in sign of the z potential, and the concentration of such a species (e.g., a polymer [18,19]) that is required to reverse the sign of the z potential can also be termed the IEP. The present book is devoted to pH-dependent surface charging, and there is no need to emphasize repeatedly that the IEP is a pH value. However, in other publications, the abbreviation “IEP” may refer to species other than protons, and certain situations require a clear indication of which species induced sign reversal. For example, the primary surface charging of silver halide colloids is governed by silver and halide ions in solution, and their IEP is expressed in terms of pAg or pX. One of these

Introduction

9

quantities is sufficient, since their sum is equal to pKs, where Ks is the solubility product of the silver halide. In most studies of pH-dependent surface charging reported in the present book, the pH was adjusted by addition of an acid or base that has an anion or cation in common with the inert electrolyte. In an electrokinetic study of apatite [20], the pH was adjusted with KOH (standard procedure), and in another series of measurements, the pH was adjusted with K2HPO4. The z potentials were substantially different in two series of measurements, but the IEP was consistent. In apatite and other materials that undergo selective leaching out of components, the concentrations of the leaching products in solution affect the surface charge. They are not all independent variables, because they are interrelated by solubility product and by equilibria in solution. Not surprisingly, the PZC/IEP of apatite and other materials that undergo selective leaching out of components, obtained from studies in which pH was the sole adjusted and/or controlled variable, are less consistent than the PZC/IEP of materials that show negligible solubility. In numerous IUPAC publications (e.g., [21]), pI is used as an abbreviation for isoelectric point. Although the above recommendations refer chiefly to electrophoresis of proteins, the nature of electrokinetic phenomena in proteins and in colloids is basically the same, and there is no need for two different abbreviations for isoelectric point. Not surprisingly, several authors in the colloid chemistry literature have also used the abbreviation pI. The present author prefers IEP as a more common and less confusing abbreviation (pI may suggest minus the logarithm of iodide concentration—and indeed it is used with such a meaning in this book). An interesting semantic problem is faced in [22], which reports isoelectric points of protein molecules in solution as well as those of larger particles formed by these molecules. Another abbreviation for isoelectric point, namely pH(I), is recommended in [21]. Several authors ignore IUPAC recommendations and use their own terms and abbreviations. The term “zero point of charge” (abbreviated as ZPC), which has the same meaning as PZC defined above, has been used in a popular textbook [5] and in several other publications (e.g., [23]). The term “point of zero zeta potential” (PZZP) has been used for the IEP. In the present book, “ZPC” and other atypical terminology (e.g., “pHz”) have been translated into the recommended terminology when necessary and possible. Already in 1968, Somasundaran [24] complained about use of the terms IEP and PZC outside their normal meaning. IEP and PZC are two different physical quantities, and they must be distinguished even when they happen to be numerically equal. Numerous examples of confusion between IEP and PZC can be found in the literature. For example, in [25], the IEP is termed the PZC. In such cases, the proper terminology has been used in the present book and the terminology used in the original papers has been ignored. The present study is focused on materials with variable (pH-dependent) surface charge, and the methods and definitions are adjusted to this type of materials. Clay minerals and other materials with a dominant role of permanent charge need a different approach. Clay minerals do not show a clear CIP of charging curves

10

Surface Charging and Points of Zero Charge

obtained at various ionic strengths; thus, the above definition that identifies the PZC with the CIP is not applicable. For example, [26] defines five different zero points for soils, and recommends detailed methods for their determination. Reference [26] also gives a list of PZCs (determined by different methods) for common materials. In [27], Sposito discussed PZCs of materials with permanent charge. In [28] and [29], he challenged the application of well-established methods (designed for materials having variable surface charge). Sposito argued that particles with local positive and negative charge may show substantial electrophoretic mobility when their net electrokinetic charge is zero.

1.2 SCOPE The present book reviews PZC/IEP data reported for well-defined, homogeneous materials without surface coating; that is, ill-defined materials (e.g., most natural soils), physical mixtures consisting of grains of various materials (as in [30]), and surface-engineered materials are deliberately omitted. For example, commercial pigments (pigments used as obtained) often consist of core materials with organic and inorganic coatings. Such coatings constitute a small fraction of the mass of the pigment, but severely affect their surface charging properties. In several studies (e.g., [31,32]), the presence of such coatings is explicitly stated. In a few other studies, the composition of the core material is reported, but the presence of the coating is not mentioned. The present author does not possess knowledge about the presence of surface coatings in commercially available materials unless this is explicitly reported in the cited papers. It may very well be that several PZC/IEP values reported for allegedly pure core materials were in fact obtained for surface-engineered materials. The PZCs/IEPs presented in this book are organized primarily according to the chemical formula of the adsorbent. The materials considered here have been organized into the following classes: 1. Simple, sparingly soluble (hydr)oxides. Within this class, compounds are sorted alphabetically by chemical symbol of the electropositive element (usually metal), then by degree of oxidation (lower degree of oxidation first), and then by degree of hydration (lower degree of hydration first). 2. Aluminosilicates and clay minerals. Within this class, compounds are sorted alphabetically by their names. There are numerous, often multilevel, classifications of clay minerals, and different names are often assigned to the same material or to very similar materials. Such materials are listed under the names used in the original publications and interconnected by cross-references. 3. Mixed oxides, that is, materials composed of two or more sparingly soluble (hydr)oxides. The solubility of the components is a key factor distinguishing between mixed oxides and salts (see Class 4 below). For example, MgSiO3 is considered as mixed oxide, since both MgO and

Introduction

4.

5. 6. 7. 8. 9.

10. 11. 12.

13.

11

SiO2 are sparingly soluble, whereas CaSiO3 is considered as a salt, since CaO is soluble. Mixed oxides are organized alphabetically by chemical symbol of the electropositive element in the main component, and then by chemical symbols of the electropositive elements in the other components. The reader looking for a given mixed oxide is advised to check under all components, since information appears only once in the book and no cross-references are provided. The class of mixed oxides comprises salt-type stoichiometric compounds on the one hand and series of nonstoichiometric compounds with broad ranges of compositions on the other. IEPs of mixed oxides are often very different from the weighted average of the IEPs of their components [33]. Salts. These are sorted alphabetically according to the chemical symbols of the anion-forming elements. Salts that can be considered as composed of two sparingly soluble oxides are considered as mixed oxides (see Class 3 above). Glasses. Carbon. Data are given for natural diamond, graphite, and fullerene, and then for commercial and home-made activated carbons. Other well-defined inorganic materials. These include sulfur, ice, and air bubbles. Natural inorganic materials. Coatings. Composite materials with a thick external layer and a core, where the latter practically does not contact the solution, are organized based on the nature of the coating (external layer) according to the principles explained under Classes 1–4 above. Well-defined low-molecular-weight organic compounds and their mixtures. Synthetic polymers (macroscopic specimens). These are sorted alphabetically by chemical names. Latexes. Commercial products are sorted by manufacturer’s name and trade name as the primary identifiers (irrespective of the chemical nature of the monomers). These are followed by home-made latexes. Natural high-molecular-weight organic compounds. These include humic substances and natural organic matter, asphaltene, and cellulose.

Different specimens with the same chemical formula are arranged into three subclasses: A. Commercially available materials. These are sorted alphabetically by manufacturer’s/retailer’s name and/or trade name. When manufacturer’s/ retailer’s name and trade name were reported in the original publication, the materials are sorted primarily by manufacturer/retailer name and then by trade name. Otherwise, the trade name is used as a sole identifier. Cross-references are provided between categories that are likely to represent the same material.

12

Surface Charging and Points of Zero Charge

B. Home-synthesized materials. In a few instances, the recipes for certain chemical compound are organized into a few smaller subclasses according to the method, precursor, etc. C. Natural materials. These are organized alphabetically by country of origin. Most scientific papers report sufficient information to assign the material of interest to one of subclasses A–C and then to a smaller subclasses. Several specimens could not be classified because of insufficient information in the original papers. Although the usefulness of the information about PZCs/IEPs of such materials is limited, they are also reported in the present compilation. Such materials are referred to as “origin unknown.”

1.3 INERT ELECTROLYTES The idea of an inert (indifferent) electrolyte was coined in the context of electrocapillary studies using the Hg electrode. Grahame [34] found a series of electrolytes that produced the same PZC (determined as the electrocapillary maximum) irrespective of the nature or concentration of the electrolyte. Such behavior suggests that the ions of these electrolytes interact with the surface only by a Coulombic force. In contrast, many other electrolytes induced a shift in the PZC, with the magnitude and direction of this shift depending on the nature or concentration of the electrolyte. A shift in the PZC suggests that ions of these electrolytes can be positively adsorbed in spite of electrostatic repulsion; that is, they interact with the surface by a noncoulombic force. This phenomenon is termed specific adsorption. Thus, an inert electrolyte does not show specific adsorption of either ion. The above terminology (“inert” vs. “specific”) was adopted for studies of the surface charging of colloids. Different experimental methods are used and different quantities are measurable for colloids than for the Hg electrode, but the model of an electrical double layer is analogous. Studies of pH-dependent surface charging of colloids are usually carried out in the presence of an inert electrolyte and an acid or base (used to adjust the pH) with an anion or cation in common with the inert electrolyte. Products of dissolution of the solid are also present in solution at low concentration (we are only interested in sparingly soluble solids), but are ignored in most studies. Sometimes, the concentration of dissolution products is measured, and very occasionally the concentration of dissolution products (which are water-soluble salts) is controlled by addition of these salts to the dispersion. The effect of addition of Al(iii) salt on the z potential of alumina was studied in [35]. At the IEP, the solubility of Al species is low; thus, the IEP was not very different from that in a 1-1 electrolyte. The solubility problem is discussed in more detail in Section 1.6. Parks [1] found that any combination of Na or K on the one hand and of Cl, NO3, or ClO4 on the other constitutes an inert electrolyte with respect to metal oxides, and this has been generally accepted since then. Interestingly, some

Introduction

13

electrolytes that are inert with respect to Hg show specific adsorption of either ion by metal oxides, and vice versa. Halide anions are usually inert with respect to metal oxides, but are potential-determining ions for silver halides. Thus, the term “inert electrolyte” is relative. In surface charging studies of nonconductive materials, a shift in the IEP induced by addition of a salt may be used as a criterion for the presence or absence of specific adsorption. Increasing the concentration of an inert electrolyte at constant pH induces an asymptotic decrease in the absolute value of the z potential without sign reversal. In contrast, increasing the concentration of specifically adsorbing counterions at constant pH leads to sign reversal. Several experimental studies of the effect of ionic strength on the z potential at constant pH have confi rmed this rule. The z potential as a function of ionic strength was also studied in [36], but the pH was not reported. Electrolytes that show inert behavior at concentrations up to about 0.1 M may induce a sign reversal of the z potential at concentrations of about 1 M in aqueous solution. In mixed and nonaqueous solvents, 1-1 electrolytes that are inert in water show specific adsorption of cations, which induces shifts in the IEP to high pH [37]. In principle, specific adsorption of anions induces an increase in the negative electrokinetic charge and a shift in the IEP to low pH, and specific adsorption of cations induces an increase in the positive electrokinetic charge and a shift in the IEP to high pH. However, sorption of heavy metal cations often induces surface precipitation, and then the IEP of the new surface is similar to that of the surface coating, that is, of the (hydr)oxide of the heavy metal cation. In such systems, the direction of the shift in the IEP depends upon the relative position of the IEP of the original surface on the one hand and that of the surface coating on the other. For example, in the presence of U(vi) (cationic species dominate in the pH range of interest), the IEP of hematite shifts to low pH [38]. This is because the IEP of U(vi) oxide is lower than that of hematite. Group 1 metal ions other than Na + and K+ are often used as constituents of inert electrolytes. The applicability of Li+ as a constituent of inert electrolytes is limited by the low solubility of its salts (e.g., the carbonate). Bromides and iodides show indifferent behavior toward metal oxides and related compounds, but adsorption of fluorides is usually specific. Reference [16] discusses F- as an inert ion, and specific adsorption of F- on alumina is considered as an exception. Reference [39] describes the adsorption of nitrate, perchlorate, and chloride as nonspecific on quartz, titania, and alumina, but as specific on zirconia and thoria. With SnO2 and Fe2O3, adsorption of chloride was found to be specific, and adsorption of nitrate and perchlorate to be nonspecific. Further examples of such exceptions are discussed in Chapter 2. Reference [40] shows that sodium and potassium trichloroacetate, trifluoroacetate, and trifluoromethanesulfonate also act as inert electrolytes. Ammonium and tetraalkylammonium salts are possible candidates for inert electrolytes for metal oxides, but not for silica. Namely, 10-3 M solutions of TMA, TEA, and TPA salts induce shifts in the IEP of silica to high pH, and 10-2 M solutions induce shifts to even higher pH [41]. The IEP of Si3N4 shifts to high pH in the presence of (C2H5)4NCl with respect to NaCl [42,43].

14

Surface Charging and Points of Zero Charge

The usual approach to inert electrolytes assumes that a broad pH range is covered, and the inert character of both ions of the electrolyte is essential. In studies that cover a narrow pH range far from the PZC, the character of the counterion (the ion and the surface have charges of opposite sign) is essential, and the inert/ specific character of co-ions, which are practically absent in the interfacial region, is less important. In the presence of CaCl2 in the strongly acidic range and in the presence of Na2SO4 in the strongly basic range, Fe(OH)3 behaves as in the presence of NaCl (the molarity of a 1-1 salt must be twice as high as the molarity of a 2-1 salt to produce the same concentration of monovalent ions). The CIP of goethite in Na2SO4 was only marginally different from those found in NaCl or NaNO3 [44]. The nature of the co-ion can be ignored over a limited pH range, and electrolytes with inert counterions act as inert electrolytes. Electrokinetic studies in which only NaOH and H2SO4 were used to adjust the pH, and no inert electrolyte was added, belong to a similar category. Although H2SO4 may induce a shift in the IEP, a pristine IEP may still have been obtained in such studies. That is, the results in neutral and basic pH in such studies are obtained without H2SO4 addition; thus the specific/nonspecific character of anion adsorption can be ignored. The presence or absence of a CIP of charging curves is not a criterion for an inert electrolyte. Figure 1b in [45] shows charging curves of alumina-coated titania at three KCl concentrations, and the figure caption claims that “these curves do not intersect at a common point, suggesting that Cl is specifically adsorbing on the oxide.” Such an interpretation is not acceptable. Charging curves of metal oxides at different concentrations of a heavy metal nitrate show a CIP [46], in spite of specific adsorption of heavy metal cations. That CIP falls at different pH values for different salts, and it does not correspond to the point of zero proton charge. On the other hand, coincidence of the CIP and IEP supports the hypothesis that an electrolyte is inert. Different research groups use different terminology in describing surface charging behavior in the presence of specific adsorption. Specifically adsorbed ions contribute to the surface charge. Some authors use the term “surface charge” as a synonym for proton charge, whereas others consider surface charge as the sum of proton charge and the charge due to adsorption of species other than the proton. Numerous electrokinetic studies (see, e.g., [47]) have been carried out in the presence of pH buffers. These results are not used in the present compilation, because the components of pH buffers usually show specific adsorption. Mixed evidence is found in the literature regarding specific/nonspecific character of adsorption of short-chain carboxylic acids. Reference [48] suggests an absence of a shift in the IEP of alumina (0.5 g/L) in the presence of >0.001 M organic acids. The effect of specific adsorption on the electrokinetic curves became visible at pH < IEP. No shift in the IEP of titania in the presence of CH3COONa or C2H5COONa was observed [49], but sodium salts of higher carboxylic acids induced a shift in the IEP to low pH. The PZC/IEP under pristine conditions is (by definition) independent of the nature and concentration of the electrolyte, and these details are often omitted in

15

Introduction

scientific publications. Otherwise, in the presence of specifically adsorbing ions, pH0 refers to a specific nature and concentration of electrolyte, which should be clearly indicated, for example, in the caption or key of a figure presenting surface charging behavior. Such information is generally provided, with some exceptions; for example, in [50], the IEP was most likely obtained in the presence of a dispersant (phosphate), although this was not indicated on the figure or in its caption, and the reported IEP could be easily confused with the pristine IEP. In a few studies (e.g., [51]), potentiometric titrations were carried out in the presence of NH4NO3. The disadvantage of this electrolyte and of other salts involving weak acid or weak base is substantial buffer capacity. The electrolytebackground-corrected uptake of protons is obtained as a difference of two large and almost equal numbers; thus, the value and even the sign of the difference is uncertain. This problem is less significant in electrokinetic methods, except that larger amounts of acid/base have to be used to adjust the pH than with salts of a strong acid and a strong base.

1.4

THE SIGNIFICANCE OF PARKS’ REVIEW

Parks’ review [1] introduced several ideas in the field of surface charging of metal hydr(oxides) that seem obvious now but at the time were revolutionary. Examples include the collection of PZC/IEP data from different sources, inert electrolytes (Section 1.3), and the possible correlation between PZC and wellestablished physical quantities such as the bond valence and the degree of oxidation or hydration. Not surprisingly [1] has been a source and an inspiration for many followers, and with over 2000 citations it is one of the most successful papers in the field of colloid chemistry ever published. Figure 1.13 presents the history of citations of [1]. Even now, the knowledge of many scientists about pH-dependent surface charging of metal oxides is chiefly based upon that

120 100

Citations

80 60 40 20 0 1965 1970 1975 1980 1985 1990 1995 2000 2005

FIGURE 1.13 Citations of Parks’ review [1].

16

Surface Charging and Points of Zero Charge

classical publication. For example, as recently as in 2006, one of the plenary lectures in a specialized colloidal conference was based on Parks’ ideas originally published in [1]. Also, the present compilation is in some senses a continuation of Parks’ work. Certainly, the results presented in a review can be only as good as the results in the publications upon which that review is based. The experimental techniques upon which the determination of PZC/IEP is based have improved considerably over the last four decades. Therefore, the experimental results reported in recent publications are (on average) more credible than those that were available in the literature in the mid-1960s. Surprisingly, much from [1] remains valid over 40 years after publication, but a few results and hypotheses have turned out to be incorrect. Both correct and incorrect results from Parks’ review have been repeated in recent papers. A few examples of such uncritical citations will be presented below. In a few instances, the PZC/IEP value, experimental conditions, or methods reported in [1] differ from those in the original paper cited as the source of these results. For example, the results cited in [1] from [52] are substantially different from those in the latter paper. Numerous papers have cited the incorrect value, following [1], rather than the value from the original paper [52]. Further similar examples are presented in Chapter 3. I would like to emphasize, however, that the rate of erroneous citations in [1] is not particularly high, compared with that in other publications. A few scientific papers cited in [1] report results that do not represent PZCs/ IEPs by today’s standards, but these results are quoted as PZC/IEP in [1]. For example, the solubility of W(vi) in HCl was studied in [53] by titration of Na2WO4 with HCl, and the authors found the pH of the solubility minimum (at a molarity of HCl of about 0.5, observed in a certain kinetic regime) and termed it the “isoelectric point of tungstic acid solubility.” The corresponding pH value (0.43) was cited in [1] as the “isoelectric point of hydrous WO3 obtained by electrophoresis,” and it was then cited following [1] in numerous papers. More examples like this are presented in Chapter 3. Although these results do not represent actual PZCs/ IEPs, some of them “made careers” as PZCs/IEPs widely cited in the scientific literature, and they are discussed as such in the present review. Even theories were built upon these results. The relationship between PZC and valency (PZC < 0.5 for M2O5 oxides, etc.) often quoted following Parks [1] is limited. Recent experiments with Nb2O5 and Ta2O5 indicate that the PZCs of these oxides are substantially higher than 0.5 (cf. Chapter 3). Similarly, the relationships between PZC and hydration (less hydrated compounds have lower PZC) and between PZC and degree of oxidation (oxides at a higher degree of oxidation have a lower PZC) often quoted following Parks [1] are also limited. Comparison between hematite and hydrous iron oxide on the one hand and between magnetite and hematite on the other (cf. Chapter 3) does not confirm these rules. The above criticism does not refer to Parks’ review, but rather to uncritical quotation of hypotheses (which might seem reasonable 40 years ago) without survey of more recent literature.

17

Introduction

1.5 STRUCTURE OF ADSORBENTS The acidity of surface oxygen atoms in the adsorbents of interest depends on the spatial distributions of atoms. Various representations have been used to illustrate these distributions. A perspective view of a few dozens of MO4 tetrahedra or MO6 octahedra (M = metal) that share corners, edges, or faces is the most common representation (Figures 1.14 and 1.15). A few models show just the polyhedra, and other models indicate possible locations of surface groups or possible mechanisms of binding of various species to the surface. In ball-and-stick models, particular atoms are represented as small balls in different colors (or shades), and the neighboring balls are connected by sticks of different lengths (Figure 1.16). The balls represent the positions of the centers of atoms, but not their size. The ball-and-stick and polyhedral representations may be combined. Wire-frame models show only bonds (sticks), and the atoms are not explicitly shown. In ball models, particular atoms or ions (metal, oxygen, and OH-) are represented as balls in different colors (or shades), but, in contrast with ball-and-stick models, the bonds are not explicitly shown, the balls are relatively large and touch each other, and the sizes of the balls usually represent the sizes of the corresponding atoms. A perspective view of a few dozens of balls shows positions of atoms in a particular crystallographic face. Different types of software are available to create these models. A few literature references reporting such models in graphical form are collected below. The crystallographic data upon which models are based are collected in the Appendix.

1.5.1

ALUMINA

Octahedral and ball models of gibbsite are presented in [54]. Octahedral models of the 0001 and 1-102 faces of a-alumina shown in Figure 3 of [55] and (a)

(b)

(010)

(001)

FIGURE 1.14 Structure of manganite: (a) the 010 plane is in the plane of the paper; (b) the 001 plane is in the plane of the paper. The 010 plane is indicated by the dashed lines. (Reprinted from Ramstedt, M. et al., Langmuir, 20, 8224, 2004. Copyright 2004 American Chemical Society. With permission.)

18

Surface Charging and Points of Zero Charge

FIGURE 1.15 An origami by Michał Kosmulski representing the octahedral model.

Figure 1 of [56] indicate the location of possible adsorption sites for metal cations. The octahedral models shown in Figures 3.10 and 3.15 of [57] illustrate the formation of gibbsite, bayerite, and boehmite from solution monomers. Balland-stick models of the 100, 010, and 001 surfaces of gibbsite are shown in Figure 9 of [58]. An original model of different planes of a-alumina was used

d¢

d

a

c

c¢ a

b

(110)

c¢ d¢

b

a

d c

(100)

FIGURE 1.16 Structure of rutile: white circles, O2-; black circles, Ti4+; large gray circles, O of adsorbed water; small gray circles, H of adsorbed water. Lower-case letters denote various surface species. (Reprinted from Imanishi, A. et al., J. Am. Chem. Soc., 129, 11569, 2007. Copyright 2007 American Chemical Society. With permission.)

19

Introduction Surface OH– Subsurface OH– 1st layer Al3+ 1st layer O2– 2nd layer Al3+

FIGURE 1.17 View of the 0001 plane of sapphire. The projection of multiple unit cells is indicated by the dashed lines. (Reprinted from Kershner, R.J., Bullard, J.W., and Cima, M.J., Langmuir, 20, 4101, 2004. Copyright 2004 American Chemical Society. With permission.)

in Figures 1 and 10 of [59] (Figure 1.17). Different layers of atoms in alumina were indicated by different colors. An octahedral model of diaspore is shown in Figure 7d of [60].

1.5.2

IRON (HYDR)OXIDES

Ball-and-stick models of the 001 planes of goethite (Figure 1), akanegeite (Figure 2), and lepidocrocite (Figure 3), the 110 plane of solvated goethite (Figure 5, also showing a wire-frame model), and the 1120 plane of hematite (Figure 4), are shown in [61]. Ball-and-stick models of the 001 plane of goethite (Figure 3) and the 111 plane of magnetite (Figure 2) are shown in [62]. Octahedral models of different iron (hydr)oxides are shown in [63]. Octahedral models of goethite and hematite, and of the phase transformation from goethite to hematite, are shown in Figures 1 and 11 of [64]. An octahedral model of hematite is shown in Figure 3.11 of [57]. A ball-and-stick model of the 012 surface of hematite in the XZ and YZ planes is shown in Figure 1 of [65]. Figure 5 of [66] shows a ball-and-stick model of the 100 face of goethite in plan and in section. An octahedral model shown in Figure 3.12 of [57] illustrates the formation of goethite from solution monomers. Color was used in an octahedral model of goethite shown in Figure 4 of [67]. Octahedral models of the 001 and 110 faces of goethite generated by the computer program ATOMS and shown in Figure 1 of [68] indicate a possible binding mechanism of phthalate. Octahedral models of the 100 and 110 faces of goethite shown in Figure 5 of [69] and of the 001 and 100 faces of lepidocrocite shown in Figure 8 indicate a possible binding mechanism of metal cations. An octahedral model of the ab plane of goethite shown in Figure 11 of [70] indicates a possible binding mechanism of metal cations. An octahedral model of goethite shown in Figure 1 of [71] indicates possible binding mechanisms of U(vi). Figure 1 of [72] shows typical morphologies of FeOOH crystals (goethite and lepidocrocite), and Figure 2 shows an octahedral model of FeOOH projected onto the 001 plane. Octahedral models of the 110 plane of goethite shown in Figure 12 of [73] and Figure 1 of [74], and of the 110 and 001 planes shown in Figure 5 of [75] and Figure 4 of [76], indicate the locations of different types of surface oxo and

20

Surface Charging and Points of Zero Charge

hydroxo groups. Ball-and-stick models of the 101 and 001 faces of goethite shown in Figure 6 of [77] indicate the locations of different types of surface oxo and hydroxo groups. Ball models of dry and hydrated 100 surfaces of goethite are shown in Figure 1 of [78].

1.5.3

MAGNANESE OXIDES

Octahedral models of various Mn oxides are shown in Figure 4 of [79] and Figure 1 of [80]. Octahedral models of manganite are shown in Figure 4 of [81] and Figure 1 of [82]. Octahedral models of the 001 and 010 planes of manganite are shown in Figure 2 of [83] and Figure 9 of [84]. An octahedral model of hausmannite is shown in Figure 1 of [82]. An octahedral model of birnessite shown in Figure 1 of [85] indicates a possible binding mechanism of metal cations.

1.5.4

SILICA

A tetrahedral model of quartz is shown in Figure 1 of [86] (cited from [87]). A ball-and-stick model of b-cristobalite is shown in Figure 1 in [88].

1.5.5

TITANIA

An octahedral model of the 101 plane of anatase shown in Figure 4 of [89] indicates the locations of different types of surface oxo and hydroxo groups and a possible binding mechanism of metal cations. A ball-and-stick model of the 110 surface of rutile is shown in Figure 3 of [90]. Figures 2 and 3 of [91] and Figure 10 of [92] show the 110 and 100 planes of rutile. A modified ball-and-stick model is used in [91], in which atoms are represented by their chemical symbols rather than by balls. Octahedral models of the 110 plane of rutile shown in Figure 1 of [93] and Figure 2 of [94] indicate the locations of different types of surface oxo and hydroxo groups. Octahedral models of rutile and brookite and a ball-and-stick model of anatase are shown in Figure 1 of [95]. Ball models of the 110, 100, and 001 faces of rutile are shown in Figure 9 of [96]. Octahedral models shown in Figure 3.20 of [57] illustrate the formation of anatase and rutile from solution monomers. Figures 3.16 and 3.18 of [57] show analogous processes for other metal (hydr)oxides.

1.5.6

CLAY MINERALS

A polyhedral model of hectorite is shown in Figure 3 of [97]. Figure 1 of [98] shows ball-and-stick model of kaolinite. A combined polyhedral/ball-and-stick model of kaolinite is shown in Figure 1 of [99]. A ball-and-stick model of kaolinite is shown in Figure 1 of [100]. A ball-and-stick model of the 010 plane of montmorillonite is shown in Figure 1 of [101]. Ball-and-stick models of kaolinite, pyrophyllite, and illite are shown in Figure 7 of [60].

Introduction

1.5.7

21

NITRIDES

A ball-and-stick model of b-Si3N4 is shown in Figure 1 of [88].

1.6 SOLUBILITY The present review is devoted to pH-dependent surface charging of relatively insoluble materials. Materials of solubility higher than about 0.001 M or 0.1 g/dm3 are outside the scope of this book, although PZCs/IEPs of relatively soluble materials can be found in the literature. The above solubility limit refers to nearly neutral pH, and at extreme pH values the solubility of so-called insoluble materials often increases by many orders of magnitude with respect to that at neutral pH. The solubility of so-called insoluble materials is often ignored in surface charging studies, but it must be realized that a certain fraction of the adsorbent undergoes dissolution in the form of various species. In some experiments, this solubility is in fact immaterial, but in a few other experiments, solubility matters. Solubility may be responsible for irreproducibility of experiments and for scatter in the PZCs/IEPs reported in the literature. Solubility depends on temperature, pH, and ionic strength. Solubilities of thermodynamically stable forms are lower than those of less stable forms, and solubilities of small crystals are higher than those of large crystals. Moreover, dissolution is a slow process, and the concentration of dissolved species in solution in many experiments is well below saturation. Thus, thermodynamic (equilibrium) data on solubility are of limited relevance to surface charging experiments with short equilibration times. Chemical dissolution of metal oxides and related materials is reviewed in [102]. Most studies were devoted to dissolution in the presence of organic ligands, which form stable complexes with metal ions in solution and/or enhance the dissolution of iron and manganese oxides by reduction of Fe(iii) and Mn(iv) [103]. Few studies have been carried out solely in the presence of inert electrolytes. Specific information on solubility of particular specimens can be found in the original literature. Usually, the experimentally determined concentration of a given element in a given kinetic regime is plotted against pH. Plotting dissolved amount as a function of time is another common mode of presentation. Ney [104] expressed the solubilities of various materials in terms of conductivities of saturated solutions. A kinetic study was also carried out.

1.6.1

SIMPLE (HYDR)OXIDES

1.6.1.1 Alumina Reference [105] reports solubilities of two aluminas as functions of pH. The solubility of alumina was also studied in [106] (Figure 3), [107] (Figure 1), [108] (Figure 3), [109], [110] (Figure 1), [111] (Figure 7), and [112] (Figure 4). The solubility of alumina in the basic range is substantially depressed in the presence of

22

Surface Charging and Points of Zero Charge

silicate [113]. Dissolution of boehmite was studied in [114] (Figure 8), and measured and calculated solubilities of gibbsite are compared in [115]. 1.6.1.2 Indium (Hydr)oxides The solubility of indium (hydr)oxides was studied in [116]. 1.6.1.3 Iron Oxides The solubility of magnetite was studied in [117] and that of iron(iii) hydroxide in [118]. Figure 2 of [119] shows the solubilities of different iron (hydr)oxides: amorphous >> goethite >> hematite. The lowest, pH-independent solubility is at pH 6–10, and ranges from 10-8 M (amorphous) to 10-12 M (hematite). 1.6.1.4 Manganese (Hydr)oxides Dissolution of manganite was studied in [84], and the solubilities of three samples of MnO2 are reported in Figure 9 of [120]. d-MnO2 dissolves at pH < 2 [121]. 1.6.1.5 NiO The solubility of NiO was studied in [122]. 1.6.1.6 PbO The concentration of Pb(ii) in solutions of different initial pH in contact with PbO at 40°C as a function of time (0–24 h) was studied in [123]. Only numerical values are reported and units are not specified. 1.6.1.7 Silica Silica is more soluble than most other materials studied in this book. Not surprisingly, more studies have been devoted to the solubility of silica than to solubilities of less soluble materials. An overview of the older literature was presented in [124]. The solubility of silica was studied in [1787]. Solubilities of various silicas in the range from 10-3.75 M (quartz) to 10-2.5 M is reported in [126]. The solubility increased with specific surface area. Silicate concentration was measured at different pH values and NaCl concentrations in [127]. A solubility of silica of 10-2.43 M at pH 2 was found in [128]. The kinetics and temperature dependence of the solubility of silica were studied in [129] and the kinetics and ionic strength dependence in [130], in both cases at pH 2–10. The kinetics, pH dependence, and effect of alkali pretreatment were studied in [131]. Solubilities of 11 ppm for quartz and 116 ppm for amorphous silica are reported in [86]. The same study reports 10–80 ppm of silica in natural waters. 1.6.1.8 Titania The low solubility of titania is documented in [132]. Figure 9 of [133] reports the solubility of titania.

Introduction

23

1.6.1.9 ZnO The solubility of ZnO in water and in 0.001 M KCl was studied in [134]. The solubility of original (commercial) and washed ZnO after 3-day equilibration was studied in [135]. Solubilities of Zn oxides and carbonates were studied in [136]. ZnO is soluble in dilute acids and bases, and remains sparingly soluble over a relatively narrow pH range.

1.6.2

OTHER MATERIALS

Solubility of materials other than simple oxides is a complex phenomenon, and usually leads to selective leaching of different elements and to changes in the chemical character of the surface. The concentration of more than one element in solution has to be followed. 1.6.2.1 Clay Minerals Reference [137] reports the absence of significant dissolution of illite. In contrast, [138] reports considerable release of Si and Al from illite. Dissolution of illite, that is, Al, Si, Ca, and Mg concentrations at pH 3–9, was studied in [139]. Dissolution of kaolinite at acidic pH was studied in [140]. Reference [141] reports the release of Si, Fe, Al, and Mg from montmorillonite as a function of pH. Concentrations of Si and Al in solution during titration of smectite are reported in [142]. Solubility of laponite is discussed in [143] and references therein. 1.6.2.2 Aluminum Silicate The Al concentration in solutions of synthetic aluminum silicate was studied in [144]. 1.6.2.3 Carbonates The solubility of FeCO3 and MnCO3 at 5 × 104 Pa CO2 was studied in [145]. 1.6.2.4 Apatite Calcium and phosphate concentrations were measured as a function of pH in [20]. The pH was adjusted by the addition of KOH, KF, Ca(NO3)2, or K2HPO4. Dissolution is inhibited in the presence of high-molecular–weight organic compounds [146]. 1.6.2.5 Niobate Reference [147] reports nonstoichiometric leaching of components from PbMg1/3Nb2/3O3 (Mg > Pb >> Nb in neutral and basic pH). The IEP depends on the solid-to-liquid ratio. 1.6.2.6 Titanate Acid treatment of BaTiO3 (Ba-containing supernatant removed) gives a product with an IEP similar to that of TiO2 [148]. Selective leaching of Ba from BaTiO3

24

Surface Charging and Points of Zero Charge

was also studied in [149]. The IEP depends on the solid-to-liquid ratio. Probably, similar effects are observed for other salts.

1.7

SOLID PHASE TRANSFORMATION AT ROOM TEMPERATURE IN CONTACT WITH SOLUTION

Numerous surface charging experiments have been carried out with materials that are not thermodynamically stable in contact with aqueous solution. Theoretically, the unstable phase can be transformed into a stable phase, but the rate of transformation is difficult to predict or control. In numerous experiments, the degree of transformation is negligible, and it may take years to see any change. On the other hand, a substantial difference in standard Gibbs energies between stable and unstable forms may induce an appreciable degree of phase transformation in the course of adsorption experiments, especially when equilibration times are long. It can also happen that, for kinetic reasons, one unstable form is converted to another unstable form rather than to a stable form. Thus, the initial state of the adsorbent (specific surface area, chemical formula, and crystallographic form), which is usually reported in scientific papers, is not necessarily relevant to the state at which the adsorption measurement was carried out. The thermodynamic data relevant to assessment of stability of different chemical compounds and of different crystallographic forms of the same compound are compiled in the Appendix. The Gibbs energy is not directly related to the rate of transformation; that is, the existence of a driving force does not imply that the transformation actually occurs. The phase transformation is usually ignored in surface charging experiments, and this may be responsible for irreproducibility of experiments and for scatter in the PZCs/IEPs of certain materials reported in the literature. A few specific examples of studies of phase transformation under experimental conditions relevant to studies of surface charging are discussed below. Hydration or dehydration and transformation between different crystallographic forms of the same compound have attracted more attention than redox reactions. Redox conditions are seldom controlled in surface charging experiments, with the exception of studies of surface charging of metal sulfides and nitrides and a few other redoxsensitive compounds. Thermodynamic stability of metal (hydr)oxides against formation of carbonates or basic carbonates is another relevant, but often ignored, aspect. Elementary thermodynamic calculations indicate that, for many sparingly soluble metal oxides, the equilibrium oxide + CO2  carbonate is shifted to the right at a partial pressure of CO2 that is found in the atmosphere; that is, oxides may convert into carbonates, and preformed carbonates will not spontaneously decompose. Surface charging experiments are often carried out in an atmosphere of inert gas in order to minimize the amount of CO2, but the effectiveness of measures aimed at exclusion of CO2 is limited. The experimental problems related to the presence/exclusion of CO2 are discussed in more detail in Chapter 2.

Introduction

1.7.1

25

ALUMINA

Spontaneous conversion of g-alumina into bayerite in contact with solution is reported in [110]. A diffuse reflectance Fourier transform infrared (DR-FTIR) study demonstrated transformation of g-alumina into bayerite-like phase on the surface [150]. Surface regions in a- and g-alumina convert to hydrated alumina similar to gibbsite or bayerite after exposure to water, according to [136]. Incorvati [151] observed transformation of a-alumina into bayerite or gibbsite at room temperature within 1 day.

1.7.2

CdO

CdO is transformed into hydroxide in NaClO4 medium and into basic chloride in NaCl medium [152].

1.7.3

CUO

Reference [153] reports conversion of Cu(OH)2 into CuO (a change in color is visible after 18 hours).

1.7.4

IRON (HYDR)OXIDES

Transformation of goethite into hematite by grinding at room temperature was detected by X-ray diffraction (XRD) [154]. Amorphous iron hydroxide was found to crystallize to goethite, according to [118]. Changes in the specific surface area and in the chemistry of the surface were observed. Storage of hydrous ferric oxide (HFO) for 16 weeks as a dispersion under nitrogen induced no substantial change in its crystallinity [155]. The fraction of oxalate-extractable Fe in aged HFO varied over the same period (in [155], Figure 11 and the text report opposite trends). The effect of aging at different pH values in the presence of different anions on the conversion of ferrihydrite into goethite or hematite at 20°C was studied in [156]. The conversion was slow at pH 7 (half-conversion time > 1 year), but it was faster at high pH. At pH 11, the half-conversion times ranged from 37 days (in the presence of nitrate) to 53 days (in the presence of sulfate). Goethite was the predominant product of conversion at pH 11, while at pH 8 and 9, hematite was the main product. Partial conversion of ferrihydrite into goethite in dispersion after over 4 weeks’ storage at room temperature was reported in [157], but no trace of goethite was detected after 10 days. Magnetite was partially converted into maghemite and akageneite on storage in aqueous medium for 3 years [158].

1.7.5

OTHER SYSTEMS

The above examples refer to simple systems containing only metal oxides and aqueous solution of salts of alkali metal cations. Other metal cations originally present in solution can be built into new phases formed upon sorption, as observed in studies of interaction of heavy metal cations with quartz [86] and with kaolinite [159].

26

Surface Charging and Points of Zero Charge

1.8 SOLID PHASE TRANSFORMATION ON HEATING Calcination of powders in the presence of different gases may induce solid phase transformation, which in turn affects the PZC/IEP. Hydrogen-treated and untreated zirconia were studied in [160], but no substantial shift in CIP was detected. Two titanias were heated in O2 or in H2 at 530 or 600°C, but no substantial change in IEP or CIP was observed in one sample [161]. Dehydration of titania (rutile) as a function of temperature was studied in [162]. The s0 of silica was depressed by a factor of 10 by heating at 800°C for 3 hours. Further heating (up to 36 hours) did not affect s0. Rehydration of heated powders for 3–56 days brought about a gradual increase in s0 [163]. A few examples of different phase transformations induced in the same initial material by calcination at various temperatures are presented in Chapter 3.

1.9 KINETICS In principle, kinetics is beyond the scope of the present book, which presents and discusses results obtained under pseudo-equilibrium conditions. However, some information about the kinetics of processes relevant to surface protonation is necessary to properly design pseudo-equilibrium experiments and to understand the significance of their results. Reference [164] presents an overview of the kinetics of adsorption. As the present book is focused on pH-dependent surface charging, the following types of kinetic experiments are directly relevant. 1. Solid is added to a solution. 2. Acid, base, or inert salt is added to a pre-equilibrated dispersion. 3. D2O or T2O is added to a pre-equilibrated dispersion. The time dependence of the following quantities has been studied: 1. 2. 3. 4. 5.

pH The concentration of products of dissolution of the solid The concentration of ions of inert electrolyte Distribution of nuclides Electrokinetic potential

Obviously, the time dependence of pH is of primary interest, and the other quantities have attracted less attention. The course of kinetic curves of adsorption/ isotope exchange at solid/liquid interfaces is qualitatively similar to that referring to kinetics in solution; that is, the changes are rapid at the beginning of the process, becoming slower in course of the experiment. This phenomenon is important in the planning of pseudo-equilibrium experiments. For example, in a system that has attained a certain degree of equilibration within 1 hour, equilibration for the next 5 minutes is unlikely to bring about substantial change.

Introduction

27

There are two classical ways to design a kinetic experiment: 1. The volume of samples taken to control the concentrations of the reagents is negligibly small compared with the volume of the system, or the concentrations are controlled without sample withdrawal (ion-selective electrodes). 2. The reaction is started in many identical reactors at the same time. Only one sample is taken from each reactor (at different times). Both solutions assure that the course of the reaction is not affected by sample withdrawal, and the reaction proceeds toward the same equilibrium state. Results obtained in experimental systems designed in this way often fit theoretical equations corresponding to certain transport models. Certainly, the fact that the results match a model calculation does not imply that the model is physically correct. Several kinetic studies reported in the literature disobey the above rules; that is, the volume of the samples withdrawn during the kinetic experiment is comparable to the volume of the system. Results of such kinetic experiments may be still interesting, but they are unlikely to fit any theoretical equation that assumes that the system tends to the same equilibrium state during the entire experiment. Each sample withdrawal changes the proportions of components in the system, and thus the equilibrium state also changes. Protonation/deprotonation reactions are among the fastest reactions in solution, and it is believed that surface protonation/deprotonation reactions are also fast. Therefore, the experimentally observed kinetics in surface protonation experiments is transport-controlled. Different models of kinetics of ion exchange with intraparticle rate control are discussed in [165]. Kinetic models based on a series of consecutive and/or branched reactions and experimental setups for kinetic measurements are reviewed in [166]. The experimentally observed pH after addition of a reagent (e.g., in potentiometric titration) does not reach a constant value, but changes at a variable rate even over very long times. Some arbitrary assumption is necessary to establish the “equilibrium” value. A few examples of kinetic experiments of surface protonation are briefly presented in this section.

1.9.1

PROTON ADSORPTION

1.9.1.1 Alumina The kinetics of proton adsorption by alumina was studied in [167,168]. The z potential was studied as a function of exposure time (1–14 days) in [169]. 1.9.1.2 Cr2O3 The z potential was studied as a function of exposure time (1–14 days) in [169].

28

Surface Charging and Points of Zero Charge

1.9.1.3 Iron (Hydr)oxides The kinetics of equilibration at a hematite single-crystal aqueous interface was studied in [170]. Relaxation times for proton adsorption–desorption on hematite and magnetite were studied as functions of pH in [171] using a pressure jump technique. The kinetics of proton desorption from natural hematite was studied in [172]. Rate constants were calculated for different salts at different concentrations. The time dependence of the pH during titration of ferrihydrite is shown in [173]. Figure 1 of [174] shows the time of equilibration after addition of base to a goethite dispersion as a function of pH. The kinetics of proton adsorption by goethite was also studied in [168]. The final pH of dispersions of hematite and corundum (with different amounts of acid or base added) after 2 hours’, 1 day’s, and 4 days’ equilibration is reported in [175]. The curves obtained for different equilibration times differ significantly over the pH range 5–7. The z potential of natural hematite as a function of aging time was studied in [176]. The variation of pH with time on addition of base to a hematite dispersion is reported in [119]. 1.9.1.4 Manganese Oxides The kinetics of OH and alkali metal ion uptake by l-MnO2 was studied in [177]. 1.9.1.5 Silica The kinetics of proton adsorption by silica was studied in [168]. After addition of quartz to a solution [178], the fast stage (the first 4 minutes) was followed by a slower, linear decrease of pH with time. 1.9.1.6 Titania The kinetics of proton adsorption/desorption on anatase was studied using a pressure jump technique in [179], and rate constants were calculated. Reference [161] presents the kinetics of proton adsorption for TiO2. References [180–182] report the changes in pH in a fresh titania dispersion at natural pH in water and in 0.005 M NaCl. A constant value was established in about 10 hours. The z potential was studied as a function of exposure time (1–14 days) in [169]. The variation of pH with time on addition of base to titania is reported in [183]. 1.9.1.7 Apatite The kinetics of proton uptake at was studied under different conditions. Proton uptake was accompanied by calcium release [184].

1.9.2

ISOTOPE EXCHANGE

The kinetics of tritium exchange between water and d-MnO2 was studied in [185]. The kinetics of tritium exchange between water and five different samples of silica was studied in [186].

Introduction

1.9.3

29

DISSOLUTION

1.9.3.1 Alumina The concentration of dissolved species as a function of exposure time (1–14 days) was studied in [169]. The rate of dissolution of alumina is reported in [187]. The rate of dissolution of alumina as a function of pH is reported in [188]. The rate of dissolution of corundum is reported in [189]. The kinetics of dissolution of alumina was studied in [110], and that of gibbsite in [190]. 1.9.3.2 BeO The rate of dissolution of BeO was studied in [187]. 1.9.3.3 Cr2O3 The concentration of dissolved species was studied as a function of exposure time (1–14 days) in [169]. 1.9.3.4 Cu(OH)2 Kinetics of dissolution was studied in [153]. 1 ppm of Cu was found at pH 5, and maximum concentration in solution was reached after 2 h. 1.9.3.5 Iron (Hydr)oxides The kinetics of dissolution of goethite in 0.5–2 M NaCl and NaNO3 was studied in [191]. 1.9.3.6 Silica The rate of dissolution of quartz, also in the presence of Al(iii), was studied in [192]. The rate of dissolution of quartz at 25°C and higher temperatures as a function of pH is reported in [188]. The dissolution rate of silica at pH 10 increases as the Na concentration in solution (as chloride or sulfate) increases [193]. The dissolution kinetics of silica as the function of pH and ionic strength was studied in [194]. The kinetics of dissolution of silica at low pH was studied in [195]. The rate of dissolution of bamboo phytoliths, which are composed chiefly of silica, is reported in [196]. 1.9.3.7 Titania The concentration of dissolved species was studied as a function of exposure time (1–14 days) in [169]. The kinetics of dissolution of titania was also studied in [197]. 1.9.3.8 Clay Minerals The kinetics of dissolution of kaolinite was studied in [189]. The kinetics of dissolution of aluminosilicates was studied as a function of pH in [188]. 1.9.3.9 Silicates Reference [198] reports dissolution rates of silicate minerals. The kinetics of forsterite (MgSiO4) dissolution was studied in [199].

30

Surface Charging and Points of Zero Charge

1.9.3.10 Carbonates The rates of dissolution of various carbonates were studied in [200]. The kinetics of magnesite dissolution was studied in [201] and that of dolomite dissolution in [202,203].

1.10 SOLUTION CHEMISTRY—PH SCALE Probably many readers of the present book do not expect that something as selfevident as pH measurements might cause a problem. Yet, apparent easiness and obviousness is a pitfall. Different aspects of the pH scale and of pH measurements have been discussed in numerous handbooks of chemistry. Reference [204] is a special monograph devoted solely to pH measurements. A few aspects of the pH of solutions, not directly related to surface charging or adsorption, are discussed in this section. The approach to proton adsorption from aqueous solution must be different from the approach to adsorption of other solutes, because water molecules can provide or absorb a practically unlimited number of protons (higher by several orders of magnitude than the concentration of any other species in solution and the concentration of surface sites) to balance the changes induced by adsorption. Thus, adsorption isotherms based on the concept of a distribution of a limited amount of adsorbate molecules between solution and surface are not applicable. Most authors accept this obvious fact, but a few others have used the same formalism for proton adsorption as is used for other solutes. For example, in [205], the surface charging of alumina is discussed in terms of adsorption isotherms (amount adsorbed vs. equilibrium concentration). Positive adsorption of protons is equivalent to negative adsorption of OH-, and vice versa. In adsorption experiments, uptake of protons and release of OH- cannot be distinguished. Only the net result of uptake/release of H+ and OH- can be obtained, and independent curves of H+ and OH- adsorption reported in the literature [206,207] must be based on measurements of other quantities. The normal pH scale is from 0 to 14 (the upper end of the pH scale corresponds to the logarithm of the reciprocal autoprotolysis constant of water, pKw at 25°C), but extremely acidic or extremely basic solutions induce numerous difficulties. Most commercially available pH electrodes give reliable results only in the pH range from about 2 to about 12. Very acidic and very basic solutions are caustic, and they dissolve many materials of interest that are insoluble at neutral pH. Very acidic and very basic solutions have intrinsically high ionic strengths; thus, concepts and methods that require low ionic strength are not applicable, and there are limited possibilities to study the effect of ionic strength on different quantities. For example, an ionic strength of 0.01 M is often sufficient to induce rapid coagulation of colloidal dispersions. Therefore, most studies of pH-dependent surface charging at solid/liquid interfaces are limited to the pH range 2–12. An experiment to confirm a hypothetical PZC/IEP at pH < 2 or >12 would be very difficult. Certainly, the limits 2 and 12 are not sharp, and the difficulties mentioned above gradually increase as the acid or base concentration increases. The width of the

Introduction

31

pH scale practically available for surface charging studies is then about 10 pH units; that is, 1 pH unit constitutes about 10% of the available pH scale. A difference of 1 pH unit is then significant, and a difference in excess of 2 pH units (20% of the available scale) is huge. A measurement, calculation, or estimation that produces an error of 2 pH units must not be considered as successful. An error of ±2 pH units covers up to 40% of the available pH scale, that is, such result is not much better than lack of any pH information. A few commercially available pH meters display a pH value with 3 decimal digits, and most commercially available meters display 2 decimal digits. The 3rd decimal digit displayed by a pH meter is not stable, even in a well-buffered system. The 2nd decimal digit displayed by the meter may be stable under certain circumstances and over limited periods of time, but it must not be considered as significant in many pH measurements, especially in an unbuffered system. In measurements related to pH-dependent surface charging, the 2nd decimal digit is usually uncertain. Thus, the PZCs/IEPs reported in the literature are usually rounded to the next 0.1 pH unit. Rare examples of PZCs/IEPs reported with 2 decimal digits are due to carelessness (insignificant digits are not rounded off), rather than to extraordinary accuracy. The uncertainty in the measured pH values is often ignored in scientific papers. For instance, in graphs presenting the electrokinetic potential as a function of pH, vertical error bars are often plotted, reflecting the uncertainty in the measured electrokinetic potential (Figure 1.7). It often happens that, even with a broad margin of error in the electrokinetic potential, it is still not possible to draw a smooth electrokinetic curve through all data points, and the outstanding points usually occur at nearly neutral pH. This problem can be fixed when the uncertainty in the pH values is taken into account (Figure 1.18). The procedure of pH measurement is not limited to insertion of a combination electrode into a solution (dispersion) and waiting until a constant value is displayed. Some pH value will be displayed, even when the rules given in every user manual are disobeyed. Typical errors are inadequate calibration of the pH electrode, use of outdated pH buffers, old electrodes (2 years is a typical lifetime), insufficient flow in the salt bridge between reference electrode and solution (or incorrect level and/or composition of the solution in the bridge), and insufficient electrical contact between solution and electrode. These examples of carelessness are commonplace in scientific laboratories, and typically induce errors in the range of a few tenths of a pH unit. It is not obvious to all scientists that the pH reported in z(pH) or s0(pH) plots (from which the IEP or PZC is determined) is the equilibrium pH of the dispersion used for the measurements. The following description was found in [208]. The authors equilibrated their particles in a solution 1 of pH 1, 1.9, 3, 5, 7, 8, 11, or 13. The particles were then separated from solution 1 and redispersed in pure water. The new dispersion (particles in solution 2) was used to measure the electrophoretic mobility. Obviously, the pH of the solution 2 formed by equilibration of pretreated particles with water was different from the pH of solution 1, and most scientists would have plotted the z potential against the pH of solution 2 to

32

z

Surface Charging and Points of Zero Charge

Data points

0

pH

FIGURE 1.18 Electrokinetic curve with one outstanding point. In order to explain the difference between the outstanding point and the smooth curve connecting all other points solely in terms of the error in the z potential, broad margin of error has to be allowed. The same discrepancy may be explained by allowing relatively narrow margin of error in the pH.

obtain the IEP. But, in [208], the z potential was plotted against the pH of solution 1. Not surprisingly, unusual values of the apparent IEP were obtained. The following problems related to pH measurement and interpretation are directly related to the problems discussed in this book.

1.10.1

PROBLEM 1: CONCENTRATION VERSUS ACTIVITY

The pH is minus the logarithm of the activity of protons rather than of their concentration. For ionic strengths less than 0.001 M, the difference in numerical value between the activity and the concentration is immaterial, but with concentrations of a 1-1 electrolyte greater than 0.01 M, the difference is in excess of 0.1. This is especially important when the recorded pH values are used to calculate the chemical speciation (solution of the chemical equilibrium problem), for which the measured activity has to be properly converted into concentration in the mass balance calculation.

1.10.2

PROBLEM 2: EXPERIMENTS AT CONSTANT IONIC STRENGTHS

When the ionic strength is high enough, and the required pH is sufficiently close to 7, the acid or base added to adjust the pH does not contribute to the total ionic strength. In contrast, with low ionic strengths, the pH adjustment often affects the overall ionic strength. For example, [209] reports measurements in a 0.00001 M 1-1 electrolyte at pH 3–12; [210] reports measurements in a 0.00001 M electrolyte solution at pH 2; according to [211], the IEP of silica in 0.0001 M NaCl (pH 1–2) is supposed to be different from that in HCl only; and [212] reports measurements

Introduction

33

in a 0.00001 M 1-1 electrolyte at pH 3–9, with the negative z potential supposed to be substantially greater than in a 0.0001 M 1-1 electrolyte. In those studies, the contribution of 1-1 salts to the total ionic strength at pH 3 was insignificant, and the total ionic strength (due to the presence of acid or base) was much higher than the salt concentration. It is impossible to carry out an experiment at pH 3 and ionic strength (total electrolyte concentration) less than 0.001 M, and the apparent effects of salt concentration were in fact due to some other factor that was not sufficiently controlled.

1.10.3

PROBLEM 3: BUFFERED VERSUS UNBUFFERED SYSTEM

Attempts at pH measurement in an unbuffered system at nearly neutral pH (e.g., in high-purity water) result in a very unstable display on a pH meter, and the amplitude of the oscillations may be of the order of 1 pH unit. This is an intrinsic property of electrometric pH measurements, and nothing can be done about it. Very dilute dispersions in 1-1 electrolytes used in microelectrophoresis and solutions in contact with monoliths (in capillary electro-osmosis) are typical examples of unbuffered systems. Results of pH measurements in such systems are sometimes quoted in the literature with two or even three decimal digits, while in fact even the first decimal digit is uncertain. IEPs based on such measurements are only rough estimates. The problem of unstable pH reading may be fi xed by using pH buffers. However, the components of these buffers are usually surface-active, and induce shifts in the IEP. Moreover, pH adjustment in a buffered solution requires a substantial amount of acid or base, thus leading to the effects discussed above in Section 1.10.2. In concentrated dispersions (e.g., in potentiometric titrations and electroacoustic measurements), the solid surface acts as a buffer, and the problem disappears.

1.10.4

PROBLEM 4: SODIUM EFFECT

In spite of progress in the technology of glasses for pH electrodes, their sensitivity to ions other than protons at high pH is still a problem. Even the highest-quality pH electrodes are sensitive to sodium and lithium salts at pH > 12. The difference between the display of the pH meter and the proton activity increases as the ionic strength and pH increase. This problem can be reduced (but not completely avoided) when low-sodium-effect electrodes (specially designed for high-pH measurements) are used.

1.10.5

PROBLEM 5: SUSPENSION EFFECT

When two separate electrodes (glass and reference) are used in concentrated dispersions, the display of the pH meter depends on the location of the electrodes in the dispersion. Moving the electrodes up and down can induce a difference in the apparent pH in excess of 0.2 pH units. The dispersion effect in pH measurements is discussed in [213].

34

1.10.6

Surface Charging and Points of Zero Charge

PROBLEM 6: DIFFERENT PH SCALES

The standard pH scale is designed for 25°C, atmospheric pressure, ionic strength less than 1 M, and solvent water. The upper end of the pH scale equals pKw, which depends on temperature, pressure, and ionic strength. The center of the pH scale, which corresponds to an ideally neutral solution, equals 0.5pKw. Measurements at high or low temperatures, high pressures (>107 Pa), or very high ionic strengths, or in mixed or nonaqueous solvents, require calibration by means of special pH buffers. In other words, a pH electrode calibrated under standard conditions must not be used to measure pH under nonstandard conditions. A pH meter calibrated under standard conditions will certainly display some value under nonstandard conditions, but that value is not the actual pH. Standard pH buffers for common mixed solvents are commercially available. There is no simple relationship between the pH scales for standard and nonstandard conditions. pH measurements at high ionic strengths are discussed in detail in [214]. Autoprotolysis constants of water are reported in [215] for numerous nonaqueous and mixed solvents, in [216] for numerous mixed solvents, and in [217] for aqueous dioxane. Gibbs energies of proton transfer from water to mixed solvents are reported in [218,219].

1.10.7

PROBLEM 7: ELECTROLYSIS

The pH measured just before injection of dispersion into an electrophoretic cell is not necessarily relevant to the pH in the cell during the measurement. The products of electrolysis in electrophoretic cell make the pH more basic. The effect of products of electrolysis on the pH in the cell is more significant with a short distance between the electrodes, high voltage, long measurement time, and low solid-to-liquid ratio. This problem is discussed in more detail in [220].

1.11

VERY DILUTE SOLUTIONS

This book focuses on surface charging of solids dispersed in solutions of inert electrolytes, in the absence of surface-active species. In real experiments, surface-active species are not completely absent, but occur at very low concentrations. Such impurities are often referred to in order to explain unexpected results. The state of matter in very dilute solutions is seldom considered in the scientific literature, and it has been the subject of numerous misinterpretations. The principles of solution chemistry known from elementary handbooks apply in a concentration range of about 10-6 –1 M. The procedures and methods that work very well at concentrations greater than 10-6 M must not be extrapolated to lower concentrations. This is because distilled water used in the laboratory is not pure water, but contains dissolved components of air, materials leached from the container (e.g., silica), and other components. The contribution of the solutes to the physical and chemical properties of water is negligible when their concentrations are low enough, and the presence of impurities in distilled water can be

Introduction

35

ignored in typical solution chemistry experiments. It is tacitly assumed that impurities are absent and that the solute is homogeneously distributed in the entire volume of solution, but this is an idealized model rather than physically realistic. The range of very high dilution requires a different approach. Typical distilled (deionized) water contains a few solutes at a level greater than 10-5 M (a few ppm), a few dozens of solutes at a level greater than 10-6 M (a few hundred ppb), and hundreds of solutes at a level greater than 10-8 M (a few ppb). The concentrations of impurities vary from one sample of distilled/deionized water to another, and it is difficult to select a representative sample. Very likely, the distribution of impurities is nearly Zipfian. Zipf’s law was originally formulated to describe the frequency of occurrence of words in English language, but it also applies to many natural phenomena. It was found that the product of the rank in a list (ordered by descending frequency) and the frequency is nearly constant. In other words, the frequency is inversely proportional to the rank. Exact inverse proportionality is seldom observed, but the type of frequency distribution in an assembly of different species in which a few most frequent species constitute a large part of the assembly and numerous less frequent species constitute a small part is more common than the type of distribution in which all species are equally represented. The validity of Zipf’s law has been examined for distribution of concentrations of various compounds [221], but not of impurities in distilled water. It would be a difficult task to find a complete distribution of the concentrations of impurities, which are often beyond the range of available analytical methods, and their distribution in solution is not necessarily homogeneous. Namely, adsorption on walls of a vessel or on dust particles, which has a negligible effect on the distribution of a solute in a concentrated solution, may substantially affect the distribution of solutes in a dilute state. This effect is well known for radioactive nuclides (radiocolloids), for which it can be easily followed, but it occurs for nonradioactive substances as well. Relatively concentrated solutions can be obtained by dilution of more concentrated solutions by a certain factor. It is tacitly assumed that the water used for dilution does not contain the solute of interest. Such an assumption is acceptable when relatively concentrated solutions (>10-4 M) are diluted. Even when water used for dilution contains, say 10-10 M of the solute of interest as an impurity, the contribution of that impurity to the total amount of the solute of interest in diluted solution is still negligible. The assumption that the solute of interest is absent in water used for dilution becomes risky when a diluted solution (<10-6 M) is further diluted. Very likely, water used for dilution will contain substance(s) similar to the substance of interest, or even the substance of interest itself, at concentration(s) comparable to the desired concentration of diluted solution. Water used for dilution may also contain substance(s) that react with the substance of interest. This effect is negligible when the concentration of the solute of interest is much higher than the concentrations of these substances, but becomes significant at sufficiently low concentration. The adsorption on dust particles and on the walls of the container discussed above makes the distribution of the substance of interest far from homogeneous. Therefore, the amount of the substance of interest in a very dilute

36

Surface Charging and Points of Zero Charge

solution is not necessarily proportional to the volume of the solution. In 1 cm3 of a 1 M solution, there are about 10-3 mol of the substance of interest, but the amount in 1 cm3 of a 10-9 M solution can be very different from 10-12 mol. Therefore, the possibility of obtaining a very dilute solution of the desired concentration by a series of consecutive dilutions is limited. Homeopathy is an example of an erroneous approach to very dilute solutions. A few examples of experiments with solutes at “homeopathic” dilution can be found in the scientific literature. The actual concentration of the solute of interest in these experiments might be different from the desired concentration calculated from the concentration of the stock solution used to obtain the studied solution by the dilution method. The errors in the determination of the actual concentration are due to the solute of interest, which may be present as an impurity in the solvent, and to the heterogeneous distribution of the solute. It is also possible that the solute of interest reacts with another solute present in the solvent as impurity and it is converted into another compound. This effect is negligible as long as the concentration of the solute of interest is sufficiently high, but it becomes significant at “homeopathic” dilutions. When the solute of interest reacts with an impurity present in distilled water, its actual concentration after dilution will be lower than the “theoretical” concentration calculated assuming that the solvent was pure water. The allegedly pure solids used in adsorption experiments are also potential sources of impurities. For example, in X-ray photoelectron spectroscopy (XPS) surface analysis, carbon is always detected as a result of adsorption of organic substances by solids from air. Sources of impurities in adsorption studies are discussed in [222]. The difficulties discussed above refer to control over the concentration of a component that occurs at low concentrations. In contrast, very low concentrations of a species (see Section 1.12) can be easily controlled when other species containing the same components are available at sufficiently high concentrations. For example [H+] = 10-10 M in 0.0001 M NaOH solution or in a commercially available buffer solution (a mixture of a weak base with its salt).

1.12

SPECIATION IN SOLUTION

The terms “components” and “species” in chemistry have specific meanings different from those in common parlance. There are a limited number of components, which define the composition of the solution. Species are chemical entities that actually occur in the solution. Each species can be obtained as a product of chemical reaction from components, but a component cannot be obtained as a product of chemical reaction from other components. For example, in aqueous NaCl, there are two components, namely water and NaCl, and numerous species, namely water and the ions H+ (aq), OH- (aq), Na + (aq), and Cl- (aq). The above list of species is usually sufficient to describe the behavior of dilute solutions, but it is not complete. Specific problems may require consideration of other species, such as ion pairs in aqueous NaCl. The concept of components and species was originally introduced in solution chemistry, but it can also be used in surface

Introduction

37

chemistry. Adsorption is considered as the formation of new species as a result of reaction between surface sites (components) and components of a solution. Components are present in solution in the form of different species. The concentrations of these species depend on the concentrations of all components in the system. Metal cations form aquo complexes and other complexes in which one or more water molecules are replaced by ligands other than water. This problem is discussed in basic handbooks of inorganic and analytical chemistry. Speciation in simple systems can be easily calculated when the stability constants of particular species are available. Specialized software that facilitates calculation of speciation in more complex systems is available. Many errors and misinterpretations related to speciation in solution can be found in the literature. It often happens that one species representing a certain component is dominant and the concentrations of other species are negligible, but it is important to clearly distinguish between the total concentration of a component and the concentrations of certain species. The number of species actually present in the system is much higher than the number of species for which stability constants are available in the literature. Many species are present at very low concentrations, and their contribution to the properties of the solution is negligible. This is probably another example of the Zipfian behavior discussed above; that is, a few species occur at high concentrations, and significantly affect the properties of the solution, and numerous species occur at low concentrations, and practically do not affect the properties of the solution. Any attempt at determining the stability constants of various species must involve a selection of a few most abundant (most important) species and truncation of all other species. In other words, complex reality (all species) is represented by a model (a few species) that is easier to handle mathematically. The experimental results are then fitted to the model, and the best-fit stability constants of the species that belong to the model are reported. Certainly, the numerical values of these stability constants depend on the model, that is, on the choice of the species that are taken into account. When the same experimental data are handled in terms of two models with two different sets of species, the numerical values of the stability constants of species that are common to both models will be different. The best-fit stability constants are then used to calculate the speciation for any experimental conditions. Such a calculation must be based on a set of stability constants calculated for a certain model (a certain set of species). Combination of numerical values of stability constants taken from different sources is incorrect, because stability constants that might have been calculated for various models are unlikely to produce proper speciation. Examples of apparent speciation calculated from stability constants of particular solution species taken from various sources can be found in the literature [223]. Combinations of stability constants of particular surface species taken from various sources are commonplace in the literature. Apparently, the authors of these papers considered the stability constants as independent physical constants. In fact, a stability constant is only valid as part of a certain model, and is not applicable outside that model. Polynuclear complexes are often neglected in calculation of speciation in solution. According to [224], silica occurs in water as dimeric species

38

Surface Charging and Points of Zero Charge

Si2O2(OH)5- and as monomeric Si(OH)4. The higher polymeric species are less abundant. The fraction of polymeric species increases with pH and with silica concentration. The literature data on stability constants of various species are not consistent, for the reasons explained above. Ligand-exchange reactions in solution have various rates; for example, in Cr(iii) complexes, they are very slow. Thus, the system of interest is not necessarily in equilibrium with respect to these reactions, even with vigorous stirring and long equilibration times.

2

Methods

The PZC values compiled in the present book are based on results found in the literature. Different strategies were used to localize relevant sources. A few journals (e.g., Journal of Colloid and Interface Science) that have published large numbers of relevant papers were analyzed paper by paper to find relevant sources. The journals that have published fewer relevant papers were searched by means of tools provided by their publishers within their Internet services to find articles containing certain phrases (e.g., “point of zero charge”) or citing certain articles (e.g., Parks’ compilation of PZCs [1]). The Thomson Scientific database was searched using similar strategies. The Internet was searched by means of various search engines using similar strategies. Numerous sources were localized as references in already acquired articles. Several articles were obtained directly from their authors. Relevant sources were also located by accident during different activities of the present author, not directly aimed at a compilation of a PZC database. Results reported in secondary sources (publications reporting previously published results) were avoided in the present compilation, and attempts were made to access the primary source. This process often consisted of many steps, because what appeared to be a primary source often happened to be another secondary source. Secondary sources were chiefly used to acquire information about primary sources. The results from PhD theses, conference proceedings, and publications using non-Latin alphabets are often cited after secondary sources when the original source was not accessible or difficult to understand. It was not always easy to distinguish between primary and secondary sources. In a few papers, it was not clear if they reported an original pH0, with the reference being cited only for a method, or if the reference was also cited for the value of pH0. Such problems could not be solved without inspection of the reference. Experimental results are often re-published. Re-published results are reported only once in the present review, but with as many literature references as possible. This approach is different from that adopted in [2], in which only one of many literature references reporting the same results was selected. It was not always clear if the same data were re-published. It might very well have happened that re-published results appear as separate entries on the one hand or that two independent studies are grouped as one entry on the other. Assessment of originality or of precedence was not the goal of the present study. 39

40

Surface Charging and Points of Zero Charge

Different modes of presentations of PZC/IEP results have been found in the original literature. A graph showing surface charge density or electrokinetic potential as a function of pH is the most common form of presentation of the results of surface charging experiments. The advantage of this form of presentation is that the correctness of determination of PZC/IEP from the data points can be assessed. Normally in these graphs, low pH values are to the left and high pH values are to the right, and positive s0 and z are above and negative s0 and z are below the pH axis, and this natural convention will be used in this book. Several cited authors used the opposite conventions; that is, with low pH values to the right or with positive s0 and z below the pH axis (e.g., [225]). In older publications, the original concentration of acid or base is often reported, rather than the equilibrium pH (e.g., [226,227]), and consumption of acid or base is reported rather than s0 (e.g., [228]). Sometimes (e.g., [229]), the results are plotted against pH0 -pH rather than against pH, and pH0 cannot be directly read from the graph. Several studies report the results in tabular form instead of graphs (e.g., [230], z vs. pH) or in addition to them ([229], mobility vs. pH). Several authors used a subjective interpolation (see Figure 1.11) or even extrapolation (see Figure 1.12) to obtain their PZCs/IEPs. In such cases, the authors’ PZCs/IEPs are given with suitable comment. In a few cases, the PZC/IEP reported in the text was in contradiction with the PZC/IEP presented in a figure. It was difficult to assess which was correct, and both values were reported. In a few studies (e.g., [231]), a pH range is reported in the text rather than a precise value of the IEP. This is an alternative solution to an arbitrary interpolation of an electrokinetic curve in a range where data points near the IEP are not available (see Figure 1.11). Even in carefully designed and conducted experiments, there is no realistic possibility of determining PZCs/IEPs with accuracy better than 0.1 pH unit. This is due to the intrinsic properties of pH electrodes on the one hand and of dispersed systems on the other. Surface charging is always accompanied by other phenomena that affect the pH and that are unavoidable and difficult to control. Several authors (e.g., [23,71,100,232–234]) report their PZCs/IEPs with two decimal digits. This gives a false impression that the second digit is significant. Such results are rounded to the nearest one-tenth of pH unit in the present compilation. Numerous studies report only PZCs/IEPs without data points upon which those PZCs/IEPs are based. There is no ground to challenge the correctness of such results, but it is possible that such a PZC/IEP was not obtained according to the standards recommended in the present book. The literature references reporting only PZCs/IEPs without data points are clearly indicated as such in the present compilation. In another mode of presentation of experimentally determined surface charging data, values of parameters of a certain model of an electrical double layer, adjusted to the experimentally determined results, are reported rather than the PZC. Usually, this information is sufficient to calculate the PZC, and the result of such a calculation (rounded to the nearest one-tenth of pH unit) is used in the present compilation when the PZC is not explicitly reported in the original publication. A few studies report the results (usually electrokinetic potentials) for

41

Methods

one [235], two [236,237]), or a few selected pH values (e.g., only a negatively charged surface was studied in [238]), without attempting to determine the PZC/ IEP. In [239], only the sign of the charge of colloidal particles of common minerals at neutral pH is reported. Such forms of presentation give only a rough idea of the position of the PZC/IEP, and such results were usually ignored in the present review.

2.1 EXPERIMENTAL SETUP IN ELECTROKINETIC MEASUREMENTS Electrokinetic phenomena are irreversible processes, in which an electric force induces a coupled mechanical flux or a mechanical force induces a coupled electric flux, in the direction tangential to a charged surface. The z potential is calculated from the phenomenological coefficients in the relationships between the force and the coupled flux in these phenomena. The pH0 obtained by means of electrokinetic measurements is reported as “iep” in the “Method” columns in the tables in Chapter 3. The trade names of commercial instruments or short descriptions of home-made instruments used for electrokinetic measurements are given when possible. The present approach is different from that in [2], in which the type of instrument was not specified. Moreover, the present book does not consider pH0 values obtained by means of an electroacoustic method as a separate category, and they are also reported as “iep.” An introduction to electrokinetic phenomena can be found in [240] and in handbooks of colloid chemistry. The choice of method and instrument suitable for the character of a sample is key to successful electrokinetic measurements. In principle, all techniques and all instruments should produce the same z potential and the same IEP in a system of interest. A few multi-instrument studies have been published. For example, [241] reports IEPs obtained by streaming potential and by electrophoresis (using a commercial apparatus). A multi-instrument electrokinetic study of alumina in 0.01 M NaNO3 is reported in [242]. The IEP was also relatively consistent with different solid-to-liquid ratios. Glass capillaries with inner sides coated with spherical nanosize hematite particles showed an IEP at pH ⬇ 5, while the IEP of the original hematite obtained by electrophoresis was at pH 9.3 [243].

2.1.1

ELECTROPHORESIS

The movement of colloidal particles in an electric field is termed electrophoresis. Most commercially available zetameters are designed to measure the electrophoretic mobility ue of particles. The z potential is not measured directly, but is calculated from ue. The Smoluchowski equation ueh = ez

(2.1)

is often used. Equation 2.1 is valid at ka >> 1, where k is the reciprocal Debye length and a is the particle radius and for low z potential. The relationship between ue and z has been extensively studied, and many more or less complex equations

42

Surface Charging and Points of Zero Charge

have been proposed for moderate or low ka and for high z potential. An analytical relationship for the most general case (any value of ka and z potential) is not available. Electrophoresis is especially useful for fine particles that form stable dispersions. Large particles will settle down before the measurement can be carried out. Unsuccessful electrokinetic measurements with two samples of relatively coarse (1 and 8 μm diameter) hematite particles are reported in [244]. Materials in the form of large particles or macroscopic specimens can be ground to a finer size, but the new surface exposed by grinding may have different properties from the original (external) surface. Sedimentation is slower for particles with specific densities close to that of the solution. To be visible, the material of interest must have a refractive index sufficiently different from that of the dispersing medium. Electrophoresis is especially useful when a limited amount of material is available, because a very small amount of the material of interest (a fraction of a milligram for sufficiently fine particles with a high refractive index) is sufficient to perform a measurement in modern devices. Electrophoresis is suitable for dilute dispersions, but it cannot be used directly for dense dispersions or in colored liquids that are not transparent to light. The electrophoretic mobility of particles in a concentrated dispersion is determined by dilution of a portion of the dispersion with a supernatant obtained from a larger portion. Dilution of a dispersion with water or with some solution other than the supernatant in order to produce a transparent dispersion is not recommended, because the z potential of particles in equilibrium with the new solution (of different composition) may be substantially different from the z potential of the same particles in the original solution. Electrophoresis is not recommended for measurements at high ionic strengths. A typical limit is 0.1 M, but a few modern devices can be used up to about 1 M. Electrophoresis can be used to independently determine the z potentials of two or more kinds of particles present in the same dispersion. Many devices produce results in the form of mobility histograms (shown, e.g., in [245]), in which peaks corresponding to various types of particles can be distinguished (Figure 2.1). Basically, an electrophoretic measurement can be carried out with a dispersion of conductive particles, although the popular equations used to calculate the z potential from the mobility are valid for insulating particles only. Electrophoresis of metal particles was studied in [246]. Reference [247] reports experimental problems that precluded an electrophoretic study of sulfur at pH < 4. The nature of those problems was not specified. Electrophoresis does not require calibration against a standard dispersion, but standard dispersions (usually latexes) are offered for control of the performance of instruments. A goethite–phosphate system with a controlled solid-to-liquid ratio, pH, ionic strength, and phosphate concentration was recommended as a standard dispersion in [248]. Similar z potentials for that standard dispersion were obtained in five laboratories, with three types of instruments. Electrophoresis is always accompanied by Brownian motion; that is, the mobility of a single particle measured at given time point is not necessarily representative of that particle or of the entire population. Brownian motion is responsible for

43

Intensity

Methods

Mobility

FIGURE 2.1 Mobility histogram. The narrow peak represents large particles of one material and the broad peak represents fine particles of another material simultaneously present in the same dispersion.

the shapes of mobility histograms (see [249] for specific examples), and it can be used to estimate particle size (smaller particles produce broader peaks; Figure 2.1). The errors due to Brownian motion can be eliminated by taking an average mobility of many particles. A few illustrations of home-made electrophoresis cells can be found in the older literature [225,250,251]. Several designs have gained popularity, and they are named after their inventors: Abramson (flat cell), Briggs, Briggs–Mattson, Hamilton–Stevens, Mattson [252,253], Riddick, and van Gils. A moving-boundary cell is shown and described in [7,47]. Nowadays, the use of commercial instruments prevails, and studies using home-made machines are rare. The tables in Chapter 3 (with the literature search having been completed in 2007) report results obtained by the following commercial instruments based on electrophoresis, in which the mobility is calculated from the velocity of colloidal particles: • • • • •

From Bel Japan: Zetasizer 4 From Brookhaven (BI, BIC): 90 Plus, ZetaPlus, and Zeta PALS From Coulter: Delsa models 440 and 440 SX From Jiangsu: DXD-11 From Malvern: models 3000 HSA (HAS) and 5000; AZ-6004; Nano ZP; Nano ZS; Zetamaster S, 5002, and PCS; Zetasizer (Z-sizer) 2, 2c (IIc), IIe, 3 (III, illustrated in [254]), 4 (IV, MK IV), 2000, 3000, 3000 HS, 5000, ZEN 2010, ZEN 3600, and ZET 5004 • From Microtec (Japan): Zeecom and ZC-1500 • MRK (Japan): velocity of single particles in a flat cell

44

Surface Charging and Points of Zero Charge

• Nicomp 380/ZLS and Particle Sizing Systems • From Otsuka: Leza 600, Photal ELS (ELS) 800, 3800 (Doppler shift, flat cell), and ELS-8S (Doppler shift) • From Pen Kem: models 102, 500, 3000, and 3000 S (S 3000); Laser Zee Meter models 500 and 501 • From Perkin-Elmer: model 39 (moving-boundary electrophoresis) • From Rank Brothers (Rank): Mark I and Mark II (MK II, illustrated and described in [255]). • From Repap (Sweden): velocity of single particles in a flat cell • From Sephy (CAD): Zetaphoremeter models II (or Sephy 2100, Z 2300, and Z 3000: velocity of single particles in a rectangular cell), III (rectangular cell, velocity of single particles processed by digital image analysis software), IV (Z 4000: velocity of single particles processed by digital image analysis software), 4000, and 4.20 • From Shanghai Zhongshun: Powereach JS94 H and JS94G+ • From Sugiura (Japan): 2VD • From Arthur H. Thomas & Co. (flat cell, reported in pre-World War II papers). • From Zeiss (Karl Zeiss): Cytophoremeter (rectangular cell) • From Zeta-Meter (ZM, Z-Meter, Riddick): Zeta-Meter (there is a photograph and description of a model without a number in [104]) models 2.0, 3.0, 3.0+ (illustrated in [256–258]), 77, and 80 Technical data on current versions of these instruments can be found on the manufacturers’ Web pages. Most of the above instruments are no longer available on the market, but many pieces of older equipment are still running in different laboratories. Various spellings of the above trade and company names occur in the literature. The number of different trade names listed above is probably higher than the number of substantially different designs of instruments. The above information about the names and principle of operation of instruments in based on the scientific literature rather than on manufacturers’ data. In older commercial instruments, the velocity of individual particles was observed in a microscope and measured by means of a stopwatch. In more advanced models the particles were displayed on a screen and various facilities were added to eliminate the subjectivity factor. Measurement of Doppler shift of the wavelength of light scattered by moving particles made it possible to follow many particles in a short time. Home-made electrophoresis machines have been designed for special applications that are beyond the operational range of commercial instruments. A hightemperature electrophoresis apparatuses is described in [259–262]. Illustrations of home-made apparatuses for measurements of the electrophoretic mobility of gas bubbles can be found in [263,264]. A few methods of determination of the z potential based on electrophoresis use quantities other than particle velocity. The z potential can be calculated from the mass of particles transported in an electric field. This idea was commercialized by Micromeritics in an instrument called EMTA 1202 and by Numinco in an

45

Methods

instrument called MIC 1201. Home-made machines based on electrophoretic mass transport have also been used [265–267]. Illustrations of a cell are presented in [265–268]. The IEPs obtained by means of these machines are classified as “Electrophoresis” in the “Instrument” columns in the tables in Chapter 3. Electrophoresis is also accompanied by electro-osmosis, that is, the movement of liquid in an electrophoretic cell caused by the electric field. Analytical equations for electro-osmotic flow are known for the most popular cell geometries, namely, cylindrical and with a rectangular cross-section. The general equation for a rectangular cell is complicated, but it simplifies for a flat cell (high aspect ratio). Different ideas have been proposed to eliminate electro-osmosis or to properly correct for it. The measured velocity of particles with respect to fixed elements of the apparatus is the sum of the electrophoretic velocity of the particles and the electro-osmotic velocity of the liquid. Fortunately, for simple, highly symmetrical cell geometries, a stationary layer can be found; that is, at a certain distance from the cell walls, the electro-osmotic velocity is zero and the measured velocity of particles is not affected by the movement of the liquid. In the idealized case shown in Figure 2.2, there are two stationary levels, which are situated symmetrically with respect to the cell axis. Vertical lines represent the cell walls, and a uniform electric field is applied along the cell axis. The measured velocity of the particles (circles) depends on their position in the cell and is equal to the sum of the electrophoretic velocity of the particles with respect to the liquid (which is independent of position in the cell) and the electro-osmotic velocity of the liquid with respect to the cell, which depends on its position in the cell. At the stationary levels, the electro-osmotic velocity is zero and the measured velocity of the particles is equal to their electrophoretic velocity. Away from these levels, the measured velocity of particles is different from their electrophoretic velocity (indicated by a

Apparent velocity

Actual velocity of particles

Stationary levels Cell walls

Position in the cell

FIGURE 2.2 Electro-osmotic velocity of liquid (dashed parabola) and apparent velocity of particles (circles) in a flat cell. Zero velocity is represented by the horizontal solid line.

46

Surface Charging and Points of Zero Charge

two-headed arrow). In practice, the actual electro-osmotic profile often shows deviations from the theoretically calculated shape. There are also technical limitations related to the focusing of the optical system at the desired position in the dispersion. Therefore, electro-osmosis causes errors in electrophoretic measurements, especially in the early devices, which used elongated cells. These problems can be controlled in the “parabola method,” that is, measurement of the entire profile of apparent mobility across the symmetry axis of the cell rather than the mobility at a fixed distance from the cell wall (Figure 2.2). The shape of such a mobility profile nearly corresponds to a second-degree polynomial in a rectangular cell. The parabola method is tedious and not very popular, and the number of data points in one profile (seven points in Figure 2.2) is a question of subjective choice. Examples of such studies can be found in [269–272]. In several modern devices, the distance between the electrodes is comparable to the cross-section of the cell, and special cell designs reduce the problems with electro-osmosis. The parabola method makes it possible to measure the z potential of cell walls. Usually, the cell is made of quartz, and the parabola method thus offers the possibility of determining the IEP of one material that has already been extensively studied. The z potentials of macroscopic specimens of other materials can also be determined from the mobility profile [273–275] by replacement of the original cell wall of a commercial electrophoretic cell by a flat specimen of the material of interest. For example, in [276], the IEP of a basal plane of mica found from the mobility profile was different from the IEP of a mica dispersion. Only a few types of electrophoretic devices (most of which are no longer available on the market) can be used to determine z potentials by means of electro-osmosis.

2.1.2

ELECTRO-OSMOSIS

When the solid phase is fixed (e.g., as a capillary, membrane, or porous plug), an electric field induces a flow of liquid termed electro-osmosis. The character of the flow depends on the construction of the apparatus. For example, in an electrophoretic cell, the liquid flows in one direction near the walls and in the opposite direction in the center of the cell, and the net flow across the cell cross-section is zero (Figure 2.2). Electro-osmosis can also be demonstrated as a difference in pressure (height of a water column) generated as a result of an electric field applied to a capillary, membrane, or porous plug. Electro-osmosis has been chiefly discussed as a phenomenon accompanying electrophoresis (Section 2.1.1), but it also occurs separately and can be used to determine the z potential and the IEP. Electro-osmosis is recommended for macroscopic specimens, for fibers, and for large particles, which do not form stable dispersions. Opaque solutions do not pose a problem. A difference in the refractive index between solution and particles is not required. A relatively large amount of material is necessary to carry out a measurement. Electro-osmosis is not recommended for measurements at high ionic strengths (>0.1 M). Electro-osmosis in a mixture of different materials produces an averaged result, without the possibility of separating the components.

Methods

47

In principle, electro-osmosis is designed for nonconductive particles. At high field strengths and with conductive particles, the velocity may be higher by one or two orders of magnitude than that predicted by the Smoluchowski equation [277]. This phenomenon is termed electro-osmosis of the second kind. The other limitation of electro-osmosis is that the cell of the apparatus (the housing used to fix the porous plug) also induces an electro-osmotic flow. The measured quantity is a combination of the flow induced by the material of interest and that induced by the cell. Under certain conditions, the contribution of the latter can be negligible, but it can be significant in some systems. The same recommendations and limitations apply to measurements based on streaming potential (see Section 2.1.3, where a specific example of error induced by the streaming potential of the material of the cell is discussed). Equipment for measurements of z potentials based on electro-osmosis is not commercially available. A few descriptions of home-made electro-osmosis devices can be found in the literature [278–283].

2.1.3

STREAMING POTENTIAL

When the solid phase is fixed (e.g., as a capillary, membrane, or porous plug), a forced flow of liquid induces an electric field. The potential difference is sensed by two identical electrodes. The streaming potential or streaming current can be used to determine the z potential. The streaming potential and electro- osmosis can be observed in similar experimental setups, except that the natures of the force and the flux are reversed. Thus, the recommendations and limitations discussed in Section 2.1.2 also apply to measurements based on the streaming potential. For example, the instrument cell induces a streaming potential, which may contribute substantially to the result of the measurement. A linear dependence between the z potential obtained by electrophoresis and the streaming current measured by a commercial apparatus was observed in [284], but the line did not cross the origin; that is, a streaming current of zero was not equivalent to the IEP obtained by electrophoresis. This discrepancy was caused by the cell in the streaming current apparatus (used to fi x the porous plug), which had an IEP much lower than the IEP of the material of interest, and which contributed to the measured streaming current. In principle, the streaming potential method applies to nonconductive materials, but [285] reports z potentials of Ti and Ti6Al4V alloy (or, rather, of their corrosion products) obtained using the EKA apparatus (Paar). The tables in Chapter 3 report results obtained using the following commercial instruments based on streaming potential: • • • •

EKA from Brookhaven (BI, BIC, illustrated in [286]) Zetacad from CAD Inst. (France) ECA 2000 from Chemtrac Systems, USA EKA and SurPASS from Paar (Anton Paar, an illustration of the measurement cell can be found in [287])

48

Surface Charging and Points of Zero Charge

A few illustrations and descriptions of home-made streaming potential devices can be found in the literature [235,288–297]. An illustration and a description of a radial flow apparatus designed to measure streaming potential can be found in [298]. A streaming current detector based on a completely different principle than the above instruments is presented in [299]. The dispersion is in a narrow space between a vertical cylindrical vessel and a coaxial piston, which moves back and forth along the axis. The potential between two gold electrodes on the wall of the cylinder at different heights is measured, and its zero value is identified with the IEP. The apparatus’ own response corresponds to the electrokinetic behavior of the piston and cell materials. In the presence of a colloid, the piston and the cell are assumed to be covered with colloidal particles. The above design has been utilized in some commercial instruments: • PCD 02 and 03 from Mutek (illustrated in [286]) (the name of this instrument, which is derived from “particle charge detector,” is somewhat misleading) • Milton Roy Generation 1 from Pryde Instruments Pty. Ltd A rotating disk in an electrolyte solution induces a difference of electric potential between an electrode placed near the center of the disk and another electrode placed far from the disk [300,301]. The measured voltage is proportional to the 3/2 power of the rotation rate and to the z potential of the surface of the disk.

2.1.4

SEDIMENTATION POTENTIAL

The electric field induced by sedimentation of colloidal particles under gravity is termed the sedimentation potential. The potential difference is sensed by two identical electrodes placed at different heights. No commercial or home-made apparatus for measurements of z potential and IEP based on sedimentation potential have been reported in the recent literature. For the following commercial instruments referred to in the literature, the principle of operation (probably one of classical electrokinetic phenomena) has not been reported: ZP-10 B from Shimadzu, Japan; Zeta Reader Mark 21, Mitamura Riken; and Sugiura 2 VD.

2.1.5

ELECTROACOUSTIC METHODS

In classical electrokinetic phenomena, the forces and fluxes are independent of time. Electroacoustic effects are analogs of electrophoresis and sedimentation potential in which the forces and fluxes are variable in time. Alternating forces induce alternating fluxes of the same frequency, with a time delay. The phenomenological coefficients between the force and coupled flux can be used to calculate the z potential. The phase shift is a source of additional information about the system. The electric sonic amplitude (ESA) is the amplitude of the ultrasonic field

49

Methods

induced by an alternating electric field. The alternating electric field induces vibrations of colloidal particles and of ions of the supporting electrolyte. The contribution of the latter to the overall signal is negligible at low ionic strengths and high solid loads, but becomes significant at high ionic strengths and low solid loads. The ESA signal of a 1-1 electrolyte is proportional to [302] m- - rV- - (m+ - rV+ )r 1+ r

(2.2)

where r is the specific density of the solution; m and V are, respectively, the molar masses and volumes of the anion and the cation (subscripts + and -); and r is the anion-to-cation mobility ratio. The ESA signals of a few salts (e.g., LiNO3) are low owing to the mutual compensation of the anion and cation signals, while other salts (e.g., NaI and CsCl) produce strong ESA signals. A solution containing two salts each of which produces a strong ESA signal may have a negligible ESA signal owing to the compensation for the signals of the two salts. O’Brien derived a theory for ESA-based instruments. The signal of the colloidal particles is given by Ê Dr ˆ ESA = A(w ) f Á · m ÒZ Ë r ˜¯ D

(2.3)

where A(w) is an empirical frequency-dependent instrument constant, f is the solid volume fraction, r is the specific density of the solution, Dr is the difference in specific density between particles and the solution, Z is another empirical instrument constant, and · mD Ò is the particle-averaged dynamic mobility, defined as mD =

2 ez Ê wa 2 ˆ [1 + f (l, w¢ )] G 3h ÁË v ˜¯

(2.4)

where

G(a ) =

Ê1 ˆ 1 + (1 + i ) Á a ˜ Ë2 ¯ Ê1 ˆ 1 + (1 + i ) Á a ˜ Ë2 ¯

f (l, w¢ ) =

1/2

1/2

(2.5)

Ê1 ˆ + i Á a ˜ (3 + 2 Dr /r ) Ë9 ¯

1 + iw¢ - (2l + iw¢er / e ) 2(1 + iw¢ ) + 2l + iw¢er / e

(2.6)

50

Surface Charging and Points of Zero Charge

w¢ =

we K•

(2.7)

l=

Ks K• a

(2.8)

In Equations 2.4 through 2.8, K is the conductivity, a is the particle radius, and n (= h/r) is the kinematic viscosity. The subscripts relate to the following: S, liquid near the surface; •, bulk solution; and r, solid particles. The colloid vibration current (CVI) is the amplitude of the alternating current induced by an ultrasonic field. The potential difference is sensed by two identical electrodes. The theory of instruments based on CVI is discussed in detail in [303]. Recommendations and limitations are similar for CVI and ESA. Both techniques require calibration against standard dispersions or solutions, and then the quality of the results depends on the quality of the standard. The electroacoustic method can be used for a broad range of particle sizes, as well as for unstable dispersions. Sedimentation is prevented by a stirrer or peristaltic pump. The specific density of the particles must be substantially different from that of the solution. The refractive index of the particles is of limited significance. The electroacoustic method requires a substantial amount of material to produce reliable results. A low solid-to-liquid ratio implies a weak signal of the particles (Equation 2.3). Thus, the method is not suitable for dilute dispersions, but it can be used directly for dense dispersions. The electroacoustic method can be used at high ionic strengths. Such measurements require correction for the electrolyte signal. Special high-ionic-strength calibration is required in certain types of commercial equipment [304]. Commercial instruments have an electrolyte-correction procedure built into their software. The electroacoustic method produces an overall signal when two or more kinds of particles are present in the same dispersion, and the contributions of the components cannot be distinguished. The particles must not be electrically conductive. An introduction to electroacoustic methods and a discussion of their advantages and disadvantages can be found in the review [305]. The tables in Chapter 3 report results obtained by means of the following commercial instruments based on the electroacoustic method: • From Colloidal Dynamics: Acustosizer, Acustosizer II, and Zeta Probe • From Dispersion Technology: DT models 300 and 1200 (illustrated in [306]) • From Matec: ESA models 8000, 8050, and 9800; MBS models 8000 and 8050 • From Pen Kem: Acustophoretic Titrator 7000

Methods

51

2.2 EXPERIMENTAL CONDITIONS IN ELECTROKINETIC MEASUREMENTS A typical preparation of dispersions for electrophoretic or electroacoustic measurements consists of the following steps: 1. The original powder (e.g., from a commercial source) is subjected to washing, drying, and/or calcination. 2. A dispersion is prepared by mixing the powder with a solution of 1:1 salt (or with water). 3. The dispersion is aged for a certain time and/or ultrasonicated. 4. The solid-to-liquid ratio, pH, and ionic strength of a portion of the dispersion are adjusted by dilution, and a salt, acid, or base added. 5. The new dispersion is aged for a certain time and/or ultrasonicated. 6. A portion of the new dispersion (or of the supernatant obtained by settling under gravity or by centrifugation) is injected into the cell of the instrument. The pH is measured just before or during the electrokinetic measurement. Some of the above steps can be omitted, for example, in instruments equipped with an automatic titrator and pH probe. Steps 1 through 6 can be modified by using different types of labware (glass or plastic), protection against atmospheric CO2 (using freshly boiled water or bubbling of solutions and dispersions with nitrogen or another inert gas), thermostatting (many commercial instruments are equipped with a thermostat, but some are not), different types of stirrers or shakers set to different speeds, different concentrations of acid or base, different times of aging and modes of ultrasonication (time and intensity), different modes of filling and washing the cell of the instrument and different delay times between the injection and the measurement, and finally different instrument settings (adjustable parameters depend on the type of instrument). The above examples indicate how many experimental protocols can be designed. In many publications, the preparation of samples for electrokinetic measurements and the measurement itself are described in detail. In a few other papers, the description is limited to the type of instrument. The z potential is unequivocally defined by the composition of the solution in contact with solid particles. Therefore, conditions such as the solid-to-liquid ratio, aging, and ultrasonication should not affect the IEP. The use of optimum conditions for electrokinetic measurements may improve the reproducibility of results, but the IEP under different experimental conditions will be the same. In fact, in only a few studies was the experimental protocol indeed optimized, and in many other studies the experimental protocol was copied from other publications or arbitrarily selected. When the z potential and IEP depend on the experimental conditions, information on these experimental conditions is essential. For example, the acidic branch of the electrokinetic curves (using the Acoustosizer) reported in [307] was rather

52

Surface Charging and Points of Zero Charge

insensitive to the solid load, and on the basic branch the z potential increased with the solid load. The IEP of commercial aluminum hydroxycarbonate reported in [308] depended on dilution. The usefulness of an IEP that applies only to strictly defined experimental conditions is very limited. However, this is not obvious if the parameters that define the experimental conditions and that are easy to control are alone responsible for the observed discrepancies. Other parameters that are beyond control might have caused the discrepancies. In modern devices, certain parameters (e.g., time of measurement) are adjusted by the instrument software, and the experimentalist has limited control over them. The electrophoretic mobility depends on the z potential and on the shapes and sizes of the particles (see the more detailed discussion in Section 2.4.4). Particles that have the same z potentials but different shapes and sizes have different mobilities. In polydispersed colloids with irregular particle shapes, the z potential can only be estimated from the electrophoretic mobility, and the result depends on the approach to the definition of the size of an irregularly shaped particles. The size of a particle with irregular shape may be defined as: • The diameter of a sphere with same volume as the particle • The diameter of a sphere with same surface area as the particle • The diameter of a sphere with same surface-to-volume ratio as the particle • The diameter of a sphere with same drag resistance (or free-falling speed) as the particle • The diameter of a circle with same projected area as the particle (in selected or random orientation) • The width of the minimum square aperture through which the particle has passed In polydispersed assemblies of particles, different types of average size can be calculated, for example, as follows: • • • •

An average of linear dimensions Based on the square root of an average of surface areas Based on the cube root of an average of volumes Based on the ratio of the sum of surface areas to the sum of linear dimensions • Based on the ratio of the sum of volumes to the sum of surface areas • Based on the square root of the ratio of the sum of volumes to the sum of linear dimensions The above averages may be taken over actual dimensions or over dimensions of equivalent spheres of a certain type (see above). Different methods of calculation of equivalent sizes of irregularly shaped particles and of an average in an assembly of polydispersed particles can produce very different average particle sizes in the same assembly of particles. The problem of equivalent size of irregularly shaped

Methods

53

particles and different types of averages in assemblies of polydispersed particles is discussed in more detail in handbooks of colloid chemistry. Numerous electrokinetic studies have been carried out with monodispersed colloids, that is, assemblies of particles that have the same shape and size (with some scatter). Preparations and properties of monodispersed colloids are reviewed in [309,310]. The electrokinetics of monodispersed colloids are reviewed in [311]. In assemblies of identical spherical particles, the z potential can be calculated exactly from the electrokinetic mobility. The advantage of spherical shape and monodispersity, which make exact calculation of the z potential possible, is attained at the expense of purity; that is, monodispersed particles are usually not very pure. z potentials at one concentration of a specific inert electrolyte are sufficient to determine the IEP. Yet several publications report z potentials obtained at various concentrations and/or in the presence of various inert electrolytes. These studies demonstrated the independence of the IEP of the nature and concentration of the inert electrolyte. For example, [312–320] report z potentials obtained at three different ionic strengths, [321–324] report z potentials obtained at four different ionic strengths, and [325,326] report z potentials obtained at five different ionic strengths. The IEP of rutile in the presence of three alkali chlorides is reported in [327], and [328] reports a similar study of hematite (three sodium salts). Reference [329] reports z potentials obtained at two ionic strengths in five electrolytes, and [330] reports z potentials in the presence of two salts, each at two ionic strengths. Reference [331] reports z potentials obtained by means of electrophoresis with two instruments, at five and two ionic strengths, respectively. Numerous publications report specific solid-to-liquid ratios used in electrokinetic experiments. These ratios are of limited significance when the dispersion is unstable, and the dispersion in the instrument cell has a different composition from that originally prepared. The range of solid-to-liquid ratios used in electrophoresis is illustrated in Tables 2.1 and 2.2. The volume fraction can be converted into mass fraction, and vice versa, when the specific densities of the components are known. The specific densities of most powders of interest are in the range of 2000–6000 kg/m3, and their mass fractions are about two to six times higher than their volume fractions, thus both quantities are of the same order of magnitude. The range of solid-to-liquid ratios shown in Tables 2.1 and 2.2 is very broad, covering over four orders of magnitude. The range 0.00005–0.001 is very popular, and studies with very high and very low solid-to-liquid ratios are rare. The range of aging conditions used in electrophoretic measurements is illustrated in Table 2.3. The options for the preparation of dispersions for electroacoustic measurements are similar to those discussed above for electrophoresis, except that the experiments are usually carried out in titration mode and long equilibration before each measurement is not practiced, although long equilibration and/or sonication before the titration are commonplace. Various experimental protocols in electroacoustic measurements were compared in [423], for example, using a stirrer versus a pump and simultaneous measurements of the z potential and size versus using a pre-assumed size.

54

Surface Charging and Points of Zero Charge

TABLE 2.1 Mass Fractions of Solid Particles Used in Electrophoretic Measurements Mass Fraction 0.00000025 0.000001 0.00001 0.000014–0.00014 0.000015 0.00002 0.00003 0.00003–0.00005 0.00005 0.00005–0.002 0.000075 0.0001 0.0001–0.0003 0.0001–0.001 0.0001–0.01 0.00014 0.00015 0.0002 0.0003 0.0004 0.0005 0.0008 0.001 0.00125 0.0013 0.00167 0.0025 0.003 0.005 0.01 0.015 0.2

Reference [332] [333] [334] (latex), [335] [314] (results obtained with different solid mass fractions are similar) [336] [249] [337] [338] [334] (hematite), [339–347] [348] (results obtained with different solid mass fractions differ substantially) [349] [350–370], [371] (allowed to settle down, and only supernatant taken for measurements), [372,373] [374,375] [104] [376,377] [378] [379] [271,380–383] [123,382], [181] (allowed to settle down, and only supernatant taken for measurements) [384] [43,60,385–387] [388] (allowed to settle down, and only supernatant taken for measurements) [259,318,389–392] [393] [394] (centrifuged, and only supernatant taken for measurements) [395] [396] [258,397] (allowed to settle down, and only supernatant taken for measurements) [398], [399] (only supernatant taken for measurements) [400] (only supernatant taken for measurements), [401] [402] (allowed to settle down, and only supernatant taken for measurements) [403] (mass transport electrophoresis)

55

Methods

TABLE 2.2 Volume Fractions of Solid Particles Used in Electrophoretic Measurements Volume Fraction 0.00001 0.0001 0.0005 0.001

Reference [404] [147,405–411] [412] [413]

The range of solid-to-liquid ratios used in electroacoustics is illustrated in Tables 2.4 and 2.5. Generally, the solid-to-liquid ratios in electroacoustics are much higher than in electrophoresis.

2.3

CO2 AND SILICA PROBLEM

Silica and CO2 are omnipresent impurities that affect surface charging and may induce a shift in the PZC/IEP in certain systems. The discrepancies in the PZC/ IEP of the same material reported in various sources may be due to limited control over the silica, CO2, and other surface-active impurities.

2.3.1

THE CO2 PROBLEM

CO2 is absorbed from the atmosphere by solutions and dispersions, and induces a shift of their pH to lower values and an increase in their buffer capacity, especially at neutral and weakly basic pH. This pH shift is especially important in the interpretation of the results of potentiometric titration (Section 2.5) but is less significant in electrokinetic measurements. Moreover, dissolved carbonates show a certain degree of surface activity, which is important in all kinds of surface charging studies. Typical CO2 concentrations are 102.42 Pa in the atmosphere and 10-3 M (total inorganic carbon) in river or marine water [445]. In many studies, freshly boiled water and bubbling of solutions and dispersions with inert gases were used as protection against atmospheric CO2. For example, rigorous exclusion of silica and CO2 in [446] resulted in a relatively high PZC for goethite. In many other studies, less attention was paid to the exclusion of silica and CO2. For example, in [447], the IEP was determined in the presence of 0.001 M NaHCO3. That result was quoted in [448] as a pristine IEP. It is likely that IEPs obtained in the presence of carbonates are cited as pristine IEPs in many other secondary sources. A few systematic studies of the effect of CO2 on PZC/IEP have been carried out. Reference [449] reports an insignificant effect of CO2 on the charging of goethite. In contrast, [450] reports a shift in the IEPs of aluminum and iron oxides to low pH by about 1 pH unit in dispersions titrated with a Na2CO3 solution with respect to dispersion titrated with NaOH solution.

56

Surface Charging and Points of Zero Charge

TABLE 2.3 Aging and Ultrasonication before Electrophoretic Measurements Aging

Ultrasonication Yes 30 s 10 min 15 min >30 min

0–21 d 0–33 d 15 min 20 min–overnight 25 min 30 min

10 min, before aging

2h Overnight

15 h 15–18 h 1d

Before aging

1d 1d 1d 1d

15 min, before aging 3–5 min, before aging 15 min, before aging 5 min, after aging

>1 d 2d 3 and 15 d 10 d

15 min, before aging 3 min, before aging

Reference [414] [373] [411] [407] [384] (otherwise the results were irreproducible) [415] [416] [60,393,417] (at 25°C under nitrogen) [376,377] [402] (only supernatant taken for measurements) [181] (only supernatant taken for measurements) [418] [371] (after aging, dispersion was diluted, ionic strength and pH were adjusted, dispersion was aged for an additional 15 min with stirring, allowed to settle for 5 min, and supernatant was taken for measurements) [397] (after aging, pH of dispersion was adjusted and dispersion was aged for another 20 min and supernatant taken for measurements) [352] (argon) [336] [258] (dispersion was allowed to settle for 5 min, and supernatant was taken for measurements), [346] (in darkness), [398] (25°C, in polyethylene bottle), [419] (only supernatant taken for measurements) [123,347,396] [410] [271] (20°C, in polyethylene flasks) [420] [388] (only supernatant taken for measurements) [421] (dispersion aged after pH adjustment) [422] [349] (under nitrogen) [394] (centrifuged, and supernatant taken for measurements)

57

Methods

TABLE 2.4 Mass Fractions of Solid Particles Used in Electroacoustic Measurements Mass Fraction

Reference

0.025 0.03–0.05 0.05 0.05–0.07 0.05–0.45 0.1 0.13 0.2

[424,425] [376] [426] [377] [427] [428,429] [430] [431,432]

There is also mixed evidence about the effect of CO2 on the CIP of charging curves. Reference [451] reports an insignificant role of CO2 in the titration of alumina. In contrast, a substantial effect was found at a carbonate-to-aluminum ratio greater than 0.1 [452]. Shifts in the CIP in opposite directions in the presence of CO2 have been reported. Reference [453] reports a shift in the CIP of titania to high pH by 0.4 pH unit in the presence of 0.001 M NaHCO3. On the other hand, the CIP of goethite was shifted to low pH by about 1 pH unit in a system equilibrated with the atmosphere with respect to a CO2-free system [66,454].

2.3.2

THE SILICA PROBLEM

Numerous examples of underestimated IEPs in the literature are due to the adsorption of silicate on the materials of interest. The solubility of silica in water was

TABLE 2.5 Volume Fractions of Solid Particles Used in Electroacoustic Measurements Volume Fraction

Reference

0.001 0.003–0.025 0.005 0.01 0.01 or 0.05 0.02 0.03 0.05 0.1

[433] [350] [357,434] [435–437] [438,439] [440,441] [442] [443] [444]

58

Surface Charging and Points of Zero Charge

discussed in Section 1.6. The silica problem was not generally recognized until the 1970s. Cleaning methods described in early publications (e.g., Soxhlet extraction) might have induced silica contamination as a result of long contact of the material of interest with solutions saturated with products of dissolution of glass at high temperature. Silica leached out from glassware at room temperature induces shifts in the IEPs of certain materials to low pH. Long contacts of dilute dispersions of metal oxides with neutral and basic solutions in glass containers usually resulted in low IEPs. A few systematic studies of this effect have been carried out. The effect of storage of alumina and latex [455], and titania [455,456] dispersions in glass containers on their IEPs has been studied. Aging of alumina dispersions in Schott glass containers induced a shift in the IEP to low pH, while aging in a plastic container did not [457]. The effect of storage in glass on the IEPs of alumina and chromia were studied in [458] and [331], respectively. The effect of storage in glass on the PZC of iron oxide was studied in [459]. Silica present in natural iron (hydr)oxides produces low IEPs of natural materials compared with silica-free synthetic materials. Leaching of silica from natural ferrihydrite induced a shift in the CIP to a higher pH [460]. A correlation between the CIP and the silica-to-iron ratio was found in a series of natural and synthetic silica-containing ferrihydrites [460]. Uptake of silica from a 110ppm solution by alumina, iron(III) oxide, and clay minerals was studied in [461]. At pH 7–10, iron(III) oxide adsorbed silica completely. The uptake by alumina peaked at pH 9, but residual silica was also present in solution. Uptake of silica by clay minerals was observed in the basic range; in the acidic range, the silica concentration in dispersions was higher than the initial concentration, owing to leaching. Nowadays, measures against silica contamination are often undertaken, and this has become a standard procedure, too obvious to be specified in scientific papers. Plastic labware was used in the synthesis of iron (hydr)oxides in [462]. Contact with sources of silica was avoided in a cleaning procedure of alumina flat plates in [463]. Attempts to avoid silica are not always successful. An abnormally low IEP was found in a study of the force between two single-crystal sapphire platelets [464]. The authors explained the positive surface potential at pHs as low as 6.7 by the sorption of silica or other species from the solution. Silica is not the only surface-active anionic impurity that may be responsible for the abnormally low IEPs reported in the literature. The other impurities are less abundant (see Section 1.11), but they may be more surface-active than silica, and in certain systems the shift in the IEP to a low pH may be chiefly due to anionic impurities other than silica. The silica problem is a specific case of a general problem of surface-active anionic impurities, with silica being the most wellknown example of such an impurity. The specific nature of surface-active anionic impurities other than silica is not known. Thus, it is difficult to control and avoid them, and measures undertaken against silica contamination are not necessarily efficient against other surface-active anionic impurities. The discrepancy between the IEP of alumina monoliths (pH ⬇ 5) and that of alumina powders (pH ⬇ 9) has divided the scientific community into two groups. One group considers the low IEP of monoliths to be a well-established experimental

Methods

59

fact, resulting solely from alumina–inert electrolyte solution interactions. Another group challenges the validity of these low IEP measurements. Incorrect procedures or insufficient purity of the reagents have been invoked as the reason for the low IEPs of monoliths. For example, a shift in the IEP to low pH may be due to specific adsorption of anions. A low solid-to-liquid ratio makes the monoliths more sensitive to impurities as compared with the same material in the form of a fine powder. The ability of certain low-molecular-mass surface-active solutes to induce a substantial shift in the IEP can be assessed by comparing the number of surface-active molecules with the number of surface sites in the system of interest. The number of surface-active molecules must be at least comparable to the number of surface sites to induce a substantial effect. Otherwise, the contribution of surface-active molecules to surface charging is negligible. In potentiometric titrations and electroacoustics, a typical solid-to-liquid ratio of 100 g/dm3 (Table 2.4) produces 10,000 m2/dm3 for a 100 m2/g powder. Assuming 6 surface sites/nm2, which is a typical value used in model calculations (see Section 2.9.1), 10,000 m2/dm3 (titration and electroacoustics) corresponds to 0.1 mol/dm3 of surface sites. The concentration of surface sites exceeds the concentrations of impurities by several orders of magnitude; thus, the contribution of impurities to the surface charge is negligible. In microelectrophoresis, a typical solid-to-liquid ratio of 0.1 g/dm3 (Table 2.1) produces 10 m2/dm3, and 10-4 mol/dm3 of surface sites with a 100 m2/g powder. The concentration of surface sites is comparable to typical concentrations of silica found in laboratory water, and it exceeds the concentrations of other surface-active impurities. Under such circumstances, a shift in the IEP can be caused by silica, and the concentrations of other impurities are too low to induce a substantial shift. With a monolith, the solid-to-liquid ratio is in the region of 0.1 m2/dm3 (1 cm2 of sample in contact with 1 cm3 of solution), that is, 10-6 mol/dm3 of surface sites for the same material. The concentration of surface sites is much lower than the typical concentrations of silica found in laboratory water, and it may be comparable to the concentrations of other surface-active impurities. Under such circumstances, a shift in the IEP is almost certain. Even very strict measures against silica can hardly assure a silica concentration below 10-6 mol/dm3, and a few other impurities can also contribute to the shift, because their concentrations are comparable to the concentrations of surface sites.

2.4 EXPERIMENTAL RESULTS: z POTENTIAL The IEPs are compiled in Chapter 3. Other aspects of electrokinetic curves are discussed in this section. Figure 1.2 shows a typical set of three z(pH) curves obtained at different concentrations of an inert electrolyte. Similar curves (sets of curves) have been obtained in numerous real systems. With typical data sets, it is easy to determine the IEP. A few examples of less typical courses of electrokinetic curves reported in the literature will be discussed below. Specific values of the z potential are not indicated in Figure 1.2. Sufficiently far from the IEP, the z potentials assumed values in the range of about ±100 mV in the presence of a 0.001 M (or more dilute) 1-1 electrolyte, about ±60 mV in the

60

Surface Charging and Points of Zero Charge

presence of a 0.01 M electrolyte, and about ±40 mV in the presence of a 0.1 M electrolyte in many studies (see [2] for numerous examples). In several studies, the absolute values of the z potential at the respective ionic strengths were substantially lower, even very far from the IEP. The Smoluchowski equation, which is built into the software of most commercial zetameters, substantially underestimates the z potentials of fine particles at low ionic strengths (low ka, where k is the reciprocal Debye length and a is the particle radius), especially in the range of high z potentials. Underestimated values of the z potential may be due to erroneous calculations of the z potential from experimental data. A few unusually high values are reported in [465]: +120 mV for Fe(OH)2 and -180 mV for ZrO2 (at pH 10). A z potential in excess of -250 mV in an aqueous medium (from streaming current, using a home-made apparatus) is reported in [466]. Electrophoretic mobilites are usually below ±8 × 10-8 m2 V-1 s-1. A mobility in excess of -30 × 10-8 m2 V-1 s-1 in an aqueous medium is reported in [212]. Calculation of the z potential from experimental data is discussed in more detail in Section 2.4.4.

2.4.1

SHAPES OF INDIVIDUAL ELECTROKINETIC CURVES

The idealized electrokinetic curves shown in Figure 1.2 are smooth. Real curves are less smooth, and local minima and maxima are found. These represent a scattering of results rather than actual minima or maxima. The z potentials of silica in 0.01 M KCl (from electrophoretic mobility) plotted in the form of error bars showed standard deviations of 5–10 mV [249]. The z potentials of SiC plotted in the form of error bars showed standard deviations of about 2 mV [272]. Such a range of scattering is typical for electrophoretic measurements. Reference [397] reports a standard deviation below 0.5 mV in a series of 10 electrophoretic measurements. The reported electrokinetic curves are far from smooth, and this suggests that the standard deviation was underestimated in [397]. The rest of discussion in this section relates to the shapes of smoothed electrokinetic curves, disregarding the local minima and maxima caused by the scattering of results. The idealized electrokinetic curves shown in Figure 1.2 are symmetrical with respect to the IEP, and most experimental electrokinetic curves reported in the literature are nearly symmetrical. An asymmetrical z(pH) curve with a high z potential on the basic side is reported in [467]. An asymmetrical z(pH) curve with a high z potential on the acidic side is reported in [468]. The idealized curves shown in Figure 1.2 steadily decrease with pH and have no more than one IEP, but numerous electrokinetic curves reported in the literature show different shapes. The electrophoretic mobility of alumina in 0.1 M NaNO3 was pH-independent at pH 4–8 [469]. The apparent z potential of MoO3 increased with increasing pH [470]. Also, in one of the hematite samples studied in [471], a positive z potential is reported at high pH and a negative z potential at low pH. An increasing electrokinetic curve (e.g., curve “a” in Figure 8 of [472]) may even show z = 0 at a certain pH, but only sign reversal from positive to negative as the pH increases is considered as an IEP

Methods

61

in the present book. Electrokinetic curves with maxima and minima and multiple IEPs are commonplace in materials that undergo selective leaching (Section 1.6). A nearly symmetrical eletrokinetic curve for one sample of synthetic yttrium–iron garnet and atypical shapes (broad pH ranges with very low positive z below the IEP) for three other samples are reported in [473]. Many examples of materials that show positive z potentials at very low and very high pHs and negative z potentials at moderate pH (two IEPs) are reported in [104]. ZrY0.8O3.2 [474] and PbSO4 [475] showed three points of charge reversal. Numerous examples of atypical electrokinetic behavior, with negative z potential at low pH and positive z potential at high pH or with multiple points of sign reversal, were observed for sulfides [391]. Several publications report electrokinetic curves with maxima or minima of the z potential (beyond the scatter of data points) but without multiple IEPs. A minimum (maximum in absolute value) in the basic range is reported in all systems but one studied in [225], in [476], and in [266,477] (silica, with various KCl concentrations). A maximum in the z potential of FeOOH at pH ª 4.5 was found in [478]. These maxima or minima may be caused by an increase in ionic strength when the dispersion is adjusted to very high or very low pH.

2.4.2

POSITION OF IEP

Many experimental studies confirmed an insignificant effect of the nature or concentration of an inert electrolyte (Section 1.3) on the IEP. For example, the IEP of rutile at pH 6 was observed in the presence of three alkali chlorides [327], and the IEP of hematite at pH 7.5 was observed in the presence of three different sodium salts [328]. Only a few exceptions are reported in the literature. Reference [479] reports a shift in the IEP of titania induced by 0.001 M NaCl with respect to a salt-free system. Measurements of single planes of sapphire using a commercial streaming potential analyzer [59] resulted in irregular changes in the IEP (shifts in excess of 1 pH unit) with KCl concentration (0.001–0.1 M). Reference [480] reports a shift in the IEP of thoria by 2 pH units on increasing the NaCl concentration from 0.0001 to 0.001 M, and a shift by an additional 4 pH units on increasing the concentration from 0.001 to 0.01 M. The IEPs of iron (hydr)oxides found in [332] in 0.01 M KNO3 and NaNO3 matched, but those of manganese oxides showed substantial discrepancies. IEPs of a few specimens of MnO2 were found to increase with increasing ionic strength (>0.001 M NaNO3) in [481], but the IEPs of other specimens in the same study were independent of ionic strength (up to 1 M). The IEP of cobalt spinel obtained from streaming potential measurements [482] depended on NaCl concentration. The IEP of kaolinite shifited to low pH as the NaCl concentration increased, according to [483].

2.4.3

AGING AND HYSTERESIS

Numerous systematic studies of the effect of aging on electrophoretic mobility have been carried out. No substantial difference between samples aged for 1–14 days was observed in [484]. Also, the difference in electrophoretic mobility

62

Surface Charging and Points of Zero Charge

between dispersions of titania aged for 3 hours and 1 day was insignificant [485]. A drift in the z potential in time, and even sign reversal, were observed in [104]. The effect of aging at different pHs and ionic strengths on the z potential of quartz was studied in [486]. A substantial effect of aging (in glass and Teflon, at different pHs) on the electrophoretic mobility of mica is reported in [487]. Aging affected the electrophoretic mobility of silica–alumina composite material [488]. Aging of natural apatite in water induced sign reversal in 1 hour [489]. The effect of aging in these systems may be due to selective leaching out of components. The substantial difference in IEPs between fresh and aged dispersions of SiC [272] and Si3N4 [490] was probably due to oxidation. Electroacoustic measurements are usually carried out in titration mode, and several papers report results of both acid and base titration. Substantial hysteresis (Figure 1.9) was found in [242,427,491–493]. Other studies in similar systems report negligible hysteresis [444,449,494,495]. Four cycles of titration in ESA measurements reported in [496] produced different values of the z potential in the acidic range but a common IEP. Similar IEPs were observed in titrations of alumina from pH 2 to 12 and back, but in titrations from pH 1 to 12, the IEP was shifted to high pH [497]. Generally, more pronounced hysteresis is expected in titrations over a wider pH range.

2.4.4

EFFECT OF IONIC STRENGTH ON THE NUMERICAL VALUE z POTENTIAL

OF THE

The effect of ionic strength on the numerical value of the z potential is usually presented in the form of graphs similar to Figure 1.2. A few studies present plots of z potential as a function of ionic strength at constant pH in addition to (e.g., [249]) or instead of (e.g., [235]) graphs similar to Figure 1.2. High ionic strength induces a depression in the z potential of all kinds of surfaces. Many publications report a decrease in the z potential at constant pH as the ionic strength increases, according to expectations (Figure 1.2), but surprisingly many exceptions to this rule can be found in the literature. The papers reporting unusual ionic strength effects seldom discuss or attempt to explain this atypical behavior. A few types of abnormal effects of ionic strength on the numerical value of the z potential can be distinguished. An increase in the absolute value of the z potential at constant pH with increasing ionic strength (which is a trend opposite of expectations) is reported in [498]. The z potential of polystyrene latex increased in absolute value with increasing ionic strength [499], but silica studied in the same paper behaved normally. The mobility of goethite was found to increase with increasing ionic strength in [468]. The absolute value of z potentials reported in [343,500] decreased with increasing ionic strength in the acidic range but increased in the basic range. In contrast, the absolute value of z potentials reported in [501] increased with increasing ionic strength in the acidic range but decreased in the basic range. The mobility of kaolinite was found to increase in absolute value with NaCl concentration at pH < 5, but the usual behavior was observed at pH > 5 [483]. z potentials (from

Methods

63

the Smoluchowski equation) in the absence of an electrolyte reported in [257] are lower in absolute value than in 0.001 M NaCl in the range of very negative z potentials. In the range of less negative z potentials, the ionic strength effect complied with expectations. z potentials (from the Smoluchowski equation) in the absence of an electrolyte reported in [502] are lower in absolute value than in 0.005 M NaCl in the basic range. In the acidic range, the ionic strength effect roughly complied with expectations. z potentials (from the Smoluchowski equation) in 0.0002 M NaCl reported in [503] were lower in absolute value than in 0.002 M NaCl in the basic range. In the neutral and acidic range, the z potentials in 0.0002 and 0.002 M NaCl were equal, and higher electrolyte concentrations depressed the z potentials, as expected. In several studies, insignificant effects of ionic strength on electrophoretic mobility [66,382,504] and on the z potential [83,144,323,325,393,413,505–507] were reported. The effect of ionic strength on the absolute value of the z potential was insignificant in one sample of zirconia studied in [508], but two other samples behaved normally. Another common type of abnormal behavior is that the electrophoretic mobility or the z potential is independent of ionic strength over a certain range of pH or ionic strengths, with normal behavior being observed outside that range. For example, the electrokinetic curves reported in [319] are insensitive to ionic strength (0.01–0.3 M) in the acidic range. In the basic range, the electrokinetic curves obtained in 0.01 and 0.03 M electrolytes match, and only in the 0.3 M electrolyte was the z potential substantially lower in absolute value, according to expectations. Increasing the ionic strength from 0.01 to 0.1 M had a rather insignificant effect on the positive z potentials of alumina and zirconia determined in [509] by the electroacoustic method. The absolute value of the negative z potential was clearly depressed as the ionic strength increased, according to expectations. The z potential of hematite reported in [510] was rather insensitive to the ionic strength on the basic branch, but the acidic branch showed normal behavior. The difference in the mobility of silica in 0.001 and 0.01 M NaCl reported in [511] was insignificant, but 0.1 M NaCl significantly depressed the absolute value of mobility. An insignificant effect of KCl concentration on the z potential of anatase over the pH range 2–10 was reported in [512]. The effect of KNO3 was insignificant only in the basic range, and normal behavior was observed in the acidic range. Irregular effects of ionic strength, that is, minima and maxima in the z potential at constant pH as a function of ionic strength, have been reported in [513], [514] (there are many exceptions to the expected behavior of the system), [515] (the highest absolute value of the z potential is reported for the highest ionic strength in the basic range), [59] (the z potential of single planes of sapphire measured by a commercial streaming potential analyzer), and [516] (for a titania pigment, surface-modified with silica, alumina, and organic groups). The unusual effects of ionic strength on the apparent z potential may, to some extent, be due to improper calculation of the z potential from directly measured quantities. The Smoluchowski equation applies for large particles, high ionic

64

Surface Charging and Points of Zero Charge

strengths (large ka), and low z potentials. It underestimates z potentials of fine particles at low ionic strengths. Many numerical values of the z potential of fine particles at low ionic strengths reported in the literature were calculated by means of the Smoluchowski equation; thus, they are underestimated. Recalculation of these results using other methods that are more suitable for fine particles than the Smoluchowski equation would produce substantially higher z potentials at low ionic strengths, and only slightly higher z potentials at high ionic strengths. An example of such a correction for spherical particles a = 100 nm is presented in Figure 2.3. The apparent z potentials calculated using the Smoluchowski equation are equal for three different KCl concentrations (the thick solid line in Figure 2.3). The z potentials calculated from the same experimental results using the O’Brien– White theory [517] depend on the KCl concentration. With 0.1 M KCl, the difference between the z potentials from the Smoluchowski equation and those from exact theory is insignificant, but with 0.01 M KCl, the Smoluchowski equation substantially underestimates the z potential, and with 0.001 M KCl, the difference between the Smoluchowski equation and exact theory is even more significant. The results calculated using the O’Brien–White theory follow the expectations; namely, the absolute value of the z potential at constant pH decreases with increasing ionic strength. With 0.001 M KCl, the highest and lowest electrophoretic mobilities exceed the theoretical maximum/minimum, which corresponds to ±4.73 × 10-8 m2 V-1s-1 at ±122 mV. The calculations presented in Figure 2.3 apply to spherical particles of a specific size. With larger particles, the Smoluchowski equation is valid up to higher electrolyte concentrations, and a substantial difference between the Smoluchowski equation and exact theory is observed at higher ionic strengths. 100 80 0.001 M KCI 0.01 M KCI 0.1 M KCI

60

z (mV)

40 20 0 –20 –40 –60 –80 –100 pH

FIGURE 2.3 z potentials of spherical particles a = 100 nm at various KCl concentrations. The thick solid line represents apparent z potentials calculated by means of the Smoluchowski equation, which produced identical results for three ionic strengths. Thin lines with points represent z potentials calculated from the same experimental results by means of O’Brien–White theory. With 0.001 M KCl, the highest and lowest electrophoretic mobilities exceeded the theoretical maximum/minimum, which corresponds to ±4.73 ¥ 10-8 m2 V-1 s-1 at ±122 mV.

65

Methods

Exact theory does not produce an analytical solution, and the mobility at a given z potential is obtained as a result of successive approximations. Numerous equations give a good approximation to the exact theory over a broader range of ka than the Smoluchowski equation, for instance, the following Dukhin– Semenikhin equation: ÏÔ ˘ Ê1 ˆ È Ê1 ˆ Ê 1 ˆ Ô¸ 6 Ì y(1 + 3m) sinh 2 Á y˜ + Í2 sinh Á y˜ - 3my ˙ ln cosh Á y˜ ˝ Ë4 ¯ Î Ë2 ¯ Ë 4 ¯ ˛Ô 3heue 3 y Ô ˚ = - Ó 2 ekT 2 Ê1 ˆ Ê1 ˆ ka + 8(1 + 3m)sinh 2 Á y˜ - 24 m ln cosh Á y˜ Ë4 ¯ Ë4 ¯ (2.9) where ue is the electrophoretic mobility, y = ez/kT is the dimensionless z potential, and m ª 0.15 for aqueous solutions. Equation 2.9 is valid for a 1-1 electrolyte and ka >> 1.

2.4.5 EFFECT OF THE NATURE OF THE SALT ON THE NUMERICAL VALUES OF THE z POTENTIAL

z

The IEP is rather insensitive to the nature of an inert electrolyte, and the numerical values of the z potential far from the IEP are insensitive to the nature of the co-ion, but they do depend on the nature of the counterion. Thus, the acidic branch of an electrokinetic curve depends on the nature of the anion, and the basic branch depends on the nature of the cation. Therefore, in a series of inert electrolytes with a common anion (Figure 2.4), the acidic branch is common for all salts, and the differences are observed in the basic range; and in a series of inert electrolytes with a common cation (Figure 2.5), the basic branch is common for all

IEP

0

Cation 1 Cation 2 Cation 3 pH

FIGURE 2.4 z potentials in the presence of equal concentrations of three inert electrolytes with a common anion.

66

z

Surface Charging and Points of Zero Charge

Anion 1 Anion 2 Anion 3 IEP

0

pH

FIGURE 2.5 z potentials in the presence of equal concentrations of three inert electrolytes with a common cation.

salts, and the differences are observed in the acidic range. The specific effects of anions and cations of inert electrolytes on surface charging will be discussed in more detail in Chapter 4. Numerous examples of the usual behavior can be found in the literature, but there are also surprisingly many examples of abnormal behavior. Those papers reporting unusual effects of the nature of the electrolyte seldom discuss or attempt to explain that atypical behavior. The electrokinetic curves of alumina in the presence of NaCl and NaClO4 reported in [518] differ over the entire pH range (only a difference in the acidic range is expected). The acidic branch of the z potential (pH) curves (KBr vs. KNO3) was independent of the anion, while the basic branches were slightly different [519]. The anion effect (0.01M KCl, KBr, and KI) reported in [322] was negligible in the acidic range, but KI produced more negative z potentials than other salts in the basic range. A significant cation effect on both sides of the IEP is reported in [520]. A significant cation effect (with z potentials in KCl higher than those in NaCl) in the acidic range is reported in [521]. Unusual effects of the nature of 1-1 electrolytes on the electrokinetic behavior of a titania pigment (surface-modified with silica, alumina, and organic groups) are reported in [516].

2.5

EXPERIMENTAL CONDITIONS: TITRATION

Surface charging curves similar to those presented in Figure 1.1 are obtained in two steps. A dispersion containing a known amount of solid and a known amount of inert electrolyte is stirred (usually in a thermostated vessel, under an atmosphere of inert gas), and its pH is recorded. Small volumes of acid or base solution are added in pre-assumed time intervals or once the pH has reached a stable value (according to a certain criterion) after the previous addition. The titration is continued until a pre-assumed pH value is reached. Potentiometric titrations of dispersions produce plots of pH (the stable value or just before an addition of the

67

Methods

Electrolyte (experimental) Electrolyte (theoretical) Dispersion

pH

DV

Apparent PZC

DV

Volume of acid

FIGURE 2.6 Determination of DV (Equation 2.10) from potentiometric titration data (correction for inert electrolyte titration).

next portion of acid or base) as a function of volume (number of moles) of acid or base added (circles in Figure 2.6). A titration curve of dispersion alone is not sufficient to determine the PZC, and further information is required. Namely, analogous titrations are carried out for the electrolyte in the absence of colloidal particles (triangles in Figure 2.6). The titration curve of dispersion or electrolyte may be composed of two segments obtained by acid and by base titration starting at the natural pH. Alternatively, once base titration is complete, the same dispersion can be titrated with acid back to the natural pH and further in a more acidic direction; or acid titration can be carried out first, and, once it is complete, the same dispersion can be titrated with base back to the natural pH and further in a more basic direction. In another modification, the initial base titration is replaced by the addition of one large portion of base, and the dispersion is then titrated with acid back to the natural pH and further in a more acidic direction; or one large portion of acid is added, and the dispersion is then titrated with base back to the natural pH and further in a more basic direction. In all cases, proper bookkeeping of all added portions of acid or base is necessary. A blank titration curve can be easily calculated, and, at least in the nearly neutral pH range, the experimental curves do not differ much from theoretical predictions. A blank titration of a supernatant obtained at a natural pH rather than of pure electrolyte was recommended in [522]. The raw surface charge density is obtained by subtraction of the volume (number of moles) of acid or base (1 mole of base is equivalent to minus 1 mole of acid: double-headed arrows in Figure 2.6) that was used to bring about the same pH in the dispersion on the one hand and in the electrolyte solution on the other; that is, s0 =

Fc DV mA

(2.10)

68

Surface Charging and Points of Zero Charge

where c is the concentration of acid and base used in the titration, DV is the difference in volume of acid used to bring about the same pH in the dispersion on the one hand and in the electrolyte solution on the other, F is the Faraday constant, m is the mass of solid particles, and A is their specific surface area. Equation 2.10 assumes that the molarities of acid and base used in titration are equal and constant. In a more general case of variable molarity, s0 =

F Dn mA

(2.11)

where Dn is the difference in number of moles of acid (1 mole of base is counted as minus 1 mole of acid) used to bring about the same pH in the dispersion on the one hand and in the electrolyte solution on the other. The apparent s0 (in C/m2) is obtained from Equation 2.10 or 2.11. The surface charge density can also be expressed as charge per unit mass (in C/g) [523,524], especially when A is not available. The two representations (charge per unit mass or per unit surface area) produce different numerical values of charge density but the same PZC. In [525] and other papers from the same research group, the surface charge density is expressed as Z, the number of protons reacted per surface site. Z = 0 in their terminology is not necessarily the PZC [75]. Such results can be obtained when the number of surface sites per unit mass or per unit surface area is known. The procedure illustrated in Figure 2.6 (titration at one ionic strength) produces an apparent PZC (the apparent s0 from Equation 2.11 is equal to 0), which, under certain circumstances, can be equal to the actual PZC. When a charging curve is available at just one ionic strength, the apparent s0 from Equation 2.11 and the apparent PZC are the final results, which have been reported in many publications. Such results are indicated as “pH” in the “Method” columns in the tables in Chapter 3. The apparent PZC is nearly equal to the natural pH of the dispersion (with no acid or base added) and is equal to the actual PZC when the powder does not contain acid or base. This is theoretically possible, but it does not occur very often in reality. Even very pure materials contain certain amounts of acid or base, which are very difficult to remove or control, and which contribute to the apparent s0 from Equation 2.11. Therefore, determination of the PZC based solely on titration at one ionic strength is not particularly reliable. For example, the natural pH of dispersions in a series of iron hydroxides precipitated at different pHs (6–9) and from different iron precursors (chloride, nitrate, and sulfate) was similar to the pH of precipitation [526]. The natural pH of dispersions in a series of treated carbons was acidic for acid-treated and basic for base-treated carbon [527]. These examples indicate that the equilibrium pH of a dispersion is influenced by the liquid occluded in the powder. The natural pH values of dispersions reported in the literature were usually obtained at one ionic strength. Only in a few studies are the natural pH values of dispersions at different ionic strengths reported. For example, the natural pH of chromia dispersions was independent of KCl concentration, but decreased when the KNO3 concentration increased [528].

69

s0

Methods

CIP = common PZC

New “0” Original “0” Apparent PZC (c3)

c1 c2

Apparent PZC (c2) Apparent PZC (c1)

c3

pH

FIGURE 2.7 Correction for acid or base associated with solid particles (Equation 2.12).

The amount of acid or base associated with the powder (irrespective of the character of the interaction) can be estimated when a set of titration curves at various ionic strengths is available. The raw surface charging curves obtained at various ionic strengths have a CIP, which often corresponds to an apparent s0 π 0 (Figure 2.7), and the apparent PZC depends on the ionic strength. Such curves are corrected by the addition of a constant number to the raw values s0 from Equation 2.10; that is, the corrected s0 is calculated from the following equation: s0 =

Fc DV + sx mA

(2.12)

where sx is adjusted such that the CIP corresponds to s0 = 0, and the PZC is independent of ionic strength (Figure 2.7). The actual PZC coincides with the CIP (crossover point) of the charging curves obtained at various ionic strengths; such results are reported as “cip” in the “Method” columns in the tables in Chapter 3. The actual PZC (CIP) is usually different from the apparent PZC determined from titration at one ionic strength. The term “crossover point” has been used as a synonym for CIP, but it also has another meaning. For instance, in [529], the term “crossover point” denotes the equilibrium pH of a dispersion in 0.001 M KCl (“Method” = “pH”). sx reflects the difference between the original horizontal axis (the dot-dashed line in Figure 2.7) and the new horizontal axis (the solid line), and it can be calculated when titration curves at different ionic strengths are available. In [530], a CIP was not observed directly but was estimated by extrapolation. In principle, two ionic strengths are sufficient to obtain an intersection point and to calculate the correction. In [531], the intersection of two charging curves was recommended as a method to determine the PZC. However, the fact that the charging curves obtained at two different ionic strengths intersect at a certain point does not imply that all charging curves obtained at different ionic strengths will intersect at the

70

Surface Charging and Points of Zero Charge

s0

same point. The reproducibility and reversibility of charging curves are not perfect (see Figures 1.4 and 1.6 through 1.10), and this may result in a set of charging curves without a CIP. Each pair of charging curves in Figure 2.8 produces a different intersection point. The assessment of whether three charging curves have one (Figure 1.1) or more (Figure 2.8) intersection points is subjective. More precisely, the three intersection points shown in Figure 2.8 fall in a certain pH range. A narrow range (<0.1 pH unit) is interpreted as a CIP (one intersection point), and a broader range (>0.1 pH unit) is interpreted as the absence of a CIP (three intersection points). The absence of a CIP can be due to experimental error or to the intrinsic properties of the system of interest. The CIP is obtained by taking into account titrations at three or more ionic strengths. Apparent PZCs obtained from the intersection of two charging curves (only two different ionic strengths) are indicated as “Intersection” in the “Method” columns of the tables in Chapter 3 to distinguish them from PZCs obtained from the intersection of three or more charging curves. The fact that the charging curves obtained at three different ionic strengths intersect at a certain point implies that most likely the charging curves obtained at other ionic strengths will also intersect at the same point. The correction in Equation 2.12 reflects the presence of a certain amount of acid or base associated with solid particles, which is very difficult to remove (e.g., chemisorbed or occluded in narrow pores) and which contributes to the acid–base balance. The steps illustrated in Figures 2.6 and 2.7, that is, correction for acid or base used for the titration of an electrolyte and for an acid or base introduced with solid particles, are standard procedures, which were described in early publications and appear in numerous handbooks. They are seldom specified in scientific publications; only corrected titration curves are usually presented. In a few studies, the second correction (sx in Equation 2.12) was ignored. For example, in [532], a CIP was obtained, but uncorrected PZCs for particular ionic strengths

c1 c2 c3 pH

FIGURE 2.8 A set of charging curves without CIP.

Methods

71

were reported, and uncorrected charging curves were modeled. A linear scale is usually used to plot corrected and uncorrected s0, and nonstandard presentations are rare. The logarithm of the absolute value of an uncorrected s0 was plotted as a function of pH in [533]. It should be emphasized that the correction illustrated in Figure 2.7 applies for surface charging curves obtained by titration, but not for electrokinetic curves. A series of matching (or not matching) IEPs (z = 0) at different ionic strengths is obtained from a series of individual electrokinetic curves. In a few papers (e.g., [512]), the intersection of electrokinetic curves obtained at various ionic strengths is used to determine the IEP. Such an approach was used in [534,535], and the intersection of electrokinetic curves occurred at a high negative z potential. Thus, the numerical values of “PZC” reported in [534,535] are erroneous. The correct IEPs are reported in the tables in Chapter 3, and the original authors’ incorrect values are ignored. The same symbol is used for corrected (Equation 2.10) and uncorrected (Equation 2.12) s0, and the details of data handling are seldom reported in the experimental parts of scientific papers. A few publications report PZCs obtained by titration without clear explanations of whether they were obtained as CIPs or if titration was performed at only one ionic strength. Such results are indicated as “Titration” in the “Method” columns of the tables in Chapter 3. A few methods that give a PZC equivalent to that from the potentiometric titration method are described in Section 2.8.4.

2.5.1

THE CHOICE OF AN INERT ELECTROLYTE AND THE RANGE OF IONIC STRENGTHS

The standard procedure based on titrations at exactly three concentrations of the same salt (Figure 2.7) was used to obtain the CIP in numerous studies. Different inert electrolytes were selected by different authors, with NaCl, KCl, NaNO3, and KNO3 being more popular than other 1–1 salts. There is no fundamental reason to prefer one of these salts in surface charging studies. Usually, the lowest ionic strength was about 0.001M (difficulties in studies at lower ionic strengths are discussed in Section 1.10.2), the highest ionic strength was about 0.1M, and the difference between the highest and lowest electrolyte concentrations was a factor of 10 or more, with a few exceptions. In [536], the CIP of charging curves obtained in 0.1, 0.3, and 0.7M NaCl is reported. In [537], the difference between the highest (0.2M) and lowest (0.04M) ionic strengths was only a factor of 5; in [83] (two ionic strengths), it was only a factor of 3_13 . Not surprisingly, the difference in slopes between particular charging curves was not very significant. A difference in ionic strength by an order of magnitude leads to a substantial difference in the slopes of charging curves. The most popular (but entirely arbitrary) selections of electrolyte concentrations for surface charging studies are 0.001, 0.01, 0.1, and 1M. Usually, each dispersion for titration at a certain ionic strength is prepared from a separate portion of powder. Alternatively, one portion of powder can be used in consecutive titrations at increasing ionic strength; that is, the calculated amount of

72

Surface Charging and Points of Zero Charge

inert salt is added to the dispersion once the titration at a lower ionic strength is completed. This procedure was termed the “combined method” in [538] (backand-forth titration was followed by salt addition and a new titration), but, in the tables in the present book, “Combined Method” is considered as a variant of “Method” = “cip.” The results obtained with one portion of powder in all titrations are not affected by possible differences in properties between particular portions of powder. On the other hand, the error in Dn in Equation 2.11 increases with the total number of portions of acid or base added in a series of consecutive titrations of the same portion of powder. Another experimental procedure minimizes the error in Dn in Equation 2.11 but maximizes the error due to differences in properties between particular portions of powder. That is, each data point on a charging curve can be obtained with a separate portion of powder. In this approach, only one portion of acid or base is used to obtain a point on a charging curve, and propagation of errors resulting from addition of multiple portions of acid or base is avoided. Titrations at four ionic strengths are presented in [539,540], at five ionic strengths in [319,324,541–543], at six ionic strengths in [544], and in seven ionic strengths in [545]. Titrations at three concentrations of four salts are presented in [44], at four concentrations of one salt and one concentration of another salt in [546,547], at eight concentrations of five salts in [548], and at five or six concentrations of four salts in [549]. Titrations of rutile at two concentrations of five salts [327] and of hematite at three concentrations of three salts [328] have been carried out.

2.5.2

SOLID-TO-LIQUID RATIO

Typically, the solid-to-liquid ratios in titrations are fixed in a series of titrations (constant for all ionic strengths) and are relatively high (e.g., 1:10 by mass in [550]). Titrations at two different solid-to-liquid ratios, but only one ionic strength, are reported in [525]. Titrations at three different solid loads are reported in [551,552]. Titrations at different solid-to-liquid ratios are reported in [553]. The typical mass fraction of the solid in titrations is a few percent. Lowsurface-area powders require a high solid-to-liquid ratio. Reference [554] reports titrations at a solid load as low as 1% by mass, and [44] reports titrations at a solid load as low as 0.75% by mass. The solid-to-liquid ratios in other studies were higher, and the upper limit of the solid-to-liquid ratio is determined by the viscosity of the dispersion.

2.5.3

OTHER TITRATION PARAMETERS

The titration protocol (for a selected electrolyte at a certain concentration and a fixed solid-to-liquid ratio) defines the starting and end points of titration, the distances between the data points, and the rate of titration. The distances between data points can be defined by a fixed amount of titrant added per data point or by fixed differences in pH between data points. The rate of titration can be defined by a fixed time of equilibration or by an accepted rate of pH drift (the data point is taken once the rate drops below a pre-assumed value). Even in fast titrations,

Methods

73

long equilibration before taking the first data point is commonplace. For example 1 day’s equilibration before titration is reported in [554] and more than 8 hours’ equilibration of PbS in an acidic medium before base titration is reported in [13]. The titration can be carried out manually or automatically. A computer-controlled titrator was used in [555,556]. The results of titration performed according to a given experimental protocol are not necessarily representative of the system of interest. Even the reproducibility of titration with a fixed protocol is often limited. Apparently, in addition to the parameters discussed above, which are easy to control, the course of titration is also affected by factors that are difficult to control. Starting and end points of titration can be read from titration curves reported in the literature. In studies aimed at determining the PZC, the starting and end points should be selected so that the expected PZC lies between them. Specific solids have a limited pH range of low solubility, and titrations outside that range are not recommended. The direction of titration (from low to high or from high to low pH) is not always specified in scientific papers. Most papers report the results of titrations performed in one direction. Base titration starting at a low pH is often preferred, because of easier removal of CO2 from acidic than from basic solutions (see Section 2.3.1 for a discussion of the CO2 problem). Results of backand-forth titrations are reported in [45,112,119,336,530,557–566] (see Section 2.6.2 for more details). The typical distance between the data points in titrations, which can be read from titration curves reported in the literature, is 0.1–1 pH unit. The advantage of a substantial pH difference between consecutive points is that the volume of acid or base in Figure 2.6 is obtained as a sum of relatively few portions of the titrant, and the error in DV in Equation 2.10 is low. The advantage of a small pH difference between consecutive points is that a data point in the close neighborhood of the PZC is always available, and interpolation is not necessary to determine the CIP. The advantages of both strategies, that is, low error in DV and availability of data points near the PZC, are combined in the following titration program. One large portion of acid or base is added to almost reach (but not to exceed) the PZC. Then, titration is continued in small steps. In other words, the data points densely cover the narrow pH range on both sides of the PZC, but there are very few (or no) data points outside that range. Such a titration program is recommended in titrations aimed at determining the PZC rather than of the entire s0(pH) curve. An approximate position of the PZC can be determined in a preliminary experiment with a more uniform distribution of data points over a broad pH range. A broad range of titration rates has been reported. Fast titration with 3–5 minutes per data point was performed in [567]. Equilibration for a few days (until a constant pH is reached) was allowed in [553], 3 days’ equilibration was allowed in [568], and 1 day’s equilibration in [44]. In these studies, each data point was taken using a separate portion of dispersion. In [569], a data point was recorded when the drift was less than 0.1 mV/s (about 0.002 pH unit/s). A 10–48 hour equilibration period produced similar titration curves of kaolinite, but with 5 minutes’

74

Surface Charging and Points of Zero Charge

equilibration time, the titration curve was different, especially in the acidic range [140]. A study of the effect of equilibration time on charging curves is reported in [570]. The advantage of fast titrations is that the result is rather insensitive to slow processes such as dissolution and recrystallization of the solid phase. In fast titrations, the adsorption/desorption of protons may be not complete. The effect of an ultrasonic field on titration was studied in [571].

2.6 RESULTS: TITRATION PZCs obtained by titration are compiled in Chapter 3. Other aspects of titration curves will be discussed in this section. Figure 1.1 shows a typical set of s0(pH) curves obtained at three different concentrations of an inert electrolyte. Similar sets of curves have been obtained in numerous real systems. A few examples of less typical courses of surface charging curves reported in the literature will be discussed below.

2.6.1

PRESENCE OR ABSENCE OF CIP

Raw titration curves need a correction according to Equation 2.12, which is applicable only for sets of charging curves with a CIP. Therefore, the presence or absence of a CIP is essential. CIPs are usually observed for metal oxides, and sets of charging curves without a CIP are typical of silica (see Section 2.6.3) and clay minerals (see Section 2.6.6). The presence of a CIP implies that the absolute value of s0 increases with ionic strength on both sides of the PZC. Insignificant effects of the concentration of (C2H5)4NCl (0.001–0.1 M range) on the charging curves of silica [127], and of the concentration of NaNO3 (0.001–0.1 M range) on the charging curves of Fe2O3 [572], were observed over the entire pH range. Decreasing s0 with increasing ionic strength is reported in [573,574]. Irregular behavior (decreasing or increasing s0 with increasing ionic strength over different ranges of pH and/or ionic strength) was reported for alumina [575], hematite (normal behavior in the acidic range and abnormal behavior in the basic range) [576], and anatase [515]. The charging curves of hydrous manganese oxide reported in [577] merge at pH < 3; at pH > 3, the apparent charge density decreased in absolute value with increasing ionic strength (0.015–1.5 M). The basic branches of charging curves were almost insensitive to CsCl concentration, and s0 of red mud in the presence of NaCl showed an irregular ionic strength dependence [578]. In a few sets of charging curves, s0 was independent of ionic strength over a certain pH range, and it increased in absolute value with increasing ionic strength outside that range. Charging curves that merge at a low pH, and an increasing absolute value of s0 with increasing ionic strength at a high pH, were reported in [579] (hematite; merged at pH < 6 in the presence of two salts, but exhibited the usual behavior in the presence of a third salt), [580] (alumina), [581] (rutile; merged at pH < 5), [582] (titania coating on silica; merged at pH < 4), [39] (alumina; merged at pH < 5, three different electrolytes), [583] (rutile and cassiterite; merged

Methods

75

FIGURE 2.9 A set of charging curves at three electrolyte concentrations (c1 < c2 < c3) that merge at low pH.

at pH < 5), and [83] (manganite; merged at pH < 8). The charging curves of goethite presented in [584,585] merged at pH > 8.5, and the charging curves of FeOOH presented in [586] merged at pH > 10. The ionic strength in [586] was low (up to 0.002 M); at a high pH, the amount of base added to adjust the pH was high compared with the amount of salt. The charging curves of alumina presented in [587] had an intersection point at pH 8.2, but merged in the basic range. Charging curves that merge at one end of the pH scale are illustrated in Figures 2.9 and 2.10. The position of the pH axis (s0 = 0) is uncertain; it is indicated by the dashed lines in Figures 2.9 and 2.10. The upper or lower limit of the pH range in which the charging curves merge is a characteristic pH for a set of titration curves, but this

FIGURE 2.10 A set of charging curves at three electrolyte concentrations (c1 < c2 < c3) that merge at high pH.

76

Surface Charging and Points of Zero Charge

point is not sharp, and it is not recommended to identify that point with the PZC. More examples of merging s0(pH) curves are reported in the tables in Chapter 3 (“Merge” in the “Method” or “pH0” column). The charging curves of aluminum (hydr)oxides reported in [112] merge at pH 6–8 (no clear CIP), and they behave nearly as expected outside that pH range. The charging curves of goethite in [537] showed a CIP in the presence of NaNO3 and NaCl, but in the presence of Li salts there was no clear CIP. Other sets of charging curves without a clear CIP are reported in [160,588–590]. The charging curves obtained in a 0.005–0.06 M electrolyte in [319] had a CIP, but the charging curve obtained in a 0.3 M electrolyte failed to have a CIP with other curves. The charging curves of ZnO obtained at the lowest ionic strengths in [549] had a CIP, but the charging curves obtained in an electrolyte over 0.1 M did not cross the other curves at that point. For sets of charging curves without a clear CIP, the PZC cannot be independent of the ionic strength, irrespective of the value of the correction term in Equation 2.12. Thus, the concept of an inert electrolyte in the sense discussed in Section 1.3 is not applicable for the set of charging curves shown in Figure 2.8.

2.6.2

REPRODUCIBILITY AND REVERSIBILITY

The question of reproducibility of titrations has been addressed in a few publications (e.g., the results of repeated titrations are reported in [570]) but are ignored in many others. Poor reproducibility of silica titration curves at low ionic strength and good reproducibility at high ionic strength are reported in [591]. Poor reproducibility of charging curves of amorphous HFO is reported in [592]. Studies of reversibility (acid titration vs. base titration) are more numerous. Good reversibility (negligible hysteresis) of acid and base titrations was demonstrated for gibbsite (pH 5–10) [530,557], bayerite (pH 5–10) [557], goethite (pH 4–11 [558] and pH 5–10 [336]), and alumina (pH 6–10) [559]. Ceria nanoparticles pre-aged in different solutions produced reversible titration curves, but the CIP depended on the pH at which they were aged [593]. Negligible hysteresis for fast titration and more significant hysteresis for slower titration (20 minutes’ equilibration) were found in [560]. The hysteresis in titration curves of silica was negligible between pH 3 and 4.5, but when the titration direction was reversed at pH 8.5, substantial hysteresis was observed [561]. Significant hysteresis was observed in the titration of aluminas (pH 4–10) [112], gibbsite [562], hematite (slow titration) [119], goethite (at pH ª 7) [563], alumina-coated rutile [45], montmorillonite (from natural pH to pH 4 and then to pH 9) [564], another sample of montmorillonite [565], and carbon [566]. The first titration of humic acid produced different results, owing to incomplete dispersion, but the following titrations were fully reversible [594]. Storage of zirconia for 1 year in air induced a shift in the CIP by 1.4 pH units [595]. The CIP of a-alumina was insensitive to aging in water at 100∞C for 1 day [106]. The CIP of zirconia aged at pH 4.4 overnight was at pH 8, and that of the same zirconia aged at pH 9.4 overnight was at pH 7.2 [596].

77

Methods

In principle, the course of charging curves and the CIP should be independent of the solid-to-liquid ratio, and systematic studies in this direction are rare. The CIP in a yttria–NaClO4 system was found to shift to a high pH as the solid load increased [597].

2.6.3

SHAPE OF CHARGING CURVES AND TYPICAL VALUES OF s0

s0

Most charging curves reported in the literature are relatively smooth. A few studies resulted in irregular charging curves with local inflection points. For example, [598] reports smooth charging curves for Fe hydrous oxide and irregular charging curves for Al hydrous oxide. The irregular shape of the latter charging curves is probably due to the dissolution of the solid phase (which is difficult to control) accompanying surface charging or to incomplete dispersion or wetting rather than to the surface charging itself. The irregular shape of the charging curves has also been interpreted in terms of surface heterogeneity (see Section 2.9.3.2). All of the charging curves shown in Figures 1.1, 2.9, and 2.10 have similar shapes. Their slopes are negative and pH-dependent. The slope is more negative far from the PZC (on both sides) and less negative near the PZC; that is, a curve has its inflection point near the PZC. An extreme case of this type of behavior, namely an s0 of alumina equal to 0 at pH 5–7 (slope = 0), is presented in [39]. Usually, the difference in slopes between particular pH ranges is less spectacular. Lyklema and co-workers [599,600] demonstrated the similarity of charging curves of various metal oxides at a certain ionic strength and temperature when s0 was plotted against pH-PZC, and the only difference between the different materials was in the positions of their PZCs. The similarity of the shapes of the charging curves demonstrated for selected samples of hematite, rutile, and RuO2 was impressive, but the charging curves of other samples of oxides are not that similar.

PZC

0 c1 c2 c3 pH

FIGURE 2.11 A set of charging curves at three electrolyte concentrations (c1 < c2 < c3) with high absolute value of the slope near the PZC.

78

Surface Charging and Points of Zero Charge

s0

c1 c2

c3 pH

FIGURE 2.12 (c1 < c2 < c3).

A set of charging curves of silica at three electrolyte concentrations

In contrast with Figure 1.1, in a few studies, the slopes of the charging curves were less negative far from PZC and more negative near the PZC (Figure 2.11), or the slope constantly increased or decreased (no inflection point). The charging curve of maghemite reported in [601] is a straight line (constant slope) over the pH range 3–10. The charging curves of silica shown in Figure 2.12 have basic branches similar to those obtained for metal oxides (Figure 1.1). In the acidic range, the s0 of silica tends asymptotically to zero, positive s0 is not observed, and there is no CIP. A substantial positive s0 and an intersection point for quartz are reported in [602]. A substantial positive s0 of silica (but without a clear CIP) is reported in [603,604]. An unusual course of titration curves of silica, with a high slope at a low pH, is reported in [41]. The highest absolute values of s0 of metal oxides obtained by titration 2–3 pH units from the PZC are usually about 0.1 C/m2 for a 0.001 M electrolyte and 0.3 C/m2 for a 0.1 M electrolyte. These values are substantially higher than those of Hg and AgI, which are in the region of 0.05 C/m2 in the presence of a 0.1 M electrolyte [605]. Comparison of the s0 of mercury, of AgI, and of oxides can be made assuming that 1 pH or pI unit corresponds to 59 mV (Nernst equation). Silica (Figure 2.12) shows a relatively low s0 in the acidic and neutral ranges (as compared with metal oxides), and s0 of silica at pH 8 is in the same range as that of metal oxides. The ranges of s0 values reported in different publications for given materials are illustrated in numerous compilations. For example, charging curves of different aluminas in 1 M electrolyte solution are compiled in Figure 1 of [557]. Charging curves of common oxides in 0.001–1 M electrolyte solutions are compiled in [2]. Discrepancies by a factor of up to 3 in s0 values of certain oxides obtained by different authors (at the same pH and ionic strength) are commonplace, but discrepancies by an order of magnitude are rare.

79

Methods

The discrepancies in reported s0 values are to some degree due to the discrepancies in the specific surface areas reported in different publications for the same material. A few examples of surprisingly low or surprisingly high s0 can be found in the literature. A s0 as low as 0.01 C/m2 in 0.1 M electrolyte, 4 pH units below the PZC, was found for high-surface-area goethite in [569]. An absolute value of s0 of UO2 exceeding 1 C/m2 (on both sides of the PZC) in 0.1 M electrolyte is reported in [590].

2.6.4

EFFECT OF IONIC STRENGTH ON CHARGING CURVES

The effect of ionic strength on the charging curves can be quantified in a form of the Esin–Markov coefficient: Ê dpH ˆ b=Á Ë d log asalt ˜¯ s

(2.13) 0

which was originally introduced for the Hg electrode and was later adopted by Lyklema [606] for oxides. In typical charging curves, b = 0 at PZC, b Æ 1 for high positive s0, and b Æ -1 for high negative s0. In the vicinity of the PZC, b decreases smoothly from a maximum value (typically between 0.6 and 1) to a minimum value (typically between -0.6 and -1) [607]. A positive b on the negative branch and a negative b on the positive branch of charging curves correspond to a decreasing absolute value of s0 as the ionic strength increases. A few examples of such abnormal behavior are presented in Section 2.6.1. A very few studies (e.g., [579] for hematite/KNO3, in the basic range) report a maximum in the absolute value of b exceeding 1. Merging of charging curves (b = 0 over a broad pH range far from the PZC) is an extreme case of a low absolute value of b, and a few examples of such charging curves were discussed in Section 2.6.1. Charging curves of aged magnetite with a maximum b = 0.4 are reported in [158]. The same aged magnetite in the basic range and fresh magnetite showed absolute values of b in the usual range. Charging curves of hematite with a maximum b = 0.5 are reported in [608]. Charging curves of goethite with a maximum b = 0.4 and a minimum b = -0.2 are reported in [609]. The same paper reports charging curves of alumina with a minimum b = -0.2, while the b of the charging curves of titania (positive and negative branch) and of alumina (positive branch) was in the usual range. Charging curves of brucite with a maximum b = 0.1 are reported in [507].

2.6.5

EFFECT OF THE NATURE OF THE SALT ON NUMERICAL VALUES OF s0

The CIP is rather insensitive to the nature of an inert electrolyte. This was demonstrated for rutile (five salts) [327], hematite (three salts) [328], and many other systems. Numerical values of s0 far from the CIP are insensitive to the nature of the co-ion, but do depend on the nature of the counterion. Thus, the acidic branch of charging curves depends on the nature of the anion, and the basic branch of charging

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Surface Charging and Points of Zero Charge

curves depends on the nature of the cation. Therefore, in a series of inert electrolytes with a common cation, the acidic branch is common for all salts, and the differences are observed in the basic range; and in a series of inert electrolytes with a common anion, the basic branch is common for all salts [610,611], and the differences are observed in the acidic range. Charging curves obtained at the same ionic strength in a series of salts with a common anion or common cation have a course analogous to the electrokinetic curves shown in Figures 2.4 and 2.5, except that the salt that produces the highest absolute value of the z potential gives the lowest absolute value of s0, and vice versa. The specific effects of anions and cations of inert electrolytes on surface charging will be discussed in more detail in Chapter 4. Numerous examples of the typical behavior described above can be found in the literature, and only a few examples of abnormal behavior have been reported. The papers reporting unusual effects of the nature of the electrolyte seldom discuss or attempt to explain that atypical behavior. A substantial effect of the nature of an inert electrolyte on the CIP was reported for alumina (KNO3 vs. KCl) [559], titania (CsCl vs. NaCl) [612], goethite [44], and b-FeOOH [613]. The charging curves of titania reported in [614] are insensitive to the nature of the electrolyte (0.1M NaCl, KCl, NaNO3, or KNO3). In contrast, the s0 of titania in the presence of NaCl reported in [615] was lower than in NaClO4 on both sides of the PZC.

2.6.6

SURFACE CHARGING OF MATERIALS OTHER THAN METAL OXIDES

The surface charging behavior of materials other than metal oxides reported in the literature is less consistent than that of metal oxides. A few studies suggest similarity to metal oxides (see Figure 1.1), but other studies suggest completely different behavior. The presence or absence of a CIP of charging curves obtained at different ionic strengths is an example of a property for which contradictory results have been reported. A clear CIP (for three or more ionic strengths) has been reported for kaolinite [616], hydroxyapatite [617], synthetic hydroxyapatite [618], various activated carbons [619,620], and bacterial cell walls [621]. An intersection point of titration curves obtained at two ionic strengths has been reported for kaolinite and monomorillonite [125] and for activated carbon [622]. Mixed evidence (the presence of a CIP for certain specimens or at certain conditions, and the absence of a CIP for other specimens or at different conditions) has been reported for homoionic illite [623], silicon nitride [624], and Al- and Ti-doped MCM-41 [625]. Ionic-strengthindependent charging curves (and thus the absence of a CIP) have been reported for glass [626], bentonite [36], kaolinite [100,627], sepiolite [628], and humic acid [629,630]. Nearly parallel charging curves (and thus the absence of a CIP) have been reported for kaolinite [631,632], montmorillonite [564,632], and humic and fulvic acids [633]. Sets of charging curves without a CIP have also been reported for kaolinite [189], fulvic acid [634], humic acid [594], and bacteria [635].

2.7 RELATIONS OF RESULTS OBTAINED BY DIFFERENT METHODS For numerous samples of pure sparingly soluble metal oxides, the IEPs and PZCs (CIPs) obtained by titration matched or nearly matched. A matching PZC obtained

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by different methods and under different experimental conditions is more significant as a characteristic quantity for a given material than a PZC obtained by one method at specific conditions. A few publications report substantial discrepancies between the PZC and IEP [636,637]. In common models of the electrical double layer at a metal oxide–inert electrolyte interface (see Section 2.9), the PZC and IEP must be equal; thus, a discrepancy between these quantities is considered as an indication of the presence of impurities or of experimental error. Interpretation of potentiometric titration data in terms of s0 requires numerous assumptions, which are often not verified. For example, water-soluble species, which may contribute to the consumption of acid or base in titration, must be absent or properly corrected for. An analysis of supernatants for products of dissolution was carried out in [127], but in most publications the consumption of an acid or base is entirely attributed to surface charging. It is often the case that different size fractions are used in titrations on the one hand and electrophoresis on the other. These fractions may have somewhat different properties, but a large difference between the PZC and IEP is not expected. Several models allow differences between the PZC, CIP, and IEP, and the equality of these quantities has been challenged in a few publications [638–641], even for sparingly soluble metal oxides. Rejection of the assumption that CIP = PZC implies that the correction for an acid or base associated with solid particles illustrated in Figure 2.7 is not applicable, and the correction term in Equation 2.12 has to be determined by another means. With materials other than sparingly soluble metal oxides, the charging curves obtained at different ionic strengths often do not exhibit a CIP, and even if they do, it is not necessarily equal to the IEP. Discrepancies between CIP and IEP have been reported for various activated carbons [619].

2.8 OTHER METHODS 2.8.1

METHODS INVOLVING NONAQUEOUS SOLVENTS

An acid–base scale for solids based on titrations with 1-butylamine or trichloroacetic acid in benzene in the presence of indicators was described in [642]. In [643], 0.2 g of material was mixed with 3 g of heptane and 0.01 cm3 of pH indicator solution. A series of indicators was used, and the apparent pH detected by these indicators was identified with the PZC. These methods are reported as historical curiosities, and they are not recommended by the present author.

2.8.2

ELECTRICAL METHODS

The surface charging of materials that show a certain degree of electric conductivity can be measured directly by electrical methods. Such measurements are not used to determine the PZC. The potential of a hematite electrode prepared as a coating on Pt [243] was Nernstian (59 mV/pH unit) at 20∞C in 0.005 M KCl. Also, a monocrystalline hematite electrode [644] had a nearly Nernstian potential in the acidic range in 0.0005 M NaNO3, but the slope was lower in the basic range and

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in 0.0068 M NaNO3. Hysteresis (acid vs. base titration) was observed in the potential of a monocrystalline hematite electrode [170]. A monocrystalline anatase electrode showed 82% of Nernstian slope in 0.001 M NaClO4, and 65% of Nernstian slope in 0.001 M NaCl [615], and even lower slopes are reported in [645]. The properties of an anatase electrode formed as a layer on the surface of metallic Ti were studied in [646]. The open-circuit potential of TiO2 films on Ti was studied in [647]. The slope was about 41 mV/pH unit in the pH range 5–10. A monocrystalline pyrite electrode was studied in [648]. The PZC was estimated from capacitance–voltage characteristics in electrolyte–insulator–semiconductor structures in [649], but this method is not recommended by the present author.

2.8.3

SUM FREQUENCY GENERATION AND SECOND-HARMONIC GENERATION

The orientation of water dipoles at a charged surface affects light reflected from that surface. This phenomenon can be used to determine pH0. A few efforts in this direction have been published. Selective sum frequency vibrational spectroscopy was proposed as a tool to determine pH0 [650]. Several publications are devoted to second-harmonic generation, in which two photons of the same frequency are combined. The experimental setup is shown in [651,652]. Monochromatic (w) and polarized laser light is reflected at a corundum–liquid interface (from the solution side or from the solid side in a total internal reflection geometry), and the intensity of the second-harmonic frequency (2w) is measured in the reflected light. In [651], the second-harmonic field strength increased when the pH increased, and the pH effect became more significant when the ionic strength decreased. The curves obtained at different ionic strengths intersected at pH 5–6, which was taken to be the PZC. The experiments were carried out with three sodium salts, and the intersection points were consistent. However, the course of the second-harmonic field strength versus pH curves at pH > 5 was strongly anion-dependent. This result does not support the hypothesis that the intensity of the second-harmonic frequency is solely dependent of the surface potential, as postulated in [651]. Namely, at pH > pH0, the surface charge and surface potential are rather insensitive to the nature of the anion (see Figure 2.4). Qualitatively similar results were obtained in [652], but only one salt was used. Different crystallographic faces of corundum produced different intersection points in the pH range 4–5. Possible sources of discrepancies between the pH0 obtained by the methods discussed in this section on the one hand and by standard methods on the other are discussed in Section 2.3.2.

2.8.4

METHODS EQUIVALENT TO TITRATION

A few methods may produce PZCs equivalent to those obtained by potentiometric titration (with or without correction for acid or base associated with solid particles). There are a limited number of such methods, although some of them have been “re-invented” several times, and given different names. Only a few of these names are used in the tables in Chapter 3. The methods that produce results

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equivalent to potentiometric titration without correction for acid or base associated with solid particles (natural pH of dispersion) are referred to as “pH” in the “Method” columns of those tables. The methods that produce results equivalent to the CIP are referred to as “cip.” The terms “batch equilibration” [653], “pH drift” method [654], “addition method” [552], “solid addition method” [655], “powder addition method” (cited in [656] after [654]), “potentiometric titration” [234] (“sic”—in the present book, the term “potentiometric titration” is reserved for a different method, described in Section 2.5), and “salt addition” [573] (“sic”—in the present book, the term “salt addition” is reserved for a different method, described later in this section) refer to the same method, which is now described. A series of solutions of different pHs is prepared and their pHs are recorded. Then, the powder is added and the final pH is recorded. The addition of a solid induces a shift in the pH in the direction of the PZC. The pH at which the addition of powder does not induce a pH shift is taken to be the PZC. Alternatively, the PZC is determined as the plateau in the pHfinal(pHinitial) curve. The method assumes that the powder is absolutely pure (free of acid, base, or any other surface-active substance), which is seldom the case. Even with very pure powders, the above method is not recommended for materials that have a PZC at a nearly neutral pH. Namely, the method requires accurate values of the initial pH, which is the pH of an unbuffered solution. The display of a pH meter in unbuffered solutions in the nearly neutral pH range is very unstable, and the readings are not particularly reliable. The problem with pH measurements of solutions is less significant at strongly acidic or strongly basic pHs (see Section 1.10.3). The above method (under different names) became quite popular, and the results are referred to as “pH” in the “Method” columns in the tables in Chapter 3. The experimental conditions in the above method (solid-to-liquid ratio, time of equilibration, and nature and concentration of electrolyte) can vary, but little attention has been paid to the possible effects of the experimental conditions on the apparent PZC. The plateau in the pHfinal(pHinitial) curve for apatite shifted by 2 pH units as the solid-to-liquid ratio increased from 1:500 to 1:100 [653]. Thus, the apparent PZC is a function of the solid-to-liquid ratio. The “potentiometric mass titration” method [657,658] produces results equivalent to those of the “drift method” described above. The same amount of base is added to three dispersions with different solid-to-liquid ratios and a constant ionic strength. The dispersions are titrated with acid, and the pH is recorded as a function of the amount of acid added. The intersection point of the obtained curves is taken as the PZC. In other words, the PZC is identified with the pH at which solid addition does not induce a change in pH. The “drift method” and mass titration are based on the same principle, the difference being that in “potentiometric mass titration,” the reagents are added in a different order. Potentiometric mass titration is affected by the acid or base associated with the powder in the same way as in the “drift method” and mass titration. The advantage of potentiometric mass titration over the “drift method” is that in the former the pH is measured only in buffered systems.

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In the set of charging curves shown in Figure 1.1, the pH of a dispersion equilibrated at a certain pH shifts in the direction of the CIP on the addition of an inert electrolyte. This property is used in the salt addition method, which dates back to the 1960s [659]. This method was termed “salt addition” in [660] and “salt titration” in [661]. In the present book, the term “salt titration” is reserved for a different method, described below. In a classical salt addition method, a series of dispersions of constant solid-to-liquid ratio and different pH is prepared, and DpH (the shift in pH induced by an increase in the KNO3 concentration from 0.01 to 0.1 M) is plotted as a function of pH. The PZC is determined as the intersection of the curve with the pH axis. Such a PZC is equivalent to the intersection of the charging curves obtained in 0.01 and 0.1 M KNO3. Different salts and different concentrations produce different values of DpH, but similar PZCs. The advantage of the salt addition method is that deviations in the solid-to-liquid ratio, in the amount of dispersion, or in the salt concentration before and after salt addition have limited effects on the results. These deviations may affect the value of DpH, but the sign is always positive below the PZC and negative above it. The pH in the salt addition method is measured in a wellbuffered system; thus, the reading of a pH meter is stable and reliable. The method is insensitive to the acid or base associated with the solid particles. The disadvantage of the salt addition method is that it gives only the PZC, but not s0. The salt addition method is based on the assumption that the intersection of the charging curves at two ionic strengths represents the CIP, which in real systems is not always the case (see Section 2.6.1). Therefore, the salt addition method is not recommended for materials other than sparingly soluble metal oxides. Certainly, the choice of salt in the salt addition method is limited to an inert electrolyte. The idea of using a similar procedure with non-inert electrolytes [662,663] has also appeared in the literature, but such a method does not produce a pristine PZC. For spinels [664], the salt addition method gave reproducible results with KCl but irreproducible results with KNO3. The salt titration method [666] is a modification of the salt addition method. A portion of salt is added to a dispersion, and the DpH is recorded. When DpH > 0, base is added to shift the pH to an even higher value. When DpH < 0, acid is added to shift the pH to an even lower value. Once a constant pH has been established, a new portion of salt is added, and DpH is recorded again. The series of salt additions followed by acid or base additions is continued until DpH = 0. The advantage of the salt titration method as compared with the classical salt addition method is that only one portion of dispersion is used. Thus, PZC determination requires a smaller amount of solid and only one reaction vessel. Moreover, a series of measurements (e.g., at different temperatures or at different concentrations of a nonaqueous co-solvent) can be carried out with the same portion of solid, and effects due to a difference in surface properties between different portions of solid are avoided. The number of consecutive salt additions in the salt titration method is limited, because the sensitivity of DpH to an addition of the same amount of salt decreases as the initial salt concentration increases.

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In the mass titration method, the PZC is determined as the natural pH of a concentrated dispersion. A detailed description of the experimental procedure can be found in [667]. Mass titration become popular in the late 1980s [668,669], but the same method was already known in the 1960s as the “pH drift” method [183]. Usually, a series of natural pH values of dispersions with increasing solid loads is reported, but only the natural pH of the most concentrated dispersion is actually used. The only role of the data points obtained at lower solid loads is to confirm that a plateau was reached in pH as a function of solid load; that is, a further increase in the solid load is unlikely to bring about a change in pH. The mass titration method is based on the assumption that the solid does not contain acid, base, or other surface-active impurities. This is seldom the case, thus mass titration often produces erroneous PZCs. In this respect mass titration is similar to the potentiometric titration without correction illustrated in Figure 2.7, only the solid-to-liquid ratio is different. The experimental conditions in mass titration (solid-to-liquid ratio, time of equilibration, nature and concentration of electrolyte, and initial pH) can vary, but little attention has been paid to the possible effects of experimental conditions on the apparent PZC. The effect of an acid or base associated with solid particles on the course of mass titration was studied in [670]. To this end, a series of “artificially contaminated samples” was prepared by the addition of an acid or base to a commercial powder. The apparent PZC of silicon nitride obtained in [671] by mass titration varied from 4.2 (extrapolated to zero time of equilibration) to 8.2 for time of equilibration longer than 20 days. The method termed “mass titration” was used in [672], but it was different from the method discussed above. A potentiometric titration curve often has an inflection point at the PZC (Section 2.6.3). This property has been proposed as a method to determine the PZC [673]. The “inflection point” method gained some popularity after a publication by Zalac and Kallay [670]. Also, the “differential potentiometric titration” described in [674] is equivalent to the inflection point method. This method is not recommended by the present author as a standalone method to determine the PZC, but a few results obtained by the “inflection point” method, usually in combination with other methods, are reported in the tables in Chapter 3 (as “Inflection” in the “Methods” columns). In [675], the potentiometric titration curve of one sample had two inflections, and the inflection at the lower pH was assumed to be the PZC. The potentiometric titration curves of other samples had one inflection each. Reference [676] reports an inflection point in the titration curve of niobia at pH 8, which is far from the pH0 reported in the literature. A few examples of charging curves without an inflection point or with multiple inflection points are discussed in Section 2.6.3. In classical potentiometric titration, soluble species produced by dissolution of the solid may contribute to the consumption of an acid or base and induce an error in the calculated s0. This error is not corrected for in back titrations of an inert electrolyte (Figure 2.6). The back-titration method was designed to avoid the error induced by the dissolution of the solid phase, and it has been used for solids that show appreciable solubility. For solids that are practically insoluble, the

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back-titration method would probably produce the same results as classical titration, although this has not been confirmed experimentally. In the back-titration method, which gained popularity among soil scientists, a series of dispersions with different final pHs is prepared, and each supernatant is titrated. In [451], the initial pH values of solutions (before powder addition) were recorded, and each supernatant was titrated back to the respective initial pH. The amount of acid/base consumed in each back titration was used in Equation 2.10 to calculate s0. In [677], each supernatant was titrated to pH 7, and s0 was calculated from the difference in the amount of acid/base used to adjust the pH of the dispersion on the one hand and in the back titration of the supernatant to pH 7 on the other. Typically, the equilibration time in the back-titration method is long (about 1 day), but in principle the same procedures can be followed with shorter equilibration times. Back titration at one ionic strength has the same disadvantage as classical titration at one ionic strength, namely, an acid or base associated with solid particles induces an error in s0. This error can be corrected for by performing back titration at three or more ionic strengths, and the correction is calculated in the same way as in classical titration (Figure 2.7). Back titration has a serious drawback, which has been overlooked by its adherents. Equilibration of alumina (taken as an example of a solid that shows appreciable solubility) at a high or low pH produces water-soluble aluminum species. In back titration, these species form a colloid of high surface area. The nucleation process is rather unpredictable and difficult to control. Thus, the properties of colloidal particles are irreproducible. The acid or base is used up not only in neutralizing the charged solution species, but also in charging the colloidal particles produced in the titration process. Owing to the unpredictable properties of colloidal particles, the later process is difficult to account for, and when the surface charging of the precipitate is ignored in the interpretation of back-titration results, the calculated surface charge is erroneous. The error caused by surface charging of colloidal particles is less significant at high solid-to-liquid ratios, and it can be eliminated when the supernatant is titrated to the pH of the PZC of the material of interest (about 9 for alumina). Then, an acid or base is not used to charge the colloid. However, the exact position of the PZC is unknown before the titration is completed. Certainly, the back-titration method produces correct results when the solubility of the powder is negligible, but in such cases classical titration will give similar results. The above criticism is not aimed at the idea of correction for soluble species in solution—it only points out that back titration (in the form described in the literature) does not solve the problem. The charging curves of alumina obtained by means of back titration [677] were not smooth (there were many local minima and maxima and inflection points), and the pH0 (CIP) was substantially lower than typical values observed for alumina. An original approach to determining the PZC was presented by Pechenyuk et al. [678,679]. They precipitated series of materials from the same precursor at various pH values, and studied the natural pH of the dispersions of the precipitate at different ionic strengths. Not surprisingly, the natural pH of these dispersions (of fresh or aged precipitates) was similar to the pH of precipitation due to an acid or base associated with solid particles. The pH of precipitation, which was equal

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to the natural pH of the dispersion of the precipitate, was identified with the PZC. Indeed, the PZC obtained by means of the method described above matched the PZC obtained by well-established methods. The nomenclature used by Pechenyuk et al. does not meet the standard recommended in the present book. The method of Pechenyuk et al. is applicable to a series of materials precipitated from the same precursor at various pH values, but is not applicable to specific materials that might have been obtained by methods other than precipitation. A coulometric method to determine s0 (with OH- ions being generated electrochemically) was suggested in [680].

2.8.5

FORCE BETWEEN PARTICLES

The force between particles is the sum of a pH-independent van der Waals component, which is always attractive, and a pH-dependent electrostatic component, which can be attractive or repulsive. In Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, the z potential is used to calculate the interaction force or energy as a function of the distance between the particles. Atomic force microscopy (AFM) makes it possible to directly measure the force between the particles as a function of the distance, and commercial instruments are available to perform such measurements. Different approaches have been proposed to utilize the results obtained by AFM to determine the pH0. The quantity obtained by AFM corresponds to the IEP rather than the PZC. AFM was used to measure the force between SiO2 (negative z potential over the entire studied pH range) and Si3N4 (IEP to be determined) in [681]. The pH at which the force at a distance of 17 nm was equal to zero was identified with the IEP. The van der Waals forces are negligible at such a distance, and the force is governed by an electrostatic interaction. The experimental results were consistent with DLVO theory. AFM was used to measure the force between an Si3N4 tip and Al2O3, SiO2, and SnO2 surfaces in [682]. The force changed its sign at pH0 of the tip or of the surface. Reference [683] reports a pH0 determined by scanning force microscopy. In spite of the sign reversal of the electrostatic force, there is no abrupt change in the total interaction force at the pH0, and the pH0 can rather be roughly estimated than exactly determined from the AFM results. AFM is not usually employed as a standalone method to determine the pH0, but rather to verify the IEP obtained by other methods. A few examples are given in the tables in Chapter 3. Coagulation behavior is a direct consequence of the interaction force, and a maximum coagulation rate, maximum aggregate size, and maximum sedimentation rate coincide with the IEP. Different techniques have been used to quantify coagulation behavior, and different physical quantities (e.g., intensity of transmitted or of scattered light, and mass of sediment) have been directly measured. A more or less sharp minimum or maximum of the measured quantity was observed at the IEP. Sharp extrema are observed at low ionic strengths. Coagulation is not usually employed as a standalone method to determine the pH0, but rather to verify the IEP obtained by other methods. A few examples of such studies are reported in the tables in Chapter 3. Studies reporting IEPs based on coagulation

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behavior that were not verified against other methods [481,684,685] are ignored in Chapter 3. The pH dependence of the coagulation behavior of silica is not fully understood, and is very different from that observed for metal oxides [686].

2.8.6

NONSTANDARD METHODS

A few nonstandard methods to determine the PZC have been proposed. These methods are not recommended as replacements for standard methods, but they may be useful in certain systems for which standard methods are not applicable. The PZC of titania was obtained in [687] as the pH at which the rate constant of reduction of methyl viologen in the presence of titania was independent of ionic strength. Adhesion of positively and negatively charged latex was used to estimate the IEP of stainless steel (original and heated in air for 2 hours at 1000∞C) [688]. Adhesion occurs when the signs of the charge of the studied surface and of the latex are opposite. The same method has been used for other metals [689]. The nonzero electrical conductivity of metals excludes measurements of their IEP by means of standard methods. A different version of the adhesion method was used in [690]. An amidinegrafted polystyrene latex with IEP at pH 6 (electrophoresis) was used. IEPs of thin films of iridium and tungsten oxides (among other materials) were determined, and the results complied with standard methods. Coincidence between the maximum in contact angle as a function of pH and IEP has been claimed [691–693]. A method of determining the IEP based on measurements of the contact angle would be beneficial for studies of thin films and of single faces in monocrystals. To be considered as a reliable method, it has to be supported by a theory, and to pass extensive tests against materials with well-established IEPs. Some IEPs reported by adherents of the contact angle method matched those determined by standard methods, but others did not. The contact angles of kaolinite, pyrophyllite, and illite as functions of pH are reported in [60]. The angles were rather insensitive to pH, and did not show a clear maximum at the IEP. A chromatographic method to determine the s0 of materials with low surface area was proposed in [694]. s0 was calculated from the diffuse front of a breakthrough curve. Measurements at pH ª 7 are not possible in this method, since the solution is unbuffered and it is difficult to obtain a solution of well-defined pH. As is classical potentiometric titration, the charging curves usually require a correction for an acid or base associated with solid particles. The uptake of anions of a 1-1 electrolyte by materials that show pH-dependent surface charging decreases with increasing pH and the uptake of cations of 1-1 electrolyte increases. At a certain pH, the uptake of both ions of a 1-1 electrolyte is equal, and such a pH has been taken as the PZC, especially in soil chemistry [26]. The present author does not consider measurements of uptake of ions of a 1-1 electrolyte as a reliable method to determine the PZC. In many theoretical models, the point of equal uptake coincides with the PZC, but this coincidence is

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of limited practical importance. The uptake of ions of an inert electrolyte near the PZC is usually low (see Section 2.9.3.3 and Chapter 4 for more detailed discussion) and rather insensitive to pH. Then there is a broad pH range in which the uptake of the anion and cation of an inert electrolyte are almost equal, and the apparent PZC (point of equal uptake) is very sensitive to accidental scatter of results and to experimental errors. The points of equal uptake of ions of 1-1 electrolytes reported in the literature are ignored in the tables in Chapter 3, although they have been quoted in secondary sources as the PZC. A few PZCs reported in [1] (and quoted after [1]) were obtained by methods other than titration or electrokinetic methods. The principles of these methods were not described in detail, but names such as “suspension effect,” “by adsorption of Zn and Co,” and “minimum gelation rate” suggest that these PZCs do not meet the standards recommended in the present book, and such results are ignored in Chapter 3. On the other hand, a few PZCs obtained by means of the “drift method” cited after [1] are cited as such in Chapter 3. The pH of the minimum of solubility of calcite was termed the “PZC” or “IEP” in [695,696]. The same authors report PZCs obtained from flotation by anionic and cationic collectors. These “PZCs” (which have been quoted in numerous papers) do not meet the standards recommended in the present book and are ignored in the tables in Chapter 3. The rate of suction in filter paper in contact with a dispersion as a function of pH was observed [697] in a specially designed apparatus, originally described and illustrated in [698], and a shallow minimum in suction time was observed at the IEP. A method of determination of the PZC from the filtration rate was proposed in [699]. However, it is difficult to point to any advantage of methods based on filtration rate other than originality.

2.9 ADSORPTION MODELS The present discussion is focused on models of primary surface charging, that is, of adsorption of protons in the presence of inert electrolytes. These models are elements of more general models, which describe adsorptions of all kinds of species. Basically, the models discussed in this section apply to metal oxides, but similar models have been used for other materials. For example, a model of proton and heavy metal binding by humic acid described in [700] is similar to models used for oxides.

2.9.1

DENSITY OF PROTONABLE SURFACE GROUPS

In the absence of surface-active species, the surface charge of metal oxides is due solely to the adsorption/desorption of protons. The ions of an inert electrolyte remain at some distance from the surface and affect the surface charging indirectly. In most models, proton adsorption and desorption is interpreted as the protonation and deprotonation of discrete surface sites. Direct spectroscopic observation of these surface sites is difficult, and it does not give clear and

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unequivocal information about the nature and density of surface sites. The surface of titania at various pH values was studied by internal reflection spectroscopy in the infrared range in [701], and different wavenumbers were assigned to different degrees of protonation of surface TiOH groups. An X-ray photoelectron spectroscopy (XPS) study [702] indicated the presence of ⬅SiOH2+ and of two other surface species on the surface of silica. In view of the limited success of spectroscopic methods, indirect information is often used to gain information about surface sites. A common approach is that in certain materials the number of surface sites is proportional to the surface area, which is the product of mass and specific surface area. Specific surface area is an important element of characterization of adsorbents, and varies widely from one sample to another. Available data for particular samples are reported in Chapter 3. The values of specific surface areas reported for certain commercial materials in different publications are usually consistent, but serious discrepancies are also common. These discrepancies may reflect actual differences between particular lots of material with the same trade name. The specific surface areas reported in Chapter 3 often refer to purified or ground materials, which may differ substantially from the original material. Most specific surface areas reported in the literature have been obtained by means of the Brunauer–Emmett–Teller (BET) method, and numerous types of commercial instruments for such measurements are offered. Many publications report specific surface areas of commercial materials provided by manufacturers. Various techniques, differing in the number of data points, the range of pressures, and even the nature of the gas adsorbed, are termed BET techniques (more precisely, techniques based on the BET equation for the adsorption isotherm), and experimental details are seldom reported. Nitrogen is the gas most commonly used in the BET method, but krypton BET has also been used [703]. A few studies report comparisons of results obtained by the BET method in different laboratories or under different conditions. A perfect match between nitrogen and krypton specific surface area is reported in [704]. Argon and nitrogen specific surface areas of three powders reported in [705] matched within 5%, but over 20% difference was obtained with the fourth powder. Specific surface areas of five materials from three laboratories reported in [538] show differences by a factor up to 2. There was no regular trend; that is, low and high values were found among results from each laboratory. These and other problems with BET surface area are discussed in [706]. Techniques other than BET can give substantially different specific surface areas. For example, ethylene glycol monomethyl ester (EGME) penetrates the interlammelar spaces in clay minerals, and with these materials it produces a substantially higher specific surface area than the BET method. Nitrogen and H2O specific surface areas for a series of minerals are reported in [707], and a good correlation was found between specific surface area and anion adsorption capacity. Specific surface areas and particle radii determined by different methods are compared in [708]. The surface area given by the manufacturer was re-determined by three different methods in [709]. The three methods were used to determine the specific surface area in [144], and the results nearly matched. The surface area was

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determined by means of room temperature water vapor adsorption in [710,711] and by the glycerol method or by paranitrophenol adsorption from xylene in [711]. Phosphate adsorption was used to determine the specific surface area in [229]. In monodispersed colloids, the specific surface area can be calculated from the specific density of particles and their geometrical dimensions. The concentration of surface sites is usually reported as site density per unit surface area. Different approaches to the nature of surface sites responsible for primary surface charging can be found in the literature. Different definitions of surface sites are discussed in [712]. Not surprisingly, different approaches lead to different site densities. In older publications, the surface sites were identified with the surface OH groups that are formed by surface reactions of sparingly soluble oxides with liquid water or with atmospheric water (dissociative adsorption). Densities of surface OH groups of a few common materials obtained by infrared spectroscopy, thermogravimetric analysis (TGA), and LiAlH4 titration are reported in [713], and the results are rather consistent: about 3 nm-2 for silicas and about 5 nm-2 for titania. Concentrations of surface OH groups in various materials obtained by different methods are reported in [8,714] and, for goethite, in [715]. BET specific surface areas and surface densities of OH groups in 21 materials obtained by means of the Grignard method are summarized in [716]. Site densities of 44 sites/nm2 for Al(OH)3 and 5–11 sites/nm2 for silica, Fe(OH)3, and for Al(OH)3-coated silica were obtained by deuterium exchange in [717]. The surface density of exchangeable hydrogen associated with a rutile surface outgased at different temperatures was studied by deuterium exchange in [718]. The concentration of surface OH groups was determined by reaction with KI in dimethylformamide (DMF) (liberation of iodine) in [720]. Site densities in different faces of common oxides determined from crystallographic data in [721] were about 2 sites/ nm2 for all faces in all materials. The above examples refer to the determination of total site density, irrespective of the variable proton affinities of particular surface sites. In models of a heterogeneous surface, certain (but not all) types of surface oxygen atoms are considered as surface sites. Namely, only a fraction of surface oxygen atoms undergo protonation and deprotonation over the pH range of interest and thus contribute to the pH-dependent surface charge. The surface concentrations of different types of oxygen atoms (singly, doubly, and triply coordinated) in various faces of hematite and of goethite calculated from crystallographic data in [722] were in the range 1.5–14 nm-2. The surface site density obtained by means of the aforementioned independent methods can be used to interpret potentiometric titration data. Alternatively, the titration data can be used to calculate the best-fit surface site density (or densities of various types of sites) as parameter(s) of a certain model. In such a calculation, knowledge about the nature of the surface sites is not required. The site densities have also been calculated (e.g., in [723]) as parameters of adsorption isotherms of various adsorbates (usually small ions). The problem with such site densities is that protons behave differently from other adsorbates, and sites that are capable of binding protons are not necessarily capable of binding other species, and vice versa.

92

Surface Charging and Points of Zero Charge

2.9.1.1 Model without Surface Sites The concept of protonable surface sites does not explain the experimentally observed (see Chapter 3) pH-dependent surface charging of gas bubbles or of droplets of hydrocarbons. The dispersed phase does not provide oxygen atoms, which may be considered as surface sites, and the surface charging is due to the protonation/deprotonation of the surface layer of water [724]. This phenomenon is rather insensitive to the nature of the dispersed phase, and indeed many materials that do not have protonable hydroxyl groups on their surfaces show IEPs at pH ª 4, which seems to be the IEP of a water/inert gas interface. Preferential adsorption of hydroxide ions (with respect to protons) at a water/hydrophobic interface was found in a recent molecular dynamics study [725]. Protons are more hydrophilic than hydroxyl ions, and at neutral pH there is an excess of protons in bulk solution and an excess of hydroxyl ions in the interfacial layer, and a bubble is negatively charged. In other words, the activity coefficient of protons in the surface layer is very much greater than 1, and the activity coefficient of hydroxyl anions is very much lower than 1. When the pH decreases, the concentration of hydroxyl ions in the interfacial layer decreases and the concentration of protons in the interfacial layer increases, and, at sufficiently low pH, the sign of the surface charge is reversed to positive. This result is in line with the difference in Gibbs energy of solvation, which is more negative for protons than for hydroxyl ions [726]. A spontaneous increase in the concentration of hydroxyl ions in the interfacial layer at a neutral pH may contribute to the overall surface charge of all materials, including those that acquire their surface charge chiefly owing to a protonation of surface sites, with the relative significance of the two mechanisms of surface charging depending on the density of surface sites. A mixed mechanism of surface charging is also responsible for discrepancies in the PZCs of materials that have surface sites with the same proton affinities, with only their concentrations being different. The discrepancies in the PZC are more significant for materials that have PZCs far from 4 (e.g., alumina) and less significant for materials that have PZCs close to 4 (e.g., titania).

2.9.2

ELECTROSTATIC MODELS

The protonation and deprotonation of a surface site in contact with solution ⬅S-x + H+  ⬅SH1-x

(2.14)

where -x (0 < x < 1) is the charge of deprotonated site, is governed by an expression similar to the law of mass action: Ka =

{∫ SH1- x } Ê ey ˆ exp Á 0 ˜ -x + Ë kT ¯ {∫S }{H }

(2.15)

where {} denote activities of surface species and of protons, and y0 is the surface potential, which cannot be measured directly. The fractional (rather than

93

Methods

integer) charge of protonated and deprotonated surface sites, which seems counterintuitive at first glance, will be explained later in this chapter. In this approach, the surface concentrations of various species rather than their surface excesses (adsorption) are used. The exponential factor in Equation 2.15 reflects the electrostatic work accompanying the transfer of an ion (proton) from the bulk solution to the surface, which has an electric potential y0 with respect to the bulk solution. The surface potential y0 is related to s0, which in turn depends on the number of protonated and deprotonated sites. The relationship between s0 and y0 is a part of a model of the charged interface called an electrostatic model, and various such models have been proposed. An extensive set of simulations of surface charging within various electrostatic models can be found in Chapter 5 of [2]. 2.9.2.1 Non-Electrostatic Model In the simplest model, called the non-electrostatic model [727,728], the exponential factor in Equation 2.15 is set equal to 1, that is, the electrostatic work is neglected, and Equation 2.15 reduces to a simple mass-law expression. The nonelectrostatic model is simple, but unphysical, and it overestimates the effect of pH on s0. It does not explain the effect of ionic strength on s0 unless reactions other than Equation 2.14 contribute to s0. An ion exchange approach to adsorption of ions from solution was popular in the old literature, but has seldom been used in recent work [729]. Studies of the effect of ionic strength on the specific adsorption of ions provide a strong argument against the ion exchange approach. Namely, the specific adsorption of ions is often insensitive to ionic strength, and sometimes it even increases with ionic strength. This apparent paradox can be quantitatively explained in terms of the electrosorption models discussed below (see [2] for specific examples). 2.9.2.2 Nernst Equation The other simple expression for y0 is the Nernst equation:

y0 =

kT (pH 0 - pH) e

(2.16)

The Nernst equation reflects the fact that adsorption of positively charged species (protons) produces a positive surface potential, which prevents further adsorption of positively charged species. The surface potential calculated from Equation 2.16 changes by 59 mV per 1 pH unit at 25∞C. The applicability of the Nernst equation to metal oxide surfaces is discussed in [730], where it is concluded that oxide surfaces are Nernstian, at least near the PZC. A few results presented in Section 2.8.2 suggest the validity of the Nernst equation for metal oxides, and a few other results suggest that the absolute value of the surface potential changes by less than 59 mV per 1 pH unit. Thus, Equation 2.16 sets the upper limit of |dy0/dpH|.

94

Surface Charging and Points of Zero Charge

Combination of Equations 2.15 and 2.16 gives pH- and ionic-strengthindependent {⬅SH1-x}/{⬅S-x}. When the activities of surface species are proportional to their concentrations, pH- and ionic-strength-independent {⬅SH1-x}/ {⬅S-x} are equivalent to pH- and ionic-strength-independent s0, which is in obvious contradiction with experimental facts. The contradiction disappears when the activities of surface species in Equation 2.15 are not proportional to their concentrations [731,732] or when reactions other than Reaction 2.14 contribute to s0. A model with Nernstian surface potential and activity coefficients of charged surface groups calculated from the Debye–Hückel equation (with the site density and the permittivity of the interfacial region as adjustable parameters) quantitatively reflects the experimentally observed effect of ionic strength and pH on s0. 2.9.2.3 Constant Capacitance Model The constant capacitance model is based on the expression s0 = Cy0

(2.17)

where the capacitance C of the electrical double layer is independent of pH, but depends on the nature and concentration of the electrolyte. The capacitance of the electrical double layer reflects the fact that the adsorption of each cation (proton) leaves one excess anion (e.g., chloride ion) in solution. That anion is attracted by a positively charged surface, but its hydration shell sets the limit of closest approach. An analogous explanation applies to a negatively charged surface. A version of the constant capacitance model with two different values of C (below and above pH0) has also been used. The capacitance of a flat capacitor is equal to e/d, where d is the thickness of the capacitor, which in the case of a double layer reflects the size of the hydrated counterion. With d = 0.3 nm and e equal to the permittivity of water, a capacitance C of the electrical double layer of 2.3 F/m2 is expected. The best-fit C reported in the literature [2] is usually about 1 F/m2. The constant capacitance model is able to reproduce existing experimental data, but it has a limited ability to predict the course of charging curves at ionic strengths for which experimental data are not available. 2.9.2.4 Diffuse Layer Model The diffuse layer model is based on the expression sd =

ekkT [exp(ey d /2 kT ) - exp( - ey d /2 kT )] e

(2.18)

where the subscript d refers to the diffuse layer, and the reciprocal Debye length k is defined by k2 =

N A e2 Âi ci zi 2 ekT

(2.19)

Methods

95

in which ci is the concentration (in mol/m3). Equation 2.18 reflects the interaction between adsorbed protons and excessive anions in solution, which is more complex than in the constant capacitance model. The distance between an anion in solution and a positively charged surface is limited not only by the thickness of the hydration shell of the anion, but also by the mutual repulsion of the anions in the interfacial region. Therefore, the electrical double layer is thicker than the distance of closest approach, especially at low ionic strengths. Equations 2.18 and 2.19 contain only physical constants and measurable quantities; thus the diffuse layer model does not require any adjustable parameters. The reciprocal Debye length increases with the electrolyte concentration; thus, the diffuse layer model predicts an increase in sd at constant yd when the ionic strength increases. 2.9.2.5 Stern Model The purely electrostatic diffuse layer model often underestimates the affinity of the counterions to the surface. In the Stern model, the surface charge is partially balanced by chemisorbed counterions (the Stern layer), and the rest of the surface charge is balanced by a diffuse layer. In the Stern model, the interface is modeled as two capacitors in series. One capacitor has a constant capacitance (independent of pH and ionic strength), which represents the affinity of the surface to chemisorbed counterions, and which is an adjustable parameter; the relationship between sd and yd in the other capacitor (the diffuse layer) is expressed by Equation 2.18. A version of the Stern model with two different values of C (below and above pH0) has also been used. The capacitance of the Stern layer reflects the size of the hydrated counterion and varies from one salt to another. The correlation between cation size and Stern layer thickness was studied for a silica–alkali chloride system in [733]. Ion specificity of adsorption on titania was discussed in terms of differential capacity as a function of pH in [545]. The Stern model with the shear plane set at the end of the diffuse layer overestimated the absolute values of the z potential of titania [734]. A better fit was obtained with the location of the shear plane as an additional adjustable parameter (fitted separately for each ionic strength). Chemisorption of counterions can also be quantified within the chemical model in terms of expressions similar to the mass law (Section 2.9.3.3). 2.9.2.6 More Complex Electrostatic Models The electrostatic models discussed in Sections 2.9.2.1 through 2.9.2.5 apply to a simple chemical model involving one reaction (Reaction 2.14) of the transfer of one species (proton) from the solution to the surface. More complex chemical models involving the transfer of two or more species from the solution to the surface and/or allowing various distances of the adsorbed solution species from the surface require more complex electrostatic models. Usually, three or more capacitors in series are considered. All the capacitors but one have constant capacitances, and the relationship between sd and yd in one capacitor (diffuse layer) is expressed by Equation 2.18.

96

2.9.3

Surface Charging and Points of Zero Charge

SURFACE ACIDITY

Different chemical models can be combined with either of the electrostatic models. The chemical models quantify the uptake of protons and of the ions of an inert electrolyte in terms of expressions similar to the mass law. 2.9.3.1 1-pK versus 2-pK The model based on a single reaction (Reaction 2.14) was originally introduced in [735] with x = ½ and ⬅S = ⬅AlOH, and is called the 1-pK model. The equilibrium constant of Reaction 2.14 defined by Equation 2.15 can be calculated directly from the experimentally determined PZC [2], Ê1 - xˆ log K a (Reaction 2.14 ) = PZC - log Á Ë x ˜¯

(2.20)

and, in the special case of x = ½, log Ka (Reaction 2.14) = PZC. One equilibrium constant is sufficient to describe surface protonation and deprotonation, and, at the PZC, the charge of negatively charged sites is balanced by the charge of positively charged sites. The 1-pK model can be considered as a refinement of the 2-pK model [736], in which two-step protonation and deprotonation of one type of site is considered: ⬅SOH2+  ⬅SOH + H+

Ka1

(2.21)

⬅SOH  ⬅SOH- + H+

Ka2

(2.22)

where Ka1 and Ka2 are defined by equations analogous to Equation 2.15. It can easily be shown that pKa1 + pKa2 = 2PZC

(2.23)

More precisely, the PZC calculated from the best-fit pKa1 and pKa2 in a 2-pK model by means of Equation 2.23 matches the experimental PZC when the acidic and basic branches of the charging curves are nearly symmetrical. Otherwise, the PZC in the best-fit model curve calculated from Equation 2.23 may deviate substantially from the experimental PZC. Several PZC values reported in Chapter 3 were calculated by means of Equation 2.23. Namely, several publications report the best-fit acidity constants rather than the experimental PZC. In the classical version of the 2-pK model, sites at three different degrees of protonation coexist in the vicinity of the PZC. Coexistence of solution species at three different degrees of protonation seldom occurs in small molecules, and this has been used as an argument against the 2-pK model and in favor of the 1-pK model. Namely, similarity between protonation of surface species and of analogous solution species is expected. To avoid three different degrees of protonation

Methods

97

of the same site, the 2-pK model has been interpreted in terms of pairs of neighboring sites [737], of which one can be only protonated and another can be only deprotonated. Not necessarily all oxide surfaces are amphoteric. Koopal [738,739] defined silica-type (deprotonation-only) and gibbsite-type (amphoteric) surface charging behavior. 2.9.3.2 Multisite Approach The models discussed above can be refined by allowing several types of surface sites, which differ in their proton affinities. A two-site model was used in 1971 [740] to interpret the proton and alkali metal affinities of silica (ion exchange approach). The multisite approach has a sound physical basis, namely, not all surface oxygen atoms have the same coordination environment. In this respect, the “overall” acidity constants discussed above can be considered as weighted averages of acidity constants of various types of sites. In several publications, the parameters of the distribution function of acidity constants (discrete or continuous) have been considered as adjustable parameters. Certainly, by increasing the number of adjustable parameters, one can obtain a better fit. On the other hand, only a limited number of adjustable parameters can be unequivocally derived from experimental data; that is, with too many adjustable parameters, multiple different sets of parameters produce similar model curves. Most distributions of acidity constants derived from experimental charging curves by data fitting are not unique solutions, although this problem is seldom addressed in publications presenting such models. The pKa of five or six types of discrete sites were calculated from charging curves of alumina and of HFO at one ionic strength in [741], and the continuous distributions of acidity constants were considered as sums of Gaussian-type distributions around particular discrete values. A continuous proton affinity distribution of alumina calculated from a titration curve had four broad maxima, which were assigned to pKa values of certain types of surface sites [742]. Similar proton affinity distributions were obtained [743] for various ionic strength and at various temperatures, but each charging curve was analyzed separately. A substantial effect of the ionic strength on the shape of the apparent distribution curves indicated their limited significance. Parameters of two-parameter Freundlich-type isotherms were fitted to the proton adsorption data in [744]. Three different Freundlich-type isotherms have been tested. The MUSIC (multisite complexation) model was originally introduced in [446,745] and later modified [746–748]. In contrast with the curve-fitting approach discussed above, the site densities and acidity constants of particular types of surface groups in the MUSIC model are derived from crystallographic data and from the correlation between the coordination environment of a surface oxygen atom and its proton affinity. Different types of such correlations are discussed in [749]. Prediction of surface acidity constants from bond valence was discussed in [58]. Each crystallographic face has different surface densities of oxygen atoms of a particular type, a different s0, and a different PZC. The s0 of the edge plane of gibbsite and the 100, 010, and 001 planes of goethite were calculated in [446]. The s0 of different faces of a-alumina was calculated in [750]. The overall s0 of

98

Surface Charging and Points of Zero Charge

a powder is obtained as a weighted average of the contributions of particular crystallographic planes and depends on crystal morphology. This effect was studied for two goethite crystals of two different morphologies [77]. Only certain types of surface oxygen atoms contribute to s0. Other types of surface oxygen atoms, and even entire crystallographic planes, may remain uncharged over the entire pH range of interest. For example, the 001 face of hematite was found to be uncharged at pH 3–9 [751]. Different types of surface oxygen atoms may show very similar proton affinities, in spite of different coordination environments. Therefore, only a few types of surface oxygen atoms have to be distinguished (in terms of their proton affinity) in the calculations of s0, even in crystals of complex morphology. For example, six types of surface sites were considered in MUSIC calculations for gibbsite [752]. 2.9.3.3 Binding of Inert Electrolyte Ions The triple-layer model (TLM) [753] considers surface protonation and deprotonation according to Reactions 2.21 and 2.22 (2-pK model) and two additional types of surface species: +

⬅SOH2+ + X-  ⬅SOH2 ◊ X

-

+ ⬅SOH- + Y+  ⬅SOH ◊ Y

(2.24)

(2.25)

which contribute to s0. The surface species on the right-hand sides of Reactions 2.24 and 2.25 are analogs of ion pairs, which occur in concentrated electrolyte solutions. Reactions 2.24 and 2.25 are governed by mass-action expressions similar to Equation 2.15, in which the electrostatic potential of the ions of the inert electrolyte involved in the species on the right-hand sides of Reactions 2.24 and 2.25 is taken into account. The inert electrolyte ions are adsorbed at a certain distance from the surface (called the b-plane), which is equal for the cation and anion of an inert electrolyte in the original TLM. The TLM uses a special electrostatic model that involves two capacitances. The capacitance between the surface and the b-plane and the capacitance between the b-plane and the d-plane (the center of the charge of the diffuse layer) are assumed to be constant and are adjustable parameters of the model. The equilibrium constants of Reactions 2.24 and 2.25 are related; that is, only one of them is an adjustable parameter. Thus, the possibility of explaining the effect of the nature of the counterion on s0 (without a shift in the PZC) in terms of different equilibrium constants of Reactions 2.24 and 2.25 for particular ions is limited. Six parameters are effectively adjusted in the TLM, and this can be comfortably done by means of FITEQL [754,755] or by other speciation programs. One set of TLM parameters can reproduce the course of charging curves obtained at multiple ionic strengths in many systems, in which the models discussed above (the diffuse layer and Stern models) fail. It should be emphasized that the TLM parameters produced by speciation programs are not unique; that is, multiple sets of parameters of the TLM produce practically

99

Methods

identical model curves [609,756,757]. In this respect, the values of the TLM parameters reported in the literature, and the correlations between the best-fit TLM parameters and physical constants (e.g., the dielectric constant of the solid particles [641]), are of limited significance. In a four-layer model [758], the same types of surface species are considered as in the TLM, but the anions and cations of the inert electrolyte are adsorbed at different distances from the surface rather than in a common b-plane. The fourlayer model requires an additional capacitance as an adjustable parameter. A similar effect may be achieved by using two different capacitances for the positive and negative branches of the charging curves in the classical TLM. Different affinities of particular anions and cations of 1-1 electrolytes to goethite can be also explained in terms of a charge distribution (CD) model [537]. Different electrostatic positions of an adsorbed ion are quantified as fractions of the charge of that ion attributed to each of two planes at different distances from the surface. The CD model was originally designed for specific adsorption, but was later adopted for adsorption of inert counterions. Reactions analogous to Reactions 2.24 and 2.25 can be used to modify the 1-pK model [744], but such a combination has been less popular than the TLM. Counterion binding and surface heterogeneity can be combined in one model. Equal affinities for ion pair formation (KNa1 = KNa2 and KCl1 = KCl2) have been assumed for two types of surface groups [734] in the following two-site MUSICtype model with counterion binding: ⬅TiOH-1/3 + Na +  ⬅TiOH-1/3 – Na + (⬅Ti)2OH-2/3 + Na +  (⬅Ti)2OH-2/3 – Na +

KNa1

KNa2

(2.26)

(2.27)

⬅TiOH2+2/3 + Cl-  ⬅TiOH2+2/3 – Cl-

KCl1

(2.28)

(⬅Ti)2OH+1/3 + Cl-  (⬅Ti)2OH+1/3 –Cl-

KCl2

(2.29)

Different ion binding constants were allowed for particular monovalent anions and cations. The MUSIC model with counterion binding has been tested against a large set of data: two types of goethite, at different concentrations of NaCl and NaNO3 [759]. The counterion and proton affinities of particular types of surface sites may be considered as independent variables, which may be correlated or uncorrelated [640]. 2.9.3.4 Materials Other than Oxides The above models were designed in principle for oxide surfaces. Models of surface charging of clay minerals (with permanent charge) are discussed in [760].

100

Surface Charging and Points of Zero Charge

The basal planes and edges in clay minerals have different acid–base properties. PZCs of the edge (at pH 8) and of the Al layer (at pH 6) of kaolinite are reported in [761]. The IEP of the edge surface of Na-kaolinite at pH 7.3 was obtained [762] as the intersection point of Bingham yield stress (pH) curves at various ionic strengths. A three-site 2-pK model for primary surface charging of montmorillonite was used in [763,764]. Site densities and acidity constants of 27 types of sites responsible for surface charging of montmorillonite are reported in [765]. A model of surface charging of bentonite [766] involves silanol and aluminol sites (two-step protonation and counterion binding) and ion exchange sites. A model of surface charging of montmorillonite (edge and basal planes) involved surface heterogeneity [767]. Models used for surface charging of Na-montmorillonite are summarized in [768]. Different authors have used a 1-pKa or 2-pKa TLM with one or two types of sites (in a few models attributed to Al and Si) with or without additional ion exchange (permanent charge) sites. A multisite model of surface charging of illite is discussed in [769]. Multisite models analogous to those discussed in this section have been applied to humic acid [633,770,771]. Also, charging curves of ZnS have been interpreted in terms of protonation/deprotonation of multiple surface species [772].

3

Compilation of PZCs/IEPs

The PZCs/IEPs of materials are presented in this chapter in tabular form. The organization of the tables and the abbreviations therein are explained in detail in Chapters 1 and 2. Note that, throughout the tables, T is in °C.

3.1 3.1.1

SIMPLE OXIDES ALUMINUM (HYDR)OXIDES

Aluminum has only one stable oxidation state (+3) within the electrochemical window of water, but it forms numerous relatively stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. The nominal degree of hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of hydration. PZCs/IEPs of aluminum (hydr)oxides are presented in Tables 3.1 through 3.263. PZCs/IEPs of aluminum oxide and of gibbsite are compiled in [773]. Acid– base properties of the Keggin A13 polymer are discussed in [774]. 3.1.1.1 Aluminum Oxide PZCs/IEPs of aluminum oxides (nominally Al2O3) are presented in Tables 3.1 through 3.181. Previous compilations of PZCs/IEPs of aluminum oxides were published in [54,775–778]. A previous compilation of IEPs of aluminum oxides was published in [519] (powders and single crystals). 3.1.1.1.1 Commercial PZCs/IEPs of aluminum oxide from different commercial sources are presented in Tables 3.1 through 3.148. 3.1.1.1.1.1 g-Alumina from Akzo Properties: BET specific surface area 208 m2/g [779], 265 m2/g [780], 270 m2/g (product code DRUM 1696) [781]. 101

102

Surface Charging and Points of Zero Charge

TABLE 3.1 PZC/IEP of γ-Alumina from Akzo Electrolyte

T

Method

Instrument

pH0

Reference

0.1 M NaNO3

25

pH

Two solid-to-liquid ratios

7.5

[781]

3.1.1.1.1.2 RA45E from Alcan Properties: a-form, 99.8% pure, XRD pattern, EDXRF spectrum available [105].

TABLE 3.2 PZC/IEP of RA45E from Alcan Description

Electrolyte

T

As received

0.001–0.1 M KNO3

Method

Instrument

Mass titration

pH0

Reference

7.6

[105]

3.1.1.1.1.3 Aluminas from Alcoa 3.1.1.1.1.3.1 A 11 Properties: a-form, BET specific surface area 8.8 m2/g [373].

TABLE 3.3 PZC/IEP of A 11 from Alcoa Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

9.2a

[373]

0.001 M KNO3 a

Arbitrary interpolation.

3.1.1.1.1.3.2 A 12 Properties: a–form [389,458], detailed analysis available [458], BET specific surface area 10.6 m2/g, average particle size 300 nm [389].

TABLE 3.4 PZC/IEP of A 12 from Alcoa Electrolyte 0.001 M KNO3 a

T

Method iep

Subjective interpolation.

Instrument Malvern Zetasizer 3000

pH0 9.2

a

Reference [389]

103

Compilation of PZCs/IEPs

3.1.1.1.1.3.3 A 14 Properties: a-form, 0.04% Si, 0.01% Ga, 0.03% Fe, 0.02% Ca, 0.001% Mg, 0.02% Na, 0.005% Ti [458].

TABLE 3.5 PZC/IEP of A 14 from Alcoa Description Stored for 10 d in borosilicate glass HF-treated a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaClO4

20

iep

Zeta-Meter

8.7a

[458]

8.9a

Subjective interpolation.

3.1.1.1.1.3.4 A-16 Obtained by the Bayer process. Properties: a-form [151,782], 99.8% pure [784,785], 510 ppm Na2O, 60 ppm CaO, 360 ppm MgO, 290 ppm SiO2, 130 ppm Fe2O3 [151], BET specific surface area 9.3 m2/g [784–787], 10.3 m2/g [788], specific surface area 9 m2/g [151], mean particle size 1.15 mm [788], d10 = 0.24 mm, d50 = 0.4 μm [784,785], average diameter 0.38 mm [786]. TABLE 3.6 PZC/IEP of A 16 from Alcoa Electrolyte 0.01 M NaNO3 0.01 M NaCl None 0.01 M NaNO3 0.001 M KNO3 0.001 M NaNO3 a

b

c d

T

Room

Method iep iep iep iep iep iep

Instrument Zeta-Meter 2.0 Acoustosizer Zeta-Meter 3.0+ Zeta-Meter 2.0 Zeta-Meter 3.0 ESA 8000

pH0 a

7.6 8.2 8.6 8.8b 9.2c 9.9

Reference [787] [307] [782] [784d,785] [788] [786]

Subjective interpolation. IEP roughly matches the maximum in the yield stress in a 25 vol% dispersion. The maximum in the yield stress and the minimum in the stability roughly match the IEP from the electrophoretic measurements. Subjective interpolation. Only value, no data points.

3.1.1.1.1.3.5 A 16-SG Obtained by the Bayer process. Properties: a-form [267,789–792,798], 99.9% pure [791,796], >99.8% [793], 99.8% Al2O3 [794], 99.7% [792], 99% pure [790], contains MgO [795], 0.08% Na2O, 0.025% SiO2, 0.01% Fe2O3, 0.02% K2O [792], 0.08% Na2O, 0.1% CaO, 0.05% SiO2, 0.5% Fe2O3 [789], 0.05% Na2O, 0.02% CaO, 0.02% SiO2, 0.01% Fe2O3, 0.01%

104

Surface Charging and Points of Zero Charge

MgO [796], 0.08% Na2O [794], BET specific surface area 11 m 2/g [796,797], 10 m 2/g [795], 10.2 m 2/g [794], 9.6 m 2/g [792], 9.5 m 2/g [798], 9 m 2/g [793], specific surface area 8.4 m 2/g [789], 8–10 m 2/g (according to the manufacturer) [589], 9 m 2/g [790], size range 0.1–1 mm [792], average size 0.2 mm [267], mean diameter 350 nm [789], 2 μm [794], particle size up to 10 mm [790], average particle size 500 nm [793], d50 = 300 nm [798], average particle size 600 nm [320], 700 nm [791], particle size 400–500 nm (manufacturer) [589], TEM image available [267], AFM and TEM images available [589], XRD pattern available [798].

TABLE 3.7 PZC/IEP of A 16-SG from Alcoa Description

Electrolyte

As received

0.001 M KCl 0.001 M NaCl 0.01 M NaCl

T

20b

0.001–0.1 M KNO3

Method iep iep iep pH iep

Instrument Malvern Zetasizer 4 Acoustosizer ESA 8000 Matec Malvern Zetasizer 4

Titration None Washed in 0.01, 0.1 M boiling water NaCl 2.5 5 10 15 vol%

0.01 M KCl

0.001 M KCl 0.001 0.01 0.1 M KCl a b c d e f

25

iep iep

Malvern Zetasizer MK 11 Rank Brothers Mark II

25 25

iep iep

ESA 8050 Matec Acustosizer

25 iep 20d pH

Rank Brothers Mark II

pH0

Reference

8.1 8.3a 8.5 8.5 8.6c

[796,797] [589] [793] [790]e [320]

8.7

Reference 6 in [798] [799] [789]

8.7 8.8 9 9 8.7 8.3 8.3 9.2 9.9 10 10.1

[791]e [792]f

[794] [795]

The charging curves did not show a clear CIP (merge at pH 7–9). Also 10 and 40°C. IEP matches the maximum in viscosity of 75 mass% dispersion. Also 40 and 60°C. Only value, no data points. IEP roughly matches the maximum in viscosity and yield stress of 25 vol% dispersion.

3.1.1.1.1.3.6 A-152 Obtained by the Bayer process. Properties: a-form, 380 ppm Na2O, 110 ppm CaO, 45 ppm MgO, 390 ppm SiO2, 235 ppm Fe2O3, specific surface area 4.6 m2/g [151].

105

Compilation of PZCs/IEPs

TABLE 3.8 PZC/IEP of A-152 from Alcoa Description

Electrolyte

T

Instrument

pH0

a

As received Washed a

Method pH/iep

9.3/9.5 9.8

Reference [151]

Only values, no data points. Similar results are reported for two lots of A-152.

3.1.1.1.1.3.7 A-1000 SG Obtained by the Bayer process. Properties: 99.8% pure, 0.1% Na2O, D50 = 400 nm, specific surface area 9 m2/g [800].

TABLE 3.9 PZC/IEP of A-1000 SG from Alcoa Electrolyte

T

KOH + HNO3 (acid titration)

Method

Instrument

pH0

Reference

iep

DT 1200

10

[800]

3.1.1.1.1.3.8 CL2500SG Properties: a-form, specific surface area 1.5 m2/g, particle diameter 2.3 μm, >99.8% Al2O3, 0.02% SiO2, 0.02% Fe2O3, 0.05% Na2O, 0.02% CaO by mass [801].

TABLE 3.10 PZC/IEP of CL2500SG from Alcoa Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

25

iep

AcoustoSizer

8.1

[801]

3.1.1.1.1.3.9 3.5 μm [791].

CL3000SG Properties: a-form, 99.8% pure, particle diameter

TABLE 3.11 PZC/IEP of CL3000SG from Alcoa Electrolyte

a

T

Method

Instrument

pH0

Reference

25

iep

ESA 8050 Matec

9a

[791]

Only value, no data points.

106

Surface Charging and Points of Zero Charge

Properties: a-form, 99.7% pure, particle diame-

3.1.1.1.1.3.10 CT1200SG ter 1.3 μm [791].

TABLE 3.12 PZC/IEP of CT1200SG from Alcoa Electrolyte

a

T

Method

Instrument

pH0

Reference

25

iep

ESA 8050 Matec

9a

[791]

Only value, no data points.

3.1.1.1.1.3.11 CT3000SG Properties: 99.9% of a-form [802,803], 99.7% of a-form [804,805], 99.85% pure [806], 0.02% Na2O, 0.05% SiO2, 0.03% Fe2O3 [803], BET specific surface area 7 m2/g [802,803], specific surface area 9 m2/g [806], 6 m2/g [804,805], D50 = 500–800 nm [806], d50 = 600 nm [804,805], average particle size 0.7 μm [802,803]. Properties are also presented in Reference 20 of [493]. TABLE 3.13 PZC/IEP of CT3000SG from Alcoa Electrolyte

T

Method

Instrument

pH0

0.01 M KCl + KOH or NaOH 0.01 M KNO3 None

25

iep

AcoustoSizer

8a

[493]

pH iep

PCD, Mutek

8.3 9.1b

[804,805] [802] [803]

a

b

Reference

Various IEP in a range 7.9–8.9 were obtained for different solid-to-liquid ratios, bases (NaOH, KOH, NH3) and directions of titration. Data points closest to IEP: pH 8.4, 9.1, and 11.1. The axis label in Figure 1 in [803] suggests that s0 was measured rather than z potential.

3.1.1.1.1.3.12 CT3000SE Properties: a-form, 99.7% pure, XRD pattern, EDXRF spectrum available [105].

TABLE 3.14 PZC/IEP of CT3000SE from Alcoa Description

Electrolyte

As received

0.001–0.1 M KNO3

T

Method Mass titration pH

Instrument

pH0

Reference

8.4 6.9

[105]

107

Compilation of PZCs/IEPs

3.1.1.1.1.3.13 F 1 Properties: g-form [807], g-form, with small amounts of gibbsite and boehmite [522], BET specific surface area 250 m2/g (manufacturer) [807], 287 m2/g [522], specific surface area 210 m2/g [808,809].

TABLE 3.15 PZC/IEP of F 1 from Alcoa Description

Electrolyte

T

HCl- and waterwashed (different sequences) NaOH-washed 0.05, 0.5 M NaClO4 NaOH-washed 0.001–0.1 M NaNO3 a

Method a

iep

Instrument Streaming potential

Intersection cip 48 h equilibration

20

pH0

Reference

6.2 7.3 8.9 7.4 8.1

[809]

[522] [807]

Only values, no data points.

3.1.1.1.1.3.14 T-60

TABLE 3.16 PZC/IEP of T-60 from Alcoa Description

Electrolyte

T

Method

Instrument

Acid-washed

KNO3

25

iep

Streaming potential

a

pH0 Reference 7.5a

[288]

Arbitrary interpolation.

3.1.1.1.1.3.15

XA-139 Properties: a-form [810].

TABLE 3.17 PZC/IEP of XA-139 from Alcoa Electrolyte

T

Method Titration

a

Only value, no data points.

Instrument

pH0 a

8.8

Reference [810]

108

Surface Charging and Points of Zero Charge

3.1.1.1.1.3.16 g-Alumina

TABLE 3.18 PZC/IEP of g-Alumina from Alcoa Description

Electrolyte

Washed

0.1 M KNO3

T

Method

Instrument

pH0

Reference

8.2

[741]

pH

3.1.1.1.1.3.17 Alcoa, Type Unknown Properties of several aluminas from Alcoa are reported in Sections 3.1.1.1.1.3.1 through 3.1.1.1.1.3.16 and in [806]. Properties of A-39 are reported in [151]. Properties of A-3000 FL and of EK8R are reported in [800].

TABLE 3.19 PZC/IEP of Unspecified Aluminas from Alcoa Description

Electrolyte

a form, average size 0.001 M NaCl 2 μm, >99% pure 800 nm particles 0.001 M KNO3 a

T

Method

Instrument

pH0

Reference

25

iep

Streaming potential

7.6

[811]

iep iep

Matec ESA 9800 Laser ZeeMeter

7.8 8.7a

[433] [812]

Maximum in viscosity at pH 9.

3.1.1.1.1.4 Aluminas from Aldrich 3.1.1.1.1.4.1 a-Alumina Properties: 0.6 m2/g [813], >99.7% [502], 99% [814], BET specific surface area 7.3 m2/g [502,814].

TABLE 3.20 PZC/IEP of a-Alumina from Aldrich Description Washed and calcined at 700°C

Electrolyte

T

Method

Instrument

pH0

Reference

0–0.005 M NaCl

25

iep

Malvern Zetasizer 3000 HS

6.7

[502]

3.1.1.1.1.4.2 Brockmann I Properties: g-form, BET specific surface area 159 m2/g (measured), 155 m2/g (manufacturer), pore diameter 5.8 nm (manufacturer) [815].

109

Compilation of PZCs/IEPs

TABLE 3.21 PZC/IEP of Brockmann I from Aldrich Electrolyte

T

0.1 M NaCl

Method

Instrument

pH

pH0

Reference

5.3

[815]

3.1.1.1.1.4.3 Mesoporous Properties: g-form and amorphous material, pore size 6.5 nm, TEM image available, specific surface area 284 m2/g [816].

TABLE 3.22 PZC/IEP of Mesoporous Alumina from Aldrich Electrolyte

T

0–0.1 M NaCl

3.1.1.1.1.4.4 [817,818].

Method

Instrument

cip

pH0

Reference

9.1

[816]

Other Properties: g-form, specific surface area 47.7 m2/g

TABLE 3.23 PZC/IEP of Unspecified Alumina from Aldrich Description Washed

Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaClO4/NaCl

20

iep cip

Pen Kem Laser ZeeMeter 501

7.7/7.5 7.8/8.1

[518]

3.1.1.1.1.5 Alumina from Alfa Aesar Properties: a-form [819], 99.99% of a-form [428], 99,99% pure [819,820], BET specific surface area 12.8 m2/g [428], particle size 1 mm [819], <1 mm [820], volume average size 3.1 mm [428].

TABLE 3.24 PZC/IEP of Alumina from Alfa Aesar Electrolyte 0.001 M KCl 0.01 M NaCl a

T

Method iep iep iep

Instrument

pH0

Reference

Malvern Zetasizer 3 Malvern Zetasizer 3 Zeta Probe, Colloidal Dynamics

9.1 9.1 9.1a

[819] [820] [428]

Only value, data points not reported.

110

Surface Charging and Points of Zero Charge

3.1.1.1.1.6 a-Alumina from Aluminium Co. Canada specific surface area 0.4 m2/g [39].

Properties: 99.9% pure,

TABLE 3.25 PZC/IEP of α-Alumina from Aluminium Co. Canada Electrolyte

T

0.001–1 M KNO3, KCl, NaNO3 a

25

Method

Instrument

pH0

Reference

a

pH

5–7

[39]

s0 = 0 at pH 5–7 for KNO3, only positive branch of charging curves reported for other salts.

3.1.1.1.1.7 Aluminas from Aluminium-Pechiney See also Section 3.1.1.1.1.55. 3.1.1.1.1.7.1 a-Alumina Properties: 0.04% Na2O, 0.07% SiO2, 0.02% Fe2O3, 0.03% CaO, BET specific surface area 3 m2/g [821], 3.7 m2/g [822].

TABLE 3.26 PZC/IEP of α-Alumina from Aluminium-Pechiney Electrolyte

T

Method

Instrument

cip a

pH0 9.1

Reference [821]a

Only value, no data points.

3.1.1.1.1.7.2 Aluminium-Pechiney, Type Unknown Properties: BET specific surface area 9.7 m2/g, average size 500–700 nm [823]. 3.1.1.1.1.8 Alumina from Asahi Properties: a-form, high purity, TEM image available, particle size 40–600 nm, 50 ppm Na, 10 ppm Fe, 10 ppm Si, specific surface area 10 m2/g [824].

TABLE 3.27 PZC/IEP of Alumina from Asahi Electrolyte HCl + NH3

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.7

[824]

3.1.1.1.1.9 a-Alumina from ATO Chem available [773].

Properties: platelets, SEM image

111

Compilation of PZCs/IEPs

Table 3.28 PZC/IEP of α-Alumina from ATO Chem Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

3.5–7.2

[773]

0.01 M NH4Cl

3.1.1.1.1.10 Alumina from BDH Properties: g-form, high purity [825], BET specific surface area 86.4 m 2/g (original), 106.4 m 2/g (calcined at 665°C for 12 h) [1093].

TABLE 3.29 PZC/IEP of Alumina from BDH Description Calcined at 665°C for 12 h Etched in 4 M KOH a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M KNO3 0.0001, 0.001 M KCl

25

cip iep iep

Rank Brothers Mark II Streaming potential

3.6 8.5 4.6

[636]a [825]

Only value, no data points.

3.1.1.1.1.11 CR6 from Baikalox Properties: a-form [589], 94% of the a-form [416], 99.99% pure [416], detailed chemical analysis available [589], BET specific surface area 6 m2/g [416], specific surface area 5–7 m2/g (manufacturer) [589], mean particle size <1 mm [416], particle size 250 nm [589], AFM and TEM images available [589].

TABLE 3.30 PZC/IEP of CR6 from Baikalox Description

Electrolyte

Calcined at 500°C 0.001 M NaCl As received 0.001–0.1 M NaCl, NH4Cl a b

T

Method

Instrument

pH0

Reference

25

iep cipb iep

Rank Brothers Mark II Acoustosizer

8.8a 8.8

[416] [589]

IEP changes on aging, only value reported. Charging curves merge at pH 8–9.5 (no clear cip).

3.1.1.1.1.12 Single-Crystal Wafers from Bicron Samples were washed in 0.001 M HNO3 and heated at 300°C in N2 to reduce carbon contamination.

112

Surface Charging and Points of Zero Charge

TABLE 3.31 PZC/IEP of Single-Crystal Wafers from Bicron Crystal Face 0001 1−102

Electrolyte

T

Method

0.001–0.1 M NaNO3

Instrument

Second-harmonic generation

pH0

Reference

4.1 5.2

[652]

3.1.1.1.1.13 Linde A from Buehler See also Linde and Union Carbide. Properties: a-form [609,826], well-crystallized a-form and g-form [136], BET specific surface area 12.6 m2/g [826], 16 m2/g [136], 12 m2/g [609], particle size 1 μm [609], well-crystallized a-form particle size 0.1–0.5 μm, g-form, average diameter 20 nm, the latter accounts for 60% of the surface area [136].

TABLE 3.32 PZC/IEP of Linde A from Buehler Electrolyte

T

Method

0.005–0.14 M NaNO3

25

cip

Instrument

pH0

Reference

8.9

[609] [826]

3.1.1.1.1.14 Aluminas from Cabot 3.1.1.1.1.14.1 a-Alumina, from a Dispersion, 40% by Mass Properties: primary spherical particles 20 nm in diameter form aggregates 150 nm in diameter [827].

TABLE 3.33 PZC/IEP of α-Alumina from Cabot Electrolyte 0.001 M KNO3 a

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

6.5a

[827]

One data point near the IEP. The other data points at pH > 8 or pH < 4.5.

3.1.1.1.1.14.2 Alon Made by hydrolysis of AlCl3. Properties: Predominantly g-form [447,448,828], 90% of g-form [541,709], g- or d-form [229], d-form [354,829], 120 m2/g [447], BET specific surface area 69.6 m2/g [354,829], specific surface area 117 m2/g [541,828], 98 m2/g (phosphate adsorption) [229], 100 m2/g (manufacturer), 117 m2/g determined by three methods [709], 120 m2/g [448], average diameter 30 nm [229,447,448,541,709].

113

Compilation of PZCs/IEPs

TABLE 3.34 PZC/IEP of Alon from Cabot Description NaOH-washed NaOH-washed

Electrolyte

T

Method

0.1 M NaClO4 0.001–0.1 M NaCl

25 25

pH cip iep pH iep iep iep

0.01 M NaOH-washed 0.01 M NaCl

25

0.01 M NaClO4 0.01 M NaCl a b c

25

Instrument Brigg’s cell Rank Brothers Mark II Pen Kem 102 Zeta-Meter 3.0

pH0

Reference

8.3 8.5 8.7 8.5a 9.1b 9.1c 9.7a

[828] [541] [447,448] [229] [354]

Only value, no data points. IEP obtained in the presence of 0.001 M NaHCO3. Quoted in further publications as a pristine IEP. Arbitrary interpolation.

3.1.1.1.1.15

Alumina from Catalysis Chemical Industry

TABLE 3.35 PZC/IEP of Alumina from Catalysis Chemical Industry Electrolyte

T

KNO3 a

Method

Instrument

pH0

Reference

iepa

Rank Bros.

8.8

[830,831]

Only value, no data points.

3.1.1.1.1.16 Aluminas from Ceralox Reference [832] reports physical properties of different powders of the Ceralox HPA series. 3.1.1.1.1.16.1 HPA Properties: a-form, 99.99% pure, average particle size 500 nm [791]. TABLE 3.36 PZC/IEP of HPA from Ceralox Electrolyte

T

Method a

iep a

Instrument

pH0

Reference

Matec ESA 8050

9

[791]

Only value, no data points.

3.1.1.1.1.16.2 HPA-05 See also Section 3.1.1.1.1.18.1. Properties: 99.97% pure [832], 0.05% MgO [832], 291 ppm Mg, BET specific surface area 8.9 m 2/g [476], 8.6 m2/g [833], 9.5 m2/g [832], d50 = 490 nm [476], average particle size 300 nm [833], 500 nm [832].

114

Surface Charging and Points of Zero Charge

TABLE 3.37 PZC/IEP of HPA-05 from Ceralox Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep iep iep

Matec ESA 8050 ESA Matec ESA 8000

8.7 9 9.5

[832] [476] [834]

3.1.1.1.1.16.3 HPA 1.0 (from Ceralox or Condea Vista) Properties: >99.99% pure, specific surface area 4.6 m2/g [835], BET specific surface area 4 m2/g [833], d90 = 4.5 μm, d50 = 650 nm, d10 = 350 nm [835], average particle size 600 nm [833]. TABLE 3.38 PZC/IEP of HPA 1.0 from Ceralox or from Condea Vista Electrolyte

T

Method

Instrument

pH0

Reference

iep

Matec ESA

10

[833]

HNO3 + KOH

Properties of SPA-TMXX3 from Ceralox are reported in [833]. 3.1.1.1.1.17 Alumina from Chlorovinyl Another sample studied by the same research group is described in Section 3.1.1.1.1.36. Properties: Amorphous (80%) + g-form (20%), BET specific surface area 60 and 140 m2/g, IR spectrum available [836]. TABLE 3.39 PZC/IEP of Alumina from Chlorovinyl Electrolyte

T

Method

Instrument

pH0

Reference

iep

ZetaPlus Brookhaven

9.8

[836,837]

HCl + NaOH

3.1.1.1.1.18 Aluminas from Condea 3.1.1.1.1.18.1 HPA05 without MgO See also Section 3.1.1.1.1.16.2. Properties: a-form, d50 = 350 nm, specific surface area 9.5 m2/g [838]. TABLE 3.40 PZC/IEP of HPA05 without MgO from Condea Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0+

9a

[838]

0.01 M KCl a

Arbitrary interpolation.

115

Compilation of PZCs/IEPs

3.1.1.1.1.18.2 Condea, Type Unknown Properties: g-form [839,840], BET specific surface area 206 m 2/g [840], 119 m 2/g (material pretreated in air at 1048 K for 1 day) [839]. TABLE 3.41 PZC/IEP of Unspecified Aluminas from Condea Electrolyte

T

0.1 M NaNO3 γ + 5–10% δ

Method

Instrument

Titration cip

b

Reference

8 8.25

γ + 56% δ a

pH0 a

[840] [841]b

no cip

Only acidity constants reported. Also composites with 5% of silica, Zr, or La. Only values, no data points.

3.1.1.1.1.19 Alumina(s) from Cyanamid Properties: g-form [668,669,742, 743,842–844], Cu 100 ppm, Fe 70 ppm, Na 40 ppm, S and Pd 10 ppm, Mo and As 1 ppm [742,743,842], BET specific surface area 140 m2/g [742,743,842], 190 m2/g [668,843], 195 m2/g, [669], 205 m2/g [844], particle size 60 mm [668], 225 mm [843], pore volume 0.85 cm3/g [742,743,842], 0.484 cm3/g [669]. TABLE 3.42 PZC/IEP of Alumina(s) from Cyanamid (Including SN 7053) Description SN 7053 calcined at 600°C for 16 h SN 7053

Electrolyte

b c

Instrument

pH0

Reference

pH

6.8

[842]

0.0001–0.1 M NaNO3

cip

7

[742]

pH Mass titration cip

7.8 7.2 7.4

[843]

cip/ 24 h Mass equilibration titration Mass titration iep ZM-3

7.5/7.4 7.8/7.8

[668]

23a 0.001–0.1 M NaNO3 0.001–0.1 M NaCl

None 0.001 M KCl a

Method

0.1 M NaNO3

Ground Calcined at 600°C for 6 h Original Calcined at 500°C for 16 h

T

Also 23–82°C. Also 10–50°C. +12 mV at pH 7.8, −5 mV at pH 9.

25b

8.3 <9c

[743]

[669] [844]

116

Surface Charging and Points of Zero Charge

3.1.1.1.1.20 Alumina from Dalian Luming Light Technology Properties: g-form, particle size <2 μm [845].

Science

and

TABLE 3.43 PZC/IEP of Alumina from Dalian Luming Light Science and Technology Electrolyte

T

Method

Instrument

pH0

Reference

25

iep

JS94G+

6.2

[845]

3.1.1.1.1.21 Type C from Degussa (See also Section 3.1.1.1.1.37) Obtained by a high-temperature hydrolysis process (flame hydrolysis of AlCl3). Properties: g- or e-form with admixture of a second material [723], g-form [108,437,469,677,846–861,876–879,886,887], d- or g-form [862,863], g- + d-form [864], d-form [115,187,451,559,829,865–872,881,883,885], d-form with admixture of gibbsite and bayerite (10%) [873], 99.6% pure (manufacturer) [860], >99.6% pure [469,874], >99.5% pure [437], >97% pure [854], 97% pure [875], 99% pure [864], <0.1% TiO2 [854], <0.5% HCl [559], BET specific surface area 90.1 m2/g [469,723], 92.8 m2/g [876], 96 m2/g [865], 96.9 m2/g [829], 100 m2/g [437,491,850,852,855,856,858,861,862,868,877,878], 100 ± 15 m2/g [437,855,856], 100 ± 15 m2/g (manufacturer) [108,451,559,677,847–849,851, 854,857,860,863,872,874,875,879–883], 100.6 m2/g [115], 105 m2/g [873,884], 108 m2/g [885], 108 m2/g (original) and 130 m2/g (washed) [886], 119 m2/g [887], 110 m2/g [846], 113 m2/g [187], 130 m2/g [853], single point BET specific surface area 102.9 m2/g [866,870], EGME specific surface area 75 m2/g (original) and 76.1 m2/g (washed) [849], 80 m2/g [859], 95 m2/g [848], 83.1 m2/g [888], 130 m2/g [889], specific surface area 82 m2/g [890], 96 m2/g [871], 100 m2/g [230], 107 m2/g [864], 100–200 m2/g [891], particle size 13 nm [559], 20 nm [108,451,677,851– 856,867,873,879,881,885,886,888,892], average particle size 20 nm [863,872], average primary particle size 13 nm [437], particle diameter 13 nm [883], 20 μm [878] (probably a typographic error), average diameter 26 nm (washed material) [859], 13 nm [230,860,861], average radius 13 nm [469], average particle diameter 60 nm (multiangle photon correlation in 0.01 M NaClO4 at pH 5.7) [115], mean size 50 nm [299], nonporous [852,856,861,867,884,885], spheres [861,873,884], TEM image available [723], HRTEM image available [889].

Washed Washed Dialyzed, 0.17% Cl

C 100

Calcined at 1000°C for 6 h

0.1 M NaClO4 25

22

0.1 M NaClO4

0.001–0.1 M NaClO4

20 25 25

Room

0–0.1 M NaCl NaCl 0.001–0.01 M KCl

0.0001–0.5 M NaNO3 0.005–0.5 KNO3 0.001–0.1 M KNO3 HCl + NH3

pH pH

pH cip

cipd cip Intersection iep pH

cip Mass titration pH cip cip cip iep

25

0–0.05 M NaCl None

As received

Water-washed NaOH-washed Acid-washed Calcined at 600°C for 16 h As received

Method pH Mass titration cip

T 25 25 20

Electrolyte

1 M NaClO4 0.1 M NaCl 0–0.1 M NaCl

Description

TABLE 3.44 PZC/IEP of Alumina C from Degussa

Pen Kem Laser Zee Meter 501 Four different solid-to-liquid ratios

ESA 8000

Back titration, 1 d equilibration

Instrument

[846] [847] [872]

[896] [897]

8.6b 8.7

continued

[895] [677]

8.6 8.6f

[451] [859] [873]b [884] [886]e

[848] [852] [862] [849] [559,894] [632] [491]

Reference

pH0 6.4a 6.9b 7.2 7.9 7.3 7.4 7.8b 7.9c 8 8.2 8.3, 8.6 (hysteresis) 8.3 8.4b 8.5 8.6 8.5

Compilation of PZCs/IEPs 117

Electrolyte

0.005–0.5 M KCl

0.001–1 M LiCl, KCl

0.01 M NaClO4

Not explicitly indicated as type “C”

0.01 M NaOH-washed

0.001 M 0.025 M 0.1 M NaClO4

0.0001–0.1 M NaClO4 NaNO3 0.0001–0.01 M KNO3

0–1 M KCl

Original dialyzed and calcined at 1000°C

Cited from literature

As received 0.01 M HCl- and KOH-washed

Description

TABLE 3.44 (continued)

Room

25

25 25

T

Method

iep

iep

iep iep cip

iep

iep ? iep

cip EMF iep cip iep

Streaming potential cip Malvern Zetasizer III

Malvern Zetamaster S

Electrophoresis Provided by manufacturer Laser Zee Model 500

Rank BrothersMark II

Zeta-Meter

Instrument

pH0

8.6 9.2 9.1h 9.2b

[115]

[854]

[883] [882] [559]

[855,858]

[878] [899] [877] [108]

9b 9 9.6 9 9 9.5 9.7g 9 9.1b 9.2

[853] [876] [861]

[875]

Reference

8.8 8.9b 9–9.5

8.7

118 Surface Charging and Points of Zero Charge

j

i

h

g

f

e

d

c

b

a

Matec ESA 9800

iep

iep iep iep

None 0.05 M NaClO4

None 0.001–0.007 M NaCl 0.03, 0.05 M

30 20

Laser Zee meter 500 Delsa 440 Pen Kem S3000 Zeta-Meter 3.0 Milton Roy I, Pryde; streaming potential ESA 8000 Pen Kem Laser Zee meter 501 Zeta-Meter 80

iep iep iep iep iep

25

0.01 M NaClO4 0.001–0.1 M NaCl 0.001 M NaCl 0.15 M NaCl 0.001 M KCl

Zeta-Meter 3.0 Zeta-Meter 3.0

iep iep

0.1 M NaNO3 0.01 M NaCl

9.8 9.5 9.9j

9.6 9.7

9.4 9.5 9.5 9.5 9.6i

9.3 9.3

Also 40 and 60°C. Only value, no data points. Only acidity constants (different models) reported. Back titration. [900] reports PZC of γ-alumina at pH 8.7. Back titration produced CIP at pH 7.5. Shifts in the IEP at high electrolyte concentrations were reported by other authors. CIP was observed in the presence of KCl. The charging curves obtained in the presence of three concentrations of LiCl did not show a CIP. The value obtained by streaming potential measurement was extrapolated. Roughly matches a maximum in yield stress of 11.7–19.9 mass% dispersions.

As obtained

As received As received

Not explicitly indicated as C type

[437]

[888]

[850] [48]

[469] [866] [870]b [851] [230] [856] [880] [299]

Compilation of PZCs/IEPs 119

120

Surface Charging and Points of Zero Charge

3.1.1.1.1.22 Na-A from Design & Quality Enterprise, Taipei Distributed in form of 30% dispersion. Properties: a-form, micrographs available [497].

TABLE 3.45 PZC/IEP of Na-A from Design & Quality Electrolyte

T

Method

Instrument

pH0

Reference

iep

Titration

4

[497]

KOH + HNO3

3.1.1.1.1.23

A 160 from Dia Showa Properties: particle size 500 nm [901].

TABLE 3.46 PZC/IEP of A 160 from Dia Showa Description

Electrolyte

Milled

KOH + HCl

T

Method

Instrument

pH0

Reference

iep

Pen Kem Acoustophoretic Titrator 7000

10

[901]

3.1.1.1.1.24 Alumina from Duke Scientific particle diameter 1.2 μm [902].

Properties: high purity, mean

TABLE 3.47 PZC/IEP of Alumina from Duke Electrolyte 0.01 M KCl

T

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee Meter 500

8.5

[902]

3.1.1.1.1.25 Alumina from Du Pont Properties: Pure, BET specific surface area 10.1 m2/g [455]. TABLE 3.48 PZC/IEP of Alumina(s) from Du Pont Description

Electrolyte

T

Method

Instrument

pH0

Reference

As obtained

0.001 M KNO3 0.001 M KNO3

25

iep iep

Malvern Zetasizer 2c Rank Brothers

9.2 9.7a

[903] [455]

a

Only value, no data points.

121

Compilation of PZCs/IEPs

3.1.1.1.1.26 Aluminas from Fisher 3.1.1.1.1.26.1 a-Alumina Properties: a-form [829,904], BET specific surface area 0.6 m2/g [904], 0.9 m2/g [829]. TABLE 3.49 PZC/IEP of α-Alumina from Fisher Description Acid-washed a

Electrolyte

T

Method a

0.01, 0.1 M NaCl

Instrument

Intersection

25

pH0

Reference

8.9

[904]

Also 60°C

3.1.1.1.1.26.2 Chromatographic Alumina 80–200 mesh [907].

Properties: g-form [905,906],

TABLE 3.50 PZC/IEP of Chromatographic Alumina from Fisher Description Water-washed a

Electrolyte

T

Method a

0.005–0.1 M KNO3

30

Instrument

cip

pH0

Reference

9.1

[907]

PZC at higher temperatures available.

3.1.1.1.1.26.3 80–200 mesh Activated Alumina Properties: amorphous, specific surface area 118 m2/g [816]. TABLE 3.51 PZC/IEP of 80–200-Mesh Activated Alumina from Fisher Electrolyte

T

Method

0–0.1 M NaCl

3.1.1.1.1.26.4

Instrument

cip

pH0

Reference

8.7

[816]

Whatman Anodisc 47

TABLE 3.52 PZC/IEP of Whatman Anodisc 47 from Fisher Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Streaming potential

8

[292]

Physical properties of unspecified alumina from Fisher (analytical grade) are also reported in [908].

122

Surface Charging and Points of Zero Charge

3.1.1.1.1.27 Aluminas from Fluka 3.1.1.1.1.27.1 Reagent-Grade α-Alumina Properties: Average diameter 3 μm [494]. TABLE 3.53 PZC/IEP of Reagent-Grade α-Alumina from Fluka Description Washed

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaNO3

25

iep

Acoustosizer

9.3

[494]

3.1.1.1.1.27.2

507 C Coated with a layer of Al4(OH)10CO3 · H2O [552].

TABLE 3.54 PZC/IEP of 507 C from Fluka Electrolyte

T

0.001–0.1 M KNO3

3.1.1.1.1.27.3 0.9 m2/g [323].

Method

Instrument

pH0

Reference

iep

cip Mass titration

7

[552]

α-Alumina, >99.7%

Properties: BET specific surface area

TABLE 3.55 PZC/IEP of α-Alumina, >99.7% from Fluka Description

Electrolyte

T

Method

Instrument

pH0

Reference

Washed, then calcined at 700∞C

0–0.001 M

25

iep

Malvern Zetasizer 3000 HS

7.2

[323]

3.1.1.1.1.27.4 Fluka, Type Unknown Properties: BET specific surface area 150 m2/g [875], specific surface area 155 m2/g (manufacturer) [909,910].

TABLE 3.56 PZC/IEP of Unspecified Alumina from Fluka Electrolyte 0–1 M KCl

T

Method cip EMF

Instrument

pH0

Reference

7.8

[875] [909]

123

Compilation of PZCs/IEPs

3.1.1.1.1.28 q-Alumina Powder from Forever Chemical, Taiwan TABLE 3.57 PZC/IEP of θ-Alumina Powder from Forever Chemical Electrolyte

T

Method

HCl + NH4OH a

Instrument

iep

pH0

Reference

a

Malvern Zetasozer NS

9.2

[414]

Matches the maximum in average particle size.

3.1.1.1.1.29 T-126 from Girdler Properties: g-form [911,912,470], BET specific surface area 188 m2/g [911]. TABLE 3.58 PZC/IEP of T-126 from Girdler Electrolyte 0.001 M KCl 0.001 M KCl 0.001 M NaCl 0.001 M KNO3 0.001 M NH4Cl

T

Method

Instrument

pH0

Reference

22.5

iep iep

Zm-77 Zeta-Meter ZM-77

8.8 8.8 8.8 8.6 8.6

[911] [912] [470]

3.1.1.1.1.30 g-Alumina from Goodfellow specific surface area 142 m2/g [315].

Properties: 99.995% pure, BET

TABLE 3.59 PZC/IEP of γ-Alumina from Goodfellow Description Dialyzed

3.1.1.1.1.31

Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.01 M KCl

25

iep cip

Malvern Zetasizer 2000

9.2

[315]

Flat Plates from Harrick Properties: a-form, 0.7% fluoride [463].

TABLE 3.60 PZC/IEP of Alumina Flat Plates from Harrick Description Multistep cleaning procedure 0.001 M KCl a

Electrolyte 0.0001, 0.001 M KNO3

Confirmed by AFM results.

T

Method iep AFM

Instrument

pH0

Reference

Streaming potential

4.2a

[463]

9.3

[819]

124

Surface Charging and Points of Zero Charge

3.1.1.1.1.32 Alumina from Harshaw Properties: g-form [913–915], specific surface area 170 m2/g [913], 180 m2/g [914,915]. TABLE 3.61 PZC/IEP of Alumina from Harshaw Description

Electrolyte

Calcined at 500∞C

HNO3 + NH3 0.1 M NaCl

a

T

Method

Instrument

pH Mass titration

Overnight equilibration

pH0

Reference

7.6a

[913]

7.8a

[914]

Only value, no data points.

3.1.1.1.1.33 Alumina from Houdry 3.1.1.1.1.33.1 Alumina 415 (or Ho 415), 100–150 mesh Properties: g-form [580,588,916–919], 0.23 mmol Na/g [588], 0.05% SiO2, 0.7% Na2O by mass [917], specific surface area 123 m2/g [580,588,916–921,924] (probably BET, crushed, calcined at 600∞C), 190 m2/g [922]. TABLE 3.62 PZC/IEP of Alumina 415 (Ho 415) from Houdry Description Original 0.31 0.39 0.62 0.98 1.6 2.5 mmol Na/ga

Crushed, calcined at 600∞C for 12 h

a

b c

d

Electrolyte

T

Method

0.001–0.1 M KNO3

25 cip

0.001–0.1 M KNO3

25 cip Titration Intersection

0.001 and 0.1 M KNO3 0.01 M NH4NO4

25 iep

Instrument

Rank Brothers Mark II

pH0

Reference

5.3 9.6 9.7 9.8 9.3 9.8 10.1 5.3 5.6 5.9

[588] [921]

[580b,917d] [920,923] [922]

<8.7c

[918–920d,924]

Prepared by impregnation of the original powder with different amounts of NaNO3, drying at 110°C, and calcination at 600°C. Similar results were obtained in analogous experiments with LiNO3 [921]. Also 10–50∞C. +8 mV at pH 7.2, −3 mV at pH 8.7. [918] reports also a charging curve in 0.1 M NH4NO3 that suggests a PZC at substantially lower pH. PZC at pH 5.3 is reported in text. Only value, data points not reported.

125

Compilation of PZCs/IEPs

3.1.1.1.1.33.2 Alumina 417 Properties: g-form, 0.05% SiO2, 0.1% Na2O by mass, specific surface area 147.5 m2/g [917].

TABLE 3.63 PZC/IEP of Alumina 417 from Houdry Electrolyte

T

Method

0.001–0.1 M KNO3 a

Instrument

pH0

Reference

a

cip

3.9

[917]

Only value, no data points.

3.1.1.1.1.33.3 Alumina 425 Properties: g-form, 0.01% Na2O by mass, specific surface area 171.3 m2/g (original sample) [917].

TABLE 3.64 PZC/IEP of Alumina 425 from Houdry Description Original Washed Calcineda a

Electrolyte

T

0.001–0.1 M KNO3

Method

Instrument

cip

pH0

Reference

3.6 3.6 9.9

[917]

Prepared by impregnation of the original powder with 0.45 M NaNO3, drying at 110°C for 2.5 h and calcination at 600°C for 12 h.

3.1.1.1.1.34 SR from Indian Aluminium Co. Ltd surface area 0.7 m2/g [787].

Properties: BET specific

TABLE 3.65 PZC/IEP of SR from Indian Aluminium Co. Ltd Electrolyte

T

0.01 M NaNO3 a

Method

Instrument

pH0

Reference

iep

Zeta-Meter 2.0

8.1a

[787]

Subjective interpolation.

3.1.1.1.1.35 Alumina from Institute of Chemistry and Chemical Technology, Silesian Engineering College Properties: g-form with admixture of a-form, BET specific surface area 25 m2/g [925].

126

Surface Charging and Points of Zero Charge

TABLE 3.66 PZC/IEP of Alumina from Institute of Chemistry and Chemical Technology, Silesian Engineering College Description

Electrolyte

Acid-washed

0.001–0.01 M NaCl

T

Method

Instrument

cip

pH0

Reference

8.1

[925]

3.1.1.1.1.36 Alumina from Institute of Surface Chemistry, Kalush, Ukraine Another sample studied by the same research group in described in Section 3.1.1.1.1.17. Properties: BET specific surface area 150 m2/g [926].

TABLE 3.67 PZC/IEP of Alumina from Institute of Surface Chemistry, Kalush, Ukraine Electrolyte

T

0.001 M NaCl

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000

9.7

[926]

3.1.1.1.1.37 Aluminum Oxide C from Japan Aerosil Obtained by hydrolysis of AlCl3 in flame. Likely to be the same product as Degussa C (Section 3.1.1.1.1.21). Properties: g-form [927–929], BET specific surface area 100 m2/g [930], specific surface area 100 ± 15 m2/g [927], 100 m2/g (manufacturer) [928,929], uniform submicron particles [927].

TABLE 3.68 PZC/IEP of Aluminum Oxide C from Japan Aerosil Description NaOH-washed Electrodialyzed Electrodialyzed a b

Electrolyte

T

Method

Instrument

pH0

HNO3

25

Electrophoresis

0.001–0.1 M NaNO3

25

iep pH cip

>7 8.3a 8.3b

Reference [931] [927] [930]

Only value, no data points. Only acidity constants, no data points.

3.1.1.1.1.38 ALO-4 (from JRC) Properties: g-form [932], 1.5 ppm Na, 0.5 ppm Fe2O3, 1.9 ppm TiO2, 0.3 ppm CaO, specific surface area 177 m2/g [933], BET specific surface area 155 m2/g [932,934].

127

Compilation of PZCs/IEPs

TABLE 3.69 PZC/IEP of ALO-4 from JRC Description Washed

Electrolyte

T

Method

0.1 M NaNO3

25

pH

Instrument

pH0

Reference

8.4

[932]

3.1.1.1.1.39 RP-1 from Japan Fine Ceramics Center (JFCC) Properties: a-form, specific surface area 1.9 m2/g, d10 = 0.63 μm, d50 = 1.85 μm, d90 = 4.48 μm [935]. TABLE 3.70 PZC/IEP of RP-1 from JFCC Electrolyte

T

0.001 M NH4NO3

a

Method

Instrument

iep

Matec ESA 8000 Mutek PCD

pH0 7.7

Reference

a

[935]

Different solid-to-liquid ratios.

3.1.1.1.1.40 Alumina Identical with Material of Membranes from Jiangsu Jiusi High-Tech Co. Ltd China Properties: a-form [936]. TABLE 3.71 PZC/IEP of Alumina Identical with Material of Membranes from Jiangsu Jiusi High-Tech Co. Ltd Electrolyte

T

0.001–0.1 M NaCl

Method

Instrument

pH0

Reference

iep

Electro-osmosis

5.7

[936]

3.1.1.1.1.41 Aluminas from Johnson Matthey 3.1.1.1.1.41.1 g-Alumina Properties: g form [205,937,938], 99.999% pure [205,937], 99.99% pure [938], BET specific surface area 55 m2/g (manufacturer) [205], specific surface area 79 m2/g [937], 115 m2/g (manufacturer) [938], mean particle diameter 1 mm [205], mean diameter 10 nm [937]. TABLE 3.72 PZC/IEP of γ-Alumina from Johnson Matthey Description

Electrolyte

T

Method

Instrument

pH0

Reference

As obtained

0.001 M NaNO3

23

pH

1 d equilibration

4

[205]

128

Surface Charging and Points of Zero Charge

3.1.1.1.1.41.2 a-Alumina Properties: 99.99% pure, a-form, BET specific surface area 10.9 m2/g [939,940]. TABLE 3.73 PZC/IEP of α-Alumina from Johnson Matthey Description

Electrolyte

10% HNO3- and 10% NaOH-washed a

T

Method a

0.01–1 M NaNO3

25

Instrument

pH0

Reference

9.1

[940]

cip

Also at 30–70∞C.

3.1.1.1.1.42 Grade A Alumina from Konig Keramik Properties: Particle diameter calculated from specific surface area 60 nm [242]. TABLE 3.74 PZC/IEP of Grade A Alumina from Konig Keramik Electrolyte

T

0.01 M NaNO3 a

Method

Instrument

iep

pH0

PCD Mutek

Reference

7.2–9.3

a

[242]

Hysteresis; the result depends on the solid-to-liquid ratio.

3.1.1.1.1.43 Aluminas from LaRouche 3.1.1.1.1.43.1 a-Alumina Properties: BET specific surface area 30 m2/g [14]. TABLE 3.75 PZC/IEP of α-Alumina from LaRouche Description

Electrolyte

Calcined at 1050∞C for 4 h

T

0.1 M NaNO3

Method

Instrument

Mass titration

pH0

Reference

8.5

[14]

3.1.1.1.1.43.2 g-Alumina Properties: BET specific surface area 138 m2/g [14]. TABLE 3.76 PZC/IEP of γ-Alumina from LaRouche Electrolyte 0.1 M NaNO3

T

Method Mass titration

Instrument

pH0

Reference

8

[14]

129

Compilation of PZCs/IEPs

3.1.1.1.1.44 Aluminas from Linde 3.1.1.1.1.44.1 Linde A (Linde A from Union Carbide or from Praxair) See also Sections 3.1.1.1.1.13 and 3.1.1.1.1.78. Obtained by controlled calcination of pure ammonium alum. Properties: 90% a + 10% g [941], large particles (230 nm) are made up of highly crystalline a-form, and smaller particles (17 nm) are predominantly g-form [942], a-form [703,943,944], relative surface area 40% a-form, 60% g-form [945], high-purity [703,947], impurities (ppm): Si 200, Ga 30, Fe 30, Ca 7, Cu 7, Mg 5 [944], BET specific surface area 15 m2/g [941], [703] (krypton), [943,944,946,947], specific surface area 14 m2/g [948], mean diameter 0.3 mm [941], average diameter 100 nm [944], TEM image available [942,945], electron diffraction patterns available [945]. TABLE 3.77 PZC/IEP of Linde A Electrolyte

T

Method

None

iep

0.002 M NaCl

23b

pH

0.002 M NaCl

23

iep

0.001–0.1 M KCl, KNO3, KClO4

25

cip iep

Instrument Laser Zee Meter, Pen Kem 501

pH0 >8a

Reference [949]

8.8

[703]

Zeta-Meter

9.1

[943]

Zeta-Meter

9.1

[944]

Zeta-Meter

<9.5c

[950]

Coagulation iep a b c

+11 mV at pH 8, −30 mV at pH 11. Also 43∞C. +20 mV at pH 7, −15 mV at pH 9.5.

3.1.1.1.1.44.2 Linde B, Union Carbide Produced by Controlled Firing of Ammonium Alum Properties: a-form [455], g-form [108,951], silica <0.04% by mass [455], BET specific surface area 80 m2/g [455,951], 75–90 m2/g (data provided by manufacturer) [108], radius 10 nm [951], particle size 50 nm [108]. TABLE 3.78 PZC/IEP of Linde B Electrolyte 0.0001–0.01 M KNO3

T 25

0.001 M KNO3 a

Only value, no data points.

Method

Instrument

pH0

Reference

iep iep Coagulation iep

Electrophoresis Rank Brothers Mark II

8.5a 8.9

[108] [951]

Rank Brothers

8.9

[455]

130

Surface Charging and Points of Zero Charge

3.1.1.1.1.44.3 Synthetic Sapphire Properties: a-form [109,293,326,952, 953], BET specific surface area 10 m2/g [109,952], specific surface area 1.5 m2/g [953], particle size 0.3–1 mm [109,952]. All samples studied in [293] were obtained obtained by crushing of large single crystals, magnetic separation of iron, hot concentrated HCl leaching, and water washing of the powder. The powder was then stored in a Pyrex glass beaker under water.

TABLE 3.79 PZC/IEP of Synthetic Sapphire from Linde Description Washed and sintered at 1000°C Original Ignited at 1000°C Ignited at 1000°C then aged in water for 7 d Crushed, HCl-washed, aged in water a b

Electrolyte

T

Method

NaOH + HCl

Titration iep iep

0.00001–0.1 M NaCl

iep

Instrument

pH0 8.8

Reference

a

[953]

Streaming potential

9b

[293]

Streaming potential

9.4

[326]

Only value, no data points. The results reported in [293] deserve special attention, as one of the most frequently quoted (usually after [1]) sources of information about the IEP of α-alumina. All the values of IEP reported in [1] as the results from [293] (samples calcined and aged at various conditions) are based on arbitrary inter- or extrapolation. In [293], there are no data points for pH between 9 and 11. For the original (not calcined) alumina, there are four data points for pH 9 (0 to +10 mV) and two data points for pH 11 (−30 and −35 mV). Then the uncertainty of determination of the IEP is at least about 0.5 pH unit. There are even fewer data points for the calcined samples. For example, the IEP of the sample calcined at 1400°C and not aged in water is based on the following three data points: (pH 3, +92 mV; pH 7.5, −40 mV and pH 11, −112 mV). Only two selected IEPs of calcined samples from [293] are reported in Table 3.79.

3.1.1.1.1.45 Alumina from Lonza Properties: a-form, 99.6% pure, detailed analysis available, particle size 5–60 μm [954].

TABLE 3.80 PZC/IEP of Alumina from Lonza Electrolyte NaOH + HNO3

T

Method

Instrument

pH0

Reference

iep

DT 1200

8.8

[954]

131

Compilation of PZCs/IEPs

3.1.1.1.1.46 Alumina 6 m2/g [955].

from

Mager

Properties: Specific surface area

TABLE 3.81 PZC/IEP of Alumina from Mager Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

9a

[955]

Only value, no data points.

3.1.1.1.1.47 Aluminas from Mandoval 3.1.1.1.1.47.1 AKP 30 See Section 3.1.1.1.1.72.8. 3.1.1.1.1.47.2 AES11C (or AES11) Properties: 99.8% pure, BET specific surface area 8.1 m2/g, mean particle size 0.4 mm [956]. More information in Reference 20 of [493].

TABLE 3.82 PZC/IEP of AES11C (or AES11) from Mandoval Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KCl + KOH or NaOH

25

iep iep

Malvern Zeta Master AcoustoSizer

7.5a 7.9b

[956] [493]

a b

Only value, no data points. Various IEPs in a range 7.9–9.1 were obtained for different bases (NaOH, KOH, NH3) and directions of titration.

3.1.1.1.1.47.3 g-Alumina Properties: 99.99% pure, BET specific surface area 140 m2/g [957].

TABLE 3.83 PZC/IEP of γ-Alumina from Mandoval Electrolyte 0.1 M NaCl

T

Method

Instrument

pH0

Reference

iep

Laser Zee Meter 501

8.2

[957]

132

Surface Charging and Points of Zero Charge

3.1.1.1.1.48 Aluminas from Martinswerk or Martinswerke 3.1.1.1.1.48.1 HRA10 Properties: a-form [440,442,958,959], 97% of aform [496], >99.99% pure [440,442,958,959], impurities: Na2O < 30 ppm, SiO2 < 50 ppm, Fe2O3 <12 ppm, MgO < 8 ppm [442,958], Na2O 30 ppm, SiO2 50 ppm, Fe2O3 12 ppm, MgO 8 ppm CaO 5 ppm, MgO 8 ppm [496], BET specific surface area 10 m2/g [440,442,496,958,959], d50 = 0.4 mm [496], mean particle size 0.5 mm [442,958], <0.6 mm [440], <0.5 μm [959].

TABLE 3.84 PZC/IEP of HRA10 from Martinswerk Electrolyte

T

Method

HNO3 + KOH

25

iep

ESA 8000

iep

MBS 8050 Matec

KOH + HCl a

Instrument

pH0

Reference

9.3 9.2 9.3

[442,958] [440]a [496]

Only value, data points not reported.

MR70 Properties: a-form [960].

3.1.1.1.1.48.2

TABLE 3.85 PZC/IEP of MR70 from Martinswerke Electrolyte

T

HCl + NaOH

Method

Instrument

pH0

Reference

iep

ESA 8000

8.3

[960,961]

3.1.1.1.1.49 Aluminas from Meller 3.1.1.1.1.49.1 Alumina 180 Properties: a-form [810].

TABLE 3.86 PZC/IEP of Alumina 180 from Meller Electrolyte

T

Method Titration

a

Only value, no data points.

Instrument

pH0 a

8.8

Reference [810]

133

Compilation of PZCs/IEPs

3.1.1.1.1.49.2

Alumina 183 Properties: g-form [810].

TABLE 3.87 PZC/IEP of Alumina 183 from Meller Electrolyte

T

Method

Instrument

a

pH0 8.8a

Titration

Reference [810]

Only value, no data points.

3.1.1.1.1.50 Aluminas from Merck 3.1.1.1.1.50.1 g-Alumina(s) Properties: 99.5% pure [105], 0.004% phosphate [962], BET specific surface area 130 m2/g [963,964], 155 m2/g [965], 50 m2/g [962], XRD pattern, EDXRF spectrum available [105].

TABLE 3.88 PZC/IEP of γ-Alumina(s) from Merck Description

Electrolyte

Water-washed

0.001–0.1 M KNO3

As received

0.001–0.1 M KNO3

Washed Acid-washed Washed

KCl

0.01–1 M NaCl, LiCl, CsCl Soxhlet-extracted, 0.01 M NaCl, calcined at 0.025 M NaCl 1000°C

a b c

T

Method a

20

25b 25

25

cip Mass titration pH Salt titration cip cip iep

Instrument Equilibration time 2 min

pH0 Reference 8.2

[965]

8.2 6.8 8.4 8.7c 8.8

[105]

Cytophoremeter, 8.9 Zeiss

[962]

[666] [964] [963]

Also up to 60°C. Also 15 and 35∞C. Average of the CIP observed at 15 and 35°C.

3.1.1.1.1.50.2 g-Alumina, Basic Type Standardized for chromatographic adsorption analysis according to Brockmann. Properties: loss of ignition maximum 1% [966], BET specific surface area 90 m2/g [966], particle size 70 μm, porosity 2.5–3 nm [966].

134

Surface Charging and Points of Zero Charge

TABLE 3.89 PZC/IEP of γ-Alumina, Basic Type from Merck Description

Electrolyte

T

Method

Instrument

pH0 a

pH a

8

Reference [966]

Only value, no data points.

3.1.1.1.1.50.3 Alumina 90 Properties: 99.999% pure, g-form [967], BET specific surface area 150 m2/g [110], specific surface area 135.5 m2/g [967], agglomerates of 100 μm [110].

TABLE 3.90 PZC/IEP of Alumina 90 from Merck Electrolyte 0.1 M NaNO3 a b

T

Method

25b

cip pH

Instrument

pH0

Reference

8.2a 8.6

[110] [967]

Only value, no data points. Also 50∞C.

3.1.1.1.1.50.4 Alumina 90 a Properties: poorly crystalline h-form, 30 mm particles [873], 4 nm pores, 0.18% Cl, BET specific surface area 117 m2/g [873,884,1209], 97 m2/g, g-form, grain size 60–200 μm [968].

TABLE 3.91 PZC/IEP of Alumina 90 a from Merck Description

Electrolyte

T

Method

Instrument

pH0

Reference

As obtained

0.001–0.01 M KCl

25

Intersection iep

Pen Kem Laser Zee Meter 501

8.5 8.4

[873,1209] [884]

135

Compilation of PZCs/IEPs

3.1.1.1.1.50.5 Chromatographic Alumina 90, Neutral Properties: BET specific surface area 129 m2/g [969].

TABLE 3.92 PZC/IEP of Chromatographic Alumina 90, Neutral from Merck Description

Electrolyte

T

Method

Instrument

pH0

Reference

Washed

0.1 M NaCl

25

pH iep

Laser Zee Meter 501 Pen Kem

7.8 <8.5a

[969]

a

−10 mV at pH 8.5.

3.1.1.1.1.50.6 Chromatographic Alumina 90, Basic specific surface area 155 m2/g [970,971].

Properties: BET

TABLE 3.93 PZC/IEP of Chromatographic Alumina 90, Basic from Merck Description

Electrolyte

T

Method

Acid-washed

NaClO4

25

cip

Instrument

pH0

Reference

8.8

[970,971]

3.1.1.1.1.50.7 Chromatographic Alumina 150, Basic Properties: BET specific surface area 93 m2/g, a-form with admixture of low temperature g- and q-forms [925].

TABLE 3.94 PZC/IEP of Chromatographic Alumina 150, Basic from Merck Description

Electrolyte

Acid-washed

0.001–0.01 M NaCl

T

Method cip

Instrument

pH0

Reference

8.2

[925]

136

Surface Charging and Points of Zero Charge

a-Alumina

3.1.1.1.1.50.8

TABLE 3.95 PZC/IEP of α-Alumina from Merck Electrolyte

T

Method iep Coagulation

a

Instrument Electrophoresis

pH0

Reference

a

8.8

[972]

Only value reported, no data points.

Properties of other types of Alumina from Merck are reported in [973,974] (1077 neutral), and in [975] (a-alumina). 3.1.1.1.1.51 Alumina from Monsanto Electronic Materials Wet-classified and air-classified. Properties: contains organic impurities (FTIR) [976].

TABLE 3.96 PZC/IEP of Alumina from Monsanto Electronic Materials Description

Electrolyte

Wet, 11 μm Wet, 7 μm Air, 11 μm

0.001 M KNO3

T

Method

Instrument

iep

Pen Kem Laser Zee Meter

pH0 <5.6 if any <5.6 if any <5.6 if any

Reference [976]

3.1.1.1.1.52 Sapphire Single Crystal from MTI The 0001, 11-20, 10-10, and 1-102 planes were studied, different cleaning procedures.

TABLE 3.97 PZC/IEP of Sapphire Single Crystal from MTI Electrolyte 0.001 M KBr, KNO3 a

T

Method

Instrument

pH0

Reference

iep

Streaming potential

5.1a

[519]

IEP at pH 5–6.5 (for different planes) was estimated from AFM measurements.

3.1.1.1.1.53 Alumina(s) from Nanotek Properties: g-form [977], mainly g-form [978], BET specific surface area 47 m2/g [978], mean particle size 36 nm [978], average primary particle size 33 nm [977], spherical particles [977].

137

Compilation of PZCs/IEPs

TABLE 3.98 PZC/IEP of Alumina(s) from Nanotek Electrolyte

T

0.03 M NaCl 0.01 M NaCl a

Method

Instrument

iep iep

pH0

Reference

9.3 9.6a

[978] [977]

Pen Kem 501 Laser Zee Meter Leza 600, Otsuka

Roughly matches the maximum in viscosity of 3 vol% dispersion.

3.1.1.1.1.54 AE-11 from Nishio Properties: (calcined at 500°C) g-form, BET specific surface area 233 m2/g [979].

TABLE 3.99 PZC/IEP of AE-11 from Nishio Description

Electrolyte

T

Method

Calcined at 500°C

0.01 M KCl

40

pH

Instrument

pH0

Reference

7

[979]

3.1.1.1.1.55 Aluminas from Pechiney See also Section 3.1.1.1.1.7. 3.1.1.1.1.55.1 P152SB Properties: a-form [457,980], 200 ppm Na2O, 400 ppm CaO, 100 ppm MgO, 800 ppm SiO2, 500 ppm Fe2O3, purity 99.8%, particle diameter 1.25 μm, BET specific surface area 2.9 m2/g [457], 3 m2/g [980], average grain size 1.35 μm [980]. TABLE 3.100 PZC/IEP of P152SB from Pechiney Electrolyte

T

Method iep iep

0.01 M NaNO3

Instrument Matec ESA 8000 Rank Brothers Mark II

pH0

Reference

8 8.4

[980] [457]

3.1.1.1.1.55.2 P172SB Properties: a-form, mean particle diameter 0.4 μm, BET specific surface area 10 m2/g [981–983].

TABLE 3.101 PZC/IEP of P172SB from Pechiney Electrolyte 0.005 M NaCl

T

Method

Instrument

pH0

Reference

iep

Malvern 5000

9.2

[981–983]

138

Surface Charging and Points of Zero Charge

3.1.1.1.1.55.3 P662B Properties: a-form, 150 ppm Na2O, 400 ppm CaO, 200 ppm MgO, 1000 ppm SiO2, 600 ppm Fe2O3, purity 99.8%, particle diameter 4.4 μm, BET specific surface area 1.4 m2/g [457]. TABLE 3.102 PZC/IEP of P662B from Pechiney Electrolyte

T

0.01 M NaNO3

Method

Instrument

pH0

Reference

iep

Rank Brothers Mark II

6.8

[457]

3.1.1.1.1.55.4 P772SB Properties: a-form, 450 ppm Na2O, 500 ppm CaO, 1000 ppm MgO, 600 ppm SiO2, 600 ppm Fe2O3, purity 99.7%, particle diameter 400 nm, BET specific surface area 7.5 m2/g [457]. TABLE 3.103 PZC/IEP of P772SB from Pechiney Electrolyte

T

0.01 M NaNO3

Method

Instrument

pH0

Reference

iep

Rank Brothers Mark II

8.7

[457]

3.1.1.1.1.56 Alumina(s) from POCh Properties: g-form [984,985], BET specific surface area 154 m2/g [984,985], 174 m2/g [986]. TABLE 3.104 PZC/IEP of Alumina(s) from POCh Description Water-washed Water-washed

a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaCl

cip

8.5

[986]

0.01–0.1 M NaBr

cipa

8.8

[984]

0.001–1 M NaCl, NaBr, NaI, KCl, CsCl

cip iep

8.1

[985]

Electrophoresis

Only value, data points not reported.

3.1.1.1.1.57 Aluminum Oxide from Pred Materials International Properties: a-, d-, and q-phases, average size 158 nm, XRD pattern, particle size distribution, SEM image available [987]. TABLE 3.105 PZC/IEP of Aluminum Oxide from Pred Materials International Electrolyte

T

Method

Instrument

pH0

Reference

None

25

iep

Malvern NanoZS

>7

[987]

139

Compilation of PZCs/IEPs

3.1.1.1.1.58

Properties: g-form [847].

Spheralite from Procatalyse

TABLE 3.106 PZC/IEP of Spheralite from Procatalyse Electrolyte

T

Method

Instrument

0.1 M NaCl

25

Mass titration

pH0

Reference

8.4

[847]

3.1.1.1.1.59 Aluminas from Prolabo 3.1.1.1.1.59.1 Powder for Polishing Properties: BET specific surface area 53 m2/g [988]. TABLE 3.107 PZC/IEP of Powder for Polishing from Prolabo Electrolyte

T

Method

0.05 M NaNO3

20

pH

Instrument

pH0

Reference

7.2

[988]

Pure Alumina Properties: g-form, specific surface area

3.1.1.1.1.59.2 133 m2/g [989].

TABLE 3.108 PZC/IEP of Pure Alumina from Prolabo Electrolyte

T

Method

Instrument

pH0

Titration a

Reference

a

9.4

[989]

Only value, no data points.

3.1.1.1.1.60 a-Alumina from Queensland Alumina surface area 57 m2/g [990].

Properties: BET specific

TABLE 3.109 PZC/IEP of α-Alumina from Queensland Alumina Description HNO3-washed

a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

25

pH iepa

Rank Brothers Mark II

8.6 8.7

[990]

Only value, data points not reported.

140

Surface Charging and Points of Zero Charge

3.1.1.1.1.61 RHCP or RC-HP DMB from Reynolds Properties: 0.05% Mg [991,992], specific surface area 8.2 m2/g [991], d50 = 350 nm [992]. TABLE 3.110 PZC/IEP of Alumina from Reynolds Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

8.7

[991,992]

0.01 M KCl or KNO3

3.1.1.1.1.62

Alumina from Riedel de Haen

Properties: 98% pure [993].

TABLE 3.111 PZC/IEP of Alumina from Riedel de Haen Electrolyte

T

0.01 M KCl 0.01 M NaCl a

Method

20 25

Instrument

iep iep

pH0 a

Malvern Zetasizer 3000 HS Malvern Zetasizer 2000

8.3 9

Reference [993] [994]

For equilibration times 2 and 5 d. For 2 h equilibration, IEP was at pH 7.5. Arbitrary interpolation.

3.1.1.1.1.63

Single Crystal of Sapphire from Rubicon Technology

TABLE 3.112 PZC/IEP of Single Crystal of Sapphire from Rubicon Technology, Different Planes Electrolyte

T

Method

Instrument

iep

Brookhaven EKA

0.001–0.1 M KCl, (CH3)4NCl

3.1.1.1.1.64

pH0

Reference

4 5.8 6

[59]

Membralox Membrane from SCT Properties: a-form.

TABLE 3.113 PZC/IEP of Membralox Membrane from SCT Description New Used and cleaned a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

25

iep

Streaming potentiala

>8 6.4

[995]

Confirmed by electroviscous effect.

141

Compilation of PZCs/IEPs

3.1.1.1.1.65 Alumina from Shandong Aluminum Corporation (SALCO), China Properties: a- and g-form, XRD pattern, TEM image available, BET specific surface area 89 m2/g [532], d50 = 1.6 μm [532]. TABLE 3.114 PZC/IEP of Alumina from Shandong Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M KNO3

25

iep cip

Malvern Zetasizer 2000

9.5 8

[532]

3.1.1.1.1.66 Alumina from Shanghai Wusi Chemicals Properties: a-form, mean particle size 4 μm, BET specific surface area 17 m2/g [365]. TABLE 3.115 PZC/IEP of Alumina from Shanghai Wusi Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

25

iep

JS94H, Shanghai Zhongshun

8.9

[365]

3.1.1.1.1.67

Aluminas from Showa Denko

3.1.1.1.1.67.1 Al-160SG-1 Properties: a-form, >99.9% pure, <0.05% Na, average diameter 0.56 mm [996,997], BET specific surface area 3.1 m2/g [996], 8.1 m2/g [997]. TABLE 3.116 PZC/IEP of Al-160SG-1 from Showa Denko Electrolyte

T

Method iep

a

Instrument Electrophoresis

pH0 8

a

Reference [996,997]

Only value, no data points.

3.1.1.1.1.67.2 Al-160SG-4 Properties: 99.89% of a-form [697,998], average diameter 0.6 μm [998], 0.5 mm [697], BET specific surface area 7.9 m2/g [697,998]. TABLE 3.117 PZC/IEP of Al-160SG-4 from Showa Denko Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Malvern 3000 HAS or HSA

9.1

[697,998a]

Maximum in viscosity of 12.8 vol% dispersion matches IEP.

142

Surface Charging and Points of Zero Charge

3.1.1.1.1.67.3 a-Alumina Properties: 99.995% pure [999], specific surface area 2.6 m2/g [1000], 10.7 m2/g [999], mean diameter 0.7 mm [1000], average diameter 500 nm [999].

TABLE 3.118 PZC/IEP of α-Alumina from Showa Denko Electrolyte

T

Method

Instrument

pH0

Reference

25

pH iep

Pen Kem 500

9 9.2a

[1000] [999]

0.001 M KNO3

a

Only value, no data points.

3.1.1.1.1.68 Alumina from Sigma-Aldrich Properties: a-form, BET specific surface area 7 m2/g [1001].

TABLE 3.119 PZC/IEP of Alumina from Sigma-Aldrich Electrolyte

T

Method

Instrument

Mass titration a

pH0

Reference

8.6a

[1001]

Only value, no data points.

3.1.1.1.1.69 a-Alumina from Silica Source Technology Properties: Free of impurities [1002].

TABLE 3.120 PZC/IEP of α-Alumina from Silica Source Technology Electrolyte HCl/KOH a

T

Method

Instrument

pH0

Reference

7

[1002]a

Results of AFM force measurements between alumina and silica at various pH are reported.

3.1.1.1.1.70 Amperit 740.1 from Stark Original and plasma-sprayed. Properties: Original, a-form, after spraying, g-form with admixture of a, XRD patterns available, specific surface area: original, 0.4 m2/g, after spraying, 1 m2/g [1003].

143

Compilation of PZCs/IEPs

TABLE 3.121 PZC/IEP of Amperit 740.1 from Stark Description Original Original, washed Sprayed Sprayed, washed Sprayed

Electrolyte

T

0.01 M NaCl

Method

Instrument

pH0

Reference [1003]

DT 1200

8.5 8.6 9.2 8.8 9.2

Mass titration

0.001 M NaCl

20

iep

[783]

3.1.1.1.1.71 Alumina from Strem Chemicals Properties: g-form, BET specific surface area 134 m2/g [1004], BET specific surface area 100 m2/g [1005].

TABLE 3.122 PZC/IEP of Alumina from Strem Electrolyte 0.001 M KCl

T

Method

Room

iep

0.001 M KCl a

iep

Instrument Zeta-Meter 3.0+ Zm-77

pH0

Reference

a

[1004]

8.7

[1005]

7.7

Arbitrary interpolation.

3.1.1.1.1.72 Aluminas from Sumitomo 3.1.1.1.1.72.1 AA2 Properties: >99.9% pure, a-form, d50 = 2 μm [1006], SEM image available [59].

TABLE 3.123 PZC/IEP of AA2 from Sumitomo Electrolyte KNO3 0.01 M KNO3 a b

T

Method iep iep

Instrument Brookhaven Zeta PALS Zeta-Meter 3.0b

pH0 3.8 9

a

Reference [59] [1006]

Arbitrary interpolation. Unpublished results cited in [519] (AA alumina) produced the same IEP.

3.1.1.1.1.72.2 AA04 Properties: >99.9% pure, a-form, d50 = 700 nm, micrograph available [1006].

144

Surface Charging and Points of Zero Charge

TABLE 3.124 PZC/IEP of AA04 from Sumitomo Electrolyte

T

0.01 M KNO3

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

9.3

[1006]

3.1.1.1.1.72.3 AA05 Properties: 99.9% pure, elementary analysis available, specific surface area 3.1 (measured), 3.2 (manufacturer) m2/g, particle diameter d50 = 0.51 μm (manufacturer) [1007]. TABLE 3.125 PZC/IEP of AA05 from Sumitomo Electrolyte

T

0–0.05 M KCl a

25

Method

Instrument

iep

Acoustosizer

pH0

Reference a

9–9.8

[1007]

Hysteresis, higher IEP at higher electrolyte concentration.

3.1.1.1.1.72.4 AA07 Properties: >99.9% pure, a-form, d50 = 840 nm [1006].

TABLE 3.126 PZC/IEP of AA07 from Sumitomo Electrolyte

T

0.01 M KNO3

3.1.1.1.1.72.5

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

9

[1006]

AKP 10 Properties: a-form, 1.1 μm diameter [1008].

TABLE 3.127 PZC/IEP of AKP 10 from Sumitomo Description

Electrolyte

T

Method

Instrument

pH0

Reference

As obtained

0.001 M KNO3

25

iep

Rank Brothers Mark II

4.8

[1008]

3.1.1.1.1.72.6 AKP 15 Properties: a-form [978,1006,1008–1011], >99.99% pure [1010], 99.999% pure [1011], >99.9% pure [1006], specific surface area 3.8 m2/g [1010], BET specific surface area 3.6 m2/g [369,978], average particle

145

Compilation of PZCs/IEPs

size 1 mm [1009], 850 nm diameter [1008], mean particle size 700 nm [369,978,1010], d50 = 590 nm [1006], micrograph available [1006].

TABLE 3.128 PZC/IEP of AKP 15 from Sumitomo Electrolyte

T

As obtained 0.001 M KNO3 25 0.03 M NaCl 0.01 M KNO3 0.001 M KNO3 25 a b

Method iep iep iep iep iep

Instrument

pH0

Rank Brothers Mark II 4.3 Zeta-Meter 3.0 >7.5a Pen Kem 501 Laser Zee-Meter 8.9 Zeta-Meter 3.0 9 Acoustosizer Matec 9b

Reference [1008] [369] [978] [1006] [1010]

+5 mV at pH 7.5, −10 mV at pH 9. Matches the maximum in yield stress of 30 vol% dispersion.

3.1.1.1.1.72.7 AKP 20 Properties: a-form [1010,1012], purity 99.99% [1012], >99.99% pure [1010], BET specific surface area 4.5 m2/g [1012], 4.3 m2/g [1010], mean particle diameter 0.56 mm, range 0.2–1.8 mm [1012], mean particle size 540 nm [1010].

TABLE 3.129 PZC/IEP of AKP 20 from Sumitomo Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.01M NaCl 0.001 M KNO3

25

iep iep

Zeta-Meter 3.0 Acoustosizer Matec

8.2 9a

[1012] [1010]

a

Yield stress of 30 vol% dispersions in 0.01 M KNO3 peaks at pH 9.

3.1.1.1.1.72.8 AKP 30 (from Sumitomo or from Mandoval) Properties: a-form [242,1008,1010,1013–1017] and [521] (from Mandoval), purity: >99.995% [1014], >99.99% [793,835,1010,1015], 99.99% [521], impurities (ppm): Fe 20, Si 50, Cu 10, Mg 10, Na 10 (manufacturer) [521], Si 8, Na 2, Mg 2, Cu 1, Fe 5 [1018], density 3970 kg/m3 [1015,1018], BET specific surface area 5.9 m2/g [1014], 6.5 m2/g [667] (the column headings in Table 1 of [667] were probably swapped) [1013], 7 m2/g [835,1015,1019,1020], 7.1 m2/g [1016], 7.5 m2/g [1017,1018], 10 m2/g [793], specific surface area 6.8 m2/g [443,1010], mean diameter 0.3 μm [1015,1018,1019], 360 nm [1010], average particle size 390 nm [1013], 400 nm [1008], average particle diameter 0.3–0.5 μm [1016], 0.37 μm [1014], average

146

Surface Charging and Points of Zero Charge

particle size 0.4 μm [793], 300 nm [1017], d90 = 610 nm, d50 = 350 nm, d10 = 200 nm [835], d50 = 400 nm [1020], median diameter 310 nm [242], volume mean diameter 400 nm, number mean diameter 340 nm [521], mean diameter 270 nm [443], oblong particles, aspect ratio < 2:1 [1018,1019].

TABLE 3.130 PZC/IEP of AKP 30 from Sumitomo or from Mandoval Description As obtained

Electrolyte 0.001 M KNO3

Soxhlet washed with water KNO3 Mandoval

T

Method

25 iep Mass titration iep iep

0.0001–0.1 M NaCl, KCl, NaNO3 0.01 M NaCl 0.01, 0.1 M NaCl 0.006 M NaCl 0.01 M NH4Cl 0.01 M NaNO3

iep Intersection 22 iep iep 22 iep

0.001 M KNO3

25 iep

0.01, 0.05 M NaCl

20 iep pH 25 iep

0.001, 0.01 M KNO3, Na and K trichloroacetate, trifluoroacetate and trifluoromethanesulfonate 0.01 M KCl

0.01–1 M NaNO3, KNO3, CsNO3, KCl, KBr, KI 0.01 M LiNO3

Instrument Rank Brothers Mark II

Brookhaven Zeta PALS Malvern Zetasizer II, Zetamaster ESA 8000 Matec

pH0

Reference

3.7

[1008]

7.9

[667]

8a

[59]

8c

[521]

8.7 8.7 Acustosizer 8.7b Sugiura 2 VD 9 Malvern Zetasizer 9d 3000 HS, Matec ESA 8000 and 9800 PCD Mutek DT 1200 Acoustosizer 9e Matec ESA 8000 Matec 9 7.6 Malvern Nano ZP 9.2 DT 1200 Acoustosizer II

[1017] [1014] [1016] [1013] [242]

iep

Acoustosizer Matec

9.4

[443]

25 iep

Acoustosizer

9.4–9.5 [1015,1018, 1019e,1021]

[1010] [793f,835g, 1020] [40]

continued

147

Compilation of PZCs/IEPs

TABLE 3.130 (continued) Description

Electrolyte

Original and washed

0.01–1 M KNO3

a b

c

d

e f g

T

Method

Instrument

25 cip Malvern Nano ZP iep DT 1200 Salt titration Acoustosizer

pH0

Reference

9.6 9.4 9.2

[492]

Arbitrary interpolation. IEP roughly matches maxima in viscosity, in apparent particle size and in sedimentation volume in a 2 vol% dispersion. IEP obtained in different electrolytes at different concentrations showed substantial scatter (7.5–8.2), but no systematic trend. For volume fractions of 5% and 10%. IEP observed with 1% volume fraction was substantially higher. PCD produced lower IEP than other instruments and a substantial hysteresis. Matches maximum in yield stress of 20–30 vol% dispersion. Also 10 and 40°C. Only value, no data points.

3.1.1.1.1.72.9 AKP 50 or LAKP-50 Obtained by hydrolysis of very pure organometallic precursors, followed by calcination at >1100°C and ball-milling [106]. Properties: a-form [106,344,371,509,519,978,1006,1009–1011,1022,1023 (LAKP-50), 1024–1026,1028,1029,1033], purity >99.99% [1010], 99.99% [106,1011], >99.9% [1006], 99.9% [1028], >99.9% [509], 99.995% [371,1029,1030], high purity (LAKP-50) [1023], impurities: 8 ppm Si, 8 ppm Fe, 3 ppm Mg, Cu, and Na (according to manufacturer) [371], 15 ppm Si, 4 ppm Fe, 2 ppm Mg [106], specific density 3970 kg/m3 [509], 3940 kg/m3 [1009], BET specific surface area 7 m2/g [1031], 10–12 m2/g [509], 9.9 m2/g [1009], 10 m2/g [106], 11.5 m2/g [1026], 10.9 m2/g [978], 10.8 m2/g [1022], 9.7 m2/g [371], specific surface area 10.5 m2/g [1010], 9.5 m2/g [1029], 11.5 m2/g [1027], 10 m2/g [1028], mean particle size 0.3 mm [1028], 180 nm [1010], 200 nm [978], average particle size 0.2 mm [1032], average diameter 200 nm [1009,1033], 220 nm [1027], particle diameter 100–300 nm [106], particle size 100–300 nm [371], 220 nm [1026], mean diameter 200 nm [1022], 210 nm [1029], particles consist of 2–3 smaller (80 nm) particles [106], mean particle diameter 0.2 mm [509], d50 = 250 nm [344,519,1024,1025], 230 nm [1006], spherical particles [1026], TEM image available [106].

TABLE 3.131 PZC/IEP of AKP-50 or LAKP-50 from Sumitomo Description

Electrolyte KCl CH3COOH + (CH3)4NOH

T

Method

Instrument

pH0

Reference

iep iep

Malvern Nano ZS Electrophoresis, Matec ESA 8000

7.9 8

[1031] [1027]

continued

148

Surface Charging and Points of Zero Charge

TABLE 3.131 (continued) Description

Electrolyte

T

Method

0.01 M NaCl

iep

0.005 M KCl 0.01–0.02 M NH4NO3, NaNO3 0.01 M NH4Cl

iep iep

Zetasizer MKII, Malvern Pen Kem 501 ESA 8000, Matec

iep

Zeta-Meter 3.0

0.03 M NaCl

iep

0.005 M KNO3 0.001 M KNO3

iep iep

0.001 M KNO3

25 iep

0.01 M KNO3 0.005 M KNO3 0.01 M KBr, KNO3 Original and 0.0027–0.102 M after aging in NaNO3 water at 100°C 0.001 M KNO3 for 1 d 1 M HNO30–0.1 M NaNO3 washed Calcined at 0.025, 0.1 M 1200°C for 5 h NaNO3 0.01 M NH4Cl

b c d e f g

pH0

Reference

8.1

[371]

8.2 8.7

[1023] [1030] [1032]a [1011] [978] [1022]c [1025] [1028] [1024]c

iep iep iep iep

8.7 9b Pen Kem 501 Laser 8.9 Zee Meter Zeta-Meter 3.0 9 Zeta-Meter 3.0 9 Pen Kem 501 Malvern Zetasizer 3 MBS 8000 Matec Acoustosizer 9d Matec 9.1 Zeta-Meter 3.0 9.3 Zeta-Meter 3.0 9.3 Matec Acoustosizer 9.3–9.5e

cip iep

Coulter Delsa 440 SX

[106]

9.3 9

cip

9.5

Intersection

9.2f

iep

25 iep 0.01, 0.1 M NaNO3, NaCl, NaClO4, NaBrO3 a

Instrument

[1010] [1033] [1006] [344] [519]

Zeta-Meter 3.0

9.5

[773]

Acoustosizer

9.6g

[509]

Arbitrary interpolation. Broad stability minimum around IEP. Only value, no data points. Matches maximum in yield stress of 30 vol% dispersion. A misleading horizontal line in Figure 7 in [519] corresponds to ζ ≈ 15 mV. The charging curves obtained at three ionic strengths (0, 0.025, 0.1 M NaNO3) do not have a CIP. Maximum of the yield stress of dispersions (0.25 volume fraction) matches IEP.

149

Compilation of PZCs/IEPs

3.1.1.1.1.72.10 AKP HP40 Properties: a-form, BET specific surface area 5.3 m2/g, mean particle diameter 0.45 mm [567].

TABLE 3.132 PZC/IEP of AKP HP40 from Sumitomo Electrolyte

T

Method

0.001, 0.01 M KNO3 20 (text) 25 (figures)

Instrument

Intersection iep Stability

Zetasizer 3, Malvern Zee Meter 501, Pen Kem

pH0

Reference

9 9 9

[567]

3.1.1.1.1.72.11 AKP-G015 Properties: g-form, BET specific surface area 140 m2/g [1034]. Similar material identified as g-alumina from Sumitomo. Properties: 99.995%, BET specific surface area 140 m2/g [150,1035–1037], 152 m2/g [1038].

TABLE 3.133 PZC/IEP of AKP-G015 from Sumitomo Description

Electrolyte

T

Method

Aged

0.1 M NaCl 0.1 M NaCl

25 25

pH pH

a

Instrument

pH0

Reference

8.2 8.4a

[1035] [1034]

Only acidity constants reported, no data points.

3.1.1.1.1.72.12 a-Alumina Properties: Purity: 99.9% [1039], >99.99% [1040,1041], BET specific surface area 9.7 m2/g [1039], specific surface area 10.5 m2/g [1040], particle size 100–300 nm [1039].

TABLE 3.134 PZC/IEP of α-Alumina from Sumitomo Electrolyte KOH + HCl 0.0001–0.01 M NaCl

a

T

Method

25

Only value reported, no data points.

Instrument

pH0

Reference

iep iep

Zeta-Meter Pen Kem 7000

8 8.3a

[1040] [1041]

cip iep

Rank Brothers II

8.5 8.7

[1039]

150

Surface Charging and Points of Zero Charge

3.1.1.1.1.73 Aluminas from Tamei (or Taimei) 3.1.1.1.1.73.1 TM-DAR Properties: a-form [1042–1044], 99.99% pure [832], >99.99% pure [1042–1044], detailed analysis available [1042], BET specific surface area: 13.4 m2/g [1042–1044], 14.3 m2/g [832], d50 = 116 nm [1042–1044], average size 220 nm [832], SEM image available [1042]. A sample calcined for 4 hours at 400°C was studied in [1042–1044]. TABLE 3.135 PZC/IEP of TM-DAR from Taimei Aging

Electrolyte

16 h 1h 16 h

T

Method

Instrument

pH0

Reference

25 ± 2

iep iep/pH

DT 1200 DT 1200

9.1 9.3/7.2 9/7.2

[1043,1044] [1042]

3.1.1.1.1.73.2 Alumina from Tamei (or Taimei), Type Unknown Properties: a-form [1045,1046], 99.99% pure [1046], BET specific surface area 14.7 m2/g [1045], 17.4 m2/g [1046], particle size 210 nm [1045]. TABLE 3.136 PZC/IEP of Unidentified Alumina from Tamei (or Taimei) Electrolyte 0.01 M NaNO3 a

T

Method

Instrument

pH0

Reference

20a

iep

Zeta-Meter

9.1

[1046]

Also studied at 10–40∞C.

3.1.1.1.1.74 Microfiltration Membrane from Terronic (Czech Republic) Crushed and milled. Properties: a-form [418,1047]. TABLE 3.137 PZC/IEP of Microfiltration Membrane from Terronic Electrolyte None 0.001 M NaCl 0.005 M NaCl None 0.001 M NaCl 0.01 M NaCl a

T

25

Arbitrary interpolation.

Method

Instrument

pH0

Reference

iep

Zeta PALS Brookhaven

[1047]

iep

Zeta PALS Brookhaven

3.5 4.5 4.5a 3.8 3.8 4.1

[418]

151

Compilation of PZCs/IEPs

3.1.1.1.1.75 Alumina from Thiokol Properties: BET specific surface area 0.14 m2/g [30,1048].

TABLE 3.138 PZC/IEP of Alumina from Thiokol Description

Electrolyte

Washed with hot HCl

3.1.1.1.1.76

T

0.1, 1 M NaCl 0.001 M NaCl

Method

Instrument

pH0

Reference

pH iep

Streaming potential

8.2 8.5

[30] [1048]

Sapphire Single Crystal from Tyco

TABLE 3.139 PZC/IEP of Sapphire Single Crystal from Tyco Electrolyte 0.01, 0.05 M NaBr 0.001 M NaCl

a

T 20–25

Method iep iep

Instrument

pH0

Reference a

Electro-osmosis Electro-osmosis

3.1–3.5 3.3

[1049] [278]

The same study reports σ0 (pH) curves calculated from combined electrokinetic and radiotracer measurements (Na and Br adsorption) for two NaBr concentrations.

3.1.1.1.1.77 Alumina from UCAR Properties: a-form, specific density 3.92 g/cm3 [1050].

TABLE 3.140 PZC/IEP of Alumina from UCAR Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Rank Brothers

7.5

[1050]

3.1.1.1.1.78 Aluminas from Union Carbide (Praxair) 3.1.1.1.1.78.1 Linde A See Sections 3.1.1.1.1.13 and 3.1.1.1.1.44.1. 3.1.1.1.1.78.2 3.1.1.1.1.78.3 14 m2/g [1051].

Linde B See Section 3.1.1.1.1.44.2. Nonporous a-Alumina Properties: Specific surface area

152

Surface Charging and Points of Zero Charge

TABLE 3.141 PZC/IEP of Nonporous α-Alumina from Union Carbide Electrolyte

T

Method

0.03 M NaCl

43

pH

Instrument

pH0

Reference

8

[1051]

3.1.1.1.1.79 Chromatographic Alumina from Veb Lab Apolda Properties: BET specific surface area 67.3 m2/g, particle diameter 2–5 mm [1052]. TABLE 3.142 PZC/IEP of Chromatographic Alumina from Veb Lab Description As received a

Electrolyte

T

0.0001–1 M KCl

Method

25

cip

Instrument

a

pH0

Reference

8.9

[1052]

Sample was also studied by means of electrophoresis. The ζ potential at pH < 8 was positive. No results at pH > cip were reported.

3.1.1.1.1.80 Aluminas from Whitfield and Sons 3.1.1.1.1.80.1 SDK 160 Properties are reported in [1053]. TABLE 3.143 PZC/IEP of SDK 160 from Whitfield and Sons Electrolyte None 0.001 M NaCl, KCl 0.05 M NaCl, KCl 0.01 M KCl + KOH or NaOH a b

T

25

Method

Instrument

pH0

Reference

iep

AcoustoSizer

[307]

iep

AcoustoSizer

7.4 7.9a 8.2a 8.1b

[493]

Base titration. Acid titration produces IEP higher by about 0.2 pH unit. Various IEP in a range 8.1–9.1 were obtained for different bases (NaOH, KOH, NH3) and directions of titration.

3.1.1.1.1.80.2 SDK 161

Properties are reported in [1053].

TABLE 3.144 PZC/IEP of SDK 161 from Whitfield and Sons Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KCl + KOH or NaOH

25

iep

AcoustoSizer

7.6a

[493]

a

Various IEP in a range 7.5–8.2 were obtained for different bases (NaOH, KOH, NH3) and directions of titration.

153

Compilation of PZCs/IEPs

3.1.1.1.1.81 Alumina 200 from Woelm Pharma Properties: BET specific surface area 143.2 m2/g, average particle size 3.8 mm, average pore radius 3.6 nm [1054].

TABLE 3.145 PZC/IEP of Alumina 200 from Woelm Pharma Description

Electrolyte

T

Method

Acid-washed

0.001–0.1 M KNO3

25

cip

Instrument

pH0

Reference

8.7

[1054]

3.1.1.1.1.82 Alumina from Wusong Fertilizer Factory Properties: a-form [407,1055,1056], BET specific surface area 4.4 m2/g [1055], 26.3 m2/g [407, 1056].

TABLE 3.146 PZC/IEP of Alumina from Wusong Electrolyte

T

0.001 M NaCl 0.001 M KCl a

Method

Instrument

pH0

Reference

iep iep

ZetaPlus Brookhaven ZetaPlus Brookhaven

8.2a 8.3

[407,1056] [1055]

Based on arbitrary interpolation.

3.1.1.1.1.83 Alumina from Wu-Xi Chemical Reagent Factory, Shanghai Properties: g-form, BET specific surface area 117 m2/g [167].

TABLE 3.147 PZC/IEP of Alumina from Wu-Xi Description

Electrolyte

T

Method

Water-washed

0.01–1 M NaNO3

30

cip

a

Also 17 and 45°C.

Instrument

pH0

Reference

7.7

[167,1057a]

154

3.1.1.1.1.84

Surface Charging and Points of Zero Charge

Origin Unknown

TABLE 3.148 PZC/IEP of Aluminas from Unknown Commercial Sources Description

Electrolyte

T

NaOH + HCl α, molten at 2010– 2050°C, then crushed, washed in 6% HCl at 60°C 1 M KCl α, reagent grade γ, chromatographic, 180 m2/g, calcined for 1 d at 800°C Chromatographic grade, activated α, high purity, 280 m2/g Chromatographic, 115 m2/g

a

b c d e

iep

Electroosmosis

pH0

Reference [1058]

pH

7.1d

[1059]

0.0005–0.01 M NaCl

pH

7.3a

[575]

0.001 M NaCl

iep

8b

[1060]

0.0001 M KNO3, KCl

iep

8.3

[825]

0.1 M KCl 0.1 M KBr 0.1 M KNO3

iep

8.3

[1061]

8.5

[1062,1063]

iep

α, 29.8 m2/g, crystallite 0.001–0.1 M KNO3 size 191 nm, SEM image available 0.01 M NaCl α, reagent grade, acid- and basewashed, 9.3 m2/gc Analytical grade, 0.01 M KNO3 99.5% pure, Si 500 ppm, Ca 700 ppm, Fe 270 ppm, 220 m2/g

Chromatographic, as received

Instrument

6.7

α, >99.9% pure, 720 nm average diameter, 9.1 m2/g

α, ground membrane

Method

0.001–0.1 M KCl

Streaming potential Streaming potential

PCD Mutek

25

cip

8.9

[112]

25

pH

9

[1064]

30

iep

Zeta-Meter

9.1

[1065]e

iep

Pen Kem 3000

9.5–10 [1066]e

Titration Drift

10 9.8

[1067]e

Charging curves obtained at different ionic strengths do not show a clear CIP, and the ionic strength effect on σ0 is irregular. Arbitrary interpolation. Cited after [533], in which γ-alumina was studied. From Table 2. Fig. 1 suggests a higher PZC. Only value/range, data points not reported.

155

Compilation of PZCs/IEPs

3.1.1.1.2 Synthetic Aluminas PZCs/IEPs of home-synthesized aluminum oxides are presented in Tables 3.149 through 3.179. 3.1.1.1.2.1 Obtained by Hydrolysis of Alkoxides 3.1.1.1.2.1.1 From Aluminum Isopropoxide, Calcined for 1 day at 873K Properties: BET specific surface area 174 m2/g [1068].

TABLE 3.149 PZC/IEP of Alumina from Aluminum Isopropoxide, Calcined for 1 d at 873K Electrolyte

T

Instrument

pH0 a

Mass titration cip

0.001–0.1 M NaNO3 a

Method

8.2 8.5

Reference [1068]

Only value, data points not reported.

3.1.1.1.2.1.2 From Aluminum sec-Butoxide, Recipe from [416] Aluminum sec-butoxide was mixed with 100 molar parts of water. The mixture was heated to 90°C and 0.07 mol of HCl was added per mole of aluminum sec-butoxide. The sol was dried at room temperature and calcined. Properties: mean particle size, BET specific surface area, and structure are given in Table 3.150 [416].

TABLE 3.150 PZC/IEP of Alumina from Aluminum sec-Butoxide, Recipe from [416] Calcination Size BET (°C) (µm) (m2/g) Structure Electrolyte T Method Instrument pH0a 25 300 500 800 1100 1400 a

<0.5 2 2 2 2 2

285 234 232 206 6 3

δ-AlOOH 0.001 M NaCl γ+δ γ+δ γ θ+α α

25

iep

Rank Brothers Mark II

Reference

9.4 10.2 8.6 10.6 9.2 8.3

[416]

Initial IEP. Aging induced a shift in the IEP to low pH, up to 1 pH unit for 30 days’ aging.

3.1.1.1.2.1.3 From Aluminum sec-Butoxide, Recipe from [1069] Aluminum sec-butoxide was mixed with 100 parts of water. The mixture was heated to 75°C for 30 min, then 0.05 mol of HNO3 was added per mole of aluminum sec-butoxide at 85°C, and the mixture was stirred at this temperature for 3 h. The sol was dried at room temperature, then at 150°C, and calcined for 5 h at 470°C.

156

Surface Charging and Points of Zero Charge

Properties: g-form, BET specific surface area 319 m2/g, size of crystallites 2.5 nm [1069].

TABLE 3.151 PZC/IEP of Alumina from Aluminum sec-Butoxide, Recipe from [1069] Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M KNO3

25

iep cip

Matec Acustosizer

8.6

[1069]

3.1.1.1.2.1.4 From Aluminum sec-Butoxide, Recipe from [1070] Reference [1070] cited in [1004] for recipe does not report specific recipe, but cites other papers. Calcined at 750°C for 6 h. Properties: BET specific surface area 265 m2/g [1004].

Table 3.152 PZC/IEP of Alumina from Aluminum sec-Butoxide, Recipe from [1070] Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

Room

iep

Zeta-Meter 3.0+

8.2

[1004]

3.1.1.1.2.1.5 From Aluminum Isopropoxide, Recipe from [1071] Emulsogen OG and b-alanine (10% by mass with respect to alumina) were dissolved in 500 cm3 of methoxyethanol. Aluminum isopropoxide and acetic acid were added. The solution was refluxed for 3 h. 3 mol of water and 1 mol of aluminum isopropoxide were added, and the solution was refluxed for 3 h. Then the dispersion was adjusted to pH 2.5 with acetic acid or to pH 8 with ammonia, and a dispersion of seed particles of a-alumina was added. The dispersion was ballmilled for 2 days and dried at 80°C for 1 day. Calcined at 1050°C. Properties: a-form, specific surface area, TEM images, and XRD patterns available [1071].

TABLE 3.153 PZC/IEP of Alumina from Aluminum Isopropoxide, Recipe from [1071] Obtained at pH 2.5 8

Electrolyte None

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer

8.7 9.2

[1071]

157

Compilation of PZCs/IEPs

3.1.1.1.2.1.6 From Aluminum sec-Butoxide, Recipe from [1072] [1073], which is cited in [312] does not report a recipe but cites another paper. Aluminum sec-butoxide was added dropwise to water at >80°C with stirring. 1.5 dm3 of water was used per mole of butoxide. Then 0.07 mol of HNO3 was added per mole of butoxide. The mixture was boiled until butanol evaporated, and then it was refluxed for 16 h. Properties: g-form, specific surface area 250 m2/g [312].

TABLE 3.154 PZC/IEP of Alumina from Aluminum sec-Butoxide, Recipe from [1072] Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaCl

25

iep

Malvern Zetasizer 3000 HSa

8.3

[312]

3.1.1.1.2.1.7 Obtained by Heating of a Hydroxide Properties: g form [1074].

TABLE 3.155 PZC/IEP of Alumina Obtained by Heating of a Hydroxide Electrolyte

T

NaOH a

20

Method iep

Instrument Electrophoresis

pH0 8

Reference

a

[1074]

Only value, data points not reported.

3.1.1.1.2.2 Obtained by Hydrolysis of Inorganic Precursors at Room Temperature 3.1.1.1.2.2.1 From Nitrate and Ammonia, Recipe from [658] Ammonia was added to Al(NO3)3 at pH 10. The dispersion was aged at 25°C for 5 h, and filtered. The solid was dried at 110°C for 1 day and calcined in air for 5 h at 500°C. Properties: g-form [658], specific surface area 230 m2/g [674].

TABLE 3.156 PZC/IEP of Alumina from Nitrate and Ammonia, Recipe from [658] Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M KNO3

25

cip iep

Malvern Zetasizer 5000

8.6 8.2

[657b,658,674]a

a b

The results of mass titration and inflection point are also reported. Only value, data points not reported.

158

Surface Charging and Points of Zero Charge

3.1.1.1.2.2.2 From Nitrate and Ammonia, Recipe from [1075] 1:1 ammonia was added dropwise to 0.1 M Al(NO3)3 with stirring up to pH 8. The gel was aged for 1 day, water-washed, and dried for 4 days at 120°C. It was ground to 250 mesh, and calcined at 450°C for 5 h in air. Properties: g-form, BET specific surface area 214 m2/g [1075].

TABLE 3.157 PZC/IEP of Alumina from Nitrate and Ammonia, Recipe from [1075] Electrolyte

T

HCl + KOH

Method

Instrument

pH0

Reference

iep

Rank Mark II

8.2

[1075]

3.1.1.1.2.2.3 From Chloride and NaOH, Modified Recipe from [1076] 10 cm3 of 0.35 M NaOH was slowly added to 10 cm3 of 0.13 M AlCl3, shaken for 15 min and centrifuged. Properties: Traces of gibbsite and bayerite, median diameter 160 nm, size distribution available [353].

TABLE 3.158 PZC/IEP of Alumina from Chloride and NaOH, Modified Recipe from [1076] Electrolyte 0.001 M NaCl a

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

9.5a

[353]

Only value, data points not reported. The minimum in CCC matches the IEP (only acidic branch available).

3.1.1.1.2.2.4 From Nitrate and Ammonia, Recipe from [1077] Solution of nitrate was adjusted to pH 2 with HNO3, and then treated with excess of ammonia. The precipitate was washed with water, calcined at 600°C for 5 h, washed with water again, calcined at 600–1400°C for 3 h, and washed with water again. Properties: g-structure below 800°C, partial transition to a at 1000°C, and complete transition at >1200°C [1078], lattice spacing data [1077] and specific surface area available [1078]. Recipe from [33]. Hydroxide was obtained from 1 M Al(NO3)3 and a 10% excess of 3 M ammonia, washed with water, and calcined at 600°C for 6 h. The oxide was washed with water until constant conductivity. Properties: 20 nm in diameter [33].

159

Compilation of PZCs/IEPs

TABLE 3.159 PZC/IEP of Alumina from Nitrate and Ammonia, Recipe from [1077] Second Calcination Temperature (°C) None 1200 600 800 1000 1200 1400

Electrolyte

T

0.001 M NaCl 25 0.001 M NaCl 25 0.001 M NaCl 25

Method

Instrument

pH iep iep

Streaming potential Streaming potential Streaming potential

pH0 Uncrushed/ Crushed Reference 9.2 9.6 11.4/11.2 11.2 9.7/11 9.6/9.7 9.6/9.6

[33] [1077] [1078]

3.1.1.1.2.2.5 From Nitrate and Ammonia, Recipe from [250] Dilute ammonia was added to Al(NO3)3. The precipitate was washed and ignited. Properties: Ignition at 1000°C produced a-Al2O3. The lower the temperature, the stronger the gibbsite lines [250].

TABLE 3.160 PZC/IEP of Alumina from Nitrate and Ammonia, Recipe from [250] Heated at (°C) 300 600 1200

Electrolyte 0–0.005 M KCl, KNO3, KClO4

T

Method

Instrument

pH0

Reference

30

iep

Electrophoresis

9.2 8.2–8.5 6.8–7.7

[250]

3.1.1.1.2.2.6 Obtained from AlCl3 and NaOH (Cited by [1] and by Many Others as IEP of Amorphous Al2O3 Properties: Cl/Al2O3 mole ratio 0.005 in solid [1079].

Table 3.161 PZC/IEP of a Precipitate Obtained from AlCl3 and NaOH (Cited by [1] and by Many Others as IEP of Amorphous Al2O3) Electrolyte NaCl

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

8.1

[1079,2226]

160

Surface Charging and Points of Zero Charge

3.1.1.1.2.2.7 From Aluminum Dross Tailings Chemical Waste Leaching with NaOH and precipitation with different agents. Calcination of the precipitate at 600°C for 3 h. Properties: g-form [1080]. TABLE 3.162 PZC/IEP of Alumina from Aluminum Dross Tailings Chemical Waste Precipitation Agent

BET (m2/g)

H2O2 NH4Al(SO4)2 Al(OH)3 seeds

243 169 176

a

Electrolyte

T

Method

Instrument

pH0a

Reference

HCl + KOH

Room

iep

Zeta-Meter 3.0

8.5 8.6 8.4

[1080]

Arbitrary interpolation.

3.1.1.1.2.2.8 From Natural Bauxite from India Leaching with NaOH and precipitation with different agents. Calcination of the precipitate at 600°C for 3 h. Properties: g-form [1080]. TABLE 3.163 PZC/IEP of Alumina from Natural Bauxite from India Precipitation agent

BET m2/g

H2O2 NH4Al(SO4)2 Al(OH)3

244 170 158

a

Electrolyte

T

Method

Instrument

pH0a

Reference

HCl + KOH

Room

iep

Zeta-Meter 3.0

8.5 8.6 9

[1080]

Arbitrary interpolation.

3.1.1.1.2.2.9 From Chloride and NaOH, Recipe from [1081] 400 cm3 of 2 M NaOH was slowly added to 200 cm3 of 1.5 M AlCl3. The precipitate was washed with water and with 95% ethanol, and dried at 70°C for 1 day. Properties: Amorphous, BET specific surface area 209 m2/g [381].

TABLE 3.164 PZC/IEP of Alumina Obtained from Chloride and NaOH, Recipe from [1081] Description

Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

9.4

[381]

161

Compilation of PZCs/IEPs

3.1.1.1.2.3 Hydrolysis of Inorganic Precursor at Elevated Temperature Solution 0.2 M in Al(NO3)3 and 50 g/dm3 in urea was heated at 95°C for 100 min.

TABLE 3.165 PZC/IEP of Alumina Obtained by Hydrolysis of Nitrate at 95°C Electrolyte

T

Method

Instrument

pH0

Reference

iep

ZetaPlus Brookhaven

8.2

[1082]

0.001 M KNO3

3.1.1.1.2.4 Controlled Dehydration of Hydroxides 3.1.1.1.2.4.1 Thermal Decomposition of Gibbsite Properties: a-form [225], g-form in samples decomposed at lower temperatures, a-form in sample calcined at 1350°C. In sample calcined at 1000°C, a-form was found with admixture of g-form [1083], g-form, BET specific surface area 26 m2/g, crystallite size 10 nm, SEM image, XRD pattern available [112].

TABLE 3.166 PZC/IEP of Alumina Obtained by Thermal Decomposition of Gibbsite Decomposition Temperature (°C) 1200 550, 1.5 h

Electrolyte

T

Method

NaOH + HCl 0.001–0.1 M KNO3

iep cip

Electrophoresis

25

3a 7b

[225] [112]

iep

Streaming potential

7.9 8.6 7.4 9.1 9.2

[1083]

400 600 800 1000 1350 a b

Instrument

pH0

Reference

Arbitrary interpolation. Reported in text. The curves shown in Figure 6 merge at pH 5–8.

3.1.1.1.2.4.2 Obtained by Calcination of Baker Al(OH)3 for 2 days at 1400°C Properties: a-form, BET specific surface area 3.7 m2/g [189].

TABLE 3.167 PZC/IEP of Alumina Obtained by Calcination of Baker Al(OH)3 Electrolyte

T

Method

0.001, 0.1 M NaNO3

25

Intersection

Instrument

pH0

Reference

8.4

[189]

162

Surface Charging and Points of Zero Charge

3.1.1.1.2.4.3 for 4 h

a-Al2O3 Obtained by Calcination of g-AlOOH at 1150°C

TABLE 3.168 PZC/IEP of α-Al2O3 Obtained by Calcination of γ-AlOOH at 1150°C for 4 h Electrolyte

T

Method cipa

0.005–0.5 M NaClO4 a

Instrument

pH0

Reference

9.4

[3215]

Only value, no data points.

3.1.1.1.2.4.4 Calcination of Diaspore at 500°C specific surface area given in Table 3.169 [1084].

Properties: a-form,

TABLE 3.169 PZC/IEP of Alumina Obtained by Calcination of Diaspore at 500°C BET (m2/g) 28 32 89 130

Electrolyte

T

HCl + NaOH

Method

Instrument

pH0

Reference

pH

1 h, 1 d equilibration

8.8 8.4 8.9 9.2

[1084]

3.1.1.1.2.4.5 Calcination of Boehmite at 800°C for 16 hours in Air Properties: g-form, specific surface area 270 m2/g [989].

TABLE 3.170 PZC/IEP of Alumina Obtained by Calcination of Boehmite at 800°C for 16 h in Air Electrolyte

T

Method Titration

a

Instrument

pH0 a

8.2

Reference [989]

Only value, data points not reported.

3.1.1.1.2.4.6 Calcination of Spherical Boehmite at 1200°C for 30 Minutes Properties: a-form, BET specific surface area 6 m2/g [1085].

163

Compilation of PZCs/IEPs

TABLE 3.171 PZC/IEP of Alumina Obtained by Calcination of Spherical Boehmite at 1200°C for 30 min Electrolyte

T

Method

Instrument

pH0

Reference

iep AFM

Malvern Zetamaster

5.6a 5

[1085]

NaCl, different concentrations a

Only value, data points not reported.

3.1.1.1.2.5 High-Temperature Reactions 3.1.1.1.2.5.1 Oxidation of Aluminum sec-Butoxide in Air at 1400°C Properties: Specific surface area 220 m2/g, XRD pattern available [1086]. TABLE 3.172 PZC/IEP of Alumina Obtained by Oxidation of Aluminum sec-Butoxide Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000

8.8

[1086]

NaOH + HCl

3.1.1.1.2.5.2 High-Temperature Hydrolysis of AlCl3 in Hydrogen Flame Properties: g-form, larger particles with admixture of cubic phase in the surface layer, particle size 10–50 nm, specific surface area 144 m2/g [1087]. Table 3.173 PZC/IEP of Alumina Obtained by High-Temperature Hydrolysis of AlCl3 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

7

[1087]

3.1.1.1.2.5.3 Low-Temperature Plasma Synthesis Properties: >99.9% pure, spherical particles 78 nm in diameter, a-form, specific surface area 43 m2/g [587]. TABLE 3.174 PZC/IEP of Alumina Obtained by Low-Temperature Plasma Synthesis Electrolyte

T

0.01, 0.1 M NaNO3

a

Arbitrary interpolation.

Method

Instrument

pH0

Reference

Intersection iep

Electrophoresis

8.2 7.8a

[587]

164

Surface Charging and Points of Zero Charge

3.1.1.1.2.5.4 a-form [1088].

Flame-Fused Ground in mullite ware, not cleaned. Properties:

TABLE 3.175 PZC/IEP of Flame-Fused Alumina Description

Electrolyte

T

Aged for <1 d

Method

Instrument

pH0

Reference

iep

Electrophoresis

7.5–8.2

[1088]

3.1.1.1.2.6 Explosion Synthesis from Elements admixture of q-form [1089].

Properties: d-form with

TABLE 3.176 PZC/IEP of Alumina Obtained from Elements Electrolyte

T

0.0001 M KCl 0.2 M KCl or KNO3 a

Method iep pH

Instrument

pH0

Reference

Electrophoresis

a

[1089]

7 6.3

Based on arbitrary interpolation.

3.1.1.1.2.7

Other Synthetic Aluminas

3.1.1.1.2.7.1 From AlCl3 and Propylene Oxide Propylene oxide was added to AlCl3 solution in methanol. The methanol was removed by rinsing in diethyl ether. Diethyl ether was evaporated. Properties: 99.38% Al2O3, 0.37% Cl, BET specific surface area 341 m2/g [1090].

TABLE 3.177 PZC/IEP of Alumina from AlCl3 and Propylene Oxide Electrolyte 0.001–0.1 M NaNO3

T

Method cip

Instrument

pH0

Reference

7.2

[1090]

3.1.1.1.2.7.2 From Greek Bauxite Properties: g-form, 0.28% Na2O by mass, specific surface area 122.5 m2/g [917].

165

Compilation of PZCs/IEPs

TABLE 3.178 PZC/IEP of Alumina from Greek Bauxite Electrolyte

T

Method

0.001–0.1 M KNO3 a

Instrument

pH0

Reference

a

cip

5.5

[917]

Only value, data points not reported.

3.1.1.1.2.7.3 Recipe Not Specified Properties: g-form [533], BET specific surface area 9.3 m2/g [533], 9.6 m2/g [345], d50 = 216 nm [345].

TABLE 3.179 PZC/IEP of Synthetic Aluminas, Recipe Not Specified Electrolyte 0.0001 M NaNO3 0.1 M NaCl a b

T

Method

25b

Instrument

iep pH

Zeta-Meter 3.0

pH0 a

8.5 9.3

Reference [345] [533]

Arbitrary interpolation. Also 60°C.

3.1.1.1.3 Natural PZCs/IEPs of natural aluminum oxides are presented in Table 3.180.

TABLE 3.180 PZC/IEP of Natural Aluminas (All in α-Form) Description From Madagascar, ground, dialyzed, and dried Calcined at 1000°C HCl- and waterwashed, dried at 120°C, 0.94% SiO2

Instrument

pH0

Reference

NaOH + HCl

Electrolyte

T

Method iep

Electrophoresis

2.3

[225]

KOH

iep iep

Electrophoresis Streaming potential

8.4 9.4

[1091] [1092]

166

3.1.1.1.4

Surface Charging and Points of Zero Charge

Origin Unknown

TABLE 3.181 PZC/IEP of Aluminas from Unknown Sources Description a Sapphire a, average size 370 nm a g a

Pure

Electrolyte 0.1 M KNO3 HCl + NaOH

30 0.001 M KCl 0.001, 0.1 M NaNO3 NaCl NaNO3 CsCl CsNO3 0.01 M NaCl 20

125 m2/g

a b c

pH iep iep

Instrument

NaCl

pH0 Reference

6 7 Brookhaven ZetaPlus 7a

[1094] [1095]b [1096]

Salt addition iep Zetasizer 4 Intersection

7.1 7.5 7.5

[1097] [1098] [736]

Titration

7.8 7.6 8.5 8.3 8

[1099]

8.3

[1101]

8.3

[1102, 1103]b [1104]

iep

Zetasizer MKII, Malvern

Electro-osmosis

8.5b

iep

HCl + NaOH g, 71 m2/g g, 147 m2/g g, 188 m2/g q, 77 m2/g h, 180 m2/g Particle diameter 0.0001 M 100 nm KNO3 Pure corundum, 0.002 M ground KNO3 a, >99.9% pure, 100 nm average size, 8.5 m2/g, TEM image available a 37 μm, 122 m2/g g

Method

Titration iep iep

114 m2/g a, 99.2% pure, 770 nm g, 100 m2/g a

T

Titration iep Titration pH

Electrophoresis Matec ESA 8000 1 h, 1 d equilibration

iep Coagulation iep Rank Brothers Mark II iep Malvern Zetasizer 4

8.5 8.8 7.4 8.8 8.8 8.8 8.6 9.4 8.9

[1100]

[1105]b [1106]b [1084]

[1107]

9

[1108]

9

[1109]

pH Titration

9 9b

[1110]b [1111]

Titration

9.1

[1112]c

Arbitrary interpolation. Only value, no data points. Only acidity constants, data points not reported.

167

Compilation of PZCs/IEPs

3.1.1.2 Aluminum Oxide Hydroxide PZCs/IEPs of aluminum oxide hydroxides (nominally AlOOH) are presented in Tables 3.182 through 3.209. 3.1.1.2.1 Commercial Boehmite PZCs/IEPs of boehmite from various commercial sources are presented in Tables 3.182 through 3.190. 3.1.1.2.1.1 Boehmite from BA Chemical Properties: BET specific surface area 175 m2/g, 260 nm in diameter [1113].

TABLE 3.182 PZC/IEP of Boehmite from BA Chemical Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern ZetaMaster S

9.2

[1113]

3.1.1.2.1.2 Boehmites from Condea 3.1.1.2.1.2.1 Dispersal (see also Micrographs available [497].

Section

3.1.1.2.1.6) Properties:

TABLE 3.183 PZC/IEP of Dispersal from Condea Electrolyte

T

Method

KOH + HNO3

Instrument

iep

pH0

Reference

9

[497]

3.1.1.2.1.2.2 Boehmite from Condea (Condea Vista), Type Unknown Properties: Purity 99.6% [525,1036], 99.2% [1034,1114], BET specific surface area 180 m2/g [525,1034,1036,1115], 180 m2/g (original), 183 m2/g (after 4 months in aqueous dispersion) [1114], 270 m2/g [114].

TABLE 3.184 PZC/IEP of Unspecified Boehmite from Condea Electrolyte

T

Method

0.1 M NaCl

25

pH

Instrument

pH0

Reference

8.6

[525,1034,1114]

3.1.1.2.1.3 Boehmite from Electronic Space Product Industries Properties: 98% boehmite, <0.05% Fe2O3, BET specific surface area 44 m2/g, 300 nm in diameter [1116].

168

Surface Charging and Points of Zero Charge

TABLE 3.185 PZC/IEP of Boehmite from Electronic Space Product Industries Electrolyte

T

Method

0.001–0.1 M KNO3

25

iep cip Salt addition

Instrument Malvern Zetasizer 2c Rank Brothers Mark II

pH0

Reference

9.1 8.5 8.6

[1116]

3.1.1.2.1.4 Boehmite from Neftekhim (or Research Institute of Petroleum Industry) Obtained from NaAlO2 and HNO3. Properties: 0.01% Si, 0.001% Fe, 0.001% Mg, 0.01% Ga, 0.03% Na [504], detailed chemical analysis [547,1117,1118], BET specific surface area 198.5 m2/g [504], 124 m2/g [547], specific surface area 124 m2/g [1117–1119], particle size 1.5–3 nm [504], 8–10 nm [1118]. TABLE 3.186 PZC/IEP of Boehmite from Neftekhim Electrolyte

T

Method

0.001–1 M NaCl

20

0.001, 0.01 M NaCl, KCl

20

pH iep pH iep

0.001–1 M NaCl 1 M KCl a

Instrument

pH0

Electrophoresis Malvern Zetasizer 4 Abramson cell

cip

9.5 (extrapolated) 9.5 8.6 8.6 8.8

Reference [504] [330,1117a–1119]

[547]

The same paper reports IEP of another AlOOH, obtained from AlCl3, also at pH 8.6 (under the same conditions).

3.1.1.2.1.5 Brockmann Alumina, Analytical Grade from Reanal Properties: g-AlOOH, boehmite [1120,1121], BET specific surface area 107 m2/g [1120,1121], particle size 7 mm [1120]. TABLE 3.187 PZC/IEP of Brockmann Alumina, Analytical Grade from Reanal Description

Electrolyte

T

KNO3 Ground a b

0.01–1 M KNO3

Only value, data points not reported. Only positive branch reported.

Method Titration iep cip

Instrument Malvern Zetasizer 4

pH0 9a 9b 8.7

Reference [1120] [1121]

169

Compilation of PZCs/IEPs

3.1.1.2.1.6 Disperal 40 from Sasol See also Section 3.1.1.2.1.2.1. Properties: Boehmite, average particle size 350 nm [283].

Table 3.188 PZC/IEP of Disperal 40 from Sasol Electrolyte

T

Method

0.01 M KNO3

iep

Instrument Acoustosizer II Electro-osmosis Streaming potential

pH0 Reference 9 9.5 9.5

[283]

3.1.1.2.1.7 Boehmite from Shandong Properties: Pseudoboehmite, BET specific surface area 166 m2/g, d50 = 6.4 μm, XRD pattern, TEM image available [532].

TABLE 3.189 PZC/IEP of Boehmite from Shandong Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M KNO3

25

iep cip

Malvern Zetasizer 2000

9.5 8.6

[532]

3.1.1.2.1.8 Boehmite from VEB Laborchemie Apolda cific surface area 110 m2/g [548].

Properties: BET spe-

TABLE 3.190 PZC/IEP of Boehmite from VEB Laborchemie Apolda Electrolyte

T

Method

0.001–1 M NaCl, LiCl, KCl, NaNO3, NaI

25

cip

Instrument

pH0 Reference 7.2

[548]

3.1.1.2.2 Synthetic Boehmite PZCs/IEPs of home-made boehmites are presented in Tables 3.191 through 3.204. 3.1.1.2.2.1 Hydrolysis of Alkoxides 3.1.1.2.2.1.1 From sec-Butoxide, Modified Recipe from [1122] Aluminum sec-butoxide was mixed with water (1:100 molar ratio). The solution was heated at 90°C, and HCl was added to produce a transparent gel, which was then heated.

170

Surface Charging and Points of Zero Charge

TABLE 3.191 PZC/IEP of Boehmite Obtained from Aluminum sec-Butoxide, Modified Recipe from [1122] Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

9.4

[1123]

3.1.1.2.2.1.2 From sec-Butoxide, Modified Recipe from [1124] A mixture of aluminum sec-butoxide and water was stirred at 83°C for 1–2 h. Properties: BET specific surface area 217 m2/g [1125,1126], 167 m2/g [1127], 40 ppm Fe [1126].

TABLE 3.192 PZC/IEP of Boehmite Obtained from Aluminum sec-Butoxide, Modified Recipe from [1124] Electrolyte

T

0.01 M KNO3 a

Method

Instrument

iep

Pen Kem 3000

pH0 a

>7

Reference [1127]

No data points for pH > 7.

3.1.1.2.2.2 Hydrolysis of Inorganic Precursor at Room Temperature 3.1.1.2.2.2.1 From Chloride, Recipe from [52] 820 cm3 of 2 M CO2-free NH4OH was added to a solution of 50 g of AlCl3 in 200 cm3 of water at 18°C. The precipitate was washed, dialyzed, and dried at 105°C. Properties: Admixture of bayerite [52].

TABLE 3.193 PZC/IEP of Boehmite Obtained from Chloride, Recipe from [52] Description

Electrolyte NaOH + HCl

a

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

8.8a

[52]

Only IEP reported (no experimental data points).

3.1.1.2.2.2.2 From Na3AlO3, Recipe from [52] Air was passed through a Na3AlO3 solution of specific gravity 1150 kg/m3 (sample B) or through the same solution diluted 1:100 (sample C). The precipitate was washed, dialyzed, and dried at 105°C.

171

Compilation of PZCs/IEPs

TABLE 3.194 PZC/IEP of Boehmite Obtained from Na3AlO3, Recipe from [52] Sample B C a

Electrolyte

T

Method

NaOH + HCl

Instrument

iep

pH0

Reference

a

Electrophoresis

7.6 6.5a

[52]

Only IEP reported (no experimental data points).

3.1.1.2.2.3 Hydrolysis of Inorganic Precursor at Elevated Temperature 3.1.1.2.2.3.1 From Chloride, Recipe from [1128] 0.1 M AlCl3 was adjusted to pH 11 by slow addition of NaOH with stirring. It was aged with stirring for 10 min at room temperature and heated in an autoclave at 160°C for different times. Properties: TEM image, FTIR spectra, XRD pattern available [1128].

TABLE 3.195 PZC/IEP of Boehmite Obtained from Chloride, Recipe from [1128] Time of Heating 2h 1d

Electrolyte

T

HCl + NaOH

Method

Instrument

pH0

Reference

iep

Pen Kem S3000

9.3 9

[1128]

3.1.1.2.2.3.2 Pseudoboehmite (Poorly Crystalline Boehmite), Recipe from [1129] A solution 0.6 M in NaOH and 4 M in NaCl was added dropwise to a solution 0.4 M in AlCl3 and 4 M in NaCl (OH:Al ratio 2.95). It was centrifuged, aged for 20 h at 60°C in plastic bottles, washed, and dried at 60°C. Properties: BET specific surface area 287 m2/g [1129].

TABLE 3.196 PZC/IEP of Pseudoboehmite, Recipe from [1129] Electrolyte

T

Method

Instrument

pH a

pH0 a

9.3

Reference [1129]

Only acidity constants, data points not reported.

3.1.1.2.2.3.3 From Chloride and Perchlorate, Recipes from [1130] 0.0001–0.01 M AlCl3 containing HCl (Cl:Al mole ratio 3–4.5) was aged at 125°C

172

Surface Charging and Points of Zero Charge

for different times, and then cooled in ice–water. Analogous experiments were carried out with Al(ClO4)3–HClO4 mixtures. Properties: Boehmite, TEM and SEM images available [1130].

TABLE 3.197 PZC/IEP of Boehmites Obtained from Chloride and Perchlorate According to Recipes from [1130] Description

Electrolyte

T

0.005 M AlCl3, 3 days 0.005 M Al(ClO4)3, 3 days a

Method

Instrument

iep

pH0 Reference

Rank Brothers

8a 9.3

[1130]

Arbitrary interpolation.

3.1.1.2.2.3.4 Recipe from [1131] 1 M Al(NO3)3 or AlCl3 was adjusted at room temperature to pH 6–10 with 1–10 M ammonia. The precipitate was washed and autoclaved for 6 h at 100–300°C. Properties: XRD results, TEM image available [1132], BET specific surface area 203 m2/g [1132,1133].

TABLE 3.198 PZC/IEP of Boehmite Obtained According to Recipe from [1131] Electrolyte

T

Method

0.001–1 M KNO3, KCl, KBr, KI

20

pH

Instrument

pH0

Reference

>7

[1132]

3.1.1.2.2.4 Controlled Dehydration of Hydroxide 3.1.1.2.2.4.1 Calcination of Gibbsite from Prolabo Properties: (calcination at 450°C for 5 h) BET specific surface area 246 m2/g, XRD image available [1134], (calcination at 350°C for 16 h) well-crystallized, specific surface area 318 m2/g [989].

TABLE 3.199 PZC/IEP of Boehmite Obtained by Calcination of Gibbsite from Prolabo Electrolyte

T

Method Titration

a

Only value, data points not reported.

Instrument

pH0

Reference

7.7a

[989]

173

Compilation of PZCs/IEPs

3.1.1.2.2.4.2

Calcination of Gibbsite at 300°C

TABLE 3.200 PZC/IEP of Boehmite Obtained by Calcination of Gibbsite at 300°C Electrolyte

T

Method

Instrument

pH0

Reference

iep

Streaming potential

7.7

[1083]

3.1.1.2.2.4.3 Aging of Amorphous Hydroxide

TABLE 3.201 PZC/IEP of Boehmite Obtained by Aging of Amorphous Hydroxide Electrolyte

T

Method

Instrument

pH0

Reference

NaOH

20

iep

Electrophoresis

9.4

[1074,1142]

3.1.1.2.2.5 Other Recipes 3.1.1.2.2.5.1 Recipe from [1135] using Perchlorate Three different recipes are reported in [1135]. Properties: BET specific surface area 41.2 m2/g [1136].

TABLE 3.202 PZC/IEP of Boehmite Obtained According to Recipe from [1135] Electrolyte 0.0001–0.01 M NaClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

10.4

[1136]

3.1.1.2.2.5.2 Oxidation of Aluminum Powder in the Presence of HgCl2 Aluminum powder, 100 mesh, was treated with 0.0005 M HgCl2 for 10 min, then washed, and then treated with an excess of 1:4 aqueous acetic acid at 75°C. The dispersion was cooled to room temperature and aged overnight. It was then boiled at constant volume for 8 h (water added) to remove the excess acetic acid, following which, it was heated at 170°C for 8 h in a pressure vessel. The sediment was freeze-dried, resuspended in 30% H2O2, and boiled at constant volume for 6 h (water added). It was freeze-dried again. Properties: Fibers, 400–600 nm long and 50 nm in diameter, BET specific surface area 187.2 m2/g [529]. (Slightly modified procedure): boehmite, BET specific surface area 216 m2/g [1137].

174

Surface Charging and Points of Zero Charge

TABLE 3.203 PZC/IEP of Boehmite Obtained by Oxidation of Al Powder in the Presence of HgCl2 Electrolyte

T

0.1 M KCl 0.001 M KCl

Method

Instrument

pH0

Reference

pH iep

Pen Kem Laser Zee Meter 501

7.2 9.4

[529]

3.1.1.2.2.5.3 Oxidation of Aluminum Foil in the Presence of HgCl2 Aluminum foil (99.99% pure) was amalgamated with 0.025 M HgCl2, and then reacted with moist air. It was then exposed to boiling water for 3 min. Then purified by flotation, the precipitate was dried in vacuum, ground, and dried at 90°C. Properties: Pseudoboehmite, 160 ppm Hg, <40 ppm Cl, 22–27% water [1138]. TABLE 3.204 PZC/IEP of Boehmite Obtained by Oxidation of Al Foil in the Presence of HgCl2 Electrolyte

T

Method

Instrument

pH0

Reference

0.01 NaNO3

25

iep pH

Zeta-Meter

9.2 6.2

[1138]

3.1.1.2.3 Natural Boehmite White Bantam bauxite, ground, dialyzed, and dried. TABLE 3.205 PZC/IEP of Natural Boehmite Electrolyte

T

Method

Instrument

pH0

Reference

NaOH + HCl

25

iep

Electrophoresis

<2 if any

[225]

3.1.1.2.4 Natural Diaspore PZCs/IEPs of natural diaspores are presented in Tables 3.206 through 3.208. 3.1.1.2.4.1 From Great Wall, 90% Pure TABLE 3.206 PZC/IEP of Diaspore from Great Wall Electrolyte

T

Method

0.001 M KNO3

25

iep

Instrument MRK electrophoresis apparatus

pH0

Reference

5.7

[1141]

175

Compilation of PZCs/IEPs

3.1.1.2.4.2 From Rosebud, Ground, Dialyzed, and Dried Table 3.207 PZC/IEP of Diaspore from Rosebud Electrolyte

T

NaOH + HCl

3.1.1.2.4.3

Method

Instrument

pH0

Reference

iep

Electrophoresis

<2 if any

[225]

Other Natural Diaspores

TABLE 3.208 PZC/IEP of Other Natural Diaspores Description

Electrolyte

T Method

Henan, >90% pure 0.001 M KCl or KNO3

iep

Missouri

iep

NaOH + HClO4

Instrument Brookhaven ZetaPlus Zeta-Meter

pH0 Reference 6.4

[60]

10

[104]

pH0

Reference

iep pH pH

9.7 6.8 5.8a

[1143]a

cip iep

8.8b 8.1

[1059] [1059]

iep Electrophoresis Intersection iep

8.1 8.2 6

[1145]

3.1.1.2.5 Other Samples of AlOOH

TABLE 3.209 PZC/IEP of Other Samples of AlOOH Description

Electrolyte

Boehmite Boehmite

HCl + NaOH

a, reagent grade

0.0001–1 M KCl

g, reagent grade

0.0001-0.01 M KCl 0.001, 0.01 M KCl

g c 330 m2/g Diaspore a b c

T

Method

Instrument

[1144]

[1146]a

Only acidity constants, data points not reported. Extrapolated. Also two unspecified aluminas: a and g were studied in [1145] with IEP at pH 8 and 8.3, respectively.

3.1.1.3 Hydrous Aluminum Oxide PZCs/IEPs of hydrous aluminum oxides (nominally Al2O3 · nH2O) are presented in Tables 3.210 through 3.214. There may be some overlap between materials presented in this section, and those presented in Sections 3.1.1.2 and 3.1.1.4.

176

Surface Charging and Points of Zero Charge

3.1.1.3.1 Commercial 3.1.1.3.1.1 From Carlo Erba Prepared by Brockmann method. Properties: Amorphous [711,1147–1149], specific surface area 54 m2/g [673], and 48 m2/g [711,1147] ( p-nitrophenol adsorption from xylene), 52 m2/g (original) and 16 m2/g (calcined) [710] (water vapor adsorption), 52 m2/g (lauric acid method) [1148,1149].

TABLE 3.210 PZC/IEP of Hydrous Aluminum Oxide from Carlo Erba Electrolyte

T

Method

KNO3 0.1, 0.001 M NaNO3 0.1, 0.001 M KNO3 0.001 M KNO3 a b

Instrument

Titration Intersection Intersectionb Mass titration

pH0

Reference

a

6.9 7.5 7.5 7.5

[710] [1150] [673] [1149]

Only value, data points not reported. Arbitrary interpolation.

3.1.1.3.1.2 From Condea Properties: Specific surface area 250 m2/g [847].

TABLE 3.211 PZC/IEP of Hydrous Aluminum Oxide from Condea Electrolyte

T

0.1 M NaCl

25

Method

Instrument

Mass titration

pH0

Reference

7.9

[847]

3.1.1.3.2 Synthetic 3.1.1.3.2.1 Obtained by Calcination of Mallinckrodt Al(OH)3 for 5 Hours at 400°C Properties: Composition: Al2O3 · 0.46H2O, contains gibbsite and bayerite, microporous [1151].

TABLE 3.212 PZC/IEP of Hydrous Aluminum Oxide Obtained by Calcination of Mallinckrodt Al(OH)3 Electrolyte NaNO3

T

Method

Instrument

pH0

Reference

Salt addition

1 h equilibration

8.3

[1151]

177

Compilation of PZCs/IEPs

3.1.1.3.2.2 From Sulfate Solutions containing aluminum (0.0001–0.01 M) and sulfate (0.0001–0.03 M) ions were aged for different times at 99°C. Properties: For aluminum concentrations of 0.0003–0.005 M and aluminumto-sulfate molar ratios of 1:1 to 1:2, monodispersed sols are obtained, TEM and SEM images available, modal diameter 100–700 nm [1152,1153], electron micrograph available [1154].

TABLE 3.213 PZC/IEP of Hydrous Aluminum Oxide Obtained from Sulfate Description

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis, van Gils cell Electrophoresis, van Gils cell

7 9.3 9.4

[1152]

Deionized Base-washed 25

iep

[1153] [1154]

3.1.1.3.2.3 Recipe from [1155] Properties: Amorphous, specific surface area 392 m2/g (glycerol), XRD pattern available [1156].

TABLE 3.214 PZC/IEP of Hydrous Aluminum Oxide Obtained According to Recipe from [1155] Electrolyte

T

Method

0.01–1 M NaNO3

25

cip

a

Instrument

pH0

Reference

9a

[1156]

Only value, data points not reported.

3.1.1.4 Aluminum Hydroxide PZCs/IEPs of aluminum hydroxides (nominally Al(OH)3) are presented in Tables 3.215 through 3.263. 3.1.1.4.1 Gibbsite PZCs/IEPs of gibbsites are reviewed in [752]. 3.1.1.4.1.1 Commercial 3.1.1.4.1.1.1 Gibbsites from Alcoa 3.1.1.4.1.1.1.1 C-31 Properties: Gibbsite [1157–1159], 100 ppm SiO2, 40 ppm Fe2O3, 0.15% Na2O [1159], BET specific surface area 0.1 m2/g [1157,1158], 25 m2/g (ground to 310 nm) [1159], nominal particle size 50 μm [1159], average particle size 63 mm [1157].

178

Surface Charging and Points of Zero Charge

TABLE 3.215 PZC/IEP of C-31 from Alcoa Description Ground, washed

a

Electrolyte

T

0.0001–0.01 M NaCl

Method Titration iep

Instrument

pH0

Reference

a

Rank Brothers Mark II, Malvern Zetasizer IIc

9.2

[1159]

Only value, data points not reported; a maximum in sedimentation rate at pH 10.

3.1.1.4.1.1.1.2

Hydral 705

TABLE 3.216 PZC/IEP of Hydral 705 from Alcoa Electrolyte

T

Method

Instrument

pH0

Reference

25

iep

Electrophoresis

8.9

[1160]

3.1.1.4.1.1.1.3 Hydral 710 Properties: Gibbsite [1161,1162], impurities: Si 0.02%, Fe 0.01%, Na 0.33% (manufacturer) [1162], 400 ppm SiO2, 0.45% Na2O, 100 ppm Fe2O3 [1159], BET specific surface area 7.2 m2/g [1159], ethylene glycol surface area 8.3 m2/g [1162], specific surface area 6–8 m2/g [1161], particle diameter: 80% in the range 2–4.5 μm [1162], d32 = 620 nm [1159], median particle size 1 mm [1161].

TABLE 3.217 PZC/IEP of Hydral 710 from Alcoa Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaCl 0.0001–0.01 M NaCl

25

iep Titration iep

Acoustosizer Rank Brothers Mark II, Malvern Zetasizer IIc

9.1 10.4a

[1161] [1159]

a

Roughly matches maximum in yield stress of a 17% (by mass) dispersion.

3.1.1.4.1.1.1.4 Gibbsite from Alcoa, Type Unknown See also Section 3.1.1.4.1.2.2. Properties: >95% gibbsite [1163], <0.006% Fe2O3, <0.07% SiO2, <0.42% Na [761], BET specific surface area 5.9 m2/g [1164], 11.2 m2/g [761], specific surface area 13 m2/g [1163,1165].

179

Compilation of PZCs/IEPs

TABLE 3.218 PZC/IEP of Unidentified Gibbsite from Alcoa Description

Electrolyte 0.001–0.1 M NaCl 0.001–0.1 M NaNO3 NaClO4

T 25 25

As obtained a b

Method

Instrument

pH0 a

cip cip Titration titration

8.4 8.7a 8.9b 9.4b

Reference [1166] [1163] [1167] [761]

Extrapolated. Only value, data points not reported.

3.1.1.4.1.1.2 Gibbsite from Baker Properties: Specific surface area 0.9 m2/g [856].

TABLE 3.219 PZC/IEP of Gibbsite from Baker Description

Electrolyte

As received

0.001 M NaCl

T

Method

Instrument

iep

Pen Kem 3000

pH0 Reference 5

[856]

3.1.1.4.1.1.3 Martifin from Martinswerk Properties: Gibbsite, hexagonal particles, 2 mm across, diameter-to-thickness ratio 5:1–10:1, <1% of other crystalline aluminum (hydr)oxides than gibbsite, BET specific surface area 7.4 m2/g, impurities in washed material (mass%): Fe2O3 0.01, Na2O 0.36, SO3 0.03, organic C 0.007, SiO2 0.01, Cl 0.12, P2O5 0.002 [1168].

TABLE 3.220 PZC/IEP of Martifin from Martinswerk Description Base- and Acid-washed a

Electrolyte

T

Method

Instrument

pH0

Reference

0.004 M NaCl

25

iep

Electrophoresis

9.1a

[1168]

Only value, data points not reported.

3.1.1.4.1.1.5 Gibbsite from Prolabo 10 m2/g [989], 2.9 m2/g [813].

Properties: BET specific surface area

180

Surface Charging and Points of Zero Charge

TABLE 3.221 PZC/IEP of Gibbsite from Prolabo Electrolyte

T

Method

Instrument

Reference

a

Titration a

pH0 5.4

[989]

Only value, data points not reported.

3.1.1.4.1.1.6 Rehydragel HPA from Reheis No direct reference to gibbsite. TABLE 3.222 PZC/IEP of Rehydragel HPA from Reheis Electrolyte

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440

11.5

[1169]

3.1.1.4.1.1.7 Origin Unknown Properties: BET specific surface area 10 m2/g, crystallite size 227 nm, SEM image available [112]. TABLE 3.223 PZC/IEP of Gibbsite from Unknown Commercial Source Electrolyte

T

0.001–0.1 M KNO3 25 a

Method

Instrument

pH0

Reference

a

cip

6.2

[112]

Reported in text. Curves shown in Figure 6 merge at pH 6–8.

3.1.1.4.1.2 Synthetic 3.1.1.4.1.2.1 Hydrolysis of Inorganic Precursor at Room Temperature 3.1.1.4.1.2.1.1 Recipe from [1170] Metallic aluminum was dissolved in a plastic vessel in 3 M NaOH at 65°C. The solution was aged for 7 days at 25°C, then centrifuged, and the precipitate was washed with diluted HNO3 (pH 4) and with water. Properties: Gibbsite with 10–12% of bayerite [562], specific surface area 4 m2/g [562,1170], SEM images available [1170]. TABLE 3.224 PZC/IEP of Gibbsite Obtained According to Recipe from [1170] Electrolyte 0.001–0.1 M NaNO3 a

T 25

Method

Instrument

cip

Few data points near PZC, no clear CIP. Hysteresis.

pH0 a

8.2

Reference [562]

181

Compilation of PZCs/IEPs

3.1.1.4.1.2.1.2 Gibbsite from Chloride NH4OH was added to AlCl3 solution at 18°C, the precipitate was washed with cold water, and kept for 90 days in 1 M KOH, then washed with cold water and dried at 105°C.

TABLE 3.225 PZC/IEP of Gibbsite from Chloride Electrolyte

T

NaOH + HCl a

Method

Instrument

iep

Electrophoresis

pH0 Reference 5.3a

[225]

Arbitrary interpolation.

3.1.1.4.1.2.1.3 Gibbsite from Na3AlO3 This was prepared by aging of a Na3AlO3 solution of specific density of 1150 kg/m3. The precipitate was washed, dialyzed, and dried at 105°C. Leaching of silicate from the bottle might have resulted in a silica-containing precipitate (comment by the present author).

TABLE 3.226 PZC/IEP of Gibbsite from Na3AlO3 Electrolyte NaOH + HCl a

T

Method

Instrument

iep

Electrophoresis

pH0 Reference 4.9a

[52]

Only IEP reported (no experimental data points).

3.1.1.4.1.2.1.4 Recipes from [1171] Gastuche and Herbillon [1171] studied the crystallization of aluminum hydroxide precipitates obtained under a broad range of conditions. The general scheme consists of precipitation by addition of 6 M HCl to Na3AlO3 (6.5 g Al/dm3) at pH 8 or by addition of 4 M NaOH to AlCl3 (6.5 g Al/ dm3) at pH 4.5 or 6.5, followed by aging in mother liquor for different times and at different temperatures, dialysis and aging in deionized water, and drying for 1 day at 105°C. Specific surface areas, water contents, crystalline forms, and TEM images of samples prepared at different conditions are reported in [1171]. Recipe from [1171] cited in [530]: 0.33 M AlCl3 was slowly neutralized with 1 M NaOH to pH 4.5. The dispersion was dialyzed for 28 days at 70°C. It was then flocculated at pH 8 in 1 M NaCl and dialyzed again. The dispersion was stored at 4°C for 5 years. Recipe from [1171] cited in [1172]: 1 M AlCl3 was slowly neutralized with 4 M NaOH to pH 4.6. The dispersion was aged for 2 h at 40°C, then dialyzed for >28 days at 50°C. It was then aged for 9 months. Recipe from [1171] cited in [557]: 1 M Al(NO3)3 was titrated to pH 4.5 with 4 M NaOH in a plastic vessel under nitrogen. It was then dialyzed under different

182

Surface Charging and Points of Zero Charge

conditions: GH for 3–4 weeks (solution refreshed daily) against water at 70°C, GL for 8 weeks (solution refreshed daily) against water at 4°C, and then for 2 months at 70°C. Properties: Gibbsite [557,1173], BET specific surface area 29.8 m2/g [1172], 19.8 2 m /g [446,530], 18 and 40.3 m2/g (GH), 40.8 m2/g (GL) [557], specific surface area from AFM 53 m2/g (non-aged material) [1172] specific surface areas obtained by electron microscopy are available [557], 500 nm in diameter [446], diameter 202 nm, thickness 8.5 nm [1172], plates 250 nm in diameter, 9 nm thick [1174], size distribution available [530], hexagonal platelets [1172], TEM image available [530,1173].

TABLE 3.227 PZC/IEP of Gibbsite Obtained According to Recipes from [1171] Code

GH GL a b

Electrolyte

T

Method

Instrument

pH0

Reference

0.02, 0.1 M NaCl 0.1 M NaCl 0.05–0.5 M NaCl 0.005–0.5 M NaCl 0.005, 0.1 M NaNO3

25

Intersection iep cip cip Intersection

Malvern Zetasizer 4

9 10 10a 10b 10 (merge) 10 (merge)

[1172]

21 20 20

[446] [530] [557]

Only a few data points for 0.5 M NaCl are reported. Extrapolated.

3.1.1.4.1.2.1.5 Precipitation, Recipe from Reference 13 of [1120] Properties: g-Al(OH)3 or bayerite, particle size 10–20 nm, BET specific surface area 320 m2/g [1120].

TABLE 3.228 PZC/IEP of g-Al(OH)3 or Bayerite Obtained by Precipitation According to Recipe from Reference 13 in [1120] Electrolyte KNO3

a

T

Method

Instrument

pH0

Reference

Titration iep

Malvern Zetasizer 4

8.3 9

[1120]a

Only value, data points not reported.

3.1.1.4.1.2.1.6 Recipe from [1175] 4 M NaOH was slowly added to 1 M AlCl3 until pH 4.6. The gel was heated at 40°C for 2 h, then dialyzed for 36 days. Properties: Gibbsite [1175,1176], chiefly gibbsite, bayerite as a impurity [1177,1178], BET specific surface area 48 m2/g [1179], 56.5 m2/g [866], single point BET specific surface area 32.9 m2/g [1177], 45 m2/g [1176], 66.5 m2/g [1178],

183

Compilation of PZCs/IEPs

56.5 m2/g [870], specific surface area 31 m2/g [1181], 47 m2/g [1175] (dialyzed for 23 days at 60°C) 47 and 58 m2/g (two samples) [1180], 56.5 m2/g [866], hexagonal shapes, side of 130 nm [1175], hexagonal plates [1179].

TABLE 3.229 PZC/IEP of Gibbsite Obtained According to Recipe from [1175] Description

47 58 m2/g

a b

Method

Instrument

pH0

0.01 M NaCl

Electrolyte

T

iep

Zeta-Meter 3.0

9.4

0.01–1 M NaCl

cip

0.001 M NaCl 0.01–1 M NaNO3 20 0.001 M NaCl

iep cip iep iep

9.5 7.8 Zeta-Meter 3.0 9.6 9.8 Zeta-Meter 3.0 9.8 Electrophoresis 10

Reference [866] [870]a [1180]a,b [1177a,1178] [1179]b [1176] [1182]

Only value, data points not reported. No direct reference to the recipe from [1175].

3.1.1.4.1.2.2 C-730 (Probably from Alcoa [1183]) Properties: Wellcrystallized gibbsite, specific surface area 10 m2/g [1183], single point BET specific surface area 7.8 m2/g [450].

TABLE 3.230 PZC/IEP of C-730 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

9

[450]

0.01 M NaCl

3.1.1.4.1.3

Natural Gibbsites

TABLE 3.231 PZC/IEP of Natural Gibbsites Location Brazil Steinbach New Caledonia a

Electrolyte NaOH + HClO4 NaOH + HCl

T

Method iep iep

Instrument

pH0

Zeta-Meter <2.5 if any Electrophoresis 4.8a 5.2a

Arbitrary interpolation; the samples were ground, dialyzed, and dried.

Reference [104] [225]

184

Surface Charging and Points of Zero Charge

3.1.1.4.1.4

Gibbsite, Origin Unknown

TABLE 3.232 PZC/IEP of Gibbsite from Unknown Sources Description

Electrolyte

T

Method

Instrument

pH iep

Streaming potential

HCl + NaOH Original Calcined at 200°C a

pH0

Reference

5.7 3.8 5.1

[1144]a [1083]

Only acidity constants reported, no data points.

3.1.1.4.2 Bayerite 3.1.1.4.2.1 From Nitrate 0.1 M Al(NO3)3 was alkalized (OH:Al ratio 6:1), then titrated to pH 8 with HNO3 at 70°C in a plastic vessel under nitrogen. The precipitate was aged in the mother liquid at room temperature overnight, then washed. Properties: Bayerite, BET specific surface area 13.1 m2/g [557].

TABLE 3.233 PZC/IEP of Bayerite Obtained from Nitrate Electrolyte

T

0.005, 0.1 M NaNO3

Method

Instrument

Intersection

pH0

Reference

9

[557]

3.1.1.4.2.2 From Chloride and Ammonia 820 cm3 of 2 M ammonia were mixed with 200 cm3 of solution containing 50 g of AlCl3. Properties: Well-crystallized bayerite, lauric acid adsorption specific surface area 27.9 m2/g [1149].

TABLE 3.234 PZC/IEP of Bayerite Obtained from Chloride and Ammonia Electrolyte 0.001 M KNO3

T

Method Mass titration

Instrument

pH0 6.5

Reference [1149]

3.1.1.4.2.3 From Chloride and Ammonia at 70°C 820 cm3 of 2 M CO2-free NH4OH was added to a solution of 50 g of AlCl3 in 200 cm3 of water at 70°C. The precipitate was washed, dialyzed, and dried at 105°C.

185

Compilation of PZCs/IEPs

TABLE 3.235 PZC/IEP of Bayerite Obtained from Chloride and Ammonia at 70°C Electrolyte

T

Method

NaOH + HCl a

Instrument

iep

pH0 a

Electrophoresis

7.5

Reference [52]

Only IEP reported (no experimental data points).

3.1.1.4.2.4 From Chloride and NaOH at pH 11 0.1 M AlCl3 was adjusted to pH 11 by slow addition of NaOH under stirring. It was aged under stirring for 10 min at room temperature and heated at 50°C for different times. Properties: TEM image, FTIR spectra available, the sample heated for 2 h contains boehmite (20%), and gibbsite (a few%) [1128]. TABLE 3.236 PZC/IEP of Bayerite Obtained from Chloride and NaOH at pH 11 Time of Heating 2h 1d 7d

Electrolyte

T

Method

HCl + NaOH

iep

Instrument

pH0

Reference

Pen Kem S3000

8.5 9.1 9.3

[1128]

3.1.1.4.2.5 From Chloride and NaOH 0.5 M AlCl3 was titrated at 2 cm3/min with 0.5 M NaOH to pH 7, aged for 1 d, washed, and stored in a polypropylene container. Properties: IR spectrum available [1184]. TABLE 3.237 PZC/IEP of Bayerite Obtained from Chloride and NaOH at pH 7 Electrolyte

T

Method

0.01–0.2 M KCl

Instrument

cip

pH0

Reference

9.7

[1184]

3.1.1.4.2.6 Hydrolysis of Purified Al Ethoxide TABLE 3.238 PZC/IEP of Bayerite Obtained by Hydrolysis of Aluminum Ethoxide Description Washed, aged

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

9.3

[1088]

186

Surface Charging and Points of Zero Charge

3.1.1.4.2.7 From Isopropoxide Properties: bayerite + pseudoboehmite, low crystallinity [1185,1186], BET specific surface area 231 m2/g [1186], 197.2 m2/g [1185].

TABLE 3.239 PZC/IEP of Bayerite Obtained from Aluminum Isopropoxide Electrolyte

T

Method

Instrument

pH0

Titration a

Reference

a

9.3

[1185,1186]

Only value reported, no data points.

3.1.1.4.2.8 From Na3AlO3 CO2 was passed through Na3AlO3 solution of specific density of 1150 kg m- 3. The temperature is not specified, but very likely it was 70°C. The precipitate was washed, dialyzed, and dried at 105°C.

TABLE 3.240 PZC/IEP of Bayerite Obtained from Na3AlO3 Electrolyte

T

Method

NaOH + HCl a

iep

Instrument Electrophoresis

pH0 a

5.4

Reference [52]

Only IEP reported (no experimental data points).

3.1.1.4.2.9 Other Properties: Specific surface area 3 m2/g [1140].

TABLE 3.241 PZC/IEP of Other Bayerites Recipe

Electrolyte

Aging of amorphous hydroxide [1139]a

NaOH

a

1 M KNO3

T

25

Method

Instrument

pH0

Reference

iep

Electrophoresis

9.2

[1074,1142]

6.6

[1140]

pH

Al amalgam was treated with water at 25°C for 89 h.

187

Compilation of PZCs/IEPs

3.1.1.4.2.10 Bayerite, Origin Unknown TABLE 3.242 PZC/IEP of Bayerite from Unknown Source Electrolyte HCl + NaOH a

T

Method

Instrument

pH0

Reference

a

pH

5.5

[1144]

Only acidity constants reported, no data points.

3.1.1.4.3 Synthetic Amorphous Al(OH)3 3.1.1.4.3.1 Precipitated from Inorganic Precursor at Room Temperature 3.1.1.4.3.1.1 From Nitrate at pH 7 3.1.1.4.3.1.1.1 Recipe from [1187] 1 M Al(NO3)3 was pumped into a beaker held at pH 7. The precipitate was aged for 30 min, freeze-dried, water-washed, and freeze-dried again. TABLE 3.243 PZC/IEP of Amorphous Al(OH)3 Obtained by Recipe from [1187] Electrolyte

T

0.01 M NaNO3 a

Method

Instrument

Salt addition

pH0

Reference

9a

[1187]

Only value reported, no data points.

3.1.1.4.3.1.1.2 Recipe from [1151] Al(NO3)3 solution was neutralized to pH 7 with NaOH in a polypropylene beaker within 15 min. The dispersion was aged at pH 7 for 1 h, and diluted before use. TABLE 3.244 PZC/IEP of Amorphous Al(OH)3 Obtained by Recipe from [1151] Electrolyte NaNO3 a b

T

Method Salt addition

Only value reported, no data points. Second sign reversal at pH 10.2.

Instrument

pH0

Reference

1 h equilibration

9.4

[1188a,1151b]

188

Surface Charging and Points of Zero Charge

3.1.1.4.3.1.2 From Nitrate and 0.5 M NaOH 0.5 M NaOH was added dropwise to a solution containing 12 g Al/dm 3. The precipitate was aged for 40 min. TABLE 3.245 PZC/IEP of Amorphous Al(OH)3 Obtained from Nitrate and 0.5 M NaOH Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

8.5

[1189]

0.3 M NH4NO3

3.1.1.4.3.1.3 Recipe from [577] Stoichiometric amount of NaOH was added dropwise to 0.02 M Al(NO3)3, and the dispersion was aged for 4 h. Properties: Amorphous (XRD results available) [577], BET specific surface area 411 m2/g [577,1190], mean diameter 30 μm [577], 7.5 μm [1190], SEM image available [577,1190]. Table 3.246 PZC/IEP of Amorphous Al(OH)3 Obtained According to the Recipe from [577] Electrolyte

T

Method

0.006–1.2 M NaNO3

25 25

Titration cip

a

Instrument

pH0

Reference

8.6a 8.9

[1190] [577]

Only value, data points not reported.

3.1.1.4.3.1.4 From Nitrate at pH 8 A solution 0.3 M in HNO3 and 0.1 M in Al(NO3)3 was adjusted to pH 8 by rapid addition of 3 M NaOH. The pH was maintained at 8 for 2 h. Properties: BET specific surface area 41 m2/g [1191,1192]. TABLE 3.247 PZC/IEP of Amorphous Al(OH)3 Obtained from Nitrate at pH 8 Electrolyte

T

Method iep

a

Instrument Electrophoresis

pH0 a

8.9

Reference [1191,1192]

Only value reported, no data points

3.1.1.4.3.1.5 From Chloride and 2 M NaOH 400 cm3 of 2 M NaOH was added at 50 cm3/min with stirring to 200 cm3 of 1.5 M AlCl3. The precipitate was washed with water. Properties: Amorphous, single point BET specific surface area 128 m2/g [450, 1193].

189

Compilation of PZCs/IEPs

TABLE 3.248 PZC/IEP of Amorphous Al(OH)3 Obtained from Chloride and 2 M NaOH Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

9.3

[450,1193]

0.01 M or 0.1 M NaCl

3.1.1.4.3.1.6 From Chloride and 1 M KOH 0.5 M AlCl3 was titrated at 1 cm3/min with 1 M KOH until pH 9.5, allowed to stand for 1 d, and washed.

TABLE 3.249 PZC/IEP of Amorphous Al(OH)3 Obtained from Chloride and 1 M KOH Electrolyte

T

Method

0.0005–0.6 M KCl

Instrument

cip

pH0

Reference

9.6

[1194]

3.1.1.4.3.1.7 From Chloride and 6 M NaOH 1 M AlCl3 was adjusted to pH 8.3 with 6 M NaOH under nitrogen. The dispersion was aged for 2 h.

TABLE 3.250 PZC/IEP of Amorphous Al(OH)3 Obtained from Chloride and 6 M NaOH Electrolyte

a

T

Method

Instrument

pH0

Reference

25

iep

Electrophoresis

9a

[1195]

Only positive branch reported.

3.1.1.4.3.1.8 From Chloride, Recipe from [1196] 0.0016 M AlCl3 + NaOH (various amounts), aged for 15 min.

TABLE 3.251 PZC/IEP of Amorphous Al(OH)3 Obtained from Chloride According to Recipe from [1196] Electrolyte NaCl

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

9.1–9.2

[1196]

190

Surface Charging and Points of Zero Charge

3.1.1.4.3.1.9 From Chloride at pH 7 AlCl3 solution was slowly titrated to pH 7 with 1 M NaOH. This pH was maintained for 7 d. Dispersion was then dialyzed until Cl-free and dried at 40°C. The hydration–drying cycle was repeated 9 times. Properties: Specific surface area 49 m2/g [598].

TABLE 3.252 PZC/IEP of Amorphous Al(OH)3 Obtained from Chloride at pH 7 Electrolyte

T

Method

0.001–0.1 M NaCl

Instrument

cip

pH0

Reference

10.2

[598]

3.1.1.4.3.1.10 From Chloride Recipe from Ref. [1197] Precipitates were obtained by hydrolysis of 0.1 M AlCl3 (NaOH:Al ratio 2 or 2.5), and dilution at neutral pH to a total Al concentration of 0.002 M.

TABLE 3.253 PZC/IEP of Amorphous Al(OH)3 Obtained from Chloride According to Recipe from [1197] NaOH:Al

Electrolyte

T

Method

Instrument

pH0

Reference

2 2.5

0–1 M NaCl

25

cip/iep

Laser Zee Meter 501 Pen Kem

8.4/8.4 8.2/8.2

[1197,1198]

3.1.1.4.3.1.11 From Chloride and Ammonia Ammonia was added dropwise to AlCl3 solution to adjust the pH to 9. Properties: Amorphous (XRD) with traces of pseudo-boehmite and bayerite[1199], BET specific surface area 182 m2/g [1199,1201,1202].

TABLE 3.254 PZC/IEP of Amorphous Al(OH)3 Obtained from Chloride and Ammonia Electrolyte 0.01–1 M KCl a

T

Method cip

Instrument

pH0

Reference

9.4

[1199,1201–1203]a

Only value, no data points. Ref. [1203] reports also CIP of precipiated iron hydroxide and of hydrous silica.

191

Compilation of PZCs/IEPs

3.1.1.4.3.1.12 From Chloride and Ammonia, Dried at 200°C TABLE 3.255 PZC/IEP of Amorphous Al(OH)3 Obtained from Chloride and Ammonia, Dried at 200°C Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

20

iep

Electrophoresis

8.5

[1204]

3.1.1.4.3.1.13 Hydrolysis Products of Basic Aluminum Chloride Three different samples. TABLE 3.256 PZC/IEP of Hydrolysis Products of Basic Aluminum Chloride Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

10.2 10.5 >10.5

[1205]

3.1.1.4.3.1.14 From Sulfate A solution of 2.77 g of Al2(SO4)3·18H2O in 250 cm3 of water was mixed with the stoichiometric amount of 1 M NaOH under stirring. The dispersion was aged with stirring for 1 h, centrifuged, and washed. It was aged in aqueous dispersion for 6 d before use. Properties: Specific surface area (from arsenate and phosphate adsorption) 690 m2/g [229]. TABLE 3.257 PZC/IEP of Amorphous Al(OH)3 Obtained from Sulfate Electrolyte 0.01 M NaClO4 0.01 M NaClO4 a b

T 25

Method iep iep

Instrument Briggs electrophoresis cell Pen Kem 102

pH0 a

8.5 8.6a

Reference [1206] [229]b

Arbitrary interpolation. No direct reference to the above recipe.

3.1.1.4.3.1.15 Aluminum Gel, Recipe from [1207] Al wire was dissolved in concentrated HClO4. The solution was adjusted to pH 7 with 0.5 M NaOH. Then NaClO4 and water were added to produce 1 M NaClO4 in the supernatant. Properties: BET specific surface area 209.9 m2/g [866] (single point), 292 m2/g (original), 242 m2/g (washed and aged for 1 month in water) [1207].

192

Surface Charging and Points of Zero Charge

TABLE 3.258 PZC/IEP of Al Gel Obtained According to Recipe from [1207] Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

9.3

[866]a

0.01 M NaCl a

Termed “amorphous oxide” in [866].

3.1.1.4.3.2 Precipitated at Elevated Temperature Ammonia was added to 0.01 M Al(NO3)3 at 80–90°C. The precipitate was washed and electrodialyzed. TABLE 3.259 PZC/IEP of Amorphous Al(OH)3 Precipitated at Elevated Temperature Electrolyte 0.01 M NaNO3

T

Method

Instrument

pH0

Reference

22–25

iep

Electrophoresis

8.5

[1208]

3.1.1.4.3.3 Origin Unknown TABLE 3.260 PZC/IEP of Amorphous Al(OH)3 from Unspecified Source Electrolyte NaOH a

T

Method

Instrument

pH0

Reference

20

iep

Electrophoresis

9.4

[1074a,1142]

Two recipes are reported.

3.1.1.4.4 Al(OH)3 Structure Unknown 3.1.1.4.4.1 Recipe from [679] 1.8 M Al(NO3)3 in 1 M HNO3 was diluted 1:6 with water and adjusted to a different pH with 2 M NaOH within 30 min. Then the precipitate was washed with water. TABLE 3.261 PZC/IEP of Al(OH)3 Obtained According to Recipe from [679] Electrolyte

T

0.01–1 M NaCl a

Nonstandard method.

Method cip

a

Instrument

pH0

Reference

8.3

[679]

193

Compilation of PZCs/IEPs

3.1.1.4.4.2 Precipitated from 0.001 M Salt, Filtered, and Washed with Water TABLE 3.262 PZC/IEP of Precipitate Obtained from 0.001 M Salt Electrolyte KOH + HNO3

T

Method

Instrument

pH0

Reference

22

iep

Zeta-Meter

8.4

[370]

3.1.1.4.5 Al(OH)3 Origin and Structure Unknown

TABLE 3.263 PZC/IEP of Al(OH)3 of Unknown Origin and Structure Description

Electrolyte

T

Commercial, 75% Al2O3, 0.12% 0.02 M NH4NO3 TiO2, 0.008% SiO2, 209 m2/g 0.01–1 M KNO3 275 m2/g 3 m2/g (N2), 388 m2/g (H2O) 0.001 M KCl None 20

a

Method

pH0

Reference

pH

7.3

[1210]

cip

8 6.5 9.2 9.3

[45]a [1211] [1787]

9.4

[1212]a

iep iep

Instrument

Delsa 440 Malvern Zetasizer 3

Only value, data points not reported.

3.1.2

BERYLLIUM (HYDR)OXIDES

Beryllium has only one stable oxidation state (+2) within the electrochemical window of water, but it forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. PZCs/IEPs of beryllium (hydr)oxides are presented in Tables 3.264 through 3.266. 3.1.2.1

BeO Commercial, Origin Unknown, Water-Washed, and Dried at 110°C TABLE 3.264 PZC/IEP of Commercial BeO Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M KCl

25

iep

Rank Mark II

7.1

[1213]

194

3.1.2.2

Surface Charging and Points of Zero Charge

Hydrous BeO, Origin Unknown

TABLE 3.265 PZC/IEP of Hydrous BeO of Unknown Origin Electrolyte T

Method iep

Instrument

pH0

Reference

Electro-osmosis

10.2

[1214]

3.1.2.3 Hydrolysis Products of Carrier-Free 7BeCl2

TABLE 3.266 PZC/IEP of Hydrolysis Products of Carrier-Free 7BeCl2 Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaNO3

25

iep Coagulation

Home-made

11

[1215]

3.1.3 Bi2O3 Bismuth has only one stable oxidation state (+3) within the electrochemical window of water, but it forms several relatively stable oxides, which differ in their crystallographic structure. PZCs/IEPs of Bi2O3 are presented in Tables 3.267 and 3.268. 3.1.3.1 Synthetic 0.1 M Bi(NO3)3 in 1 M HNO3 was mixed with excess of NaOH at 97°C. The precipitate was digested for 2 h at hot conditions, aged for 1 d at room temperature, water-washed, dried, washed, and dried again. Properties: XRD results available, specific surface area 2 m2/g [1216].

TABLE 3.267 PZC/IEP of Synthetic Bi2O3 Electrolyte 0.1 M NaNO3

a

T

Method pH Mass titration

Only value, data points not reported.

Instrument

pH0

Reference

6.8 6.8

[1216]a

195

Compilation of PZCs/IEPs

3.1.3.2 Origin Unknown

TABLE 3.268 PZC/IEP of Bi2O3 of Unknown Origin Description

Electrolyte

1.8 m2/g

0.01 M KCl

a

3.1.4

T

Method

Instrument

pH0

Reference

iep

Electro-osmosis

9.4

[1103a,1217]

Only value reported, no data points.

Ca(OH)2

Ca(OH)2 is the only compound of calcium with oxygen and hydrogen that is stable in contact with water, and it shows substantial solubility and high affinity to atmospheric CO2. The IEP of Ca(OH)2 of unknown origin is presented in Table 3.269.

TABLE 3.269 PZC/IEP of Ca(OH)2 Electrolyte

3.1.5

T

Method

Instrument pH0 Reference

iep

12

[1218]

CADMIUM (HYDR)OXIDES

Cadmium has only one stable oxidation state (+2) within the electrochemical window of water, but it forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. PZCs/IEPs of cadmium (hydr)oxides are presented in Tables 3.270 through 3.275. 3.1.5.1 Product of Hydrolysis of 10-7 M Cd Salt

TABLE 3.270 PZC/IEP of Product of Hydrolysis of 10 −7 M Cd Salt Description 2 h aged 7 d aged

Electrolyte

T

Method

Instrument

pH0

Reference

None

22

iep Coagulation

Home-made

11.5 10.5

[1219]

196

3.1.5.2

Surface Charging and Points of Zero Charge

CdO

3.1.5.2.1 Commercial from POCh Properties: BET specific surface area 2.4 m2/g (original), 7.3 m3/g (aged in 0.1 M NaClO4), the original oxide is transformed into hexagonal hydroxide [152]. TABLE 3.271 PZC/IEP of Commercial CdO Electrolyte

T

Method

0.001–0.1 M NaClO4

25

cip

Instrument

pH0

Reference

10.1

[152]

3.1.5.2.2 Prepared by Ignition of Cd(OH)2 Properties: Structure confirmed by XRD, contains 5% of Cd3SiO5 · 2H2O [1088]. TABLE 3.272 PZC/IEP of CdO Prepared by Ignition of Cd(OH)2 Electrolyte

3.1.5.2.3

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

10.4

[1088]

Origin Unknown

TABLE 3.273 PZC/IEP of CdO of Unknown Origin Electrolyte

T Method

0.01 M KCl a

iep

Instrument

pH0

Reference

Electro-osmosis

10.6

[1102a,1103a,1217]

Only value reported, no data points.

3.1.5.3 Hydrous CdO or Cd(OH)2 CdCl2 + KOH, water-washed, aged. TABLE 3.274 PZC/IEP of Hydrous CdO or Cd(OH)2 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

>10.5

[1088]

197

Compilation of PZCs/IEPs

3.1.5.4

Cd(OH)2, Precipitated

TABLE 3.275 PZC/IEP of Precipitated Cd(OH)2 Electrolyte

T Method

0.001 M NaNO3 0.05 M NaClO4 a

3.1.6

Instrument

pH0

Delsa 440 10.3a Pen Kem Laser Zee Meter 500 11

iep iep

Reference [1220] [1221]

Precipitated from 0.005 M Cd(NO3)2 with stoichiometric amount of NaOH. Not washed. IEP from figures and text. IEP at pH 10 reported in abstract.

CERIUM (HYDR)OXIDES

Cerium forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation (+3 to +4), degree of hydration, and crystallographic structure. Nominal degree of oxidation and hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of oxidation and hydration. PZCs/IEPs of cerium (hydr)oxides are presented in Tables 3.276 through 3.291. 3.1.6.1 CeO2 3.1.6.1.1 Commercial 3.1.6.1.1.1 CeO2 from Aldrich 3.1.6.1.1.1.1 90% and 99.9% Pure Properties: 90% pure: particle size 600 nm, 99.9% pure: particle size 450 nm, BET specific surface area 9.8 m2/g [1222]. TABLE 3.276 PZC/IEP of 90% and 99.9% Pure CeO2 from Aldrich Purity

Electrolyte

90% 0.01 M NaNO3 99.9%

T

Method

Instrument

pH0 Reference

24

iep

Pen Kem Zee Meter 501

6 6

[1222]

3.1.6.1.1.1.2 CeO2 from Aldrich, Type Unknown Properties: BET specific surface area 17.9 m2/g, size of crystallites 95 nm [1223]. TABLE 3.277 PZC/IEP of Unspecified CeO2 from Aldrich Electrolyte 0.005–0.3 M KNO3

T

Method Instrument pH0 cip

8

Reference [1223]

198

Surface Charging and Points of Zero Charge

3.1.6.1.1.2 Tizox from Dervey

Properties: 99.9% pure [1224].

TABLE 3.278 PZC/IEP of Tizox from Dervey Electrolyte

T

None

a

Room

Method

Instrument

iep

DT-1200 Malvern Zetasizer 2000

pH0 a

6

Reference [1224]

IEP shifts to high pH in 0.1 M NaCl. Viscosity and yield stress in 18 mass% dispersions peak at IEP.

3.1.6.1.1.3 CeO2 from Shin-etsu

Properties: 99.9% pure [1041].

TABLE 3.279 PZC/IEP of CeO2 from Shin-etsu Description

Electrolyte

T

0.1% by volume KOH + HCl

Method

Instrument

iep

Pen Kem 7000

pH0 Reference 6.7

[1041]

3.1.6.1.1.4 CeO2 from Sigma-Aldrich Properties: Cerianite (cubic), average size 157 nm, XRD pattern, particle size distribution, SEM image available [987]. TABLE 3.280 PZC/IEP of CeO2 from Sigma-Aldrich Electrolyte

T

Method

Instrument

pH0

Reference

None

25

iep

Malvern NanoZS

>7

[987]

3.1.6.1.2 Synthetic 3.1.6.1.2.1 Hydrolysis of Ce(NO3)3 at Room Temperature was washed and treated with HNO3. Properties: XRD pattern available [1225].

The precipitate

TABLE 3.281 PZC/IEP of CeO2 Obtained by Hydrolysis of Ce(NO3)3 at Room Temperature Electrolyte

T

Method iep

a

Instrument Electrophoresis

Based on arbitrary interpolation (data points for pH 4.8 and 6.5).

pH0 a

6.2

Reference [1225]

199

Compilation of PZCs/IEPs

3.1.6.1.2.2 Hydrolysis of Inorganic Precursors at Elevated Temperature 3.1.6.1.2.2.1 From Sulfate, Recipe from [1226] A solution of Ce(SO4)2 and H2SO4 was aged at 90°C. A: water-washed B: A NaOH-washed C: B calcined at 600°C for 2 h Properties: Face-centered cubic structure, TEM and SEM images available, spheres 100 nm in diameter, BET specific surface area 19.3 m2/g. Different Ce(SO4)2 and H2SO4 concentrations produce different particle size and morphology. Ce(NH4)2(NO3)6 was also used as Ce precursor [1226].

TABLE 3.282 PZC/IEP of CeO2 Obtained from Sulfate According to Recipe from [1226] Description A B C

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

5.9 6.1 5.2

[1226]

0.001 M NaNO3

3.1.6.1.2.2.2 From Sulfate, Recipe from [321] Ammonia was added to Ce(SO4)2 solution, and the precipitate was boiled under reflux for 10 d. Properties: BET specific surface area 196 m2/g [321].

TABLE 3.283 PZC/IEP of CeO2 Obtained from Sulfate According to Recipe from [321] Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaNO3

35

cip iep

Electrophoresis

7.6

[321]

3.1.6.1.2.2.3 Thermal Hydrolysis of 0.2 M (NH4)2Ce(NO3)6 at 240°C for 1 day

TABLE 3.284 PZC/IEP of CeO2 Obtained from Nitrate at 240°C Electrolyte

T

Method

Instrument

pH0

Reference

iep

DT-1200

11.2

[1227]

200

Surface Charging and Points of Zero Charge

3.1.6.1.2.3 Calcination of Salts 3.1.6.1.2.3.1 Calcination of CeOHCO3 at 450°C for 1 Minute Properties: Fluorite structure, TEM image available, spherical particles, mean size 245 nm, BET specific surface area 33.4 m2/g [338].

TABLE 3.285 PZC/IEP of CeO2 Obtained by Calcination of Basic Carbonate Electrolyte

T

0.01 M NaCl

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer

7.3

[338]

3.1.6.1.2.3.2 Calcination of Ammonium Cerium(IV) Nitrate at 800°C for 6 Hours Properties: Specific surface area 12 m2/g [14].

TABLE 3.286 PZC/IEP of CeO2 Obtained by Calcination of Ammonium Cerium(IV) Nitrate Electrolyte

T

Method

Instrument

Mass titration

0.1 M NaNO3

pH0

Reference

7.1

[14]

3.1.6.1.2.3.3 Calcination of Hydrolysis Product of Chloride in Oxygen CeCl3 was dissolved in 1:1 HCl, heated at <100°C to dryness, and calcined at 550°C in oxygen for 1 h. The solid was milled, and calcined again for 1 h; then milled, and calcined again for 1 h. It was then washed in water and dried at 80°C. Properties: XRD results available, BET specific surface area 16.6 m2/g, size of crystallites 100 nm [1223].

TABLE 3.287 PZC/IEP of CeO2 Obtained by Calcination of Hydrolysis Product of Chloride in Oxygen Electrolyte 0.005–0.3 M KNO3

T

Method cip

Instrument

pH0

Reference

8.1

[1223]

201

Compilation of PZCs/IEPs

3.1.6.1.2.3.4 Calcination of CeO2 · 0.5 HNO3 · 4H2O Nanoparticles Properties: Specific surface area 40 m2/g [593].

TABLE 3.288 PZC/IEP of Product of Calcination of CeO2 ⋅ 0.5 HNO3 ⋅ 4H2O Nanoparticles Electrolyte

T

Method

0.1–1 M NaClO4

25

cip

Instrument

pH0

Reference

8.6

[593]

3.1.6.1.3 Origin Unknown

TABLE 3.289 PZC/IEP of CeO2 of Unknown Origin Electrolyte

T

None HCl + NaOH 0.01 M KCl a

Method iep iep iep

Instrument

pH0

Reference

Brookhaven Delsa 440 SX Electro-osmosis

6 6.5 8.2

[1228] [719]a [1217]

Also IEP of silica and ceria-coated silica (detailed recipes reported).

3.1.6.2 Hydrous CeO2 Obtained from CeCl4 and NaOH.

TABLE 3.290 PZC/IEP of Hydrous CeO2 Obtained from CeCl4 and NaOH Electrolyte 0.02 M a

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.8

[1229]a

Only value, data points not reported. The same IEP is reported in [2226] for a precipitate termed hydroxide.

3.1.6.3 Nanoparticles CeO2 · 0.5HNO3 · 4H2O From Ce(NO3)4, recipe in [1230]. Properties: Specific surface area 400 m2/g, 5–7 nm in diameter, TEM image available [593]. A: allowed to equilibrate with neutral solution, then titrated B: allowed to equilibrate with basic solution, then titrated

202

Surface Charging and Points of Zero Charge

TABLE 3.291 PZC/IEP of Nanoparticles CeO2 · 0.5HNO3 · 4H2O Description A B

3.1.7

Electrolyte

T

Method

0.1–1 M NaClO4

25

cip

Instrument

pH0

Reference

10 8.4

[593]

COBALT (HYDR)OXIDES

Cobalt forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation (+2 to +3), degree of hydration, and crystallographic structure. Nominal degree of oxidation and hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of oxidation and hydration. PZCs/IEPs of cobalt (hydr)oxides are presented in Tables 3.292 through 3.305. 3.1.7.1 Co(OH)2 3.1.7.1.1 Hydrolysis of Perchlorate, Washed TABLE 3.292 PZC/IEP of Co(OH)2 Obtained from Perchlorate Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

25

iep

Zeta-Meter

11

[1231]

3.1.7.1.2 From CoCl2 and NaOH TABLE 3.293 PZC/IEP of Co(OH)2 Obtained from Chloride Electrolyte

T

0.01 M a

Method

Instrument

pH0

Reference

iep

Electrophoresis

11.4

[1229]a

Only value, data points not reported. The same IEP is reported in Ref. [2226] for a precipitate termed hydroxide.

3.1.7.1.3 Precipitated TABLE 3.294 PZC/IEP of Precipitated Co(OH)2 Electrolyte 0.002, 0.02 M NaCl

T

Method

Instrument

pH0

Reference

iep

Riddick-type cell

11.4

[1232]

203

Compilation of PZCs/IEPs

3.1.7.1.4 Origin Unknown Properties: Impurity level <0.1%, detailed analysis available, structure confirmed by XRD, BET specific surface area 16.8 m2/g [1233].

TABLE 3.295 PZC/IEP of Co(OH)2 of Unknown Origin Description Washed

a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.01 M KNO3

25

cip iep

Zeta-Meter

11.4 11.5

[1233]a

Also 40–80°C.

3.1.7.2 Co3O4 3.1.7.2.1

Commercial, Co3O4 from Ventron

TABLE 3.296 PZC/IEP of Commercial Co3O4 Description

Electrolyte

High purity

0.005–0.2 M KNO3 0.005–0.2 M KNO3

a

T

Method cip cip iep

Instrument

pH0

Reference

Mark II Rank Brothers

8.8 8.9 8.7

[1235]a [1235]a

Only value, no data points.

3.1.7.2.2 Synthetic 3.1.7.2.2.1 From Nitrate, Recipe from [1236] Co(NO3)2 solution in 2-propanol was dried at <100°C. It was then calcined for 1 h at 400°C in air, crushed, milled, and calcined again. Properties: BET specific surface area 9 m2/g [1236, 1237]. TABLE 3.297 PZC/IEP of Co3O4 Obtained According to Recipe from [1236] Description

Electrolyte

T

0.005–0.3 M KNO3

25

3 h at 400°C in oxygen 0.005–0.1 M KNO3 a

Only PZC, no data points.

25

Method Instrument

pH0

Reference

cip

7.2a

[1236]

cip

a

[1237]

7.6

204

Surface Charging and Points of Zero Charge

3.1.7.2.2.2 Calcination of Nitrate in a Stream of Oxygen at Different Temperatures Properties: Samples prepared at temperatures <500°C contain excessive oxygen (up to Co3O4.4) [1235].

TABLE 3.298 PZC/IEP of Co3O4 Obtained by Calcination of Nitrate in Oxygen Description

Electrolyte

T

a

Decomposed at (°C): 0.005–0.2 M KNO3 200–500 600 650 700 350, in nitrogen a

Method cip/iep

Instrument Mark II Rank Brothers

pH0

Reference [1235]

7.5/7.5 8.2/8.2 8.2/8.2 9.3 7.5/7.5

Data points available for sample decomposed at 300°C (only s0), and at 200°C (only z).

3.1.7.2.2.3 Calcination of Oxalate Oxalate was obtained from 1 M Co(NO3)2 and a 10% excess of oxalic acid, washed with water, and calcined at 600°C for 6 h, then at 800–1400°C for 6 h. The oxide was washed with water until constant conductivity. Not-crushed, crushed, and evacuated samples produce similar IEPs. Properties: Reduction to CoO at T > 1000°C [33].

Table 3.299 PZC/IEP of Co3O4 Obtained by Calcination of Oxalate Second Calcination Temperature (°C) None 800 1000 1200 1400 Evacuation at 800°C a

Electrolyte

T

0.001 M NaCl 25

Only value, no data points.

Method

Instrument

pH0

Reference

pHa

Streaming potential

7.9 8.4 10 10.5 10.6 10.5

[33]

205

Compilation of PZCs/IEPs

3.1.7.2.2.4 Hydrolysis of Acetate 0.01 M cobalt(ii) acetate was adjusted to pH 7.3 and aged at 100°C for 4 h. Precipitate was acid-washed. Properties: Cubic particles, TEM images available [1238]. TABLE 3.300 PZC/IEP of Co3O4 Obtained by Hydrolysis of Acetate Electrolyte

T

0.01 M KNO3

Method

Instrument

pH0

Reference

iep

Rank Brothers

5.5

[1238]

3.1.7.2.2.5 Thermal Decomposition of Basic (?) Carbonate in Oxygen Atmosphere for 12 Hours Properties: Structure confirmed by XRD; for specific surface area, see Table 3.301 [1239]. TABLE 3.301 PZC/IEP of Co3O4 Obtained by Thermal Decomposition of Carbonate Decomposition Temperature (°C) 200 (150 m2/g) 250 300 (90 m2/g) 350 400 500 600 700 (10 m2/g) 800 a

Electrolyte 0.005–0.12 M KNO3

T

Method cip/iepa

Instrument

pH0

Mark II 7.4/7.2 Rank Brothers 7.1/7.1 7.4/7.4 —/7.1 7.2/7.2 6.9/6.9 6.6/6.6 6.6/6.6 7.3/7.2

Reference [1239]

Data points available only for sample decomposed at 200°C.

3.1.7.2.2.6 Recipe from [1240] 0.125 M Co(NO3)2 was acidified with concentrated HNO3 (1 cm3 per 1 dm3 of solution), evaporated at 90°C, calcined at 250°C in air, and at 400°C in oxygen for 3 days. It was then quenched in liquid nitrogen. Properties: XRD pattern available [1240]. TABLE 3.302 PZC/IEP of Co3O4 Obtained According to Recipe from [1240] Electrolyte 1 M KNO3 a

T

Method pH

Only value, data points not reported.

Instrument

pH0

Reference

6.8

[1240]a

206

Surface Charging and Points of Zero Charge

3.1.7.2.3 Origin Unknown Properties: Impurity level <0.1%, detailed analysis available, structure confirmed by XRD, specific surface area 4.4 m2/g [1233].

TABLE 3.303 PZC/IEP of Co3O4 of Unknown Origin Description

Electrolyte

T

Method

Washed

0.001–1 M NaNO3

25

pH

Merge

5

[1241]

Active mass of Co3O4 electrode Washed

0.001–0.1 M KCl

iep

Streaming potential

7.2

[1242]

cipa iep

Zeta-Meter

11.4 11.4

[1233]

a

0.001–0.01 M KNO3

25

Instrument

pH0 Reference

Only value, data points not reported. Also 40–80°C.

3.1.7.3 Co2O3 Origin unknown. TABLE 3.304 PZC/IEP of Co2O3 Electrolyte

T

0.01 M KCl a

Method

Instrument

pH0

Reference

iep

Electro-osmosis

6.9

[1102a,1103a,1217]

Only value reported, no data points.

3.1.7.4 CoOOH Oxidation of b-Co(OH)2 in an ambient atmosphere. Properties: BET specific surface area 10.7 m2/g [1243].

TABLE 3.305 PZC/IEP of CoOOH Electrolyte 0.001 M KNO3

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.2

[1243]

207

Compilation of PZCs/IEPs

3.1.8

CHROMIUM (HYDR)OXIDES

Chromium at oxidation state +3 forms several sparingly soluble compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. Nominal degree of hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of hydration. Chromium also has stable compounds at oxidation state +6, but those compounds are beyond the scope of the present book, since they are water-soluble. PZCs/IEPs of chromium(iii) (hydr)oxides are presented in Tables 3.306 through 3.329. 3.1.8.1 Cr2O3 PZCs/IEPs of chromium oxide are compiled in [528]. 3.1.8.1.1 Commercial 3.1.8.1.1.1 Cr2O3 from Fluka Properties: BET specific surface area 4 m2/g, XRD and TGA results available [1244].

TABLE 3.306 PZC/IEP of Cr2O3 from Fluka Electrolyte

T

Method

0.001–0.1 M KCl

22

pH

a

Instrument

pH0

Reference

6.7a

[528,1244]

With KNO3, equilibrium pH decreased when salt concentration increased.

3.1.8.1.1.2 Amperit 704.1 from Stark, Fused Original and plasma-sprayed. Properties: Eskolaite, original and after spraying, XRD patterns available, specific surface area original 0.2 m2/g, after spraying 2.8 m2/g [1003].

TABLE 3.307 PZC/IEP of Amperit 704.1 from Stark Electrolyte Original Original, washed Sprayed Sprayed, washed

0.01 M NaCl

T

Method Mass titration

Instrument

pH0

Reference

4.7 5.4 4 5.5

[1003]

208

Surface Charging and Points of Zero Charge

3.1.8.1.1.3 Origin Unknown

TABLE 3.308 PZC/IEP of Cr2O3 of Unknown Origin Description

Electrolyte

Water-washed, and 0, 0.001 M KCl dried at 110°C 40 m2/g 0.001–0.1 M NaCl

1.2 m2/g

0.01 M KCl 0.001 M KNO3

Commercial, a

0.01 M KCl

a

T 25

25

Method

Instrument

pH0

Reference

iep

Rank Mark II

2.2

[1213]

Intersection iep

Electrophoresis

6.1 6.1 7 7.2 7.3

[1245] [1246]a [1103a,1217] [1247]a

7.9

[1248]

iep Titration

Electro-osmosis

iep

Electrophoresis

Only value, no data points.

3.1.8.1.2 Synthetic 3.1.8.1.2.1 Recipe from Ref. [1078] Nitrate was adjusted to pH 2 with HNO3, and then treated with excess of ammonia. The precipitate was washed with water, calcined at 600°C for 5 h, washed with water again, calcined at 600–1400°C for 3 h, and washed with water again. Properties: Rhombohedral Cr2O3-type structure [1077,1078], lattice spacing data available [1077], specific surface area available [1078].

TABLE 3.309 PZC/IEP of Cr2O3 Obtained According to Recipe from [1078] Second Calcination Temperature (°C)

Electrolyte

T

Method

Instrument

1200

0.001 M NaCl

25

iep

600 800 1000 1200 1400

0.001 M NaCl

25

iep

Streaming potential Streaming potential

pH0 Uncrushed/ Crushed 7 10.3/9.5 9 7.5/9.2 6.1 4.8/9

Reference [1077] [1078]

209

Compilation of PZCs/IEPs

3.1.8.1.2.2 Calcination of a-HCrO2 in Air for 4 Hours at 400°C Properties: specific surface area 31.4 m2/g [1243]. TABLE 3.310 PZC/IEP of Cr2O3 Obtained by Calcination of α-HCrO2 in Air for 4 h at 400°C Electrolyte

T

0.001 M KNO3 a

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.8a

[1243]

Only value, no data points.

3.1.8.1.2.3 Reduction of CrO2 in H2 for 2 Hours at 310°C Properties: amorphous, TEM image available [1243]. TABLE 3.311 PZC/IEP of Cr2O3 Obtained by Reduction of CrO2 in H2 for 2 h at 310°C Electrolyte

T

0.001 M KNO3 a

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.8a

[1243]

Only value, no data points.

3.1.8.1.2.4 From Nitrate and Urea A solution of 120 g of Cr(NO3)3·9H2O and 200 g of urea in 3 dm3 of water was aged at 95°C for 5 h. It was washed, dried, and calcined at 500°C for 3 h. Properties: Spherical particles 32 nm in diameter, a-form, BET specific surface area 42 m2/g [1249]. TABLE 3.312 PZC/IEP of Cr2O3 Obtained from Nitrate and Urea Electrolyte

T

Method

KNO3

25

Salt addition

Instrument

pH0

Reference

6.4

[1249]

3.1.8.1.2.5 From Chloride and KOH 0.01 M CrCl3 was added dropwise to boiling KOH solution (pH 10.6). After 5 h, the pH was adjusted to 7.5 with KOH, and the precipitate was washed and dried at 110°C for 1 d.

210

Surface Charging and Points of Zero Charge

Properties: XRD and TGA results available. The original sample is hydrous and amorphous. Specific surface area 75 (original), 9 m2/g (calcined at 800°C) [1244].

TABLE 3.313 PZC/IEP of Cr2O3 Obtained from Chloride and KOH Description

Electrolyte

Original Calcined at 800°C for 4 h

0.1 M KCl

T

Method

Instrument

pH

pH0

Reference

4.7 4

[1244]

hhhhhhh

3.1.8.2

Hydrous Cr2O3

3.1.8.2.1 Thermal Hydrolysis and Aging of CrCl3 Solution Properties: BET specific surface area 41 m2/g [1250].

TABLE 3.314 PZC/IEP of Hydrous Cr2O3 Obtained by Thermal Hydrolysis and Aging of CrCl3 Solution Electrolyte

a

T

Method

23

pH

Instrument

pH0

Reference

6.2a

[1250]

Only value, no data points.

3.1.8.2.2 Aging of 0.0004 M CrK(SO4)2 for 21 Hours at 75°C Properties: Particle diameter: 0.31 mm, electron micrograph available [1153,1154].

TABLE 3.315 PZC/IEP of Hydrous Cr2O3 Obtained by Aging of 0.0004 M CrK(SO4)2 for 21 h at 75°C Electrolyte

T

Method

Instrument

pH0

Reference

25

iep

Electrophoresis, van Gils cell

7.9

[1153,1154]

3.1.8.2.3 Aging of 0.0002 M CrK(SO4)2 for 6 Hours at 85°C Properties: SEM image available [1251].

211

Compilation of PZCs/IEPs

TABLE 3.316 PZC/IEP of Hydrous Cr2O3 Obtained by Aging of 0.0002 M CrK(SO4)2 for 6 h at 85°C Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

7.3

[1251]

0.01 M

3.1.8.2.4 Hydrolysis of Nitrate Properties: Average particle size 260 nm [1252], BET specific surface area 316 m2/g [1252,1253].

TABLE 3.317 PZC/IEP of Hydrous Cr2O3 Obtained by Hydrolysis of Nitrate Description

Electrolyte

T

Method

Amorphous

0.01 M KCl 0.001 M KNO3

25 25

iep iep

a

Instrument Electrophoresis Delsa 440

pH0

Reference

8.3 9.2a

[1248] [1252–1254]

In Ref. [1253], only value, data points not reported.

3.1.8.2.5 Recipe from [1255] 1 M KOH was added dropwise at 3 cm3/min to 0.1 M KCr(SO4)2 until pH 9. The suspension was aged at 80–85°C for 2 d with stirring. The precipitate was then washed. Washing procedure A: with NaOH (pH 11) until sulfate was not detectable. It was then neutralized with HClO4 to pH 8, and washed with NaOH (pH 8 [?MK]) until constant conductivity. It was then stored in dilute HClO4 as a dispersion (sample A-1) or dried in air at 60°C (A-2). Washing procedure B: with HClO4 (pH 3.5) until sulfate was not detectable. It was then rinsed with NaOH (pH 8) and dried at 60°C. Properties: Amorphous, specific surface area 30 m2/g (all samples), sulfate: <0.02% (sample A-1, A-2), 2.6% (B), TEM image available [1255].

TABLE 3.318 PZC/IEP of Hydrous Cr2O3 Obtained According to Recipe from [1255] Description A-1 A-2 B

Electrolyte

T

Method

0.001–0.1 M KNO3

25

cip/stability

Instrument

pH0

Reference

8.4/8.4 7.9/8 5.5/8

[1255]

212

Surface Charging and Points of Zero Charge

3.1.8.2.6 From 1 M Cr(NO3)3 and Aqueous Ammonia Properties: Amorphous, TEM image available, specific surface area 203 m2/g [1243]. TABLE 3.319 PZC/IEP of Hydrous Cr2O3 Obtained from 1 M Cr(NO3)3 and Aqueous Ammonia Electrolyte

T

Method

0.001 M KNO3 a

Instrument

iep

Electrophoresis

pH0 7.3

Reference

a

[1243]

Only value, no data points.

3.1.8.2.7 From 0.2 M Cr(NO3)3 and Aqueous Ammonia 30 cm3 of 27% ammonia was added to 600 cm3 of 0.2 M Cr(NO3)3 at 90°C. The precipitate was aged for 1 h, washed, and dried at 60°C. Properties (freshly prepared/stored for 1 year in vacuum): Amorphous, particle diameter 400 nm, 28/11 mol of H2O per mol of Cr2O3, BET specific surface area 6.1/36.2 m2/g [1256]. TABLE 3.320 PZC/IEP of Hydrous Cr2O3 Obtained from 0.2 M Cr(NO3)3 and Aqueous Ammonia Description

Electrolyte

Freshly prepared Stored for 1 year a

0.001 M KCl

T 25

Method iep

Instrument Pen Kem S 3000

pH0 a

8.6 8.5

Reference [1256]

Arbitrary interpolation.

3.1.8.2.8 From 0.02 M Cr(NO3)3 and NaOH NaOH was added to 0.02 M Cr(NO3)3 at 2.5:1 molar ratio. The precipitate was aged for 2 d at 80°C, and NaOH was further added to reach 3:1 molar ratio. The precipitate was aged for further 2 d at 80°C, washed and dried at 50°C. Properties: Amorphous, 14 mol of H2O per mol of Cr2O3, BET specific surface area 240 m2/g, particle diameter 200 nm [1256]. TABLE 3.321 PZC/IEP of Hydrous Cr2O3 Obtained from 0.02 M Cr(NO3)3 and NaOH Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

25

iep

Pen Kem S 3000

8.3a

[1256]

a

Arbitrary interpolation.

213

Compilation of PZCs/IEPs

3.1.8.2.9

From CrCl3 and NaOH

TABLE 3.322 PZC/IEP of Hydrous Cr2O3 Obtained from CrCl3 and NaOH Description

Electrolyte T

pH was adjusted to 7–11 with NaOH. Precipitate was washed and aged for 2 h in 1 M NaCl at 80°C 10% excess of NaOH: washed Washed and aged for 4 months Washed at aged at elevated T Cr:OH = 1:3: washed Washed and aged for 4 months Washed at aged at elevated T 10% deficient NaOH: washed Washed and aged for 4 months Washed at aged at elevated T a

Method

0.01–1 M NaCl

Instrument

pH

iepa

pH0

Reference

5.9–9.6

[678]

Electrophoresis 6.5 7 7.2 6.7 7 7.2 7.1 7.3 7.4

[1257]

Most likely the results presented in [1257] refer to a quantity that is not related to electrokinetic phenomena. Namely, in another paper by the same authors [1258] (also cited in [1]) the term “IEP” is used outside the meaning defined in the present book. The “IEP” from [1257] has been cited (after [1]) in several publications.

3.1.8.3

CrOOH

3.1.8.3.1 Hydrothermal Hydrolysis of Cr(NO3)3 Properties: a-form [1248,1243], BET specific surface area 39.3 m2/g (sample obtained from 0.3 M Cr(NO3)3 at 245°C for 1 h) [1243], TEM image and particle size distribution available [1243].

TABLE 3.323 PZC/IEP of CrOOH Obtained by Hydrothermal Hydrolysis of Cr(NO3)3 Conditions

Electrolyte

200°C, 2.5 MPa 0.03 M Cr(NO3)3 at 120°C for 10 d 0.02 M Cr(NO3)3 at 130°C for 12 d 0.3 M Cr(NO3)3 at 245°C for 1 h

0.01 M KCl 25 0.001 M KNO3

iepa iepa

0.001 M KNO3

iep Electrophoresis pH coagulation

a b

T

25

Method

Instrument Electrophoresis

Only value, no data points. The results reported in Figure 1 and Table 2 do not match.

pH0 Reference 9.1 7.3 7.5

[1248]b [1243]

7

[1243]

214

Surface Charging and Points of Zero Charge

3.1.8.3.2

Hydrothermal Treatment of Hydrous Oxide at 400°C, 1.5 × 108 Pa for 1 day Properties: a-form, TEM image and particle size distribution available, BET specific surface area 4.1 m2/g [1243].

TABLE 3.324 PZC/IEP of CrOOH Obtained by Hydrothermal Treatment of Hydrous Oxide at 400°C Electrolyte

T

Method iep

0.001 M KNO3 a

Instrument Electrophoresis

pH0 6.8

a

Reference [1243]

Only value, no data points.

3.1.8.4 Cr(OH)3 3.1.8.4.1 From Sulfate 0.0004 M KCr(SO4)2 was aged for 1 d at 75°C (or 0.0004 and 0.0008 M KCr(SO4)2 was aged for 18 h at 75°C). Properties: Spherical particles, modal diameter 320 nm [331], modal diameter 313 nm, TEM image available [1259].

TABLE 3.325 PZC/IEP of Cr(OH)3 Obtained from Sulfate Description Washed with borax + NaOH buffer pH 10, three times Washed with water, 0.001 M HClO4 and 0.001 M NaOH

Electrolyte

T

Method iep

0.0001–0.1 M NaClO4

25

iep

Instrument

pH0

Electrophoresis 7.5–7.8

Pen Kem 3000 Delsa

8.4

Reference [1259]

[331]

3.1.8.4.2 Recipe from [1260] A solution 1.4 M in HCl, containing 24 g of CrCl3/dm3 was diluted and adjusted to a certain pH with NaOH.

215

Compilation of PZCs/IEPs

TABLE 3.326 PZC/IEP of Cr(OH)3 Obtained According to Recipe from [1260] pH of precipitation 7 8 9 10 11

3.1.8.4.3

Electrolyte

T

0.001/0.01/ 0.1 M NaCl

Method

Instrument

pH

pH0

Reference

5.5/6.4/6.9 7/7.3/7.8 9.3/8.6/8.5 10.6/9.8/9.3 —/10.5/9.8

[1260]

Precipitated from 0.001 M Salt, Filtered, and Washed with Water

TABLE 3.327 PZC/IEP of Cr(OH)3 Precipitated from 0.001 M Salt Electrolyte

T

Method

Instrument

pH0

Reference

KOH + HNO3

22

iep

Zeta-Meter

9.3

[370]

3.1.8.4.4

From Chloride

TABLE 3.328 PZC/IEP of Cr(OH)3 Obtained from Chloride Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer

8.5

[393]

pH0

Reference

5.5 8.5

[1103]a [1262]

0.0001–0.01 M KCl

3.1.8.4.5

Origin Unknown

TABLE 3.329 PZC/IEP of Cr(OH)3 of Unknown Origin Description

Electrolyte

Precipitated

0.002 M KNO3

a

T

Method iep iep

Instrument Electro-osmosis Rank Brothers Mark II

“Cl(OH)3” in the English translation (typographic error). Only value, no data points.

216

Surface Charging and Points of Zero Charge

The “IEP” of chromium hydroxide at pH 5 claimed in [1261] was not obtained by electrokinetic measurement. That value was cited in [1] and then by the others.

3.1.9

COPPER (HYDR)OXIDES

Copper at oxidation states +1 and +2 forms several sparingly soluble compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. Nominal degree of hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of hydration. PZCs/IEPs of copper (hydr)oxides are presented in Tables 3.330 through 3.343. 3.1.9.1 Cu2O PZCs/IEPs of Cu2O are presented in Tables 3.330 and 3.331. 3.1.9.1.1 Reduction of Fehling’s Solution Fehling’s solution (pCu 2.2–3.2) was reduced by 0.00133 M glucose at 90–95°C. Properties: Monodispersed, cubic particles, modal edge length 0.4 mm (pCu 3.2) to 1.6 mm (pCu 2.2) [1153], electron micrograph available [1154,1153].

TABLE 3.330 PZC/IEP of Cu2O Obtained by Reduction of Fehling’s solution Electrolyte

T

Method

Instrument

pH0

Reference

25

iep

Electrophoresis, van Gils cell

5

[1153,1154]

3.1.9.1.2 Natural, Origin Unknown, Water-Washed, and Dried at 110°C

TABLE 3.331 PZC/IEP of Natural Cu2O Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M KCl

25

iep

Rank Mark II

11.5

[1213]

3.1.9.2 CuO PZCs/IEPs of CuO are presented in Tables 3.332 through 3.337.

217

Compilation of PZCs/IEPs

3.1.9.2.1

Commercial

3.1.9.2.1.1 Aldrich

TABLE 3.332 PZC/IEP of CuO from Aldrich Electrolyte

T

Method

Instrument

a

iep iep

0.005 0.05 0.1 M NaClO4 a

Brookhaven ZetaPlus Zeta-Meter

pH0 b

8.5 9.2 9.6 9.4

Reference [1263] [1264]

Only value, no data points. Aldrich or Fisher.

b

3.1.9.2.1.2 Merck

Properties: Tenorite [1265].

TABLE 3.333 PZC/IEP of CuO from Merck Electrolyte

T

Method

b

pH0 a

pH iep

0.001 M KClO4 KNO3

a

Instrument Rank Bros.

7.6 8.5b

Reference [1265] [830] [831]

Figure 1 suggests PZC at pH 6.9. Only value, no data points.

3.1.9.2.1.3 Reachim

Properties: Tenorite [1266].

TABLE 3.334 PZC/IEP of CuO from Reachim Electrolyte 0.001–0.1 M KNO3, NaCl, KCl

T

Method pH

Instrument

pH0

Reference

7.6, 8, 8.5

[1266]

218

Surface Charging and Points of Zero Charge

3.1.9.2.2 Synthetic 3.1.9.2.2.1 From Nitrate 0.2 M NaOH and 0.1 M Cu(NO3)2 solutions were simultaneously introduced with stirring into 100 cm3 of water at 10 cm3/min for 2 min at 20°C. This was then aged at 20°C for 5 d. Properties: SEM and TEM image, XRD results available [1267]. TABLE 3.335 PZC/IEP of Synthetic CuO Electrolyte

T

HNO3 + NaOH

Method

Instrument

iep

Coulter Delsa 440

pH0 Reference 7.5

[1267]

3.1.9.2.2.2 Thermal Decomposition of Oxalate Oxalate was obtained from 1 M Cu(NO3)2 and a 10% excess of oxalic acid, washed with water, and calcined at 600°C, washed, and then calcined at 800–1400°C for 6 h. The oxide was washed with water until constant conductivity. TABLE 3.336 PZC/IEP of CuO Obtained by Calcination of Oxalate Second Calcination Temperature (°C) None 800 1000 1100 1200

3.1.9.2.3

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

25

pH

Streaming potential

9.8 9.6 9.3 9.2 9.2

[33]

Origin Unknown

TABLE 3.337 PZC/IEP of CuO of Unknown Origin Description

Electrolyte

T

Method

Instrument

pH0 Reference

Room

iep iep

Electro-osmosis Electrophoresis

9.4 [1103a,1217] 9.5 [1088]

0.01 M KCl Washed, aged at 100°C, structure confirmed by XRD a

Only value, no data points.

Two recent papers report IEPs of CuO at pH 4 [3094] and 8 [3159]. Both values were obtained by arbitrary interpolation.

219

Compilation of PZCs/IEPs

3.1.9.3 Hydrous CuO PZCs/IEPs of hydrous CuO are presented in Table 3.338. A dispersion containing Cu precursor and NaOH was aged for 18 h at 75°C. The particles were water-washed. Properties: Electron micrographs available [1268].

TABLE 3.338 PZC/IEP of Hydrous CuO Recipe

Electrolyte

0.001 M Cu(NO3)2, 0.01 M NaOH, 0.002 M KH2PO4 0.001 M Cu(NO3)2, 0.01 M NaOH, 0.001 M KH2PO4 0.001 M Cu(NO3)2, 0.01 M NaOH, 0.0005 M KH2PO4 0.001 M Cu(NO3)2, 0.01 M NaOH 0.001 M CuSO4, 0.002 M NaOH

0.01 M NaNO3

T

Method

Instrument

iep

Rank Brothers

pH0 Reference 4

[1268]

5 5 4 5

3.1.9.4 Cu(OH)2 PZCs/IEPs of Cu(OH)2 are presented in Tables 3.339 through 3.343. 3.1.9.4.1 From Sulfate and Acetate A solution was prepared by adding reagents in the following order: Cu salt, NH3, NaCH3COO, and NaOH (different final concentrations) at room temperature. The precipitate was water-washed and dried. A: 0.04 M CuSO4, 0.14 M NH3, 0.5 M NaCH3COO, and 1.2 M NaOH. Properties: needle-like particles <500 nm, TEM image and XRD results available [153] B: 0.013 M CuSO4, 0.047 M NH3, 0.17 M NaCH3COO, but no NaOH. Properties: irregularly shaped particles <150 nm [153] C: 0.04 M Cu(CH3COO)2, 0.14 M NH3, 0.5 M NaCH3COO, and 1.2 M NaOH. Properties: Bundles of needle-like particles, average size 2 μm, TEM image available [153].

TABLE 3.339 PZC/IEP of Cu(OH)2 Obtained from Sulfate and Acetate Description A B C

Electrolyte 0.01 M NaClO4

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

9.5 10 9.5

[153]

220

3.1.9.4.2

Surface Charging and Points of Zero Charge

Obtained from Cu(NO3)2 and NaOH at 0°C, Washed and Aged at 0°C

TABLE 3.340 PZC/IEP of Cu(OH)2 Obtained from Cu(NO3)2 and NaOH at 0°C Electrolyte

3.1.9.4.3

T

Method

Instrument

pH0

Reference

0

iep

Electrophoresis

9.4

[1088]

Precipitated from Cu(NO3)2 Solution with 0.01 M NaOH at 23°C, not Washed

TABLE 3.341 PZC/IEP of Cu(OH)2 Obtained from Cu(NO3)2 and 0.01 M NaOH Electrolyte

T

0.001 M NaNO3 a

Method

Instrument

pH0

Reference

iep

Delsa 440

>8.2

[1220]

a

+10 mV at pH 8.2, −20 mV at pH 9.8.

3.1.9.4.4

Precipitated from Cu(NO3)2 Solution

Table 3.342 PZC/IEP of Cu(OH)2 Obtained from Cu(NO3)2 Description Cu(NO3)2 + NaOH Washed

Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3 0.001 M NaNO3

25 25

iep iep

Zeta-Meter Zeta-Meter 3.0

8.5 10.3

[391] [348]

3.1.9.4.5 Other TABLE 3.343 PZC/IEP of Other Specimens of Cu(OH)2 Description CuCl2 + dilute NaOH

Electrolyte 0.002 M NaCl

CuCl2 + NaOH, hydrous <0.01 M Precipitated 0.002, 0.02 M NaCl a

Only value, data points not reported.

T Method iep iep iep

Instrument Malvern Zetasizer II Electrophoresis Riddick-type cell

pH0 Reference 9.5 7.6a 9.4

[1269] [1270] [1229] [1232]

221

Compilation of PZCs/IEPs

3.1.10

Dy2O3

IEP of commercial Dy2O3 from Shin-etsu is presented in Table 3.344. Properties: 99.9% pure [1041]. TABLE 3.344 PZC/IEP of Dy2O3 from Shin-etsu Description

Electrolyte

0.1% by volume

KOH + HCl

a

T

Method

Instrument

pH0

Reference

iep

Pen Kem 7000

8.8a

[1041]

Only value, data points not reported.

3.1.11

Er2O3

IEP of commercial Er2O3 from Shin-etsu is presented in Table 3.345. Properties: 99.9% pure [1041]. TABLE 3.345 PZC/IEP of Er2O3 from Shin-etsu Description

Electrolyte

0.1% by volume

KOH + HCl

3.1.12

T

Method

Instrument

pH0

Reference

iep

Pen Kem 7000

8.8

[1041]

IRON (HYDR)OXIDES

Iron forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation (+2 to +3), degree of hydration, and crystallographic structure. Nominal degree of oxidation and hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of oxidation and hydration. PZCs/IEPs of iron (hydr) oxides are presented in Tables 3.346 through 3.581. Different properties of iron (hydr)oxides (PZCs/IEPs, electron micrographs, preparation recipes) are reviewed in [63,1271]. 3.1.12.1 Fe(OH)2 Parks [1] reports IEPs of Fe(OH)2 obtained by electro-osmosis after [1272] (or its abstract in CA). The result from [1] was then cited in numerous studies. In fact, [1272] (in Polish, with extended abstract in German; the present author is a native speaker of Polish) reports the degree of oxidation of Fe(OH)2 in air at 18°C and the Fe(iii) phases formed at various pH values. The term “isoelectric point” was indeed used, but the value (pH 11.5–12.4) reported in [1272] was obtained as an inflection point in the degree of oxidation (pH) curve, and is unrelated to the IEP obtained from electrokinetic measurements.

222

Surface Charging and Points of Zero Charge

3.1.12.2 Fe3O4 (Magnetite) Reference [117] is a review of PZCs/IEPs of magnetites with 15 references. PZCs/ IEPs of magnetites (nominally Fe3O4) are presented in Tables 3.346 through 3.379. 3.1.12.2.1 Commercial 3.1.12.2.1.1 Magnetite from Alfa Aesar 97% area 8 m2/g [1273] 5.6 m2/g [316].

Properties: BET specific surface

TABLE 3.346 PZC/IEP of Magnetite from Alfa Aesar Electrolyte

T

Method

Instrument

pH0

Reference

iep cip

Laser Zee Meter

6.5a 8.2

[316] [1273]

NaClO4 0.001–0.1 M NaNO3 a

No data points at pH 3–6.5.

See also Section 3.1.12.2.1.2. 3.1.12.2.1.2 Puratronic from Johnson Matthey Properties: Contains hematite and maghemite (approximately 20%) [1274], purity: 99.997% [1275,1276], 99.997% (metal basis) [1274], impurities: 10 ppm Cr, 1 ppm Mg, 1 ppm Mn, 2 ppm Si [1276], BET specific surface area 1.8 m2/g [1276], 2 m2/g [1275], 2.9 m2/g [1277], mean particle size 33.3 mm [1276], SEM image available [1274].

Table 3.347 PZC/IEP of Puratronic from Johnson Matthey Description

Electrolyte

T

pH

0.1 M NaNO3 Treated for 14 d at 500°C 0.03, 0.3 M with Ni/NiO/H2O, NaCF3SO3 0.9 m2/g a b

c

Method

50

Intersection

Instrument

pH0

Reference

6.3 [1276a,1278b] 6.5 6.3c [1274]

PZC at pH 6.3 (Table 2) or 6.6 (Table 6). Acidity constants reported in [1278] are probably based on results from [1276]. Magnetite from Alfa Aesar with BET specific surface area of 1.6 m2/g was studied in [1278]. Charging curves at 25°C are also reported, and intersection points of charging curves at 100–250°C.

223

Compilation of PZCs/IEPs

3.1.12.2.1.3 Magnetite from Kanto 4.3 m2/g [932,1279].

Properties: BET specific surface area

TABLE 3.348 PZC/IEP of Magnetite from Kanto Description Washed

Electrolyte

T

Method

0.1 M NaNO3

25

pH

3.1.12.2.1.4 Magnetite from Kebo face area 5.6 m2/g [957].

Instrument

pH0

Reference

6.3

[932,1279]

Properties: 97% pure, BET specific sur-

Table 3.349 PZC/IEP of Magnetite from Kebo Electrolyte

T

Method

0.1 M NaCl a

iep

Instrument Laser Zee Meter 501

pH0 7

a

Reference [957]

Arbitrary interpolation.

3.1.12.2.1.5 Magnetite from Mitsui Mining & Smelting Co. Ltd Mean diameter 200 nm [1280].

Properties:

TABLE 3.350 PZC/IEP of Magnetite from Mitsui Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Nano Z

4.8

[1280]

3.1.12.2.1.6 Electrodialyzed Magnetite from Toda confirmed by XRD [1281].

Properties: Structure

TABLE 3.351 PZC/IEP of Electrodialyzed Magnetite from Toda Electrolyte

T

Method

0.002 M TMAClO4

25

pH

Instrument

pH0

Reference

7.1

[1281]

224

Surface Charging and Points of Zero Charge

3.1.12.2.1.7 Magnetite from Toda Kogyo Properties: BET specific surface area 4.8 m2/g [1282].

TABLE 3.352 PZC/IEP of Magnetite from Today Kogyo Description

Electrolyte

T

Method

Washed with 0.1 M HNO3 and water, dried at room temperature

0.1 M NaCl, NaClO4, NaNO3

25

pH

Instrument

pH0

Reference

5.4

[1282]

3.1.12.2.2 Synthetic Magnetites 3.1.12.2.2.1 From Fe(II) Precursor 3.1.12.2.2.1.1 Oxidation of Fe(II) Hydroxide Gel with Nitrate Properties: Impurities in ppm: Co 17, Si 19, Ni 5, Mn 100 [907], BET specific surface area 1.7 m2/g [934,1283], Specific surface area 35 m2/g [1284], mean particle diameter 1 μm [934,1283], XRD pattern and isotherms of water adsorption available [1284].

TABLE 3.353 PZC/IEP of Magnetite Obtained by Oxidation of Fe(II) Hydroxide Gel with Nitrate Description Dispersion aged for 4 h at 90°C in the presence of excess FeII FeSO4 + NaOH + KNO3

a

Electrolyte 0.1 M NaNO3

T

Method Instrument

pH0

Reference

25

pH

6.5

[1283]

0.005–0.5 M KNO3 25a NaOH + HNO3

cip pH

6.6 7.2

[907] [1284]

PZC at 35–90°C available.

3.1.12.2.2.1.2 Modified Recipe from [1285] 12.5 cm3 of 1 M KOH and 25 cm3 of 2 M KNO3 were added to 205 cm3 of nitrogen-saturated water, and nitrogen purging was continued for 2 h. Then 7.5 cm3 of 1 M FeSO4 in nitrogen-saturated water were added. The mixture was heated at 90°C for 4 h. After cooling, the supernatant was removed and the particles were washed with

225

Compilation of PZCs/IEPs

water and then with ethanol, and stored in ethanol. A similar process was carried out with heating at 90°C in the presence of a uniform magnetic field. Properties: SEM images, XRD patterns available [1286].

TABLE 3.354 PZC/IEP of Magnetite Obtained According to Modified Recipe from [1285] Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta PALS, Brookhaven

7.3

[1286]a

0.002 M NaNO3 a

IEP at pH 6.6 was observed in presence of pH buffers.

3.1.12.2.2.1.3 From FeSO4, KNO3, and KOH Properties: BET specific surface area 3.3 m2/g [1287] 3.7 m2/g, TEM image available, average diameter 520 nm [347]. SEM, TEM images available of particles prepared according to the original recipe [1285].

TABLE 3.355 PZC/IEP of Magnetite Obtained from FeSO4, KNO3, and KOH Description 1 d-aged Fresh aged for: 7 d 14 d 21 d

Electrolyte

T

Method

Instrument

0.001, 0.01 M NaNO3 0.001 M KNO3

25

iep

Malvern Zetasizer 2000

25

iep

Malvern Zetasizer 2000

25 30

iep iep

0.01 M KNO3 Recipe from 0.01 M KNO3 [908], NaOH instead of KOH a b c

pH 0 6.3

6.5a 5.5 4.6 <4 if any Malvern Zetasizer 2000 7b Zeta-Meter 7c

Reference [347] [415]

[1288] [1065, 1234]

Figure legend “commercial magnetite” in Figure 5 is erroneous. Arbitrary interpolation. Ref. [465] reports PZC of magnetite at pH 6.5.

3.1.12.2.2.1.4 From Fe(OH)2, Nitrate, and Hydrazine Properties: Structure confirmed by XRD Mossbauer spectra [1289], and BET specific surface area 5.4 m2/g [1289,1290], 5 m2/g [1291], average diameter 0.22 mm [1289,1290], average size 0.15 mm [1291], spherical [1289].

226

Surface Charging and Points of Zero Charge

TABLE 3.356 PZC/IEP of Magnetite Obtained from Fe(OH)2, Nitrate, and Hydrazine Electrolyte 0.001–0.1 M KNO3 0.001 M KNO3 a

b

T

Method

25 30 25 25

iep cip iep iep

Instrument Karl Zeiss Cytopherometer

Karl Zeiss Cytopherometer

pH0

Reference

6.5 6.8 6.9 6.9

[1292]a [1289,1290b] [1289,1290]b [1291]

The above recipe is not directly indicated in [1292], which reports six different recipes for magnetites. Electron micrographs of three powders and specific surface areas of two powders are reported. IEP (data points not reported) was given without specification of method. Also 30–80°C.

3.1.12.2.2.1.5

From Fe(II) and Nitrate at 90°C

TABLE 3.357 PZC/IEP of Magnetite Obtained from Fe(II) and Nitrate at 90°C FeII/FeIII 0.45 0.35

Electrolyte

T

KNO3

Method

Instrument

Titration

pH0

Reference

6.6 7.2

[1293]

3.1.12.2.2.2 From Fe(II + III) Precursor 3.1.12.2.2.2.1 From Chlorides and Ammonia at 25°C 29.6% ammonia was added to a solution 0.2 M in FeCl3 and 0.1 M in FeCl2 at 25°C with stirring. The pH was adjusted to 10. The mixture was heated at 80°C for 30 min, washed with water and ethanol, and dried in vacuum at 70°C. Properties: TEM image, XRD pattern available, mean diameter 13 nm [1294].

TABLE 3.358 PZC/IEP of Magnetite Obtained from Chlorides and Ammonia at 25°C Electrolyte

T

0.001 M NaCl a

Method

Instrument

pH0

Reference

iep

Malvern ZEN 2600

6.7a

[1294]

Arbitrary interpolation.

3.1.12.2.2.2.2 Recipe from [1108] NaOH was slowly added to solution containing Fe(ii) and Fe(iii) at 1:1 ratio at 70°C.

227

Compilation of PZCs/IEPs

TABLE 3.359 PZC/IEP of Magnetite Obtained According to Recipe from [1108] Electrolyte

T

Method

Instrument

pH0

Reference

iep

Rank Brothers Mark II

6.8

[1108]

0.002 M KNO3

3.1.12.2.2.2.3 Recipe from [1295] 10 cm3 of solution 2 M in FeCl2 and 2 M in HCl and 40 cm3 of solution 1 M in FeCl3 were mixed and slowly added to 400 cm3 of 0.9 M ammonia. The particles were washed with water. All solutions were bubbled with nitrogen. Properties: BET specific surface area 95.2 m2/g [316], 95.3 m2/g (original), 28.4 m2/g (aged for 3 y) [158], particle size distribution [158], TEM images [316], (fresh and aged for 6 y) [158], XRD pattern (aged sample contains akageneite and maghemite) [158], XRD pattern and SEM image [316] available. TABLE 3.360 PZC/IEP of Magnetite Obtained According to the Recipe from [1295] Description

Electrolyte

T

0.001–0.1 M NaClO4 Fresh Fresh Aged for 6 yrs

0.002 M NaCl 0.01–1 M NaCl 0.001–1 M NaCl

Method iep

25 25

iep cip cip/iep

Instrument

pH0

Z-sizer Laser Zee Meter Malvern Zetasizer 4 Malvern Nano ZS

6

[316]

8

[1296, 1297] [1296, 1297] [158]

8 7

Reference

3.1.12.2.2.2.4 From Sulfate and Ammonia A solution 0.5 M in FeCl3 and 0.25 M in FeSO4 was titrated with ammonia to pH 11–12 (ammonia) in a nitrogen atmosphere at 55°C. It was aged for 2 h at 65°C. Properties: TEM image, particle size distribution available [1298]. TABLE 3.361 PZC/IEP of Magnetite Obtained from Sulfate and Ammonia Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

DXD-2 (Electrophoresis)

3.6a

[1298]

A horizontal line in Figure 7 does not indicate V = 0.

3.1.12.2.2.2.5 From Chlorides and Ammonia at 80°C A 1:2 mixture of Fe(ii) and Fe(iii) in 1 M HCl was slowly added to NH3 solution at 80°C with

228

Surface Charging and Points of Zero Charge

stirring. All solutions were prepared in nitrogen-saturated water. The precipitate was washed with nitrogen-saturated water. Properties: Hydrodynamic diameter 56 or 82 nm [1299]. TABLE 3.362 PZC/IEP of Magnetite Obtained from Chlorides and Ammonia at 80°C Electrolyte

T

Method

Instrument

iep a

Pen Kem 3000

pH0 6.2

a

Reference [1299]

A horizontal line in Figure 2 does not indicate zero mobility.

3.1.12.2.2.2.6 Recipe from [1300] TABLE 3.363 PZC/IEP of Magnetite Obtained According to Recipe from [1300] Electrolyte

T

Method

0.1 M NaClO4 a

Instrument

iep

pH0

Reference

6a

[1300]

Only value, data points not reported.

3.1.12.2.2.3 From FeCl3, Na2SO3, and NH4OH TABLE 3.364 PZC/IEP of Magnetite Obtained from FeCl3, Na2SO3, and NH4OH Electrolyte

T

Method

Instrument

iep a

pH0

Reference

7a

[1301]

Only value, data points not reported.

3.1.12.2.2.4 Prepared at High Temperature 3.1.12.2.2.4.1 Reduction of Fe2O3 in CO–CO2 Mixture TABLE 3.365 PZC/IEP of Magnetite Obtained by Reduction of Fe2O3 in CO–CO2 Mixture Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.5

a

Cited in [1] (and by others) after [1302]. In fact, the IEP of magnetite obtained by reduction of Fe2O3 in a CO–CO2 mixture is not reported in [1302].

229

Compilation of PZCs/IEPs

3.1.12.2.2.4.2 Particles Formed in the Oxygen–Hydrogen Flame Two samples. Properties: Magnetite with admixture of hematite, XRD results, and HTEM and SEM images available [1303].

TABLE 3.366 PZC/IEP of Magnetite Formed in Oxygen–Hydrogen Flame Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep

Electrophoresis Streaming potential

5.1 5.1

[1303]

3.1.12.2.2.4.3 From Metallic Fe Pure iron was oxidized in air at 1400°C for 3 h to produce magnetite. It was then heated in air at different temperatures.

TABLE 3.367 PZC/IEP of Magnetite Obtained from Metallic Fe Calcination Temperature (°C) 200 400 800 1000 1200

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

25

iep

Streaming potential

9 8.8 8 5.3 5.2

[1304]

3.1.12.2.2.5 Recipe from [1305] Properties: Specific surface area (argon) 49 m2/g, after autoclave treatment 3–4 m2/g [1247].

TABLE 3.368 PZC/IEP of Magnetite Obtained According to Recipe from [1305] Description Original After 18 h in water in autoclave at 280°C

Electrolyte 0.001 M KNO3

T

Method Titration

Instrument

pH0

Reference

7.3 6.7

[1247]

230

Surface Charging and Points of Zero Charge

3.1.12.2.3

Magnetite, Origin Unknown

TABLE 3.369 PZC/IEP of Magnetites of Unknown Origin Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.7

[1306]

3.1.12.2.4 Natural 3.1.12.2.4.1 From Quebec Cartier Mining silica and traces of Mg, Cu, and Al [579].

Properties: >99% pure, contains

TABLE 3.370 PZC/IEP of Magnetite from Quebec Cartier Mining Electrolyte

T

Method

0.001–1 M KNO3

25

cip

Instrument

pH0

Reference

6.4

[579]

3.1.12.2.4.2 From Gong-ChangLing, China, Ground Properties: 72% Fe, 0.5% SiO2 [1309].

TABLE 3.371 PZC/IEP of Magnetite from Gong-ChangLing, China Electrolyte

T

Method

Instrument

pH0

Reference

None

22

iep

Brookhaven ZetaPlus

6.6

[1309]

3.1.12.2.4.3 Magnetite Concentrate from Luzhong, China Properties: 68.1% Fe, 1.6% SiO2, 0.4% Al2O3, 2.2% MgO, 1% CaO, BET specific surface area 0.2 m2/g, particle size distribution available [1310].

TABLE 3.372 PZC/IEP of Concentrate from Luzhong, China Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta PALS

4.4

[1310]

231

Compilation of PZCs/IEPs

3.1.12.2.4.4 From Baljevci na Ibru, Serbia Properties: 8.4% SiO2, 1.2% CaO, 0.8% Al2O3, 1% MgO, 0.16% NiO, XRD pattern available [117]. TABLE 3.373 PZC/IEP of Magnetite from Baljevci na Ibru, Serbia Original Washed with 3 M HCl

Electrolyte

T

Method

0.01–1 M KCl

25

pH

Instrument

pH0

Reference

6.5 4

[117]

3.1.12.2.4.5 Rudna Glava, Serbia Properties: 2.4% SiO2, 0.91% Al2O3, 0.12% MgO, 0.11% NiO [1311,1312], BET specific surface area 2.2 m2/g [1312]. TABLE 3.374 PZC/IEP of Magnetite from Rudna Glava, Serbia Electrolyte

T

Method

0.1 M NaCl, KCl 0.01, 0.1 M NaCl

23 20

pH pH

a

Instrument

pH0

Reference

6.5 9.9a

[1311] [1312]

Charging curves obtained at different ionic strengths do not intersect.

3.1.12.2.4.6 Sweden [664].

Properties: 1.5% SiO2, 6.9% Al2O3, 2% MgO, 1.4% CaO

TABLE 3.375 PZC/IEP of Magnetite from Sweden Electrolyte

T

0.01 M KCl

Method

Instrument

Salt addition

3.1.12.2.4.7 Bingol-Miskel, Turkey lite [313].

pH0

Reference

6.5

[664]

Properties: 97.7% pure, contains actino-

TABLE 3.376 PZC/IEP of Magnetite from Bingol-Miskel, Turkey Electrolyte 0–0.01 M KNO3

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0+

5

[313]

232

Surface Charging and Points of Zero Charge

3.1.12.2.4.8 Port Henry, New York, Dry-Ground TABLE 3.377 PZC/IEP of Magnetite from Port Henry, NY Electrolyte

T

Method

Instrument

iep a

pH0

Electrophoresis

a

6.5

Reference [1302]

Arbitrary interpolation.

3.1.12.2.4.9 Natural, Origin Unknown Properties: Grain size <180 μm, BET specific surface area 18.3 m2/g, 2.4% SiO2 [1275]. TABLE 3.378 PZC/IEP of Natural Magnetites Location

Electrolyte

T

Method

Instrument

pH0

Reference

3 [1313]a 3.5 Grängesberg NaOH + HClO4 iep 4 [104] None iep 4.2 [1314] 0.01–1 M NaNO3 cip 5.5 [1275]b 0.0006 M NaClO4 iep EMTA 1202, Micromeritics 6.8 [1315] iep 7 [1316] a A material termed magnetite in the abstract is in fact a filter cake from an iron ore-processing plant (ill defined material). b Only value, data points not reported. iep

3.1.12.2.5

Pen Kem Laser Zee Meter 501; EKA, Brookhaven Zeta-Meter

Chemically Pure, Origin Unknown

TABLE 3.379 PZC/IEP of Chemically Pure Magnetite, Origin Unknown Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep

Pen Kem 300

6.7

[1317]

3.1.12.3 Fe2O3 Compilations of PZCs/IEPs of iron(iii) (hydr)oxides can be found in [571,756,1245,1318]. A compilation of model parameters can be found in [1319]. Reference [63] presents preparation methods, XRD patterns, TEM images,

233

Compilation of PZCs/IEPs

Mossbauer spectra, also of iron(iii) (hydr)oxides substituted with other metals. PZCs/IEPs of iron(iii) oxide (nominally Fe2O3) are presented in Tables 3.380 through 3.467. 3.1.12.3.1 Maghemite 3.1.12.3.1.1 Commercial 3.1.12.3.1.1.1 Maghemite from Aldrich, >99% TABLE 3.380 PZC/IEP of Maghemite from Aldrich, >99% Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

25

iep

Malvern Zetasizer 2000

5.2

[415]a

a

Only value, data points not reported.

3.1.12.3.1.1.2 Nanoark from Alfa Aesar Properties: Purity 99.95%, BET specific surface area 26 m2/g, particle size 71 ± 17 nm, spherical [1320].

TABLE 3.381 PZC/IEP of Nanoark from Alfa Aesar Electrolyte

T

Method

HCl a

Instrument

iep

pH0

Zeta Probe, Colloidal Dynamics

7.7

Reference

a

[1320]

Only value reported, no data points.

3.1.12.3.1.1.3 From NanoPhase Tech. [1321].

Properties: XRD pattern available

TABLE 3.382 PZC/IEP of Maghemite from NanoPhase Tech. Electrolyte

T

Method iep

Instrument

pH0

Reference

<2 if any

[1321]

3.1.12.3.1.1.4 Maghemite from Nanotek Properties: Structure confirmed by XRD (hematite present as an impurity), BET specific surface area 48.5 m2/g, particle diameter 26 nm, TEM image and particle size histogram available [1322].

234

Surface Charging and Points of Zero Charge

TABLE 3.383 PZC/IEP of Maghemite from Nanotek Electrolyte

T

Method

0.001–0.1 M KNO3

25

cip iep

a

Instrument

pH0

Delsa 440 Coulter

7.2 7.3a

Reference [1322]

Only value reported, no data points.

3.1.12.3.1.2 Synthetic 3.1.12.3.1.2.1 From Goethite by Dehydration, Reduction, and Oxidation Properties: BET specific surface area 23.8 m2/g [601], 18.6 m2/g [1323,1324], acicular [601], structure confirmed by XRD, electron micrograph available [1324]. TABLE 3.384 PZC/IEP of Maghemite Obtained from Goethite by Dehydration, Reduction, and Oxidation Washed

Original Hydrated for 20 h

Electrolyte

T

Method

0.01 M KCl 0.01–1 M KCl

25

pH cip

0.01–1 M KCl 0.00004 M

20

cip/iep iep

Instrument

Electrophoresis

3.1.12.3.1.2.2 Calcination of FeOOH, Washed traces of g-FeOOH [1302].

pH0

Reference

5.5 5.5

[601] [1323]

5.5 6.8

[1324]

Properties: Contains

TABLE 3.385 PZC/IEP of Maghemite Prepared Commercially by Chemical Precipitation Electrolyte

T

Method iep

a

Instrument Electrophoresis

pH0 a

6.7

Reference [1302]

Arbitrary interpolation.

3.1.12.3.1.2.3 Heating of Magnetite at 200°C for 10 days Properties: BET specific surface area 8 m2/g [707].

235

Compilation of PZCs/IEPs

TABLE 3.386 PZC/IEP of Maghemite Obtained by Heating of Magnetite at 200°C for 10 days Electrolyte

T

Method

NaCl a

Instrument

Salt titration

pH0

Reference

7.2a

[707]

Only value reported, no data points.

3.1.12.3.1.2.4 From FeCl2 CO2-free air was bubbled through a mixture of 0.1 M FeCl2 and ammonia buffer (pH 7.5) for 6 h at 45°C. The pH was maintained at about 7 by addition of ammonia. The precipitate was washed and dried at 65°C. Properties: BET specific surface area 30 m2/g [707]. TABLE 3.387 PZC/IEP of Maghemite Obtained from FeCl2 Electrolyte

T

Method

NaCl a

Instrument

Salt titration

pH0

Reference

7.3a

[707]

Only value reported, no data points.

3.1.12.3.1.2.5 From FeCl2 and FeCl3 50 cm3 of aqueous solution 0.33 M FeCl2 and 0.66 M FeCl3 was added to 450 cm3 of 1 M NH3 at room temperature. the precipitate was washed, and heated to 240°C for 2 h in air. Properties: Structure confirmed by XRD [1322,1325], BET specific surface area 65.1 m2/g [1322], 89.7 m2/g [1326], particle diameter 12 nm [1322,1325], average particle diameter 32 nm [1326], TEM image and particle size histogram available [1322], SEM image, XRD pattern available [1326]. TABLE 3.388 PZC/IEP of Maghemite Obtained from FeCl2 and FeCl3 Electrolyte

T

0.001–0.1 M KNO3

25

0.1, 0.5 M NaNO3

25

TMAOH + HNO3 TMAOH + HClO4 a

Method cip iep pH iep iep

Instrument Delsa 440 Coulter Malvern Zetasizer 4 DT 1200

Particles obtained by oxidation of magnetite with Fe(NO3)3 at 100°C.

pH0

Reference

6.6 6.6 6.6, 6.3 6.2 7 7.2

[1322,1325] [1326] [1308]a

236

Surface Charging and Points of Zero Charge

3.1.12.3.1.2.6 From FeSO4 An aqueous solution of 0.1 M KOH, 0.2 M KNO3, and 0.05 M FeSO4 was heated at 90°C for 1 d. The precipitate was washed, and heated to 240°C for 2 h in air. It was then washed with HCl. Properties: BET specific surface area 26.6 m2/g, particle diameter 55 nm, particle size histogram available [1322].

TABLE 3.389 PZC/IEP of Maghemite Obtained from FeSO4 Electrolyte

T

Method

0.001–0.1 M KNO3

25

pH

Instrument

pH0

Reference

6.7

[1322]

3.1.12.3.1.2.7 From FeCl2 and NaNO2 5 cm3 of a solution 2 M in FeCl2 and 0.01 M in HCl and 5 cm3 of 1.4 M NaNO2 were added to a solution of 200 mg of gelatin in 80 cm3 of water. After 10 min, the solution was titrated to pH 9.5 with 1 M NaOH. The addition of solutions and titration were repeated 4 more times. Then the dispersion was aged at 60°C for 1 h. The particles were washed with water. Properties: TEM and HRTEM image, XRD pattern available [1327].

TABLE 3.390 PZC/IEP of Maghemite Obtained from FeCl2 and NaNO2 Electrolyte

T

Method

Instrument

iep

Malvern Zetasizer 3000HSA

pH0 Reference 6.8

[1327]

3.1.12.3.2 Hematite PZCs/IEPs of hematites are compiled in [510]. 3.1.12.3.2.1 Commercial 3.1.12.3.2.1.1 Hematite from AEA/Harwell Obtained according to the recipe described in Section 3.1.12.3.2.2.2.8. Properties: Particle diameter 55 nm, BET specific surface area 19 m2/g [1328,510]. TEM image available [510].

237

Compilation of PZCs/IEPs

TABLE 3.391 PZC/IEP of Hematite from AEA/Harwell Description

Electrolyte

T

Method

0.1, 0.01 M NaClO4

iep

pH0 a

pH

Fresh 0.001, 0.1 M Aged for 1 or 2 d NaClO4 a

Instrument

Malvern ZetaMaster

7.2 7.8a 9.5 7.5

Reference [1328] [510]

Only values reported, no data points.

3.1.12.3.2.1.2 Hematite from Aldrich Properties: Purity: >99%, [343], 99.5% [1329], >99.7% [1330], contains goethite [1329], 0.13% Al, 0.08% Si, 0.2% Mn [343], BET specific surface area 4.9 m2/g [1330], 9.2 m2/g [948], 6 m2/g, [343], 13.8 m2/g (ground material) [1329], particle size <5 μm [343]. TABLE 3.392 PZC/IEP of Hematite from Aldrich Description Original Sintered

a

Electrolyte

T

Method

23

iep

Streaming potential

0.001, 0.01 M NaNO3 25

iepa iep

Brookhaven ZetaPlus Malvern Zetasizer 2000

0.001 M KNO3

Instrument

pH0 5.2 3.7 6.8 8

Reference [261]a [1263] [343]

Only value reported, no data points.

3.1.12.3.2.1.3 Hematite from Alfa Properties: 330 ppm Ca, 480 ppm S, 150 ppm C [1331], BET specific surface area 8.4 m2/g [1022,1331], specific surface area 7.4 m2/g [1332], spheres [1331]. TABLE 3.393 PZC/IEP of Hematite from Alfa Electrolyte Acid- and base-washed

T

0.01 M KCl

Method iep Titration pH iep

a

Only value reported, no data points.

Instrument Malvern Zetasizer Nano

pH0 Reference 5.4

[334]

7.3a 8.2 8.3a

[1331] [1332]a [1022]

238

Surface Charging and Points of Zero Charge

3.1.12.3.2.1.4 Hematite from Alfa Aesar Properties: 94% of hematite, 6% of goethite [428], BET specific surface area 4.6 m2/g [428], 8.4 m2/g [1333]. TABLE 3.394 PZC/IEP of Hematite from Alfa Aesar Electrolyte

T

Method

Instrument

pH0

Reference

iep iep

Zeta-Meter 3.0, DT 1200 Zeta Probe, Colloidal Dynamics

6.5 9a

[1333] [428]

0.03 M NaCl 0.01 M NaCl a

Only value reported, no data points.

3.1.12.3.2.1.5 Hematite from Alfa Division, Danvers Properties: specific surface area 6.5 m2/g [670]. TABLE 3.395 PZC/IEP of Hematite from Alfa Division Electrolyte

T

0.0001 M KNO3 0.001 M NaNO3

a

Method a

25 25

Instrument

Mass titration Mass titration Inflection

pH0

Reference

6.1 5.9

[1334] [670]

Also 5–35°C

3.1.12.3.2.1.6 Hematite from Alfa, Johnson Matthey, Karlsruhe, Germany Properties: 99.999% pure [1335], BET specific surface area 8.8 m2/g [1336–1340], 8.5 m2/g [1335], mean particle size 30 mm [1335]. TABLE 3.396 PZC/IEP of Hematite from Alfa, Johnson Matthey Description

Electrolyte

T

Method

Instrument

pH0

Reference

Mass titration iepc Mass titration cipc Mass titration pH

Otsuka ELS-800

6.2

[1340,1341]

6.2 6.3 6.5 8.1

[1336]c [1338,1339a]

Washed

0.001 M KNO3

25

Washed Washed

0.001 M KNO3 0.005–0.1 M KNO3

25a 25

0.1 M NaNO3

a b

c

[1335]c [1278]b

Also 10–45°C. Acidity constants reported in [1278] are probably based on results from [1335]. Hematite from Alfa Aesar with specific surface area of 6 m2/g was studied in [1278]. Only value, data points not reported.

239

Compilation of PZCs/IEPs

3.1.12.3.2.1.7 Hematite from Atlantic Equipment Engineers Properties: 99.9% pure, mean diameter 307 nm [231]. TABLE 3.397 PZC/IEP of Hematite from Atlantic Equipment Engineers Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

25

iep

Brookhaven ZetaPlus

8.8

[231]

3.1.12.3.2.1.8 Hematite from Baker Properties: BET specific surface area 7 m2/g [1342], 8 m2/g [947], 9 m2/g [1343,1345], 10.1 m2/g [1344], average diameter 1 μm [1343], diameter 150–300 nm [1344]. TABLE 3.398 PZC/IEP of Hematite from Baker Description NaOH-washed

a

Electrolyte

T

0.001–0.1 M NaCl

Method iep cip

Instrument LaserZee Meter 501

pH0 a

8.5

Reference [1343,1345]

Only value reported, no data points.

3.1.12.3.2.1.9 Hematite from Baker and obtained by calcination of sulfate in air or in O2. Properties: Detailed analysis available [1].

Adamson Reagent-grade,

TABLE 3.399 PZC/IEP of Hematite from Baker and Adamson Description Washed, aged Washed, aged a

Electrolyte

T

Method

Instrument

pH0

Reference

21

iep Titration

Electrophoresis

0–0.1 M KNO3

8 8.4a

[1346] [1347]

Or iep [1348].

3.1.12.3.2.1.10 Pigment from Bayer Properties: Hematite, specific surface area 17.9 m2/g [374,375]. TABLE 3.400 PZC/IEP of Hematite Pigment from Bayer Electrolyte 0.001 M KNO3

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000

5.5

[374,375]

240

Surface Charging and Points of Zero Charge

3.1.12.3.2.1.11 Hematite from Carlo Erba 3.1.12.3.2.1.11.1 Purity 99.999% Properties: a-form [1349]. TABLE 3.401 PZC/IEP of 99.999% Hematite from Carlo Erba Electrolyte

T

Method

0.001–0.1 M NaNO3 0.001–0.1 M NaClO4

Instrument

pH0

Reference

8.5 8.2

[1349]

cip

3.1.12.3.2.1.11.2 Purity 99.99% Properties: a-form, specific surface area 2.3 m2/g [825]. TABLE 3.402 PZC/IEP of 99.99% Hematite from Carlo Erba Electrolyte

T

Method

KNO3 a

cip and iep

Instrument Streaming potential

pH0 8.5

a

Reference [825]

Only value, data points not reported.

3.1.12.3.2.1.12 Hematite from Commercial Minerals Properties: Contains lepidocrocite, D50 = 2 μm [431]. TABLE 3.403 PZC/IEP of Hematite from Commercial Minerals Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

22

iep

Acoustosizer, Matec

5.6a

[431]

a

Matches the maximum in settling rate and in yield value of 20 mass% dispersion.

3.1.12.3.2.1.13 RP 200M from Delta Colours Properties: Hematite, BET specific surface area 10.8 m2/g (N2), 10 m2/g (Kr), particle diameter 200 nm, TEM image available [665]. TABLE 3.404 PZC/IEP of RP 200M from Delta Colours Description

Electrolyte

Water-washed NaNO3

T

Method

Instrument

pH0

Reference

26

Salt addition

30 min–1 h equilibration

7.1

[665]

241

Compilation of PZCs/IEPs

3.1.12.3.2.1.14 Hematite from Fluka Properties: >99.3% hematite, BET specific surface area 4.2 m2/g [817,1350–1352]. TABLE 3.405 PZC/IEP of Hematite from Fluka Electrolyte

T

Method

0.01 M CsCl

20

pH

Instrument

pH0

Reference

7.4

[1350,1352]

3.1.12.3.2.1.15 FB 220 from Gesellschaft für Elektrometallurgie Properties: 100 mesh, a-form, 0.24% Mn, 0.11% Ti, 0.0025% P, BET specific surface area 6.5 m2/g [1353].

TABLE 3.406 PZC/IEP of FB 220 from Gesellschaft für Elektrometallurgie Description

Electrolyte

T

Soxhlet-extracted

0.005 M NaCl, NaNO3 25

Method

Instrument

pH0

Reference

iep

Electrophoresis

4

[1353]

3.1.12.3.2.1.16 From Gregory, Bottley & Lloyd Properties: Mean diameter 285 nm [1354]. TABLE 3.407 PZC/IEP of Hematite from Gregory, Bottley & Lloyd Electrolyte

T

0.01 M NaClO4

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer IIc

6.3

[1354]

3.1.12.3.2.1.17 Hematite from Johnson Matthey See also Alfa. Properties: >99.9% pure, BET specific surface area 8.5 m2/g [1355].

TABLE 3.408 PZC/IEP of Hematite from Johnson Matthey Electrolyte 0.1 M NaNO3 a

T

Method pH

Only value, data points not reported.

Instrument

pH0

Reference

8.1a

[1355,1356]

242

Surface Charging and Points of Zero Charge

3.1.12.3.2.1.18 Hematite from Kranz area 20.5 m2/g [1353].

Properties: BET specific surface

TABLE 3.409 PZC/IEP of Hematite from Kranz Electrolyte

T

Method

Instrument

pH0

Reference

0.005 M NaCl

25

iep

Electrophoresis

6.5a

[1353]

a

Only value reported, no data points.

3.1.12.3.2.1.19 Hematite from VEB Laborchemie Apolda Properties: BET specific surface area 6.8 m2/g [1357].

TABLE 3.410 PZC/IEP of Hematite from VEB Laborchemie Apolda Description NaOH- and HNO3-washed

a

Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaCl

25

pH iep

Malvern Zetasizer 3000

7 7a

[1357]

Based on arbitrary interpolation.

3.1.12.3.2.1.20 Hematite from Nanostructured and Amorphous Materials, Inc. Properties: Purity >99.9%, BET specific surface area 19 m2/g, particle size 67 ± 45 nm, spherical [1320].

TABLE 3.411 PZC/IEP of Hematite from Nanostructured and Amorphous Materials, Inc. Electrolyte HCl a

T

Method iep

Only value, no data points.

Instrument Zeta Probe, Colloidal Dynamics

pH0 8.6

a

Reference [1320]

243

Compilation of PZCs/IEPs

3.1.12.3.2.1.21 Hematite from Reachim area 6 m2/g [727,1358–1360].

Properties: BET specific surface

TABLE 3.412 PZC/IEP of Hematite from Reachim Description Washed with HNO3 and NaOH 0.1 M NaCl-washed

a b

Electrolyte

T

Method

0–1 M NaCl

25a

0.1 M NaCl

25

Instrument

pH0

Reference

cip

8.2

[727,1359]a

pH

8.5

[1358,1360]b

Also 60 and 100°C. Also 50 and 75°C.

3.1.12.3.2.1.22 Hematites from Ventron 3.1.12.3.2.1.22.1 Purity 99.99% Properties: a-form, specific surface area 1.6 m2/g [825].

TABLE 3.413 PZC/IEP of 99.99% Hematite from Ventron Electrolyte

T

KNO3 a

Method

Instrument

pH0 Reference

cip and iep

Streaming potential

8.2a

[825]

Only value, data points not reported.

3.1.12.3.2.1.22.2 Purity 99.9% area 9.1 m2/g [1361].

Properties: Hematite, BET specific surface

TABLE 3.414 PZC/IEP of 99.9% Hematite from Ventron Electrolyte

T

Method Titration iep

a

Only values, no data points.

Instrument

pH0

Reference

6.4a 7.8a

[1361]

244

Surface Charging and Points of Zero Charge

3.1.12.3.2.1.23

Other

TABLE 3.415 PZC/IEP of Unspecified Commercial Hematites Properties >99.7% pure, 9 m2/g Reagent grade, 7.9 m2/g Analytical grade, 8.8 m2/g

Electrolyte

T

Method

Instrument

pH0

Reference

KCl 0.002 M NaCl 0.001 M KNO3

23

pH iep Titration

Zeta-Meter

6 8.5 7.5

[1362] [943] [1247]

3.1.12.3.2.2 Synthetic 3.1.12.3.2.2.1 Thermal Decomposition of Oxide Hydroxide 3.1.12.3.2.2.1.1 Grinding of Goethite (Commercial or Synthetic) for 70 h Properties: Contains silica, TEM images, XRD patterns available; for particle diameter and BET specific surface area, see Table 3.416 [154].

TABLE 3.416 PZC/IEP of Hematite Obtained by Grinding of Goethite Description 2

73 m /g, 15 nm 61 m2/g, 17 nm a

Electrolyte

T

HNO3 + KOH

Method iep

a

Instrument

pH0

Reference

Malvern Zeta Master

8.2 8.2

[154]

Only value, no data points.

3.1.12.3.2.2.1.2 Decomposition of Lepidocrocite at 350°C Properties: BET specific surface area 110 m2/g [1363].

TABLE 3.417 PZC/IEP of Hematite Obtained by Decomposition of Lepidocrocite at 350°C Electrolyte 0.01–1 M NaCl

T

Method cip

Instrument

pH0

Reference

6.7

[1363]

245

Compilation of PZCs/IEPs

3.1.12.3.2.2.1.3

Thermal Treatment of Oxide Hydroxides

TABLE 3.418 PZC/IEP of Hematite Obtained by Thermal Treatment of Oxide Hydroxides

Precursor Goethite Lepidocrocite Feroxyhite at 560°C for 20 h Goethite from Toda Kogyo at 450°C for 15 min under nitrogen, then base-, acid-, and water-washed, and air-dried at 75°C Goethite at 415°C for 1 h

Specific Surface Area (m2/g)

Electrolyte

14 36 64

NaCl

23.7

0.05–1 M NaNO3 NaCl, NaClO4

17

0.001– 0.1 M NaCl

T

25

pH0

Reference

Salt addition

Method

7.3 5.9 7.1

[707]

cip

7.5

[1282]

7.8 8

[1245]

Intersection iep

Instrument

Electrophoresis

3.1.12.3.2.2.2 From chloride 3.1.12.3.2.2.2.1 Addition of 1 M FeCl3 to Boiling Diluted HCl 490 cm3 of 0.004 M HCl was heated to boiling. 10 cm3 of 1 M FeCl3 was added. The solution was boiled for 1 d. The precipitate was washed with 0.001 M HCl. In [1364], the concentration of HCl was 0.002 M. In [1365], 50 cm3 of 0.72 M FeCl3 in 0.001 M HCl were added to 1.95 dm3 of boiling 0.004 M HCl, and the dispersion was aged for 1 d at 100°C. Properties: BET specific surface area 17.4 m2/g [1365], 23 m3/g [1364], particle diameter 50 nm [1364], TEM image, particle size distribution available [1366].

246

Surface Charging and Points of Zero Charge

TABLE 3.419 PZC/IEP of Hematite Obtained by Addition of 1 M FeCl3 to Boiling Diluted HCl Electrolyte

Method

Instrument

pH0

Reference

0.01 M NaCl

Salt addition pH iep

Malvern Zetasizer IV

8.5a

[1364]

0.001 M KCl

iep

Malvern Zetasizer 3

9.2

[1366]

9.3

[1365]

0.006–0.5 M NaClO4 a

T

25

cip

IEP is based on subjective interpolation (no data points for pH 8–10).

3.1.12.3.2.2.2.2 Addition of 0.72 M FeCl3 to 0.00375 M HCl at 96°C 25 cm3 of 0.72 M FeCl3 was added to 975 cm3 of 3.75 × 10- 3 M HCl solution at 96°C, and aged at 100°C for 1 d. The precipitate was washed with 0.001 M HClO4. In [1365], only the final FeCl3 concentration (0.02 M) is reported, HCl concentration was 0.002 M, and the suspension was aged for 3 d at 98°C. Properties: Hematite (electron diffraction) [723], BET specific surface area 33 m2/g [1365], 70.8 m2/g [723], 15.1 m2/g [1367], particle radius 46 nm [1367], TEM image available, [723,1367].

TABLE 3.420 PZC/IEP of Hematite Obtained by Addition of 0.72 M FeCl3 to 0.00375 M HCl at 96°C Electrolyte

T

Method

Instrument

0.005–0.1 M NaClO4 0.005–0.5 M NaNO3

25 25

cip cip iep Stability

Zetasizer 3, Malvern

pH0

Reference

9.1 9.2

[1365] [1367]

3.1.12.3.2.2.2.3 Addition of Diluted FeCl3 Solution to Boiling Water Properties: BET specific surface area 83 m2/g [1365], 5 nm in diameter [1368].

247

Compilation of PZCs/IEPs

TABLE 3.421 PZC/IEP of Hematite Obtained by Addition of Diluted FeCl3 to Boiling Water Recipe

Electrolyte

50 cm3 of 0.02 M FeCl3 added at 2 drops s−1 to 450 cm3 of boiling water. Boiled for further 5 min. Dialyzed against HClO4 at pH 3.5 100 cm3 of fresh 0.105 M FeCl3 added to 2 L of boiling water. Refluxed for 1 d a

T

25

0.005–0.1 M NaClO4

Method

Instrument

pH0

Reference

iepa

Electrophoresis

8.3

[1368]

9.2

[1365]

cip

Only value reported, no data points.

3.1.12.3.2.2.2.4 Addition of 0.5 M FeCl3 to Boiling Water 50 cm3 of 0.5 M FeCl3 was added dropwise to 950 cm3 of boiling water. The solution was dialyzed against water. Properties: XRD pattern, TEM image available [1369]. TABLE 3.422 PZC/IEP of Hematite Obtained by Addition of 0.5 M FeCl3 to Boiling Water Description 12 nm 32 nm

Electrolyte 0.001–0.1 M NaCl

T

Method

Instrument

pH0

Reference

iep

Brookhaven Zeta PALS

7.8 8.2

[1369]

3.1.12.3.2.2.2.5 Aging at 100°C of Precipitate Obtained from 6 M NaOH and 2 M FeCl3 A gel was made by addition of 100 cm3 of 6 M NaOH to 100 cm3 of 2 M FeCl3 at room temperature within 10 min. The bottle was sealed and aged at 100°C for 3 d. The precipitate was washed with water and dialyzed. A modified recipe (from [1370]): 8 d at 100°C followed by cooling to room temperature for 3 d. BET specific surface area 27.4 m2/g, [1367] 28.3 m2/g, [1371] particle radius 61 nm [1367], number average particle diameter 119 nm [1371] TEM image available [1367,1371].

248

Surface Charging and Points of Zero Charge

TABLE 3.423 PZC/IEP of Hematite Obtained by Aging at 100°C of Precipitate Obtained from 6 M NaOH and 2 M FeCl3 Description 2 d at 100°C

Electrolyte

T

Method

Instrument

pH0

Reference

0.005–0.5 M NaNO3

25

cip iep Stability Titration cip

Zetasizer 3, Malvern

9.2

[1367]

9.2a 9.5

[1370] [1371]

0.001–0.1 M NaNO3 0.005–0.5 M NaNO3 a

PZC reported, no data points.

3.1.12.3.2.2.2.6 Aging at 180°C of Precipitate Obtained from 8 M NaOH and 2 M FeCl3 Recipe from [1372]: A gel made by slow addition of 40 cm3 of 8 M NaOH to 40 cm3 of 2 M FeCl3 was stirred at room temperature for 10 min. The gel was autoclaved at 180°C for 2 h. It was washed with water. Properties: Hematite, BET specific surface area 3.4 m2/g (N2), 2.9 m2/g (Kr), particle diameter 2–6 μm, TEM image available [665].

TABLE 3.424 PZC/IEP of Hematite Obtained by Aging at 180°C of Precipitate Obtained from 8 M NaOH and 2 M FeCl3 Electrolyte

T

Method

Instrument

pH0

Reference

NaNO3

26

Salt addition

30 min–1 h equilibration

7.4

[665]

3.1.12.3.2.2.2.7 Calcination at 300°C of the Product of Precipitation and Aging 0.5 M FeCl3 was neutralized with 0.5 M NaOH, and the dispersion was aged at 80°C. The precipitate was washed, calcined at 300°C, and ground. Properties: Hematite, BET specific surface area 44 m2/g [1373].

TABLE 3.425 PZC/IEP of Hematite Obtained by Calcination at 300°C of the Product of Precipitation and Aging Electrolyte

T

Method iep

Instrument

pH0

Reference

6.5

[1373]

Compilation of PZCs/IEPs

249

3.1.12.3.2.2.2.8 Aging of Acidified FeCl3 Solution at 100°C Solutions containing FeCl3 (usually 0.009–0.45 M) and HCl (usually 0.001–0.3 M) were kept at about 100°C for different times. Different cleaning procedures were used to remove excess of chloride. For a similar recipe, but without HCl, see Section 3.1.12.3.2.2.2.9. Properties: Different structures (hematite or b-FeOOH) were obtained, depending on the experimental conditions [1374]: hematite with admixture of d-FeOOH [1375], hematite [352,510,571,608,1376–1386], BET specific surface area 6.4 m2/g [608], 12.7 m2/g [1380], 13.2 m2/g [571], 13.3 m2/g [1378], 14.4 m2/g [1379], 16 m2/g [1377], 16.6 m2/g [1386], 16.7 m2/g [1383], 20 m2/g [328], 20.1 m2/g [352], 20.7 m2/g [1381], 30 m2/g [1384], 34.5 m2/g [430], 68 m2/g [1375], 1.7 m2/g [1387], diameter 145 nm [510], 70 nm [1388], 60 nm [1376], average diameter 100 nm [1379], 90 nm [1380], mean diameter 96 nm [1386], 100 nm [1383], 600 nm [608], modal diameter 125 nm [1378], 120 nm [328,352,571], 100 nm [1384], 300 nm [1389], particle radius 43 nm [1385], number averaged size 120 nm [1377], 65 ± 3 nm [1369], average size 199 nm [1381], d10 = 56 nm, d50 = 96 nm, d90 = 152 nm [1390], Different shapes were obtained, depending on the experimental conditions [1374]: rounded cubes [1377], spheres [352,510,571,1364,1378–1380,1388], polyhedral particles 200 nm in diameter [1387], XRD pattern available [1369], TEM image available [1374,1382,1369,1387], EM image available [1389], SEM image available [510,608,1374,1383], AFM image available [1381]. 3.1.12.3.2.2.2.9 Aging of FeCl3 Solution (no HCl added) at 100°C Fresh 5–50 mM FeCl3 solution was refluxed, then dialyzed at 100°C against water [1393]. Properties: Hematite, diameter 3–25 nm, TEM image available [1393]. From 0.1 M FeCl3 aged for 10 d at 100°C. The precipitate was washed with water [1394]. Properties: >98% hematite [38], contains 0.3 mol% of Cl with respect to Fe, which is not removable by water washing, cubic particles [1394], BET specific surface area 34 m2/g [38], average size 120 nm, uniform particles [38], electron micrograph available [1394].

FeCl3 0.018 M, HCl 0.001 M, 24 h at 100°C, 30 washing cyclesb

FeCl3 0.0015 M, HCl 0.001 M, 1 d at 100°C, 4 M NaOH-washed FeCl3 0.02 M, HCl 0.001 M, 1 d at 105°C, NaOH-washed

Cubic hematite, FeCl3 0.09 M, HCl 0.01 M, 24 h at 150°C (apparently a typographic error) Double-ellipsoidal Hematite, FeCl3 0.018 M, HCl 0.05 M, 7 d at 100°C Spherical Hematite, FeCl3 0.0315 M, HCl 0.005 M, 14 d at 100°C FeCl3 0.0315 M, HCl 0.005 M, 14 d at 100°C FeCl3 0.0002 M, HCl 0.001 M, 1 d at 100°C FeCl3 0.019 M, HCl 0.0012 M, 28 h at 105°C

FeCl3 0.0015 M, HCl 0.001 or 0.01 M, 1–14 d at 90°C FeCl3 0.0015 M, HCl 0.001 M, 2 d at 90°C, dispersion 2 d aged. The same particles aged in HClO4 at pH 1.3 for 3 d, dispersion aged for a few minutes

Description

25 25

0.01 M NaClO4 0.001–0.1 M NaCl 0.01 M

25

20 25 25

25

T

0.001–0.1 M NaNO3

0.0001 M KCl 0.01 M HCl 0.01 M NaNO3

Unspecified KNO3 KCl 0.01 M NaNO3

0.1 M NaClO4

Electrolyte

cip iepa iep

iep cip iep

iep iep iep

iep Salt titration Salt titration iep

iep iep

Method

TABLE 3.426 PZC/IEP of Hematite Obtained by Aging of Acidified FeCl3 Solution at 100°C

Zetasizer IIc

Malvern Zetasizer IIc

Rank Brothers Mark II

Rank Brothers Mark II

Electrophoresis Rank Brothers Rank Brothers Mark II

Rank Brothers

Laser Zee 501, Pen Kem

Malvern ZetaMaster

Instrument

7.3 7.4 7.5

7.1 7.2 7.3

7 7 7

6

6

6 8 8.8 6.7

8.5d

<5 if any <5 if any

pH0

[1377]

[1376]

[1379]

[571]

[1389] [1382] [1384]

[1374]

[1388]

[1391] [510]

Reference

250 Surface Charging and Points of Zero Charge

0.001, 0.01 M NaNO3 0.001 M KCl

FeCl3 0.0015 M, HCl 0.001 M, 1 d at 100°C, water-washed

e

d

c

b

a

Arbitrary interpolation. Lower IEP with fewer washing cycles. 28°C reported in text, 23°C in figure. Only value reported, no data points. IEP shifts to high pH at high ionic strengths, recipe from [1390].

FeCl3 0.005 M, HCl 0.002 M, refluxed for 2 d, then dialyzed for 7 d against water

23

25

25

25

25

iep

iep

0.02 M NaNO3 0.001–0.1 M NaCl 0.001–1 M NaNO3

Acid- and base-washed FeCl3 0.02 M, HCl 0.002 M, 10 d at 98°C FeCl3 0.02 M, HCl 0.001 M, 1 d at 100°C

0.001 M NaNO3

25

0.01 M NaCl

0.02 M FeCl3, 0.001 M HCl, 1 d at 100°C [1392]

FeCl3 0.0015 M, HCl 0.001 M, 1 d at 100°C

25

0.001–1 M NaNO3

FeCl3 0.04 M, HCl 0.001 M, 7 d at 100°C 25

cip iep iep cip iep pH iep iep iep cip iep Intersection iep

0.0001–0.1 M NaCl

Zeta-Meter 3.0 Pen Kem 501 Malvern Zetasizer 3 Brookhaven ZetaPlus

Rank Brothers MK-2

Pen Kem 3000

Acustosizer Brookhaven Zeta PALS Acoustosizer

Malvern Zetasizer 3000

Pen Kem Laser ZeeMeter501 Acoustosizer

van Gills cell

iepd

0.001 M NaNO3

FeCl3 0.018 M, HCl 0.001 M, 1 d at 105°C, 0.001 M HNO3-washed FeCl3 0.018 M, HCl 0.001 M, 1 d at 110°C, 0.001 M HClO4-washed 24 h at 100°C, concentrations of reagents not indicated

28c

Zeta-Meter 3.0 Pen Kem 501 Rank Brothers Mark II

0.003–0.1 M NaNO3, NaCl, NaClO4 0.01 M NaNO3

iep cip iep

FeCl3 0.0015 M, HCl 0.001 M, 1 d at 100°C

[352]

[337]

10e

[1385]

[1386]

[430] [1369] [1383]

[1381]

[608]

[1375]

[1378]

[1380]

[328]

9.5

9.2

8.7 8.8 9 9 9.2

8.3 6 8.3 8.5 8.5

7.9

7.6

7.5

Compilation of PZCs/IEPs 251

252

Surface Charging and Points of Zero Charge

TABLE 3.427 PZC/IEP of Hematite Obtained by Aging of FeCl3 Solution at 100°C Description

1 d at 100°C,

Electrolyte

T

0.0001 M KCl

20

iep

25

Inflection Coagulation iep

0.0005 M NaCl

25

Method

Instrument

pH0

Reference

Pen Kem Laser Zee Meter 501

<3 if any

[1394]

Rank Brothers

7.5

[1393]

7.6

[38]

3.1.12.3.2.2.2.10 Aging of Hematite Seeds in Acidified FeCl3 Solution 1 dm3 of solution, 0.018 M in FeCl3 and 0.00375 M (or 0.004 M) in HCl was aged for 1 d at 100°C. The sol was flocculated by addition of solid KCl (final concentration 0.15 M). The precipitate was washed with 0.001 M HClO4. The particles obtained in the first step were then used as seeds in next steps. In the next steps, 2 dm3 of solution, 0.005 M in FeCl3 and 0.09 M in HClO4, was heated, and seed particles from the previous step were added when the temperature reached 100°C. The dispersion was aged for up to 30 h at 100°C. The particles were washed with 0.001 M HClO4 and used as seeds in the next cycle. Typically, three cycles of seeding were used. Properties: BET specific surface area 26.5 m2/g [243], 14.4 m2/g (modified recipe: flocculation with KCl was omitted; instead, the particles were washed in 0.001 M HClO4 and water) [1395], specific surface area 4.6 m2/g [1396], 17.4 m2/g (calculated from particle size) [1397,1398], particle size 66 nm [1397,1398], 50 nm [1399], particle diameter 96 nm [1400], 250 nm in diameter, [1396], radius 40 nm [243], TEM and SEM image available, particle size at consecutive stages of growth reported [1401], spherical, monodispersed [243,1400].

TABLE 3.428 PZC/IEP of Hematite Obtained by Aging of Hematite Seeds in Acidified FeCl3 Solution Electrolyte

T

Method

0.006–0.5 M NaClO4

25

0.01–0.27 M NaClO4

25

cip Titration Coagulation cip Salt titration iep cip

0.001–0.5 M NaNO3

Instrument

pH0

Reference [1399,1400] [1396]a

Brookhaven ZetaPlus

8.1 8.6 8.7 9.2 8 9.4

[1397,1398]

[1395] continued

253

Compilation of PZCs/IEPs

TABLE 3.428

(continued)

Electrolyte

T

0.01–1 M KCl

25

0.1 M KCl

25

a b

c

Method cip iepc pH

Instrument

pH0

Reference

Malvern Zetamaster 2

9.5 9.5 9.5

[243,1402a] [243]b

Only values reported, no data points. The sample studied in [1403] (heterodispersed hematite) after long aging was coated with hematite using a procedure described in [1401]. The coating-to-core ratio is less than 3:7. BET specific surface area 27.4 m2/g [243]. Matches the maximum in coagulation velocity reported in Ref. [1414].

3.1.12.3.2.2.3 From Nitrate 3.1.12.3.2.2.3.1 Addition of 0.1 M Fe(NO3)3 to Boiling Water 100 cm3 of 0.1 M Fe(NO3)3 was added to 1 dm3 of boiling water with stirring, and then dialyzed. In the original recipe from [1404] 1 M FeCl3 was added at a rate of 2 drops/s. Properties: BET specific surface area 109 m2/g, 10–12 nm spherical particles [1405].

TABLE 3.429 PZC/IEP of Hematite Obtained by Addition of 0.1 M Fe(NO3)3 to Boiling Water Electrolyte

T

Method

0.1 M NaNO3

25

pH

Instrument

pH0

Reference

8.5

[1405]

3.1.12.3.2.2.3.2 Addition of 1 M Fe(NO3)3 to Boiling Water 200 cm3 of 1 M Fe(NO3)3 was added dropwise to 2.5 dm3 of boiling water. The solution was dialyzed. Properties: BET specific surface area 67.5 m2/g, XRD pattern available [1326].

TABLE 3.430 PZC/IEP of Hematite Obtained by Addition of 1 M Fe(NO3)3 to Boiling Water Electrolyte

T

Method

0.1 M NaNO3

25

pH

a

Only acidity constants reported, no data points.

Instrument

pH0

Reference

7.5a

[1326]

254

Surface Charging and Points of Zero Charge

3.1.12.3.2.2.3.3 Aging at 140–150°C of Precipitate Obtained from Fe(NO3)3 and KOH KOH was added dropwise to boiling 0.4 M Fe(NO3)3 until pH 7. The precipitate was decanted and aged at 140–150°C for 8 h. It was washed at pH 9. Properties: BET specific surface area 32.3 m2/g [1412], 43 m2/g [1413], 29.6 m2/g [243], 31, 18, and 21 m2/g (3 samples) [1403], 31, 18, and 35 m2/g [1406], 48 m2/g [1407], 29 m2/g (slightly modified recipe) [1408,1409], 43 m2/g [1410], 68.5 m2/g [1411], specific surface area 29 m2/g [825], mean size 50 nm [1410,1413], parallelograms, included angle of 60°C [1413], irregular shapes and sizes, radii about 50 nm [243].

TABLE 3.431 PZC/IEP of Hematite Obtained by Aging at 140–150°C of Precipitate Obtained from Fe(NO3)3 and KOH Description

Original Washed

Electrolyte 0.001–0.1 M NaCl 0.01–1 M NaCl 0.002–1 M KCl 0.0001–1 M KCl, LiCl, KNO3 KCld

T

25 20 20

KNO3

Autoclaved for 12 h

Aged for several years, washed with HCl Autoclaved for 1 d

a b c d

e

Method

Instrument

cip Stability cip Stability cip iep cip cip

20e

21 21

cip pH

0.002–0.1 M KNO3

20

cip iep

Reference a

cip cip cip

0.005–1 M KNO3 0.001–0.1 M NaNO3, KNO3, NaClO4 0.001–0.1 M KNO3 0.01 M KNO3

pH0

Malvern Zetasizer II Pen Kem 3000

8–8.5 8.3b 8.4 9.5 8.5

[1406]

8.5

[1403]

8.6b

[825]

8.7 8.7

[1409] [1349]

8.9 8.9

[1413] [1410]

9.1

[1412]

[1411] [1407] [243]c

No clear cip. Only value reported, no data points. The same material as studied in [1403,1406] after long storage. PZC at the same pH in the presence of NaCl, CsCl, NaNO3, KNO3, and CsNO3 is reported in the conclusion. Also 60°C.

255

Compilation of PZCs/IEPs

3.1.12.3.2.2.3.4 Calcination of Precipitate Obtained from Acidified Fe(NO3)3 and Ammonia Nitrate was adjusted to pH 2 with HNO3, and then treated with excess of ammonia. The precipitate was washed with water, calcined at 600°C for 6 h, washed with water again, calcined at 600–1400°C for 3 h, and washed with water again [1077,1078]. Hydroxide was obtained from 1 M Fe(NO3)3 and a 10% excess of 3 M ammonia, washed with water, and calcined at 600°C for 6 h. The oxide was washed with water until constant conductivity. It was then calcined for 3 h at different temperatures and washed again [33,1304]. Properties: Conversion to magnetite at >1200°C [1078], lattice spacing data available [1077], hematite (heated below 1200°C), magnetite with admixture of hematite (1400°C) [1304]. Specific surface area of the samples obtained by second calcination at 600, 800 [1078,1304], and 1000°C [1304]: 6.7, 1.5, and <0.1 m2/g, 100 nm in diameter [33]. TABLE 3.432 PZC/IEP of Products of Calcination of Precipitate Obtained from Fe(NO3)3 and Ammonia Second Calcination Temperature (°C) 1200 None 600 800 1000 1200 1400 600 800 1000 1200 1400 a

Electrolyte 0.001 M NaCl 0.001 M NaCl 0.001 M NaCl

0.001 M NaCl

T

Method

25 25 25

25

a

iep iepa iepa

iepa

Instrument Streaming potential Streaming potential Streaming potential

Streaming potential before/after further purification

pH0 Uncrushed/ Crushed Reference 4.3 8.9 9.1 9.3/9.1 4/8.5 4.3/9 4/8.8 9.5/9.4 9.4/9.5 7.5/4 4/4.6 3.4/4

[1077] [33] [1078]

[1304]

Only values, data points not reported.

3.1.12.3.2.2.3.5 Aging of Acidified Fe(NO3)3 Solution at 100°C Solutions containing Fe(NO3)3 (usually 0.0027–0.18 M) and HNO3 (usually 0.001–0.3 M) were kept at 100°C for different times.

256

Surface Charging and Points of Zero Charge

Properties: Hematite [883,1415,1416], hematite with 1–10% of goethite [1374], BET specific surface area 42.5 m2/g [332,1417], 46.5 m2/g [1416], 48 m2/g [883], average size: 50 nm [1416], 100–600 nm in diameter, [883], ellipsoids, dimensions 250–400 nm [1415,1418], ellipsoidal particles were obtained over a wide range of experimental conditions [1374], TEM and SEM images available [1374].

TABLE 3.433 PZC/IEP of Hematite Obtained by Aging of Acidified Fe(NO3)3 Solution at 100°C Description

Electrolyte

T

Fe(NO3)3 0.018 M, 0.01 M NaCl HNO3 0.005 M at 100°C Ellipsoidal 0.01 M NaNO3 Hematite, Fe(NO3)3 0.018 M, HNO3 0.05 M, 24 h at 100°C 8.3 g of Fe(NO3)3 • 0.01 M NaNO3 H2O (?) was added 0.01 M KNO3 to 1 L of 0.002 M HNO3, at 98°C, and aged at 98°C for 7 d Hematite, Fe(NO3)3 0.05 M, HNO3 0.05 M, 6.5 h at 100°C, aged in darkness for 1 d before washing 25 Acidic (or acidified 0.01 M KCl ?) Fe(NO3)3 solution refluxed for 1 d a

Method

Instrument

pH0

Reference

iepa

Pen Kem 3000, Rank Brothers Mark II

6

[1415,1418]

iep

Rank Brothers

6.7

[1374]

iep

Malvern Zetasizer 3000HSa

7.3 7.2

[332,1417]a

iep

Malvern Zetamaster S

8

[883]

iep

Karl Zeiss citopherometer

8.5

[1416]

Only values, data points not reported.

3.1.12.3.2.2.3.6 Aging of Fe(NO3)3 Solution (no acid added) at 100°C Properties: Structure confirmed by XRD [462], BET specific surface area 15 m2/g [543], 34–44 m2/g [1180,1420], 21 m2/g [119], specific surface area 63 m2/g [1419], 30 m2/g [462], diameter of 20 nm [1419], spherical [1419].

257

Compilation of PZCs/IEPs

TABLE 3.434 PZC/IEP of Hematite Obtained by Aging of Fe(NO3)3 Solution at 100°C Description 0.25 M Fe(NO3)3 was boiled for 18 d, different washing procedures 0.25 M Fe(NO3)3 was boiled for 18 d, different washing procedures 0.25 M Fe(NO3)3 was boiled for 18 d, different washing procedures 0.25 M Fe(NO3)3 was boiled for 18 d, different washing procedures 0.25 M Fe(NO3)3 was boiled for 18 d, different washing procedures Refluxed, KOH-washed, aged, 23 m2/g 7 d at 98°C Refluxed, washed, aged Refluxed, washed, aged a b c d e

Electrolyte

T

Method

Instrument

pH0

0.002 M NaCl

10

0.001–0.1 M NaClO4

iep

Rank Brothers Mark II

6.3

[1419]b

22

cip

Fast titrationa Slow titration

8.3 8.4

[119]

0.002 M (CH3)4NCl

25

pHb

8.4

[1281]

0.0001–1 M KNO3 1 M KNO3

21

cip

8.5c

[543]

0.002–1 M KCl

20

cip

8.6 9.3 8.4 8.9

[1180b,1420]

0–1 M NaNO3, NaCl, NaClO4

25

Titration

8.7b

[1421]

0.003–0.1 M NaNO3 0.001–0.1 M KNO3 0–0.01 M KNO3 1 M KNO3

25

cip

8.8

[462]

25

Titration

9b,d

[1422]

21

Titration

9e 8.8

[1347]

KOH-washed Dialyzed KOH-washed Dialyzed

Reference

Also 35 and 60°C. Only value, data points not reported. PZC from [543] is cited as 8.8–9 (dependent on ionic strength) in [1]. Or IEP ([1423]). [571] reports IEP at pH 8.4 and 9 (Reference 6, apparently the same original source).

258

Surface Charging and Points of Zero Charge

3.1.12.3.2.2.3.7 Calcination of Precipitate Obtained by Refluxing of Fe(NO3)3 Solution Fe(NO3)3 solution was boiled under reflux for 18 d, and then purified by electrodialysis. This was followed by thermal treatment. It was not purified. Not explicitly addressed as hematite.

TABLE 3.435 PZC/IEP of Fe2O3 Obtained by Calcination of Precipitate Obtained by Refluxing of Fe(NO3)3 Solution Heated at (°C) 300 700 1000

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl, KNO3

30

iep

Electrophoresis

6.9 6.9 6.3

[250]

3.1.12.3.2.2.4 From Perchlorate Solutions containing Fe(ClO4)3 (0.0045 to 2.25 M) and HClO4 (0.01 to 0.2 M) were kept at 100°C for 1–14 d. Properties: Hematite, different shapes obtained dependent on the experimental conditions [1374], BET specific surface area 14 m2/g [1424], TEM and SEM images available [1374], IR spectra available [471].

TABLE 3.436 PZC/IEP of Hematite Obtained from Perchlorate Description Bipyramidal hematite, Fe(ClO4)3 0.018 M, HClO4 0.05 M, 3 d at 100°C Fe(ClO4)3 0.02 M, initial pH 2, 2 d at 120°C, mean diameter 350 nm Fe(ClO4)3 0.04 M, initial pH 1.75, 5 d at 100°C, mean diameter 450 nm Fe(ClO4)3 0.02 M, initial pH 1.4, 2 d at 120°C, mean diameter 1.3 μm

Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaNO3

iep

Rank Brothers

6

[1374]

0.01 M

iep

Malvern Zetasizer II

6.7

[471]

Multiple

<1.5 if any

3.1.12.3.2.2.5 From Sulfate Synthetic Fe2O3, from FeNH4(SO4)2 and NH3, washed with 5% NH4NO3, then with water. Not explicitly addressed as hematite.

259

Compilation of PZCs/IEPs

TABLE 3.437 PZC/IEP of Fe2O3 Obtained from Sulfate Description

Electrolyte

T

Method

Original Calcined at 850°C for 2 h a

iep

Instrument

pH0

Electrophoresis Titration

a

Reference

>7 6.5

[1091]

The original uncalcined material is a hydrated oxide rather than hematite. The extrapolated IEP of this material (pH 8) was cited in [1] and by many others as the IEP of hematite.

3.1.12.3.2.2.6 From Phosphate 3.1.12.3.2.2.6.1 From Phosphate and Perchlorate A solution 0.1 M in Fe(ClO4)3 and 0.0045 M in KH2PO4 and 0.1 M in urea was heated at 100°C for 1 d. Washed in 7.5 M NaOH. Properties: Uniform particles 298 nm long and 64 nm wide, TEM image and IR spectrum available [1426]. TABLE 3.438 PZC/IEP of Hematite Obtained from Phosphate and Perchlorate Electrolyte 0.01 M KNO3

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440

6

[1426]

3.1.12.3.2.2.6.2 From Phosphate and Chloride A solution containing 0.02 M FeCl3 and 0.0002 M NaH2PO4 was heated at 100°C for 2 d, and then the precipitate was washed with water. Properties: a-form [1251,1427,1428], [364], ellipsoidal particles, major axis 420 nm, minor axis 190 nm [1429], particles 600 nm long, axial ratio 4–5 [1251], elongated particles: 193 nm × 75 nm and 163 nm × 43 nm [364], particle length and axial ratio reported, also for different phosphate concentrations [1430], TEM image available [364,1251,1429–1431], SEM image available [1251,1427,1428,1431], XRD pattern available [364,1428].

TABLE 3.439 PZC/IEP of Hematite Obtained from Phosphate and Chloride Description 0.0004 M NaH2PO4

Electrolyte 0.01 M NaNO3

T

Method iep

Instrument Delsa Pen Kem 3000

pH0

Reference

6.5

[1251,1431a]

continued

260

TABLE 3.439

Surface Charging and Points of Zero Charge

(continued)

Description

Electrolyte

0.0004 M NaH2PO4, 3 d aged 0.0003 M NaH2PO4 4 d aged 0.0003 M NaH2PO4 0.0003 M NaH2PO4 a b

T

Method

25

iep iep

Rank Brothers Mark II 7 Delsa 440 7.5

25 25

iep iep iep iep

Malvern Zetasizer 2c Malvern Zetasizer 2c Pen Kem 3000

0.01 M KNO3 0.01 M NaNO3 0.01 M NaNO3 0.001 M NaOH + HCl

Instrument

pH0

7.5b 7.5b 8.5 8.8

Reference [1429] [1432] [364] [364] [1428] [1427]

Only value, no data points. Arbitrary interpolation.

3.1.12.3.2.2.7 High Temperature 3.1.12.3.2.2.7.1 Calcination of Magnetite at 600°C in Air There is no clear statement about the chemical nature of the material studied in [1303]. Properties: SEM image available [1303].

TABLE 3.440 PZC/IEP of Iron Oxide Obtained by Calcination of Magnetite at 600°C in Air Electrolyte 0.001 M KNO3

T

Method

Instrument

pH0

Reference

iep

Streaming potential

5.1

[1303]

3.1.12.3.2.2.7.2 Heat Treatment of Maghemite at 550°C The recipe for maghemite is reported in [1323]. Properties: BET specific surface area 16 m2/g [1323,1324], TEM image available [1324].

TABLE 3.441 PZC/IEP of Hematite Obtained by Heat Treatment of Maghemite Description Original Hydrated for 20 h

Electrolyte

T

0.01–1 M KCl 0.01–1 M KCl

25 20

Method cip cip/iep iep

Instrument

pH0

Reference

Electrophoresis

6.7 6.7 7.9

[1323] [1324]

261

Compilation of PZCs/IEPs

3.1.12.3.2.2.7.3 Calcination of Nitrate at 450°C for 2 hours and Grinding Properties: Hematite, BET specific surface area 58.1 m2/g [656].

TABLE 3.442 PZC/IEP of Hematite Obtained by Calcination of Nitrate Electrolyte

T

Method

Instrument

pH a

pH0

Reference

8.8a

[656]

Only value, no data points.

3.1.12.3.2.2.8 Other 3.1.12.3.2.2.8.1 Recipe from [1433] Properties: Cubic of 1 mm side [1434].

TABLE 3.443 PZC/IEP of Hematite Obtained According to Recipe from [1433] Electrolyte

T

0.01 M NaClO4

Method

Instrument

pH0

Reference

pH iep

Rank Brothers Mark II

6.8 6.8

[1434]

3.1.12.3.2.2.8.2 Recipe from [1435] Reference [1435] is cited in [1436] for the recipe. Actually, no specific recipe is reported in [1435], but another paper is cited. Properties: Specific surface area 18.8 m2/g [1436].

TABLE 3.444 PZC/IEP of Hematite Obtained According to Recipe from [1435] Electrolyte KNO3 a

T

Method cip

Instrument

pH0 8.2

a

Reference [1436]

Only value reported, no data points.

3.1.12.3.2.2.8.3 Recipe from [1437] Anhydrous FeSO4 precursor was calcined in air at 600–800°C for 4–24 h. Properties: 99.9% pure, BET specific surface area 100 m2/g [576].

262

Surface Charging and Points of Zero Charge

TABLE 3.445 PZC/IEP of Hematite Obtained According to Recipe from [1437] Electrolyte

T

Method

0.001–0.1 M KCl a

Instrument

pH0

Reference

6a

[576]

pH

No clear CIP, abnormal ionic strength effect in basic range.

3.1.12.3.2.2.8.4 Recipe from [1438] TABLE 3.446 PZC/IEP of Hematite Obtained According to Recipe from [1438] Electrolyte

T

Method

0.005–0.1 M NaNO3

Instrument

pH0

Reference

9.4

[747]

cip

3.1.12.3.2.2.8.5 Unspecified Recipe from [1374] See Sections 3.1.12.3.2.2.2.8, 3.1.12.3.2.2.3.5, and 3.1.12.3.2.2.4 for specific recipes for hematite from [1374]. Properties: a-form, specific surface area 3.1 m2/g, particle size 300 nm, spherical [1439]. TABLE 3.447 PZC/IEP of Hematite Obtained According to Unspecified Recipe from [1374] Electrolyte

T

Method

NaNO3 a

cip or salt titration cip Only value, data points not reported.

3.1.12.3.2.2.8.6

Instrument

pH0

Reference

Rank Brothers MK-2

7.5a 7.2a

[1439]

Other

TABLE 3.448 PZC/IEP of Other Synthetic Hematites Recipe, Properties

Electrolyte

Reference 6 in [225], dialyzed

NaOH + HCl

T

Method iep

Instrument Electrophoresis

pH0

Reference

1.9

[225]

continued

263

Compilation of PZCs/IEPs

TABLE 3.448

(continued)

Recipe, Properties

Electrolyte

6.7 m2/g, d50 516 nm

0.0001 M NaNO3

T

iep

Precipitated

b

Instrument

pH0

0.001– 0.1 M 25 cip KNO3 iep

Reference

7.8a [345]

Zeta-Meter 3.0

Titration

7.3 m2/gb

a

Method

8.7 Rank Brothers Mark II

9.3 4.2

Reference 12 in [571] [636]

IEP at pH 7.8 is reported in text, and at pH 7.3 in a figure. Ref. [1093] cited in [636] for details about hematite, fails to report such an information.

3.1.12.3.2.3 Natural 3.1.12.3.2.3.1 From Middleback Range, South Australia Properties: 69% Fe [1440,1441], contains silica [1441].

TABLE 3.449 PZC/IEP of Hematite from Middleback Range, South Australia Electrolyte

T

0.01–0.1 M KNO3

3.1.12.3.2.3.2

Method

Instrument

pH0

Reference

Salt addition iep

Rank Brothers Mark II

6.8 2.7

[1440,1441]

Minas Gerais, Brazil

TABLE 3.450 PZC/IEP of Hematite from Minas Gerais, Brazil Electrolyte KNO3 a

T

Method

Instrument

pH0

Reference

iep

Rank Bros

6.8a

[830,831]

Only value reported, no data point.

3.1.12.3.2.3.3 From Labrador, Acid-Washed, Ground, Aged 99.8% Fe2O3, 0.05% FeO, 0.09% SiO2 [1].

Properties:

264

Surface Charging and Points of Zero Charge

TABLE 3.451 PZC/IEP of Hematite from Labrador Description

Electrolyte

T

Method a

iep iepa

Washed in hot 0.0001 M KNO3 alcoholic KOH, hot water, HNO3 for 3 h and water for 3 d in Soxhlet extractor a

Instrument

pH0

Reference

Electrophoresis Streaming potential

6.6 6.9

[1088] [1422]

Only value, data points not reported.

3.1.12.3.2.3.4 From Quebec Cartier Mining and traces of Mg, Cu, and Al [579].

>99% pure, contains silica

TABLE 3.452 PZC/IEP of Hematite from Quebec Cartier Mining Electrolyte

T

Method

0.001–1 M KCl, KNO3, NaClO4

25

Merge

Instrument

pH0

Reference

5.2

[579]

3.1.12.3.2.3.5 Specularite from NanFen, China, Ground Fe, 1.2% SiO2 [1309].

Properties: 69%

TABLE 3.453 PZC/IEP of Hematite from NanFen, China Electrolyte

T

Method

Instrument

pH0

Reference

None

22

iep

Brookhaven ZetaPlus

5.8

[1309]

3.1.12.3.2.3.6 From China (Specularite) TABLE 3.454 PZC/IEP of Hematite from China Electrolyte

T

0.01 M NaCl a

Arbitrary interpolation.

Method

Instrument

pH0

Reference

iep

Pen Kem 300

5.4a

[1317]

265

Compilation of PZCs/IEPs

3.1.12.3.2.3.7 From Bolani, India Al2O3, 1.4–2.3% loss of ignition [1108].

Properties: 1.5–3.3% SiO2, 2.2–4.7%

TABLE 3.455 PZC/IEP of Hematite from Bolani, India Electrolyte

T

0.002 M KNO3 a

Method

Instrument

pH0

Reference

iepa

Rank Brothers Mark II

7

[1108]

Only value, data points not reported.

3.1.12.3.2.3.8 From Rio Marina, Elba, Italy Properties: BET specific surface area 4.6 m2/g [332,1417].

TABLE 3.456 PZC/IEP of Hematite from Rio Marina, Elba, Italy Electrolyte

T

a

0.01 M NaNO3, KNO3 a

Method iep

Instrument

pH0

Reference

Malvern Zetasizer 3000HSa

6.8

[332,1417]

Only value, no data points.

3.1.12.3.2.3.9

From Vesuvius

TABLE 3.457 PZC/IEP of Hematite from Vesuvius Electrolyte

T

0.0005 M NaNO3 a

Method

Instrument

pH0

Reference

iep

Otsuka ELS-800

6.1a

[644]

Only value reported, no data points.

The results of potentiometric titration are presented in [170]. 3.1.12.3.2.3.10

From Kiruna, Sweden

TABLE 3.458 PZC/IEP of Hematite from Kiruna, Sweden Electrolyte

T

Method pH

Instrument

pH0

Reference

10.3

[1442]

266

Surface Charging and Points of Zero Charge

3.1.12.3.2.3.11 From Malmberget, LKAB, Sweden Properties: 97.9% Fe2O3, particle size distribution available, specific density 4990 kg/m3 [1443].

TABLE 3.459 PZC/IEP of Hematite from Malmberget, LKAB, Sweden Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem, Laser Zee Meter 501

5.3

[1443]

3.1.12.3.2.3.12 From Clinton, New York Properties: BET specific surface area 8.2 m2/g [332,1417].

TABLE 3.460 PZC/IEP of Hematite from Clinton, NY Electrolyte 0.01 M NaNO3, KNO3 a

T

Method

Instrument

pH0

Reference

iepa

Malvern Zetasizer 3000HSa

<4

[332,1417]

Only value, data points not reported.

3.1.12.3.2.3.13 From Minnesota, Obtained from Ward’s Natural Sciences Establishment Obtained from Ward’s, prepared by roll-crushing and sieving. Properties: 94% of hematite, 6% of quartz [176].

TABLE 3.461 PZC/IEP of Hematite from Minnesota Electrolyte T

a

Method

Instrument

pH0

Reference

iep pH

Streaming potential Electrophoresis

3 7.1

[176]a

Only PZC and IEP reported, no data points.

267

Compilation of PZCs/IEPs

3.1.12.3.2.3.14 Other Natural Hematites TABLE 3.462 PZC/IEP of Other Natural Hematites Description From Morocco, ground, dialyzed, dried Vallenar, Chile, 7.1% SiO2 HCl- and water-washed, dried at 120°C HCl washed, aged From Sweden, 0.05% of quartz From Brazil

Electrolyte

pH0

Reference

Electrophoresis

2.2a

[225]

0.001, 0.01 M KCl

iep

Zeemeter 501

3.3

[898]

iep

Streaming potential

<4.3b

[1092]

Titration iep

0.006 M NaCl, NaNO3, NaClO4 0.0006 M

NaNO3

From Rachelshausen 43 m2/g

NaOH + HClO4

c

Instrument

iep

Specular, 1.8 m2/g

b

Method

NaOH + HCl

Washed, dried, and 0–0.001 M activated at 700°C NaCl 99% pure, 0.7% SiO2, 0.3% Al2O3, 1.7 m2/g Vallenar, Chile, 4.3% 0–0.01 M KCl SiO2 4 m2/g 1.8% SiO2, 0.27% 0.001–0.1 M Al2O3, 0.02% TiO2, NaClO4 0.04% CaO, 0.06% P2O5, 0.09% As2O5, 0.07% Sb2O5 HCl- and water-washed, dried at 120°C

a

T

4.5–5 4.7

[1444] [1445]

Streaming potential Malvern Zetasizer 3000 HS

5.4

[1446]

5.8

[506]

Streaming potential

6

[898]

6

[1447]

Electrophoresis

6.7

[1091]

iep Electrophoresis cip or salt Rank Brothers titration MK-2 iep iep Zeta-Meter Titration

6.7 7.8c

[1448] [1439]

7c 9 10.1c

[104] [1449]

iep 25

iep

iep

Electrophoresis

cip

iep

Arbitrary interpolation. Extrapolated value (pH 4.2) was cited in [1] and by many others. Only value reported, no data points.

268

Surface Charging and Points of Zero Charge

3.1.12.3.2.4 Hematite, Origin Unknown

TABLE 3.463 PZC/IEP of Hematites of Unknown Origin Description Glowed at 1200°C

a

Electrolyte

T

Method

Instrument

pH0

Reference

iep cip iep

Repap

7a 8.5

[351] [1450]

0.001 M KCl 0.0025–0.1 M NaCl or KCl

Arbitrary interpolation.

3.1.12.3.3 Amorphous Fe2O3 Commercial from Polysciences. Properties: Amorphous, small amount of crystalline fraction [1451], BET specific surface area 3.6 m2/g [1452] 9.6 m2/g [572,1451], particle size 400–800 nm [1451].

TABLE 3.464 PZC/IEP of Fe2O3 from Polysciences Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaNO3

25

iep pH

Pen Kem 501 Brookhaven ZetaPlus

<3 if any 3

[572,1451,1452]

3.1.12.3.4 Fe2O3, Structure Unknown 3.1.12.3.4.1 Commercial, Red Iron Oxide R 2199, >99% Fe2O3, from Harcros Pigments

TABLE 3.465 PZC/IEP of R 2199 from Harcros Pigments Electrolyte

T

Method

Instrument

pH0

Reference

iep

ESA 8000, Matec

8.2

[1030]

269

Compilation of PZCs/IEPs

3.1.12.3.4.2 Iron Oxide Yellow from Chr. Hansen eter 3.56 μm [1453].

Properties: Particle diam-

TABLE 3.466 PZC/IEP of Iron Oxide Yellow from Chr. Hansen Electrolyte 0.01 M NaCl a

T

Method

Instrument

pH0

Reference

25

iep

Malvern Zetasizer ZEN 3600

>8a

[1453]

+20 mV at pH 8, −40 mV at pH 10.

3.1.12.3.4.3

Other

TABLE 3.467 PZC/IEP of Fe2O3 of Unknown Structure and Origin Description Reagent grade ? 265 m2/g 23 m2/g

a b c

Electrolyte 0.0001–0.1 M KCl 0.001 M KCl 0.001 M KCl 0.01 M KCl

T

20c

Method cip iep pH iep

Instrument

pH0

Reference

Electro-osmosis

6 6.1b 6.2 8.2

[1454]a [1455] [1456] [1103]b [1217]

[1457] is quoted in [1454] as a source of these results, but apparently the source is different. Only value reported, no data points. Also 30 and 40ºC.

3.1.12.4 Fe2O3 –FeOOH Composites 3.1.12.4.1 Hematite–Goethite Composite Synthetic goethite was heated at 140°C overnight. Properties: XRD pattern, Mossbauer spectrum available [1318]. PZC/IEP of hematite–goethite composite is presented in Table 3.468.

TABLE 3.468 PZC/IEP of Hematite–Goethite Composite Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaNO3

25

cip iep

Acoustosizer DT 1200

9.4 8.8

[1318]

270

Surface Charging and Points of Zero Charge

3.1.12.4.2 Goethite–Maghemite Composite 0.01 M Fe(ClO4)2 was adjusted to pH 6 with CO2-free 0.1 M NaOH under nitrogen. Then the nitrogen was replaced with CO2-free air, and air was passed for 2.5 h. The solid was water-washed. PZC/IEP of maghemite–goethite composite is presented in Table 3.469. Properties: Goethite and maghemite, BET specific surface area 135.2 m2/g, AFM image available [1458].

TABLE 3.469 PZC/IEP of Goethite–Maghemite Composite Electrolyte

T

Method

0.01–1 M NaCl a

Instrument

pH0 a

cip

7

Reference [1458]

Only value reported, no data points.

3.1.12.5 FeOOH PZCs/IEPs of iron hydroxide oxide (nominally FeOOH) are presented in Tables 3.470 through 3.528. 3.1.12.5.1 Goethite Compilations of PZC of goethites are presented in [174,715]. A compilation of PZCs and specific surface areas of goethites is presented in [73]. A compilation of surface acidity constants and other model parameters obtained for goethites is presented in [1459]. 3.1.12.5.1.1 Commercial 3.1.12.5.1.1.1 Goethite from Alfa Aesar Properties: Purity >99.9%, BET specific surface area 21 m2/g, length 100 - 900 nm, acicular [1320].

TABLE 3.470 PZC/IEP of Goethite from Alfa Aesar Electrolyte HCl a

T

Method

Instrument

pH0

Reference

iep

Zeta Probe, Colloidal Dynamics

8.8a

[1320]

Only value reported, no data points.

271

Compilation of PZCs/IEPs

3.1.12.5.1.1.2 Goethite from BASF Properties: BET specific surface area 45 m2/g [1278], 25 m2/g [1460], 21.4 m2/g [1461], sticks 0.1 mm × 1 mm size [1460].

TABLE 3.471 PZC/IEP of Goethite from BASF Electrolyte

T

Method

Instrument

pH a

pH0

Reference

8.8a

[1278]

Only acidity constants reported, no data points.

3.1.12.5.1.1.3 Goethites from Bayer 3.1.12.5.1.1.3.1 Eisenoxidgelb 910 (or Bayferrox 910, Standard 86) Properties: BET specific surface area 14.7 m2/g [1462], 15 m2/g, structure confirmed by Mossbauer spectroscopy, XPS spectrum available [1463].

TABLE 3.472 PZC/IEP of Bayferrox 910 from Bayer Electrolyte

T

Method

KNO3 a

Instrument

Titration

pH0 7.9

Reference

a

[1462]

Only acidity constants reported, no data points.

3.1.12.5.1.1.3.2 Pigment Properties: Goethite, 80 m2/g [375].

TABLE 3.473 PZC/IEP of a Goethite Pigment from Bayer Electrolyte 0.001 M KNO3

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000

8.1

[375]

3.1.12.5.1.1.4 Fe-52 from Organic-Inorganic Chemical Corp. Properties: BET specific surface area 21.3 m2/g [1464,1465], 24 m2/g (purified material) [1466], SEM image available [1465].

272

Surface Charging and Points of Zero Charge

TABLE 3.474 PZC/IEP of Fe-52 from Organic–Inorganic Chemical Corp. Description 0.001 M HNO3- and NaOH-washed

Electrolyte

T

Method

0.01–1 M NaNO3

Instrument

cip

pH0

Reference

7.8 7.9

[1464] [1467]

3.1.12.5.1.1.5 From Toda, Electrodialyzed Properties: Structure confirmed by XRD [1281]. TABLE 3.475 PZC/IEP of Electrodialyzed Goethite from Toda Electrolyte

T

Method

0.002 M TMAClO4

25

pH

3.1.12.5.1.1.6 From Toda Kogyo 40.1 m2/g [1282].

Instrument

pH0

Reference

8.2

[1281]

Properties: BET specific surface area

TABLE 3.476 PZC/IEP of Goethite from Toda Kogyo Description Washed with 0.1 M HNO3 and water, dried at room temperature

Electrolyte

T

Method

0.1 M NaCl, NaClO4, NaNO3

25

pH

Instrument

pH0 Reference 5.6

[1282]

3.1.12.5.1.2 Synthetic Goethites Specific surface areas and other properties of synthetic goethites are reviewed in [1468]. 3.1.12.5.1.2.1 From Nitrate 3.1.12.5.1.2.1.1 Aging at 55–90°C of Precipitate Obtained From Fe(NO3)3 and Excess of NaOH or KOH The most frequently cited recipes of this type were published by Atkinson et al. [1420,1469]. Original recipe from [1420]: 200 cm3 of 2.5 M KOH was added to solution containing 50 g of Fe(NO3)3 · 9H2O and 825 cm3 of water until the pH was about 12 in a Pyrex glass container, it was then aged for 1 d at 60°C, and then dialyzed. A recipe quoted after [1420]: 6.5 dm3 of 0.5 M Fe(NO3)3 in 0.21 M HNO3 was slowly added to 12.6 dm3 of 1.55 M KOH in plastic. Dispersion was aged for 36 h at 70°C (described in [449]).

Compilation of PZCs/IEPs

273

Another recipe quoted after [1420]: 800 cm3 of 5 M NaOH was added dropwise to 4 dm3 of 0.1 M Fe(NO3)3 under nitrogen. The dispersion was aged for 3 d at 60°C, and then dialyzed (described in [336]). Original recipe from [1469]: 0.45 M Fe(NO3)3 was partially neutralized with 2.5 M NaOH (OH:Fe molar ratio < 2) and aged for 7 min–17 d at 21°C. It was then alkalized to pH > 11.5 with NaOH, and aged for 3–4 d (or 14 d, in a modification described in [468]) at 62°C. This was followed by washing and freeze-drying. Reference [1469] describes in detail eight recipes (termed 1a–d and 2a–d), in which the amount of NaOH added in the first and second step and the aging times between the first and second NaOH addition were different. Three preparations resulted in the presence of hematite in the product. Electron micrographs and specific surface areas of a few products are reported. Many modifications of the above recipes have been published, with or without reference to the Atkinson et al. papers. References [77,1470] emphasize the difference between slow (as in [446]) and fast (as in [1113]) addition of base. Different concentrations of Fe(NO3)3 and of KOH or NaOH, different OH/Fe molar ratios or final pH values, and different temperatures and times of aging are examples of possible modifications. Similar recipes may lead to hematite or to other products. The CO2 and silica problems (Section 2.3) and measures against them in the preparation of goethite (e.g., preparation in an inert atmosphere and the use of plastic rather than glass containers) have been also discussed. Another frequently cited recipe was published by McLaughlin et al. [1207]: 0.2 M Fe(NO3)3 was adjusted to pH 11 with 0.2 M NaOH. It was aged for 2 d at room temperature, then at 90°C for 16 h. Schwertmann and Cornell [63] report several recipes for goethite, which are frequently cited, sometimes without reference to a specific recipe. Properties: Poorly crystallized goethite, goethite (two samples) [866], 25% of well-crystallized needle-like particles, 75% of fine particles and amorphous material [874], goethite (electron diffraction) [723], pure a-form [1472,1475], structure confirmed by XRD [462,1476,1477], well-crystallized (XRD) [1478], goethite with hematite impurity [1177,1178]. BET specific surface area 16 m2/g [707], 17 m2/g [1207], 19 m2/g [1479], 20 m2/g [1480], 21 m2/g [1475], 22 m2/g [1481,1482], 23 m2/g [76], 27 m2/g [69,468,1483–1485], 27.7 m2/g [536], 28 and 29 m2/g (two samples) [551], 30.8 m2/g [723,876], 31.2 m2/g [829], 32.7 m2/g [462,584], 33 m2/g [69], 34 m2/g [896], 35 m2/g [585,1115], six powders (36–83 m2/g) [1486], 36.4 m2/g [1113], 36.5 m2/g [1487], 37 m2/g [68,76,1476], 39 m2/g [1488], 39.1 m2/g [1329,1489], 39.9 m2/g [174], 40 m2/g [361,1490], 40.2 m2/g [1318], 40.7 m2/g [1487,1491,1492], 42.5 m2/g [1177,1178], 43 m2/g [68,1034,1493], 43.2 m2/g [1494], 43.7 m2/g [1567], 44 m2/g [1495], 44.4 m2/g [1496,1497], 45 m2/g [71,878,1439,1470,1471,1477,1498–1502], 47.5 m2/g [1503], 47.6 m2/g [1504], 48 m2/g [1249], 48.8 m2/g [1505], 49 m2/g [77,558], 49.2 m2/g [1506], 49.6 m2/g [1507–1509], 50 m2/g [44,1510], 50.1 m2/g [1511], 51.8 m2/g [655,1512], 52 m2/g [609,1513–1516], 54 m2/g [1517], 54.8 m2/g [656], 55 m2/g [1518,1519] 58.5 m2/g [1520], 62 m2/g [990], 64.3 m2/g [1521], 65 m2/g [1522], 66 m2/g [1472,1473], 68 m2/g [1523], 70 m2/g [1470,1498,1524– 1526] 70.2 m2/g [449], 70.5 m2/g [563], 70.8 m2/g [336,1527], 70.9 m2/g [1420],

274

Surface Charging and Points of Zero Charge

75 m2/g [1522], 76 m2/g [874,1528,1529], 76.3 m2/g [332,1417], 79.4 m2/g [1530,1531,1572], 80 m2/g [66,1522,1532], 81 m2/g [1533–1536], 82 m2/g [629,707], 82.2 m2/g [1537], 84 m2/g [500], 85 m2/g [1538,1539], 86 m2/g [756], 88 m2/g [1540], 89 m2/g [1541,1542], 90 m2/g [68,1476,1498,1543], 93.9 m2/g [1544], 94 m2/g [634,1470,1502,1545–1547], 95 m2/g [77,747,1501,1548,1549], 96.4 m2/g [1550–1553], 96.8, 88.9, and 117 m2/g (three batches) [1554], 96.8 m2/g [1555], 97.9 m2/g [1556], 98 m2/g [556], 98.6 m2/g [537,1539,1557], 100 m2/g [74,446], 104 m2/g [1558], 105 m2/g [1466,1551,1559], 117 m2/g [1560], 153 m2/g [1561], single point BET specific surface area 34.4 m2/g [1562,1563], 43.7 m2/g [1176], 63.7 m2/g [866,870], 84 m2/g [248], 148.8 m2/g [866], specific surface area 21.8 m2/g [450], 25–40 m2/g [759], 27 m2/g [1564], 40 m2/g [1565], 42 m2/g [1566], 49 m2/g [1568], 55 m2/g [1569], 57 m2/g [1478], 62 m2/g [1449], 68 m2/g [1570], 79.4 m2/g [1572], 80.3 m2/g [379], 90 m2/g [759], 105 m2/g [1573], electron microphotographs: 69 m2/g [1472], 76 m2/g (EGME) [1571], 112 m2/g (ethylene glycol) [454]; for specific surface area, see also Table 3.477. Particle diameter (PCS) 975 nm [1113], needles, 50 nm long, 20 nm wide [1534], 50 nm × 15 nm × 10 nm crystals [1535], 50 nm × 15 nm [66], rod-like particles, 60 nm × 20 nm [1536], acicular, 60 nm × 20 nm [248], acicular, 62 nm × 13 nm [756], needles, 80 nm long, 35 nm wide [1532], needles 94 nm long, 10 nm in diameter [446], needles 100 nm long, 10 nm in diameter [74], needles 150–400 nm long and 10–50 nm wide [896], 150 nm × 15 nm [629], dimensions 160 nm × 26 nm × 6.5 nm [1574], needles 300 nm long [44], needles 300–500 nm long and 30–50 nm wide [174], needles 400–1000 nm long, 30–65 nm wide [336], 500 nm long [1497], crystal size 500 nm × 50 nm [1514], rod-shaped, 500 nm × 50 nm [1419], 0.5–1 μm long needles [1485], acicular, 600 nm long, 40 nm wide [1478], needles 100 nm × 1000 nm [1543], needles 1 μm × 60 nm (modal) [1523], needles 1–3 μm long, 100–150 nm in diameter [585], needles 1.6 mm long and 0.095 mm wide (?) [1480], aspect ratio 10:1 [1481], particle size distribution available [468]. Detailed study of morphology and dissolution of six powders obtained by different methods based on Atkinson recipe [1486]. TEM image available [248,585,723], SEM image available [1468,1484,1485,1558,1561], 100 face predominant [1534,1574], 90% of 110 face, 10% of 021 face [629], XRD pattern available [536,602,1318], TGA results available [1468], Mossbauer spectrum available [1318], IR spectra available [1574]. 3.1.12.5.1.2.1.2 Aging at 25°C of Precipitate Obtained from Fe(NO3)3 and Excess of KOH 50 cm3 of 1 M Fe(NO3)3 was added to 450 cm3 of 1 M KOH. The dispersion was aged for 14 d at 25°C. The precipitate was washed with water, 0.4 M HCl, and water, then dialyzed and freeze-dried. Properties: BET specific surface area 63.5 m2/g [1424,1581,1582].

Electrolyte

0.1 M NaClO4

NaCl

Recipe in footnote i

0.001–0.1 M KNO3

0.01–0.7 M NaCl, KCl

0.01 M NaNO3, no protection against CO2 NaCl NaOH + HNO3

NaCl

0.1 M NaClO4

0.01 M NaNO3

Two batches

78 m2/g

Recipe in footnote h

Recipe in footnote f Recipe in footnote g

Recipe in footnote d

Recipe in footnote a Recipe in footnote b

Description

25

25

25

22–24

25

T

Salt titration

pH

iep cip

cip

iep pH iep cip pH pH Solid addition Salt titration iep pH iep iep

iep

Method

Rank Mark II Malvern Zetasizer 3000 HS

Rank Brothers Mark II

Malvern ZetaMaster S Zetaphoremeter II

JS94G+

Instrument

7.5c 7.6c 7.6c

7.5c 7.5

continued

[707]

[1512]c [655] [1604,1605] [1249] [1576] [896]

[1540] [656] [551] [1575] [707] [1495] [1475] [1568] [1561]

6.8c 7c 7 7.1 c 7.2c 7.2c 7.4c 7.4 7.5 7.5

[1113] [1488]

[845]

Reference

6.7 6.7c

>6.5

pH0

TABLE 3.477 PZC/IEP of Goethite Obtained by Aging at 55–90°C of Precipitate Obtained from Fe(NO3)3 and Excess of NaOH or KOH

Compilation of PZCs/IEPs 275

Recipe in footnote p

Recipe in footnote o

Recipe in footnote m

Recipe in footnote h

Recipe in footnote k

Recipe in footnote j

Description

Electrolyte

NaClO4

0.005–0.1 M NaCl 0.01–0.1 M NaNO3 0.001,0.1 M NaClO4 0.001–0.1 M NaNO3

0.015, 0.15 M NaClO4 0.01 M NaCl NaNO3

0.002–1 M KCl 0.01 M KNO3 KCl 0.001 M NaNO3 0.001–0.1 M NaNO3 0.001–0.1 M KNO3 NaOH + HNO3 0.1 M NaNO3 NaNO3 0.001–0.1 M NaCl

TABLE 3.477 (continued)

25

20 25

25

25 ± 3

cip cip Intersection iep cip Titration pH iep Titration

cip

cip cip iep Salt titration Intersection iep cip

25

25

25

cip pH Titration iep cip Titration iep

Titration

Method

20

T 7.6

c

Electrophoresis

ZetaPlus Brookhaven

CO2 present

Pen Kem 3000

Acoustosizer

8 8c 8–9 8 7.8 8.1c 8.3n 8.3c

8c

7.9c 7.9 8.2 8c 8 8 8n

7.6 7.7c 7.7c Brookhaven ZetaPlus >7.7l 1 d equilibration 7.8 7.8c Malvern Zetasizer 3000 HS 7.9 3 d equilibrated

Instrument

pH0

[1534] [1477] [1478]

[459] [1522] [379] [1513,1515n, 1516n] [1572]c [1531] [1530] [1535,1536] [585] [468,1485c]

[876] [449]

[1541] [1542] [1420] [1577] [1506] [1484] [1571] [1527] [500]

Reference

276 Surface Charging and Points of Zero Charge

Recipe in footnote r Recipe in footnote s Exposed to atmosphere Recipe from [1536]

11 15 18 m2/g

0.001–0.1 M NaNO3 0.001–0.1 M NaCl NaNO3 NaClO4 25

cip cip

iep pH

25

0.005 M 0.1 M NaNO3

iep cip cip cip cip

25 25

0.001 M NaCl 0.1–0.7 M NaCl 0.003–0.1 M NaNO3 0–0.1 M NaNO3

iep Titration iep

cip iep Titration pH iep

Titration pH

0.005–0.05 M NaClO4

10

25

0.001 M KNO3

0.002 M NaCl

20

25 25

0.01–1 M NaCl 0.1 M NaNO3 0.01 M KCl

0.01 M KClO4 0.005 M KNO3 0.001–0.1 M NaClO4

1 d equilibration

Malvern Zetasizer 3

Zeta-Meter 3.0

Rank Brothers Mark II

Pen Kem 501 Laser Zee Meter Electrophoresis

8.5 8.5 8.6 8.2

8.5 8.4 8.5 8.5

8.4 8.4 or 8.9 8.4 8.2 7 8.5 8.5 8.5 8.5c

8.3c 8.3 8.5 8.3 8–9.2 8.4 8.4 8.4

continued

[248] [1487,1492, 1494] [1564] [44]

[1528,1560c]

[1177c,1178] [536] [462,584] [1483]

[1523] [1570] [1419]

[1510]c [174] [1511]c

[1566]

[1518q,1569] [1507nq–1509]

Compilation of PZCs/IEPs 277

Two samples

60 m2/g

Recipe in footnote p

Description

25

20

25

0–0.1 M NaCl 0.015–0.2 M NaNO3, NaCl

0.001–0.1 M NaClO4

25

0.01–0.5 M NaNO3

0.01, 0.1 M NaClO4 0.003–0.1 M NaClO4 0.01–0.1 M NaClO4

0.001 M NaCl 0.1 M NaCl KCl 0.001–0.1 M NaNO3 0.01 M NaCl 20

25

0.1 M KCl, (CH3)4NCl

0.001–1 M NaCl

25 25

0.001 M NaNO3 0.005–0.09 M NaNO3

T 25

Electrolyte

0.001–0.7 M NaNO3

TABLE 3.477 (continued) Method

Instrument

pH0

9 9 9.7

iep cip iep

8.6t 9.5u 8.7 8.7 8.8 8.8 8.8v 7.8w 8.9 8.9 8.9

8.6–9

8.5 8.9 8.6 8.6

cip cip Electrophoresis CO2-free Pen Kem 3000

Zeta-Meter 3.0

Zeta-Meter 3.0

Malvern IIc

Rank Brothers Mark II

8.9 9.2 9 9

cip

Intersection cip cip

iep pH pH cip iep

cip

pH

cip iep iep cip

Reference

[1578] [537x,1538c, 1539y] [1567]c [66]

[1470,1502n] [558] [878c,1471, 1499c, 1500c] [77]

[1176] [563] [1474] [602] [866,870c]

[1556]

[361] [609, 1515n, 1516n] [1521]n

[1439]

278 Surface Charging and Points of Zero Charge

Recipe in footnote E

Recipe in footnote D

Recipe from [1420]

Recipe modified according to [446]

72.3 m2/g Recipe in footnote B

Recipe in footnote z

Recipe in footnote z

Recipe in footnote m

0.005–0.1 M NaNO3 0.01 M NaCl 0.005–0.1 M KNO3

0.005–0.1 M NaNO3 0.005–0.1 M NaNO3, NaCl, NaClO4

0.1 M NaNO3 0.01–0.1 M NaCl 0.015–0.1 M NaNO3 0.003–0.1 M NaNO3

0.1 M NaNO3 0.01 M NaNO3 0.1 M NaNO3 0.002–0.09 M KNO3 0.01–0.24 M NaNO3

0.001 M KNO3

0.001–0.1 M NaCl

25

25

cip iep cip iep cip

Zeta-Meter 3.0 Malvern Zetamaster 5002

9.3c

9.3 9.3 9.3

9.3 9.3 or 9.2

cip

20

cip

9.2 9.2 9.2 9 9.2

Titration pH cip

25

25

9.1 9.1 Rank Bros Model II 9.1 8.5A Rank Bros Model II 9.1 9.3 9.2 Malvern Zetasizer 3000HSa 9.2 9.2 9.2 9.2 9.2c

Titration cip iep Titration iep pH pH iep pH Merge cip

25 25 10 25

continued

[1472,1473]

[74] [1476] [1470I,1525, 1526] [556,634, 1545–1547]c [1544] [1549,1550, 1552] [1551]c [747] [450] [336]

[71]c [1579]c [1476] [629] [1470I,1502n] [1555]

[990]

[1449]c [756] [1529]

Compilation of PZCs/IEPs 279

0.1 M NaNO3

Recipe from [1420]

f

e

d

c

b

a

0.1 M NaNO3

Recipe in footnote G

25 21

20

25

25

pH iep pH iep cip cip

Method

CO2-free

Pen Kem 3000

Malvern Zetasizer III

Malvern Zetasizer Acoustosizer DT 1200 Acoustosizer

Instrument

9.5 9.5c 9.5 9.6 9.7 10.2H

9.4 9.5

9.4

9.4

9.4

9.3 9.2 9.3

pH0

[1466 (2 d aged), 1551c,1559, 1573c] [68] [1532] [68] [1580]c [454] [446]

[76]

[1318]

[759]

[1554]c

Reference

100 cm3 of 1 M Fe(NO3)3 and 180 cm3 of 3.75 M KOH were diluted to 2 L under stirring. Aged at 70°C for 60 h. 180 cm3 of 5 M KOH was added to 100 cm3 of 1 M Fe(NO3)3, and diluted to 2 L. Aged for 60 h at 70°C. Only value reported, no data points. 200 cm3 of 1 M NaOH was quickly added to 200 cm3 of 0.25 M Fe(NO3)3 with stirring. Aged for >2 d at 60°C at pH 12, washed with water, dried at 70°C and ground. Fe(NO3)3 and NaOH were mixed at 1:3.5 molar ratio. Aged for 2 d at 60°C. Washed and dried at 65°C. A solution of 250 g of Fe(NO3)3 ⋅ 9H2O in 4.1 L of water was slowly mixed with 1 L of 2.5 M KOH for 30 min. Aged for 1 d at 60°C. Water-washed, and dried in vacuum oven. Very likely the same sample was studied in [1568] (IEP at pH 7.4).

0.001–0.1 M NaI 0.005–0.1 M NaNO3

0.005–0.1 M NaNO3

Recipe in footnote F

0.001–0.1 M NaNO3 0.1 M NaI 0.01–2 M NaNO3

iep cip cip iep iep cip iep cip

0.003–0.6 M NaCl

Two samples

T cip

Electrolyte

Recipe modified according to [446], three samples

Description

TABLE 3.477 (continued)

280 Surface Charging and Points of Zero Charge

I

H

G

F

E

D

C

B

A

z

y

x

w

v

u

t

s

r

q

p

o

n

m

l

k

j

i

h

g

100 cm3 of 1 M Fe(NO3)3 and 180 cm3 of 5 M NaOH were diluted to 2 L with stirring. Aged at 70°C for 60 h. 180 cm3 of 5 M KOH was added to 100 cm3 of 1 M Fe(NO3)3, diluted to 2 L. Aged for 60 h at 60°C. Fe(NO3)3 and NaOH were mixed at 1:1 molar ratio. Aged for 3 d at room temperature. pH adjusted to 12.3. Aged for 2 d at 55°C. Washed and dried at 65°C. Fe(NO3)3 solution was aged at room temperature at pH 1.9 for 2 d, then at pH 11.7 at 60°C for 3 d, then dialyzed. 10 M NaOH was added to 1 M Fe(NO3)3 with stirring to pH 11.5–12. Aged for 1 d at 70°C in a polyethylene bottle. +12 mV at pH 7.7; −15 mV at pH 9.8; the value of 8.5 in the text is based on arbitrary interpolation. 0.001 or 0.1 M Fe(III) solution in 0.1 M NaNO3 at 50°C, adjusted to pH 10.5 with NaOH and aged for 14 d. Then cooled to 20°C and adjusted to pH 7 with NaOH. Incomplete conversion of amorphous iron hydroxide to goethite, see also Section 3.1.12.8.6.3. Only acidity constants reported, no data points. 180 cm3 of 5 M KOH was added to 100 cm3 of 1 M Fe(NO3)3, and diluted to 2 L. Aged for 80 h at 70°C. Dialyzed for several days. 0.2 M Fe(NO3)3 was titrated with 0.2 M NaOH to pH 11. Aged for 2 d at 22°C, and for 16 h at 90°C. Water-washed, and dried at 70°C for 16 h. Also temperature effect. 180 cm3 of 5 M KOH was added to 100 cm3 of 1 M Fe(NO3)3, and diluted to 2 L. Aged for 70 h at 60°C. Washed, stored in water at 4°C for 6 months. pH adjusted to 12–13. Aged for 60 h at 70°C. Plastic labware. Text. Figure. Goethite. Poorly crystallized goethite. Charging curves in the presence of Li salts did not show a clear CIP. Only PZC reported (for two samples of Goethite), no data points. Fe(NO3)3 solution was aged at pH 1.6 for 1 d, then titrated dropwise with 2.5 M NaOH to pH 12 and aged for 5 d at 60°C. Only value reported, no data points. PZC from titration at 70°C is also available. 0.5 M Fe(NO3)3 was titrated with 2.5 M KOH at 10 cm3/min to pH 12. Aged at 85°C for 4 d. Dialyzed for 14 d. Special attention was paid to CO2 removal. Fresh 0.5 M Fe(NO3)3 was slowly titrated with 2.5 M NaOH up to pH 12 and aged for 3 d at 60°C. 1 M Fe(NO3)3 was mixed with 5 M KOH at OH:Fe molar ratio 9:1. Aged at 70°C for 60 h. Centrifuged, water-washed, and dried at 70°C. Fresh 0.5 M Fe(NO3)3 was slowly titrated with 2.5 M NaOH to pH 12 and aged for 90–110 h (or 2 d in [1466]) at 60°C. Dialyzed for 14 d. 0.5 M Fe(NO3)3 was titrated with 2.5 M KOH at 10 cm3/min to pH 12. Aged at 80°C for 2 d. Dialyzed for 14 d. Extrapolated. Intersection.

Compilation of PZCs/IEPs 281

282

Surface Charging and Points of Zero Charge

TABLE 3.478 PZC/IEP of Goethite Obtained by Aging at 25°C of Precipitate Obtained from Fe(NO3)3 and Excess of KOH Electrolyte

T

Method

0.005–0.1 M NaClO4 a

Instrument

cip

pH0

Reference

8.4a

[1581,1582]

Only value reported, no data points.

3.1.12.5.1.2.1.3 Aging at Room Temperature of Precipitate Obtained from 0.2 M Fe(NO3)3 and Excess of NaOH 0.2 M Fe(NO3)3 was titrated with 10% NaOH up to pH 11.7 and aged with stirring at this pH for 10 d at room temperature. Properties: Structure confirmed by XRD, ethylene glycol specific surface area 95.2 m2/g, acicular crystals [699,1583], particle length 400 nm [1583]. TABLE 3.479 PZC/IEP of Goethite Obtained by Aging at Room Temperature of Precipitate Obtained from 0.2 M Fe(NO3)3 and Excess of NaOH Electrolyte

T

0.001, 0.01 M NaNO3 a

Method

Instrument

Intersection

pH0

Reference

7.9

[699,1583a]

Only value reported, no data points.

3.1.12.5.1.2.1.4 Aging at Room Temperature of Precipitate Obtained from 0.1 M Fe(NO3)3 and Excess of NaOH 1 M NaOH was added to 0.1 M Fe(NO3)3 to adjust the pH to 11, and the dispersion was aged for 10 d at room temperature. It was washed with water, 3 M HNO3, and water again. Properties: TEM image available, rods 150 nm × 25 nm × 10 nm [1584]. TABLE 3.480 PZC/IEP of Goethite Obtained by Aging at Room Temperature of Precipitate Obtained from 0.1 M Fe(NO3)3 and Excess of NaOH Electrolyte

T

Method cip

a

Only value reported, no data points.

Instrument

pH0 a

9

Reference [1584]

283

Compilation of PZCs/IEPs

3.1.12.5.1.2.1.5 Aging at Room Temperature of Precipitate Obtained from Fe(NO3)3 and Ammonia Ammonia was added to Fe(NO3)3 solution. The precipitate was aged with stirring for 19 h at room temperature in KOH solution, and stored as a dispersion. Properties: Structure confirmed by XRD [1585], BET specific surface area 149 m2/g [1586], specific surface area (Stroehlein) 132 m2/g[1585,1587], XRD results and SEM image available [1587].

TABLE 3.481 PZC/IEP of Goethite Obtained by Aging at Room Temperature of Precipitate Obtained from Fe(NO3)3 and Ammonia Electrolyte

T

Method

Instrument

pH0

Reference

27

iep iep

Rank Brothers Mark II Rank Brothers Mark II

6.8 7.5

[1585] [1587]

3.1.12.5.1.2.1.6 Aging at 60°C of Precipitate Obtained from Excess of Fe(NO3)3 and NaOH 10 dm3 of 0.5 M Fe(NO3)3 was titrated at 10 cm3/min with 2.4 dm3 of 2.5 M NaOH and aged for 100 h at 60°C. It was dialyzed for 14 d. Properties: BET specific surface area 85 m2/g [76,1588], TEM image available [76].

TABLE 3.482 PZC/IEP of Goethite Obtained by Aging at 60°C of Precipitate Obtained from Excess of Fe(NO3)3 and NaOH Electrolyte

T

Method

0.003–0.1 M NaNO3

25

cip

Instrument

pH0

Reference

9.4

[76]

3.1.12.5.1.2.1.7 Recipe from [1589] 900 cm3 of 7/9 M KOH was added to 100 cm3 of 1 M Fe(NO3)3. The precipitate was aged at 60°C for 7 d. It was washed with water and stored at 5°C as an aqueous dispersion in PTFE bottles.

284

Surface Charging and Points of Zero Charge

Properties: Structure confirmed by XRD and IR [333,1589], BET specific surface area 34 m2/g [333,1589,1590].

TABLE 3.483 PZC/IEP of Goethite Obtained According to Recipe from [1589] Electrolyte

T

0.0001–1 M KNO3

25

Method

Instrument

pH0

Reference

iep cip

Pen Kem, Zee Meter 501

8.4 8.6

[333,1589,1590]

3.1.12.5.1.2.1.8 Recipe from [1271] From Fe(NO3)3 and NaOH. Properties: BET specific surface area 71 m2/g [1591,1592].

TABLE 3.484 PZC/IEP of Goethite Obtained According to Recipe from [1271] Electrolyte

a

T

Method

Instrument

pH0

Reference

20

cip iep

Osuka ELS-800

8.5

[1591,1592]a

Only value reported, no data points.

3.1.12.5.1.2.1.9 From Fe(NO3)3 by Rapid Precipitation

TABLE 3.485 PZCs/IEPs of Goethite Obtained from Fe(NO3)3 by Rapid Precipitation Description 31 m2/g

Electrolyte 0.1 M NaNO3

T

Method pH

Instrument

pH0

Reference

8.6

[1593]

3.1.12.5.1.2.1.10 Refluxing of Fe(NO3)3 Solution Fe(NO3)3 solution was boiled under reflux for 18 d, and then purified by electrodialysis.

285

Compilation of PZCs/IEPs

TABLE 3.486 PZC/IEP of Goethite Obtained by Refluxing of Fe(NO3)3 Solution Description Unwashed Washed

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

30

iep

Electrophoresis

6.9 8.7

[250]

3.1.12.5.1.2.1.11 Boiling of Dispersion Obtained from Fe(NO3)3 and Na2CO3 Solutions 10 cm3 of 2.4 M Na2CO3 was added to 25 cm3 of 0.2 M Fe(NO3)3 under stirring to reach pH 2. It was then heated in a microwave oven until boiling and quenched in ice water. After three cycles of boiling and quenching, the dispersion was dialyzed against HNO3 solution (pH 4). Properties: Highly disordered goethite, BET specific surface area 306 m2/g, particle size 6 ± 1 nm. [569].

TABLE 3.487 PZC/IEP of Goethite Obtained by Boiling of Dispersion Obtained from Fe(NO3)3 and Na2CO3 Solutions Electrolyte

T

Method

0.001–0.1 M NaNO3

Instrument

cip

pH0

Reference

8.6

[569]

3.1.12.5.1.2.2 From Chloride A solution of 380 g of FeCl3·6 H2O in 500 cm3 of 1 M HCl was mixed with 1 dm3 of water, and titrated with 1 M NaOH up to pH 3. The dispersion was heated to 70°C and allowed to settle for 1 d. The precipitate was then washed and dried for 2 d at 110°C. Properties: Specific surface area 50 m2/g [1594].

TABLE 3.488 PZC/IEP of Goethite Obtained from Chloride Electrolyte

T

Method

Instrument

iep

Zeta-Meter

pH0 Reference 10

[1595]

286

Surface Charging and Points of Zero Charge

3.1.12.5.1.2.3 82 m2/g [1136].

From Perchlorate Properties: BET specific surface area

TABLE 3.489 PZC/IEP of Goethite Obtained from Perchlorate Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

9

[1136]

0.0001–0.01 M NaClO4

3.1.12.5.1.2.4 From Sulfate 50 cm3 of 0.1 M Fe2(SO4)3 was mixed with 2.5 M NaOH at an OH/Fe molar ratio of 0.35, and the mixture was aged for 4 h at 21°C. 1.5 M Na2CO3 was added to adjust the pH to 10, and the system was aged at 40°C for 2 d and at 60°C for 3 d. Properties: Goethite, structure confirmed by XRD [1596], needles, 60 nm long, axial ratio of 6 [1597], particle size distribution (of length and width), XRD pattern, TEM image available (also in a series of goethites obtained under different conditions) [1596]. TABLE 3.490 PZC/IEP of Goethite Obtained from Sulfate Electrolyte

T

Method

0.01 M KNO3 a

iep

Instrument ZetaPlus Brookhaven

pH0 a

8.1

Reference [1597]

Only value reported, no data points.

3.1.12.5.1.2.5 Aging of Suspension of Freshly Precipitated Iron Hydroxide

TABLE 3.491 PZC/IEP of Goethite Obtained by Aging of Suspension of Freshly Precipitated Iron Hydroxide Electrolyte 0.01 M KCl a

T 25

Method iep

From Table 2. Figure 1 suggests IEP at pH 9.

Instrument Electrophoresis CO2-free atmosphere

pH0 a

8.4

Reference [1248]

287

Compilation of PZCs/IEPs

3.1.12.5.1.2.6 From Fe(II) 3.1.12.5.1.2.6.1 From FeCl2 The pH of 0.01 M FeCl2 was adjusted to 7 with NaHCO3. Air was bubbled at 25 cm3/min for 2 d. The same procedure was used in D2O to obtain deuterated goethite. Properties: BET specific surface area 219.8 m2/g (deuterated 228.7 m2/g), SEM image available [1598].

TABLE 3.492 PZC/IEP of Goethite Obtained from FeCl2 Description

Electrolyte

T

FeOOH FeOOD a

Method iep

Instrument Brookhaven ZetaPlus

pH0

Reference

8.3 4.3

[1598]a

Only values reported, no data points.

3.1.12.5.1.2.6.2 Oxidation of the Product of Reaction Between FeSO4 and NH4OH Properties: Goethite, detailed chemical analysis and electron micrograph available, BET specific surface area 24 m2/g [547,1117].

TABLE 3.493 PZC/IEP of Goethite Obtained by Oxidation of Product of Reaction between FeSO4 and NH4OH Electrolyte 0.001–1 M KCl 0.01 M NaCl 0.001, 0.01 M KCl, NaCl 0.001–1 M NaCl 1 M KCl a

T

20

Method

Instrument

cip iep iep cip

Malvern Zetasizer 4 Electrophoresis

pH0 7.6a 7.2 7.6 8

Reference [1117] [330] [547]

Course of titration curves near PZC was different in the presence of NaCl.

3.1.12.5.1.2.6.3 Oxidation of the Product of Reaction between FeSO4 and NH4OH with Oxygen 0.4 M FeSO4 was mixed with NaOH at 40°C and OH:Fe ratio 2:1, and the final pH was 6.9. Oxygen was passed through the suspension at 0.12 cm3/s for 5 h with stirring. The precipitate was water-washed and vacuumdried. Properties: Goethite [1599].

288

Surface Charging and Points of Zero Charge

TABLE 3.494 PZC/IEP of Goethite Obtained by Oxidation of Product of Reaction between FeSO4 and NaOH with Oxygen Electrolyte

T

NaClO4 a

Method

Instrument

pH0

Reference

iep

Rank Brothers Mark II

5.6a

[1599]

Only value reported, no data points.

3.1.12.5.1.2.6.4 Oxidation of the Product of Reaction between FeSO4 and Na2CO3 125 cm3 of oxygen-free 0.9 M Na2CO3 was thermostated at 40°C, and 125 cm3 of oxygen-free 0.6 M FeSO4 was added under stirring. Air was bubbled at 2 dm3/min for 3 h. Then the precipitate was washed, and dried at 50°C. Properties: Goethite, needles, 213 nm long and 44 nm wide, TEM and HR TEM images, IR spectrum, TGA and DTA results available [1600]. Properties of particles obtained at different reagent concentrations and temperatures are also described in [1600], but IEP is only available for one recipe.

TABLE 3.495 PZC/IEP of Goethite Obtained by Oxidation of Product of Reaction between FeSO4 and Na2CO3 Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep

Malvern Zetamaster

9.1

[1600]

3.1.12.5.1.2.6.5 From FeSO4 Containing Sodium Lauryl Sulfate 0.5 M FeSO4 containing sodium lauryl sulfate was adjusted to pH 10 with 2 M Na2CO3 and then to pH 12 with 2 M NaOH. Oxygen was bubbled through the dispersion for 12 h. The precipitate was washed with water, and the precipitate was dried at 90°C for 6 h. Properties: Particle size 8.8 μm, BET specific surface area 103 m2/g [1601].

289

Compilation of PZCs/IEPs

TABLE 3.496 PZC/IEP of Goethite Obtained from FeSO4 Containing Sodium Lauryl Sulfate Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

6.7

[1601]

0.1 M KCl

3.1.12.5.1.2.6.6 Oxidation of the Product of Reaction between Fe and CO2-Saturated Water 10 g of iron powder (35 μm sieved) was put into 10 dm3 of oxygen-free water and was purged with oxygen-free CO2 for 3 d with stirring. The solution was filtered under oxygen-free conditions. The precipitation was induced by: A: addition of 20 cm3 of 30% H2O2 B: purging with air for 6 h C: exposure to air for 1 d at 35°C D: 1:10 dilution and exposure to air for 1 d at 35°C The precipitates were washed with water and dialyzed. They were then dried under various conditions. Properties: XRD patterns, chemical analysis (Fe2O3 and water contents) available [1602].

TABLE 3.497 PZC/IEP of Goethite Obtained by Oxidation of Product of Reaction between Fe and CO2-Saturated Water Description A B C D a

Electrolyte NaOH + HCl

T

Method

Instrument

iep

Electrophoresis

pH0a 7.2/6.8/6.8 6.9/6.8/6 6.8/6.4/5 5.9/—/4.2

Reference [1602]

Moist/dried at 60°C/dried at 100°C. For most samples, only IEP reported (no experimental data points). A few results (samples dried at 100°C) were republished in [52].

290

Surface Charging and Points of Zero Charge

3.1.12.5.1.2.7 Other 3.1.12.5.1.2.7.1 Oxidation of Fe(CO)5 with H2O2 13–35 nm [1111].

Properties: Particle size

TABLE 3.498 PZC/IEP of Goethite Obtained by Oxidation of Fe(CO)5 with H2O2 Electrolyte

T

Method

Instrument

Titration a

pH0

Reference

6.8a

[1111]

Only value reported, no data points.

3.1.12.5.1.2.7.2 Recipes from Hingston (1968b) Cited in [1180] samples

Four

TABLE 3.499 PZC/IEP of Goethite Obtained According to Recipes from Hingston (1968b) Cited in [1180] Description 28 32 17 81 m2/g 74 m2/ga a

Electrolyte

T

Method

0.01–1 M NaCl

cip

0.01–1 M NaCl

cip

Instrument

pH0

Reference

8.3 7.8 8 8 8.6

[1180]

[1363]

BET specific surface area. [1180] cited as reference for recipe.

3.1.12.5.1.3 Natural Goethites 3.1.12.5.1.3.1 Pikes Peak Batholith Properties: BET specific surface area 4 m2/g [332,1417].

TABLE 3.500 PZC/IEP of Pikes Peak Batholith Electrolyte 0.01 M NaNO3 0.01 M KNO3 a

T

Method a

iep

Only value, data points not reported.

Instrument

pH0

Reference

Malvern Zetasizer 3000HSa

7 6.7

[332] [1417]

291

Compilation of PZCs/IEPs

3.1.12.5.1.3.2

Other Natural Goethites

TABLE 3.501 PZC/IEP of Other Natural Goethites Location

Electrolyte

Alban-la-Fraysee, ground, dialyzed, dried Aueb a b

Method

Instrument

NaOH + HCl

T

iep

Electrophoresis

3.2a

pH0 Reference [225,1602]

NaOH + HClO4

iep

Zeta-Meter

9.5

[104]

Same IEP, based on different data points. Another goethite from Herdorf had multiple IEPs.

3.1.12.5.1.4

Goethite, Origin Unknown

TABLE 3.502 PZC/IEP of Goethites of Unknown Origin Description

Electrolyte

T

H2O2 washed, 58.7% Fe, 2% SiO2, 0.5% Mn, 11% loss of ignition at 800°C 2

36 m /g

iep

0.01 M KNO3 0.001–0.1 M NaCl 0.1 M NaClO4

a

b

Method

25

iep Intersection iep Titration

Instrument Streaming potential

Electrophoresis

pH0 Reference 6.7

[1603]b

7.5 7.6 7 7.8a

[1107]b [1245] [1606]

Information about temperature and electrolyte was taken from [1607], in which [1608] is cited. PZC from Figure 10 and Table 1 of [1608]. Figure 5 in [1608] suggests rather PZC at pH 6.9. Only value, data points not reported.

3.1.12.5.2 Lepidocrocite 3.1.12.5.2.1 Commercial 3.1.12.5.2.1.1 From Alfa Aesar Properties: BET specific surface area 85 m2/g, XRD pattern, SEM image available [1609]. TABLE 3.503 PZC/IEP of Lepidocrocite from Alfa Aesar Electrolyte

T

Method

Instrument

iep

ZetaPlus Brookhaven

pH0 Reference 7.1

[1609]

292

Surface Charging and Points of Zero Charge

3.1.12.5.2.1.2 Bayferrox 943 from Bayer Properties: BET specific surface area 17.1 m2/g, SEM image available [1610].

TABLE 3.504 PZC/IEP of Bayferrox 943 from Bayer Electrolyte

T

Method

0.6 M NaCl

25

pH

Instrument

pH0 Reference 7.3

[1610]

3.1.12.5.2.2 Synthetic 3.1.12.5.2.2.1 From Fe(II) 3.1.12.5.2.2.1.1 From FeSO4 and NH4Cl Recipe A: A solution containing 1 dm3 of water, 70 g of FeSO4·7H2O, and 15 g of NH4Cl was mixed with a solution containing 1 dm3 of water and 112.5 g of Na2S2O3·5H2O. Then a solution containing 0.5 dm3 of water and 27.5 g of KIO3 was added with stirring. The mixture was then heated to 45°C. Recipes B and C are similar, except that the concentrations of reagents were lower by a factor of 10 and 100, respectively than in Recipe A, and the final step took 2 and 6 h, respectively. The precipitates were washed with water and dialyzed. They were then dried under various conditions. Properties: XRD patterns, chemical analysis (Fe2O3 and water contents) available [1602].

TABLE 3.505 PZC/IEP of Lepidocrocite Obtained from FeSO4 and NH4Cl Description A B C a

Electrolyte NaOH + HCl

T

Method

Instrument

pH0a

Reference

iep

Electrophoresis

7.3/6.6/5.7 6.2/—/5.4 5.4/—/5.3

[1602]

Moist/dried at 60°C/dried at 100°C. For most samples, only IEP reported (no experimental data points). A few results (samples dried at 100°C) were republished in [52].

3.1.12.5.2.2.1.2 From FeSO4 and NaOH A solution of 250 mg of FeSO4 in 150 cm3 of CO2-free water was neutralized with 1 M NaOH to pH 6.5–7. Oxygen was bubbled through the dispersion, and NaOH solution was added to keep the pH at 6.5–7. The precipitate was water-washed. Properties: 60% lepidocrocite, 40% ferrihydrite, XRD results available, BET specific surface area 222 m2/g [1611].

293

Compilation of PZCs/IEPs

TABLE 3.506 PZC/IEP of Lepidocrocite Obtained from FeSO4 and NaOH Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Malvern Zeta Master

6.9a

[1611]

Only value reported, no data points.

3.1.12.5.2.2.1.3 From Fe(ClO4)2 500 cm3 of 0.01 M Fe(ClO4)2 was added in 100 cm3 portions, every 15 min, to a mixture of 40 cm 3 of 1 M NaHCO3, 160 cm3 of 1 M NaClO4, and 600 cm3 of water, which was pre-adjusted to pH 7.3 by purging with an air–CO2 mixture. The precipitate was washed and stored at pH 7. Properties: Structure confirmed by XRD, laths, 100–200 nm long and 10–50 nm wide, BET specific surface area 142 m2/g [896].

TABLE 3.507 PZC/IEP of Lepidocrocite Obtained from Fe(ClO4)2 Description

Electrolyte

T

Method

Two batches

0.1 M NaClO4

25

pH

a

Instrument

pH0

Reference

7.1–7.2 6.9

[896]a

Only values reported, no data points.

3.1.12.5.2.2.1.4 From Chloride, Oxidized at pH 7.4 Addition of Fe(ii) solution to NaCl–NaHCO3 mixed solution and oxidation at pH 7.4 for 1 h. Properties: BET specific surface area 171 and 181 m2/g [1612].

TABLE 3.508 PZC/IEP of Lepidocrocite Obtained from Chloride, Oxidized at pH 7.4 Electrolyte

T

Method

0.7 M NaCl

25

pH

Instrument

pH0

Reference

6.9

[1612]

3.1.12.5.2.2.1.5 From Chloride, Oxidized at pH 6.7–6.9 Properties: Structure confirmed by XRD, specific surface area 75.2 m2/g [462], BET specific surface area 59 m2/g [1510].

294

Surface Charging and Points of Zero Charge

TABLE 3.509 PZC/IEP of Lepidocrocite Obtained by Oxidation/ Hydrolysis of FeCl2 at pH 6.7–6.9 Electrolyte

T

Method

0.003–0.1 M NaNO3 0.01–1 M NaCl

25 20

cip Titration

a

Instrument

pH0

Reference

7.7 7.8a

[462] [1510]

Only value reported, no data points.

3.1.12.5.2.2.1.6 From Chloride, Oxidized at pH 6 CO2-free air was bubbled through a mixture of 0.06 M FeCl2 and ammonia buffer (pH 7.5) for 3 h at 45°C. The pH was maintained at about 6 by addition of ammonia. The precipitate was washed and dried at 65°C. Properties: BET specific surface area 50 m2/g [707].

TABLE 3.510 PZC/IEP of Lepidocrocite Obtained from Chloride, Oxidized at pH 6 Electrolyte

T

Method

NaCl a

Instrument

Salt titration

pH0 a

7.1

Reference [707]

Only value reported, no data points.

3.1.12.5.2.2.1.7 From Chloride and Pyridine Recipe from [1613]: 50.5 cm3 of pyridine was degassed under nitrogen, and mixed with 13.6 cm3 of concentrated FeCl2 solution and left overnight. The precipitate was dried, dissolved in water, and oxidized with air with stirring for 45 min. The product was washed with acetone and with ether, and dried in vacuum. Properties: g-form, BET specific surface area 61.1 m2/g [1527].

TABLE 3.511 PZC/IEP of Lepidocrocite Obtained from Chloride and Pyridine Electrolyte

T

0.001–0.1 M KNO3 a

Only value reported, no data points.

Method Titration

Instrument

pH0 7.3

a

Reference [1527]

295

Compilation of PZCs/IEPs

3.1.12.5.2.2.2 From Fe(III) A mixture of iron(iii) sulfate, sodium thiosulfate, and potassium iodate was shaken for 1 d. The precipitate was washed, and dried at 65°C. Properties: BET specific surface area 221 m2/g [707]. TABLE 3.512 PZC/IEP of Lepidocrocite Obtained from Fe(III) Electrolyte

T

NaCl a

Method

Instrument

pH0 Reference 5.8a

Salt titration

[707]

Only value reported, no data points.

3.1.12.5.2.2.3

Other

TABLE 3.513 PZC/IEP of other Synthetic Lepidocrocites Reference for Recipe [1614], in which [63] is cited [1615] [1363] [1438]

a b

pH0

Reference for pH0

Titration

6.5

[862]b

cip cip cip

7.1 7.9 8

[1363] [1617] [747]

BETa

Electrolyte

T

Method

78

0.01 M NaNO3

22–24

86 116 73

0.01–1 M NaCl 0.01–1 M NaCl 0.005–0.1 M NaNO3

Instrument

Specific surface area in m2/g, reference as for pH0. Only value, data points not reported.

3.1.12.5.2.3 Natural 3.1.12.5.2.3.1 From Siegen, Germany, Ground, Dialyzed, and Dried TABLE 3.514 PZC/IEP of Lepidocrocite from Siegen Electrolyte

T

Method

Instrument

iep

Electrophoresis

NaOH + HCl a

Arbitrary interpolation.

pH0 Reference 5.4a

[225]

296

Surface Charging and Points of Zero Charge

3.1.12.5.2.3.2 Natural Lepidocrocite from Unknown Source, H2O2Washed Properties: 56.6% Fe, 10.5% water [1302].

TABLE 3.515 PZC/IEP of Natural Lepidocrocite from Unknown Source Electrolyte

T

Method iep

a

Instrument Electrophoresis

pH0 a

7.4

Reference [1302]

Arbitrary interpolation.

3.1.12.5.2.4 Origin Unknown Properties: Specific surface area 22 m2/g [1618].

TABLE 3.516 PZC/IEP of Lepidocrocite from Unknown Source Electrolyte

a

T

Method

Instrument

Titration iep Only value, data points not reported.

pH0

Reference

6.7 7 2

[1619] [1618]a

3.1.12.5.3 Synthetic Akageneite The following PZC/IEP of akageneite are cited in [1616]: PZC at pH 7.5–8 and at pH 5.7, and IEP at pH 7.5. 3.1.12.5.3.1 Aging of Acidified FeCl3 Solution at Room Temperature 0.018 (or 0.019) M FeCl3 containing 0.001 M HCl was aged for 21 d at room temperature. Properties: Hollandite-type structure [478], ellipsoidal particles [1620,1621]: long axis 285 nm [478,1620,1621], short axis 72 nm [478,1621], 70 nm [1620].

TABLE 3.517 PZC/IEP of Akageneite Obtained by Aging of Acidified FeCl3 Solution at Room Temperature Electrolyte

T

Method

Instrument

pH0

Reference

0.0001 M NaCl

25

iep

Rank Brothers MK II

6.7a

[1621] [478]

a

Arbitrary interpolation.

297

Compilation of PZCs/IEPs

3.1.12.5.3.2 Aging of Acidified FeCl3 Solution at 100°C Solutions containing FeCl3 (0.009–0.45 M) and HCl (0.001–0.3 M) were kept at 100°C for different times. Properties: Different shapes and structures (hematite or b-FeOOH) were obtained, depending on the experimental conditions. TEM and SEM images available [1374]. BET specific surface area 10.4 m2/g, length 1 μm, width 300 nm [1622], electron micrograph available [586].

TABLE 3.518 PZC/IEP of Akageneite Obtained by Aging of Acidified FeCl3 Solution at 100°C Description

Electrolyte

b-FeOOH, rodlike, FeCl3 0.09 M, HCl 0.01 M, 24 h at 100°C

0.01 M NaCl

b-FeOOH, rodlike, FeCl3 0.09 M, HCl 0.01 M, 24 h at 100°C

0.01 M NaNO3

b-FeOOH, rodlike, FeCl3 0.09 M, HCl 0.01 M, 24 h at 90 or 100°C

0–0.002 M NaCl

a

T

Method

Instrument

22

iep

Rank Brothers Mark II

6.4

[1622]

iep

Rank Brothers

7.3

[1374]

a

[586]

25

pH

pH0 Reference

Charging curves merge at pH > 10. This may be because, at such a high pH, the amount of base used to adjust the pH became comparable to the salt concentration.

3.1.12.5.3.3 Aging of Acidified 0.1 M FeCl3 at 40°C The description is not clear. Properties: BET specific surface area 116.4 m2/g [332,1417].

TABLE 3.519 PZC/IEP of Akageneite Obtained by Aging of Acidified 0.1 M FeCl3 at 40°C Electrolyte 0.01 M NaNO3 0.01 M KNO3 a

T

Method

Instrument

pH0

Reference

iepa

Malvern Zetasizer 3000HSa

6.6 >6.7

[332] [1417]

Only value, data points not reported.

298

Surface Charging and Points of Zero Charge

3.1.12.5.3.4 Refluxing of 0.2 M FeCl3 for 1 day Properties: BET specific surface area 31 m2/g [707].

TABLE 3.520 PZC/IEP of Akageneite Obtained by Refluxing of 0.2 M FeCl3 for 1 day Electrolyte

T

NaCl a

Method

Instrument

Salt titration

pH0

Reference

7.2a

[707]

Only value, data points not reported.

3.1.12.5.3.5 Refluxing of FeCl3 Solution Containing Urea for 45 Minutes Equal volumes of 0.037 M FeCl3 and 0.75 M urea were mixed and refluxed at 95–100°C for 45 min. Properties: total iron 58.1%, b-FeOOH structure confirmed by XRD [661], specific surface area 51 m2/g (original and stored) [568], 51.6 m2/g [1319], wheatgrain shape [661], TEM image available [661]. TABLE 3.521 PZC/IEP of Akageneite Obtained by Refluxing of FeCl3 Solution Containing Urea for 45 min Description

Stored for 2 years

Electrolyte

T

0.001–0.1 M KNO3

27

0.001–0.5 M NaCl

25 25

Method Salt titration cip iep cip iep

Instrument Mark II Rank Brothers 3 d equilibration Mark II Rank Brothers

pH0 Reference 7 7.2 7.2 7 7.2

[661]

[568]

3.1.12.5.3.6 Aging of FeCl3 Solution Containing Urea for 6.5 h at 100°C 2 dm3 of solution containing 50 g of Fe(iii) and 50g* of urea was adjusted to pH 1.52* with ammonia. Then the mixture was aged for 6.5h* at 100°C*. It was then aged overnight at room temperature. The precipitate was filtered, washed with water, and dried for 5 d at 50°C. The quantities marked with * were variable. Properties: b-form, BET specific surface area 77.8 m2/g [1527]. Reference [1623] reports properties of 10 samples obtained in a similar way (quantities marked with * were different from those in the above recipe), but the surface areas of all samples studied in [1623] were different from that of a sample used in [1527].

299

Compilation of PZCs/IEPs

TABLE 3.522 PZC/IEP of Akageneite Obtained by Aging of FeCl3 Solution Containing Urea for 6.5 h at 100°C Electrolyte

T

0.001–0.1 M KNO3 a

Method

Instrument

Titration

pH0

Reference

7.9a

[1527]

Only value, data points not reported.

3.1.12.5.3.7 Aging of FeCl3 Solution Containing Urea for 13 h at 100°C 2 dm3 of solution containing 50 g of Fe(iii) (as chloride) and 200 g of urea was adjusted to pH 0.6 with HCl, and agitated at 100°C for 13 h. It was aged overnight, filtered, and the precipitate was dried at 50°C for 5 d. Properties: Akageneite, BET specific surface area 8.6 m2/g [613].

TABLE 3.523 PZC/IEP of Akageneite Obtained by Aging of FeCl3 Solution Containing Urea for 13 h at 100°C Electrolyte

T

Method

0.001–0.1 M KNO3 0.001–0.1 M KCl 0.001–0.1 M LiNO3 0.001–0.1 M NaNO3

3.1.12.5.4

Instrument

cip

pH0 Reference 7.6 8.2 7.5 7.5

[613]

Synthetic Feroxyhite (Feroxyhyte)

3.1.12.5.4.1 Hydrolysis and Oxidation of FeCl2 Simultaneous addition of NaOH and H2O2 to FeCl2 solution at room temperature. The precipitate was washed and dried at 65°C. Properties: BET specific surface area 235 m2/g [707].

TABLE 3.524 PZC/IEP of Feroxyhite Obtained by Hydrolysis and Oxidation of FeCl2 Electrolyte NaCl a

T

Method Salt titration

Only value, data points not reported.

Instrument

pH0 a

7.5

Reference [707]

300

Surface Charging and Points of Zero Charge

3.1.12.5.4.2 Recipe from [1624] Four various recipes are reported in [1624]. Properties: d-form, BET specific surface area 117 m2/g [1527]. TABLE 3.525 PZC/IEP of Feroxyhite Obtained According to Recipe from [1624] Electrolyte

T

Method

0.001–0.1 M KNO3 a

Instrument

pH0

Reference

a

Titration

8

[1527]

Only value, data points not reported.

3.1.12.5.5

FeOOH, Structure Not Specified

3.1.12.5.5.1

Nanocrystalline, Recipe from [1625]

TABLE 3.526 PZC/IEP of Nanocrystalline FeOOH Obtained According to Recipe from [1625] Electrolyte

T

0.001 M a

25

Method

Instrument

pH0

Reference

iep

Riddick type II UVA cell

9.2

[1626]

a

Reported in text. A figure suggests 22.5°C.

3.1.12.5.5.2 Natural FeOOH, Structure and Origin Unknown Water-washed, and dried at 110°C. TABLE 3.527 PZC/IEP of Natural FeOOH of Unknown Structure and Origin Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M KCl

25

iep

Rank Mark II

6.6

[1213]

3.1.12.5.5.3

Other Properties: Specific surface area 22 m2/g [1101].

TABLE 3.528 PZC/IEP of FeOOH of Unknown Structure and Origin Electrolyte

T

Method Titration iep

a

Instrument

pH0

Reference

7.2 3.1

[1101]a

Only values, data points not reported. Similar results from Ref. [1618] are reported in Section 3.1.12.5.2.4.

301

Compilation of PZCs/IEPs

3.1.12.6 Limonite Limonite is a rock that contains goethite, lepidocrocite, and other minerals. Its empirical formula is Fe2O3·nH2O (n > 1). PZCs/IEPs of limonites are presented in Tables 3.529 and 3.530. 3.1.12.6.1 Limonite from China TABLE 3.529 PZC/IEP of Limonite from China Electrolyte

T

Method a

0.01 M NaCl a

iep

Instrument

pH0

Reference

Pen Kem 300

6.6

[1317]

Arbitrary interpolation.

3.1.12.6.2 Limonite from the Netherlands FeOOH, “Limonite” from Rhederoord, Netherlands, ground, dialyzed, and dried. TABLE 3.530 PZC/IEP of Limonite from the Netherlands Electrolyte

T

Method

Instrument

iep

Electrophoresis

NaOH + HCl a

pH0 Reference 3.6a

[225]

Arbitrary interpolation.

3.1.12.7 Fe5HO8 · 4H2O, Ferrihydrite PZCs/IEPs of ferrihydrites (nominally Fe5HO8 · 4H2O) are presented in Tables 3.531 through 3.542. 3.1.12.7.1 Synthetic 3.1.12.7.1.1 Aging of Precipitate Obtained at pH 8 from 0.2 M Fe(NO3)3 and 1 M NaOH 0.2 M Fe(NO3)3 was titrated to pH 8 with 1 M NaOH. The gel was dialyzed for 10 d. It was converted into an aggregate by freezing and thawing. Properties: Two-line ferrihydrite [539,1510], BET specific surface area 327 m2/g [1510], aggregates 235 μm in diameter [539]. TABLE 3.531 PZC/IEP of Ferrihydrite Obtained by Aging of Precipitate Obtained at pH 8 from 0.2 M Fe(NO3)3 and 1 M NaOH Electrolyte

T

Method

0.01–0.3 M NaNO3 0.01–1 M NaCl

25 20

cip Titration

a

Only value, data points not reported.

Instrument

pH0

Reference

8.7 8.7a

[539] [1510]

302

Surface Charging and Points of Zero Charge

3.1.12.7.1.2 Aging of Precipitate Obtained at pH 10 from 0.05 M Fe(NO3)3 and KOH 0.05 M Fe(NO3)3 was titrated with KOH to pH 10, and the precipitate was cleaned by dialysis. Properties: Two-line ferrihydrite [1627], BET specific surface area 254.2 m2/g [1628].

TABLE 3.532 PZC/IEP of Ferrihydrite Obtained by Aging of Precipitate Obtained at pH 10 from 0.05 M Fe(NO3)3 and KOH Electrolyte

T

Method

0.001 M KCl

a

iep

Instrument Coulter Delsa 440

pH0 8.3

a

Reference [1627] [1628]

Only value, data points not reported.

3.1.12.7.1.3 Precipitated at pH 7.5 from Fe(NO3)3 and 1 M KOH 500 cm3 of solution containing 40 g of Fe(NO3)3 · 9 H2O was titrated with 310 cm3 of 1 M KOH at 100 cm3/min. The pH was adjusted to 7.5 with 1 M KOH. The precipitate was washed with 0.1 M NaCl and stored at 2°C. Properties: Two-line ferrihydrite [157,1629], structure confirmed by XRD, three-point BET specific surface area 202 m2/g [1630].

TABLE 3.533 PZC/IEP of Precipitate Obtained at pH 7.5 from Fe(NO3)3 and 1 M KOH Electrolyte 0.001–0.1 M NaCl NaCl a

T

Method

Instrument

pH0

Reference

cip iep

Malvern Zetasizer 3000

8.5 7.6

[1630]a [157] [1629]

Only value, data points not reported.

3.1.12.7.1.4 Neutralization of Acidified Fe(NO3)3 Solution Recipe from [1631]. Fe(NO3)3 was dissolved in 0.1 M HNO3, and the pH was adjusted to 8 with NaOH. Properties: XRD results available, BET specific surface area 176 m2/g [1611].

303

Compilation of PZCs/IEPs

TABLE 3.534 PZC/IEP of Precipitate Obtained by Neutralization of Acidified Fe(NO3)3 Solution Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Malvern Zeta Master

7a

[1611]

Only value, data points not reported.

3.1.12.7.1.5 Rapid Titration to pH 6–6.5 then Slow Titration to pH 7 CO2-free 0.02 M Fe(NO3)3 was titrated rapidly to pH 6–6.5 and then slowly to pH 7 with 1 M NaOH. The precipitate was washed, freeze-dried, and stored in darkness. Properties: Two-line ferrihydrite, XRD pattern available, BET specific surface area 300 m2/g [1632]. TABLE 3.535 PZC/IEP of Precipitate Obtained by Rapid Titration to pH 6–6.5 then Slow Titration to pH 7 Electrolyte

T

0.01 M NaClO4

Method

Instrument

pH0

Reference

iep

Brookhaven Zeta PALS

7.1

[1632]

3.1.12.7.1.6 Rapid Hydrolysis of FeCl3 at pH 7–8 by KOH Properties: Onepoint BET specific surface area 269 m2/g, two-line ferrihydrite structure confirmed by XRD [173]. TABLE 3.536 PZC/IEP of Precipitate Obtained by Rapid Hydrolysis of FeCl3 at pH 7–8 by KOH Electrolyte

T

Method

0.001–0.1 M NaClO4

20

cip

Instrument

pH0

Reference

8

[173]

3.1.12.7.1.7 Recipe(s) from Schwertmann and Cornell Examples of specific recipes. A: 150 cm3 of solution containing 0.3 g of Fe(NO3)3 · 9H2O was titrated with 0.1 M NaOH to pH 7.

304

Surface Charging and Points of Zero Charge

B: 4 or 0.4 g of Fe(NO3)3 was dissolved in 50 cm3 of water and saturated with N2. It was then titrated with 0.1 M NaOH to pH 7. Properties: Two-line ferrihydrite structure confirmed by XRD [637], six-line [332,1417], BET specific surface area 360 m2/g [637], 193.3 m2/g [332,1417]. Modified recipe. Properties: Two-line ferrihydrite [741,1633,1634], BET specific surface area 245 m2/g, X-ray micrographs at different levels of preparation available [1633].

TABLE 3.537 PZC/IEP of Ferrihydrites Obtained According to Recipe(s) from Schwertmann and Cornell Electrolyte 0.01 M NaNO3 0.01 M KNO3 0.1 M KNO3 0.001–0.1 M NaClO4 0.001–0.1 M NaNO3 0.1 M KNO3 a b c d

T

Method

Instrument

a

25

25

iep

Malvern Zetasizer 3000HSa

pH cip iep cip pH

Electrophoresis

pH0

Reference

6.8 6.9 7 7.8 8.7a 7.9 8, 7.2d

[332,1417] [1417] [1635]b [637] [570c,1634] [741]

Only value, data points not reported. [741] cited for recipe. [1633] cited for modified recipe, but no detailed recipe could be found there. Two specimens, recipe B.

3.1.12.7.1.8 Recipe from [460] Two recipes (for two- and six-line ferridydrite) are reported in [460]. The PZC was reported for one of these products.

TABLE 3.538 PZC/IEP of Ferrihydrite Obtained According to Recipe from [460] Electrolyte

T

Method

0.01–1 M KNO3

25

cip

Instrument

pH0

Reference

8

[460]

3.1.12.7.1.9 Short-Range-Ordered Iron Oxide (Ferrihydrite?) 3.4 dm3 of 0.118 M Fe(NO3)3 was titrated at 100 cm3/h with 3 M NaOH with stirring until pH 5. The solution was diluted to 4 dm3, aged for 4 d at 23°C, and centrifuged. The precipitate was washed with 0.2 M NaNO3, freeze-dried, and ground. Properties: EGME specific surface area 344 m2/g [1636].

305

Compilation of PZCs/IEPs

TABLE 3.539 PZC/IEP of Short-Range Ordered Iron Oxide Electrolyte

T

Method

Instrument

cip

0.001–0.1 M NaNO3

pH0 Reference 9.2

[1636]

3.1.12.7.1.10 Neutralization of 0.2 M Fe(ClO4)3 with Stoichiometric Amount of NaOH Filtered 0.2 M Fe(ClO4)3 was mixed with NaOH (OH:Fe = 3:1) under nitrogen. The dilute dispersion was aged for 21 d. Properties: BET specific surface area 244 m2/g [1637].

TABLE 3.540 PZC/IEP of Ferrihydrite Obtained by Neutralization of 0.2 M Fe(ClO4)3 with Stoichiometric Amount of NaOH

a

Electrolyte

T

Method

0.3 M NaClO4

25

pH

Instrument

pH0

Reference

8.2

[1637]a

Also cited in [1405] as Spandini, personal communication, and PZC at pH 8.3 is reported.

3.1.12.7.2 Natural Ferrihydrites from Finland Properties: In Table 3.541 [460].

TABLE 3.541 PZC/IEP of Natural Ferrihydrites from Finland Si/Fe + Si (molar)

Specific Surface C% Area (m2/g)

0.1 0.11 0.27 0.24 0.21 0.16

1.3 5 2.7 2.5 1.7 3.3

279 433 325 366 498 425

Electrolyte

T

0.01–1 M KNO3 25

Method cip

Instrument

pH0 Reference 7.5 6.3 5.3 5.5 5.4 6.1

[460]

3.1.12.7.3 Recipe from [1638] Cited in [1527] as recipe for ferrihydrite, but originally published as recipe for amorphous iron oxyhydroxide [1638]. Carbonate-free NaOH was added dropwise

306

Surface Charging and Points of Zero Charge

to Fe(NO3)3 solution. The dispersion was aged for 3 h at pH 7 and then for 1 h at the pH of interest (no washing). Properties: BET specific surface area 225 m2/g [1527].

TABLE 3.542 PZC/IEP of Precipitate Obtained According to Recipe from [1638] Electrolyte

T

Method

a

Instrument

titration

0.001–0.1 M KNO3

pH0

Reference

7.9a

[1527]

Only value, no data points reported.

3.1.12.8 Fe(OH)3 PZC of iron hydroxides, and their physical properties and preparation methods are reviewed in [10]. PZCs/IEPs of iron hydroxides (nominally Fe(OH)3) are presented in Tables 3.543 through 3.578. 3.1.12.8.1 From Nitrate 3.1.12.8.1.1 Neutralization to pH 7 with NaOH in Polypropylene Beaker Fe(NO3)3 solution was neutralized to pH 7 with NaOH in a polypropylene beaker within 15 min. The dispersion was aged at pH 7 for 1 h, and diluted before use. Properties: Amorphous [1151].

TABLE 3.543 PZC/IEP of Fe(OH)3 Obtained by Neutralization of Fe(NO3)3 to pH 7 with NaOH in Polypropylene Beaker Electrolyte NaNO3 a

T

Method Salt addition

Instrument

pH0

Reference

8.1

[1151,1188a]

Only value, no data points reported.

3.1.12.8.1.2 Neutralization of 0.4 M Fe(NO3)3 Solution to pH 7 with 1 M NaOH Properties: Amorphous, BET specific surface area 280 m2/g [1639].

307

Compilation of PZCs/IEPs

TABLE 3.544 PZC/IEP of Fe(OH)3 Obtained by Neutralization of 0.4 M Fe(NO3)3 Solution to pH 7 with 1 M NaOH Electrolyte NaClO4 a

T

Method

Room

cip

Instrument

pH0

Reference

8.1a

[1639]

Only value, no data points reported.

3.1.12.8.1.3 Dropwise Neutralization of Fe(NO3)3 with 0.1 M NaOH to pH 8 Properties: Amorphous [1640]. TABLE 3.545 PZC/IEP of Fe(OH)3 Obtained by Dropwise Neutralization of Fe(NO3)3 with 0.1 M NaOH to pH 8 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Photal ELS-800 from Otsuka

8

[1640]

0.1 M NaNO3

3.1.12.8.1.4 Dropwise Neutralization of Fe(NO3)3 with NaOH to pH 8 An acidified solution of Fe(NO3)3 was adjusted to pH 8 by dropwise addition of carbonate-free NaOH. The pH was maintained at 7.5 for 4 h. Properties: Amorphous, BET specific surface area 182 m2/g [1641]. TABLE 3.546 PZC/IEP of Fe(OH)3 Obtained by Dropwise Neutralization of Fe(NO3)3 with NaOH to pH 8 Electrolyte

T

Method

0.001–0.1 M NaNO3

25

cip Salt titration

a

Instrument

pH0

Reference

7.9

[1641]a [1642]a

Only value, no data points reported.

3.1.12.8.1.5 Dropwise Neutralization of Fe(NO3)3 with NaOH to pH 8.5 Prepared under nitrogen. Aged for 4 h.

308

Surface Charging and Points of Zero Charge

TABLE 3.547 PZC/IEP of Fe(OH)3 Obtained by Dropwise Neutralization of Fe(NO3)3 with NaOH to pH 8.5 Electrolyte 0.01 M NaNO3 a

T

Method

22–25

pH

Instrument

pH0

Reference

8

[1643]a

Only value, data points not reported.

3.1.12.8.1.6 From 0.02 M Fe(NO3)3 and 0.5 M NaOH (Added Dropwise), 40 Minutes Aged TABLE 3.548 PZC/IEP of Fe(OH)3 Obtained from 0.02 M Fe(NO3)3 and 0.5 M NaOH Electrolyte

T

0.3 M NH4NO3

Method

Instrument

pH0

Reference

iep

Zeta-Meter

<5 if any

[1189]

3.1.12.8.1.7 Rapid Neutralization of 0.1 M Fe(NO3)3 with 3 M NaOH to pH 8 A solution 0.3 M in HNO3 and 0.1 M in Fe(NO3)3 was adjusted to pH 8 by rapid addition of 3 M NaOH. The pH was maintained at 8 for 2 h. Properties: BET specific surface area 186–201 m2/g [1191,1192]. TABLE 3.549 PZC/IEP of Fe(OH)3 Obtained by Rapid Neutralization of 0.1 M Fe(NO3)3 with 3 M NaOH to pH 8 Electrolyte

T

Method

Instrument

Salt addition a

pH0

Reference

7.2a

[1191,1192]

Only value, no data points reported.

3.1.12.8.1.8 From Fe(NO3)3 and NaOH Mixed at 1:3 Molar Ratio at Room Temperature The precipitate was washed and dried at 65°C. Properties: Amorphous, BET specific surface area 348 m2/g [707]. TABLE 3.550 PZC/IEP of Fe(OH)3 Obtained from Fe(NO3)3 and NaOH Mixed at 1:3 Molar Ratio Electrolyte NaCl a

T

Method Salt titration

Only value, no data points reported.

Instrument

pH0

Reference

7.2a

[707]

309

Compilation of PZCs/IEPs

3.1.12.8.1.9 Slow Addition of NaOH Pellets to 0.5 M Fe(NO3)3 60 g of NaOH pellets were slowly added to 0.5 or 1 dm3 of 0.5M Fe(NO3)3 solution under nitrogen. The precipitate was washed with water, and dried at 20 or 25°C for 1 d. Properties: Two-line ferrihydrite with traces of goethite [1644], amorphous, BET specific surface area 200 m2/g [1488].

TABLE 3.551 PZC/IEP of Fe(OH)3 Obtained by Slow Addition of NaOH Pellets to 0.5 M Fe(NO3)3 Electrolyte

T

Method

0.01 M NaNO3

pH iep pH

0.1 M NaCl a

Instrument

pH0

Reference

Zetaphoremeter II

a

[1488]

7.7a

[1644]

5

Only value, no data points reported.

3.1.12.8.1.10 From 0.1 M Fe(NO3)3 containing NaNO3 6 cm3 of 1 M NaOH was slowly added to 20 cm3 of 0.1 M Fe(NO3)3 containing NaNO3 at 25°C in the absence of CO2. The dispersion was aged for 4 h. Properties: BET specific surface area 327 m2/g [1645].

TABLE 3.552 PZC/IEP of Fe(OH)3 Obtained from 0.1 M Fe(NO3)3 Containing NaNO3 Electrolyte

T

Method

0.3 M NaNO3

25

pH

Instrument

pH0

Reference

7.9

[1645]

3.1.12.8.1.11 Dropwise Neutralization of Acidified Fe(NO3)3 to pH 8 in Absence of CO2 Original recipe from [1646] (product termed iron oxyhydroxide, Fe2O3·H 2O am): acidified Fe(NO3)3 was added to NaNO3 solution under nitrogen and titrated with CO2-free NaOH to pH 8. It was aged for 4 h at pH 8. Reference [1646] was cited for the following recipe in [1647]: dropwise neutralization of acidified 0.04 M Fe(NO3)3 to pH 7.8 with 1 M KOH. The pH was maintained at 7.6–7.8 for 3–4 h. Properties: Amorphous, BET specific surface area 182 m 2/g [1646], 306 m 2/g [1439], specific surface area 600 m2/g [1647], spherical particles, 2 nm [1439].

310

Surface Charging and Points of Zero Charge

TABLE 3.553 PZC/IEP of Fe(OH)3 Obtained by Dropwise Neutralization of Acidified Fe(NO3)3 to pH 8 in Absence of CO2 Electrolyte

T

0.01–0.1 M NaNO3

25

0.001–0.1 M NaNO3

25

a

Method

Instrument

pH0

Reference

7.7a 7.9 7.9 7.9

Salt titration Salt titration pH cip

[1647] [1646] [1648] [1439]

Only value, no data points reported.

3.1.12.8.1.12 Neutralization of Fe(NO3)3 Solution to pH 7–8 with 1 M KOH 4 g of Fe(NO3)3 · 9H2O dissolved in 50 cm3 of water was adjusted to pH between 7 and 8 by addition of about 30 cm3 of 1 M KOH under nitrogen.

TABLE 3.554 PZC/IEP of Fe(OH)3 Obtained by Neutralization of Fe(NO3)3 Solution to pH 7–8 with 1 M KOH Electrolyte

T

Method

25 a

Instrument

pH0

Reference

a

pH

7.1

[1649]

Only value, no data points reported.

3.1.12.8.1.13 Recipe from [1650] The pH of Fe(NO3)3 solution in 0.1 M NaNO3 was adjusted to 7.5 by dropwise addition of CO2-free NaOH, and the dispersion was aged at that pH for 4 h. Properties: BET specific surface area 36.6 m2/g [468,1651,1652], particle size distribution available [468,1190], SEM image and XRD pattern available [1651].

TABLE 3.555 PZC/IEP of Fe(OH)3 Obtained According to Recipe from [1650] Electrolyte

T

Method

25

cip Titration

0.031–1.5 M

a

Only value, data points not reported.

Instrument

pH0

Reference

7.6 7.6a

[468] [1190]

311

Compilation of PZCs/IEPs

3.1.12.8.1.14 Addition of Fe(NO3)3 Solution to Ammonia Solution A solution of 405 g of Fe(NO3)3 · 9H 2O in 1 dm 3 of water was slowly added to a solution containing 3.5 mol of NH3 in 1 dm 3 of water with stirring. The precipitate was washed with water and dialyzed. It was then dried under various conditions. Properties: 16.89% Fe2O3 [1602].

TABLE 3.556 PZC/IEP of Fe(OH)3 Obtained by Addition of Fe(NO3)3 Solution to Ammonia Solution Description Moist Dried at 60°C Dried at 100°C a b

Electrolyte

T

NaOH + HCl

Method iep

Instrument Electrophoresis

pH0 a

8.5 6b 4.3b

Reference [1602]

Republished in [52]. Only IEP reported (no experimental data points).

3.1.12.8.1.15 Neutralization of Fe(NO3)3 Solution to pH 7 1 M Fe(NO3)3 was pumped into at beaker held at pH 7. The precipitate was freeze-dried, waterwashed, and freeze-dried again. Properties: Amorphous, specific surface area 250 m2/g [1187].

Table 3.557 PZC/IEP of Fe(OH)3 Obtained by Neutralization of Fe(NO3)3 Solution to pH 7 Electrolyte 0.01 M NaNO3

a

T

Method Salt addition cip

Instrument

pH0 7.8

a

Reference [1187]

Titration: 3 h per 1 pH unit

Only acidic branch reported.

3.1.12.8.1.16 Neutralization of Fe(NO3)3 Solution at Room Temperature Properties: BET specific surface area 267 m2/g. [862], 225 m2/g [1252,1253], average particle size 420 nm [1252].

0.1–0.5 M NaClO4 0.01 M KNO3 0.001 M NaNO3

Slow neutralization Dialyzed, freeze-dried Precipitated with diluted NaOH, washed

d

c

b

Only value, no data points reported. Precipitated at pH 6. Precipitated at pH 7.5. Precipitated at pH 9.

25

0.01–1 M KNO3, NaCl, NaClO4

a

25

0.0175 M KNO3

25 25 25

20 25

0.015–0.1 M NaNO3 0.001 M KNO3

T 22–24

Electrolyte 0.01 M NaNO3

Rapid hydrolysis, no exclusion of CO2, HFO or ferrihydrite Obtained in nitrogen atmosphere, [1642] cited for recipe Slow Hydrolysis, Amorphous Slow hydrolysis, amorphous Precipitated at different pH

Description

pH pH iep

pH

iep

cip iep

Method

Zeta-Meter 3.0

Delsa 440

Delsa 440

Instrument

TABLE 3.558 PZC/IEP of Fe(OH)3 Obtained by Neutralization of Fe(NO3)3 Solution at Room Temperature pH0

Reference

[526]

4.5–6.1b 5.9–7.5c 8.8–9.9d 7.9–8.5 8 8

[592,1653]a [1654] [348]

[1252]

[807] [1253a,1254]

[862]

8.2

8 8.2

6.7a

312 Surface Charging and Points of Zero Charge

313

Compilation of PZCs/IEPs

3.1.12.8.1.17 Aging at 70–75°C of Product of Neutralization of Fe(NO3)3 Solution 1:3 ammonia was slowly added to 0.5 M Fe(NO3)3 to adjust the pH to 7.5–8. The dispersion was kept at 70–75°C for 30 min, then quickly cooled. The precipitate was washed and stored in ice-cold water. The product was termed amorphous FeOOH [568,1319] or amorphous FeOOH · xH2O [661]. Properties: Total iron 48.1%, amorphous, TEM image available [661], 70 m2/g (2 y stored sample, the original sample had a higher, but unspecified specific surface area [568]), 70.7 m2/g [1319].

TABLE 3.559 PZC/IEP of Fe(OH)3 Obtained by Aging at 70–75°C of Product of Neutralization of Fe(NO3)3 Solution Description

Electrolyte 0.001–0.1 M KNO3

T 27 25

2 y aged

0.001–0.5 M NaCl

25

Method Salt titration cip iep (figure) iep (table) cip iep

Instrument

Mark II Rank Brothers 3 d equilibration Mark II Rank Brothers

pH0

Reference

7 7.2 6.5 7.1 7.4 6.5

[661]

[568]

3.1.12.8.2 From Chloride 3.1.12.8.2.1 Neutralization of 1.5 M FeCl3 with 2 M NaOH to pH 6.4 450 cm3 of 2 M NaOH was added at 50 cm3/min with stirring to 200 cm3 of 1.5 M FeCl3. The final pH was 6.4. The precipitate was washed with water and dried for 3 d at 70°C. It was then ground and sieved. The product is termed amorphous oxide in [866]. Properties: Amorphous [381,450,866,1193], single-point BET specific surface area 222.7 m2/g [866], 250 m2/g [450,1193], specific surface area 290 m2/g [381].

TABLE 3.560 PZC/IEP of Fe(OH)3 Obtained by Neutralization of 1.5 M FeCl3 with 2 M NaOH to pH 6.4 Electrolyte 0.01 M NaCl 0.01 M NaCl 0.01 M NaCl 0.1 M NaCl a

T

Method

Instrument

pH0

Reference

iep iep iep iep

Zeta-Meter 3.0 Zeta-Meter 3.0 Zeta-Meter 3.0 Zeta-Meter 3.0

7.2 8.5 8.5 8.6

[866] [1655]a [450] [1193]

The above recipe was not explicitly cited in Ref. [1655].

314

Surface Charging and Points of Zero Charge

3.1.12.8.2.2 Neutralization of FeCl3 solution with 1 M NaOH to pH 7 FeCl3 solution was slowly titrated to pH 7 with 1 M NaOH. This pH was maintained for 7 d. It was then dialyzed until Cl-free and dried at 40°C. The hydration–drying cycle was repeated nine times. Properties: EGME specific surface area 531 m2/g [598].

TABLE 3.561 PZC/IEP of Fe(OH)3 Obtained by Neutralization of FeCl3 Solution with 1 M NaOH to pH 7 Electrolyte

T

Method

0.001–0.1 M NaCl

Instrument

cip

pH0

Reference

8.8

[598]

3.1.12.8.2.3 Neutralization of Acidified FeCl3 Solution to pH 6 A solution of FeCl3 in 0.01 M HNO3, 250 mg Fe/dm3, was adjusted to pH 6 with 1 cm3 of 2.34 M NaOH. The dispersion was shaken for 12–16 h.

TABLE 3.562 PZC/IEP of Fe(OH)3 Obtained by Neutralization of Acidified FeCl3 Solution to pH 6 Electrolyte

T

0.001 M NaNO3

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000 HS

8

[224]

3.1.12.8.2.4 Neutralization of 0.1 M FeCl3 with a Stoichiometric Amount of NaOH 0.1 M FeCl3 solution was titrated with a stoichiometric amount of NaOH. Aged for 4 d at 23°C. Washed with 0.2 M NaNO3 and stored in 0.2 M NaNO3. TABLE 3.563 PZC/IEP of Fe(OH)3 Obtained by Neutralization of 0.1 M FeCl3 with Stoichiometric Amount of NaOH Electrolyte

T

0.05, 0.2 M NaNO3 a

Only value, no data points reported.

Method pH

Instrument

pH0 a

7.3

Reference [1656]

315

Compilation of PZCs/IEPs

3.1.12.8.2.5 Neutralization of 1 M FeCl3 with 7.5 M NaOH to Desired pH 7.5 M NaOH was slowly added to 100 cm3 of 1 M FeCl3 with stirring at 25°C until the desired pH value was achieved. The agitation continued for an additional 10 min.

TABLE 3.564 PZC/IEP of Fe(OH)3 Obtained by Neutralization of 1 M FeCl3 with 7.5 M NaOH to Desired pH Electrolyte

T

Method

Instrument

pH0 a

9.2 a

Reference [1657]

Only PZC reported, no data points or experimental details.

3.1.12.8.2.6 Dropwise Addition of FeCl3 Solution to 2 M NaOH The precipitate was dialyzed for 14 d.

TABLE 3.565 PZC/IEP of Fe(OH)3 Obtained by Dropwise Addition of FeCl3 Solution to 2 M NaOH Electrolyte

T

Method

0.01–1 M NaCl

22

cipa

a

Instrument

pH0

Reference

6.9

[1658]

Only value, data points not reported.

3.1.12.8.2.7 Neutralization of Diluted FeCl3 with 0.5 M NaHCO3 to pH 6 FeCl3 solution containing 7 ppm Fe, prepared by dilution of concentrated FeCl3 solution, was adjusted to pH 6 with 0.5 M NaHCO3. The dispersion was aged for 20 min with stirring.

TABLE 3.566 PZC/IEP of Fe(OH)3 Obtained by Neutralization of Diluted FeCl3 with 0.5 M NaHCO3 to pH 6 Electrolyte

T

Method iep

a

Only value reported, no data points.

Instrument

pH0

Reference

5.5a

[1659]

316

Surface Charging and Points of Zero Charge

3.1.12.8.2.8 Neutralization of 0.25 M FeCl3 with a Stoichiometric Amount of Ammonia A stoichiometric amount of 0.25 M NH3 was added to 0.25 M FeCl3. The precipitate was washed, filtered, and dried at 50°C. It was treated with hot water, washed with 10% ammonia and with water, dried at 50°C, and stored over saturated NH4Cl. Properties: DTA results available, BET specific surface area 208 m2/g [1660].

TABLE 3.567 PZC/IEP of Fe(OH)3 Obtained by Neutralization of 0.25 M FeCl3 with Stoichiometric Amount of Ammonia Electrolyte 0.001 M NaCl a

T

Method

25

pH

Instrument

pH0

Reference

6.8

[1660,1661a]

Only value reported, no data points.

3.1.12.8.2.9

Other

TABLE 3.568 PZC/IEP of Fe(OH)3 Obtained from Chloride Description Precipitated at different pH 200 cm3 of 2.5 M NH3 + 800 cm3 of 5% FeCl3, 79.5 m2/g pH was adjusted to 9 with NaOH pH was adjusted to 9 with NaOH. Precipitate was washed and aged for 2 h in 1 M NaCl at 80°C Not washed, Cl/Fe2O3 = 0.005 in solid a b c d e

Electrolyte

T

Method

Instrument

pH0

Reference

0.01–1 M 25 KNO3, NaCl, NaClO4 KNO3

pH

Titration

4.2–6.3a [526] 5.8–7.7b 8.8–9.8c 7.8d [710]

0.1,1 M NaCl

pH

8.6–8.8

[678]d

0.1,1 M NaCl

pH

8–8.3

[678]d

iep

Electrophoresis 7.1

Precipitated at pH 6. Precipitated at pH 7.5. Precipitated at pH 9. Only value reported, no data points. The same IEP is reported in Ref. [2226] for a precipitate termed hydroxide.

[1079,1229d,e]

317

Compilation of PZCs/IEPs

3.1.12.8.3 From Chloride or from Nitrate Fe(NO3)3 (or FeCl3) and NaOH were mixed at 1:4 molar ratio, dialyzed. Properties: Amorphous, spherical particles 6 nm in diameter, specific surface area 250 m2/g (aged) [1419].

TABLE 3.569 PZC/IEP of Fe(OH)3 Obtained from Chloride or Nitrate Description Fresh Dialyzed, aged

3.1.12.8.4

Electrolyte

T

Method

Instrument

pH0

Reference

0.002 M NaCl

10

iep

Rank Brothers Mark II

8.2 8.1

[1419]

From Perchlorate

3.1.12.8.4.1 Precipitated in Situ from Diluted Fe(ClO4)3 NaOH was added to 6 ¥ 10-8 or 3 ¥ 10-7 M in 0.01 M NaClO4 to adjust the pH, and then aged for 7–10 d.

TABLE 3.570 PZC/IEP of Fe(OH)3 Precipitated in Situ from Diluted Fe(ClO4)3 Electrolyte

T

0.01 M NaClO4 a

25

Method

Instrument

iep

Electrophoresis

pH0 6.7

Reference

a

[1662]

Based on arbitrary extrapolation. Scattered data points around IEP. IEP from [1662] was cited in [1] and in a few other papers as IEP of synthetic goethite. Particles were aged for 7–10 days, probably in glass at a very low solid-to-liquid ratio. The low IEP can be then explained by silicate adsorption.

3.1.12.8.4.2

Other

TABLE 3.571 PZC/IEP of Other Specimens of Fe(OH)3 Obtained from Fe(ClO4)3 Description Recipe in footnotea Recipe in footnoteb a b

Electrolyte 0.01–1 M NaCl 0.01–1 M NaCl

T

Method Instrument pH pH

pH0 5.6–10.3 5.5–10

Reference [1663] [678]

pH was adjusted to 7–11 with NaOH. pH was adjusted to 7–11 with NaOH. Precipitate was washed and aged for 2 h in 1 M NaCl at 80°C.

318

Surface Charging and Points of Zero Charge

3.1.12.8.5 From Sulfate 3.1.12.8.5.1 Neutralization of Fe2(SO4)3 Solution with Stoichiometric Amount of 1 M NaOH 25 cm3 of 1 M NaOH was added to a solution of 1.665 g of Fe2(SO4)3 in 200 cm3 of water. The precipitate was washed with water. Properties: Amorphous, soluble in 1 M HCl and in oxalate buffer (pH 3) [1664].

TABLE 3.572 PZC/IEP of Fe(OH)3 Obtained by Neutralization of Fe2(SO4)3 Solution with Stoichiometric Amount of 1 M NaOH Electrolyte

T

0.1–0.25 M NaNO3

Method

Instrument

Salt addition

pH0

Reference

8

[1664]

3.1.12.8.5.2 Other Properties: Amorphous, specific surface area (from arsenate and phosphate adsorption) 720 m2/g [229].

TABLE 3.573 PZC/IEP of Other Specimens of Fe(OH)3 Obtained from Fe2(SO4)3 Description

Electrolyte

T

Method

Precipitated at 0.01–1 M different pH KNO3, NaCl, NaClO4

25

pH

25

iep

0.01 M NaClO4

Instrument

pH0

Reference

5.8–6.5 (precipitated at pH 7.5) 8.2–9.3 (precipitated at pH 9) Pen Kem 102 9.8

[526]

[229]

3.1.12.8.6 Other 3.1.12.8.6.1 Recipe from [1665] Properties: Amorphous, specific surface area 403 m2/g (glycerol), XRD pattern available [1156].

TABLE 3.574 PZC/IEP of Fe(OH)3 Obtained According to Recipe from [1665] Electrolyte

T

Method

0.01–1 M NaNO3

25

cip

a

Only value, data points not reported.

Instrument

pH0

Reference

7.5a

[1156]

319

Compilation of PZCs/IEPs

3.1.12.8.6.2 Recipe from [1666] Prepared and stored in Teflon, in a nitrogen atmosphere, used within 1 d. Product was termed “amorphous iron oxyhydroxide, Fe2O3 · H2O.” TABLE 3.575 PZC/IEP of Fe(OH)3 Obtained According to Recipe from [1666] Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaNO3

25

cip

4–5 pH units/h

8

[1667]

3.1.12.8.6.3 Recipe from [459] 0.001 or 0.1 M Fe(iii) solution in 0.1 M NaNO3 was adjusted at 50°C to pH 10.5 with concentrated NaOH in a nitrogen atmosphere in a glass or Teflon container. It was aged for different times. See also Section 3.1.12.5.1.2.1.1. Properties: Specific surface area 320 m2/g [1449]. TABLE 3.576 PZC/IEP of Fe(OH)3 Obtained According to Recipe from [459] Electrolyte

T

Method

Instrument

Titrationa a

pH0

Reference

10.5

[1449]

Only value, data points not reported.

3.1.12.8.6.4 Recipe Cited in [1668] Reference [1669], which is cited in [1668] for the recipe, does not report a specific recipe, but cites six papers as references for recipes (including Ref. [1665], see Section 3.1.12.8.6.1). Properties: Amorphous, specific surface area 605 m2/g (glycerol method) [1668]. TABLE 3.577 PZC/IEP of Fe(OH)3 Obtained According to Recipe Cited in [1668] Electrolyte

T

Method

Instrument

Titration a

pH0 7

a

Reference [1668]

Only value, data points not reported.

3.1.12.8.6.5 Precipitated from 0.001 M Salt, Filtered, and Washed with Water TABLE 3.578 PZC/IEP of Fe(OH)3 Precipitated from 0.001 M Salt Electrolyte

T

Method

Instrument

pH0 Reference

KOH + HNO3

22

iep

Zeta-Meter

7.1

[370]

320

Surface Charging and Points of Zero Charge

3.1.12.9 Iron Hydrous Oxide PZCs/IEPs of iron(iii) hydrous oxide are presented in Tables 3.579 through 3.581. 3.1.12.9.1 Synthetic Modified recipe from [1076]: 5 cm3 of 0.34 M Fe(NO3)3 was mixed with 5 cm3 of 1.04 M NaOH, and heated in a water bath for 15 min. It was cooled and centrifuged. Properties: Amorphous, median diameter 880 nm, size distribution available [353]. TABLE 3.579 PZC/IEP of Iron(III) Hydrous Oxide Electrolyte

T

0.001 M NaCl a

Method iep

Instrument

pH0

Reference

Zeta-Meter 3.0

7.2a

[353]

Only value, data points not reported. Minimum in CCC matches IEP (but minimum in CCC is shallow).

3.1.12.9.2 Bacteriogenic Obtained by processing of a product from an Fe and Mn removal treatment unit. Properties: 37% of Fe, amorphous [1670]. TABLE 3.580 PZC/IEP of Bacteriogenic Fe2O3 Electrolyte

T

Method a

iep a

Instrument

pH0

Reference

<3 if any

[1670]

Data points not reported.

3.1.12.10 Fe Hydrous Oxide or Hydroxide (Amorphous), Origin Unknown TABLE 3.581 PZC/IEP of Fe Hydrous Oxide or Hydroxide Electrolyte HCl + KOH

a b c

T

Method titration iep iep

Instrument

pH0 a

Electrophoresis Electro-osmosis

8.1 8.6b 8.8

Reference [1671] [1672] [1214]c

Only acidity, data points not reported. Arbitrary interpolation. Sample was dialyzed for 7 days at 90°C. Only value, data points not reported.

321

Compilation of PZCs/IEPs

3.1.13

GeO2

GeO2 shows substantial solubility in water and is beyond the scope of the present book. The results of titration of GeO2 and of oxidized Ge are reported in [178]. Base was chiefly consumed for dissolution of GeO2. PZC/IEP of GeO2 (commercial, origin unknown, water-washed, and dried at 110°C) is presented in Table 3.582.

TABLE 3.582 PZC/IEP of GeO2 Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M KCl

25

iep

Rank Mark II

1.8

[1213]

3.1.14 Ga2O3 Gallium has only one stable oxidation state (+3) within the electrochemical window of water, but it forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. Nominal degree of hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of hydration. PZCs/IEPs of Ga2O3 are presented in Tables 3.583 and 3.584. 3.1.14.1 Reagent-Grade Properties: Monoclinic, BET specific surface area 4.6 m2/g [1673].

TABLE 3.583 PZC/IEP of Reagent Grade Ga2O3 Electrolyte 0.0001 M NaNO3 a

T

Method

25

iep

Instrument

pH0

Malvern Zetasizer 3000

Reference

a

9

[1673]

Continuous drift in pH made it impossible to determine the PZC as CIP or by Salt titration.

3.1.14.2

Origin Unknown

TABLE 3.584 PZC/IEP of Unspecified Ga2O3 Electrolyte 0.1 M KNO3

T

Method

Instrument

pH iep

Electro-osmosis

pH0 6 7.5

Reference [1094] [1103]

322

3.1.15

Surface Charging and Points of Zero Charge

HfO2

Hafnium forms HfO2 as the only stable compound with oxygen, and no compounds with oxygen and hydrogen. PZCs/IEPs of HfO2 are presented in Tables 3.585 through 3.587. 3.1.15.1

Commercial HfO2 from Aldrich

3.1.15.1.1 98% Pure Properties: <1 μm, 0.21% Zr, 0.17% U, BET specific surface area 8.5 m2/g [1675,1676]. TABLE 3.585 PZC/IEP of HfO2 from Aldrich, 98% Pure Description

Electrolyte

Water-washed

a

T

Method

0.001–0.1 M NaCl 25

cip iep

Instrument

pH0

Malvern Zetamaster 3000

7.8 <6a

Reference [1675] [1676]

Positive z-potential at pH 6 in 0.1 M NaCl, but negative in 0.01 and 0.001 M NaCl in [1675]. In [1676], IEP at pH 6.9 is reported in Table 1.

3.1.15.1.2 >99.95% Pure Properties: Specific surface area 1.9 m2/g [1677]. TABLE 3.586 PZC/IEP of HfO2 from Aldrich, >99.95% Pure Description Acid- and base-washed

a

T

Electrolyte

a

0.0001–0.1 M 25 KCl, NaCl, NaClO4

Method iep Electrolyte titration cip

Instrument ZetaPlus Brookhaven

pH0

Reference

7.1 7.4–7.6

[1677]

Also 15 and 35°C.

3.1.15.2 Hydrolysis of HfCl4, then Calcination at 700°C Properties: Monoclinic, BET specific surface area 35 m2/g [1678]. TABLE 3.587 PZC/IEP of HfO2 Obtained by Hydrolysis of HfCl4 Electrolyte

T

Method iep

Instrument

pH0

Reference

5

[1678]

323

Compilation of PZCs/IEPs

3.1.16 HgO Mercury forms HgO as the only stable compound with oxygen (with two crystalline forms), and no compounds with oxygen and hydrogen. PZCs/IEPs of HgO are presented in Tables 3.588 through 3.590. 3.1.16.1 Commercial Origin unknown, yellow and red, water-washed, and dried at 110°C. TABLE 3.588 PZC/IEP of Commercial HgO Electrolyte 0, 0.001 M KCl a

T

Method

25

Instrument

pH0

Reference a

iep

Rank Mark II <6 if any

[1213]

Dissolves at low pH.

3.1.16.2 Synthetic 3.1.16.2.1 Precipitated with Excess of KOH Excess of KOH was added to solution of Hg(ii) in HNO3 in ultrasonic bath. Waterwashed and stored in water. Properties: Yellow, montroydite [382]. TABLE 3.589 PZC/IEP of HgO Precipitated with Excess of KOH Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

5.8

[382]

0.0001–0.01 M KNO3

3.1.16.2.2 From Hg(NO3)2 and NaOH, Washed Properties: Structure confirmed by XRD [1088]. TABLE 3.590 PZC/IEP of HgO Obtained from Hg(NO3)2 and NaOH Electrolyte

a

3.1.17

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

7.3

[1088]a

Only value, data points not reported.

INDIUM (HYDR)OXIDES

Indium has only one stable oxidation state (+3) within the electrochemical window of water, but it forms several relatively stable compounds with oxygen

324

Surface Charging and Points of Zero Charge

and hydrogen, which differ in their degree of hydration and in their crystallographic structure. Nominal degree of hydration indicated by a chemical name/ formula reported in the literature does not necessarily reflect the actual degree of hydration. PZCs/IEPs of indium (hydr)oxides are presented in Tables 3.591 through 3.597. 3.1.17.1 In2O3 3.1.17.1.1 Commercial from Ventron Properties: Cubic [1673,1674], BET specific surface area 4.6 m2/g [1674], 5.8 m2/g [1673].

TABLE 3.591 PZC/IEP of In2O3 from Ventron Electrolyte

T

Method

0.002 M NaNO3 0.003–0.1 M NaNO3

25 25

0.01, 0.1 M NaNO3

25

iep iep cip iep

a

Instrument Acoustosizer Malvern Zetasizer 3000 Coulter Delsa 440

pH0

Reference

9 8.7

[1674] [1673]

8.7a

[350]

Arbitrary interpolation of scattered results.

3.1.17.1.2 Synthetic, Calcination of In(OH)3 3.1.17.1.2.1 At 350°C for 4 h In(OH)3 (recipe in [1679]) was calcined at 350°C for 4 h in air. Properties: Specific surface area 81 m2/g, TEM image available [1679].

TABLE 3.592 PZC/IEP of In2O3 Obtained by Calcination of In(OH)3 at 350°C for 4 h Electrolyte

T

Method

0.1 M NaNO3

25

pH

3.1.17.1.2.2 for 3 h.

Instrument

pH0

Reference

7

[1679]

At 320°C for 3 h In(OH)3 (recipe in [116]) was calcined at 320°C

325

Compilation of PZCs/IEPs

TABLE 3.593 PZC/IEP of In2O3 Obtained by Calcination of In(OH)3 at 320°C for 3 h Description

Electrolyte

T

2

Method Instrument pH0

From nitrate, size 640 nm, 37.2 m /g 0.1 M NaNO3 25 From sulfate, size 1.6 μm, 100 m2/g

pH

Reference

7.7 5.4

[116]

3.1.17.1.3 Origin Unknown

TABLE 3.594 PZC/IEP of In2O3 from Unknown Sources Description

Electrolyte

T

Method

Instrument

pH0

Reference

pH iep

Electro-osmosis

5.6 7.2

[1094] [1102,1103]a

0.1 M KNO3 10 m2/g a

Only value, data points not reported.

3.1.17.2 Synthetic In(OH)3 3.1.17.2.1 Hydrolysis at 70, 80, or 90°C Solutions 0.001–0.02 M in In, 0.04–0.5 M in 2-aminobutyric acid, and 0.0008– 0.01 M in HNO3 were aged for 0.5–48 h at 70, 80, or 90°C. Properties: Crystalline, XRD results, TGA and DTA results, SEM and TEM image available, specific surface area 56 m2/g [1679].

TABLE 3.595 PZC/IEP of In(OH)3 Obtained by Hydrolysis at 70, 80, or 90°C Electrolyte

T

Method

0.1 M NaNO3

25

pH

Instrument

pH0

Reference

7.6

[1679]

3.1.17.2.2 Hydrolysis at 100°C A solution 0.0002–0.008 M in In and 0.0003–0.01 M in HNO3 (in the presence or absence of sulfate, sulfate:In ratio 1.25) was heated at 100°C for 2 h, then rapidly quenched to room temperature and washed. Properties: SEM images available (also for different sulfate: In ratios) [116].

326

Surface Charging and Points of Zero Charge

TABLE 3.596 PZC/IEP of In(OH)3 Obtained by Hydrolysis at 100°C Description

Electrolyte

T

Method Instrument pH0 Reference

2

From nitrate, size 650 nm, 2.3 m /g 0.1 M NaNO3 25 From sulfate, size 1.7 μm, 23.2 m2/g

pH

7.7 7

[116]

3.1.17.2.3 From In(NO3)3

TABLE 3.597 PZC/IEP of In(OH)3 Precipitated at Room Temperature Description

Electrolyte

From nitrate; pH was 0.01–1 M NaCl adjusted to 7–11 with NaOH 0.1,1 M NaCl Recipe in footnotea a

T

Method Instrument

pH0

Reference

pH

5.1–10.6

[1680]

pH

5.6–9.5

[678]

pH was adjusted to 7–11 with NaOH. Precipitate was washed and aged for 2 h in 1 M NaCl at 80°C.

3.1.18 IrO2 Iridium forms compounds with oxygen and hydrogen at different oxidation and hydration states. PZCs/IEPs of iridium(iv) oxide are presented in Tables 3.598 through 3.601. 3.1.18.1 Thermal Decomposition of IrCl3 Hydrate at 500, 600, and 700°C

TABLE 3.598 PZC/IEP of IrO2 Obtained by Thermal Decomposition of IrCl3 Hydrate Electrolyte KNO3

T

Method

Instrument

pH0

Reference

pH iep

Rank Brothers Mark II

<3.9 if any <3 if any

[1681]

3.1.18.2 Calcination of Precipitate Obtained from H2IrCl6 Solution KOH solution, 10% by mass, was added to boiling H2IrCl6 solution. The precipitate, which is IrO2 hydrate, was washed and dried at 130°C, then calcined at

327

Compilation of PZCs/IEPs

350°C in oxygen for 7 h. It was washed in warm 3 M HNO3 and water, and dried for 1 h at 130°C. Properties: Poor crystallinity, BET specific surface area 160 m2/g [1682].

TABLE 3.599 PZC/IEP of IrO2 Obtained by Calcination of Precipitate Obtained from H2IrCl6 Solution Electrolyte

T

Method

0.1 M KNO3 0.01 M KNO3

25

pH iep

Instrument

pH0

Malvern Zetasizer

<2 if any 3.3

Reference [1682]

3.1.18.3 IrO2/Ti Electrode H2IrCl6 · nH2O solution in 2-propanol was decomposed at 350°C.

TABLE 3.600 PZC/IEP of IrO2/Ti Electrode Description

Partially reduced electrode a

Electrolyte

T

Method Instrument

pH0

Reference

0.001–1 M KNO3

pH

<3 if any

[1683]a

1 M KNO3

pH

5.3–5.5

[1683]a

Only value, data points not reported.

3.1.18.4

Origin Unknown

TABLE 3.601 PZC/IEP of Unspecified Samples of IrO2 Electrolyte 0.4 M KCl 0.001–1 M KNO3

3.1.19

T

Method pH pH

Instrument

pH0

Reference

4 (?) <2

[1684] [1685]

HYDROXIDES OF LANTHANIDES

Reference [1597] reports IEPs of lanthanide hydroxides at pH 5.5–7.5 without experimental details or literature references.

328

Surface Charging and Points of Zero Charge

3.1.20 La2O3 Lanthanum has only one stable oxidation state (+3) within the electrochemical window of water, but it forms stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. Nominal degree of hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of hydration. PZCs/IEPs of La2O3 are presented in Tables 3.602 through 3.604. 3.1.20.1 Commercial, from American Chemicals Corp. Properties: BET specific surface area 8 m2/g [852]. TABLE 3.602 PZC/IEP of La2O3 from American Chemicals Corp.

3.1.20.2

Electrolyte

T

Method

Instrument

None

25 Mass titration

pH0

Reference

10.3

[852]

Synthetic, from NaOH and La(NO3)3

TABLE 3.603 PZC/IEP of Synthetic La2O3 Description

Electrolyte

Refluxed and water- 0.001–0.1 M NaCl, NaNO3 washed, 185 m2/g Hydrous 0.01 M a

T

Method

35

cip iep iep

Instrument

pH0

Electro-osmosis

9.6

Electrophoresis

10.4

Reference [498] [1229]a

Only value, data points not reported. The same IEP is reported in Ref. [2226] for a precipitate (termed hydroxide) obtained from LaCl3 and NaOH.

3.1.20.3 Origin Unknown

TABLE 3.604 PZC/IEP of Unspecified Specimens of La2O3 Description

Electrolyte

T

Commercial, water- 0, 0.001 M KCl 25 washed, and dried at 110°C 0.01 M KCl a

Only value, data points not reported.

Method

Instrument

pH0

Reference

iep

Rank Mark II

6.7

[1213]

iep

Electro-osmosis

9.5

[1102a,1103a,1217]

329

Compilation of PZCs/IEPs

3.1.21

MAGNESIUM (HYDR)OXIDES

Magnesium has only one stable oxidation state (+2) within the electrochemical window of water, but it forms stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. Nominal degree of hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of hydration. PZCs/IEPs of magnesium (hydr)oxides are presented in Tables 3.605 through 3.621. 3.1.21.1 MgO PZCs/IEPs of MgO are presented in Tables 3.605 through 3.614. 3.1.21.1.1

Commercial

3.1.21.1.1.1

MgO from Baikowski TABLE 3.605 PZC/IEP of MgO from Baikowski Electrolyte

T

Method

Instrument

Titration a

pH0

Reference

12

[810]a

pH0

Reference

12

[810]a

Only value, data points not reported.

3.1.21.1.1.2 MgO from Baker, Reagent-Grade TABLE 3.606 PZC/IEP of MgO from Baker Electrolyte

T

Method

Instrument

Titration a

Only value, data points not reported.

3.1.21.1.1.3 MgO from Cerac 2 m2/g [1686,1688].

Properties: 99.95% pure, specific surface area

TABLE 3.607 PZC/IEP of MgO from Cerac Electrolyte 0.005 M NaCl

a

T

Method

Instrument

iep pHa

Pen Kem 500

Only value, data points not reported.

pH0

Reference

11 [1686a,1688] 10.4

330

Surface Charging and Points of Zero Charge

3.1.21.1.1.4 MgO from Johnson Matthey Properties: High purity, mean particle diameter 3 μm [902]. TABLE 3.608 PZC/IEP of MgO from Johnson Matthey Electrolyte

T

Method

0.01 M KCl

Instrument

iep

pH0 Reference

Pen Kem Laser Zee Meter 500 11.8

[902]

3.1.21.1.1.5 MgO from Mallinckrodt TABLE 3.609 PZC/IEP of MgO from Mallinckrodt Electrolyte

T

Method

Instrument

iep

Malvern 3000 HS

pH0 Reference 10

[147]

3.1.21.1.1.6 Magnorite from Norton, Optical-Grade TABLE 3.610 PZC/IEP of Magnorite from Norton Electrolyte

T

0.01 M NaCl a

Method iep

Instrument Streaming potential

pH0

Reference

a

12.5

[293]

Original, calcined at 600 and 1000°C. Arbitrary interpolation.

3.1.21.1.1.7 MgO from Merck, Analytical-Grade Properties: BET specific surface area 30 m2/g, 0.03% CaO, 1.5% CO3, 0.005% Fe2O3 [796] >97% [658]. TABLE 3.611 PZC/IEP of MgO from Merck Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl 0.001–0.1 M KNO3

25

iep cip iep

Malvern Zetasizer 4 Malvern Zetasizer 5000

10.8 10 12

[796] [657a,658,674a,b]c

a b c

Only value, data points not reported. Inflection point is also reported. A result of mass titration is also reported.

331

Compilation of PZCs/IEPs

3.1.21.1.1.8 MgO from Rhone Poulenc TABLE 3.612 PZC/IEP of MgO from Rhone Poulenc Electrolyte

T

Method

Instrument

0.1 M NaCl

25 Mass titration

pH0

Reference

11.5

[847]

3.1.21.1.1.9 MgO from Unknown Commercial Source Water-washed, and dried at 110°C TABLE 3.613 PZC/IEP of MgO from Unknown Commercial Source Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M KCl

25

iep

Rank Mark II

9.8

[1213]

3.1.21.1.2 Origin Unknown TABLE 3.614 PZC/IEP of MgO from Unknown Sources Description

Electrolyte

T

Method

Chemically pure, 28 m2/g

0.1 M KCl

18

Titration

a

Instrument

pH0 Reference 10.8

Only value, data points not reported.

3.1.21.2 Mg(OH)2 PZCs/IEPs of Mg(OH)2 are presented in Tables 3.615 through 3.621. 3.1.21.2.1 Commercial Mg(OH)2 from Barcroft

3.1.21.2.1.1

TABLE 3.615 PZC/IEP of Mg(OH)2 from Barcroft Electrolyte 0.01 M KCl a

T 25

Method iep

Instrument Delsa 440

Only value reported, no data points.

pH0 a

13.2

Reference [308]

[1687]a

332

Surface Charging and Points of Zero Charge

3.1.21.2.1.2 Mg(OH)2 from Ceddar Hill, Purchased from Ward Properties: 0.13% SiO2, detailed analysis, SEM images available, BET specific surface area (ground powder) 9.2 m2/g [507].

TABLE 3.616 PZC/IEP of Mg(OH)2 from Ceddar Hill, Purchased from Ward Electrolyte

T

Method

Instrument

pH0

Reference

0.001–1 M NaCl

25

iep pH

Sephy Z 3000

11

[507]

3.1.21.2.2 Synthetic 3.1.21.2.2.1

From Sulfate

TABLE 3.617 PZC/IEP of Mg(OH)2 Obtained from Sulfate Electrolyte

T

0.02 M NaNO3

3.1.21.2.2.2

Method

Instrument

pH0

Reference

iep

Zeta-Meter

10.8

[1689]

From Chloride

TABLE 3.618 PZC/IEP of Mg(OH)2 Obtained from Chloride Description

Electrolyte

0.01 M Freshly precipitated 0.01 M NaCl MgCl2 + NaOH, washed and 0.01 M NaCl dried at room temperature a

T

Method

Instrument

pH0

Reference

iep iep iep

Electrophoresis Laser Zee Meter Zetasizer MKII, Malvern

12a 11.5 12

[1229] [210] [371]

Only value reported, no data points. In Ref. [2226] IEP at pH > 12 if any reported.

3.1.21.2.3 Natural 3.1.21.2.3.1 From Wakefield, Quebec Washed in 0.001 M HCl and water, then crushed.

333

Compilation of PZCs/IEPs

TABLE 3.619 PZC/IEP of Mg(OH)2 from Wakefield, Quebec Electrolyte 0.01 M KCl a

T

Method

25

iep

Instrument

pH0

Delsa 440

14.1

a

Reference [308]

Only value reported, no data points. See also Sections 1.10.2, 1.10.4.

3.1.21.2.3.2

Origin Unknown

TABLE 3.620 PZC/IEP of Natural Mg(OH)2 from Unspecified Source Electrolyte

T

0.001 M NaClO4

Method

Instrument

pH0

Reference

iep

Zeta-Meter

>12 if any

[104]

3.1.21.2.4 Other TABLE 3.621 PZC/IEP of Mg(OH)2 from Unspecified Source Electrolyte

a

3.1.22

T

Method

Instrument

iep

Electro-osmosis

pH0 Reference 12

[1214]a

Only value, data points not reported.

MANGANESE (HYDR)OXIDES

Manganese forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation (+2 to +4), degree of hydration, and crystallographic structure. Nominal degree of oxidation and hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of oxidation and hydration. PZCs/IEPs of manganese (hydr)oxides are presented in Tables 3.622 three 3.680. Moreover, the name “manganese oxide” is often used for salt-type compounds with Group 1 and 2 metals as cations, which are discussed in Section 3.4.9.1. 3.1.22.1 MnO Manganosite, MnCO3 was heated in hydrogen at 900–1000°C for 3 h. Properties: XRD, TGA, and DTA results available [1690].

334

Surface Charging and Points of Zero Charge

TABLE 3.622 PZC/IEP of MnO Electrolyte

T

Method

Instrument

iep

Electrophoresis

0.001, 0.01 M NaCl

pH0 Reference 5.5

[1690]

3.1.22.2 Mn(OH)2 Obtained from MnCl2 and NaOH

TABLE 3.623 PZC/IEP of Mn(OH)2 Electrolyte

T

Method

Instrument

iep

Electrophoresis

0.01 M

pH0 Reference 7

[1229]

3.1.22.3 Mn3O4 3.1.22.3.1 Hausmannite from Chemetals Properties: Structure confirmed by XRD, BET specific surface area 20.4 m2/g [82].

TABLE 3.624 PZC/IEP of Hausmannite from Chemetals Electrolyte

T

Method

0.005–0.1 M NaClO4

25

cip

a

Instrument

pH0

Reference

>10 if any

[82]a

Only value reported, no data points.

3.1.22.3.2 Synthetic 0.4 M Mn(ii) acetate was aged for 2 h at 80°C. Properties: Hausmannite, XRD and IR spectra, particle size histogram, and TEM image available [1691].

TABLE 3.625 PZC/IEP of Synthetic Hausmannite Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep

Malvern Mastersizer

5.7

[1691]

335

Compilation of PZCs/IEPs

3.1.22.4 Mn2O3 + Mn3O4 Aging of 0.0001–0.005 M Mn(ii) 2,4-pentanedionate for 0.5–5 h at 40–90°C Properties: TEM images and XRD patterns available [1427].

TABLE 3.626 PZC/IEP of Mn2O3 + Mn3O4 Obtained by Aging of 0.0001–0.005 M Manganese(II) 2,4-Pentanedionate at 40–90°C Electrolyte

T

NaOH + HCl

Method

Instrument

pH0

Reference

iep

Electrophoresis

6

[1427]

3.1.22.5 Mn2O3 Bixbyite, MnO was heated in oxygen at 700–850°C for 2 h (recipe from [1692]). Properties: XRD, TGA, and DTA results available [1690].

TABLE 3.627 PZC/IEP of Mn2O3 Electrolyte

T

0.001, 0.01 M NaCl

3.1.22.6

Method

Instrument

pH0

Reference

iep

Electrophoresis

4.7

[1690]

MnOOH

3.1.22.6.1 Commercial Manganite from Chemetals Properties: Structure confirmed by XRD, BET specific surface area 9.5 m2/g [82].

TABLE 3.628 PZC/IEP of Manganite from Chemetals Electrolyte

T

Method

0.005–0.1 M NaClO4

25

cip

a

Instrument

pH0

Reference

7.4a

[82]

Only value reported, no data points.

3.1.22.6.2 Hydrolysis of Mn(II) Acetate A solution 2 M in Mn(ii) acetate and 0.2 M in HCl was aged for 1 d at 80°C. Properties: a-form (groutite), XRD and IR spectra and TEM image available [1691].

336

Surface Charging and Points of Zero Charge

TABLE 3.629 PZC/IEP of Groutite Obtained by Hydrolysis of Mn II Acetate Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Mastersizer

9.6

[1691]

0.01 M NaCl

3.1.22.6.3 Hydrolysis and Oxidation of 0.06 M MnSO4 Recipe from [1693]: 1 dm3 of 0.06 M MnSO4 was mixed with 20 cm3 of 30% H2O2 and 300 cm3 of 0.2 M ammonia. The mixture was stirred at 95°C for 6 h, then washed and dried at room temperature. Properties: Mean oxidation state of Mn 3.02 [1694], g-form[1694,1695], BET specific surface area 30.5 m2/g [1695], 32 m2/g [1694], 30 m2/g [81,84], 39 and 51 m2/g (two batches) [83] needles [84], TEM image available, [83,84,1695], SEM image available [83]. TABLE 3.630 PZC/IEP of a Product of Hydrolysis and Oxidation of 0.06 M MnSO4 Electrolyte

T

Method

0.01 M 0.01–0.1 M NaCl

a b

Instrument

Reference

a

Titration iep pH iep

25

pH0 6.2 6.3a 8.1 8.5b

Electrophoresis Acoustosizer

[1695] [1694] [83]

Only value reported, no data points. Value of 8.2 reported in text is not supported by data in Figure 4.

3.1.22.6.4 From Ilfeld, Germany and/or Pawling Mine, New York Properties: g-form (manganite), BET specific surface area 8.9 m2/g (ground sample) [1696] TABLE 3.631 PZC/IEP of Natural Manganite Electrolyte 0–0.1 M NaNO3 a

T 23

Method cip

Instrument 5 ionic strengths

pH0 5.4

a

Reference [1696]

Only value reported, no data points.

3.1.22.7 MnO2 + MnO A 2-propanolic solution, 0.006 M in Mn(ii) methoxide and 0.25 M in water was aged for 3.5 h at 60°C. Properties: TEM images and XRD patterns available [1427].

337

Compilation of PZCs/IEPs

TABLE 3.632 PZC/IEP of MnO2 + MnO Electrolyte

T

Method

Instrument

iep

Electrophoresis

NaOH + HCl

pH0 Reference 5

[1427]

3.1.22.8 Mn2O3 + MnO2 3.1.22.8.1 From Mn(II) 2,4-Pentanedionate 0.0001–0.005 M Mn(ii) 2,4-pentanedionate was aged for 0.5–5 h at 40–90°C, then treated with 30% H2O2 for 3 d. Properties: TEM images and XRD patterns available [1427]. TABLE 3.633 PZC/IEP of Mn2O3 + MnO2 Obtained from Manganese(II) 2,4-Pentanedionate Electrolyte

T

Method

Instrument

iep

Electrophoresis

NaOH + HCl

pH0 Reference 6

[1427]

3.1.22.8.2 Thermal Treatment of Precipitate Obtained from Nitrate From 1 M Mn(NO3)2, 3 M ammonia and H2O2. Heated for 3 h in air at different temperatures and washed with water. Properties: Originally amorphous MnO1.75, TGA curve available. Decomposition to Mn2O3 at about 500°C, and then to Mn3O4 at about 920°C [1697]. TABLE 3.634 PZC/IEP of Products of Thermal Treatment of Precipitate Obtained from Nitrate Treatment Temperature (°C) 200 400 500 600 800 900 1000 1200 1400

Electrolyte

T

Method

Instrument

0.001 M NaCl

25

iep

Streaming potential

pH0 Reference 3.8 4.6 9.2 9 9.1 6.9 3.8 3.9 3.5

[1697]

338

Surface Charging and Points of Zero Charge

3.1.22.9 MnOx, Nonstoichiometric 3.1.22.9.1 Evacuation of Product of Pyrolysis of Mn(NO3)2·6H2O Pyrolysis of Mn(NO3)2·6H2O at 160°C for 400 h. The product was washed, electrodialyzed, dried at 110°C for 1 d, and evacuated (0.001 Pa) for 5 h at different temperatures. TABLE 3.635 PZC/IEP of Products of Evacuation of Product of Pyrolysis of Mn(NO3)2⋅6H2O Evacuation Temperature (°C) 300 800 1000 a

MnOX

Structure, Specific Surface Area (m2/g) Electrolyte T Method Instrument pH0 Reference

1.2–1.4 b-MnO2, 2.24 1.14–1.19 Mn3O4, 0.96 1.03–1.16 Mn3O4, 0.54

iep

Streaming potential

<3 4.5 3.3

[1698]a

Only value reported, no data points.

3.1.22.9.2 Heating of Nonstoichiometric MnOx in Air Pyrolysis of Mn(NO3)2·6H2O at 160°C for 400 h. The product was washed, electrodialyzed, dried at 110°C for 1 d, and evacuated (0.001 Pa) for 5 h at different temperatures, followed by heating in air for 5 h at the same temperature. TABLE 3.636 PZC/IEP of Products of Heating of Nonstoichiometric MnOx in Air Evacuation Temperature (°C) 300 800 1000 a

MnOX

Structure, Specific Surface Area (m2/g) Electrolyte T Method Instrument pH0 Reference

1.5–2.4 b-MnO2, 1.86 1.21–1.27 a-Mn2O3, 1.31 1.11–1.15 Mn3O4, 0.6

iep

Streaming potential

<3 8.2 3.2

[1698]a

Only value reported, no data points.

3.1.22.9.3 Particles Formed in the Oxygen–Hydrogen Flame The description of the chemical nature is not clear. Properties: XRD results and HTEM and SEM images available [1303].

339

Compilation of PZCs/IEPs

TABLE 3.637 PZC/IEP of Particles Formed in the Oxygen–Hydrogen Flame Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep

Electrophoresis Streaming potential

3.9 4.3

[1303]

3.1.22.10 Mn(IV)0.84Mn(III)0.02O1.4(OH)0.6 Solution 0.125 M in MnSO4 (or in KMnO4) and 0.25 M in KBrO3 was ultrasonified at 45°C for 566 min. The precipitate was washed in water and dried at room temperature in air. Properties: Surface water: 17%, structural water: 6.3%, contains g-MnO2, BET specific surface area 301 m2/g, XRD pattern, SEM image available [234].

TABLE 3.638 PZC/IEP of MnIV0.84MnIII0.02O1.4(OH)0.6 Electrolyte

T

0.05–0.5 M NaCl

Method

Instrument

pH0

Reference

pH

3 d equilibration

2.2

[234]

3.1.22.11 Mn(IV)0.76Mn(III)0.07O1.25(OH)0.75 A solution 0.25 M in MnSO4 (or in KMnO4) and 0.5 M in KBrO3 was ultrasonified at 45°C for 4 h. The precipitate was washed in water and dried at room temperature in air. Properties: Surface water: 16.4%, structural water: 8.2%, contains g-MnO2, BET specific surface area 161 m2/g, XRD pattern, SEM image available [234].

TABLE 3.639 PZC/IEP of MnIV0.76MnIII0.07O1.25(OH)0.75 Electrolyte 0.05–0.5 M NaCl

T

Method

Instrument

pH0

Reference

pH

3 d equilibration

1.9

[234]

3.1.22.12 3MnO2 · Mn(OH)2 · nH2O (Mn(II) Manganite) KMnO4 was reduced with excess of HCl. Properties: 10 A manganite (layers containing Mn4+ sixfold coordinated with O2- are separated by a 10 Å space that contains Mn2+ coordinated with O2-, OH-, and H2O), BET specific surface area 70 m2/g [481].

340

Surface Charging and Points of Zero Charge

TABLE 3.640 PZC/IEP of 3MnO2⋅Mn(OH)2⋅nH2O Electrolyte

T

NaNO3

Method

Instrument

iep Coagulation

Electrophoresis

pH0

Reference

2 (extrapolated) 1.8

[481]

3.1.22.13 Amorphous MnO1.9–1.95 Recipe adopted from [1699] and [1700]: 250 cm3 of 0.0015 M Mn(ClO4)2 was added dropwise with stirring to 750 cm3 of solution 0.000667 M in NaOH and 0.000333 M in KMnO4. The precipitate was aged in darkness for 1 d before washing. Properties: Average particle diameter 100–350 nm, BET specific surface area 96 m2/g [883].

TABLE 3.641 PZC/IEP of Amorphous MnO1.9–1.95 Electrolyte

T

Method

Instrument

pH0

25

iep pH

Malvern Zetamaster S

HClO4 + NaOH

Reference

2 2.8

[883] [1700]

3.1.22.14 MnO2 PZC of MnO2 (nominally) are reviewed in [1701]. Most materials discussed in this section have in fact a lower O:Mn ratio than the nominal formula suggests. 3.1.22.14.1 Commercial 3.1.22.14.1.1 MnO2 from Aldrich 3.1.22.14.1.1.1 99.99% Properties: BET specific surface area 6.9 m2/g (90–300 μm fraction) [23].

TABLE 3.642 PZC/IEP of 99.99% MnO2 from Aldrich Electrolyte

a

T

Method

Instrument

pH0

Reference

Mass titration

5.6a

[23]

Only value reported, no data points.

341

Compilation of PZCs/IEPs

3.1.22.14.1.1.2 Pyrolusite

TABLE 3.643 PZC/IEP of Pyrolusite from Aldrich Electrolyte

T

0.1 M NaCl a

3.1.22.14.1.2

Method

Instrument

pH0 a

pH

5.8

Reference [1702]

Only value reported, no data points.

MnO2 from Baker

Properties: b-form [481].

TABLE 3.644 PZC/IEP of MnO2 from Baker Electrolyte

T

NaNO3

a

Method

Instrument

iep Coagulation

Electrophoresis

pH0 Reference 7.3a

[481]

Only value reported, no data points.

3.1.22.14.1.3 MnO2 from BDH Properties: b-form, BET specific surface area 2.4 m2/g [121].

TABLE 3.645 PZC/IEP of MnO2 from BDH Electrolyte LiNO3 a

T 27

Method

Instrument

pH

pH0 a

7

Reference [121]

Only value reported, no data points.

3.1.22.14.1.4 Electrolytic MnO2 from Delta (or Delta EMD) Electrolysis of acidic MnSO4 ([H]:[Mn] = 0.3) at 95°C. Properties: Pseudo-hexagonal [80], XRD pattern available [79,80], BET specific surface area 38.7 m2/g [80], 35.4 m2/g [705]. In [79] the original material was heated at 100–500°C for 1 d, then washed with 0.01 M H2SO4 and with water.

342

Surface Charging and Points of Zero Charge

TABLE 3.646 PZC/IEP of Electrolytic MnO2 from Delta (or Delta EMD) Calcination Temperature (°C), Specific Surface Area (m2/g)

Original, 33 100, 27 150, 25 200, 24 250, 25 300, 25 350, 22 400, 16 450, 13 a

Electrolyte

T

Method

Instrument

pH0

0.001–0.1 M KNO3

25

cip

6.7

0.01 M NaNO3

25

pH

4.5 4.8 4.6 5.2 4.8 5 5 5.3 6.2

Reference [80] [705]a [79]a

Only values reported, no data points.

3.1.22.14.1.5 MnO2 from Fisher Properties of the following specimens from Fisher have been reported. Pyrolusite: BET specific surface area 0.048 m2/g [1703], Analytical grade: TEM image available, specific surface area 0.6 m2/g [908]. TABLE 3.647 PZC/IEP of MnO2 from Fisher Description

Electrolyte

T

Analytical grade a

Method iep

Instrument

pH0 a

Zeta-Meter

5

Reference [1595]

Subjective interpolation.

3.1.22.14.1.6 IC-1 Obtained from Mn(ii) salt by electrolytic oxidation. Properties: g-form, BET specific surface area 43 m2/g [932,1279].

TABLE 3.648 PZC/IEP of IC-1 MnO2 Description

Electrolyte

T

Method

Acid-washed

0.1 M NaNO3

25

pH

Instrument

pH0

Reference

4.2

[932,1279]

343

Compilation of PZCs/IEPs

3.1.22.14.1.7 ICS 5 Properties: g-form with admixture of b-form, 94.5% MnO2, 5% weight loss at 405°C, BET specific surface area 72 m2/g [1704]. TABLE 3.649 PZC/IEP of ICS 5 MnO2 Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KCl 0.001 M KCl

25 18

pH iep

5.9 5.8

[1704]

Electrophoresis

3.1.22.14.1.8 IC-12 Obtained from Mn(ii) salt by chemical oxidation. Properties: g-form [932], BET specific surface area 80 m2/g [932,934,1279,1705]. TABLE 3.650 PZC/IEP of IC-12 MnO2 Description

Electrolyte

T

Method

Acid-washed

0.1 M NaNO3

25

pH

Instrument

pH0

Reference

3.8

[932,1279]

3.1.22.14.1.9 IC-16 Obtained electrochemically. Properties: g-form, O:Mn ratio 1.96, specific surface area 21.6 m2/g, average size 6.7 μm [120].

TABLE 3.651 PZC/IEP of IC-16 MnO2 Description Ground

Electrolyte

T

0.01 M NaCl 0.1 M NaNO3

Method

Instrument

pH0

Reference

iep pH

Laser Zee 500, Pen Kem

4

[120]

3.1.22.14.1.10 IC-22 Properties: Obtained from Mn(ii) salt by chemical oxidation, g-form, BET specific surface area 45.1 m2/g [932,1279,1706].

TABLE 3.652 PZC/IEP of IC-22 MnO2 Description

Electrolyte

T

Method

Acid-washed

0.1 M NaNO3 0.05–1 M NaNO3

25 25

pH cip

Instrument

pH0

Reference

4.7 4.8

[932,1279] [1706]

344

Surface Charging and Points of Zero Charge

3.1.22.14.1.11 MnO2 from Merck Properties: b-form [121,1695], BET specific surface area 2.1 m2/g [121], 214 m2/g [1695], specific surface area 2.2 m2/g [710], TEM image available [1695].

TABLE 3.653 PZC/IEP of MnO2 from Merck Electrolyte LiNO3 a

T

Method

27

Instrument

pH0

Salt addition

7

Reference

a

[121]

Only value reported, no data points.

MnO2 from POCh (see Section 3.1.22.15.3). 3.1.22.14.1.12 WSA from Sedema Properties: Pseudo-orthorhombic [80,705], XRD pattern available [80], BET specific surface area 40.4 m2/g [80,705].

TABLE 3.654 PZC/IEP of WSA from Sedema Electrolyte

T

Method

0.001–0.1 M KNO3

25

cip

a

Instrument

pH0

Reference

3.7

[80] [705]a

Only value reported, no data points.

3.1.22.14.1.13 MnO2 from Touzart and Matignon Obtained by thermal decomposition of manganese nitrate. Properties: b-form, BET specific surface area 4 m2/g [80,705], XRD pattern available [80].

TABLE 3.655 PZC/IEP of MnO2 from Touzart and Matignon Electrolyte

T

Method

0.1 M KNO3

25

pH

a

Instrument

Only value reported, no data points.

pH0

Reference

7.7

[80] [705]a

345

Compilation of PZCs/IEPs

3.1.22.14.1.14 MnO2 from Union Carbide Electrolytic product. Properties: 0.01% Mg, g-form [392,481,1707], BET specific surface area 6.7 m2/g [1707], high purity [392]. Table 3.656 PZC/IEP of MnO2 from Union Carbide Electrolyte

T

Method

Instrument

0.0001, 0.001 M NaNO3 iep Rank Brothers 0.0001–0.01 M KNO3 22 iep Zeta-Meter NaNO3 iep Electrophoresis Coagulation a

pH0

Reference

5.3 5.6 5.6 5.5

[392] [1707] [481]a

Only value reported, no data points.

3.1.22.14.2 Synthetic 3.1.22.14.2.1 Calcination of Synthetic Birnessite at 400°C for 60 h Washed in HClO4, NaOH and water. Properties: Cryptomelane, 57.2% Mn, 7% K by mass, specific surface area 23.2 m2/g [1708]. TABLE 3.657 PZC/IEP of Product of Calcination of Synthetic Birnessite at 400°C for 60 h Electrolyte

T

Method

Instrument

iep a

pH0 a

Electrophoresis

5.1

Reference [1708]

Only value reported, no data points; unwashed sample produced IEP at pH 3.1.

3.1.22.14.2.2 Calcination of Birnessite Properties: Cryptomelane, specific surface area 25.7 m2/g, SEM image available [332,1417], XRD pattern available [332, 1417]. TABLE 3.658 PZC/IEP of Product of Calcination of Birnessite Electrolyte 0.01 M NaNO3 0.01 M KNO3 a

T

Method a

iep

Instrument Malvern Zetasizer 3000HSa

Only value reported, no data points.

pH0

Reference

<6 6.2

[332,1417]

346

Surface Charging and Points of Zero Charge

3.1.22.14.2.3 Evaporation and Calcination of Mn(NO3)2 Solution Method from [1709]: A solution of Mn(NO3)2 was evaporated nearly to dryness and calcined for 2 d at 180°C. The precipitate was ground, washed, and calcined again for 1 d. Properties: Pyrolusite, stoichiometric proportion of oxygen [1709], specific surface area 3 m2/g [1709], BET specific surface area 0.15 m2/g [332,1417]. TABLE 3.659 PZC/IEP of Product of Evaporation and Calcination of Mn(NO3)2 Solution Electrolyte 0.01 M NaNO3 0.01 M KNO3 a

T

Method

Instrument

iep

Malvern Zetasizer 3000HSa

pH0

Reference

<4.3 6.6

[332]a [1417]a

Only value reported, no data points.

3.1.22.14.2.4 Thermal Decomposition of Mn(NO3)2 Properties: b-form mixed with e-form [1710], tetragonal [1711], b-form [704,1690], (Decomposition at 160°C for 500 h in air): originally b-form [1697], decomposition to Mn2O3 at about 600°C, and then to Mn3O4 at about 920°C [1697], O:Mn = 2.06 [1711], BET specific surface area 11.8 m2/g [704], specific surface area 2.3 m2/g [1710], XRD pattern [704,1690], TGA curve [704,1690,1697], and DTA results available [1690]. TABLE 3.660 PZC/IEP of Products of Thermal Decomposition of Mn(NO3)2 Treatment Temperature (°C)

Electrolyte

200 0.001 M NaCl 400 500 600 800 900 1000 1200 1400 Washed in HNO3, dried at 160°C [1692] 0.001, 0.01 M NaCl 400°C to a constant 0.01, 0.001 M NaClb weight 0.001 M KCl a b c

T 25

Method iep

Instrument Streaming potential

Drift

30

pH0 a

<3/4 <3/5.2 3.6 7.8/7.9 7.7/7.9 5.1 3.5/5.1 3.8/5.1 3.5/5.1 4–4.5

Reference [1697]

[1711]c

iep iep

Electrophoresis Electrophoresis

4.4 4.6

[1690] [704]

iep

Electrophoresis

6

[1710]

Not crushed/crushed. Mobility in other electrolytes was also measured, but only at pH 6.4. Only value, data points nor reported.

347

Compilation of PZCs/IEPs

3.1.22.14.2.5 Calcination of Mn(NO3)2·4H2O at 150°C Recipe from [1712]: Mn(NO3)2·4H2O was heated to 120–125°C until the entire mass was about to solidify. The product was washed, dried, ground, and heated at 150°C for 15 h. It was then washed with 1:1 HNO3 and with water. Properties: b-form, BET specific surface area 2.6 m2/g [121].

TABLE 3.661 PZC/IEP of MnO2 Obtained by Calcination of Mn(NO3)2 ⋅ 4H2O at 150°C Electrolyte LiNO3 a

T

Method

27

Instrument

Salt addition

pH0 7.1

Reference

a

[121]

Only value reported, no data points.

3.1.22.14.2.6 Calcination of Synthetic MnCO3 Recipe from [1712]. Finely divided synthetic MnCO3 was calcined in air for 14 h at 400°C (sample A). The product was further calcined for 3 h at 750°C and leached in 3 M HNO3 for 2 h at 80–90°C (sample B).

TABLE 3.662 PZC/IEP of MnO2 Obtained by Calcination of Synthetic MnCO3 Description

Electrolyte

A, a, 71.7 m /g B, g, 19.7 m2/g 2

a

T 27

LiNO3

Method Salt addition

Instrument a

pH0

Reference

5.4 3.9

[121]

Only value reported, no data points.

3.1.22.14.2.7 Thermal Decomposition of MnCO3 at 400°C in Air or in Oxygen Monodispersed particles, two different recipes. Properties: g-form, SEM images available, O:Mn atomic ratio: 1.83 and 1.87, average size 1 and 1.1 μm, specific surface area 80.7 and 66.4 m2/g [120].

TABLE 3.663 PZC/IEP of Products of Thermal Decomposition of MnCO3 Electrolyte 0.01 M NaCl 0.1 M NaNO3

T

Method

Instrument

pH0

Reference

iep pH

Laser Zee 500, Pen Kem

4

[120]

348

Surface Charging and Points of Zero Charge

3.1.22.14.2.8 From KMnO4 and MnSO4 Modified method from [1709]: 80 cm3 of 0.4375 M KMnO4 was poured into 100 cm3 of solution 0.5 M in MnSO4 and 2 M in acetic acid. Both solutions were preheated to 60°C before reaction. The dispersion was boiled for 20 min with stirring. The precipitate was washed, aged at 50°C for 1 d in water, and then freeze-dried. Properties: Cryptomelane [1713,1714], composition: K0.24MnO2.07(H2O)0.48, Mn oxidation state 3.9 [1713], BET specific surface area 117 and 268 m2/g [1714], specific surface area 130.7 m2/g, XRD and ED pattern, TEM image available [1713].

TABLE 3.664 PZC/IEP of MnO2 Obtained from KMnO4 and MnSO4 Electrolyte

T

Method

0.001–0.5 M NaNO3

a

Instrument

pH pH

pH0

Reference

<4 if any 2.1a

[1714] [1713]

Obtained by fast titration, only PZC reported. The charging curve reported in [1713] (only negative charge at pH > 2.5) was obtained by back titration.

3.1.22.14.2.9 From LiMn2O4 and 1 M HNO3 Properties: l-form, 97% of Li extracted [1715].

TABLE 3.665 PZC/IEP of MnO2 Obtained from LiMn2O4 and 1 M HNO3 Electrolyte

T

Method

Instrument

pH0

Reference

0–1 M LiCl, NaCl, KCl, RbCl, CsCl

25

pH

21 d equilibration

<4 if any

[1715] [1716]

3.1.22.14.2.10 Hot Acid Treatment of LiMn2O4 Properties: Ramsdellite, XRD pattern available, BET specific surface area 15.2 m2/g [80,705].

TABLE 3.666 PZC/IEP of MnO2 Obtained by Hot Acid Treatment of LiMn2O4 Electrolyte

T

Method

0.001–0.1 M KNO3

25

cip

a

Only value reported, no data points.

Instrument

pH0

Reference

<2.5 if any

[80] [705]a

349

Compilation of PZCs/IEPs

Uptake of metal hydroxide by l-MnO2 is a bulk reaction that leads to Li xMn2O4 and O2. 3.1.22.14.2.11 From Synthetic Birnessite and Hot HNO3 Recipe from [1712]. A dispersion of 30 g of synthetic birnessite in 300 cm3 of 3 M HNO3 was stirred for 5 h at 80–90°C. Properties: a-form, BET specific surface area 65.5 m2/g [121].

TABLE 3.667 PZC/IEP of MnO2 Obtained from Synthetic Birnessite and Hot HNO3 Electrolyte

T

Method

LiNO3

27

Salt addition

a

Instrument

pH0

Reference

3.3a

[121]

Only value reported, no data points.

3.1.22.14.2.12 Leaching of Synthetic Birnessite in 3 M HNO3 for 4 h at 90°C Recipe from [1712]. Properties: g-form, BET specific surface area 64.1 m2/g [121].

TABLE 3.668 PZC/IEP of MnO2 Obtained by Leaching of Synthetic Birnessite in 3 M HNO3 for 4 h at 90°C Electrolyte

T

Method

LiNO3

27

Salt additiona

a

Instrument

pH0

Reference

4.2

[121]

Only value reported, no data points.

3.1.22.14.2.13 Spray-Vapor Deposition Preparation method described in [1717]. Properties: b-form, BET specific surface area 61.2 m2/g [80].

TABLE 3.669 PZC/IEP of MnO2 Obtained by Spray-Vapor Deposition Electrolyte

T

Method

0.001–0.1 M KNO3

25

cip

Instrument

pH0

Reference

7.3

[80]

350

Surface Charging and Points of Zero Charge

3.1.22.14.2.14 From Mn(NO3)2 and NaClO3 Recipe from [1712]: 68.5 g of synthetic MnCO3 were dissolved in HNO3 (density 1420 kg/m3) and 128.4 g of NaClO3 were added with stirring. 200 cm3 of water were added, and the dispersion was left for 12 h. Properties: g-form, BET specific surface area 67 m2/g [121]. TABLE 3.670 PZC/IEP of MnO2 Obtained from Mn(NO3)2 and NaClO3 Electrolyte

T

Method

LiNO3

27

Salt additiona

a

Instrument

pH0

Reference

3.6

[121]

Only value reported, no data points.

3.1.22.14.2.15 From MnSO4 and Persulfate Recipe from [1712]: 226 g of (NH4)2S2O8, Recipe A (or K2S2O8, Recipe B) were added to a boiling solution of 100 g of hydrous MnSO4 in 2 dm3 of 0.1 M H2SO4. The dispersion was left for 5 h. Properties: a-form [121]. TABLE 3.671 PZC/IEP of MnO2 Obtained from MnSO4 and Persulfate Description 2

A, 31.1 m /g B, 28.4 m2/g γ a b

Electrolyte LiNO3 NaOH + HCl

T

Method

27 Salt addition

Instrument a

30 iep

Electrophoresis

pH0

Reference

3 3

[121]

5

[1719]b

Only value reported, no data points. Arbitrary interpolation.

3.1.22.14.2.16 Anodic Oxidation of 5% MnSO4 Recipe from [1712]: Anodic oxidation of 5% MnSO4 at pH 3–4 (Recipe A) or 2–3 (Recipe B) at 6 mA/cm2 (Recipe A) or 8–10 mA/cm2 (Recipe B). Properties: g-form [121]. TABLE 3.672 PZC/IEP of MnO2 Obtained by Anodic Oxidation of 5% MnSO4 Description 2

A, 41.7 m /g B, 59.8 m2/g a

Electrolyte LiNO3

T 27

Method

Instrument a

Salt addition

Only value reported, no data points.

pH0 4 4.1

Reference [121]

351

Compilation of PZCs/IEPs

3.1.22.14.2.17 Oxidation of Mn(OH)2 with Air Recipe from [1712]. A solution of 200 g of hydrous MnSO4 in 1.5 dm3 of water was slowly adjusted to pH 9.5 with 1:1 ammonia. The dispersion was bubbled with air for 50 h at pH 9–9.5. The precipitate was washed, dried, and leached with 3 M HNO3 for 3 h. Properties: g-form, BET specific surface area 36 m2/g [121].

TABLE 3.673 PZC/IEP of MnO2 Obtained by Oxidation of Mn(OH)2 with Air Electrolyte LiNO3 a

T

Method

Instrument a

27

Salt addition

pH0

Reference

4.2

[121]

Only value reported, no data points.

3.1.22.14.3

Natural

3.1.22.14.3.1 From UmBogma, Sinai Properties: b-form, XRD results available, TGA curve available, BET specific surface area 4.5 m2/g [704].

TABLE 3.674 PZC/IEP of MnO2 from UmBogma, Sinai Electrolyte

T

0.001 M NaCl

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.4 (figure) 4.4 (text)

[704]

3.1.22.14.3.2 From Sitpar Mine, Chindara, India Properties: Cryptomelane, K1.3–1.5Mn8O16, BET specific surface area 5.3 m2/g, SEM image available [332,1417].

TABLE 3.675 PZC/IEP of MnO2 from Sitpar Mine, Chindara, India Electrolyte 0.01 M NaNO3 0.01 M KNO3 a

T

Method iep

a

Instrument

pH0

Reference

Malvern Zetasizer 3000HSa

4.3 6.7

[332,1417]

Only value reported, no data points.

352

Surface Charging and Points of Zero Charge

3.1.22.14.3.3

Other

TABLE 3.676 PZC/IEP of MnO2 from Other Natural Sources Description

Electrolyte

T

Method

2

a

Cryptomelane, 14.9 m /g, 0.01 M NaNO3 SEM image available 0.01 M KNO3 Pyrolusite, 7.9 m2/g 0.01 M NaNO3 0.01 M KNO3 a

iep

iepa

Instrument

pH0

Reference

Malvern Zetasizer 3000HSa Malvern Zetasizer 3000HSa

6.2 >6.8 4.9 6.5

[332,1417]

Instrument

pH0

Reference

Electro-osmosis

2.5 3.8 2.4

[1217]a [1718]a [1103]a

4.7 5.4 6.4

[23]a [1241]a [1720]d

7.4 4.2 5.6c

[1721]a

[332,1417]

Only value reported, no data points.

3.1.22.14.4

Origin Unknown

TABLE 3.677 PZC/IEP of MnO2 from Unidentified Sources Description BET specific surface area 67 m2/g Catalyst Washed g Pyrolusite, three samples

a b c d

Electrolyte 0.01 M KCl 0.1 M KCl

0.001–1 M NaNO3 0.01–1 M LiClO4

T

Method

iep Room Mass titration iep

25 25

Electro-osmosis

Mass titration pH cip iep

Zeta-Meter

Only value reported, no data points. Arbitrary interpolation. Sample containing 4.3% Fe and 0.2% Zn. No impurities were detected in the other two samples. Also 0.1 M LiCl, KCl and CsCl.

3.1.22.15

Hydrous MnO2

3.1.22.15.1 Recipe from [1699] Mn(NO3)2 was slowly added to alkaline solution, 0.0046 M in KMnO4 (final molar ratio 3:2). It was centrifuged, washed, and re-dispersed in 0.015 M NaNO3 (pH 7), and the dispersion was aged for 16 h.

353

Compilation of PZCs/IEPs

Properties: Amorphous (XRD results available) [577], BET specific surface area 359 m2/g [577,1190], particle diameter 1–500 μm (distribution available) [577], 3–30 μm [1190]. TABLE 3.678 PZC/IEP of Hydrous MnO2 Obtained from Mn(NO3)2 and KMnO4 Electrolyte

T

0.015–1.5 M NaNO3

25 25

a

Method

Instrument

pH Titration

pH0

Reference

2.6 2.4

[577] [1190]a

Only value, data points not reported.

3.1.22.15.2 Heating of Suspension of Mn(II) Manganite in KCl Solution at 100°C for 10 h Properties: a-form, formula KMn8O16 or NaMn8O16 [481]. TABLE 3.679 PZC/IEP of Hydrous MnO2 Obtained by Heating of Suspension of Mn(II) Manganite in KCl Solution at 100°C for 10 h Electrolyte NaNO3

3.1.22.15.3

T

Method iep Coagulation

Instrument

pH0

Reference

Electrophoresis

4.6 4.5

[481]

MnO2 from POCh

TABLE 3.680 PZC/IEP of MnO2 from POCh Description 2

38 m /g

3.1.23

Electrolyte

T

0.01 M NaCl, KCl

Method

Instrument

iep

Malvern Zetasizer 3000

pH0 Reference 4.2

[1200]

NIOBIUM (HYDR)OXIDES

Niobium forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation (+4 to +5), degree of hydration, and crystallographic structure. Nominal degree of oxidation and hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of oxidation and hydration. PZCs/IEPs of niobium (hydr)oxides are presented in Tables 3.681 through 3.688.

354

Surface Charging and Points of Zero Charge

3.1.23.1

NbO2, Origin Unknown TABLE 3.681 PZC/IEP of NbO2 Electrolyte

T

Method

0.4 M KCl

3.1.23.2

Instrument

pH

pH0

Reference

7.3

[1684]

Nb2O5

3.1.23.2.1 Commercial 3.1.23.2.1.1

Nb2O5 from Aldrich

TABLE 3.682 PZC/IEP of Nb2O5 from Aldrich Electrolyte

T

Method

Instrument

iep

Streaming potential

0.001 M KNO3 23 a

3.1.23.2.1.2

pH0 Reference 4.4a

[261]

Only value reported, no data points.

Nb2O5 from Alfa Aesar, 99.9% Metal Basis TABLE 3.683 PZC/IEP of Nb2O5 from Alfa Aesar Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern 3000 HS

2.6

[147]

3.1.23.2.1.3 Nb2O5 from Companhia Brasiliera de Metalurgia e Mineracao Properties: Orthorhombic [830,831]. TABLE 3.684 PZC/IEP of Nb2O5 from Companhia Brasiliera de Metalurgia e Mineracao Electrolyte 0.0005–0.05 M KNO3

T

Method

Instrument

pH0

Reference

iep

Rank Brothers

4

[830,831]

355

Compilation of PZCs/IEPs

3.1.23.2.1.4 Nb2O5 from Schuchardt Properties: Mixture of monoclinic and orthorhombic form [1674], >99.9% pure [1677], BET specific surface area 1.4 m2/g [1674,1677], mean particle diameter 1.2 μm [1674].

TABLE 3.685 PZC/IEP of Nb2O5 from Schuchardt Description Acid- and base-washed Acid- and base-washed a

Electrolyte

T

Method

Instrument

pH0

Reference

0.002 M NaClO4, KCl 0.01 M NaNO3

25

iep Electrolyte titrationa iep

ZetaPlus Brookhaven Acoustosizer

4.1

[1677]

4.3

[350,1674]

25

Also 15 and 35ºC.

3.1.23.2.2

Obtained by Calcination of Hydrate

3.1.23.2.2.1 From Nb2O5·4H2O from Niobium Products, Calcined for 6 h at 500°C Properties: BET specific surface area 55 m2/g [1723].

TABLE 3.686 PZC/IEP of Nb2O5 Obtained by Calcination of Nb2O5⋅4H2O from Niobium Products Electrolyte

T

Method

Instrument

pH0

Reference

a

[1723]

4 a

3.1.23.2.2.2 [830,831].

Only value reported, no data points.

From Nb2O5· xH2O, Calcined at 550°C Properties: Monoclinic

TABLE 3.687 PZC/IEP of Nb2O5 Obtained by Calcination of Nb2O5 ⋅ xH2O at 550°C Electrolyte 0.0005–0.05 M KNO3

T

Method

Instrument

pH0

Reference

iep

Rank Brothers

4

[830,831]

356

Surface Charging and Points of Zero Charge

3.1.23.2.3 Origin Unknown TABLE 3.688 PZC/IEP of Nb2O5 from Unidentified Sources Description

Electrolyte

Washed with hot water, 3.5 m2/g 3.9 m2/g

a

T

Method

Instrument

pH0

Reference

Electrophoresis

3.5 4 3.6

[1724]

0.01 M KCl

iep pH iep

0.4 M KCl

pH

0.001–0.1 M KCl

Electro-osmosis

7.6

[1102,1103]a [1217] [1684]

Only value reported, no data points.

3.1.24

NEODYMIUM (HYDR)OXIDES

Neodymium has only one stable oxidation state (+3) within the electrochemical window of water, but it forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. Nominal degree of hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of hydration. PZCs/IEPs of Neodymium (hydr)oxides are presented in Tables 3.689 through 3.691. 3.1.24.1 Nd2O3 3.1.24.1.1

Nd2O3 from Shin-etsu, 99.9% Pure

TABLE 3.689 PZC/IEP of Nd2O3 from Shin-etsu Electrolyte

T

KOH + HCl a

Method iep

Instrument a

Pen Kem 7000

pH0 a

8.4

Reference [1041]

Only value, data points not reported; the solid-to-liquid ratio (0.1% by volume) was below standard level used in electroacoustic measurements (Chapter 2).

3.1.24.1.2 Commercial Nd2O3 from Fluka >99.9%, Calcined at 800°C TABLE 3.690 PZC/IEP of Nd2O3 from Fluka >99.9%, Calcined at 800°C Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaCl

25

iep

Acoustosizer 2

>11 if any

[1725]

357

Compilation of PZCs/IEPs

3.1.24.2 Nd(OH)3, Origin Unknown

TABLE 3.691 PZC/IEP of Nd(OH)3 Electrolyte

T

Method iep

3.1.25

Instrument Electrophoresis

pH0

Reference

>11 if any

[1726]

NICKEL (HYDR)OXIDES

Nickel forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation (+2 to +3), degree of hydration, and crystallographic structure. Nominal degree of oxidation and hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of oxidation and hydration. PZCs/IEPs of nickel (hydr)oxides are presented in Tables 3.692 through 3.713. 3.1.25.1

NiO

3.1.25.1.1

Commercial

3.1.25.1.1.1 NiO from Aldrich 3.1.25.1.1.1.1 99.99%

TABLE 3.692 PZC/IEP of NiO from Aldrich, 99.99% Electrolyte 1 M KNO3 a b c

T

a

Method iep

Instrument Pen Kem 3000

pH0 b

<8.5

Reference [1727]c

Probably a typographic error. +10 mV at pH 5.9, −20 mV at pH 8.5. Results for two synthetic materials are also reported.

3.1.25.1.1.1.2 >99% area 8 m2/g [122].

Properties: Particle size 14.3 μm, specific surface

TABLE 3.693 PZC/IEP of NiO from Aldrich, >99% Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0+

3.5

[122]

358

Surface Charging and Points of Zero Charge

3.1.25.1.1.1.3

97–99%

TABLE 3.694 PZC/IEP of NiO from Aldrich, 97–99% Electrolyte

T

Method iep

a

Instrument Brookhaven ZetaPlus

pH0 7.8

a

Reference [1263]

Only value, data points not reported.

3.1.25.1.1.2 NiO from Baker and Adamson

TABLE 3.695 PZC/IEP of NiO from Baker and Adamson Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

10.3

[1088]a

Only value, data points not reported.

3.1.25.1.1.3 NiO from Fisher Properties: BET specific surface area 4.6 m2/g, structure: pure bunsenite (XRD) [1728].

TABLE 3.696 PZC/IEP of NiO from Fisher Electrolyte

T

Method

0.1 M NaClO4

25

pH

Instrument

3.1.25.1.1.4 NiO from Joung Dong diameter 300–600 nm [1729].

pH0

Reference

8.8

[1728]

Properties: SEM image available, particle

TABLE 3.697 PZC/IEP of NiO from Joung Dong Electrolyte

a

T

Method

Instrument

iep

Brookhaven ZetaPlus

Subjective interpolation.

pH0 Reference 8.2a

[1729]

359

Compilation of PZCs/IEPs

3.1.25.1.1.5 NiO from Sigma Aldrich 3.1.25.1.1.5.1 99.999% Pure

TABLE 3.698 PZC/IEP of NiO from Sigma Aldrich, 99.999% Pure Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaNO3

25

iep

Pen Kem 501

8.1

[467]

3.1.25.1.1.5.2 7 m2/g [1031].

Purity not Specified

Properties: BET specific surface area

TABLE 3.699 PZC/IEP of NiO from Sigma Aldrich Electrolyte KCl

T

Method

Instrument

pH0

Reference

iep

Malvern Nano ZS

7.5

[1031]

3.1.25.1.2 Synthetic 3.1.25.1.2.1 Calcination for 1 h at 400°C in Air Ni(NO3)2 solution in 2-propanol was dried at <100°C, and then calcined for 1 h at 400°C in air. Properties: BET specific surface area 11 m2/g [1236].

TABLE 3.700 PZC/IEP of NiO Obtained by Calcination for 1 h at 400°C in Air Electrolyte 0.005–0.3 M KNO3 a

T 25

Method cip

Instrument

pH0 a

9.5

Reference [1236]

Only value, data points not reported.

3.1.25.1.2.2 Calcination for 3 h at 400°C in Oxygen Evaporation of Ni(NO3)2 solution in 2-propanol, then calcination at 400°C for 3 h in a stream of oxygen. Properties: Cubic (XRD), BET specific surface area 11 m2/g [1237].

360

Surface Charging and Points of Zero Charge

TABLE 3.701 PZC/IEP of NiO Obtained by Calcination for 3 h at 400°C in Oxygen Electrolyte

T

Method

0.005–0.1 M KNO3 a

Instrument

cip

pH0 9.5

a

Reference [1237]

Only value, data points not reported.

3.1.25.1.2.3 Calcination for 30 min at 300°C in Air A solution 0.01 M in Ni(NO3)2 and 0.02 M in NH3 was aged for 2 h at 90°C, and then the particles were heated in an air flow of 20 cm3/min for 30 min at 300°C. Properties: XRD and IR spectra available, admixture of Ni2O3, TEM image available [1730].

TABLE 3.702 PZC/IEP of NiO Obtained by Calcination for 30 min at 300°C in Air Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

12.7

[1730]

0.01 M NaClO4

3.1.25.1.2.4 Calcination for 4 h at 600°C in Vacuum Gaseous ammonia was introduced into Ni(NO3)2 solution. The precipitate was water-washed and dried at room temperature. It was then heated at 600°C in vacuum for 4 h. Properties: BET specific surface area 4.6 m2/g [1282].

TABLE 3.703 PZC/IEP of NiO Obtained by Calcination for 4 h at 600°C in Vacuum Electrolyte

T

Method

0.1 M NaCl, NaClO4, NaNO3

25

pH

Instrument

pH0

Reference

7.3

[1282]

3.1.25.1.2.5 From Oxalate Oxalate was obtained from 1 M Ni(NO3)2 and a 10% excess of oxalic acid, washed with water, and calcined at 600°C in air for 6 h and at 600–1400°C for 6 h. The oxide was washed with water until constant conductivity. Not-crushed and crushed samples produce similar IEPs.

361

Compilation of PZCs/IEPs

TABLE 3.704 PZC/IEP of NiO Obtained from Oxalate Calcination Temperature (°C) 600 800 100 1200 1400 a

Electrolyte 0.001 M NaCl

T

Method

25

iep

a

Instrument

pH0

Reference

Streaming potential

10.5 10 9.8 9.2 8.8

[33]

Only value, data points not reported.

3.1.25.1.3 Origin Unknown Properties: Impurity level <0.1%, detailed analysis available, structure confirmed by XRD, BET specific surface area 14 m2/g [1233].

TABLE 3.705 PZC/IEP of NiO from Unknown Sources Description

Electrolyte

Water-washed, and dried at 110°C CP grade Washed

Washed

a b

0, 0.001 M KCl 0.001 M KCl 0, 0.001 M NaCl 0.001–1 M NaNO3 0.01 M KCl 0.001–0.01 M KNO3

T

Method

25

iep

25

25

iep iep pH iep cip iep

Instrument

pH0

Rank Mark II

6.4

Zeta-Meter Electro-osmosis Zeta-Meter

7.5 7.5 8.4 10.3 11.3 11.3

Reference [1213] [1455]a [1732] [1241]a [1103]a [1217] [1233]a,b

Only value, data points not reported. Also 80°C.

3.1.25.2

Ni(OH)2

3.1.25.2.1 Synthetic 3.1.25.2.1.1 From Nitrate and Gaseous Ammonia Gaseous ammonia was introduced into Ni(NO3)2 solution. The precipitate was water-washed and dried at room temperature. Properties: BET specific surface area 108 m2/g [1282].

362

Surface Charging and Points of Zero Charge

TABLE 3.706 PZC/IEP of Ni(OH)2 Obtained from Nitrate and Gaseous Ammonia Electrolyte

T

Method

0.1 M NaCl, NaClO4, NaNO3

25

pH

Instrument

pH0

Reference

8.7

[1282]

3.1.25.2.1.2 From Nitrate and Ammonia, Aged for 2 h at 90°C A solution 0.01 M in Ni(NO3)2 and 0.02 M in NH3 was aged for 2 h at 90°C. Properties: XRD and IR spectra available, TEM image available [1730]. TABLE 3.707 PZC/IEP of Ni(OH)2 Obtained from Nitrate and Ammonia, Aged for 2 h at 90°C Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

9.3

[1730]

0.01 M NaClO4

3.1.25.2.1.3 From Nitrate and Ammonia, Aged for 1 h at 80°C 50 cm3 of 0.04 M NH3 was added to 50 cm3 of 0.01 M Ni(NO3)2 and the mixture was heated at 80°C for 1 h with stirring. The precipitate was washed with acetone. Properties: Platelets, 6 nm thick, 63 nm in diameter, XRD spectrum and TEM image available for a different preparation (0.02 M NH3) [1733]. TABLE 3.708 PZC/IEP of Ni(OH)2 Obtained from Nitrate and Ammonia, Aged for 1 h at 80°C Electrolyte

T

Method

Instrument

pH0

Reference

HNO3 + (CH3)4NOH

25

iep

Malvern Zetasizer 4

9.2

[1733]

3.1.25.2.1.4

From Nitrate and NaOH

TABLE 3.709 PZC/IEP of Ni(OH)2 Obtained from Nitrate and NaOH Description

Electrolyte

T

Washed, structure determined by XRD 0.01 M KNO3 a

Only value, data points not reported.

25

Method

Instrument

pH0

Reference

iep

Electrophoresis 11.1

[1088]a

iep

Zeta-Meter

[391]

11.5

363

Compilation of PZCs/IEPs

3.1.25.2.1.5 From Sulfate 2 M KOH was added to 1 dm3 of 0.2 M NiSO4. The final pH was 12.6. The mixture was diluted to a final volume of 2 dm3, and stirred at 80°C for 7 d. Washed in 0.0001 M KOH and dried. Properties: Hexagonal platelets, 200–400 nm in diameter. b-Ni(OH)2, XRD and IR spectra available, specific surface area 77 m2/g [1734].

TABLE 3.710 PZC/IEP of Ni(OH)2 Obtained from Sulfate Electrolyte

T

Method cip iepa

0.002–0.13 M KNO3

a

Instrument

pH0

Reference

Rank Brothers

10.4

[1734]

Arbitrary interpolation.

3.1.25.2.1.6

From NiCl2 and NaOH

TABLE 3.711 PZC/IEP of Ni(OH)2 Obtained from NiCl2 and NaOH Electrolyte

T

0.01 M a

Method

Instrument

pH0

Reference

iepa

Electrophoresis

12

[1229]

Only value, data points not reported. In Ref. [2226] IEP at pH > 12 if any is reported.

3.1.25.2.1.7 From Chloride and Ammonia Ammonia was added to hot (80°C) NiCl2. The precipitate was aged for 2 h at 80°C and for 2 d at room temperature.

TABLE 3.712 PZC/IEP of Ni(OH)2 Obtained from Chloride and Ammonia Electrolyte 0.1 M NaCl

T

Method

Instrument

pH0

Reference

Mass titration

24 h equlibration

11.3

[1731]

3.1.25.2.2 Origin Unknown Properties: Impurity level <0.1%, detailed analysis available, structure confirmed by XRD, BET specific surface area 11 m2/g [1233].

364

Surface Charging and Points of Zero Charge

TABLE 3.713 PZC/IEP of Ni(OH)2 from Unknown Sources Description Washed

T

Method a

0.001–0.01 M KNO3 0.001 M KNO3 0.0175 M KNO3 0.02 M KNO3 0.05 M NaClO4

Amorphous Amorphous

a

Electrolyte

25

25 25 22

cip iep iep iep iep iep

Instrument

pH0

Zeta-Meter

Reference

11.2 11.1 >11 >11 if any >11 if any 11.8

Delsa 440 Delsa 440 Zeta-Meter Laser Zee Model 500

[1233] [1254] [1252] [947] [1735]

Also 40–80°C.

3.1.26

LEAD (HYDR)OXIDES

Lead forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation (+2 to +4), degree of hydration, and crystallographic structure. Nominal degree of oxidation and hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of oxidation and hydration. PZCs/IEPs of lead (hydr)oxides are presented in Tables 3.714 through 3.723. 3.1.26.1 PbO 3.1.26.1.1 3.1.26.1.1.1

Commercial PbO from Alfa Aesar, 99.9%

TABLE 3.714 PZC/IEP of PbO from Alfa Aesar Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern 3000 HS

10

[147]

3.1.26.1.1.2 PbO from Thye Ming Industrial (Taiwan) grain size 400 nm [123].

Properties: Average

TABLE 3.715 PZC/IEP of PbO from Thye Ming Industrial (Taiwan) Electrolyte

T

Method

40

pH

Instrument

pH0

Reference

10

[123]

365

Compilation of PZCs/IEPs

3.1.26.1.1.3 PbO from Ventron Properties: 99.9% pure, specific surface area 0.44 m2/g, particle size 2 μm, litharge–massicot [1736]. TABLE 3.716 PZC/IEP of PbO from Ventron Description

Electrolyte

As obtained

0.0001 M NaCl

T

Method

Instrument

pH0

Reference

iep Mass titration

Pen Kem S 3000

11.3 9.8

[1736]

3.1.26.1.1.4 Commercial, Origin Unknown Water-washed, and dried at 110°C. TABLE 3.717 PZC/IEP of PbO from Unknown Commercial Source Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M KCl

25

iep

Rank Mark II

10.7

[1213]

3.1.26.1.2 Origin Unknown TABLE 3.718 PZC/IEP of PbO from Unknown Source Electrolyte

T

Method iep

a

Instrument Electro-osmosis

pH0 11.6

Reference

a

[1103]

Only value, data points not reported.

3.1.26.2 Pb(OH)2 3.1.26.2.1 Precipitated from Pb(NO3)2 Solution with 0.01 M NaOH at 23°C, not Washed TABLE 3.719 PZC/IEP of Pb(OH)2 Precipitated from Pb(NO3)2 Solution with 0.01 M NaOH Electrolyte

T

0.001 M NaNO3 a

Arbitrary interpolation.

Method iepa

Instrument Delsa 440

pH0

Reference

11.1

[1220]

366

Surface Charging and Points of Zero Charge

3.1.26.2.2 From Pb(NO3)2 and NaOH

TABLE 3.720 PZC/IEP of Pb(OH)2 Precipitated from Pb(NO3)2 and NaOH Description

Electrolyte

T

Washed, aged Containing traces of basic carbonate (XRD)

Instrument

pH0

Reference

a

Electrophoresis

9.8 11.6

[1088]

iepa

Electrophoresis

11

[1229,2226]

iep

<0.01 M a

Method

Only value, data points not reported.

3.1.26.2.3

Freshly Precipitated

Table 3.721 PZC/IEP of Freshly Precipitated Pb(OH)2 Electrolyte 0.01 M KCl a

T

Method

25

iep iep

Instrument Zeta-Meter Brookhaven ZetaPlus

pH0

Reference

>11.5 11a

[475] [223]

Maximum in turbidity at pH 9.

3.1.26.3 PbO2 3.1.26.3.1 Recipe from [1737] Anodic deposition from Pb(NO3)2 on Ti. Properties: b-form, BET specific surface area 1 m2/g [1738].

TABLE 3.722 PZC/IEP of PbO2 Obtained According to Recipe from [1737] Electrolyte

T

Method

0.0001– 0.01 M KNO3

25

cip

Instrument

pH0

Reference

9.2

[1738]

367

Compilation of PZCs/IEPs

3.1.26.3.2 Origin Unknown

TABLE 3.723 PZC/IEP of PbO2 from Unknown Sources Description Water-washed, and dried at 110°C Electrodeposited a, washed b, washed Electrodeposited

a

Electrolyte

T

0, 0.001 M KCl 0.1, 1 M KCl 0.001–1 M NaNO3

25

iep

25

Intersection pH

0.01 M KCl 0.01 M KCl

Method

iep iep iep

Instrument

pH0

Reference

Rank Mark II

1.7

[1213]

7.3 7.3 5.4

[1739] [1241]a [1740]a

8.2 8.3 8.4

[1741] [1217] [1103]a

Electro-osmosis Electro-osmosis Electro-osmosis

Only value, data points not reported.

3.1.27

PdO

PZC/IEP of PdO from Aldrich is reported in Table 3.724.

TABLE 3.724 PZC/IEP of PdO from Aldrich Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

23

iep

Streaming potential

<2 if any

[261]

3.1.28 PRASEODYMIUM (HYDR)OXIDES Praseodymium forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation (+3 to +4), degree of hydration, and crystallographic structure. Nominal degree of oxidation and hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of oxidation and hydration. PZCs/IEPs of praseodymium oxides are presented in Tables 3.725 through 3.727. 3.1.28.1 Pr6O11 3.1.28.1.1 Commercial Origin unknown, water-washed, and dried at 110°C.

368

Surface Charging and Points of Zero Charge

TABLE 3.725 PZC/IEP of Commercial Pr6O11 Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M KCl

25

iep

Rank Mark II

<2 if any

[1213]

3.1.28.1.2 Synthetic Obtained by calcination of PrOHCO3 at 800°C for 1 min. Properties: XRD results, TEM image available, spherical particles, mean diameter 595 nm, BET specific surface area 3 m2/g [338]. TABLE 3.726 PZC/IEP of Synthetic Pr6O11 Electrolyte

T

0.01 M NaCl

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer

8.3

[338]

Method

Instrument

pH0

Reference

iep

Electro-osmosis

8

[1103]a [1217]

3.1.28.2 PrO2, Origin Unknown TABLE 3.727 PZC/IEP of PrO2 Electrolyte

T

0.01 M KCl

a

Only value, data points not reported.

3.1.29 PtO2 PZC/IEP of PtO2 obtained by thermal decomposition of Pt salt is reported in Table 3.728. TABLE 3.728 PZC/IEP of PtO2 Electrolyte

a

T

Method

Only value, data points not reported.

Instrument

pH0

Reference

5

[1742]a

369

Compilation of PZCs/IEPs

3.1.30 PuO2 PZCs/IEPs of PuO2 obtained by thermal decomposition of Pu salts are reported in Tables 3.729 and 3.730. 3.1.30.1

Thermal Decomposition of Sulfate at 850°C

TABLE 3.729 PZC/IEP of PuO2 Obtained by Thermal Decomposition of Sulfate Electrolyte

a

T

Method

Instrument

pH0

Reference

iepa

Electrophoresis

9

[1743]

Only value, data points not reported.

3.1.30.2 Thermal Decomposition of Oxalate at 500–900°C TABLE 3.730 PZC/IEP of PuO2 Obtained by Thermal Decomposition of Oxalate, Ground Electrolyte

T

Method a

iep a

Instrument

pH0

Reference

Electrophoresis

8.6–8.9

[1743]

Only value, data points not reported.

3.1.31

RUTHENIUM (HYDR)OXIDES

Ruthenium forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation, degree of hydration, and crystallographic structure. Nominal degree of oxidation and hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of oxidation and hydration. PZCs/IEPs of ruthenium oxides are presented in Tables 3.731 through 3.740. 3.1.31.1 3.1.31.1.1

RuO2 Commercial, from Ventron, the Insoluble Form

Table 3.731 PZC/IEP of RuO2 from Ventron Electrolyte

T

Method

0.005–0.15 M KNO3

25

cip

a

Only value, data points not reported.

Instrument

pH0 Reference 4.8

[1744]a

370

Surface Charging and Points of Zero Charge

3.1.31.1.2 Synthetic 3.1.31.1.2.1 Calcination of RuO2 · xH2O from Ventron at Different Temperatures Properties: Originally amorphous, crystallinity increases with temperature of calcination, TGA, DTA results available [1745]. Table 3.732 PZC/IEP of Products of Calcination of RuO2 ⋅ xH2O from Ventron Calcination°C 200 300 350 500 a

Electrolyte 0.001– 0.01 M KNO3

T 25

Method Instrument cip

a

pH0

Reference

5.1 5.2 5.5 5.6

[1745]

IEP < CIP (data not shown); only values, data points not reported.

3.1.31.1.2.2 Calcination of Products of Hydrolysis of Potassium Ruthenate Ru was heated with 3 parts of KNO3 and 8 parts of KOH at 600°C for 2 h and at 800°C for 2 h. The product was cooled, dissolved in water, and brought to pH 6.5 with HNO3. The precipitate was washed with water and hydrogen peroxide solution, dried at 100°C, and calcined. Properties: Originally amorphous, crystallinity increases with temperature of calcination, TGA, DTA results available [1745]. Table 3.733 PZC/IEP of RuO2 Obtained by Calcination of Products of Hydrolysis of Potassium Ruthenate Calcination Temperature (°C) 300 350 400 450 500 a

Electrolyte 0.001–0.01 M KNO3

T 25

Method a

cip

Instrument

pH0

Reference

3.8 4.8 5.2 5.5 5.6

[1745]

IEP < CIP (data not shown); only values, data points reported only for sample calcined at 400°C.

3.1.31.1.2.3 Thermal decomposition of RuCl3 · nH2O at Different Temperatures in a Stream of Oxygen Properties: Crystalline [1746–1748], BET specific surface area 18 m2/g (decomposition at 400°C), and 13 m2/g (decomposition at 700°C) [1744,1748], 21.5 m2/g (decomposition at 405–420°C) [1746,1747], particle size 30 nm (decomposition at 405–420°C) [1746,1747].

371

Compilation of PZCs/IEPs

TABLE 3.734 PZC/IEP of RuO2 Obtained by Thermal Decomposition of RuCl3 ⋅ nH2O in a Stream of Oxygen Decomposition Temperature (°C) Electrolyte 400 700

0.005–0.15 M KNO3

300 350 400 500 600 700

0.005–0.15 M KNO3, KCl

405–420

0.01–0.25 M KNO3

a b

T

Method

Instrument

pH0 Reference

cip

Titrations started at pH 4

5.1 6.1

[1748]

25

cip/iep

Rank Brothers Mark II

4 4.7 5.1/5 5.5 5.8 6.1/6

[1744]a [1749]b

20

cip iep

Rank Brothers Mark II or Malvern Zetasizer

5.8 5.5

[1746] [1747]

Only values, data points reported only for sample calcined at 400°C. CIP only.

3.1.31.1.2.4 Evaporation and Calcination of Acidified RuCl3 Solution RuCl3 was dissolved in 1 M HCl. The solution was gently heated to dryness and then heated for 1 h at 450°C. The precipitate was crushed, milled, and heated again (total calcination time 3 h). It was then water-washed. Properties: Rutile structure [1750]. TABLE 3.735 PZC/IEP of RuO2 Obtained by Evaporation and Calcination of Acidified RuCl3 Solution Electrolyte

T

0.005– 0.05 M KNO3 a

Method

25

Instrument

a

cip

pH0

Reference

5.3

[1750]

Only value, data points not reported.

3.1.31.1.2.5

Thermal Decomposition of Ru Salt

TABLE 3.736 PZC/IEP of RuO2 Obtained by Thermal Decomposition of Ru Salt Electrolyte

T

Method

Instrument

pH0 a

5.5 a

Only values, data points not reported.

Reference [1742]

372

Surface Charging and Points of Zero Charge

3.1.31.1.2.6

Chemical Vapor Transport

TABLE 3.737 PZC/IEP of RuO2 Obtained by Chemical Vapor Transport Electrolyte

T

Method

Instrument pH0 Reference

0.005– 0.15 M KNO3

25

cip

7.3

a

[1744]a

Only value, data points not reported.

3.1.31.1.3 Origin Unknown TABLE 3.738 PZC/IEP of RuO2 from Unknown Sources Description Washed

3.1.31.2

Electrolyte

T

0.001–1 M NaNO3 0.4 M KCl

25

Method Instrument pH pH

cip

pH0

Reference

4 3.9

[1241] [1684]

RuO2 · nH2O, Commercial

3.1.31.2.1 From Alfa Properties: SEM image available, BET surface area 0.6 m2/g, particle size 236 nm [1751]. TABLE 3.739 PZC/IEP of RuO2 ⋅ nH2O from Alfa Electrolyte

a

T

Method

Instrument

25

iepa

Rank Brothers

pH0 Reference 2.8

[1751]

Only value, data points not reported.

3.1.31.2.2 From Ventron TABLE 3.740 PZC/IEP of RuO2 ⋅ nH2O from Ventron Electrolyte 0.001–0.01 M KNO3 a b

T 25

Method iep cip

Only value, data points not reported. IEP < CIP (data not shown).

Instrument

pH0 a

3.2 4.2b

Reference [1752] [1745]

373

Compilation of PZCs/IEPs

3.1.32

Sb2O5

Sb2O5 shows substantial solubility in water and is beyond the scope of the present book. PZC/IEP of Sb2O5 from an unknown source is presented in Table 3.741. TABLE 3.741 PZC/IEP of Sb2O5 Electrolyte

T

Method

Instrument

iepa a b

3.1.33

Electro-osmosis

pH0

Reference

<0.4

[1214]

Only value, data points not reported. IEP at pH 5.6 is reported in Ref. [2226] for a precipitate termed Sb hydroxide.

Sc2O3

PZCs/IEP of Sc2O3 from unknown source (specific surface area 8.9 m2/g) is presented in Table 3.742. TABLE 3.742 PZC/IEP of Sc2O3 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electro-osmosis

7.2

[1102,1103]a, [1217]

0.01 M KCl a

Only values, data points not reported.

3.1.34 SAMARIUM (HYDR)OXIDES Samarium has only one stable oxidation state (+3) within the electrochemical window of water, but it forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. These compounds absorb atmospheric CO2. Nominal degree of hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of hydration. PZCs/IEPs of Sm2O3 (nominally) are presented in Tables 3.743 and 3.744. 3.1.34.1

Sm2O3 from Shin-etsu, 99.9% Pure TABLE 3.743 PZC/IEP of Sm2O3 from Shin-etsu Electrolyte KOH + HCl a

T

Method iep

Instrument Pen Kem 7000

pH0 Reference a

8.3

[1041]

Solid-to-liquid ratio (0.1% by volume) was below standard level used in electroacoustic measurements (Chapter 2).

374

Surface Charging and Points of Zero Charge

3.1.34.2 Sm2O3, Origin Unknown Properties: Monoclinic, 7.5% CO2 [1753]. TABLE 3.744 PZC/IEP of Sm2O3 from Unknown Source Electrolyte

T

0.01–1 M NaCl/KNO3 a

3.1.35

Method

Instrument

a

25

cip

pH0

Reference

7.5/7.8

[1753]

Only value, data points not reported.

SILICA

Silicon has only one stable oxidation state (+4) within the electrochemical window of water, but it forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. PZCs/IEPs of silicas (one section for different actual or nominal degrees of hydration) are presented in Tables 3.745 through 3.914. Several silica-rich materials are discussed in Section 3.5 as glasses. PZCs of silicas are compiled in [544,778,1754]. Reference [544] also reports surface charging curves and acidity constants of various silicas. 3.1.35.1 Commercial 3.1.35.1.1 Aerosil See also Sections 3.1.35.1.5 and 3.1.35.1.20. TABLE 3.745 PZC/IEP of Aerosil Electrolyte

T

Method

pH0 Reference 3a

pH

KNO3 a

Instrument

[1755]

Only value, data points not reported.

3.1.35.1.2 Aerosil A-175 Properties: BET specific surface area 172 m2/g [1117], specific surface area 172 m2/g [1204], primary particle size 8 nm [1117]. TABLE 3.746 PZC/IEP of Aerosil A-175 Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaCl 0.01 M NaCl

20

iep iep

Electrophoresis Malvern Zetasizer 4

<3 if any 3

[1204] [1117]

375

Compilation of PZCs/IEPs

3.1.35.1.3 Precipitated Silica from Ajax Properties: BET specific surface area 117 m2/g [990]. TABLE 3.747 PZC/IEP of Precipitated Silica from Ajax Description

Electrolyte

HNO3-washed

a

T

Method

Instrument

pH0

Reference

pH iepa

Rank Brothers Mark II

<5 if any <4 if any

[990]

0.001 M HNO3 25

Data points not reported.

3.1.35.1.4 Silicas from Aldrich See also Section 3.1.35.1.64. 3.1.35.1.4.1 TLC High-Purity Grade without Binder surface area 325 m2/g [988].

Properties: BET specific

TABLE 3.748 PZC/IEP of TLC High Purity Grade Silica without Binder from Aldrich Electrolyte

T

Method

0.05 M NaNO3

20

pHa

a

Instrument

pH0

Reference

<3.5 if any

[988]

Data points not reported.

3.1.35.1.4.2

Quartz

Properties: Particle size 210–297 mm, 99% pure [1756].

TABLE 3.749 PZC/IEP of Quartz from Aldrich Description

Electrolyte

T

Method

Instrument

pH0

Reference

Base- and acid-washed

Inert

25

iep

ZetaPlus Brookhaven

<3 if any

[1756]

3.1.35.1.4.3 Davisil Properties: >99% pure, specific surface area 300 m2/g (manufacturer), 266 m2/g (measured) [287]. TABLE 3.750 PZC/IEP of Davisil from Aldrich Electrolyte 0.001 M KCl

a

T 25

Method pH iep

Instrument EKA, Anton Paar

Based on arbitrary interpolation.

pH0

Reference

a

[287]

3 3.5

376

Surface Charging and Points of Zero Charge

3.1.35.1.4.4 Ludox TM 50 [1757,1758].

Properties: Specific surface area 125 m2/g

TABLE 3.751 PZC/IEP of Ludox TM 50 from Aldrich Electrolyte

T

0.02, 0.1 M NaCl

Method

Instrument

pH

pH0

Reference

<3 if any

[1757,1759,1760]

3.1.35.1.4.5 Other Properties: Amorphous [856], fumed [366], specific surface area 69 m2/g [856], 261.7 m2/g [366] particle size 720 nm [1222]. TABLE 3.752 PZC/IEP of Other Silicas from Aldrich Description

Electrolyte

As received

0.001 M NaCl 0.01 M NaNO3 0.001–0.1 M NaCl (or NaClO4)

a

T

Method

24 25

iep iep pH iep

Instrument

pH0

Pen Kem 3000 <2 if any Pen Kem Zee Meter 501 <2 if any Malvern Zetasizer 3000 <3 if any

Reference [856] [1222] [366]a

Extrapolated PZC and IEP are reported in Ref. [1566].

3.1.35.1.5 Silica from Alfa Properties: Amorphous, fumed, specific surface area 175–200 m2/g [658], 200 m2/g [674]. TABLE 3.753 PZC/IEP of Silica from Alfa Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M KNO3

25

cip iep

Malvern Zetasizer 5000

3.1 3

[657,658,674]a

a

Results of mass titration and inflection point are also reported. Only PZC and IEP (no data points) in Ref. [674]; only IEP in Ref. [657].

Properties of Aerosil from Alfa: BET specific surface area 327 m2/g [839]. 3.1.35.1.6 Quartz from Alfa Aesar Properties: 99.5% pure [833], 99.995% pure [602], BET specific surface area 0.08 m2/g [602], 5.1 m2/g [833], average particle size 700 nm [833], XRD pattern available [602].

377

Compilation of PZCs/IEPs

TABLE 3.754 PZC/IEP of Quartz from Alfa Aesar Electrolyte

T

Method

HNO3 + KOH

iep

0.001–0.1 M NaNO3

cip

a

Instrument

pH0

Reference

2.3

[833]

2.8

[602]a

Matec ESA

Results reported in [602] refer to quartz from Alfa Aesar or from US Silica Company.

Properties of another silica from Alfa Aesar: BET specific surface area 225 m2/g [780]. 3.1.35.1.7 Stober silica from Allied Signal Properties: Specific surface area 0.7 m2/g [1761], size 4–6 mm [1761,1762], diameter 4–5 μm [463]. TABLE 3.755 PZC/IEP of Stober Silica from Allied Signal Description

Electrolyte

Soxhlet-washed for 3 d a

0.0001, 0.001 M NaNO3, KNO3

T

Method

25

iep

Instrument Rank Brothers Mark II

pH0

Confirmed by AFM results.

3.1.35.1.8

Quartz from Alminrock Indscer TABLE 3.756 PZC/IEP of Quartz from Alminrock Indscer Electrolyte

T

Method

0.001 M NaNO3

25

iep

Instrument Zeta-Meter 3.0

pH0

Reference

<3 if any

[348]

3.1.35.1.9 Chromatographic-Grade Silica from Baker Properties: BET specific surface area 257 m2/g [1763]. TABLE 3.757 PZC/IEP of Silica from Baker Electrolyte

T

Method

0.1 M NaCl

25

pH

Instrument

Reference

<3 if anya [463,1761]

pH0

Reference

<6 if any

[1763]

378

Surface Charging and Points of Zero Charge

3.1.35.1.10

Silica Spheres from Bang Laboratory

TABLE 3.758 PZC/IEP of Silica Spheres from Bang Laboratory Description

Fresh Aged

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl 22

iep

<3 if any

[1764]

None

iep

Zetaphoremeter III from Sephy Brookhaven ZetaPlus

<3 if any <5 if any

[1765]

3.1.35.1.11 Precipitated Silica from BDH Properties: BET specific surface area 56 m2/g [127], 62 m2/g [1767], specific surface area 149 m2/g [186,1766], median particle diameter 15.6 μm, detailed chemical analysis available [186]. TABLE 3.759 PZC/IEP of Precipitated Silica from BDH Description

Electrolyte

T

Method

Instrument

pH0

Reference

As obtained

0.001–1 M LiCl, KCl, CsCl, (C2H5)4NCl

25

iep pH

Streaming potential

[127]

0.01 M KNO3

25

pH

<2.3 if any 3 2.8–2.9a

a

Only value, data points not reported.

3.1.35.1.12

Quartz from Bottley, Optical Grade

TABLE 3.760 PZC/IEP of Quartz from Bottley Electrolyte

T

Method

Instrument

pH0

Reference

iep

Rank Brothers Mark II

<3 if any

[1768]

0.001 M KCl

3.1.35.1.13

Pure Quartz from Bremthaler Quarzitwerke

TABLE 3.761 PZC/IEP of Pure Quartz from Bremthaler Quarzitwerke Electrolyte NaOH + HClO4

T

Method iep

Instrument

pH0

Reference

Zeta-Meter

1.5

[104]

[186]

379

Compilation of PZCs/IEPs

3.1.35.1.14 Silicas from Cabot, Cabosils 3.1.35.1.14.1 Cab-O-Sil L-90 Properties: BET specific surface area 100 m2/g [14,668], particle size 27 nm [668].

TABLE 3.762 PZC/IEP of Cab-O-Sil L-90 Electrolyte

T

0.001–0.1 M NaCl 0.1 M NaNO3

Method

Instrument

pH0

Reference

pH Mass titration Mass titration

1 d equilibration

2–3.7 3.2 3.4

[668] [14]

3.1.35.1.14.2 Cab-O-Sil M-5 Properties: Amorphous [1769], BET specific surface area 179.4 m2/g [1770], 200 m2/g [1769,1771] 190 or 200 m2/g [717], median size 41.5 nm [1770], diameter of primary particle 15–25 nm [1769], TEM image available [717,1769].

TABLE 3.763 PZC/IEP of Cab-O-Sil M-5 Electrolyte

T

Method

0.1 M KNO3

25

Instrument

pH0

Reference

iep

Malvern Zetasizer 2000

<2 if any

[1771]

0.04 M KNO3

iep

Electrophoresis

[717]

0–0.5 M KNO3

iep iep

Malvern Zetasizer 2000 Brookhaven ZetaPlus

<2 if any Nonea 2.8

a

[1769] [1770]

z = 0 at pH 2–3, but no positive values.

3.1.35.1.14.3 Cab-O-Sil M-7 Properties: Impurities: Ca, Zn, Zr <25 ppm, Ni, Sn, Pb, Ti, Cr < 10 ppm, Cu, Mg, Mn, Mo < 5 ppm (original and after 1 d treatment with 6 M HCl at 90–95°C), Fe < 5 ppm (original) and 2–20 ppm (HClwashed), Al < 10 ppm (original) and 3–30 ppm (HCl-washed), Ar BET specific surface area 170 m 2/g (original), and 166 m 2/g (HCl washed) [1772].

TABLE 3.764 PZC/IEP of Cab-O-Sil M-7 Description

Electrolyte

T

Method

Original HCl-washed

0.01–1 M LiCl, KCl, CsCl

20

pH

Instrument

pH0

Reference

<2 if any <4 if any

[1772]

380

Surface Charging and Points of Zero Charge

3.1.35.1.14.4 Cab-O-Sil EH-5 Properties: BET specific surface area 380 m2/g [14], 332 m2/g [1773].

TABLE 3.765 PZC/IEP of Cab-O-Sil EH-5 Electrolyte

T

0.1 M NaNO3

Method

Instrument

Mass titration

pH0

Reference

3

[14]

3.1.35.1.14.5 Silica from Cabot/Cabosil (Type Not Specified) Properties: BET specific surface area (manufacturer): 200 m2/g [108,851,858,877], 300 m2/g [915], particle diameter 50 nm [851], 14 nm (data provided by manufacturer) [108].

TABLE 3.766 PZC/IEP of Cabosils/Silicas from Cabot (Type Not Specified) Electrolyte

T

Method iepa iepa

a

Instrument

pH0

Reference

<2 2

[858] [108,877]

Laser Zee Meter 500 Electrophoresis

Only value, data points not reported.

3.1.35.1.15 Fumed Silica from Chlorovinyl Another series of samples studied by the same research group is described in Section 3.1.35.1.36. Properties: 99.5% pure [1774], 99.9% pure [1775], BET specific surface area 300 m2/g [836], 270 m2/g, [1774,1775], size distribution available [1774], IR spectrum available [836]. TABLE 3.767 PZC/IEP of Fumed Silica from Chlorovinyl Electrolyte HCl + NaOH 0, 0.02 M NaCl

T

Method

Instrument

pH0

Reference

iep

ZetaPlus Brookhaven

2.2

[836,837,1775]

iep

ZetaPlus Brookhaven

2.2

[1774]

3.1.35.1.16 Chromosorb W Properties: BET specific surface area 400 m2/g [1111].

381

Compilation of PZCs/IEPs

TABLE 3.768 PZC/IEP of Chromosorb W Electrolyte

T

Method

Instrument

pH0

Titration a

2.3

Reference

a

[1111]

Only value, data points not reported.

3.1.35.1.17 Klebosols from Clariant 3.1.35.1.17.1 Klebosol 30N50 Properties: BET specific surface area 56 m2/g, particle diameter 56 or 68 nm (different methods) [1776]. TABLE 3.769 PZC/IEP of Klebosol 30N50 from Clariant Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

20

iep

Malvern Zetasizer 3

<3.5 if any

[1776]

3.1.35.1.17.2 Klebosol 150H50 Properties: BET specific surface area 51 m2/g, 36 m2/g from TEM, particle radius 36–39 nm (different methods), TEM and SEM images available [708]. TABLE 3.770 PZC/IEP of Klebosol 150H50 from Clariant Description

Electrolyte

T

Method

Instrument

pH0

Reference

Washed with 0.1 M HCl

0.003–1 M KCl

25

iep pH

Malvern Zetasizer 2000

<3.5 if any

[708]

3.1.35.1.17.3 Klebosol 1508-35 Properties: BET specific surface area 77 m2/g, 57 m2/g from TEM, particle radius 23–25 nm (different methods), TEM and SEM images available [708]. TABLE 3.771 PZC/IEP of Klebosol 1508-35 from Clariant Description Washed with 0.1 M HCl, dialyzed

Electrolyte

T

Method

Instrument

pH0

Reference

0.003–1 M KCl

25

iep pH

Malvern Zetasizer 2000

<3.5 if any

[708]

382

Surface Charging and Points of Zero Charge

3.1.35.1.17.4 Klebosol 20H12 Properties: BET specific surface area 228 m2/g, 104 m2/g from TEM, particle radius 10–13 nm (different methods), TEM and SEM images available [708]. TABLE 3.772 PZC/IEP of Klebosol 20H12 from Clariant Description Washed with 0.1 M HCl, dialyzed

Electrolyte

T

Method

Instrument

pH0

Reference

0.003–1 M KCl

25

iep pH

Malvern Zetasizer 2000

<3.5 if any

[708]

3.1.35.1.18 Silicas from Crosfield Three samples. Properties: Specific surface area, median particle diameter (see Table 3.773). Detailed chemical analysis, particle size distribution, and pore volumes and diameters available [186].

TABLE 3.773 PZC/IEP of Silicas from Crosfield Description

Electrolyte

2

450 m /g, 132 μm 300–350 m2/g, 3.8 μm 450 m2/g, 9.1 μm a

0.01 M KNO3

T 25

Method

Instrument

a

pH

pH0

Reference

2.8–2.9

[186]

Only value, data points not reported.

Properties of Gasil I from Crosfield: BET specific surface area 286 m2/g, average pore diameter 7 nm [1767]. Properties of Gasil 200 from Crosfield: BET specific surface area 750 m2/g, microporous [1767]. 3.1.35.1.19 Silica from Custer Properties: 99% pure, specific surface area 5.4 m2/g [955].

TABLE 3.774 PZC/IEP of Silica from Custer Electrolyte

T

Method a

iep a

Only value, data points not reported.

Instrument

pH0

Reference

Zeta-Meter

2

[955]

383

Compilation of PZCs/IEPs

3.1.35.1.20

Silicas from Degussa

3.1.35.1.20.1 Aerosil OX50 Obtained from SiCl4 at high temperature [363,611]. Properties: BET specific surface area 50 m2/g [163,363,491,540,611,850,1777], 43.6 m2/g (acid-washed) [1778], 43.1 m2/g [511], 42.5 m2/g [1118] (Ar BET), 48.2 m2/g [1779], a few particles <10 nm in radius, and broad distribution between 40 and 70 nm [511], mean particle size 400 nm [1779], average particle size 60 nm [1777], mean particle size 40 nm [611], particle diameter 40 nm [363]. TABLE 3.775 PZC/IEP of Aerosil OX50 from Degussa Description

Electrolyte

Original Heated at 800°C for 16 h Calcined for 2 h at 600°C in air

Dried at 147°C for 2 h

T

b

Instrument

HCl + NH3

iep

ESA 8000

0.01 M NaCl

iep pH iep pH pH

Electrophoresis

0.01 M NaCl 0.001–1 M NaCl 0.01 M KNO3, 20 LiNO3, Bu4NNO3, Me4NNO3 20 0.01 M KNO3

Reference

<2 if any, 3 [491] (hysteresis) <3 if any [1118] <4 if any <3.5 if any [540] [363]

pH

<4 if any

[163]

pH

<4 if any

[1780]

25

pH

<4 if any

[611,1777]

<4 if any <2.5 if any <4 if any 2.3a 2.6b

[1781]

25

pH iep pH iep iep

0.001–0.1 M NaCl 0.001–0.1 M KCl, KBr 0.0001–0.01 M LiCl, KCl, RbCl 0.001–0.1 M NaCl

Electrophoresis

pH0

<3.5 if any

None a

Method

Mass transport Electrophoresis Matec ESA 8000 ESA 8000

[511] [850]

In 0.001 M NaCl; IEP shifts to higher pH at higher NaCl concentrations. Apparent shift in the IEP to high pH induced by KCl was probably due to the electroacoustic signal of the electrolyte.

3.1.35.1.20.2 Aerosil 90 from Degussa Properties: Median size 71.6 nm, BET specific surface area 77.6 m2/g [1770]. TABLE 3.776 PZC/IEP of Aerosil 90 from Degussa Electrolyte

T

Method

Instrument

iep

Brookhaven ZetaPlus

pH0 Reference 2.8

[1770]

384

Surface Charging and Points of Zero Charge

3.1.35.1.20.3 Aerosil 200 Prepared by calcination of SiCl4 [1463]. Properties: Amorphous [1782,1783], >99.5% pure [790], BET specific surface area 169.3 m2/g [1783] 200 m2/g [1075,1338,1463,1789], quoted after [128] (cf. Section 3.1.35.1.20.4), 189 m2/g [603], 200 m2/g (manufacturer) [857,882], 208 m2/g [1788], 210.5 m2/g (washed with concentrated HNO3) [1782], 218.9 m2/g (original) [1782], specific surface area 160 m2/g [1786], 169 m2/g [1784], 200 m2/g [41,790], 182 m2/g [1785], primary particles 12 nm in diameter, “bunch of grapes”shaped aggregates 80–200 nm in size [1789], particle size 12 nm [790], average particle size 12 nm [603,1463]. TABLE 3.777 PZC/IEP of Aerosil 200 from Degussa Electrolyte

T

None 0.7 M NaCl 0.001–0.1 M KNO3 HCl + KOH 0.001–0.1 M NaCl

20 iep 22 pH pH iep 25 pH iep iep 25 iep

0.01 M KNO3, KBr 0.001 M KNO3, KBr 0.001, 0.01 M KBr 0.1 M NaCl 0.01 M KNO3 0.005–0.1 M KNO3

a b c

Method

Instrument Malvern Zetasizer III

Rank Mark II Moving boundary

Malvern Zetasizer III

pH 25 Mass titration 23 pH Otsuka ELS-800 iep 25 pHc Mass titration

pH0

Reference

<2 if any <4 if any <4.5 if any 1.9 2.5–3a <1 if any 2.9b 3.3 <3 if any <3 if any 3.7 3.5 <3 if any 4.4

[1787] [1788] Missing reference [1075] [603] [882] [41]

[847] [1790] [1338]

Substantial positive s0, but no CIP. Only value reported, no data points. The data points in Figure 3 do not support the value taken from Figure 2.

3.1.35.1.20.4 Aerosil OX-200 area 169.3 m2/g [128].

Properties: Amorphous, BET specific surface

TABLE 3.778 PZC/IEP of Aerosil OX-200 from Degussa Electrolyte

T

0.05, 0.1 M NaClO4 25

Method Instrument pH

pH0

Reference

<5 if any

[128]

385

Compilation of PZCs/IEPs

3.1.35.1.20.5 Aerosil 130 Properties: BET specific surface area 130 m2/g [1791], specific surface area 130 m2/g [847], particle diameter 20 nm [1791]. TABLE 3.779 PZC/IEP of Aerosil 130 from Degussa Electrolyte

T

Method

Instrument

0.01–1 M NaCl

25

Mass titration

pH0 3.5

Reference [847]

3.1.35.1.20.6 Aerosil 300 (A-300) Properties: BET specific surface area 266 m2/g [591], specific surface area 300 m2/g [554,847,1792]. TABLE 3.780 PZC/IEP of Aerosil 300 (A-300) from Degussa Electrolyte Outgased at 400°C Calcined for 2 h at 600°C in air

T

Method

0.005–0.3 M LiCl, NaCl, KCl, RbCl, CsCl 0.001–0.1 M NaCl

Instrument

pH0

Reference

pH

<4 if any

[591]

pH

<4 if any

[1780]

0.1 M NaCl

20

pH

<4 if any

[1792]

0.01–0.1 M NaCl

25

pH

[554]

0.1 M NaCl

25

Mass titration

<4.5 if any 3.6

[847]

3.1.35.1.20.7 Aerosil 380 (AE 380) from Degussa Properties: Amorphous [561,1793], single-point BET specific surface area 326 m2/g [561], 331 m2/g [1795], specific surface area 380 m2/g [847,909,910,1794], 414 m2/g [1793], spheres 15 nm in diameter, agglomerates 150–300 nm [1793], aggregates of 7 nm spheres [1794], nonporous [561]. TABLE 3.781 PZC/IEP of Aerosil 380 from Degussa Description

Electrolyte

T

0.067, 0.2 M 25 LiCl, NaCl, KCl 0.01–1 M NaCl 25 0.001–0.1 M 25 NaClO4

Method

Instrument

pH pH pH iep

Zetaphorometer III

pH0

Reference

<3 if any

[561]

<3 if any <3.5 if anya

[1794] [1793]

continued

386

Surface Charging and Points of Zero Charge

TABLE 3.781 (continued) Description

Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaCl 1 M LiCl, NaCl, KCl, CsCl 0.01 M NaCl, NaNO3

25 pH

<4 if any [376]

25 pH

<4 if any [1795]

Dried at 110°C 0.01–2.6 M HCl, for 10 h HNO3 Calcined for 2 h at 800°C 0–1 M KCl 0–1 M KCl

pH

0.1 M NaCl 0.01, 0.1 M NaCl

a b c

25 iep

Pen Kem 501 2 [376,1796] Malvern 3000 <2 if any Delsa 440 4 Acoustosizer 4 DT 1200 4 Malvern 2 3b 10 min equilibration ~3 [1797] ~3

cip Intersection EMF 25 Mass titration iep Zetaphorometer II Sephy

3c 3c 4.5 3.5

[909] [875]

3.8

[1798]

[847]

Random mixture of slightly positive and slightly negative z potentials at pH 3.5–4.8. Arbitrary interpolation. According to text. It appears from the graph that at pH 3–4, s0 = 0 for all ionic strengths studied.

3.1.35.1.20.8 TK 900 Properties: Detailed chemical analysis available [186], specific surface area 112 m2/g [186,1766], median particle diameter 4.4 μm [186]. TABLE 3.782 PZC/IEP of TK 900 from Degussa Electrolyte 0.01 M KNO3 a

T 25

Method

Instrument

pH

pH0

Reference a

2.8–2.9

[186]

Only value, data points not reported.

Properties of TK 800 from Degussa: BET specific surface area 165.8 m2/g [1767].

387

Compilation of PZCs/IEPs

3.1.35.1.21 Silica from Duke Properities: Particle size 3 μm, specific surface area 1 m2/g [413]. TABLE 3.783 PZC/IEP of Silica from Duke Electrolyte

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

>2.5a

[413]

0.001–0.01 M NaCl a

+10 mV at pH 2.5, -50 mV at pH 5.

3.1.35.1.22 Silicas from Dupont 3.1.35.1.22.1 Ludox AM 30 mass% dispersion. Properties: Contains Al2O3 [1799] (0.2% by mass), [1800] as a coating, amorphous [1800], BET specific surface area 190 m2/g [1800], 230 m2/g [1770], median size 12 nm [1770], spherical particles [1800]. TABLE 3.784 PZC/IEP of Ludox AM from Dupont Electrolyte 0.001 M KCl

T

Method

Instrument

iep

Brookhaven ZetaPlus

pH0

Reference

20

iep

25

iep

Malvern Zetasizer II c <2.5 if any Electrophoresis <1 if any

<2 if any

[1770] [1799] [1801]

3.1.35.1.22.2 Ludox AS 40 from Dupont Properties: specific surface area 96 m2/g (manufacturer) [847].

TABLE 3.785 PZC/IEP of Ludox AS 40 from Dupont Electrolyte

T

Method

0.1 M NaCl

25

Mass titration

Instrument

pH0

Reference

7.7

[847]

Properties of Ludox AS from Dupont: BET specific surface area 109 m2/g [1307]. 3.1.35.1.22.3 Ludox HS 40 (or HS 30 or HS) 30 mass% dispersion. Properties: Does not contain alumina [1799,1800], amorphous [1800], BET specific surface area 200 m2/g [740,1800], spherical [1800].

388

Surface Charging and Points of Zero Charge

TABLE 3.786 PZC/IEP of Ludox HS 40 (or HS 30 or HS) from Dupont Description

Electrolyte

HS 40, dialyzed

0.0003–0.03 M KCla 0.001 M KCl

HS

0.3 M CsCl

T

Method

Instrument

iep

Home-made apparatus

<2 if any

iep

Malvern Zetasizer II c

<2.5 if any

[1799]

<3.5 if any 2.3

[1800]

20

pH

HS 30 a

pH0

iep

Delsa 44, Coulter

Reference [266]

[1802]

In 0.08 M KCl IEP at pH ª 5.

3.1.35.1.22.4 Ludox SM 30 mass% dispersion. Properties: Specific surface area 360 m2/g, average diameter 7 nm [1803]. TABLE 3.787 PZC/IEP of Ludox SM from Dupont Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaNO3

25

iep

Malvern Zetasizer 4

< 3.5 if any

[1803]

3.1.35.1.22.5 Ludox (Other Types) See also Section 3.3.35.1.41 and 3.1.35.1.64.1. Properties: Amorphous, BET specific surface area 61.5 m2/g (acid-washed), 131.2 m2/g (base- and acid-washed) [1782], 105 m2/g [1192], 20 nm in diameter [299]. TABLE 3.788 PZC/IEP of Other Ludox Silicas from Dupont Type Description TM

Base- and acid-washed

Electrolyte

T

Method

0.01 M LiCl, NaCl, KCl 0.001 M KCl

25

pH

< 6 if any

20

iep

Milton Roy, Pryde; < 4 if any streaming potential 2.9a Rank Brothers Mark II Electrophoresis < 3 if any

iepa a

Instrument

pH0

Reference [1782] [299]

[1192]

Only value, data points not reported.

Note: Ludox CL contains 4 mass% alumina (as coating) and 26 mass% silica [1799], and is discussed in Section 3.8.1.1.1.2.

389

Compilation of PZCs/IEPs

3.1.35.1.23

Chemical–Mechanical Polishing Slurry from EEC

TABLE 3.789 PZC/IEP of Chemical Mechanical Polishing Slurry from EEC Electrolyte

T

Method iep

3.1.35.1.24

Instrument DT-1200

pH0

Reference

< 2 if any

[1804]

Silicas from EKA Nobel or EKA Chemicals

3.1.35.1.24.1 Kromasil from EKA Nobel Properties: Fe 28 ppm, Ni 6 ppm, Mg 2 ppm, Al 28 ppm [1805],specific surface area 319 m 2/g [1806], particle diameter 5 μm [1805], particle size 3.5 μm [1806], pore diameter 10–15 nm [1805].

TABLE 3.790 PZC/IEP of Kromasil from EKA Nobel Description

Electrolyte

Kromasil 100

T

Method

Instrument

pH0

Reference

23

iep

Zeta-Meter 3.0 Electro-osmosis Malvern Zeta Master S

<3.5 if any

[1806]

Batch AT 0070 0.001 M NaCl

iep

2.9

[1805]

3.1.35.1.24.2 Other Silicas from EKA Nobel Five specimens washed by ultrafiltration using salt solutions.

TABLE 3.791 PZC/IEP of Other Silicas from EKA Nobel Specific Surface Area (m2/g) 495a 490a 500a 520 890 a

Electrolyte 0.002–0.05 M NaCl

Data points not reported.

T

Method

Instrument

pH0

Reference

iep pH

ESA 8000 Matec

<3 if any

[1807]

390

Surface Charging and Points of Zero Charge

3.1.35.1.24.3 Silicas from EKA Chemicals TABLE 3.792 PZC/IEP and Properties of Silicas from EKA Chemicals Type, Particle Size (nm), Specific Surface Area (m2/g) Bindzil 15/500, 6,500 Bindzil 30b/600, 9,360 Nyacol 830b, 10, — Bindzil 40/220, 15, 220 Nyacol 2034DIb, 20, — Bindzil 50b/80, 40, 80 a b

Electrolyte

T

0.01 M NaCl

Method iep

Instrument Zeta Probe Colloidal Dynamics

pH0

Reference

4 4 <1.5 1 <1.5 <1.5

[1808]a

Other types of silica containing Al or organic stabilizer were also studied. Data points not reported.

Properties of seven types of silicas from EKA Chemicals: size 3.5, 5.5, 12, 25, 34 and 101 nm, TEM images available [1809]. 3.1.35.1.25 NCQ 325 Quartz from Ernstrom Mineral Properties: Mean diameter 2 μm. TABLE 3.793 PZC/IEP of NCQ 325 Quartz from Ernstrom Description Acid-washed

Electrolyte 0.0005 M NaCl

T

Method

Instrument

pH0

Reference

25

iep

Malvern Zetasizer MK 4

< 1 if any

[1270]

3.1.35.1.26 Eurospher from Eurochrom Properties: Fe 20 ppm, Ni 6 ppm, Mg 3 ppm, Al 28 ppm, particle diameter 5 μm, pore diameter 10–15 nm [1805]. TABLE 3.794 PZC/IEP of Eurospher from Eurochrom Electrolyte 0.001 M NaCl

T

Method

Instrument

pH0

Reference

iep

Malvern Zeta Master S

< 1.8 if any

[1805]

3.1.35.1.27 Silica Gel from Fluka Properties: BET specific surface area 550 m2/g [1810], 470 m2/g [1811].

391

Compilation of PZCs/IEPs

TABLE 3.795 PZC/IEP of Silica Gel from Fluka Electrolyte

T

Method iep

a

Instrument Malvern Zetasizer

pH0 2.9

Reference

a

[1811]

Only value, data points not reported.

3.1.35.1.28 CARiACT Q 50 from Fuji Properties: Specific surface area 94 m2/g, pore diameter 48 nm [1812]. TABLE 3.796 PZC/IEP of CARiACT Q 50 from Fuji Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaCl

25

iep

ELS 8000 Otsuka

<2 if any

[1812]

3.1.35.1.29 Silica(s) from Geltech Properties: Amorphous [1813], purity >99.9% [1813], (two samples) 99.9% pure [1814], (four samples) >99.9% pure [1815], specific surface area 14.6 and 3.3 m2/g (2 samples) [1814], 5.4 m2/g [540,610,1117], 5.8 m2/g [547], average diameter 560 nm [610], 500 nm [1117], diameter 560 nm [540,1816], nominal size 0.2, 0.5, 1, and 1.5 μm, mean size (SEM) 0.23, 0.51, 1.06, and 1.35 μm, respectively (four samples) [1815], d50 = 200 and 860 nm (two samples) [1814], particle size distribution available [1813], monodipersed spherical particles [540,547], nearly monodispersed spherical particles [1813], electron micrograph available [547,610,1117], SEM images available [1815], XRD pattern available [1813]. TABLE 3.797 PZC/IEP of Silica(s) from Geltech Electrolyte HCl 0.001 M KNO3 0.001 M LiCl, NaCl, KCl, CsCl 0.001,0.01 M NaCl 0.001–1 M NaCl 1 M KCl

T

Method

Instrument

pH0

Reference a

[1117]

iep

Malvern Zetasizer 4

<2 if any

iep

Acoustosizer

<2 if anyb

[1813]

iep pH

Electrophoresis

<4 if any <4.5 if any

[330] [547]

continued

392

Surface Charging and Points of Zero Charge

TABLE 3.797 (continued) Electrolyte

T

Method

0.001–1 M KNO3, KCl, NaCl

20

pH iep

Malvern Zetasizer 4

0.001 M KNO3 0.01 M KNO3 0.1 M KNO3

25

iep iep iep iep

Acoustosizer Malvern Zetasizer 2c Electrophoresis Electrophoresis

a

b

c

Instrument

pH0

Reference

<4.5 if any <2 if anya

[610]

[1817]c [903] [540] [1816]

2 3 3 4

0.001 M KNO3; higher electrolyte concentrations induce a shift in the IEP to high pH (e.g., about 3 in 0.01 M KNO3). 0.001 M. In 0.01 M electrolytes, positive z potential at pH about 2 is reported only for KCl. Higher electrolyte concentrations induce a shift in the IEP to high pH. Only value, data points not reported.

3.1.35.1.30 Vitreous Silica from General Electric Properties: 50 ppm Al2O3 [1818]. TABLE 3.798 PZC/IEP of Vitreous Silica from General Electric Description 60–80 mesh, washed in boiling HNO3

Electrolyte 0–0.01 M NaCl

T

Method

Instrument

pH0 Reference

iep

Streaming potential

3

[1818]

3.1.35.1.31 Syloid 244 from Grace Properties: BET specific surface area 314 m2/g, mean particle diameter 767 nm, contains 0.4% C, probably as organic modifier [1819]. TABLE 3.799 PZC/IEP of Syloid 244 from Grace Electrolyte 0.001 M NaCl

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

1.8

[1819]

Properties of unspecified silica from Grace: BET specific surface area 310 m2/g [779]. Properties of silica gel 254 from W.R. Grace: BET specific surface area 571 m2/g [1820].

393

Compilation of PZCs/IEPs

3.1.35.1.32 Silica from Harwell Properties: Specific surface area 50 m2/g, particle diameter 80 nm [230]. TABLE 3.800 PZC/IEP of Silica from Harwell Electrolyte

T

Method

0.001–0.1 M NaCl

25

iep

3.1.35.1.33

Instrument Delsa 440

pH0

Reference

<3 if any

[230]

Silica Plates from Herbert Groiss

TABLE 3.801 PZC/IEP of Silica Plates from Herbert Groiss Electrolyte

T

Method

Instrument

pH0

Reference

0.0001, 0.001 M KCl

iep

Streaming potential

<2 if any

[1821]a

0.0001 M NaNO3

iep

Streaming potential

<3 if any

[1761]

a

Water-washed, original, and treated at 1050°C.

3.1.35.1.34 Herasil I, Fused Quartz Properties: 10–50 ppm Al2O3 [278,1822]. TABLE 3.802 PZC/IEP of Herasil I Description

Electrolyte

Different cleaning 0.001 M NaCl procedures Multistep cleaning 0.01 M NaCl procedure

T

Method

Instrument

pH0

Reference

20–25

iep

Electro-osmosis

<2 if any

iep

Electro-osmosis

<2.2 if any [1822,1823]

[278]

HPLC Service, see Section 3.1.35.1.58 3.1.35.1.35 Silicas from Huber 3.1.35.1.35.1 Zeo 49 Properties: Contains Al (Si:Al atomic ratio 1:400) [851,1824], BET specific surface area 280 m2/g [851,1824], 93 m2/g [858], particle diameter 9 mm [851,1824].

394

Surface Charging and Points of Zero Charge

TABLE 3.803 PZC/IEP of Zeo 49 from Huber Electrolyte

T

Method

Instrument

pH0

Reference

iep

Laser Zee 500

<2.5 if any 1.3 <2

[851]

0.01 M NaClO4 0.025 M NaClO4 a

iep

Laser Zee 500

[899]a [858]a

Only value, data points not reported.

3.1.35.1.35.2 Zeosyl 100 from Huber Properties: Contains Al (Si:Al atomic ratio 1:800), BET specific surface area 100 m2/g, particle diameter 6 mm [851]. TABLE 3.804 PZC/IEP of Zeosyl 100 from Huber Electrolyte

T

Method

Instrument

iep

Laser Zee 500

0.01 M NaClO4 a

pH0

Reference

<3.5 if any 2

[851] [899]a

Only value, data points not reported.

Properties of Zeothix 265 from Huber: amorphous, EGME specific surface area 221 m2/g, particle size <2 μm [1825]. 3.1.35.1.36 Silica from Institute of Surface Chemistry, Kalush, Ukraine Another sample studied by the same research group is described in Section 3.1.35.1.15. Properties: Specific surface area 100, 300 m2/g [926] (2 samples). TABLE 3.805 PZC/IEP of Silica from Institute of Surface Chemistry, Kalush, Ukraine Electrolyte 0.001 M NaCl

T 25

Method

Instrument

iep

Malvern Zetasizer 3000

pH a b

pH0 a

2.2

Reference [926]

<3.5 if anyb

Specific surface area not specified. Both samples, from Figures 10a and 11a. In Figure 10b, specific values of PZC in the range 3.2–3.5 are reported for the 300 m2/g sample.

3.1.35.1.37 Silica from ICN Bromedicals Properties: 0.4% Na, 0.02% K, 0.3% Al, 0.02% Fe, single-point BET specific surface area 402 m2/g [1826].

395

Compilation of PZCs/IEPs

TABLE 3.806 PZC/IEP of Silica from ICN Description Washed with water

Electrolyte

T

Method Instrument

0.001–0.1 M KCl

22 ± 2

pH

Washed with 0.1 M HCl

3.1.35.1.38

pH0

Reference

4.5

[1826]

3.8

Silicas from Jena Glasswerke

TABLE 3.807 PZC/IEP of Silicas from Jena Glasswerke Description

Electrolyte

Cristobalite

NaOH + HClO4 NaOH + HClO4

Silica glass

T

Method

Instrument

pH0

Reference

iep iep

Zeta-Meter Zeta-Meter

1.5 2.3

[104] [104]

3.1.35.1.39 Silica Gel from Kemika Properties: Amorphous [1827,1828], 0.7% Na, 0.06% K, 0.6% Al, 0.1% Fe [1826], specific surface area 292 m2/g [1827,1828], single-point BET specific surface area 318 m2/g [1826]. TABLE 3.808 PZC/IEP of Silica Gel from Kemika Description

Electrolyte

T

Method

Washed with 0.1 M HCl

0.001–0.1 M KCl

22 ± 2

pH

Instrument

pH0

Reference

4.2

[1826]

3.1.35.1.40 F-6 from Ketjen Properties: Specific surface area 800 m2/g (original) [921]. TABLE 3.809 PZC/IEP of F-6 from Ketjen Description Original 0.083 0.166 mmol Na/ga 0.332 mmol Na/g a b

Electrolyte 0.001 M NaCl

T 25

Method b

cip

Instrument

pH0

Reference

3.3 4.4 4.4 4.7

[921]

Prepared by impregnation of original material with different amounts of NaNO3 and calcination. Only values, data points not reported; also 5–20°C.

396

Surface Charging and Points of Zero Charge

3.1.35.1.41 Ludox See also Sections 3.1.35.1.4.4, 3.1.35.1.64.1, and 3.1.35.22. Properties: BET specific surface area 180 m2/g [1829]. TABLE 3.810 PZC/IEP of Ludox Silica(s) Electrolyte

T

Method

HCl + NaOH 0.0001–4 M NaCl a

Instrument

pH0

Reference

iep

DT 300

<2 if any

[1830]

iep

DT 1200

<2 if any 2–4a

[1804,1831]

pH

[1829]

Two data points: 1 and 4 M NaCl, pH 2 with positive s0, the other data points with zero or negative s0.

3.1.35.1.42

Silicas from Macherey Nagel

3.1.35.1.42.1 Nucleosil from Machery Nagel See also Section 3.1.35.1.47. Properties: Fe 31 ppm, Mg 34 ppm, Al 92 ppm, particle diameter 5 μm, pore diameter 10–15 nm [1805]. TABLE 3.811 PZC/IEP of Nucleosil from Machery Nagel Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zeta Master S

3.5

[1805]

0.001 M NaCl

3.1.35.1.42.2 NH-R from Machinery Nagel Properties: BET specific surface area 359 m2/g (measured) [1054], 500 m2/g (manufacturer) [1054], 500 m2/g [1832,1833], average particle size 3–20 mm [1054,1832,1833], average pore radius 5.2 nm [1054,1832]. TABLE 3.812 PZC/IEP of NH-R from Machinery Nagel Electrolyte 0.01–0.1 M KNO3 KNO3

a

T

Method

Instrument

25 pH Titrationa iepa BI ZetaPlus

Only value, data points not reported.

pH0

Reference

<3 if any 3.2 3.7

[1832] [1833]

[1054]

397

Compilation of PZCs/IEPs

3.1.35.1.43 3.1.35.1.43.1

Silicas from Merck Fractosil 500

TABLE 3.813 PZC/IEP of Fractosil 500 from Merck Electrolyte

T

Method

0.1 M NaCl

Instrument

pH

pH0

Reference

<4 if any

[1834]

3.1.35.1.43.2 Lichrospher Si 100 Properties: Particle diameter 9 nm, aggregate diameter 5 μm, specific surface area 389.4 m2/g [1835]. TABLE 3.814 PZC/IEP of Lichrospher Si 100 from Merck Description Water- washed

Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaCl

25

pH iep

Laser Zee Meter 501

<4 if any

[1835]

3.1.35.1.43.3 Lichrospher Si 1000 Properties: Particle diameter 111 nm, aggregate diameter 10 μm, specific surface area 24.3 m2/g [1835]. TABLE 3.815 PZC/IEP of Lichrospher Si 1000 from Merck Description Water- washed

a

Electrolyte

T

Method

Instrument

0.001–0.1 M NaCl

25

pH iep

Laser Zee Meter 501

pH0 a

Reference

6 <4 if any

[1835]

Arbitrary interpolation.

3.1.35.1.43.4 Monospher 250, Stober Silica Properties: Amorphous [194,130], BET specific surface area 22.8 m2/g [130,194], original 18.6 m2/g, heated in air 15.4 (1 d), 15.6 (36 h) m2/g [163], 110 nm in radius [130,194]. TABLE 3.816 PZC/IEP of Monospher 250 from Merck Description

Electrolyte

T

Method

Acid-washed

0.001–0.1 M NaCl 0.01 M KNO3 (C2H5)4NNO3

20

pH pH

a

Instrument

pH0 <4 if any <4 if any

Reference [194] [163]a

Original, heated at 800°C for 3, 7, 30, and 36 h, acid-washed, and heated at 800°C for 20 h.

398

Surface Charging and Points of Zero Charge

3.1.35.1.43.5 Monospher 1000 Properties: 481 nm in radius, BET specific surface area 2.9 m2/g [1836]. TABLE 3.817 PZC/IEP of Monospher 1000 from Merck Electrolyte

T

Method

Instrument

pH0

Reference

pH iep

Matec ESA 8000

<6 if any

[1836]

0.001 M KCl

3.1.35.1.43.6 Kiesgel 60 (Silica Gel 60) Properties: BET specific surface area 425 m2/g [1460], 480–540 m2/g [1837], specific surface area 388 m2/g [964,969, 1838], 144 m2/g [1839,1840], particle size 125 μm [1460], 40–60 μm [1837]. TABLE 3.818 PZC/IEP of Kiesgel 60 (Silica Gel 60) from Merck Description

Electrolyte

T

Method

0.001 M NaCl Washed

a b

iep

0.001–0.1 M NaCl

25

pH iep

0.003–0.1 M NaClO4

25

pH

Instrument

pH0

Zetaphoremeter II, <3 if any Sephy Laser Zee Meter 501 <5 if any Pen Kem 3.8

Reference [1837] [964b,969,1838, 1841,1842a]

<3.5 if any [1840]

15 and 35°C. Only value, no data points.

3.1.35.1.43.7 Purospher Properties: Fe 100 ppm, Ni 14 ppm, Mg 4 ppm, Al 23 ppm, particle diameter 5 μm, pore diameter 10–15 nm [1805]. TABLE 3.819 PZC/IEP of Purospher from Merck Electrolyte 0.001 M NaCl

T

Method

Instrument

iep

Malvern Zeta Master S

pH0 Reference 2.3

[1805]

3.1.35.1.43.8 60 H Silica from Merck Properties: BET specific surface area 384 m2/g [1843]. Reference [1843] reports the results of titrations at different rates of washed and unwashed 60 H silica in 0.1 M NaNO3.

399

Compilation of PZCs/IEPs

3.1.35.1.43.9 Other Properties: 1.2% Na, 0.07% K, 0.5% Al, 0.08% Fe, single-point BET specific surface area 292 m2/g [1826], BET specific surface area 720 m2/g [1844].

TABLE 3.820 PZC/IEP of Unidentified Silica from Merck Description

Electrolyte

Original Washed with 0.1 M HCla a

0.001–0.1 M KCl

T 22 ± 2

Method

Instrument

pH0 Reference

pH

7.1 4.4

[1826]

Washing with water or with more dilute HCl resulted in pH0 in the range 4.4–7.1.

Properties of Monospher 100 from Merck: Amorphous, mean size 94 nm, particle size distribution available [1845]. Properties of Monospher 200 from Merck: Spheres, 200 nm in diameter, BET specific surface area 20.5 m2/g [1307]. Properties of Silica gels S4, S6, S20 and S100 from Merck: Pore diameter 4, 6, 20, and 100 nm, respectively, specific surface area 650, 400, 50, and 25 m2/g, respectively [1846]. Properties of H silica from Merck: BET specific surface area 372 m2/g [1786,1847]. 3.1.35.1.44 Syton HT50 from Monsanto Properties: Amorphous, average particle diameter 125 nm, BET specific surface area 70 m2/g [883].

TABLE 3.821 PZC/IEP of Syton HT50 from Monsanto Electrolyte

T

Method iep

Instrument Malvern Zetamaster S

pH0 Reference 3

[883]

3.1.35.1.45 Silicas from Nippon Shokubai Properties: Specific surface area 16.7 m2/g [999], average diameter 300 nm [999], TEM images available [1848]. KEP 10 original and calcined at 800°C for 1 d: BET specific surface area 43 and 32 m2/g, particle radius 59 and 58 nm. KEP 30 original and calcined at 800°C for 1 d: BET specific surface area 51 and 14 m 2/g, particle radius 158 and 144 nm [1848].

400

Surface Charging and Points of Zero Charge

TABLE 3.822 PZC/IEP of Nippon Shokubai Silicas Description

Electrolyte

KEP 10 original 0.01–1 M KCl and calcined KEP 30 original and calcined a

T

Method

Instrument

pH0

Reference

25

iep pH

Malvern Zetasizer 2000

<3 if any <4 if any

[1848]a

Stability ratios at different pH and ionic strengths are also reported.

3.1.35.1.46

Silicas from Nissan

3.1.35.1.46.1 Snowtex ZL 30 vol% dispersion. Properties: 99.99% pure [1043], BET specific surface area 32.6 m2/g [1043], specific surface area 34 m2/g [1849], particle diameter: 92 nm [1043], d50 = 97 nm [1849], SEM image available [1849]. TABLE 3.823 PZC/IEP of Snowtex ZL from Nissan Description

Electrolyte

T

Dialyzed, calcined at 400°C for 4 h Dialyzed

Method

pH0

Reference

iep

DT 1200

Instrument

<1.2 if any

[1043]

iep

DT 1200

<1.2 if any

[1849]

3.1.35.1.46.2 Other Properties: Average sizes 5, 15, 25, and 300 nm [1025], mean diameter 107 nm [1850], bimodal distribution of particle size with peaks at 209 and 690 nm [1851]. TABLE 3.824 PZC/IEP of Unspecified Silicas from Nissan Description

Washed with 0.1 M HCl

Electrolyte

T

Method

0.001, 0.1 M NaCl

iep

0.0015 M NaBr

iep

0.001–0.1 M KCl

pH

0.005 M KNO3

iep

Instrument Malvern Zetasizer 4 Brookhaven ZetaPlus

Zeta-Meter 3.0

pH0

Reference

<2 if any

[1851]

<3 if any

[1850]

<4.5 if any

[1852]

1.6

[1025]

401

Compilation of PZCs/IEPs

Properties of Snowtex XL from Nissan: Particle diameter: Number average 45 nm, mass average 52 nm, BET specific surface area 63.8 m2/g [1853]. Properties of Snowtex YL from Nissan: Particle diameter: Number average 82 nm, mass average 88 nm BET specific surface area 33.6 m2/g [1853]. 3.1.35.1.47 Nucleosil 100-30 See also Section 3.1.35.1.42.1. TABLE 3.825 PZC/IEP of Nucleosil 100-30 Electrolyte

T

Method

20% w/v NaCl

30

pH

Instrument

pH0

Reference

<4 if any

[1854]

3.1.35.1.48 Min-U-Sil or Min-U-Sil 5 from Pennsylvania Glass Sand (or Sand Glass or Glass) See also Section 3.1.35.1.68. Properties: Quartz [382,447,1641,1855], 0.2% MgO, 3.3% Al2O3, 0.9% K2O, 0.1% CaO, 0.5% FeO [1855], contains organic matter [382], BET specific surface area 3.3 m2/g [1641], 4.8 m2/g [1855], 5 m2/g [382,447], 5.9 m2/g [1395], particle size 0.5–10 mm [1855]. TABLE 3.826 PZC/IEP of Min-U-Sil 5 from Pennsylvania Glass Sand Description Min-U-Sil, refluxed in concentrated HCl

Electrolyte 0.01 M NaCl

Min-U-Sil-5, calcined 0.01 M for 1 d at 500°C, then HNO3–KOH refluxed in boiling 4 M HCl Min-U-Sil, Hot 0–0.1 M NaCl HCl-washed for 1 h Min-U-Sil 5, 0.01 M NaOH-washed a b

T

Method

pH0

Reference

iep

Pen Kem <2 if any [1415,1418]a 3000, Rank Brothers Mark II Zeta-Meter <2 if any [382]

iep pH

MK II Rank Bros

iep

25

Instrument

pH

<2.3 if [1855]b any <4 if any 2.5 [447]a

Only value, data points not reported. Minus sign is not used in text or figures in [1855], but apparently negative surface charge and z potential are reported.

402

Surface Charging and Points of Zero Charge

Properties of Min-U-Sil 30 from Pennsylvania Glass Sand: Quartz, 99,7% pure, impurities (in ppm) Fe2O3 230, Al2O3 1010, TiO2 190, BET specific surface area 0.77 m2/g, particle size 8.8 μm [87]. 3.1.35.1.49 Silica from Polysciences Properties: Particle size 5 mm [1002].

TABLE 3.827 PZC/IEP of Silica Description from Polysciences Description

Electrolyte

T

Method

Instrument

pH0

Reference

iep iep

Electrophoresis Rank Brothers Mark II

<3 if any <3 if any

[1002] [1856]

Glass spheres 0.0001–0.1 M KNO3

3.1.35.1.50 Spherosil XO75LS from Procatalyse Properties: BET specific surface area 68 m2/g [1857].

TABLE 3.828 PZC/IEP of Spherosil XO75LS from Procatalyse Electrolyte

T

0.01,0.1 M NaNO3

25

Method Instrument pH

pH0

Reference

<4 if any

[1857]

Properties of XOB015 from Procatalyse (France): BET specific surface area 29 m2/g, high sodium content, particle diameter <30 mm [1858]. 3.1.35.1.51

Silicas from Quarzwerke

3.1.35.1.51.1 Sikron 6000 SF Properties: Average particle size 2.8 μm, BET specific surface area 5 m2/g [1859].

TABLE 3.829 PZC/IEP of Sikron 6000 SF from Quarzwerke Electrolyte 0.001 M KCl

T

Method

Instrument

iep

Malvern ZetaMaster

pH0 Reference 4.2

[1859]

3.1.35.1.51.2 Sikron SF 800 Properties: Quartz, detailed analysis available, average particle diameter 2 μm, BET specific surface area 6 m2/g [377].

403

Compilation of PZCs/IEPs

TABLE 3.830 PZC/IEP of Sikron SF 800 from Quarzwerke Description

Electrolyte

T

Method

Washed Washed

0.001–0.1 M NaCl 0.01 M NaCl, NaNO3

25 25

pH iep

Washed

0.01, 0.1 M NaNO3

25

iep

3.1.35.1.52

Instrument Pen Kem 501 Malvern 3000 Delsa 440 Acoustosizer DT 1200 Acustosizer

pH0

Reference

<4 if any 2 <2 if any 2.5 <2 if any 3 <2 if any

[377] [377]

[350]

Quso Silicas

TABLE 3.831 PZC/IEP of Quso Silicas Type

Electrolyte

T

Method

G 761 G 30 a

Instrument

Titration Titration

pH0

Reference

2a 2a

[810] [810]

Only value, data points not reported.

3.1.35.1.53 Red Star Properties: Quartz [1317]. TABLE 3.832 PZC/IEP of Red Star Silica Electrolyte

T

0.01 M NaCl

3.1.35.1.54 3.1.35.1.54.1

Method

Instrument

pH0

Reference

iep

Pen Kem 300

<2 if any

[1317]

Silicas from Rhone Poulenc Tixosil

Properties: Specific surface area 250 m2/g [847].

TABLE 3.833 PZC/IEP of Tixosil from Rhone Poulenc Electrolyte

T

Method

0.1 M NaCl

25

Mass titration

Instrument

pH0 6.7

Reference [847]

404

Surface Charging and Points of Zero Charge

3.1.35.1.54.2 Unspecified Silica Gel from Rhone Poulenc TABLE 3.834 PZC/IEP of Unspecified Silica Gel from Rhone Poulenc Electrolyte

T

Method

Instrument

0.1 M NaCl

25

Mass titration

pH0

Reference

6.2

[847]

Properties of precipitated silica: BET specific surface area 15 m2/g [1861]. Reference [1860] reports the specific surface areas of four silicas from Rhone Poulenc: A: 175 m2/g, B: 320 m2/g, C: 90 m2/g and D: 160 m2/g. Properties of Spherosil B from Rhone Poulenc: BET specific surface area 25 m2/g, nominal size 40–100 μm [948]. Properties of XOA400 from Rhone Poulenc: Specific surface area 400 m2/g, mean pore diameter 8 nm [1862]. Properties of Spherosil XOB015 from Rhone Poulenc: BET specific surface area 29 m2/g [1863], >99.5% pure, specific surface area 30 m2/g, pore size 130 nm, particle size 40–100 mm [790]. 3.1.35.1.55 Silicas from Riedel de Haen Properties: Quartz, Fe-free [1353], BET specific surface area 254 m2/g [1864], 1.2 m2/g [1353]. TABLE 3.835 PZC/IEP of Silicas from Riedel de Haen Description

Electrolyte

T

Ground, hot 0.0125 M NaCl 25 water-washed Analytical quality 0.01 M NaCl 25

3.1.35.1.56

Method

Instrument

iep

Electrophoresis

iep

Malvern Zetasizer 2000

pH0 1.3 <3 if any

Reference [1353] [994]

Quartz from a Beach Sand, from Sargent

TABLE 3.836 PZC/IEP of Quartz from a Beach Sand, from Sargent Description

Electrolyte T Method

HCl- and water-washed, aged a

Only value, data points not reported.

a

iep

Instrument

pH0

Streaming potential 2.2–2.8

Reference [1865]

405

Compilation of PZCs/IEPs

3.1.35.1.57 ES from Sepserve Recipe from [1866]. Properties (original/acid-washed): Fe 109/2 ppm, Ni 17/1 ppm, Mg 12/1 ppm, Al 43/1 ppm, particle diameter 5 μm, pore diameter 10–15 nm [1805]. TABLE 3.837 PZC/IEP of ES from Sepserve Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zeta Master S

2.3/2.9a

[1805]

0.001 M NaCl a

Original/acid-washed.

3.1.35.1.58 Hypersil from Shandon or from HPLC Service Properties: Fe 154 ppm, Ni 20 ppm, Mg 20 ppm, Al 540 ppm, particle diameter 5 μm, pore diameter 10-15 nm [1805], particle diameter 3 μm, specific surface area 170 m2/g [1806]. TABLE 3.838 PZC/IEP of Hypersil from Shandon or from HPLC Service Electrolyte

T

Method

Instrument

pH0

Reference

23

iep iep

Malvern Zeta Master S Zeta-Meter 3.0 Electro-osmosis

2.1 <3.5 if any

[1805] [1806]

0.001 M NaCl

3.1.35.1.59 Spectrograde Silica from Shanghai Chemical Reagent Factory Properties: BET specific surface area 3.3 m2/g [1867].

TABLE 3.839 PZC/IEP of Spectrograde Silica from Shanghai Chemical Reagent Factory Description Washed

Electrolyte

T

Method Instrument a

0.01–1 M NaCl, Lil, 25 KCl, CsCl KNO3 Washed, then calcined 0.01–1 M NaCl 25 for 7 h at 900°C

a

Also 30°C.

pH0

Reference

pH

<4 if any

[1867]

pH

<3 if any

Missing reference

406

Surface Charging and Points of Zero Charge

3.1.35.1.60 Showa Denko Quartz Properties: BET specific surface area 11 m2/g, mean diameter 0.8 mm [1000]. TABLE 3.840 PZC/IEP of Quartz from Showa Denko Electrolyte

T

Method

0.001 M KNO3

Instrument

pH

pH0

Reference

4.2

[1000]

3.1.35.1.61 C-600 from Sifraco 3.1.35.1.61.1 C-600 Properties: Quartz [1868], purity: >99.5% [790], 98.8% [1868], specific surface area 4.3 m2/g [790], 5.1 (original), 5.5 (acid-washed), 4 m2/g (acid-washed and calcined for 9 h at 1000°C) [1868], particle size 0–10 mm [790], nonporous [790]. TABLE 3.841 PZC/IEP of C-600 Description

Electrolyte

T

Method

Instrument

Original Acid-washed Calcined

0.0007–0.14 M NaCl

25

iepa

Zeta-Meter 3.0

a

pH0 Reference 2.2 2.1 2.3

[1868]

Only value, data points not reported.

3.1.35.1.61.2 C800 from Sifraco Properties: Quartz [980, 1017], BET specific surface area 5 m2/g [980,1017], average grain size 1.5 μm [980,1017].

Table 3.842 PZC/IEP of C800 from Sifraco Electrolyte 0.01 M NaCl

a

T

Method

Instrument

pH0

Reference

iep

Matec ESA 8000

<2 if anya

[980] [1017]

Figure 4 in [980]. Table 2 reports PZC at pH 2.

Properties of quartz from Sifraco: BET specific surface area 6 m2/g [1861]. 3.1.35.1.62 Suprasil (from H.A. Groiss) Fused silica.

407

Compilation of PZCs/IEPs

Table 3.843 PZC/IEP of Suprasil Description a

In footnote In footnoteb

a

b

Electrolyte

T

Method

0.0001–0.1 M KCl 20 0.0001, 0.001 M NaNO3

iep iep AFM

Instrument

pH0

Streaming potential <3 if any Streaming potential <3 if any

Reference [1869] [1761]

Polished, washed with hot alkaline detergent, cleaned in ammoniacal peroxide, washed with water, dried at 100°C Soaked in concentrated HNO3 for 12 h, then boiled in water for 20 min and in ammoniacal peroxide for 10 min.

3.1.35.1.63 Silicas from Sigma 3.1.35.1.63.1 Fumed Properties: Specific surface area 390 m2/g [1870–1872], 200 m2/g [434], BET specific surface area 255 m2/g [1873], particle size 7 nm [1870–1872] 14 nm [434]. TABLE 3.844 PZC/IEP of Fumed Silica from Sigma Electrolyte

T

Method

Instrument

0.001 M NaNO3

25

iep iep

HCl HNO3 HClO4

25

iep

Acoustosizer Acoustosizer Malvern Zetasizer IIc Acoustosizer

pH0 <2 if any <4 if any

Reference [434] [1871,1872]

2 [1870] <1.5 if any <1.5 if any

3.1.35.1.63.2 Other Properties: Quartz [572,1451,1813], >99.9% pure [1813], BET specific surface area 5.9 m2/g [572,1451], particle size 0.5–2 μm [1451], particle size distribution available, XRD results available [1813]. TABLE 3.845 PZC/IEP of Unspecified Silicas from Sigma Electrolyte

T

Method

Instrument

pH0

Reference

0.1 M LiCl, NaCl, KCl, CsCl 0.001 M NaNO3

25

iep iep pH

Acoustosizer Pen Kem 501 ZetaPlus Brookhaven

<2 if any 2.5 4.7

[1813] [1451] [572]

408

Surface Charging and Points of Zero Charge

Properties of H 4267 silica from Sigma: Specific surface area 420 m2/g [1874]. Properties of S5130 fumed silica from Sigma: BET specific surface area 390 m2/g [1875]. 3.1.35.1.64 Silicas from Sigma-Aldrich See also Sections 3.1.35.1.4 and 3.1.35.1.63. 3.1.35.1.64.1 Ludox TM40 See also Sections 3.1.35.1.22.5 and 3.1.35.1.40. Properties: Particle diameter 33 nm, polydispersity 17% [1876,1877], SEM image available [1876]. TABLE 3.846 PZC/IEP of Ludox TM40 from Sigma-Aldrich Description

Electrolyte

Original Refluxed for 1 d

T

Method

HCl + NaOH

iep

Instrument Zetasizer 90 Brookhaven

pH0

Reference

<3 if any

[1876,1877]

3.1.35.1.64.2 Quartz Properties: Microcrystalline quartz, structure confirmed by XRD, BET specific surface area 6 m2/g [429], external specific surface area used in calculations was 1.7 m2/g [428,429]. TABLE 3.847 PZC/IEP of Quartz from Sigma-Aldrich Electrolyte

T

0.01 M LiCl, NaCl, KCl, CsCl

a

Method iep

Instrument Zeta Probe, Colloidal Dynamics

pH0

Reference

<3.5 if any

[429] [428]a

Data points not reported.

3.1.35.1.64.3

Other Properties: BET specific surface area 1 m2/g [1031].

TABLE 3.848 PZC/IEP of Unspecified Silicas from Sigma-Aldrich Electrolyte KCl

T

Method

Instrument

iep

Malvern Nano ZS

pH0 Reference 2.1

[1031]

409

Compilation of PZCs/IEPs

3.1.35.1.65

Silfa Fibers

TABLE 3.849 PZC/IEP of Silfa Fibers, >99% SiO2 Electrolyte

T

Method

Instrument

pH0

Reference

iep

EKA Anton Paar

<3 if any

[1878]

0.001 M KCl

3.1.35.1.66 Silica from Thiokol Properties: Specific surface area 0.21 m2/g [30,1048].

TABLE 3.850 PZC/IEP of Silica from Thiokol Description

Electrolyte

T Method

0.001 M NaCl Washed with hot HCl 0.1, 1 M NaCl

iep pH

Instrument

pH0

Streaming potential <2.2 if any 3.3

Reference [1048] [30]

3.1.35.1.67 Quartz Sand from Unimin, LeSueur, MN

TABLE 3.851 PZC/IEP of Quartz Sand from Unimin, LeSueur, MN Description

Electrolyte

T

Method

Instrument

HCl-washed

0.001 M KCl

25

iep

BI-EKA, Brookhaven Malvern

pH0 2 <2 if any

Reference [1879]

3.1.35.1.68 Min-U-Sil 5 from U.S. Silica Company See also Section 3.1.35.1.48. Properties: Natural crystalline silica [249], quartz [904,1873], purity 99.4% [1880], detailed analysis available (manufacturer’s data) [1880], BET specific surface area 5.5 m2/g [904], 4 m2/g [1873], median size 1.7 μm [1880], all particles <5 μm [249], angular particles [249], SEM image available [1880].

410

Surface Charging and Points of Zero Charge

TABLE 3.852 PZC/IEP of Min-U-Sil 5 from U.S.Silica Company Description

Electrolyte

0.01 M KCl Acid-washed 0.0117, 0.094 M NaCl a

T

Method

25a

iep pH

Instrument

pH0

Reference

Zetaphoremeter IV <2 if any [249,1880] <4 if any [904]

Also 60°C.

3.1.35.1.69 HDK V15 from Wacker Properties: Primary particles 16 nm in diameter, aggregates 180 nm in diameter, BET specific surface area 160 m2/g [1881]. TABLE 3.853 PZC/IEP of HDK V15 from Wacker Electrolyte

T

Method

0.1 M LiCl, CsCl

25

pH

Instrument

pH0

Reference

<4 if any

[1881]

3.1.35.1.70 Quartz (Rose) from Ward’s Properties: Electron micrograph available [598]. Figure 2.5c in [598] reports titration results in 0.001, 0.01, and 0.1 M NaCl. The PZC is difficult to read from the figure. Also Al- and Fe-coated. 3.1.35.1.71 YMC Silica Properties: Fe 1 ppm, particle diameter 5 μm, pore diameter 10–15 nm [1805]. TABLE 3.854 PZC/IEP of YMC Silica Electrolyte 0.001 M NaCl

T

Method

Instrument

iep

Malvern Zeta Master S

pH0 Reference 2.4

[1805]

3.1.35.1.72 Silica from Zhoushan Nanostructure Materials Company of China Properties: Particle size 20 nm [406].

411

Compilation of PZCs/IEPs

TABLE 3.855 PZC/IEP of Silica from Zhoushan Nanostructure Materials Company of China Electrolyte

T

Method

0.001 M NaCl

Instrument

pH0 Reference

Brookhaven ZetaPlus

2

[406]

3.1.35.2 Synthetic 3.1.35.2.1

Oxidation of Silicon

3.1.35.2.1.1 In Steam at 1000∞C TABLE 3.856 PZC/IEP of 1 µm Thick Layer of Silica on Silicon Obtained by Oxidation in Steam Description Fresh

Electrolyte

T

Method

Instrument

0.001–0.1 M NaCl

24

iep

Streaming potential

pH0 Reference 2.7

Aged

[1882]

3.2

3.1.35.2.1.2

At 1000°C for 1 h

TABLE 3.857 PZC/IEP of 100 nm Thick Layer of Silica on Silicon Obtained by Oxidation at 1000°C for 1 h Description

Electrolyte

Washed in persulfuric acid

3.1.35.2.1.3

T

0.001–0.1 M NaCl

22

Method

Instrument

pH0

Reference

iep

EKA Anton Paar

4

[1883]

Exposure to Air and UV Irradiation ( l = 172 nm)

TABLE 3.858 PZC/IEP of 2 nm Thick Layer of Silica on Silicon Generated by Exposure to Air and UV Irradiation Electrolyte 0.001 M KCl a

T

Method

25

From mobility profile.

iep

Instrument

pH0

ELS-600 Otsuka <3 if any

Reference a

[275]

412

Surface Charging and Points of Zero Charge

3.1.35.2.2 From Silicate 3.1.35.2.2.1 Partial Neutralization of Sodium Silicate Solution with H2SO4 Properties: Specific surface area 380 m2/g [847]. TABLE 3.859 PZC/IEP of Silica Obtained by Partial Neutralization of Sodium Silicate Solution with H2SO4 Electrolyte

T

Method

0.1 M NaCl

25

Mass titration

3.1.35.2.2.2

Instrument

pH0

Reference

10.6

[847]

From Na2SiO3 and HCl See also Section 3.1.35.2.6.5

TABLE 3.860 PZC/IEP of Silica Obtained from Na2SiO3 and HCl, Dialyzed Description Electrolyte

T

1% sol 0.26% sol a

Method

Instrument

pH0

Reference

iep iep

Electrophoresis Electrophoresis

1–1.5 2

[1884]a [1884]a

Only value/range, no data points. Reference [1885] cited in [1] for IEP of silica reports only the rate of gelation as a function of pH (electrokinetic potential was not studied).

3.1.35.2.2.3 From Na2SiO3 and HNO3 Solutions of Na2SiO3 and HNO3 were added simultaneously at pH 9 and at 60°C with stirring. Properties: BET specific surface area 90 m2/g, diameter 30 nm, monodispersed sol, TEM image available [1886]. TABLE 3.861 PZC/IEP of Silica Obtained from Na2SiO3 and HNO3 Electrolyte 0.1 M NaCl, LiCl, KCl a

T

Method Instrument pH

pH0

Reference a

<3.5 if any

[1886]

PZC at pH 3.5 claimed in figure caption is not supported by data.

3.1.35.2.2.4 Precipitated at pH 7 1 M Na2SiO3 was pumped into at beaker held at pH 7. The precipitate was aged for 30 min, freeze-dried, water-washed, and freeze-dried again. Properties: Amorphous, specific surface area 336 m2/g [1187].

413

Compilation of PZCs/IEPs

TABLE 3.862 PZC/IEP of Silica Precipitated from 1 M Na2SiO3 at pH 7 Electrolyte

T

0.01–1 M NaNO3

a

Method

Instrument

Salt addition pH

pH0

Reference

a

2 <4 if any

Titration: 3 h per 1 pH unit

[1187]

Only value reported, no data points.

3.1.35.2.2.5 From Na2SiO3 by Ion Exchange with Amberlite 120 Na2SiO3 solution (140 g/dm3) was passed through a column with Amberlite 120 in hydrogen form. TABLE 3.863 PZC/IEP of Silica Obtained by Ion Exchange with Amberlite 120 Electrolyte

T

Method

Instrument

pH0

Reference

iep iep

Malvern Zetasizer 3000 HSA Malvern Zetasizer 3000 HSA

1.8 2

[1887] [1888]

3.1.35.2.2.6 From Na2SiO3 by Ion Exchange with Amberlite IR 120 An aqueous solution containing 3.5% SiO2 and 1.2% Na2O was passed through a column with Amberlite IR 120. The effluent was allowed to gel and dry, and then was dried for 1 d at 110°C. Alternatively, the sol was coagulated at pH 10 with 0.5 M NaCl, filtered out, and washed with 0.1 M HCl. Properties: BET specific surface area 416 m2/g (original), 199 m2/g (coagulated) [1826], specific surface area 375 m2/g (CTAB adsorption) [1889], mean particle diameter 8 nm [1889], particle size 9 nm [1890]. TABLE 3.864 PZC/IEP of Silica Obtained by Ion Exchange with Amberlite IR 120 Description

Electrolyte

0.03 M NaCl 0.001–4 M LiCl, NaCl, KCl, CsCl Original and coagulated, 0.001–0.1 M water- and HClKCl washed

T

Method

25

pH pH

22 ± 2

pH

Instrument

pH0

Reference

<3 if any [1889] <6.5 if any [1890,1891]

4.1

[1826]

414

Surface Charging and Points of Zero Charge

3.1.35.2.2.7 In Emulsion Two emulsions: one containing 100 cm3 of 5 mass% aqueous Na2SiO3 and 110 cm3 of cyclohexane, and another containing 33 cm3 of 5 mass% aqueous HCl and 35 cm3 of cyclohexane, both containing an emulsifier, were mixed at 80°C. The solvent was removed by distillation. The particles were washed with water and acetone. Properties: BET specific surface area 182 m2/g, spherical particles, mean diameter 792 nm [1892,1893]. TABLE 3.865 PZC/IEP of Silica Obtained from Na2SiO3 in Emulsion Electrolyte

T

Method

Instrument

iep

Brookhaven ZetaPlus

0.001,0.01 M NaCl

pH0 Reference 1.7

[1892,1893]

3.1.35.2.3 Stober Silicas Monodispersed spheres obtained by hydrolysis of diluted Si(EtO)4 in aqueous ethanol (or a mixture of water with another alcohol) in the presence of ammonia are discussed in this section. Different particle sizes are obtained at different concentrations of reagents and at different temperatures. 3.1.35.2.3.1 Rapid Addition of Si(EtO)4 to 4.6 M Ammonia in Aqueous Ethanol at Room Temperature 200 cm3 of Si(EtO)4 was added rapidly to a mixture of 1.2 dm3 of 25% ammonia and 2.6 dm3 of ethanol. After 15 h, the particles were separated by centrifugation and washed with HNO3 solution, and then with water. Properties: Particle diameter 620 nm [363]. TABLE 3.866 PZC/IEP of Stober Silica Obtained by Rapid Addition of Si(EtO)4 to 4.6 M Ammonia in Aqueous Ethanol at Room Temperature Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl 0.001–0.1 M KNO3

20

iep pH

Malvern Zetasizer III

<3 if anya <3 if any

[363,524]

a

IEP at pH 2.5 was found in 0.01 M KCl; in 0.01 M Bu4N and Me4N nitrates, IEP was at pH > 6. No positive s0 was obtained by titration in 0.01 M Li, Bu4N, and Me4N nitrates.

3.1.35.2.3.2 Rapid Addition of Si(EtO)4 to 0.9 M Ammonia in Aqueous Ethanol at Room Temperature 80 cm3 of Si(EtO)4 was added rapidly to a mixture of 267 cm3 of 25% ammonia and 3.653 dm3 of ethanol. After 15 h, the

415

Compilation of PZCs/IEPs

particles were separated by centrifugation and washed with HNO3 solution, and then with water. Properties: Particle diameter 228 nm [363]. TABLE 3.867 PZC/IEP of Stober Silica Obtained by Rapid Addition of Si(EtO)4 to 0.9 M Ammonia in Aqueous Ethanol at Room Temperature Electrolyte 0.001 M KCl a

T

Method

20

iep

Instrument Malvern Zetasizer III

pH0

Reference a

<3 if any

[363]

IEP at pH 2.5 was found in 0.01 M KCl; in 0.01 M Bu4N and Me4N nitrates, IEP was at pH > 6.

3.1.35.2.3.3 Rapid Addition of Si(EtO)4 to 3.6 M Ammonia in Aqueous Ethanol at Room Temperature 5 cm3 of Si(EtO)4 was added rapidly to a mixture of 20 cm3 of 14.5 M ammonia and 60 cm3 of ethanol at room temperature. After 1 h, the mixture was diluted and boiled almost to dryness. TABLE 3.868 PZC/IEP of Stober Silica Obtained by Rapid Addition of Si(EtO)4 to 3.6 M Ammonia in Aqueous Ethanol at Room Temperature Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

25

iep

Rank Brothers MK II

<3 if any

[1894]

3.1.35.2.3.4 Aging of solution of Si(EtO)4 and Ammonia in Aqueous Ethanol at 25°C for 4 h An ethanolic solution, 0.22 M in Si(EtO)4, 2 M in NH3, and 6 M in water, was stirred at 25°C for 4 h. The precipitate was ethanol-washed in an ultrasonic bath. Properties: Spherical, 545 nm in diameter, TEM image available [1895]. TABLE 3.869 PZC/IEP of Stober Silica Obtained by Aging of Solution of Si(EtO)4 and Ammonia in Aqueous Ethanol at 25°C for 4 h Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Powereach JS94E

3.2

[1895]

416

Surface Charging and Points of Zero Charge

3.1.35.2.3.5 Aging of Solution of Si(EtO)4 and Ammonia in Aqueous Ethanol at Room Temperature for 10 h 60 cm3 of Si(EtO)4 and 200 cm3 of 25% NH3 were dissolved in 3 dm3 of ethanol and stirred for 10 h at room temperature. Properties: Particle diameter (dynamic light scattering): 271 nm, BET specific surface area 43 m2/g [1896].

TABLE 3.870 PZC/IEP of Stober Silica Obtained by Aging of Solution of Si(EtO)4 and Ammonia in Aqueous Ethanol at Room Temperature for 10 h Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M KCl

24

pH iep

4.2 4.2

[1896]

Malvern Zetasizer MK III

3.1.35.2.3.6 Si(EtO)4–H2O–NH3–Ethanol Molar Ratio 0.28:10:1.5:26.3, Temperature not Indicated Properties: Average diameter 400 nm [1897].

TABLE 3.871 PZC/IEP of Stober Silica Obtained at Si(EtO)4 –H2O–NH3 –Ethanol Molar Ratio 0.28:10:1.5:26.3, Temperature Not Indicated Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

25

iep

Coulter Delsa

<3.5 if any

[1897]

3.1.35.2.3.7 Aging of Solution of Si(EtO)4 and Ammonia in Aqueous Ethanol at 300K for 2 h A mixture of 181 cm3 of ethanol, 65 cm3 of water, 4.5 cm3 of 28% ammonia, and 70 mmol of Si(EtO)4 was shaken for 2 h at 300K. The precipitate was washed with ethanol and dried in vacuum. Properties: Spherical particles 200 nm in diameter, TEM image available [1898].

TABLE 3.872 PZC/IEP of Stober Silica Obtained by Aging of Solution of Si(EtO)4 and Ammonia in Aqueous Ethanol at 300K for 2 h Electrolyte 0.001 M NaCl

T

Method

Instrument

pH0

Reference

iep

Zeta PALS, Brookhaven

2

[1898]

417

Compilation of PZCs/IEPs

3.1.35.2.3.8 Aging of Solution of Si(EtO)4 and Ammonia in Aqueous Ethanol at 40°C for 1 h An ethanolic solution, 0.26 M in Si(EtO)4, 1.67 M in water and 1.07 M in ammonia, was heated for 1 h at 40∞C. Properties: Mean diameter 510 nm [1899]. TABLE 3.873 PZC/IEP of Stober Silica Obtained by Aging of Solution of Si(EtO)4 and Ammonia in Aqueous Ethanol at 40°C for 1 h Electrolyte

T

0.01 M KNO3

Method

Instrument

pH0

Reference

iep

Malvern Zetamaster

2.9

[1899]

3.1.35.2.3.9 Aging of Solution of Si(EtO)4 and Ammonia in Aqueous Ethanol at 40°C An ethanolic solution, 0.3 M Si(EtO)4, 3 M in water, and 1.15 M in NH3, was heated at 40°C. The precipitate was washed with water. Properties: Diameter 560 nm, TEM image available [233]. TABLE 3.874 PZC/IEP of Stober Silica Obtained by Aging of Solution of Si(EtO)4 and Ammonia in Aqueous Ethanol at 40°C Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Malvern Zetamaster

2.8

[233]

3.1.35.2.3.10 Addition of Ethanolic Solution of Si(EtO)4 to Solution of Ammonia in Aqueous Ethanol at 40°C A mixture of 1.66 kg of ethanol, 1.5 kg of water, and 0.14 kg of NH3 solution was heated at 40°C. A solution of 175 g of Si(EtO)4 in an equal volume of ethanol was added with stirring. The temperature of 40°C was maintained overnight. The original particles were then calcined in air at 500°C, and then boiled in 1 M HNO3 for 4 d. Properties: BET specific surface area 53 m2/g (original), 34 m2/g (calcined), mean diameter 100 nm, particle size distribution, TEM images available [1900]. TABLE 3.875 PZC/IEP of Stober Silica Obtained by Addition of Ethanolic Solution of Si(EtO)4 to Solution of Ammonia in Aqueous Ethanol at 40°C Description Original Calcined Boiled in HNO3

Electrolyte 0.01 M NaClO4

T

Method

Instrument

pH0

Reference

iep

Delsa 440

3.2 3.2 3.2

[1900]

418

Surface Charging and Points of Zero Charge

3.1.35.2.3.11 Addition of Si(EtO)4 to Solution of Ammonia in Aqueous Ethanol (or 2-Propanol) at 40°C Recipe from [1901]: Si(EtO)4 was added to a mixture of ethanol (or 2-propanol), water, and ammonia at 40∞C with stirring. The dispersion was aged at 40∞C for 1 d. The particles were washed with aqueous ethanol and with water, and then dried in vacuum for 1 d at 60∞C. Properties: BET specific surface area 5 m2/g (particles calcined at 700°C), particle diameter 720 nm [1902]. TABLE 3.876 PZC/IEP of Stober Silica Obtained by Addition of Si(EtO)4 to Solution of Ammonia in Aqueous Ethanol (or 2-Propanol) at 40°C Electrolyte

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440

3.7

[1902]

0.001 M HCl + KOH

3.1.35.2.3.12 Addition of Si(EtO)4 to Solution of Ammonia in Aqueous Ethanol at 42°C Under Nitrogen 14 mol of alcohol (ethanol, 2-propanol, 1:1 ethanol: methanol, or 3:1 ethanol-2-propanol), 0.7–1.2 mol of NH4OH, and 6.5–7.5 mol of water were stirred at 42∞C under nitrogen. 0.3 mol of Si(EtO)4 was added. After 1 h, ethanol and ammonia were evaporated at 80∞C, and the solid was washed. Properties: SEM images, average particle diameter available [1903]. TABLE 3.877 PZC/IEP of Stober Silica Obtained by Addition of Si(EtO)4 to Solution of Ammonia in Aqueous Ethanol at 42°C Under Nitrogen Electrolyte

T

0.001 M KBr

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000 HS

2

[1903]

3.1.35.2.3.13 Aging of Solution of Si(EtO)4 and Ammonia in Aqueous Ethanol at 45∞C for 1 h An ethanolic solution, 0.353 M in Si(EtO)4, 1.36 M in NH4OH, and 1.72 M in water, was aged at 45∞C for 1 h. The precipitate was water-washed, and dried at 50∞C. Properties: TEM image available, mean diameter 350 nm [1904]. TABLE 3.878 PZC/IEP of Stober Silica Obtained by Aging of Solution of Si(EtO)4 and Ammonia in Aqueous Ethanol at 45°C for 1 h Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep

Malvern Zetamaster

3

[1904]

419

Compilation of PZCs/IEPs

3.1.35.2.3.14 Addition of Si(EtO)4 to Solution of Ammonia in Aqueous Methanol Si(EtO)4 was added to a mixture of methanol, water, and ammonia, and stirred for 2 h. The precipitate was washed with alcohol and dried for 1 d at 100∞C. Properties: BET specific surface area 8.4 m2/g average particle size 432 nm, SEM image available [1905].

TABLE 3.879 PZC/IEP of Stober Silica Obtained by Addition of Si(EtO)4 to Solution of Ammonia in Aqueous Methanol Electrolyte

T

0.001 M KCl

Method

Instrument

pH0

Reference

iep

ELS 8000 Otsuka

2.5

[1905]

3.1.35.2.3.15 Aging of Solution of Si(EtO)4 and Ammonia in Aqueous 2-propanol at 40–45∞C A 2-propanolic solution, 0.45 M in Si(EtO)4, 3.1 M in water, and 1.16 M in NH3, was heated at 40–45∞C. Properties: TEM image available, particle diameter 780 nm [1901].

TABLE 3.880 PZC/IEP of Stober Silica Obtained by Aging of Solution of Si(EtO)4 and Ammonia in Aqueous 2-Propanol at 40–45°C Electrolyte

T

0.001 M KCl

Method

Instrument

pH0

Reference

iep

Delsa 440

3.5

[1901]

3.1.35.2.3.16 Addition of Si(EtO)4 to Solution of Ammonia in Aqueous 2-Propanol at 40∞C A solution in 2-propanol, 0.45 M in ammonia and 3.05 M in water, was brought to 40∞C, and 0.004 M Si(EtO)4 was added after 30 min. Aging at 40∞C continued for 30 min–18 h. Then the particles were filtered out and dried in vacuum for 1 d. Properties: Perfect spheres [1432].

TABLE 3.881 PZC/IEP of Stober Silica Obtained by Addition of Si(EtO)4 to Solution of Ammonia in Aqueous 2-Propanol at 40°C Electrolyte 0.01 M KNO3

T

Method

Instrument

pH0

Reference

iep

Delsa 440

2.7

[1432]

420

3.1.35.2.3.17

Surface Charging and Points of Zero Charge

Other

TABLE 3.882 PZC/IEP of Stober Silicas Description

Electrolyte

0.001 M KNO3 600 nm diameter 0.001 M KCl or KNO3 0.001 M NaCl 0.15 M NaI 300 nm diameter 0.001 M KCl 300 nm diameter 0.001–0.1 M KCl 650 nm diameter 0.001 M KCl 700 nm diameter 0.01 M LiCl, NaCl, RbCl, CsCl 700 nm diameter 0.001–0.1 M KCl a

b

T

Method

25

iep iep

Instrument

pH0

20

iep iep iep

25 25 25

iep iep iep iep

Delsa 440 <3 if any Matec MBS-8000 <4 if any Malvern Zetasizer IIc Malvern Zetasizer 3 2a Coulter Delsa 440 2–4b Malvern Zetasizer 2.6 3000 Delsa 440 3 Delsa 440 3.4 Delsa 440 3.5 Delsa 440 3.8

25

iep

Delsa 440

3.8

Reference [1906] [1907]

[1911]

[1776] [1908] [1909] [246] [314] [1211] [1910]

Arbitrary interpolation, no data points between pH 1.5 and 6. SEM image available, particle diameter 340 nm, BET specific surface area 9.5 m2/g. Positive value at pH 2, negative value at pH 4, no data points between. Recipe from Reference 7a in [1908]. TEM image available, average diameter 155–177 nm (different methods).

3.1.35.2.4 From Si(EtO)4 (other than Stober) 3.1.35.2.4.1 Calcined for 1 d at 600°C 366 cm3 of Si(EtO)4, 170 cm3 of ethanol, and 400 cm3 of water were stirred for 18 h. The dispersion was then gradually heated until gelation. The gel was dried at 110∞C in air overnight, broken into 40–80 mesh, and calcined for 1 d at 600∞C [1068]. Properties: Single-point BET specific surface area 648 m2/g [1068].

TABLE 3.883 PZC/IEP of Silica Obtained from Si(EtO)4 and Calcined for 1 day at 600°C Electrolyte 0.001–0.1 M NaNO3

T

Method pH Mass titration

Instrument

pH0

Reference

3.2 3.5

[1068]

421

Compilation of PZCs/IEPs

3.1.35.2.4.2 Calcined for 16 h at 875K From Si(EtO)4 in water–alcohol medium at room temperature, dried at 385K for 20 h, and calcined for 16 h at 875K. Properties: BET specific surface area 577 m2/g [1912]. TABLE 3.884 PZC/IEP of Silica Obtained from Si(EtO)4 and Calcined for 16 h at 875K Electrolyte

T

Method

Instrument

Mass titration a

pH0 3.8

Reference

a

[1912]

Only value, data points not reported.

3.1.35.2.4.3 Calcined at 500°C Si(EtO)4 was hydrolyzed with 28% aqueous ammonia. The product was calcined at 500∞C. Properties: BET specific surface area 428 m2/g [979]. TABLE 3.885 PZC/IEP of Silica Obtained from Si(EtO)4 and Calcined at 500°C Electrolyte

T

Method

0.01 M KCl

40

pH

Instrument

pH0

Reference

<5.8

[979]

3.1.35.2.4.4 Obtained at pH 8 27.8 g Si(EtO)4 was stirred with 58 cm3 of water adjusted to pH 2 with HNO3. 2 M NH3 was added dropwise to adjust the pH to 8. The gel was washed with water and ethanol. Properties: BET specific surface area 581 m2/g [1273]. TABLE 3.886 PZC/IEP of Silica Obtained from Si(EtO)4 at pH 8 Electrolyte 0.001–0.1 M NaNO3

T

Method pH

Instrument

pH0

Reference

5.7, merge

[1273]

3.1.35.2.4.5 In Emulsion 10 cm3 of Si(EtO)4 was added within 10 min into 270 cm3 of emulsion 5.2 M in cyclohexane, 0.72 M in water, 0.18 M in hexanol (no hexanol with Igepal), 0.12 M in Triton N-101 (or Igepal CO-520), and 0.094 M in NH4OH. The dispersion was aged for 1 d and the particles were washed with water. Properties: Particle size available (different Recipes) [1913].

422

Surface Charging and Points of Zero Charge

TABLE 3.887 PZC/IEP of Silica Obtained from Si(EtO)4 in Emulsion Description

Electrolyte

T

Method iep

a

Instrument

pH0

Malvern Zetasizer 4

3.8

a

Reference [1913]

2.5 for silica–CdS composite; only value, data points not reported.

3.1.35.2.4.6 In the Presence of Polymer 1 g of a copolymer Pluronic 127, 30 g of 2 M HCl, and 7.5 g of water were mixed. Then 2.28 cm3 of Si(C2H5O)4 was added. The mixture was stirred for 1 d at room temperature and aged for 20 h at 100∞C. The precipitate was washed, and calcined for 6 h at 500∞C. Properties: BET specific surface area 537 m2/g [1811].

TABLE 3.888 PZC/IEP of Silica Obtained from Si(EtO)4 in Presence of Polymer Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer

2.8a

[1811]

Only value, data points not reported.

3.1.35.2.5 MCM-41 3.1.35.2.5.1 Recipe from [2996] 250 cm3 of 25 % ammonia was mixed with a solution of 2 g CTABr in 270 cm3 of water. 10 cm3 of Si(C2H5O)4 were added, and the dispersion was stirred for 2 h. The precipitate was washed, dried, and calcined at 600∞C for 6 h.

TABLE 3.889 PZC/IEP of MCM-41 Obtained According to Recipe from [2996] Electrolyte 0.01 M NaNO3

T

Method pH

Instrument

pH0

Reference

7.1

[2996]

3.1.35.2.5.2 Recipe from [1811] 10 g of CTABr, 1 g of NaOH, and 90 g of water were mixed at 35∞C. Then 9 cm3 of Si(C2H5O)4 and 2.5 cm3 of 2-cyanoethyltriethoxysilane were added. The mixture was mixed at 35∞C for 30 min and heated at 150∞C for 1 d. The solid was heated in water for 10 min at 70∞C and calcined for 6 h at 650∞C. Properties: BET specific surface area 1000 m2/g [1811].

423

Compilation of PZCs/IEPs

TABLE 3.890 PZC/IEP of MCM-41 Obtained According to Recipe from [1811] Electrolyte

T

Method iep

a

Instrument Malvern Zetasizer

pH0

Reference

a

3.6

[1811]

Only value, data points not reported.

3.1.35.2.5.3 Pure Siliceous MCM-41, Recipe from [1914] 6 g of aerosil and 2 g of NaOH were dissolved in 90 g of water at 60–70∞C. A solution of 9.1 g CTABr in 30 g of water was added dropwise, and the pH was adjusted to 11 with 2 M HCl. After 3 h under stirring at room temperature, the mixture was aged for 3 d at 100∞C, and the precipitate was washed, dried, and calcined at 600∞C for 10 h. Properties: BET specific surface area 870 m2/g [1915]. TABLE 3.891 PZC/IEP of MCM-41 Obtained According to Recipe from [1914] Electrolyte

T

Method

Instrument

pH0

Reference

iep

ZetaPlus 100

6.9a

[1915]

NaOH + HNO3 a

Only value, data points not reported.

3.1.35.2.6 Other 3.1.35.2.6.1 Oxidation of Silicon Ethoxide Vapor in Air at 1100∞C Specific surface area 78 m2/g, XRD pattern available [1086].

Properties:

TABLE 3.892 PZC/IEP of Silica Obtained by Oxidation of Vapor of Silicon Ethoxide in Air at 1100°C Electrolyte

T

NaOH + HCl

Method

Instrument

pH0

iep

Malvern Zetasizer 3000

2.2

Reference [1086]

3.1.35.2.6.2 Flame Hydrolysis Deposition Properties: Amorphous, SEM image available, >99.9% pure, BET specific surface area 13.4 m2/g [604]. TABLE 3.893 PZC/IEP of Silica Obtained by Flame Hydrolysis Deposition Electrolyte 0.001–0.1 M NaCl a

T

Method

Instrument

cip

No clear CIP. PZC at pH 3.5 is reported in text.

pH0

Reference

4a

[604]

424

3.1.35.2.6.3

Surface Charging and Points of Zero Charge

A Film Deposited from SiCl4 Vapor and Wet Nitrogen

TABLE 3.894 PZC/IEP of Silica Film Deposited from SiCl4 Vapor and Wet Nitrogen Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electro-osmosis

<2.2 if any

[1823]

0.01 M NaCl

3.1.35.2.6.4

Precipitated

TABLE 3.895 PZC/IEP of Precipitated Silicas Description Two specimens

Electrolyte

T

Method

KCl

Salt addition

Several specimens, 0.002–0.04 M NaCl particle size 0.002–1 M NaNO3 10–12 nm a

Instrument a

pH0 3.5 3.4 <2.5 if any

pH iep

Reference [1916] [544,1754]

Only value, data points not reported.

3.1.35.2.6.5 Recipes from [1917], Three Samples from Sodium Silicate and HCl

TABLE 3.896 PZC/IEP of Silicas Obtained According to Recipes from [1917] BET Specific Surface Area (m2/g) 470 795 255

Electrolyte 0.01 M KCl

T

Method pH

Instrument Equilibrated for a few days

pH0

Reference

<7 if any

[553]

3.1.35.3 Natural 3.1.35.3.1 Quartz from Argentina Properties: 99.9% pure, BET specific surface area 1 m2/g [576].

425

Compilation of PZCs/IEPs

TABLE 3.897 PZC/IEP of Quartz from Argentina Electrolyte

T

Method

0.001–0.1 M KCl

3.1.35.3.2

Instrument

pH

pH0

Reference

2.3

[576]

Quartz from Brazil

Table 3.898 PZC/IEP of Quartz from Brazil Description

Electrolyte

Acid-washed

0–0.01 M KNO3

Acid-washed Hot HCl-washed 0.68 m2/g >99.9% pure, 0.09 m2/g Soxhlet extraction with HCl then with water for 8 h, aged HCl- and water-washed, ground From Minas Gerais Ground, acid- and water-washed, aged

0.01 NaCl

a b

c

0.001 M KNO3 0.001–1 M KNO3

T

Method

Instrument

35

iep

Streaming potential

22 25

iep iep iep pH

Streaming potential Electrophoresis Zeta-Meter 3.0

iep

Electrophoresis

1.5

[1922]c

iep

Streaming potential

2 1–2 2.7–3 2.3

[211]c

3.7

[1923]c

HCl 0.0001 M NaCl

pH iep

0.0001–0.1 M NaCl

iep

Rank Brothers Streaming potential Streaming potential

pH0

Reference

<2 if any [288a,486, 1918b] <2 if any [1940] <3 if any [1919] <3 if any [1920] <4 if any [178,1921]

[241]

Also 65°C. Different washing procedures, 27 or 25°C, 0–0.01 M KNO3. Also results quoted after unpublished work of Fujii, obtained at 25°C. Only value, data points not reported.

3.1.35.3.3 Opal from Brazil Properties: BET specific surface area 8.5 m2/g [1924]. TABLE 3.899 PZC/IEP of Opal from Brazil Electrolyte 0.1, 0.7 M NaCl, KCl

T

Method pH

Instrument

pH0

Reference

<6 if any

[1924]

426

Surface Charging and Points of Zero Charge

3.1.35.3.4 Quartz from Xinjiang Keketuohai, China Properties: 99.8% pure [1309]. TABLE 3.900 PZC/IEP of Quartz from Xinjiang Keketuohai, China Electrolyte

T

Method

Instrument

pH0

Reference

None

22

iep

Brookhaven ZetaPlus

<2.2 if any

[1309]

3.1.35.3.5 From Karina Mine in Columbia, Purchased from Ward’s Properties: BET specific surface area of ground samples 11.6 and 10.4 m2/g [1925]. TABLE 3.901 PZC/IEP of Quartz from Karina Mine in Columbia Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer Pen Kem Laser Zee Meter 501

<3 if any

[1925,1926]

0.002 M KNO3

3.1.35.3.6 Quartz Sand from Fontainebleau, France Properties: Elementary analysis available, BET specific surface area 5.1 m2/g [1928]. TABLE 3.902 PZC/IEP of Quartz Sand from Fontainebleau, France Electrolyte

T

Method

0.001 M NaCl a

iep/pH

Instrument Electrophoresis

pH0

Reference a

2.4/3.8

[1928]

Only value, data points not reported.

3.1.35.3.7

Obsidian from Iceland

TABLE 3.903 PZC/IEP of Obsidian from Iceland Electrolyte NaOH + HClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

2

[104]

427

Compilation of PZCs/IEPs

3.1.35.3.8 Quartz from Kanchekera, India, Ground and Acid-Washed Properties: 99.9% pure [908]. TABLE 3.904 PZC/IEP of Quartz from Kanchekera, India Electrolyte

T

0.002 M KNO3

Method

Instrument

pH0

Reference

iep

Rank Brothers Mark II

<2 if any

[1108]

pH0

Reference

<6 if any

[1929]

pH0

Reference

2.5

[1442]

3.1.35.3.9 From Mount Myoken, Japan Properties: BET specific surface area 0.5 m2/g [1929]. TABLE 3.905 PZC/IEP of Quartz from Mount Myoken, Japan Electrolyte

T

Method

0.1, 1 M NaCl

24

pH

3.1.35.3.10

Instrument

Quartz from Olden, Sweden

TABLE 3.906 PZC/IEP of Quartz from Olden, Sweden Electrolyte

T

Method

Instrument

pH

3.1.35.3.11 Quartz from Harding Mine, New Mexico, HCl- and WaterWashed, Aged TABLE 3.907 PZC/IEP of Quartz from Harding Mine, New Mexico Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

1.8

[1922]a

Only value, data points not reported.

3.1.35.3.12

Biogenic Silicas and Products of their Processing

3.1.35.3.12.1 Phytoliths A: debris of leaves and stems of bamboo (Nastus borbonicus) extracted from soil.

428

Surface Charging and Points of Zero Charge

B: A heated at 450°C. C: fresh plant pieces washed in 1 M HCl and heated at 450°C for 6 h. Properties: 2–60 μm pieces, silica 92%, water 6%, carbon 1.7%, Al 0.04%, Fe 0.08%, BET specific surface area (A, B, C) 5.2, 6.5, 159.5 m2/g, SEM image available [196]. TABLE 3.908 PZC/IEP of Phytoliths Description A B C

Electrolyte

T

Method

Instrument

0.001–0.05 M NaCl

25

iep/pH

Zetaphoremeter 4000, CAD

pH0

Reference

<2/— 2.5/5 <2/—

[196]

3.1.35.3.12.2 “Pocket” from Katadyn Products Diatomaceous earth-based filter element. Properties: BET specific surface area 2.2 m2/g, SEM image available [1930]. TABLE 3.909 PZC/IEP of “Pocket” from Katadyn Products Electrolyte

T

Method

Instrument

pH0

Reference

iep

SurPASS, Paar

<3 if any

[1930,1931]

0.001 M KCl

3.1.35.3.12.3

Other

TABLE 3.910 PZC/IEP of Other Biogenic Silicas Description a

2

Caligus mulleri, 202 m /g Biosiliceous ooze, 101 m2/g a

Electrolyte

T

0.7 M NaCl

22

Method Instrument pH

pH0

Reference

<4 if any

[1788]

Organic matter removed by enzymatic cleaning.

3.1.35.3.13

Origin Unknown

TABLE 3.911 PZC/IEP of Other Natural Silicas Description From Ishikawa, Japan

Electrolyte 0.001 M KNO3

T

Method iep

Instrument ZeeCom ZC-2000

pH0

Reference

<2.5 if any

[2023]

continued

429

Compilation of PZCs/IEPs

TABLE 3.911 (continued) Description

Electrolyte

As pure as possible Ultrapure quartz sand Warm 23% HNO3-washed Water-washed, and dried at 110°C Water-washed 16 m2/g a b

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

<2.5 if any

[227]

0.01 M NaCl

iep

Electrophoresis

<3 if any

[1932]

0.001 M KNO3

iep

Laser Zee Meter 501

1.8a

[472]

0, 0.001 M KCl 25

iep

Rank Mark II

2.2

[1213]

0.1 M NaCl

iep Titration

Rank Mark I

2.5 3b

[1933] [1449]

25

Fraction below 38 mm. Only value, data points not reported.

3.1.35.4

Origin Unknown

3.1.35.4.1 Quartz TABLE 3.912 PZC/IEP of Quartz from Unspecified Sources Description Washed with hot concentrated HCl Fused quartz capillary, 99.9% SiO2 2

5 m /g Plate

Plate 0.05 m2/g 6.5 m2/g

Electrolyte

T

None 0.0001–0.1 M 20 NaCl

0.001 M KNO3 0.0001– 0.01 M NH4NO3 0.0001 M KCl 1 M LiCl 0.1, 0.7 NaCl, KCl HCl 0.01 M KNO3

25

20

Method

Instrument

pH0

Reference

iep iep

Streaming potential <1.4 if any [1934] Streaming potential <1.5 if any [574]

iep

Streaming potential <2 if any

iep iep

Electrophoresis Zeta-Meter

<2.5 if any [1306]a <3 if any [1231]

iep

Electrophoresis, open cell

<3 if any

[499]

iep

Electrophoresis

<4 if any

[1389]

<5 if any <6 if any

[1938] [1924]

pH pH iep iep

Electro-osmosis

1 1.8

[1117,1935– 1937]

[280] [1107]b continued

430

Surface Charging and Points of Zero Charge

TABLE 3.912 (continued) Description Powder

Electrolyte

T

0.001 M KCl

Method iep

Matec ESA 8000 EKA Anton Paar Malvern Zetasizer 3000 HAS Streaming potential

Washed

25

iep

Capillary 0.01 M NaCl Capillary 60–80 mesh, 50 ppm 0–0.01 M NaCl Al2O3, washed in boiling HNO3

20

iep iep iep

a b

Instrument

Streaming potential

pH0

Reference

2 [1939] <2.5 if any 2.1

[358]b

2.5 3 3

[1119] [540] [1818]

Cited after Kim’s thesis (Reference 2). Only value, data points not reported.

3.1.35.4.2 Vitreous Silica Capillaries TABLE 3.913 PZC/IEP of Vitreous Silica Capillaries from Unspecified Sources Description

Electrolyte

T

Method

Annealed at >800°C, 0.001–0.01 M Room then aged and steamed KNO3 0.001 M KNO3 25 Acid-washed and 0.0001–0.01 M steamed KNO3 Annealed at >800°C 0.001–0.01M Room KNO3

Instrument

pH0

Reference

iep

Electro-osmosis <3 if any

[1941]

iep iep

Electro-osmosis <3 if any Streaming <3 if any potential Electro4 osmosis

[1231] [1942]

iep

[1941]

3.1.35.4.3 Other TABLE 3.914 PZC/IEP of Silicas from Unspecified Sources Description Plate, HNO3washed

Electrolyte 0.001 M KCl

T 25

Method iep

Instrument

pH0

Pen Kem 3000 <2 if any from <2 if any mobility profile

Reference [276]

continued

431

Compilation of PZCs/IEPs

TABLE 3.914 (continued) Description Colloidal, 387 m2/g

Electrolyte

T

0.01–1 M LiNO3, KNO3, CsNO3 0.001 M KCl

25

Method pH iep

0.0001–0.1 M Fused, 0.001 M KCl HNO3-washed

21

iep iep

Spherical

0.0002 M NaCl

iep

Gel, 257 m2/g

0.1, 0.7 NaCl, KCl

pH

Sol or gel

iep

340 m2/g

iep 0.1 M KCl

Room

Spherical, 500 nm

Streaming potential

<3 if any

[1943]

<3 if any

[1098]

<3.5 if any [1944] <3.5 if any [298]

Rank Brothers <4 Mark II <6 if any Electroosmosis Electroosmosis

[1945] [1924]

0.5a

[1214]

1.8

[1102]a [1103] [1718]

1.8

Brookhaven ZetaPlus

Reference

[1946–1948]a

2 2 2–3 2 2.5

[1949,1950]a [1951]

2.5

[1101,1618]a

0.1 M KCl

2.9 3

[1111]a [1112]a

KCl

pH

3.1

[1362]a

31 μm, 11 m2/g

a

Mass titration iep pH iep pH iep

Zetasizer 4

pH0

Titration iep Titration pH

a form, 3.3 m2/g

a, 4 m2/g >99.9% pure, 175 m2/g

Instrument

Only value, data points not reported.

3.1.36

TIN (HYDR)OXIDES

Tin forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation (+2 or +4), degree of hydration, and crystallographic structure. Nominal degree of oxidation and hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of oxidation and hydration. PZCs/IEPs of tin (hydr)oxides are presented in Tables 3.915 through 3.939.

432

Surface Charging and Points of Zero Charge

3.1.36.1

SnO, Origin Unknown

TABLE 3.915 PZC/IEP of SnO Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electro-osmosis

5.2

[1103a,1217]

0.01 M KCl a

Only value, data points not reported.

3.1.36.2

Hydrous SnO Obtained from SnCl2 and NaOH TABLE 3.916 PZC/IEP of Hydrous SnO Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.6

[1229]a

Only value, data points not reported. The same IEP is reported in [2226] for a precipitate termed hydroxide.

3.1.36.3 SnO2 3.1.36.3.1

Commercial

3.1.36.3.1.1 SnO2 from Aldrich Properties: 20 ppm Fe, Si 60 ppm, BET specific surface area 20–27.9 m2/g (different methods) [538], 26.6 m2/g [1952]. TABLE 3.917 PZC/IEP of SnO2 from Aldrich Purity

Electrolyte

T

Method

Instrument

99.9999% 0.0001–1 M KNO3

99.999% High

22 cip 25 iep Salt titration 25 iep 0.001 M KNO3 0.0001, 0.001 M KCl iep

Rank Brothers Mark II Rank Brothers Mark II Streaming potential

pH0

Reference

4.3 4.5 4.2 4.5 4.7

[538,1952]

[1953] [825]

3.1.36.3.1.2 Origin Unknown, Water-Washed, and Dried at 110°C Table 3.918 PZC/IEP of SnO2 from Unknown Commercial Source Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M KCl

25

iep

Rank Mark II

2

[1213]

433

Compilation of PZCs/IEPs

3.1.36.3.2

Synthetic

3.1.36.3.2.1 From Chloride 3.1.36.3.2.1.1 From SnCl4 and NH3 Properties: 0.01% Si, 0.008% Al [546], cassiterite [546], BET specific surface area 40.3 m2/g [324], specific surface area 240 m2/g [546], primary particles 3–7 nm [546].

Table 3.919 PZC/IEP of SnO2 Obtained from SnCl4 and NH3 Electrolyte

T

0.001–0.5 M NaCl 25 0.01 M NaCl 0.001–1 M KCl a

20

Method cip iep cip iep

Instrument

pH0

Reference

4.5 [324] 4.5 4.1 [546,1119]a 3.8

Thomas & Co. Electrophoresis

Purified by electrodialysis, and dried at 105°C.

3.1.36.3.2.1.2 From SnCl4 and NaOH 0.5 M NaOH was added dropwise to SnCl4 solution (24 g Sn/dm3). The precipitate was aged for 40 min.

TABLE 3.920 PZC/IEP of SnO2 Obtained from SnCl4 and NaOH Electrolyte

T

0.3 M NH4NO3

Method

Instrument

pH0

Reference

iep

Zeta-Meter

7

[1189]

3.1.36.3.2.1.3 Aging of SnCl4 Solution at 100∞C Recipe A: A solution 0.003 M in SnCl4 and 0.3 M in HCl was aged for 2 h at 100∞C. Recipe B: A solution 0.003 M in SnCl4 and 0.3 M in HCl and 0.3 M in urea was aged for 2 h at 100°C. Properties: TEM images, XRD results, IR absorption spectrum, particle size data (depends on solid-to-liquid ratio) available [1954].

TABLE 3.921 PZC/IEP of SnO2 Obtained by Aging of SnCl4 Solution at 100°C Electrolyte 0.01 M NaClO4

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440

4.2

[1954]

434

Surface Charging and Points of Zero Charge

3.1.36.3.2.2 From Alkoxide, Calcined 4.9 moles of water were added dropwise to a solution of 0.06 mole of Sn(C4H9O)4 in 44 cm3 of 2-propanol. The dispersion was stirred for 2 h at room temperature and heated for 20 h at 80∞C. Then the gel was calcined for 2 h at different temperatures. Properties: Cassiterite, XRD patterns available [1955]. TABLE 3.922 PZC/IEP of SnO2 Obtained from Alkoxide and Calcined Calcination Temperature (°C), BET Specific Surface Area (m2/g) Electrolyte 300, 95 500, 40 700, 15

T

0.01 M KNO3

Method Instrument iep

Coulter Delsa 440

pH0 Reference 4.2 3.8 3.6

[1955]

3.1.36.3.2.3 Calcination of Material Described in Section 3.1.36.4.1 at 1000∞C for 2h TABLE 3.923 PZC/IEP of SnO2 Obtained by Calcination of Material Described in Section 3.1.36.4.1 Electrolyte

T

Method

Instrument

iep

Electrophoresis

HCl + NaOH

pH0 (Fig. 2/Table 1) Reference 6.5/5.5

[1091]

3.1.36.3.2.4 From Tin Citrate Recipe from [1956]: Tin citrate solution in ethylene glycol containing HNO3 was heated at 180–200∞C. Then the product was heated at 450∞C for 4 h and at 500∞C for 15 h. Properties: BET specific surface area 32.1 m2/g [1957]. TABLE 3.924 PZC/IEP of SnO2 Obtained from Tin Nitrate Electrolyte KOH + HNO3

T

Method iep

Instrument Matec ESA 8000

pH0

Reference

3.8

[1957]

3.1.36.3.2.5 Synthetic, Sintered At Different Temperatures Properties: 0.1–0.5% Al, 0.01% Si, 0.02% Fe by mass [1958].

435

Compilation of PZCs/IEPs

Table 3.925 PZC/IEP of Synthetic SnO2 Sintered at Different Temperatures Sintering Temperature (°C)

Electrolyte

1050 1250 1400 a b c

T

Method

NaOH + HCl

iep

Instrument

pH0

Reference

Zeta-Meter

a

[1958]

>4 >5.2b >5.6c

+9 mV at pH 4, −10 mV at pH 6. +18 mV at pH 5, −10 mV at pH 6.2. +12 mV at pH 5.6, −12 mV at pH 6.8.

3.1.36.3.3

Natural Cassiterites

3.1.36.3.3.1 From Greenbushes, Australia Properties: 0.1–1% Ta, 0.1–1% Nb, 0.1–0.5% Sb, 0.5–1% Ti, 0.05–0.2% Al, 0.05–0.5% Si, 0.1–0.5% Fe, 0.05% Zr by mass [1958].

TABLE 3.926 PZC/IEP of Cassiterite from Greenbushes, Australia Description

Electrolyte

Original Water-washed

NaOH + HCl

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

6.5 6.5

[1958]

3.1.36.3.3.2 From South Palmer River, Australia Washed with hot HClO4 and HF. Properties: Impurity level (in ppm) Fe 2500, Nb 1500, Ti 600, W 1000, Si 150, V 15, BET specific surface area 1 m2/g [538].

TABLE 3.927 PZC/IEP of Cassiterite from South Palmer River, Australia Electrolyte

T

Method

0.001–1 M KNO3

22 25

cip iep Salt titration

Instrument Rank Brothers Rank II

pH0 5.2; 4.3 4.2 4.6

Reference [538]

436

Surface Charging and Points of Zero Charge

3.1.36.3.3.3 From Elsmore, Australia Washed with hot HClO4 and HF. Properties: Impurity level (in ppm) Fe 800, Nb 700, Ti 2500, W 800, Si 150, V 15, Zr 150, BET specific surface area 0.8 m2/g [538]. TABLE 3.928 PZC/IEP of Cassiterite from Elsmore, Australia Electrolyte

T

Method

0.001–1 M KNO3

22 25

cip iep Salt titration

Instrument

pH0

Rank Brothers Rank II

4.6; 4.3 4.4 4.4

Reference [538]

3.1.36.3.3.4 From Taronga, Australia Washed with hot HClO4 and HF. Properties: Impurity level (in ppm) Fe 1000, Ti 1000, W 600, Si 200, V 250, BET specific surface area 0.7–1.1 m2/g (different methods) [538].

TABLE 3.929 PZC/IEP of Cassiterite from Taronga, Australia Electrolyte

T

0.001–1 M KNO3

22 25

Method cip iep Salt titration

Instrument

pH0

Rank Brothers Rank II

4.7; 4.4 4.5 4.5

Reference [538]

3.1.36.3.3.5 From Rossarden, Australia Properties: Impurity level (in ppm) Fe 300, Ti 2500, W 200, Si 200, V 20, Zr 100, BET specific surface area 0.6–1.3 m2/g (different methods) [538].

TABLE 3.930 PZC/IEP of Cassiterite from Rossarden, Australia Electrolyte

T

0.001–1 M KNO3

22 25

Method cip iep Salt titration

Instrument

pH0

Reference

Rank Brothers Rank II

4.1 4.1 4.2

[538]

3.1.36.3.3.6 From Wenshan, Yunnan Province, China Washed with HCl. Properties: 94% pure, 4.3% SiO2, 0.1% CaO, 0.01% MgO [1959].

437

Compilation of PZCs/IEPs

TABLE 3.931 PZC/IEP of Cassiterite from Wenshan, Yunnan Province, China Electrolyte

T

Method

Instrument

pH0

Reference

iep

ZP-10B Shimadzu

4.7

[1959]

3.1.36.3.3.7 From Phuket, Thailand Properties: 0.1–1% Ta, 0.1–1% Nb, 0.5–1% Ti, 0.05–0.2% Al, 0.05–0.5% Si, 0.1–0.5% Fe, 0.05% Zr by mass [1958]. TABLE 3.932 PZC/IEP of Cassiterite from Phuket, Thailand Description

Electrolyte

Original Water-washed

NaOH+HCl

T

Method

Instrument

iep

Zeta-Meter

pH0 5 6.5

Reference [1958]

3.1.36.3.3.8 Other TABLE 3.933 PZC/IEP of Other Natural Cassiterites Description

Electrolyte

T

Method

Altenburg, Germany

None

iep

Unificada, Bolivia

NaOH/HCl NaOH/HNO3 KCl

iep

Zimbabwe Maniema, Democratic Republic of the Congo Brittany, France Potasi KCl Catair, Bolivia Bastar, India, 5 m2/g 0.0001 M KNO3 Aberfoyle, Cleveland, 0.001 M KNO3 2–6 μm, magnetically separated and acid-leached, 94% pure, 0.6% Fe, then ground

iep

Egypt

iep

HCl + NaOH

Instrument

pH0

Reference

<3 if any 3.1 3.7 3.4 3.9

[1960] [1961]b [1962]b

4.5 pH iep iep

Zeta-Meter 3.0 Hamilton-Stevens microelectrophoresis cell

4 4 4.2 4.2

[1963]b [1964] [1965]

<2 if any

Streaming potential

4.5

[1966] continued

438

Surface Charging and Points of Zero Charge

TABLE 3.933 (continued) Description

Electrolyte

St Renan Three samples, from Australia, washed and dried at 110°C: Low in Fe, 74.6% Sn High in Fe, 75.4% Sn Low in Fe, 75.8% Sn Consolidated Mining and Smelting Co. of Trail, BC; washed with hot 10% HNO3; 99.5% pure, contains SiO2 and ZrO2; 0.04 m2/g. South Woodburn, Australia, HCl- and water-washed, dried at 120°C a

b

T

0–0.01 M KCl

HCl NaOH HCl 0.001–1 M KNO3, KCl

iep iep

25

HCl + NaOH KOH

Method

Instrument Streaming potential Streaming potential

Merge

iep iep

pH0

Reference

4.5

[1967] [1968]

>5a 9.5 >5a 5.5

[583]

7.3 8.5

[1091] [1092]

Electrophoresis Streaming potential

The estimated value of 4.7 reported in [1] and cited by many others is not supported by data in the original publication. Only value, data points not reported.

3.1.36.3.4

Other

TABLE 3.934 PZC/IEP of SnO2 from Unspecified Sources Description

Electrolyte

BET specific 0.1 M KCl surface area 2.5 m2/g 0.01 M KCl

Washed a

KNO3 0.001–1 M NaNO3

T

Method

Instrument

Room Mass titration

25

Only value, data points not reported.

iep iep Coagulation pH pH

pH0 4

Electro-osmosis

Reference [1718]a

4.2 [1103a,1217] 4.4 [1107] 5.5 [1112]a 5.7 [1241]a

439

Compilation of PZCs/IEPs

3.1.36.4

Hydrous SnO2

3.1.36.4.1 From Metallic Sn and Dilute HNO3 Reacted at 80∞C for 8h. Filtered and washed.

TABLE 3.935 PZC/IEP of Hydrous SnO2 Obtained from Metallic Sn and HNO3 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

5.5/4.5a

[1091]a

HCl + NaOH a

Fig. 2/Table 1.

3.1.36.4.2 From SnCl4 Solution Neutralized with Ammonia Aged for 2 d, and dried.

TABLE 3.936 PZC/IEP of Hydrous SnO2 Obtained from SnCl4 and Ammonia Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3

3–5a

[520]

0.1 M LiNO3, KNO3, CsNO3 (experimental) or 0.01 M (results) a

Positive at pH 3, negative at pH 5.

3.1.36.4.3 From SnCl4 and Stoichiometric Amount of Ammonia A stoichiometric amount of 0.25 M NH3 was added to 0.25 M SnCl4. The precipitate was washed with 0.01 M HNO3 and with water, dried at 50°C, and stored over saturated NH4Cl. Properties: a-stannic acid, DTA results available, BET specific surface area 153 m2/g [1660].

TABLE 3.937 PZC/IEP of a-Stannic Acid Obtained from SnCl4 and Stoichiometric Amount of Ammonia Electrolyte

T

Method

0.001 M NaCl

25

pH

a

Only value, data points not reported.

Instrument

pH0

Reference

4.4

[1660,1661a]

440

Surface Charging and Points of Zero Charge

3.1.36.4.4 From SnCl4 Solution and NaOH TABLE 3.938 PZC/IEP of Hydrous SnO2 Obtained from SnCl4 Solution and NaOH Electrolyte

T

0.01 M a

Method

Instrument

pH0

Reference

iep

Electrophoresis

3.9

[1229]a

Only value, data points not reported. The same IEP is reported in [2226] for a precipitate termed hydroxide.

3.1.36.5 Sn(OH)4 A solution 0.0037 M in SnSO4, 0.18 M in HCl, and 1.48 M in urea was heated for 1 h at 80°C. Properties: Amorphous (XRD pattern available), SEM image, TGA and DTA curve available [1428]. TABLE 3.939 PZC/IEP of Sn(OH)4 Electrolyte

T

Method

Instrument

iep

Pen Kem 3000

0.001 M

3.1.37

pH0 Reference 4.5

[1428]

TANTALUM (HYDR)OXIDES

Tantalum forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation, degree of hydration, and crystallographic structure. Nominal degree of oxidation and hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of oxidation and hydration. PZCs/IEPs of tantalum (hydr)oxides are presented in Tables 3.940 through 3.948. 3.1.37.1 Ta2O5 3.1.37.1.1

Commercial

3.1.37.1.1.1

Ta2O5 from Aldrich

TABLE 3.940 PZC/IEP of Ta2O5 from Aldrich Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

23

iep

Streaming potential

4.6a

[261]

a

Only value, data points not reported.

441

Compilation of PZCs/IEPs

3.1.37.1.1.2 Ta2O5 from Merck [1677].

Properties: BET specific surface area 1.6 m2/g

TABLE 3.941 PZC/IEP of Ta2O5 from Merck Acid- and base-washed Washed

a

Electrolyte

T

Method

Instrument

pH0

Reference

0.0001–0.1 M KCl, NaCl, NaClO4 0.01, 0.1 M NaNO3

25a

iep Electrolyte titration cip iep

ZetaPlus Brookhaven

5.3 5–5.2

[1677]

Acustosizer

5.3

[350]

25

Also 15 and 35°C.

3.1.37.1.2 Synthetic 3.1.37.1.2.1 Oxidation of Ta at 1350°C 7 mm [1969].

Properties: b-form, particle radius

TABLE 3.942 PZC/IEP of Ta2O5 Obtained by Oxidation of Ta at 1350°C Electrolyte

T

Method

0.0001–1 M KCl a

Instrument

pH

pH0

Reference

5.2–8.2a

[1969]

Only value, data points not reported.

3.1.37.1.2.2 Oxidation of Ta at 500°C A 130 nm thick layer of metallic Ta was deposited on the inner surface of quartz capillary, and then oxidized in oxygen at 500∞C for 2 h.

TABLE 3.943 PZC/IEP of Ta2O5 Obtained by Oxidation of Ta at 500°C Electrolyte 0.001–0.1 M NaCl, LiCl

T

Method

Instrument

pH0

Reference

iep

Streaming potential

3.8–4.4 3.3–3.6

[1935]

3.1.37.1.2.3 Oxidation of Ta at 550°C A 130–150 nm thick layer of metallic Ta was deposited on silicon, and then oxidized in oxygen at 550∞C for 2 h. Properties: Amorphous [1882].

442

Surface Charging and Points of Zero Charge

TABLE 3.944 PZC/IEP of Ta2O5 Obtained by Oxidation of Ta at 550°C Electrolyte

T

0.001–0.1 M NaCl a

Method

24

Instrument

iep

Streaming potential

pH0 a

3

Reference [1882]

IEP in the range 2.7–3.2 was obtained under different experimental conditions: increasing or decreasing pH, fresh or 7- or 13-day aged.

3.1.37.1.2.4 Precipitation and Annealing at 800°C Properties: b-form, BET specific surface area 1 m2/g, particle radius 12.5 mm [1969]. TABLE 3.945 PZC/IEP of Ta2O5 Obtained by Precipitation and Annealing at 800°C Electrolyte

T

Method

0.0001–1 M CsCl, KCl, NaCl, LiCl

Instrument

pH

pH0

Reference

<2 if any

[1969]

3.1.37.1.2.5 Gradual Dehydration Properties: BET specific surface area 2 m2/g, amorphous, particle radius 6.5 mm [1969]. TABLE 3.946 PZC/IEP of Ta2O5 Obtained by Gradual Dehydration Electrolyte

T

Method

0.0001–1 M CsCl, KCl, NaCl, LiCl

Instrument

pH

pH0

Reference

<2 if any

[1969]

3.1.37.1.3 Origin Unknown, Washed TABLE 3.947 PZC/IEP of Ta2O5 from Unknown Source Description Washed a

Electrolyte

T

Method

0.001–1 M NaNO3

25

pH

Instrument

pH0

Reference

2.8a

[1241]

Only value, data points not reported.

3.1.37.2 Ta2O5·nH2O Solutions of Ta(C2H5O)5 in ethanol and of water and NH3 in ethanol were mixed and aged for 1 h–1 d at 20–70°C.

443

Compilation of PZCs/IEPs

Properties: Monodispersed spherical particles, TEM and SEM images, XRD results, particle size distributions available [1970].

TABLE 3.948 PZC/IEP of Ta2O5 ◊ nH2O Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee Meter 501

4.1a

[1970]

HCl + NaOH a

Arbitrary interpolation.

3.1.38

THORIUM (HYDR)OXIDES

Thorium has only one stable oxidation state (+4) within the electrochemical window of water, but it forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. Nominal degree of hydration indicated by a chemical name/ formula reported in the literature does not necessarily reflect the actual degree of hydration. PZCs/IEPs of thorium (hydr)oxides are presented in Tables 3.949 through 3.956. 3.1.38.1 ThO2 3.1.38.1.1 Commercial from Norton Properties: Cubic, >99.9% pure [39,1921], specific surface area 0.02 m2/g [39].

TABLE 3.949 PZC/IEP of ThO2 from Norton Electrolyte

T

Method

0.001–1 M KNO3, NaClO4 0.001, 1 M KNO3

25 25

pH Intersection

a b

Instrument

pH0

Reference

5.9, 6.8a 7.3b

[39] [1921]

Zalues from Table 1, only acidic branch shown in figure. Subjective interpolation.

3.1.38.1.2 Synthetic 3.1.38.1.2.1 Precipitated with Excess of NaOH at 97°C 0.1 M Th(NO3)4 in 1 M HNO3 was mixed with excess of NaOH at 97∞C. The precipitate was digested for 2 h at hot conditions, aged for 1 d at room temperature, water-washed, dried, washed, and dried again. Properties: XRD results available, specific surface area 35 m2/g [1216].

444

Surface Charging and Points of Zero Charge

TABLE 3.950 PZC/IEP of ThO2 Precipitated with Excess of NaOH at 97°C Electrolyte

T

a

Method

Instrument

pH Mass titration

0.1 M NaClO4 NaNO3

pH0

Reference

7.8 8

[1216]a

Only value, data points not reported.

3.1.38.1.2.2

From Th(NO3)4 and NaOH

TABLE 3.951 PZC/IEP of ThO2 Obtained from Th(NO3)4 and NaOH Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.8

[1229]a

0.04 M a

Only value, data points not reported. The same IEP is reported in [2226] for a precipitate termed hydroxide.

3.1.38.1.2.3 Thermal Decomposition of Oxalate Precipitated from Nitrate TABLE 3.952 PZC/IEP of ThO2 Obtained by Thermal Decomposition of Oxalate Precipitated from Nitrate Decomposition

Electrolyte

900–1100°C, then ground 20 h at 400°C, then 70 h at 900°C

a b

0.0001 0.001 0.01 M NaCl

T

Method

Instrument

pH0

Reference

17

iep iep

Electrophoresis Electrophoresis

9–9.3 9.5 8 4.2

[1743]a,b [480]a

Instrument

pH0

Oxalate precipitated at 70°C. No data points.

3.1.38.1.3 Origin Unknown TABLE 3.953 PZC/IEP of ThO2 from Unknown Sources Description

Electrolyte 1 M NaClO4

99.99% pure, 2 m2/g a b c

0.01, 0.1 M NaClO4

T

Method

25 Titration 6.5a iep Electro-osmosis 8.4 25 pH 7.5–8.8c

Only pKa1 and pKa2 reported. Only value, data points not reported. Charging curves do not show an intersection point.

Reference [1971] [1103]b [590]

445

Compilation of PZCs/IEPs

3.1.38.2 Hydrous ThO2 3.1.38.2.1 From Nitrate 1 M NaOH was added to 0.1 M Th(NO3)4 at 97°C. Properties: Amorphous, water:dry matter mass ratio 0.16, specific surface area 77 m2/g [1972].

TABLE 3.954 PZC/IEP of Hydrous ThO2 Obtained from Nitrate Electrolyte

T 25

a

Method a

Instrument

pH

pH0

Reference

7

[1972]

Also 50 and 70°C.

3.1.38.2.2 From Perchlorate, Washed

TABLE 3.955 PZC/IEP of Hydrous ThO2 Obtained by Hydrolysis of Perchlorate Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

25

iep

Zeta-Meter

9.8

[1231]

3.1.38.3

Th(OH)4, Origin Unknown

TABLE 3.956 PZC/IEP of Th(OH)4 from Unknown Source Electrolyte 0.01 M KCl

3.1.39

T

Method

Instrument

pH0

Reference

iep

Electro-osmosis

8.5

[1217]

TITANIUM (HYDR)OXIDES

Titanium(iv) forms precipitates containing various amounts of water. Calcined TiO2 often has an O:Ti atomic ratio slightly lower than 2. PZCs/IEPs of titanium (hydr)oxides are presented in Tables 3.957 through 3.1091. Titania occurs as rutile or anatase, and studies of brookite are rare. Reference [1973] suggests that the PZC of rutile is lower than that of anatase by 1 pH unit. A compilation of PZCs/IEPs focused on the difference between rutile and anatase can be found in [1974]. IEPs are compiled in [404]. Electrokinetic and surface charging behavior of titania is reviewed in [734].

446

Surface Charging and Points of Zero Charge

3.1.39.1 TiO2 3.1.39.1.1

Commercial

3.1.39.1.1.1 Aldrich (or Sigma-Aldrich) 3.1.39.1.1.1.1 Rutile Properties: Purity: >99.9% [1975], 99.99% [360], 65 ppm Ca, 5 ppm Fe [360], BET specific surface area 38 m2/g [1975], 2.3 m2/g [360], 2.1 m2/g [1976], 2 m2/g [948], specific surface area 2.8 m2/g [1977], median diameter 500 nm [148], average diameter 1 μm [1977], diameter 1 μm [430], particle size 105 nm [1975], mean particle diameter 7.4 nm [360], SEM image available [360].

TABLE 3.957 PZC/IEP of Rutile from Aldrich Description

Electrolyte

T

As obtained

0.001 M KNO3

Washed As obtained

0.001 M NaNO3 25 KCl 25a

Washed with 0.01 M 0.03 M NaNO3 NaOHb Washed 0.005, 0.1 M NaNO3 Washed 0.01, 0.1 M NaNO3 a b

c

25

25 25

Method iep iep iep Salt titration iep

Instrument

pH0 Reference

Malvern zetasizer 2c 4.8 Matec ESA 8000 5.2 Acustosizer 5.7 6

Pen Kem Laser Zee Meter 501 Intersection Acustosizer iep iep Acustosizer

[903] [148] [430] [666]

6.2

[360]

6.2c

[1977]

6.4

[350]

Also 15 and 35∞C. Unwashed sample had negative z potentials at pH 3–11, except for two positive values observed at pH ª 6. The numerical values of two “IEPs” reported in [360] are based on arbitrary interpolation. IEP roughly matches a maximum in viscosity of 38 mass% dispersion.

3.1.39.1.1.1.2 Anatase Properties: Purity: 99.9% [384,1978,1979], 99.8% [1975], >99% [1980], >99.9% [220,1981], contains phosphate [1979], BET specific surface area 10 m2/g [384,1975], 9.8 m2/g (original), 9.5 m2/g (washed) [1980], 9.5 m2/g [963], 14 m2/g (original), 3 m2/g (calcined at 800∞C for 8 h in air) [1981], 8.3 m2/g [1982], 13.5 m2/g [1566,1983], 9 m2/g [220,1976,1985,1987], particle size 93 nm [1975], mean diameter 260 nm [1984], 300 nm [1987], average diameter 300 nm [1985], primary particle size 100 nm [384], 300 nm in diameter [220], TEM image available [384,1985].

0.01, 0.1 M NaNO3

0.01 M NaNO3

Washed

Washed

Acid- and base-washed Acid- and base-washed

25

25

25

Acid- and base-washed

0.001, 0.01 M NaNO3, CCl3COONa/K, CF3COONa/K, and CF3SO3 Na/K 0.01, 0.1 M NaCl 0.001–1 M KCl

20

0.001 M NaCl 0, 0.01 M NaCl 0.01 M NaNO3

Acid- and base-washed

25

0.005–0.5 M NaNO3, NaI

Acid- and base-washed

25

0.001–0.1 M NaClO4

iep

Intersection cip iepg iep

iep

iep iep cip iep cipd iep iep iep iep

25

0.00001 M KCl (?!)

Method iep iep

T

0.001 M NaCl

Electrolyte

Water-washed

As obtained Original NaOH-washed

Description

TABLE 3.958 PZC/IEP of Anatase from Aldrich

DT 1200

Acustosizer

Delsa 440

Malvern Nano ZP

Pen Kem 501 Acoustosizer Matec Acoustosizer Matec

Acoustosizer Matec

Malvern Zetasizer 2000 Malvern ZetaMaster Malvern Zetasizer 3000

Acoustosizer Matec

Instrument

6.2

6 6 6.8 6.1

6

5.8 5.8e 5.9

<2.5 if any 2.4 6b 4.7c 5.3 5.5 5.2 5.7

pH0

continued

[495]

[350]

[963] [220]

[1982] [1978] [1987]f [1988] [40]

[1986]

[384] [1984] [1566a,1983]

[1979] [1980]a

Reference

Compilation of PZCs/IEPs 447

g

f

e

d

c

b

25 25

25

T

iep iep

iep

Titration

Method

Acoustosizer Matec DT 1200 Acoustosizer Matec Acoustosizer

Instrument

6.8 1.7

6.2 6.1 6.4

pH0

[1985] [1989]

[423]

[1981]a

Reference

Only value, data points not reported. Roughly matches the maximum in yield stress of 38 mass% dispersion. Roughly matches the maximum in yield stress of 10 and 25 vol% dispersions. Also, charging curves are reported, which apparently produce PZC at pH 4.7, but these curves show several peculiarities. Only results are reported, and there is no explanation how these results have been obtained. Atypical range of ionic strengths (0.0001–0.01 M) was studied. The absolute value of s0 in the presence of 0.001 M electrolyte reported in [384] is higher than for 0.01 M electrolyte on both sides of the PZC and much higher than the values obtained by the others (−0.3 C/m2 at pH 10 in [384], while most other sources report about −0.1 C/m2). Moreover, a minimum in ds0 /dpH is reported near the PZC, while most other papers report a maximum near the PZC. The s0 axes in Figures 4 and 5 in [1986] have incorrect labels. The corrected figures are in the erratum. The maximum in the viscosity of 38 mass% dispersion matches the IEP. A maximum in yield stress roughly matches the IEP. The z potentials at higher electrolyte concentrations obtained without background correction are also reported. <3.4 for unwashed material. Also 18–45∞C. 5 for unwashed material.

0.005 M NaNO3 HCl/NaOH

Acid- and base-washed As received

a

0.003 M NaNO3

Electrolyte

Original Calcined at 800°C for 8 h in air Acid- and base-washed

Description

TABLE 3.958 (continued)

448 Surface Charging and Points of Zero Charge

449

Compilation of PZCs/IEPs

3.1.39.1.1.1.3

Other

TABLE 3.959 PZC/IEP of Unspecified Titania from Aldrich Description

a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

23

iep

Streaming potential

8.9

[261]a

Only value, data points not reported.

3.1.39.1.1.2 Titania from Alfa Aesar 3.1.39.1.1.2.1 Rutile Properties: Purity: 99.9% [1990], 99.5% of rutile [428], BET specific surface area 8.5 m2/g [1990], 3.2 m2/g [428], 3.5 m2/g [833], average particle size 500 nm [833], volume average particle size 110 nm [428].

TABLE 3.960 PZC/IEP of Rutile from Alfa Aesar Description Original NaOH-washed

Original Calcined at 823K Calcined then rehydrated Calcined then rehydrated and evacuated a

Method

Instrument

pH0

Reference

0.01 M NaCl

Electrolyte

T

iep

3.9 5.1

[428]a

HNO3 + KOH 0.01 M NaNO3

iep pH

Zeta Probe, Colloidal Dynamics Matec ESA

5.8 7 6.2 4.3 4.7

[833] [1990]

Only value, data points not reported.

3.1.39.1.1.2.2 Anatase Properties: Anatase or brookite (electron diffraction) [723], purity 99.9% [1990], BET specific surface area 40 m2/g [1990], 8.9 m2/g [723], 11.2 m2/g [1991], specific surface area 9.5 m2/g (unspecified literature cited in [1991]), mean particle size 140 nm [1991], TEM image available [723].

450

Surface Charging and Points of Zero Charge

TABLE 3.961 PZC/IEP of Anatase from Alfa Aesar Description

Electrolyte

Original Calcined at 823K Calcined then rehydrated Calcined then rehydrated and evacuated Washed with background electrolyte

T

Method

0.01 M NaNO3

Instrument

pH

0.1 M KNO3

pH

pH0

Reference

<4 if any 6.8 6.8 5.9

[1990]

6.1

[1991]

3.1.39.1.1.3 TiNano VHP-d, Anatase from Altair Properties: 99% of anatase [1992], BET specific surface area 35.8 m2/g [1992], 39.8 m2/g [1991], 39.4 m2/g (unspecified literature cited in [1991]), mean particle size 39 nm [1991], average particle size 33 nm [1992].

TABLE 3.962 PZC/IEP of TiNano VHP-d from Altair Description

Electrolyte

Washed with background electrolyte

a

T

Method

Instrument

pH0 Reference

0.1 M KNO3

pH

6.1

[1991]

0.001–0.1 M NaNO3

cip

6.3a

[1992]

Only value, data points not reported.

3.1.39.1.1.4 Titania from Amend, Washed Properties: BET specific surface area 9.4 m2/g [3].

TABLE 3.963 PZC/IEP of Titania from Amend Electrolyte

T

KNO3 a

3.8 for unwashed sample.

Method

Instrument

pH0

Reference

iep

Delsa 440

6a

[3]

451

Compilation of PZCs/IEPs

3.1.39.1.1.5 Ultrex from Baker

Properties: Rutile [512].

TABLE 3.964 PZC/IEP of Ultrex from Baker Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 4

<4.5 if any

[512]

0.001 M KNO3

3.1.39.1.1.6 Titanias from Bayer 3.1.39.1.1.6.1 Anatase, Industrial Pigment Original and washed for 10 min with hot 2 M NaOH and then with HCl and water. Properties: Contains P (original 36, base-washed 7 μmol/g) and Cl (basewashed 7 μmol/g), specific surface area 18 m2/g (base-washed) [1993].

TABLE 3.965 PZC/IEP of Anatase, Industrial Pigment from Bayer Description

Electrolyte

Original Base-washed a

T

HCl + NaOH

Method

Instrument

pH0

Reference

iepa

Electrophoresis

3 6.4

[1993]

Only value, data points not reported.

3.1.39.1.1.6.2 Anatase The original powder contained organic coating. It was removed with hot 3 M NaOH (several cycles).

TABLE 3.966 PZC/IEP of Anatase from Bayer Electrolyte 0.005 M NaNO3 a

T 25

Method iep

Instrument Acoustosizer

pH0 >4.2

a

Reference [1994]

+20 mV at pH 4.2; −23 mV at pH 6.

3.1.39.1.1.6.3 Rutile, Industrial Pigment Original and washed for 10 min with hot 2 M NaOH and then with HCl and water.

452

Surface Charging and Points of Zero Charge

Properties: Original material contains (in μmol/g) PO4 10, SO4 11, Na 6, K 4, base-washed material contains PO4 8, and Cl 6, SO4, Na and K not detectable, specific surface area 5.6 m2/g (base-washed) [1993].

TABLE 3.967 PZC/IEP of Rutile, Industrial Pigment from Bayer Description

Electrolyte

Original Base-washed

HCl + NaOH

a

T

Method

Instrument

pH0

Reference

iepa

Electrophoresis

-1 4

[1993]

Only value, data points not reported. −1 is an extrapolated value.

3.1.39.1.1.6.4 Anatase PK 5585/1 Properties: Detailed analysis available [89], BET specific surface area 90 m2/g, [89,1995].

TABLE 3.968 PZC/IEP of Anatase PK 5585/1 from Bayer Description

Electrolyte

T

Method

Water-washed

0.1 M KNO3

25

pH

Instrument

pH0

Reference

6.6

[89]

Properties of rutile, PON 144 from Bayer: 91 m2/g [1996]. 3.1.39.1.1.7 Titanias from British Drug Houses (BDH) 3.1.39.1.1.7.1 Anatase Properties: Specific surface area 7.5 m2/g [670,1997].

TABLE 3.969 PZC/IEP of Anatase from British Drug Houses Electrolyte 0.0001 M NaNO3 0.001 M NaNO3

a

T

Method a

25 25

Instrument

Mass titration Mass titration Inflection

pH0

Reference

6 6.5 6.6

[1997] [670]

Also 5–45∞C. Only value, data points not reported.

3.1.39.1.1.7.2 Laboratory-Grade Titania spherical particles [1998].

Properties: Particle size 70 nm,

453

Compilation of PZCs/IEPs

TABLE 3.970 PZC/IEP of Laboratory Grade Titania from BDH Electrolyte

T

Method

Instrument

pH0

Reference

pH iep

Rank Bros

6.8 2.4

[1998]a

KCl

a

Only value, data points not reported.

3.1.39.1.1.8 From British Titan Products Prepared by hydrolysis of TiCl4. See also Section 3.1.39.1.1.50. Properties: Rutile [87,1231,1567,1996], BET specific surface area 23 m2/g [87,1231,1999], 17 m2/g (Cl/D 391) [1996], 20 m2/g (CL/D 528) [1567], prolate ellipsoids [1231], particles 400 nm long and 100 nm in diameter [1999].

TABLE 3.971 PZC/IEP of Titania from British Titan Products Description CL/D 428, Soxhlet-washed

Electrolyte

T

Method

Instrument

pH0

Reference

0.01–0.07 M KNO3

25

iep

Electrophoresis

4.6

[2000]

0.001 M KNO3

25

iep iep

Zeta-Meter Electrophoresis

5.6 5.8a

[1231] [1567]

CL/D 528, Soxhlet-washed a

Only value, data points not reported.

3.1.39.1.1.9 Fumed Titania from Chlorovinyl Another sample studied by the same research group in described in Section 3.1.39.1.1.20. Properties: Anatase with admixture of rutile, BET specific surface area 50 m2/g, IR spectrum available [836].

TABLE 3.972 PZC/IEP of Fumed Titania from Chlorovinyl Electrolyte HCl + NaOH

T Method iep

Instrument

pH0

Reference

ZetaPlus Brookhaven

6

[836,837]

454

Surface Charging and Points of Zero Charge

3.1.39.1.1.10 Titanias from Degussa 3.1.39.1.1.10.1 P-25 (Aeroxide) Obtained by high-temperature hydrolysis process (flame hydrolysis of TiCl4). A compilation of PZC and surface areas of P-25 (Aeroxide) from Degussa is presented in [73]. Surface charging behavior of P-25 is reviewed in [73]. Properties: Anatase [854,864,1996,2001–2003], anatase or brookite [2004], almost 100% anatase [645], chiefly anatase [367,647,2005], anatase + rutile [424,2006], anatase or brookite with admixture of rutile (electron diffraction) [723], mainly anatase, <10% of rutile [12,2007], 95% anatase [49,2008,2009], 95% anatase with 5% rutile [1993,2010], 15% rutile [2011], 86% anatase, 14% rutile [197], anatase: rutile 3.7:1 [2012], 70% anatase [911], anatase:rutile 70:30 [2013] anatase:rutile 70:30 to 80:20 [181], anatase:rutile 75:25 [479], 80:20 anatase:rutile [161,346,368,921,1560, 1975,1991,1992,2014,2015], 60% of anatase, 40% of rutile [1990,2016], 66.5% anatase, 33.5% rutile [1981], anatase:rutile 66:34 [2017], purity >99.5% [437], impurities <0.3% Al2O3 [854], <0.3% Al2O3, <0.2% SiO2, <0.1% Fe2O3 [2001], <0.3% Al2O3, <0.2% SiO2, <0.001% Fe2O3 [2015], contains (in μmol/g) Na 8, K 4, Ca 3, Cl 60 [1993], 0.1% Cl (in original sample) [2010], 820 ppm Cl [49], <0.2% SiO2, <0.01% Fe2O3, <0.3% Al2O3 [2005], BET specific surface area 25 m2/g [1031], 39.5 m2/g [723,2004], 42.4 m2/g (after heating) [161], 46.9 m2/g [1991], 47 m2/g [2005], 47 m2/g [2016], 48 m2/g [2018], 48.3 m2/g [1992], 49.9 m2/g [1560,2006,2019–2021], 50 m2/g [367,491,668,669,843,883,1975,2014,2022,2024,2025], 50 ± 15 m2/g [437,2026, 2027], 50–55 m2/g [180,182,479], 51 m2/g [1990], 51.4 m2/g [12,2003,2007,2011], 52 m2/g [49], 55 m2/g [181,346,876,1773,1981, 2013], 55.7 m2/g [197], 56 m2/g [424,1996,2002], 57.2 m2/g [2028], 59 m2/g [911], 153.8 m2/g [2029], specific surface area 30 m2/g [921], 36 m2/g [2030], 42.4 m2/g [734], 49 m2/g [2031], 50 m2/g [453,615, 645,647,658,854,864,1915,2001,2015,2032] 50 m2/g (manufacturer) [2028], 50–55 m2/g [2033], 52 m2/g [2009,2010], 53 m2/g (BET and immersion calorimetry) [2008], 53–56 m2/g [230], 55 m2/g [915,2017,2034], 55 m2/g (manufacturer) [2035], 56 m2/g [1993], modal size 25 nm [2011], particle size 20–40 nm [180,182,479], 23 nm [2032], 25–30 nm [2026], 30 nm [346,647,668,1975,2015], 25–35 nm [424], 30–40 nm [2033], 5.6 μm [2029], average primary particle size 30 nm [367,2001], average particle size 33 nm [2003], particle diameter 30 nm [230], 21 nm [883], median size 20 nm [2016], mean particle size 33 nm [1991], mean particle diameter 21 nm [2027], average radius 300 nm [49], average particle size 21 nm [437,1992,2025], 22 nm [2014], 30 nm [843,854,2005], (no quantity specified) 21 nm [2036], irregularly shaped particles [180,182,479], TEM image available [723,2012,2014,2027,2037], XRD pattern available [1915,2012,2037].

As obtained

Original exposed to radiofrequency

Original 0.65 mmol/g Nac

As received

Description

25

25

0.001 M NaCl

0.002–0.1 M KNO3

25

25

25

23

T

NaOH + HNO3

0–0.1 M NaCl 0.001 M KCl 0.002–1 M KNO3 0.005, 1 M NaCl 0.0001–0.1 M NaCl

KCl HCl + NaOH 0.01 M NaNO3 0.001–0.1 M NaCl

Electrolyte

TABLE 3.973 PZC/IEP of P-25 (Aeroxide) from Degussa

cip iep

iep Mass titration Inflection iep

cip iep cipd Intersection cip/iep

pH Mass titrationa iep iep pH cip Mass titration cip

Method

Rank Brothers Mark II

Rank Brothers Mark II

BIC 90 Plus Brookhaven

Malvern Nano ZS

1 d equlibration

Malvern Nano ZS Malvern Zetasizer 3000 HS

Instrument

6

6

4.4 4 4.5 4.7b 4.8 4.9d 4 5.4 7.7 5.7 5.8 5.8 5.8 5.8/5.8 6.5e 5.9 6

pH0

continued

[2005]

[367]

[2037] [2034]

[453] [2027] [647] [2019] [2001]

[921]

[1031] [2014] [1990] [668]

[843]

Reference

Compilation of PZCs/IEPs 455

0.001 M NaCl

Washed with 0.1 M NaOH, 3 h and 1 d aged

Original exposed to radiofrequency

Washed in boiling water

0.001 M NaCl, NaClO4

Washed

3 M NaClO4 0.001 M KCl HCl + NH3

0.1–0.25 M KNO3 NaNO3

0.002 M KNO3 in 90% water–10% methanol mixed solvent

None 0.001 M KCl

0.001–0.1 M NaCl

0.001 M KNO3 0.001 M NaCl, CH3COONa, C2H5COONa

0.0001–0.1 M NaCl, NaClO4

Electrolyte

Washed

Description

TABLE 3.973 (continued)

25i 25

20

20

25

T

pH iep iep

pH cip cip

iep

Titration cip iep Mass titration iep

iep iep

Mass titration iep iep pH iep

Method

Zm-77 ESA 8000 (hysteresis)

Rank Brothers Mark II

ZetaPlus Brookhaven

Rank Brothers Mark II

Brookhaven Zeta-PALS/ BI-MAS Malvern Zetasizer 4 Pen Kem 500 Laser Zee Meter

Malvern Zetasizer 3000

Otsuka ELS 800

Instrument

6.3 6.3 6.3, 7

6.3 6.3 6.3 j

[2002] [911] [491]

[2030] [2015] [876,2042]d

[2041]

[669] [2040]

[2039] [2010]

6.2d 6.2 6.2 >6.2g >6h 6.2

[368] [49]

[485]

[615]

[645,2038f]

Reference

6.2 6.2

6–6.3 6.4–6.6 6.1 5.8 6.2

pH0

456 Surface Charging and Points of Zero Charge

Washed

0.001–0.5 M NaCl HCl + NaOH 0–1 M KCl

0.001–1 M LiCl, KCl

0.001–0.1 M NaNO3

25

25

0.001–0.01 M NaCl

0.001–0.1 M KCl

25 20

25 25 25 25

25

25

0.001–0.1 M KNO3

Treated with HCl and reduced in 0.001 M NaCl H2 at 480°C 0.1 M NaClO4 NaCl Acid-washed 0.01–0.5 M NaCl Washed 0.0001 M KNO3 0.017–0.3 M NaNO3, KNO3

0.001–0.1 M KNO3

iep cip cip iep cip EMF

iep iep iep cip cip

cip iep iep Titration Titration iep cip pH cip iep Titration iep cip Stability

Electrophoresis

Streaming potential

Delsa 440 Malvern Zetamaster S Mark II Rank Brothers

Rank Brothers Mark II

Streaming potential Malvern Zetasizer 5000

ZetaPlus Brookhaven

Rank Brothers Mark II

Malvern Zetasizer 5000

6.5 5.3/5.5n 6.6 6.6 6.6

6.5

continued

[2008] [1993] [875]

[854]

[1992]d

[230] [883] [2007]

[1981]d [161,2045] 6.5 6.5m

6.5 6.5 6.5

[2020] [2028] [2016] [2024]d [2044]

[657,658, 674d,k] [255,2043d]

6.3 6.4 6.3 7.6 6.4 6.4 6.4 6.4l 6.4

Compilation of PZCs/IEPs 457

Original

Description

TABLE 3.973 (continued)

HCl + NaOH 0.01 M NaNO3

0.001 M NaNO3 0.01 M KNO3 0–0.0025 M KCl 0.03, 0.05 M NaOH + HNO3

25

25 25

25 25 24

0.005 M NaCl 0.01 M NaCl 0.001 M KCl None

T 21

Electrolyte

None 0 0.001, 0.005 M NaCl

iep iep

iep iep iep iep iep iep

iep iep iep iep

iep iep

Method

Instrument

Nicomp 380/ZLS ESA Matec

Brookhaven ZetaPlus Acoustosizer II Pen Kem S3000 Matec ESA 9800 Zetaplus 100 Malvern Zetamaster-S

Malvern Zetasizer Nano ZS Acoustosizer 2 Malvern Zetasizer 2000 Malvern Zetamaster-S

MBS-8000 Matec Malvern Zetamaster S

[2036] [242]

9.8t hysteresis

6.9 7 7 7s 7f 7.5

[2012] [2046] [378,2047] [180]r [182] [346] [424] [12] [437] [1915] [181]

6.7f 6.8 6.8q 6.8

Reference

[2025] [479]

pH0 6.6o 6.7p 7.2p

458 Surface Charging and Points of Zero Charge

t

s

r

q

p

o

n

m

l

k

j

i

h

g

f

e

d

c

b

a

Also 42–82°C. Arbitrary interpolation, surprisingly low z potential. Prepared by impregnation of original material with NaNO3 and calcination. Original sample studied also at 10 and 45∞C. Only value, data points not reported. 2–9 min; longer exposition to radiofrequency produced titration curves that did not have a common intersection point. Arbitrary interpolation. +8 mV at pH 6.2, −9 mV at pH 8.6. +6 mV at pH 6, −15 mV at pH 7.2. Also 10–45∞C. [876] reports PZC at pH 6.5 in Tables II and VII, but acidity constants in Table II suggest PZC at pH 6.3. Results of mass titration and inflection point are also reported. Matches IEP, details not reported. Original or heated at 530°C in H2 or in O2, with or without Soxhlet extraction after heat treatment. KCl/LiCl. Few data points below PZC. IEP matches a maximum of steady-state flux of dispersion in a specially designed filtration unit. ESA signal reported for 0.05 and 0.1 M NaCl was probably not corrected for electrolyte background; thus, the apparent IEP is incorrect. Matches maximum in mean size Arbitrary interpolation, +10 mV at pH 6, -10 mV at pH 8. IEP matches maximum in hydrodynamic particle diameter. Matches a maximum in yield stress of 16.3 mass% dispersion; however, in 19.8% dispersion, yield stress did not show a clear maximum. Only five data points are reported: +18 mV at pH 3, +10 mV at pH 5, +3 mV at pH 7, +5 mV at pH 9 and −8 mV at pH 11. Lowest colloid stability at pH 7.

Compilation of PZCs/IEPs 459

460

Surface Charging and Points of Zero Charge

TN 90 Properties: Anatase + rutile, 90 m2/g [424].

3.1.39.1.1.10.2

TABLE 3.974 PZC/IEP of TN 90 from Degussa Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

25

iep

Acoustosizer II

7

[424]

3.1.39.1.1.10.3 Other Properties: Anatase [2048], BET specific surface area 37.8 m2/g [2049], 62 m2/g [2048], average particle size 30 nm [2049], 100 nm [2048]. TABLE 3.975 PZC/IEP of Unspecified Titania(s) from Degussa Description

Electrolyte

T

Method

Instrument

As obtained

0.001–0.1 M NaClO4 0.1 M KCl

25

cip iep

Streaming potential

a

pH0 Reference 6.2 6.5a

[2049] [2048]

Only value, data points not reported.

3.1.39.1.1.11 Titania from Duke meter 2.5 μm [902].

Properties: High purity, mean particle dia-

TABLE 3.976 PZC/IEP of Titania from Duke Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee Meter 500

7.2

[902]

3.1.39.1.1.12 Rutile from Dupont Properties: BET specific surface area 9.1 m2/g, average size 400 nm [2050]. TABLE 3.977 PZC/IEP of Rutile from Dupont Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440

6

[2050]

461

Compilation of PZCs/IEPs

Properties of R100 from Dupont: 98% rutile, average diameter 230 nm, specific surface area 12 m2/g [2051]. Properties of R101 from Dupont: Rutile, particle size 500–600 nm, SEM image available, specific surface area 105 m2/g [2052]. Properties of R-900-CD from Dupont: Rutile, BET specific surface area 6.1 m2/g [87]. 3.1.39.1.1.13 Anatase from Enel [479].

Properties: Specific surface area 80 m2/g

TABLE 3.978 PZC/IEP of Anatase from Enel Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetamaster S

7.2a

[479]

None a

Matches maximum in mean size.

3.1.39.1.1.14 Anatase from Fisher Properties: >99% pure [2053], BET specific surface area 7.4 m2/g [2053], 13 m2/g [2054], average particle diameter 200 nm [2053]. TABLE 3.979 PZC/IEP of Anatase from Fisher Description Ammonia-washed

Electrolyte

T

Method

0.001–0.1 M NaCl

25

cip

Instrument

pH0 Reference 6

[2054]

3.1.39.1.1.15 Anatase from Fluka Properties: >99% pure [1736], BET specific surface area 9 m2/g [424], specific surface area 8.4 m2/g [1736], particle size 700 nm [424], 200 nm [1736]. TABLE 3.980 PZC/IEP of Anatase from Fluka Description

Electrolyte

As obtained

0.0001–0.01 M NaCl 0.01 M KNO3

a

Only value, data points not reported.

T

Method

Instrument

pH0

Reference

Pen Kem S 3000

3.5–4 6.2 3.5a

[1736]

25

iep Mass titration iep

Acoustosizer II

[424]

462

Surface Charging and Points of Zero Charge

3.1.39.1.1.16 Anatase from Glidden Properties: Ar/N2 BET specific surface area 7.1/9.8 m2/g, 100–200 nm in diameter, spherical particles [238]. TABLE 3.981 PZC/IEP of Anatase from Glidden Description

Electrolyte

a

T

Method

Instrument

pHa

0.0004–0.01 M Na salt

Dialyzed against 0.01 M NaOH

pH0

Reference

5.9

[238]

Extrapolated value, only basic branch reported; z potential was negative at pH > 8 (only basic branch reported). Coagulation rate was studied at pH > 8. Dispersions were more stable at higher pH and lower Na concentration.

3.1.39.1.1.17

Titania, Pure Grade from Hopkin and Williams TABLE 3.982 PZC/IEP of Titania from Hopkin and Williams Electrolyte

T

Method Instrument

pH0

Reference

6a

[1980]

iep a

Matches maximum in yield stress of 37.5 mass% dispersion; only value, data points not reported.

3.1.39.1.1.18 AHR from Huntsmann Properties: Anatase, particle size 150 nm, specific surface area 11 m2/g [424]. TABLE 3.983 PZC/IEP of AHR from Huntsmann Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

25

iep

Acoustosizer II

<3a

[424]

a

Only value, data points not reported.

3.1.39.1.1.19 Anatase from Inframat Properties: BET specific surface area 46 m2/g, SEM images, XRD pattern available [2055]. TABLE 3.984 PZC/IEP of Anatase from Inframat Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep

Malvern NanoZS

5.3

[2055]

463

Compilation of PZCs/IEPs

3.1.39.1.1.20 Titania from Institute of Surface Chemistry, Kalush, Ukraine Another sample studied by the same research group as described in Section 3.1.39.1.1.9. Properties: BET specific surface area 50 m2/g [926]. TABLE 3.985 PZC/IEP of Titania from Institute of Surface Chemistry, Kalush, Ukraine Electrolyte

T

Method

0.001 M NaCl

25

iep pH

a

Instrument Malvern Zetasizer 3000

pH0

Reference

6 6a

[926]

Suggested by text. Figure 11a suggests PZC at pH 4.

3.1.39.1.1.21 From Ishihara 3.1.39.1.1.21.1 ST-01 from Ishihara Properties: anatase [319], anatase (original and calcined at 700∞C) [2056,2057], BET specific surface area 308.6 m2/g [319], 320 m2/g (original), 21 m2/g (calcined at 700∞C) [2056,2057], HR-TEM image available [319], particle diameter 4.6 nm [319], particle size 9 nm (original), 53 nm (calcined at 700∞C) [2056,2057]. Reference [319] also reports physical properties according to manufacturer, and results from other sources. TABLE 3.986 PZC/IEP of ST-01 from Ishihara Description

Electrolyte

T

Method

Instrument

pH0

Reference

Water-washed

0.005–0.6 M NaCl

25

[319]

0.001 M KNO3

Malvern Zetasizer 3000 HS Zeecom ZC-1500

6.8

Original Calcined at 700°C

cip iep iep

5.5 4.2

[2056,2057]

3.1.39.1.1.21.2 Rutile from Ishihara Sangyo 0.6 mm, specific surface area 6.5 m2/g [1000].

Properties: Mean diameter

TABLE 3.987 PZC/IEP of Rutile from Ishihara Sangyo Electrolyte 0.001 M KNO3

T

Method pH

Instrument

pH0

Reference

6.1

[1000]

464

Surface Charging and Points of Zero Charge

3.1.39.1.1.22 TIO-5 from JRC Properties: Rutile, BET specific surface area 2.6 m2/g [932,1279]. TABLE 3.988 PZC/IEP of TIO-5 from JRC Description washed

Electrolyte

T

Method

0.1 M NaNO3

25

pH

Instrument

pH0

Reference

5.4

[932,1279]

3.1.39.1.1.23 Titanias from Kerr McGee 3.1.39.1.1.23.1 Tronox A2 Sulfate process. Properties: Anatase, average particle size 100 nm, BET specific surface area 10 m2/g [2058]. TABLE 3.989 PZC/IEP of Tronox A2 from Kerr McGee Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer HSA 3000

<3 if any

[2058]

3.1.39.1.1.23.2 TRHP2 Sulfate process. Properties: Rutile, >99.7% pure, median size 400 nm, BET specific surface area 7 m2/g, SEM image available [2059]. TABLE 3.990 PZC/IEP of TRHP2 from Kerr McGee Electrolyte

T

Method

Instrument

pH0

Reference

0.01, 0.1 M NaCl

25

Intersection iep

Matec ESA 8000

5.5 5.6

[2059]

3.1.39.1.1.24 Titanias from Kronos 3.1.39.1.1.24.1 Kronos 1002 Sulfate process. Properties: Anatase, BET specific surface area 10 m2/g [2058]. TABLE 3.991 PZC/IEP of Kronos 1002 Titania Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer HSA 3000

<3 if any

[2058]

465

Compilation of PZCs/IEPs

3.1.39.1.1.24.2 Anatase from Kronos (Kronos 1171) Properties: Purity >99.99% [1043], >99.8% [1044], BET specific surface area 6.4 m2/g [1044], 8.8 m2/g [1043], particle diameter 271 nm [1043,1044]. TABLE 3.992 PZC/IEP of Anatase from Kronos Description

Electrolyte

T

Method

Instrument

pH0

Reference

iep

DT 1200

5.1

[1043,1044]

Base- and acid-washed, calcined at 400°C for 4 h

3.1.39.1.1.24.3 2.9 m2/g [259].

Rutile from Kronos Properties: BET specific surface area

Table 3.993 PZC/IEP of Rutile from Kronos Description Water-washed a

Electrolyte 0, 0.001 M NaCl

T 25

a

Method

Instrument

pH0

Reference

iep

Electrophoresis

5.3

[259]

Also 120 and 200°C

3.1.39.1.1.25 Titanias from Laporte 3.1.39.1.1.25.1 Sulfate-Based Rutile Ilmenite was treated with concentrated sulfuric acid. Iron was removed and seeds of anatase were added. Then the dispersion was boiled. The product was filtered and washed, seeds of rutile were added, and the system was heated to 950∞C for 16 h. 1% of ZnO was added to prevent reduction during calcination. The ZnO was then washed out. Properties: 10% of anatase, rounded crystals, 220 nm in diameter, impurities SO4 0.01%, Zn 0.05%, Al 0.01% by mass, BET specific surface area 7.1 m2/g [2060]. TABLE 3.994 PZC/IEP of Sulfate-Based Rutile from Laporte Description

Electrolyte

Original 0.01–1 M KNO3 Washed: hot 1 M HCl (2 h), then water Washed: 0.1 M HNO3 (14 d), then water, specific surface area 15 m2/g

T

Method

Instrument

pH0

Reference

25

iep/cip

Rank Mk.II

3.4/7.5 8/3.7

[2060]

5.5/5.5

3.1.39.1.1.25.2 Chloride-Based Rutile from Laporte TiCl4 was treated with oxygen at 1000∞C. Properties: Impurities Cl 0.03%, Al 0.02% by mass, BET specific surface area 19 m2/g [2060].

466

Surface Charging and Points of Zero Charge

TABLE 3.995 PZC/IEP of Chloride-Based Rutile from Laporte Description

Electrolyte

Original 0.01–1 M KNO3 Washed: hot 1 M HCl (2 h), then water

T

Method

Instrument

pH0

Reference

25

iep/cip

Rank Mk.II

7.3/4.7 5.8/5.2

[2060]

3.1.39.1.1.26 Anatase from Matheson, Coleman and Bell specific surface area 15 m2/g [251].

Properties: BET

TABLE 3.996 PZC/IEP of Anatase from Matheson, Coleman and Bell Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

<5.5a

[251]

0.02 M KCl a

Positive value at pH 3, negative value at pH 5.5, no data points in between. The value of 5.35 in text is based on arbitrary interpolation.

3.1.39.1.1.27 Titanias from Merck 3.1.39.1.1.27.1 Anatase (M 808 or 808) Properties: 99% TiO2 [1988], contains 15% of rutile [1988], detailed analysis available [1988], BET specific surface area 7.4 m2/g (after heat treatment) [161], 16 m2/g [2061], specific surface area 9 m2/g [838], d50 = 350 nm [838]. TABLE 3.997 PZC/IEP of Anatase from Merck Description

Electrolyte

T

Method

0.001, 0.1 M KNO3, KCl, KI

25 20

iep pH iep

Rank Brothers Mark II Zeta-Meter 3.0+

<5 7–9 4b

[161]a

iep iep cip

Acoustosizer Electrophoresis

5.2 6 6

[1988] [2062] [2061]

0.01 M KCl NaOH-washed 0.01 M NaNO3 20 Washed 0.0001–0.01 M NaI Washed 0.001–0.1 M NaCl, LiCl, NaI 25 a b

Instrument

pH0 Reference

[838]

Original or heated at 600°C in H2 or in O2, with or without Soxhlet extraction after heat treatment. Few data points near IEP.

467

Compilation of PZCs/IEPs

3.1.39.1.1.27.2 Rutile from Merck Properties: >99.5% rutile [2063,2064], >99.8% rutile [1350], BET surface area 4.1 m2/g [817,1350], 14.1 m2/g [2064], 15 m2/g [2063]. Table 3.998 PZC/IEP of Rutile from Merck Electrolyte 0.01 M CsCl

T

Method

20

pH

Instrument

pH0

Reference

7.6

[1350]

3.1.39.1.1.28 Titanias from Millenium 3.1.39.1.1.28.1 PC-series Properties of PC-10: anatase, specific surface area 10 m2/g, particle size 70 nm [424]. Properties of PC-50: Anatase, particle size 20–30 nm, BET specific surface area 50 m2/g [424]. Properties of PC-500: Anatase, particle size 5–10 nm, BET specific surface area 335 m2/g [424]. TABLE 3.999 PZC/IEP of PC-10, PC-500, and PC-50 from Millenium Code PC-10 PC-500 PC-50 a

Electrolyte

T

Method

Instrument

pH0 Reference

0.01 M KNO3 0.01 M KNO3 0.01 M KNO3

25 25 25

iep iep iep

Acoustosizer II Acoustosizer II Acoustosizer II

5.7a 6.2 6.8a

[424] [424] [424]

Only value, data points not reported.

3.1.39.1.1.28.2 S5-300A Properties: Anatase, specific surface area 280 m2/g, particle size 4.5 nm [424]. Table 3.1000 PZC/IEP of S5-300A from Millenium Electrolyte

T

Method

Instrument

0.01 M KNO3

25

iep

Acoustosizer II

a

pH0 Reference 7a

[424]

Only value, data points not reported.

Properties of DT51D from Millenium: 100% anatase, BET specific surface area 88.5 m2/g.

468

Surface Charging and Points of Zero Charge

Properties of G5 from Millenium: 100% anatase, BET specific surface area 332.5 m2/g [197]. 3.1.39.1.1.29 High-Purity Rutile from National Lead TABLE 3.1001 PZC/IEP of Rutile from National Lead Description

Electrolyte

Soxhlet-extracted with HCl, 0.001 M NaCl then with water for 8 h, aged a

T

Method

Instrument

iep

Streaming potential

pH0

Reference

6.7

[2065]a

Only value, no data points.

3.1.39.1.1.30 Titania from Nanjing Titanium White (or Titanium Dioxide) Chemical Co. Ltd Sulfuric acid route, from ilmenite. Properties: Rutile [811], mean particle size 500 nm [936], average particle size 525 nm [811].

TABLE 3.1002 PZC/IEP of Titania from Nanjing Titanium White Chemical Co. Ltd Electrolyte 0.001 M NaCl 0.01 M NaCl 0.1 M NaCl 0.001 M NaCl a

T

Method

25

Instrument

iep

Malvern Zetasizer 3000 HSA

iep

Streaming potential

pH0

Reference

3.4 3.9 4.3 3.6a

[936]

[811]

Subjective interpolation.

3.1.39.1.1.31 Titania from Pfalz and Bauer surface area 8.3 m2/g [229].

Properties: Anatase, specific

TABLE 3.1003 PZC/IEP of Anatase from Pfalz and Bauer Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaClO4

25

iep

Pen Kem 102

8.3

[229]

3.1.39.1.1.32 From POCh Properties: Anatase: high purity, specific surface area 13.3 m2/g [515,2066], rutile: specific surface area 6 m2/g [2066].

469

Compilation of PZCs/IEPs

TABLE 3.1004 PZC/IEP of Anatase from POCh Description

Electrolyte

Rutile

0.1 M NaCl

Anatase ammoniawashed

0.001–0.1 M NaClO4

T

Method

Instrument

pH 25

iep cip

Pen Kem Laser Zee Meter 501

pH0

Reference

5

[2066]

5.8

[515,2066]

3.1.39.1.1.33 A-11 from Police Properties: Anatase, BET specific surface area 9.3 m2/g [612]. TABLE 3.1005 PZC/IEP of A-11 from Police Electrolyte

T

Method

0.0001–0.1 M NaCl 0.0001–0.1 M CsCl

25

cip merge

a b

Instrument

pH0

Reference

6.2 5.3

[612]a [2067]b

Hot ammonia–washed. Water-washed.

3.1.39.1.1.34 Titania from Polysciences 2% dispersion in water. Properties: Spherical, 262 nm in diameter, TEM image, particle size distribution available [1895]. TABLE 3.1006 PZC/IEP of Titania from Polysciences Electrolyte

T

0.001 M KCl

Method

Instrument

pH0

Reference

iep

Powereach JS94E

3.5

[1895]

3.1.39.1.1.35 Anatase from Precheza (Czech Republic) Properties: Mean diameter 296 nm [418]. TABLE 3.1007 PZC/IEP of Anatase from Precheza Electrolyte

T

Method

None 0.001 M NaCl 0.01 M NaCl

25

iep

Instrument Zeta PALS Brookhaven

pH0

Reference

4.8 4.9 5

[418,1047]

470

Surface Charging and Points of Zero Charge

3.1.39.1.1.36 Rutile, Single-Crystal from Princeton Scientific, 110 Surface TABLE 3.1008 PZC/IEP of Rutile Single Crystal from Princeton Scientific Electrolyte

T

Method

0.001–0.1 M NaNO3

Instrument

SHG

pH0

Reference

4.8

[94]

3.1.39.1.1.37 DT-51 from Rhone Poulenc Properties: Anatase, 98.4% TiO2, 0.7% SiO2, 0.6% S, 0.1% Na2O, 0.09% Fe2O3, 0.08% CaO, 0.05% K2O, 0.02% MgO, 0.01% Al2O3, d50 = 720 nm, BET specific surface area 85 m2/g [2068]. TABLE 3.1009 PZC/IEP of DT-51 from Rhone Poulenc Description Original NaOH- and HNO3-washed

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

25

iep

Rank Brothers Mark II

6.7 6.7

[2068]

3.1.39.1.1.38 Titanias from Sachtleben 3.1.39.1.1.38.1 Hombikat UV100 Properties: Anatase 99%, BET specific surface area 334 m2/g, particle size <10 nm [346]. TABLE 3.1010 PZC/IEP of Hombikat UV100 from Sachtleben Electrolyte

T

0.001 M NaNO3

3.1.39.1.1.38.2

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

6.2

[346]

T2

TABLE 3.1011 PZC/IEP of T2 from Sachtleben Electrolyte

T

Method

Instrument

pH0

Reference

0.00047 M KCl

20

pH iep

Acoustosizer II

7 <5.5a

[2069]b

a b

Only value, data points not reported. Also PZC and IEP of Si and Al-coated titania.

471

Compilation of PZCs/IEPs

3.1.39.1.1.38.3 T34 Sulfate process. Properties: >99.3% TiO2, rutile, BET specific surface area 5.4 m2/g [439]. TABLE 3.1012 PZC/IEP of T34 from Sachtleben Electrolyte

T

Method

Instrument

pH0

Reference

pH iep

ESA Matec

7 2.2

[439]a

0.001 M KCl

a

Only values, data points not reported; also PZC and IEP of Si- and Al-coated T34.

3.1.39.1.1.38.4 Other Three samples, sulfate process. Properties: anatase (?) [2058]. TABLE 3.1013 PZC/IEP of Other Titanias from Sachtleben Type, Properties

Electrolyte T 2

E3-588-582-001, 297 m /g, 0.5% SO4 E3-588-582-002, 102 m2/g, 0.5% SO4 E3-588-582-003, 116 m2/g, 1.5% SO4 a

Method iep

Instrument

pH0 Reference

Malvern Zetasizer HSA 3000

>5.5a >5.5a >5.5a

[2058]

No data points between pH 5.5 (positive z potential) and 7 (negative z potential). IEPs in text of [2058] are based on arbitrary interpolation.

3.1.39.1.1.39 Anatase from Sakai Different specimens. Properties: High purity [1028], BET specific surface area 20 m2/g [352], specific surface area 20 m2/g [1028], mean particle size 300 nm [1028]. Properties of another specimen: 1% SO4, 0.1% Fe, 0.1% Nb, BET specific surface area 55 m2/g, electron micrograph available [2070]. TABLE 3.1014 PZC/IEP of Anatase from Sakai Description

Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NH4NO3

25

pH iep iep

Rank Brothers Mark II Zeta-Meter 3.0 Pen Kem 501 Malvern Zetasizer 3

6.2 6.2 6.2a

[2070]

Washed with 0.001 M NaNO3 acid and base

a

Only value, data points not reported.

[352]

472

Surface Charging and Points of Zero Charge

3.1.39.1.1.40 Membralox Membrane from SCT TABLE 3.1015 PZC/IEP of Membralox Membrane from SCT Description New Used and cleaned a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

25

iep

Streaming potentiala

6.3 6.2

[995]

Confirmed by electroviscous effect.

3.1.39.1.1.41 BA0101 from Shanghai Coking Properties: Anatase, average particle diameter 237 nm, electron micrograph available [2071]. TABLE 3.1016 PZC/IEP of BA0101 from Shanghai Coking Electrolyte

T

Method

Instrument

iep a

Malvern Zetasizer 4

pH0 5.5

a

Reference [2071]

Maximum in yield stress and viscosity of a 23.8 vol% dispersion matches IEP.

3.1.39.1.1.42 Sigma-Aldrich See Sections 3.1.39.1.1.1 and 3.1.39.1.1.43. 3.1.39.1.1.43 Titanias from Sigma 3.1.39.1.1.43.1 Anatase Washed with background electrolyte. Properties: BET specific surface area 10.8 m2/g [1991], 8.3 m2/g (unspecified literature cited in [1991]), mean particle size 145 nm [1991]. TABLE 3.1017 PZC/IEP of Anatase from Sigma Electrolyte

T

Method

3.1.39.1.1.43.2

Instrument

pH

0.1 M KNO3

Other

pH0

Reference

6.1

[1991]

Properties: Particle diameter 725 nm [1453].

TABLE 3.1018 PZC/IEP of Unspecified Titania from Sigma Electrolyte

T

Method

Instrument

pH0

Reference

0.1 M NaCl

25

iep

Malvern Zetasizer ZEN 3600

3.5

[1453]

473

Compilation of PZCs/IEPs

3.1.39.1.1.44 Amperit 782.1 from Stark Original and plasma-sprayed. Properties: Rutile with admixture of Ti8O15 (original), rutile (after spraying), XRD patterns, SEM images available, specific surface area 0.3 m2/g (original), 1 m2/g (after spraying) [1003]. TABLE 3.1019 PZC/IEP of Amperit 782.1 from Stark Description Original Original, washed Sprayed Sprayed, washed

Electrolyte

T

Method

0.01 M NaCl

Instrument

Mass titration

pH0

Reference

5.3 5 5 5.3

[1003]

3.1.39.1.1.45 Rutile from a Membrane from TAMI TABLE 3.1020 PZC/IEP of Rutile from a Membrane from TAMI Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zetaphoremeter II, CAD

6.2

[2072]

0.001 M KCl

3.1.39.1.1.46 Titanias from Tayca 3.1.39.1.1.46.1 MT-500 HD Properties: XRD pattern, TEM image available [2037]. TABLE 3.1021 PZC/IEP of MT-500 HD from Tayca Electrolyte

T

Method

Instrument

pH0

Reference

iep

BIC-90 Plus Brookhaven

6.3

[2037]

3.1.39.1.1.46.2 JA1 Properties: Anatase, particle size 180 nm, BET specific surface area 9 m2/g [424]. TABLE 3.1022 PZC/IEP of JA1 from Tayca Electrolyte 0.01 M KNO3 a

T 25

Method iep

Instrument Acoustosizer II

Only value, data points not reported.

pH0 <3

a

Reference [424]

474

Surface Charging and Points of Zero Charge

3.1.39.1.1.46.3 TKP and TKS Series Properties of TKP101: anatase, particle size 6 nm, BET specific surface area 300 m2/g [424]. Properties of TKS203: Anatase, particle size 6 nm, BET specific surface area 214 m2/g [424]. Properties of TKS201: Anatase, particle size 6 nm, BET specific surface area 241 m2/g [424]. Properties of TKP103: Anatase, particle size 6 nm, BET specific surface area 280 m2/g [424]. TABLE 3.1023 PZC/IEP of TKP and TKS Titanias from Tayca Code TKP-103 TKS-201 TKP-101 TKS-203 a

Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3 0.01 M KNO3 0.01 M KNO3 0.01 M KNO3

25 25 25 25

iep iep iep iep

Acoustosizer II Acoustosizer II Acoustosizer II Acoustosizer II

<3 if anya <3 if anya 4.7 7.5a

[424] [424] [424] [424]

Only value, data points not reported.

3.1.39.1.1.46.4 Rutile Properties: BET specific surface area 28 m2/g, SEM images, XRD pattern available [2055]. TABLE 3.1024 PZC/IEP of Rutile from Tayca Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep

Malvern NanoZS

6.3

[2055]

3.1.39.1.1.47 Sulfate-Based Anatase from Teikoku Kako Properties: BET specific surface area 125.3 m2/g, particle size 0.3–1 mm [2073]. TABLE 3.1025 PZC/IEP of Anatase from Teikoku Kako Description Ammonia-washed

Electrolyte

T

Method

Instrument

pH0

Reference

iep pH

Electrophoresis

6.2 ≈5

[2073]

Properties of rutile from Teikoku-kako: BET specific surface area 22.6 m2/g [162]. 3.1.39.1.1.48 Titania from Tianjin Chemical Properties: Rutile, mass average diameter 780 nm, BET specific surface area 2.4 m2/g [2074].

475

Compilation of PZCs/IEPs

TABLE 3.1026 PZC/IEP of Titania from Tianjin Electrolyte

T

Method

Instrument

iep a

pH0

Rank Brothers MK II

Reference

a

4

[2074]

Maximum in viscosity and yield stress of 67.7% by mass dispersion at pH 6.

3.1.39.1.1.49 Titanias from Tioxide 3.1.39.1.1.49.1 TSM-1 Properties: Particle diameter 2.45 μm [1907]. TABLE 3.1027 PZC/IEP of TSM-1 from Tioxide Description Washed, heated to 70°C

Electrolyte

T

Method

Instrument

pH0

Reference

0.001, 0.01 M KCl or KNO3

25

iep

Matec MBS-8000 Malvern Zetasizer IIc

<5 if any

[1907]

3.1.39.1.1.49.2

CLDD 1910 Properties: Particle size 350 nm [31].

TABLE 3.1028 PZC/IEP of CLDD 1910 from Tioxide Electrolyte

T

Method

Instrument

pH0

Reference

iep

Matec ESA-8000, Rank Bros Mark II

6.2

[31]

0.01 M KCl

3.1.39.1.1.49.3 Anatase Properties: A-HR: 98.7% pure [2075], contains organic modifier [2075], 121 m2/g [1766], 150 nm in diameter [404], average crystal size 150 nm [2075], TEM image available [404]. TABLE 3.1029 PZC/IEP of Anatase from Tioxide Type A-HR A-HR Sulfate process a

Electrolyte

T

Method

Instrument

pH0

Reference

NaOH + H2SO4 0.001 M CH3COONH4

25

iep iep iep

Malvern Zetasizer 4 Electrophoresis Pen Kem 3000

2.4a 3.8 4

[2075] [1160] [404]

Matches maximum in yield stress of 50 mass% dispersion.

476

Surface Charging and Points of Zero Charge

3.1.39.1.1.49.4 Rutile Prepared by hydrolysis of TiCl4 followed by heating in air at 450°C (but the sample studied in [404] was prepared by the sulfate process). Properties: Rutile (electron diffraction) [723], structure confirmed by XRD [2076], rutile [951], 99.8% rutile [455], <0.01% silica, <0.03% Cl [455], 0.32% sulfate (CL/D478/1, from sulfate) [718], 0.3% Cl, 100 ppm sulfate (CL/D412, from chloride) [718], BET specific surface area 3.5 m2/g [723], 9 m2/g [447], 15.4 m2/g [455], 16.5 m2/g [951], 26 m2/g [947], 16.8 m2/g [2077,2078], 17 m2/g [2076,2079], 20.6 m2/g [356,2080], 21 m2/g [327], 28 m2/g [1536], specific surface area 5 m2/g (CL/D478/1, from sulfate) and 25 m2/g (CL/D412, from chloride) [718], 5.7 m2/g [825], 30 m2/g [90], 91 m2/g [1766], rod-like particles, 0.1–0.24 mm long and 10–45 nm wide [327], particle size 350 nm [901], 250–400 nm [50], equivalent spherical radius 45 nm [951], particle diameter 225 nm [404], median size 1.9 μm [503], elipsoids, axis ratio 4:1 [951], elliptic, aspect ratio 2–3 [50], TEM image available [404,723], SEM image available [2079].

TABLE 3.1030 PZC/IEP of Rutile from Tioxide Description

Electrolyte

Milled

KOH + HCl

Sulfate process

0.001 M CH3COONH4 KNO3

Washed

0.01 M NaOHwashed Soxhlet-washed for 72 h CLDD1597, NaOH-washed Soxhlet extraction Stored for 1 year Washed CLDD1597, NaOH-washed R-CR

0.03–1 M NaCl

0.0001, 0.001 M KNO3 0.001–0.1 M KNO3 0.0001–0.01 M KNO3 0.001 M KNO3 0.01–0.1 M NaNO3 0.001–0.1 M LiCl, CsCl, KCl, KNO3, KClO4 NaOH + H2SO4

T

Method

25 iep

Instrument

pH0

Reference

cip iep 25 cip

Pen Kem 3 Acoustophoretic titrator 7000 Pen Kem 3000 3.3 Matec MBS 8000 Streaming 5 potential 5.4

pH

5.6

[2079b, 2076–2078c, 2081c] [447]a

5.6

[2082]

5.9 5.9

[2080] [356]a [951]

5.9 6 6

[455]a [1536]a [327]

6.2

[1160]

iep

25 iep

Rank Brothers MK II Zeta-Meter 3.0

21 iep cip 25 iep Rank Brothers Coagulation Mark II iep Rank Brothers 25 cip 25 iep Pen Kem 501 Intersection 25 iep

Electrophoresis

[901]

[404] [825]a

continued

477

Compilation of PZCs/IEPs

TABLE 3.1030 (continued) Description NaOH-washed Washed

a b c d

Electrolyte

T

Method

Instrument

pH0

Reference

0.02 M KNO3 or NH4NO3 0.0002–0.2 M NaCl

22

iep

Zeta-Meter

6.2

[947]

20

iep

Pen Kem Laser Zee 500

6.2d

[503]

Only value, data points not reported. Also 10–50°C. Also 50–250°C. Confirmed by turbidity measurements.

3.1.39.1.1.49.5 Single-Crystal, Polished, and Steamed <1% tin or lead [2083].

Properties: rutile,

TABLE 3.1031 PZC/IEP of Rutile Single Crystal from Tioxide Electrolyte

T

0.001 M KNO3

3.1.39.1.1.49.6

Method

Instrument

pH0

Reference

AFM iep

Nanoscope III Electrophoresis

5.2 5.6

[2083]

Other

TABLE 3.1032 PZC/IEP of Unspecified Titania from Tioxide Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep iep

Laser Zee Meter Acustosizer

5.6 7.8

[812] [307]

3.1.39.1.1.50 Anatase HR from Titan Products

See also Section 3.1.39.1.1.8.

TABLE 3.1033 PZC/IEP of Anatase HR from Titan Products Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

3a

[108]

Only value, data points not reported.

478

Surface Charging and Points of Zero Charge

3.1.39.1.1.51 Rutile from Tiwest The original powder contained sand and alumina. Sand was removed by a few dispersion–sedimentation cycles. Alumina was removed with hot 1.5 M HCl.

TABLE 3.1034 PZC/IEP of Rutile from Tiwest Electrolyte

T

Method

Instrument

pH0

Reference

0.005 M NaNO3

25

iep

Acoustosizer

>5.8a

[1994]

a

+20 mV at pH 5.8, −20 mV at pH 7.5.

3.1.39.1.1.52 Rutile from Toho Properties: High purity, particle diameter 2 μm [96]

TABLE 3.1035 PZC/IEP of Rutile from Toho Electrolyte

T

0.001, 0.1 M KCl

Method

Instrument

pH0

Reference

iep

Brookhaven Zeta PALS

5.2

[96]

3.1.39.1.1.53 Rutile from Ventron Properties: 95% rutile, 5% anatase [2084– 2087], 90% rutile, 10% anatase [550], BET specific surface area 1.5 m2/g [2087], 2 m2/g [2084–2086], specific surface area 4 m2/g [550].

TABLE 3.1036 PZC/IEP of Rutile from Ventron Description Ammonia-washed

a

Electrolyte 0.001 M NaCl 0.001–0.1 M NaCl 0.1 M CsCl

Arbitrary interpolation.

T 20 20

Method iep cip pH

Instrument Pen Kem 501

pH0 4.6 5.3 5.4

a

Reference [2086] [550] [2085]

479

Compilation of PZCs/IEPs

3.1.39.1.1.54 Titanias from Wako

TABLE 3.1037 PZC/IEP of Titanias from Wako Description

Electrolyte

Rutile, 8.3 m2/g, 280 nm Anatase, 6.1 m2/g, 1.3 μm

T

Method

NaOH + HNO3 NaOH + HNO3

Instrument

pH pH

pH0

Reference

4.6 5.9

[2088] [2088]

3.1.39.1.1.55 Commercial Rutile, Origin Unknown Sulfate process. Properties: Al2O3 0.28%, ZnO 0.95%, SiO2 < 0.01%, P2O5 0.22%, SO3 0.2% (by mass, the sum of mass fractions of components reported in [456] exceeds 100%), Ca 220 ppm, specific surface area 7.3 m2/g [456].

TABLE 3.1038 PZC/IEP of Commercial Rutile from Unknown Source Description As received Soxhlet Acid leaching + Soxhlet Six months in air Acid leaching + Soxhlet

Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

25

iep

Rank Brothers

4.2 4.3 4.8 4.3 4.8

[456]

3.1.39.1.1.56 Commercial Titanias, Origin Unknown

TABLE 3.1039 PZC/IEP of Commercial Titanias from Unknown Sources Description Water-washed, and dried at 110°C Pigment, 6 m2/g, rutile a

Electrolyte

T

Method

pH0

Reference

0, 0.001 M KCl

25

iep

Rank Mark II

2

[1213]

iep

ZetaPlus Brookhaven

7a

[836]

HCl + NaOH

Subjective interpolation.

Instrument

480

Surface Charging and Points of Zero Charge

3.1.39.1.2 Obtained from Industrial Raw Material Isolated from a sol from Bayer, water-washed. Properties: Contains Cl, 60 μmol/g, specific surface area 200 m2/g [1993]. TABLE 3.1040 PZC/IEP of Titania Isolated from a Sol from Bayer Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.3a

[1993]

HCl + NaOH a

Only value, data points not reported.

3.1.39.1.3 Synthetic 3.1.39.1.3.1 From Chloride 3.1.39.1.3.1.1 Evaporation of 0.2 M TiCl4 Solution in 1:1 HCl 0.2 M TiCl4 in 1:1 HCl was evaporated at 90°C until dryness, and the residue was calcined at 450°C for 1 h. The oxide was aged in 0.01 M KOH for 1 d, and the pH was adjusted to 12 periodically. The precipitate was filtered, dried at 120°C in air for 1 h, and calcined at 450°C for 1 h. The aging–drying–calcination cycle was repeated three times. Properties: Rutile with admixture of anatase, XRD results available [512]. TABLE 3.1041 PZC/IEP of Titania Obtained by Evaporation of 0.2 M TiCl4 Solution in 1:1 HCl Purification Steps 1 2 3

Electrolyte 0.001 M KNO3

T

Method iep

Instrument Malvern Zetasizer 4

pH0

Reference

2.5 3 3.5

[512]

3.1.39.1.3.1.2 Evaporation of TiCl4 Solution in 1 M HCl TiCl4 was dissolved in 1 M HCl. The solution was gently heated to dryness and then heated for 1 h at 450°C. The precipitate was crushed, milled, and heated again (total calcination time of 3 h). It was then water-washed. Properties: Anatase, BET specific surface area 40 m2/g [1750].

481

Compilation of PZCs/IEPs

TABLE 3.1042 PZC/IEP of Titania Obtained by Evaporation of TiCl4 Solution in 1 M HCl Electrolyte

T

0.005–0.05 M KNO3 a

25

Method

Instrument

cip

pH0 6.3

a

Reference [1750]

Only value, data points not reported.

3.1.39.1.3.1.3 Aging of Acidified TiCl4 Solution at 60°C for 3 h Recipe from [2089]: 40 cm3 of TiCl4 was added at 2 cm3/min to a solution of 40 cm3 of concentrated HCl in 1 dm3 of ice-cold water with stirring. The dispersion was aged at 60°C for 3 h, and then electrodialyzed for 60 d. Properties: Rutile, specific surface area 174 m2/g, electron micrograph available [2090]. Specific surcface area 48.8 m2/g, average diameter 20 nm, spherical particles [359]. TABLE 3.1043 PZC/IEP of Titania Obtained by Aging of Acidified TiCl4 Solution at 60°C for 3 h Electrolyte

T

0.001 M NaCl

a b

Method

Instrument

pH0 a

Reference

iep

Electrophoresis

6.3

[2090]

Titrationb iep

Zetasizer 3000 HS

5.7

[359]

Arbitrary interpolation, broad minimum in CCC (NaNO3) around IEP. Only value, no data points.

3.1.39.1.3.1.4 Aging of TiCl4 Solution at 25 or 100°C Recipe from [2091]: 2 M TiOCl2 solution was prepared by addition of ice to cold TiCl4. Then the stock solution was diluted to 0.5 M and the temperature was raised to 25 or 100°C at different rates, and kept at the final temperature for different times. The powder was washed, dried, and calcined at different temperatures. Properties: Rutile, XRD pattern, TEM image available [2037], XRD patterns, SEM images available [2091]. TABLE 3.1044 PZC/IEP of Titania Obtained by Aging of TiCl4 Solution at 25 or 100°C Electrolyte

T

Method

Instrument

pH0

Reference

iep

BIC-90 Plus Brookhaven

2.3

[2037]

482

Surface Charging and Points of Zero Charge

3.1.39.1.3.1.5 Aging of TiCl4 Solution and Dialysis Recipe from [2092]: TiCl4 was slowly added to water at 0°C. The dispersion was dialyzed until its pH reached 3. Properties: Mean hydrodynamic diameter 13 nm, specific surface area 122 m2/g [2041], mean radius 4.6 nm [2092].

TABLE 3.1045 PZC/IEP of Titania Obtained by Aging of TiCl4 Solution and Dialysis Electrolyte

T

0.2 M

Method

Instrument

pH0

Reference

iep

Rank Brothers Mark II

4.7

[2092]

3.1.39.1.3.1.6 Aging of TiCl4 Solution at 1°C for 3 h 0.11 cm3 of cold TiCl4 (-20°C) was slowly added to 200 cm3 of water (1°C) with stirring, and kept at 1°C for 3 h.

TABLE 3.1046 PZC/IEP of Titania Obtained by Aging of TiCl4 Solution at 1°C for 3 h Electrolyte

T

Method

0.01 M

25

Inflection Coagulation

Instrument

pH0

Reference

5

[1393,2104]

3.1.39.1.3.1.7 Grown on Seeds Obtained from TiCl4 Solution at Boiling Point TiCl4 was added to ice-cold water, slowly brought to room temperature. 10% of the dispersion was heated to boiling point, and mixed with the remaining dispersion. This was then heated to 80°C for a few hours and refluxed at 105°C for a few days. Properties: Rutile [183,1407,2060,2093], 0.2% Cl by mass (removable by dialysis) [2060], BET specific surface area 28 m 2/g [2094], 41 m 2/g [2060], 43 m 2/g [183], 44.5 m 2/g [1412], 47 m 2/g [1407], 51 m 2/g [582,1408,1409], 52 m 2/g [2093,2095], needles 15 nm × 15 nm × 150 nm [2094], electron micrograph available [183].

483

Compilation of PZCs/IEPs

TABLE 3.1047 PZC/IEP of Titania Grown on Seeds Obtained from TiCl4 Solution at Boiling Point Description

Electrolyte

T

Original 0.01–1 M KNO3 Washed by dialysis 0.001–1 M NaClO4 0.001–2 M NaNO3 0.01 M KNO3 0.001 M KNO3

Dispersion boiled for 21 d

iep/cip 25a cip 25 cip cipb iep 20 iep

0.005–0.2 M KNO3 20c cip 0.001–0.1 M NaCl 20 cip 0.002–0.1 M KNO3 20 cip iepb 0.02 M KNO3

20

0.01–1 M NaCl

a b c

Method

iep iep cip

Instrument

pH0

Rank Brothers MK II

Malvern Zetasizer III

Malvern Zetasizer II Pen Kem 3000 Malvern Zetasizer II Malvern Zetasizer III

Reference

3.2/7.1 6/5.8 5.8 5.8 5.7

[2060]

5.7

[582]b

5.7 5.8 5.9

[1409] [2093, 2095b] [1412]

5.9

[2096]

6.2 5.8b

[1407]

[183] [545] [2094]

Also at 50–95°C. Only value, data points not reported. Also 5 and 50°C.

3.1.39.1.3.1.9 Aging of TiCl4 Solution in 98% Ethanol 5 g of TiCl4 was dissolved in 50 cm3 of 98% ethanol at 0°C. The solution was stirred for 2 h and then aged for 3 d at 80°C. The powder was washed with water and dried in air at 50°C. Properties: Anatase, IR spectrum, TGA curve, XRD pattern available [396].

TABLE 3.1048 PZC/IEP of Titania Obtained by Aging of TiCl4 Solution in 98% Ethanol Electrolyte HNO3 + NaOH a

T

Method iep

Instrument Malvern 3000 HSA

pH0 >6.8

Reference

a

+2 mV at pH 6.8, −42 mV at pH 9, no data points in between.

[396]

484

Surface Charging and Points of Zero Charge

3.1.39.1.3.1.8 Aging of TiCl4 Solution Adjusted to pH 7–8 with Ammonia 70 cm3 of TiCl4 was added slowly to 90 cm3 of water at 20°C under an argon atmosphere. The solution was then diluted with 350 cm3 of water and adjusted to pH 7–8 with ammonia. The precipitate was aged for 1 h, washed with water, and calcined at 500°C for 20 h. Properties: Anatase, BET specific surface area 55 m2/g, electron micrograph, XRD pattern available [2070]. TABLE 3.1049 PZC/IEP of Titania Obtained by Aging of TiCl4 Solution Adjusted to pH 7–8 with Ammonia Electrolyte

T

Method

0.001–0.1 M NH4NO3

25

pH iep

a

Instrument

pH0

Reference

Rank Brothers Mark II

5.5 5.7

[2070]a

Arbitrary interpolation.

3.1.39.1.3.1.9 Hydrolysis of TiCl4 Solution Adjusted to pH 7.5 with Ammonia 0.5 M TiCl4 in ice-cold water was added to 0.01 M HCl solution heated to 80°C. Ammonia was added simultaneously to keep the pH at 7.5. The reagents were added within 1 h, and the reaction conditions were maintained for 1 h more. The particles were washed with water, dried at 120°C, and calcined for 1 h at 500°C. Properties: Anatase, XRD pattern available [1951]. TABLE 3.1050 PZC/IEP of Titania Obtained by Hydrolysis of TiCl4 Solution Adjusted to pH 7.5 with Ammonia Electrolyte

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

4.4

[1951]

3.1.39.1.3.1.10 Hydrolysis of TiCl4 Solutions Adjusted to Different pH Values Recipe from [95]: TiCl4 was added to ice–water (different concentrations). The filtered solution was adjusted to different pH values, and the mixture was heated at 85–220°C for 1–4 h. The mixture was then aged for 1 d at room temperature, and the precipitate was washed with acetic acid–ammonium acetate

485

Compilation of PZCs/IEPs

buffer and dried at 80°C. Different conditions of synthesis led to different crystallographic structures and different morphologies. Properties: Rutile, BET specific surface area 51 m2/g [1676].

TABLE 3.1051 PZC/IEP of Titania Obtained by Hydrolysis of TiCl4 Solutions Adjusted to Different pH Electrolyte

T

Method

NaCl

25

Titration

a

Instrument

pH0

Reference

5.1a

[1676]

From Table 1; Figure 5 suggests PZC at higher pH.

3.1.39.1.3.1.11 Hydrolysis of TiCl4 Solutions Adjusted to Different pH Values with NaOH 3 cm3 of TiCl4 was poured into 50 cm3 of water. The mixture was adjusted with 45% NaOH and then with 2 M NaOH to a certain pH. The precipitate was washed with water. A few powders were dried over H2SO4 at room temperature.

TABLE 3.1052 PZC/IEP of Titanias Obtained by Hydrolysis of TiCl4 Solutions Adjusted to Different pH with NaOH pH of Precipitation

Electrolyte

4.5–10; the precipitate 0.01–1 M was washed and aged NaCl for 2 h in 1 M NaCl at 80°C 4 0.01/0.1/1 M 4.4 NaCl 4.5 5 6 7 8 9 10 Dried, pH 5 Dried, pH 7

T

25

Method

Instrument

pH0

Reference

pH

3.4–9.6

[678]

pH

3.6/3.6/4 3.4/4.5/4.5 —/4.7/— —/5.7/— 7.5/7/6.6 —/8.2/— —/8.8/— 10.6/10/9.5 —/10.8/— —/5.4/— —/7.9/—

[2097]

486

Surface Charging and Points of Zero Charge

3.1.39.1.3.1.12 Hydrolysis of TiCl4 Solution with Ammonia Added Purified by electrodialysis. Properties: Anatase [540,1117,1118], (sample calcined at 500°C) [979], Fe 0.006%, Si 0.008%, Al 0.01%, Mg 0.006%, Cu 0.002%, Ca 0.03% [614], detailed chemical analysis available [1117], BET specific surface area 330 m2/g [614], 173 m2/g (calcined at 300°C), 124 m2/g (calcined at 500°C) [979], specific surface area 240 m2/g [1118], 270 m2/g [1117], electron micrograph available [1117]. TABLE 3.1053 PZC/IEP of Titania Obtained by Hydrolysis of TiCl4 Solution with Ammonia Added Description

Electrolyte

Dried at 200°C 0.01 M NaCl Wet 0.001–0.1 M NaCl Dried at 200°C 0.001–1 M NaCl

T

Method

20 20

iep cip iep iep cip iep cip pH iep pH

0.001–1 M NaCl

Calcined at: 300°C 500°C a b c

0.01 M NaCl

20

0.01 M KCl

40

Instrument Electrophoresis Electrophoresis Malvern Zetasizer 4 Electrophoresis Electrophoresis

pH0

Reference

4.7 5.3–6a 5.3 5.8b 6 5.9c

[1204] [614]

5.9 5.7

[1118, 1119]

[1117] [540]

[979] 8.5 7.2

No clear CIP, titration curve obtained in 1 M NaCl also reported. In Figure 6, but Figure 13 reports IEP at pH 6.8 in 0.01 M NaCl. Incomplete washing resulted in IEP at pH about 5.5.

3.1.39.1.3.1.13 Hydrolysis of TiCl4 Solution with Polyethylene Imine Added Polyethylene imine was added to TiCl4 solution. The mixture was stirred and refluxed at 70°C for 160 min. The precipitate was washed with ethanol, and dried at 100°C for 12 h. Properties: Anatase, BET specific surface area 114 m2/g [2098]. TABLE 3.1054 PZC/IEP of Titania Obtained by Hydrolysis of TiCl4 Solution with Polyethylene Imine Added Electrolyte 0.01 M NaCl a

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000 HS

5.3a

[2098]

Only IEP reported, no data points.

487

Compilation of PZCs/IEPs

3.1.39.1.3.1.14 Hydrolysis of TiCl4 Solution in the Presence of H2O2 Recipe from [2099]: Freshly distilled TiCl4 was added dropwise to ice-cold aqueous H2O2. HCl was added to produce a solution 10 mM in Ti and 0.12 M in HCl, which was aged at 80°C for 4–6 h.

TABLE 3.1055 PZC/IEP of Titania Obtained in Presence of H2O2 Electrolyte

T

Method

Instrument

iep a

pH0

Reference

3.5

[2100]a

Only value, no data points.

3.1.39.1.3.1.15 Hydrolysis of TiCl4 Solution Properties: Rutile [2101], [456], Al2O3 <0.01%, SiO2 <0.01%, Cl 0.03%, Sn <0.002% (by mass), Fe <3 ppm [456], BET specific surface area 19.8 m2/g [2102], 113.7 m2/g [2103], specific surface area 20.3 m2/g [456]. TABLE 3.1056 PZC/IEP of Other Titanias Obtained by Hydrolysis of TiCl4 Solution Description Calcined at 900°C, rutile, 11 m2/g TiCl4 + NaOH fresh 12 × (Soxhlet + 450°C in air) Acid leaching + Soxhlet Six months in air Six more months in air Acid leaching + Soxhlet 850°C in air for 24 h Six months in air Calcined at 350°C, anatase, 159 m2/g

Electrolyte

0.02 M 0.01 M KNO3

T

25

Method

iep iep

iep TiCl4 redistilled; powder calcined at 150°C; then Soxhlet-extracted with water

0.001–2.9 M KNO3 0.001–0.1 M LiNO3, NaNO3, (CH3)4NCl

25

cip

Instrument

Electrophoresis Rank Brothers

Rank Brothers

pH0 Reference 3.8

[1678]

4.8 4.8 5

[1229]a,d [456]

5 5.5 5.5 5.5 4.8 4.8 5.2

[1678]

5.5

[2101]

b

5.8 5.9

[2102]

continued

488

Surface Charging and Points of Zero Charge

TABLE 3.1056 (continued) Description One-step process, ellipsoidal particles, diameter ratio 1.2, diameters 100–200 nm Hydrolysis at 100°C, hydrous rutile, washed, aged: original Heated in air for 2 h at 1000°C TiCl4 was added to two parts of water, refluxed for 4 h; precipitate was washed and freeze-dried Washed, than heated at (°C): 100 600 1000 Primary particles 10 nm, aggregates 400 nm a b

c d

Electrolyte

T

Method

Instrument

6a

iep

iep

pH0 Reference

Electrophoresis

[2094]

[1091] 6 4.7

0.009 M NaClO4

0.001 M KNO3

0.01 M NaCl

30

iep

Riddick

iep

Electrophoresis

6.2

[2103]

[250]a 6.6c 6 4.8c

iep

Acoustosizer

6.7

[2105]

Only value, data points not reported. Also Yates’ thesis cited by many. [8] identifies the sample used in Yates’ thesis with CL/D 528 from Tioxide, well-aged and purified titania originally obtained from TiCl4. This IEP is not influenced by washing. The same IEP is reported in [2226] for a precipitate termed hydroxide.

3.1.39.1.3.1.16 Aerosol Technique Aerosol of TiCl4 was hydrolyzed in a home-made apparatus. AgCl was used as nucleating material. Similar syntheses were carried out with Ti(iv) alkoxides as the TiO2 precursors. Properties: Anatase [220,1382], chiefly anatase [2106], >95% anatase [2107], 99.9% TiO2, 0.02% Ag, 0.07% Cl [2106], BET specific surface area 45 m2/g [220], specific surface area 3.5 m2/g [2107], modal particle diameter 440 nm [1382,2107], 330 nm in diameter [220], spherical particles [1382,2107], [220], TEM images available [2106], SEM image available [1382].

489

Compilation of PZCs/IEPs

TABLE 3.1057 PZC/IEP of Titania Obtained by Aerosol Technique Description

Spheres Shells (incomplete hydrolysis)

Electrolyte

T

0.001,0.01 M NaCl, NaNO3 0.001 M KNO3

25

0.001,0.01 M NaNO3

25

Method

0.1 M KCl

Instrument

pH0

Reference

iep

Rank Brothers

5

[1382]

iep

Rank Brothers Mark II

5.2 4.5

[2106]

Intersection iep iep

Rank Brothers Mark II Delsa 440

6.5 4.4 6.8

[2107] [220]

3.1.39.1.3.2 From Sulfate 3.1.39.1.3.2.1 Dropwise Addition of 0.2 M TiOSO4 Solution in 1 M H2SO4 to Water at 90°C The product of hydrolysis was aged for 30 min at 90°C, and is termed “titanyl sulfate” in [1903]. TABLE 3.1058 PZC/IEP of Titania Obtained by Dropwise Addition of 0.2 M TiOSO4 Solution in 1 M H2SO4 to Water at 90°C Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KBr

25

iep

Malvern Zetasizer 3000 HS

4.5

[1903]

3.1.39.1.3.2.2 Hydrolysis of Titanyl Sulfate Followed by Heating in Air at 450°C Properties: Anatase (0.3% rutile), Al2O3 <0.01%, SiO2 <0.01%, SO3 0.05% (by mass), Fe 7 ppm, specific surface area 7.1 m2/g [456]. TABLE 3.1059 PZC/IEP of Titania Obtained by Hydrolysis of TiOSO4 Followed by Heating in Air at 450°C Description Fresh Six months in air Soxhlet Acid leaching + Soxhlet Sample 2: 850°C in air for 5 min (4.8% rutile)

Electrolyte

T

Method

Instrument

0.01 M KNO3

25

iep

Rank Brothers

pH0 Reference 5.9 4.5 5 6 5.7

[456]

continued

490

Surface Charging and Points of Zero Charge

TABLE 3.1059 (continued) Description

Electrolyte

T

Method

Instrument

Sample 3: 850°C in air for 10 min (5% rutile) Six months in air Four more months in air Soxhlet Acid leaching + Soxhlet Sample 4: 850°C in air for 15 min (7% rutile) Six months in air Sample 5: 850°C in air for 16 h (83.2% rutile) Six months in air Six more months in air Acid leaching + Soxhlet

pH0 Reference 4.5 4 3.4 4.8 5.8 4.6 2.7 4.6 3.6 3.5 4.3

3.1.39.1.3.2.3 Neutralization of Crude Product Containing 10% of H2SO4 with Aqueous NH3 Washed and electrodialyzed. Properties: 100% anatase, BET specific surface area 144 m2/g, particle size <1 mm [179]. TABLE 3.1060 PZC/IEP of Titania Obtained by Neutralization of Crude Product Containing 10% H2SO4 with Aqueous NH3 Electrolyte

T

Method

Instrument

pH a

pH0

Reference

5.8

[179]a

Only value, data points not reported.

3.1.39.1.3.2.4 Addition of 1 M Ammonia to 1 M Ti(SO4)2 Until pH 8 Aged for 1 d, washed and filtered, but not dried. Properties: Hydrous, 3.5–4.5 parts of water per 1 part of dry matter by mass [2108]. TABLE 3.1061 PZC/IEP of Titania Obtained by Addition of 1 M Ammonia to 1 M Ti(SO4)2 Until pH 8 Electrolyte

T

Method

0.1 M NaNO3

25

pH

Instrument

pH0

Reference

6.7

[2108]

491

Compilation of PZCs/IEPs

3.1.39.1.3.2.5 Recipe from [2089] 125 cm3 of TiCl4 was added to 240 cm3 of ice-cold water with stirring. Then a solution of 312 g of (NH4)SO4 and 6 cm3 of concentrated HCl in 480 cm3 of water was added. The dispersion was boiled for 1 h. After cooling to 50°C, the dispersion was neutralized with 225 cm3 of concentrated ammonia to pH 6.7. The dispersion was aged at 60°C, and the supernatant was replaced with water. It was then electrodialyzed for 60 d. Properties: Anatase, specific surface area 57 m2/g, electron micrograph available [2090]. TABLE 3.1062 PZC/IEP of Titania Obtained According to Recipe from [2089] Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

5.5a

[2090]

Broad minimum in CCC (NaNO3) around IEP.

3.1.39.1.3.2.6 Precipitated in the Presence of Polyvinylpyrrolidone A solution 0.005 M in TiOSO4, 0.025 M in H2SO4, 0.05% in polyvinylpyrrolidone (MW 90,000), and 0.005% in hydroxypropylcellulose (MW 100,000) was aged for 1 h at 90°C. Properties: Hydrous, TEM image available [1901]. TABLE 3.1063 PZC/IEP of Titania Obtained from Sulfate in Presence of Polyvinyl Pyrrolidone Electrolyte

T

Method

Instrument

pH0

Reference

iep

Delsa 440

4.8

[1901]

0.001 M KCl

3.1.39.1.3.2.7 Other TABLE 3.1064 PZC/IEP of Other Titanias Obtained from Sulfate Description Washed, than heated at (°C): 100 300 500 700 (anatase) 1000 (rutile).

Electrolyte 0.001 M KNO3

T

Method

Instrument

30

iep

Electrophoresis

pH0 Reference [250] 5.8 5.3 5.2 3.7 3.5 continued

492

Surface Charging and Points of Zero Charge

TABLE 3.1064 (continued) Description

Electrolyte

T

Recipe from [2109], 0.001–0.1 M anatase, specific surface KNO3 area 329 or 330 m2/g, primary crystallite size 6 nm Precipitation from boiling 0.001–1 M TiOSO4 solution, NaCl anatase, 125 m2/g

25

Intersection Malvern iep Zetasizer 3000 or 2000

5.8

[335] [2110,2111]a

25

cip

5.9

[183]

a

Method

Instrument

pH0 Reference

Only value, data points not reported.

3.1.39.1.3.3 From Alkoxides 3.1.39.1.3.3.1 From Ethoxide in the Presence of HNO3 A 1:1 (by volume) mixture of Ti(EtO)4 and ethanol was mixed with 0.15 M HNO3 at a H2O:Ti:H+ molar ratio of 200:1:0.5. The alcohol was boiled off at 80°C, and the mixture was stirred for 2 d. The dispersion was dialyzed against water and calcined at 350°C. Properties: XRD pattern available, anatase–rutile mixture [2112]. TABLE 3.1065 PZC/IEP of Titania Obtained from Ethoxide in Presence of HNO3 Electrolyte 0.01 M KNO3

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000 HS

5.8

[2112]

3.1.39.1.3.3.2 From Ethoxide 0.5 M water in ethanol was poured into 0.15 M Ti(OC2H5)4 in ethanol, and mixed at high speed for 2–5 s and then at low speed for 10 min. The water:Ti molar ratio was always >2.5. The precipitate was washed with water. Properties: Amorphous [2113], amorphous (original sample) [2114], anatase [1676,2115], 40 ppm Ca, 80 ppm Si [2113], BET specific surface area 61.6 m2/g [2115], 67.1 m2/g [1676], mean diameter 400 nm [2113], particle diameter 500 nm [233], particle size distribution available [2116], TEM images available [2114,2116].

493

Compilation of PZCs/IEPs

TABLE 3.1066 PZC/IEP of Titania Obtained from Ethoxide Description

Electrolyte

T

Method

Original, 304 m /g, 0.001–0.1 M microporous KCl From butoxide 0.001 M KCl Three months aged, 0.001–0.1 M 186 m2/g, coarsened KCl anatase surface coating 0.001 M KCl Calcined at 620°C for 0.0001–0.1M 20 min NaCl

25

cip iep iep cip iepa

Rank Brothers Mark II Malvern Zeta Master Rank Brothers Mark II

iep cip iep

Rank Brothers Mark II 6.1b [2116] Pen Kem Laser Zee 6.2 [1676,2115] Meter 501 Malvern Zetasizer 3000

2

a b

25

25 25

Instrument

pH0 Reference 4 4.3 4.2 5.2 5.5

[2113] [233] [2113]

Coagulation rate shows broad minimum around IEP. Low stability at pH 6.3.

3.1.39.1.3.3.3 From Ethoxide in the Presence of Hydroxypropylcellulose A solution of 1 cm3 of titanium ethoxide in 100 cm3 of ethanol was hydrolyzed with 1 cm3 of water in the presence of 7–70 mg of hydroxypropylcellulose (MW 80,000) at 2 and 23°C. The particles were washed with methanol and water. Properties: Particle diameter 1 μm [2117]. TABLE 3.1067 PZC/IEP of Titania Obtained from Ethoxide in Presence of Hydroxypropylcellulose Electrolyte 0.0001 M KCl

T

Method

Instrument

pH0

Reference

iep

Brookhaven

4.1

[2117]

3.1.39.1.3.3.4 From Isopropoxide in the Presence of HCl 225 cm3 of a 10 vol% solution of titanium isopropoxide in ethanol was dripped into 2.25 dm3 of aqueous HCl (pH 1.1) at 4–6°C with stirring. The particles were separated by filtration, dried, and purified by dialysis. Properties: TEM image available, 85% anatase, 15% brookite, average particle size 3.5 nm [2118].

494

Surface Charging and Points of Zero Charge

TABLE 3.1068 PZC/IEP of Titania Obtained from Isopropoxide in Presence of HCl Electrolyte

T

Method

0.03, 0.3 M

Instrument

Intersection

pH0

Reference

6.7

[2118]

3.1.39.1.3.3.5 From Isopropoxide in the Presence of HCl and Urea A 2:1 (by mass) mixture of titanium isopropoxide and ethanol was titrated with 0.28 M aqueous HCl and stirred for 3 h. Then a urea–alcohol–water mixture (1:5:1 mass ratio) was added. The mixture was aged for 7 d, and the gel was washed, dried at 120°C for 1 d, and calcined at 200, 300, 400, and 500°C (four samples). Properties: Anatase, specific surface areas, XRD patterns, size distributions available [2119]. TABLE 3.1069 PZC/IEP of Titania Obtained from Isopropoxide in Presence of HCl and Urea Electrolyte

T

Method

0.01 M NaNO3

25

pH

Instrument

pH0

Reference

6.6–6.7

[2119]

3.1.39.1.3.3.6 From Isopropoxide in the Presence of HNO3 Titanium isopropoxide (11.36 parts) was slowly added to a solution of HNO3 (1 part) in water (136.4 parts). The solution was aged for 3 d, dialyzed, evaporated, and the solid sintered to 300°C. Properties: 20% rutile, 80% anatase (sintered at 300°C), BET specific surface area 180 m2/g [2120]. TABLE 3.1070 PZC/IEP of Titania Obtained from Isopropoxide in Presence of HNO3 Description

Electrolyte

Not sintered Sintered

0.01 M

T

Method iep

Instrument Pen Kem 3000

pH0

Reference

6.2 6.2

[2120]

3.1.39.1.3.3.7 From Isopropoxide in the Presence of H2SO4 310 cm3 of concentrated H2SO4 was added to 1095 cm3 of water. After cooling, 1065 g of titanium isopropoxide was added with agitation, and the temperature was kept below 60°C. Isopropanol was distilled out under vacuum, and titanyl sulfate was hydrolyzed. Then the product of hydrolysis was calcined.

495

Compilation of PZCs/IEPs

Properties: Rutile, elemental analysis available [2121], BET specific surface area 49.7 m2/g [822]. TABLE 3.1071 PZC/IEP of Titania Obtained from Isopropoxide in Presence of H2SO4 Description

Electrolyte

T

Method

Original 0.01 M NaCl H2SO4 washed for 1 h H2SO4 washed for 2 h

iep

Instrument

pH0

Reference

Pen Kem Laser Zee Meter

1.9 3.2 4.5

[2121]

3.1.39.1.3.3.8 From Isopropoxide in the Presence of Organic Acids Acetic, propanoic, or butanoic acid was added at 30 cm3/min to titanium isopropoxide with stirring at 1:1 mole ratio, and the mixture was allowed to cool to room temperature. A sample without organic acid was also studied. The mixture was slowly added to water at a Ti:water molar ratio of 1:50 at 25 or 75°C. The particles were washed with water. Properties: The products of hydrolysis contain organic matter [2122]. TABLE 3.1072 PZC/IEP of Titania Obtained from Isopropoxide in Presence of Organic Acids Acid, Temperature (°C)

Electrolyte

None, 25 None, 75 Acetic, 25 Acetic, 75 Propanoic, 25 Propanoic, 75 Butanoic, 25 Butanoic, 75

NaOH + HNO3

T

Method

Instrument

pH0

Reference

iep

ESA

5.9 7.2 5.7 6 <2 7.3 <2 <2

[2122]

3.1.39.1.3.3.9 From Isopropoxide in the Presence of NaClO4 0.00625 mol of titanium isopropoxide was mixed with a solution of NaClO4 adjusted with NaOH or HClO4 to a certain pH. It was then aged for 2 h at 25°C and for 1 d at 100°C. Properties: Anatase [2123]. TABLE 3.1073 PZC/IEP of Titania Obtained from Isopropoxide in Presence of NaClO4 Electrolyte

T

Method

0.1 M NaClO4

25

pH

Instrument

pH0

Reference

6

[2123]

496

Surface Charging and Points of Zero Charge

3.1.39.1.3.3.10 From Isopropoxide in Methanol–Ethanol Mixture Water was added dropwise to a titanium isopropoxide–methanol–ethanol mixture (molar ratio 1:1:10) at 75°C. The sample was dried, and then calcined in air for 10 h at 550°C. TABLE 3.1074 PZC/IEP of Titania Obtained from Isopropoxide in Methanol–Ethanol Mixture Electrolyte

T

Method

Instrument

pH0

Reference

pH

1 d equilibration

6.6

[2124]

0.01 M NaCl

3.1.39.1.3.3.11 From Isopropoxide in Isopropanol or Methanol different recipes. Properties: Anatase, XRD patterns available, 73–96 m2/g [2030].

Three

TABLE 3.1075 PZC/IEP of Titania Obtained from Isopropoxide in Isopropanol or Methanol Electrolyte

T

Method

Instrument

pH0

Reference

pH

3 d equilibration

6.2–6.7a

[2030]

0.01 M NaCl a

Specific values not reported.

3.1.39.1.3.3.12 Cryogel Titanium isopropoxide was hydrolyzed in 30 parts of aqueous HNO3 at pH 1 for 3 d at 30°C. The gel was freeze-dried. Properties: Anatase, BET specific surface area 142 m2/g, SEM image, XRD pattern available [2055]. Table 3.1076 PZC/IEP of Titania Cryogel Obtained from Isopropoxide Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep

Malvern NanoZS

5

[2055]

3.1.39.1.3.3.13 Evaporation of 0.2 M Titanium Butoxide Solution in 1:2 HNO3 0.2 M titanium butoxide in 1:2 HNO3 was evaporated at 90°C until dryness, and the residue was calcined at 450°C for 1 h. The oxide was aged in 0.01 M KOH for 1 d, and the pH was adjusted to 12 periodically. Filtered, dried at 120°C

497

Compilation of PZCs/IEPs

in air for 1 h and calcined at 450°C for 1 h. The aging–drying–calcination cycle was repeated three times. Properties: Anatase, XRD results available [512].

TABLE 3.1077 PZC/IEP of Titania Obtained by Evaporation of 0.2 M Ti Butoxide Solution in 1:2 HNO3 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 4

5.9

[512]

0.0001–0.01 M KCl, KNO3

3.1.39.1.3.3.14 Recipe from [2125] 0.5 M solution of titanium ethoxide, isopropoxide or tert-butoxide in corresponding alcohol was added dropwise to alcohol-water mixture. The precipitate was washed with water, redispersed in 0.075 M HNO3, and refluxed for 8 h at 80°C. Reference [2013] was also cited for the recipe, but no specific recipe (based on hydrolysis of alkoxide) is reported there. Properties: Rutile:anatase ratio 30:70, specific surface area 72 m2/g, XRD results, HR TEM image available [368].

TABLE 3.1078 PZC/IEP of Titania Obtained According to Recipe from [2125] Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 4

5.5

[368]

3.1.39.1.3.3.15 From Isopropoxide in Isopropanol 184 cm 3 of titanium isopropoxide in 400 cm3 of isopropanol was titrated with 53.4 cm3 of water in 20.8 cm 3 of isopropanol within 2 h. The dispersion was aged for 1 h at 20°C, and the precipitate was washed with water and calcined at 500∞C for 20 h. Properties: Anatase [51,2070,2126], BET specific surface area 60 m2/g [2126], 64 m2/g [51,2070], electron micrograph available [2070].

TABLE 3.1079 PZC/IEP of Titania Obtained from Isopropoxide in Isopropanol Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NH4NO3

25

pH iep

Rank Brothers Mark II

6.1 6.5

[51,2070,2126]

498

Surface Charging and Points of Zero Charge

3.1.39.1.3.3.16 Addition of Isopropoxide to Excess of Water with Stirring The precipitate was filtered after 1 h. TABLE 3.1080 PZC/IEP of Titania Obtained by Addition of Isopropoxide to Excess of Water with Stirring Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000

5.1

[1909]

3.1.39.1.3.3.17 From Isopropoxide in Ethanol A solution of titanium isopropoxide in ethanol was added dropwise to a water–ethanol mixture at room temperature with stirring. The particles were washed three times with ethanol, three times with water, dried in vacuum at 60°C for 2 d, and calcined at 700°C for 2 h (several specimens were obtained with different proportions of reagents). Properties: Rutile, BET specific surface area 2 m2/g (calcined), 220 m2/g (before calcination), XRD pattern available [1902]. TABLE 3.1081 PZC/IEP of Titania Obtained from Isopropoxide in Ethanol Electrolyte

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440

4.5

[1902]

0.001 M HCl + KOH

3.1.39.1.3.4 Other 3.1.39.1.3.4.1 Combustion of Chloride in a Flame Reactor TiCl4saturated nitrogen and air were introduced into the central tube of a flame reactor. The product was collected on a filter. Properties: Anatase, BET specific surface area 110.8 m2/g, TEM image, XRD pattern available [2014]. TABLE 3.1082 PZC/IEP of Titania Obtained by Combustion of Chloride in Flame Reactor Electrolyte

T

NaOH + HCl a

Arbitrary interpolation.

Method iep

Instrument Malvern Zetasizer 3000 HS

pH0 6.7

a

Reference [2014]

499

Compilation of PZCs/IEPs

3.1.39.1.3.4.2 Combustion of Isopropoxide in a Furnace Reactor Properties: 84% anatase, 16% rutile, BET specific surface area 74.8 m2/g, average particle size 20 nm [1992]. TABLE 3.1083 PZC/IEP of Titania Obtained by Combustion of Isopropoxide in Furnace Reactor Electrolyte

T

0.001 M 0.001–0.1 M NaNO3 a

Method

Instrument

pH0

Reference

iep cipa

Malvern Nano ZS

6 6.4

[1425] [1992]

Only value, data points not reported.

3.1.39.1.3.4.3 Rutile Obtained by Calcination of Anatase from Thann et Mulhouse at 900°C for 5 h Properties: BET specific surface area 9 m2/g [2126]. TABLE 3.1084 PZC/IEP of Rutile Obtained by Calcination of Anatase from Thann et Mulhouse Electrolyte

T

Method

Instrument

pH0

Reference

0.01–0.1 M NH4NO3

25

pH iep

Rank Brothers Mark II

5.5

[2126]

3.1.39.1.3.4.4 Recipe from [2127–2129], Ultrasonically Aided Submerged Arc Properties: Anatase with admixture of rutile, TEM and FE-SEM images, XRD pattern available [2130]. TABLE 3.1085 PZC/IEP of Titania Obtained in Ultrasonic-Aided Submerged Arc Electrolyte

T

Method

0.1 M NaCl (?)

a

iep pH

Instrument

pH0

Reference

5 2.5

[2130] [2127]a

Only value, no data points.

3.1.39.1.3.4.5 Synthetic Rutile, Recipe Unknown Properties: BET specific surface area 12 m2/g, d50 329 nm [345].

500

Surface Charging and Points of Zero Charge

TABLE 3.1086 PZC/IEP of Synthetic Rutile, Recipe Unknown Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

5.9

[345]

0.0001 M NaNO3

3.1.39.1.4 Natural 3.1.39.1.4.1 Rutile from Mexico Passed through a magnetic separator and heavy-liquid separator. Washed with hot 10% HNO3. Properties: >99% pure, contains SiO2, Fe, Nb, and traces of Cr, Ca, Al and Zr, specific surface area 0.23 m2/g [583].

TABLE 3.1087 PZC/IEP of Rutile from Mexico Electrolyte

T

Method

0.001–1 M KNO3

25

merge

3.1.39.1.4.2

Instrument

pH0

Reference

5.3

[583]

Other

TABLE 3.1088 PZC/IEP of Other Natural Rutiles Description Risør, Norway From Australian beach sand, HCl-, H2SO4-, and water-washed Water-washed From North Carolina, ground, washed, traces of Fe2O3 HCl- and water-washed, dried at 120°C Acid- and water-washed, dried at 120°C a

Electrolyte

T

Method

Instrument

iep iep

Zeta-Meter Streaming potential

3 3.5

[104] [290]

iep iepa

Rank Mark I Electrophoresis

4.1 4.7

[1933] [1088]

HCl

iep

Electrophoresis

4.8

[1091]

HCl

iep

Streaming potential

5.5

[1092]

NaOH + HClO4

0.1 M NaCl

Only value, data points not reported.

25

pH0 Reference

501

Compilation of PZCs/IEPs

3.1.39.1.5 Origin Unknown 3.1.39.1.5.1 Rutile TABLE 3.1089 PZC/IEP of Rutiles from Unknown Sources Description washed

8.2 m2/g

Electrolyte

b c

Method iep

0.001–0.1 M NaCl

pH

0.001–0.05 M KCl

iep Intersection Titration pH iep

1 M NaClO4 0.1 M NaClO4

a

T

0.001 M KNO3

25 25

Instrument Rank Brothers Mark II

Electrophoresis

pH0 3.5a

Reference [2131]

Merge at [581] pH <5 5.6 [2132] 5.8b 6.1b 7c

[2133] [2134,2135] [2136]

Materials containing Al and Zn were also studied. Only acidity constants, data points not reported. Only value, data points not reported.

3.1.39.1.5.2 Other TABLE 3.1090 PZC/IEP of Other Titanias from Unknown Sources Description 11 m2/g

Electrolyte 0.1 M KCl

Anatase Crushed xerogel 11 m2/g

0.001 M KCl 0.01 M NaCl 0.01 M KCl

T

Method

Room Mass titration iep iep iep iep

Anatase-rich Analytical grade, 0.01 M KNO3 30 99.5% pure, Si 75 ppm, Al 80 ppm, Ca 35 ppm, Fe 45 ppm, 0.6 m2/g

iep iepa

Instrument

pH0 3.6a

4 ELS 8000 Otsuka 4.5 Pen Kem 3000 5d Electro-osmosis 5 ELS 8000 Otsuka 5b Zeta-Meter 5.5

Reference [1718] [2136] [1905] [2137] [1102,1103]a [1217] [2138] [1065]

continued

502

Surface Charging and Points of Zero Charge

TABLE 3.1090 (continued) Description

Electrolyte

Particle diameter 90 nm Anatase: washed Dirty Washed and heated Aged 6 months in water Average of several samples: reagentgrade anatase and hydrous rutile, washed, aged 200 nm, 6.7 m2/g

T

0.0001 M KNO3

b c d

Instrument

pH0 a

iep Coagulation iep

0.001 M KNO3 0.001–0.1 M NaNO3 Anatase, particle HCl + diameter 20–50 nm NH4OH 0.01 M KNO3 20

a

Method

Reference

5.9

[1107]

6 5.9 5.7 4.5

[2139]

iep

Electrophoresis

6a

[1088]

iep

Malvern Zetasizer 3

6.1c

[2140]

6.6

[2141]

6.8

[2142]

7.4 7.4

[610] [2143]

cip iep

Zeta-Meter 3.0

pH iep

Only value, data points not reported. IEP at pH 5.32 is claimed in figure legend. In fact, there are no data points between pH 5 and 9. Matches maximum in viscosity of 60 mass% dispersion. Arbitrary interpolation.

3.1.39.2 Ti(OH)4 0.00625 mol of titanium isopropoxide was mixed with a solution of NaClO4 adjusted with NaOH or HClO4 to a certain pH. The product was then aged for 2 h at 25°C and for 30 min at 100°C. TABLE 3.1091 PZC/IEP of Ti(OH)4 Electrolyte 0.1 M NaClO4

T 25

Method pH

Instrument

pH0

Reference

4.1

[2123]

3.1.40 Tl2O3 PZC/IEP of commercial Tl2O3 from Aldrich (99.99% pure, avicennite [380]) is presented in Table 3.1092.

503

Compilation of PZCs/IEPs

TABLE 3.1092 PZC/IEP of Tl2O3 Electrolyte 0.01 M NaNO3

3.1.41

T

Method

Instrument

pH0

Reference

25

iep Salt titration

Malvern Zetasiter IIc

7.9

[380]

URANIUM (HYDR)OXIDES

Uranium forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation (+4 to +6), degree of hydration, and crystallographic structure. Nominal degree of oxidation and hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of oxidation and hydration. PZCs/IEPs of uranium (hydr)oxides are presented in Tables 3.1093 through 3.1103.

3.1.41.1

UO2

3.1.41.1.1 Commercial UO2 from ABB Atom (later Westinghouse Atom) Properties: Depleted (0.25% enrichment), O:U molar ratio 2.08–2.15, BET specific surface area 5.3 m2/g [590].

TABLE 3.1093 PZC/IEP of UO2 from ABB Atom Description Washed with 0.001 M HClO4 a

Electrolyte

T

Method

0.01–0.5 M NaClO4

25

pH

Instrument

pH0

Reference

5–5.5a

[590]

Charging curves do not show a CIP. The reported s0 are higher by an order of magnitude than typical values reported for oxides.

3.1.41.1.2 Synthetic 3.1.41.1.2.1 Thermal Decomposition of Uranyl Nitrate Followed by Reduction in H2 at 1000°C Properties: Structure confirmed by XRD, BET specific surface area 5.3 m2/g [2144].

504

Surface Charging and Points of Zero Charge

TABLE 3.1094 PZC/IEP of UO2 Obtained by Thermal Decomposition of Uranyl Nitrate Electrolyte 0.0025–0.025 M LiNO3 0.01, 0.025 M KNO3 a

T

Method

25a

cip pH

Instrument

pH0

Reference

5.8 4.9

[2144]

Also 40–70°C.

3.1.41.1.2.2 From Hexafluoride range [2145].

Properties: contains Cu, Mg, and Fe in ppm

TABLE 3.1095 PZC/IEP of UO2 Obtained from Hexafluoride Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M KCl, KNO3, KClO4

25

iep Coagulation

Zeta-Meter

4.5

[2145]

3.1.41.1.2.3 Thermal Decomposition of Ammonium Diuranate at 600°C in H2 + 0.4% H2O–Gas Mixture Cooled in H2 for 3 h. Ground and waterwashed. Properties: Cubic [2146]. TABLE 3.1096 PZC/IEP of UO2 Obtained by Thermal Decomposition of Ammonium Diuranate in H2 + 0.4% H2O Electrolyte

T

Method

Instrument

pH0

Reference

iep

Streaming potential

5.7

[2146]

0.01 M NaCl

3.1.41.1.2.4 Thermal Decomposition of Ammonium Diuranate at 600°C in H2 Water-quenched. Ground and water-washed. Properties: Cubic [2146]. TABLE 3.1097 PZC/IEP of UO2 Obtained by Thermal Decomposition of Ammonium Diuranate in H2 Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep

Streaming potential

4.7

[2146]

505

Compilation of PZCs/IEPs

UOx, 2 < x < 3

3.1.41.2

3.1.41.2.1 UO2.08 Thermal decomposition of ammonium diuranate at 600°C in H2. Ground and water-washed. Properties: Cubic [2146]. TABLE 3.1098 PZC/IEP of UO2.08 Electrolyte

T

Method

NaOH + HCl

iep

Instrument Streaming potential

pH0

Reference

6.6

[2146]

3.1.41.2.2 UO2.33 Thermal decomposition of ammonium diuranate in H2 + H2O–gas mixture. Ground and water-washed. TABLE 3.1099 PZC/IEP of UO2.33 Electrolyte

T

Method

Instrument

pH0

Reference

iepa

Streaming potential

6

[2146]

NaOH + HCl a

Subjective interpolation.

3.1.41.2.3 UO2.45 UO2 was heated in air at 800°C and then in nitrogen at 1300°C. It was then cooled in nitrogen, ground, and water-washed. TABLE 3.1100 PZC/IEP of UO2.45 Electrolyte

T

0.01 M NaCl

3.1.41.2.4

Method

Instrument

pH0

Reference

iep

Streaming potential

3.5

[2146]

Instrument

pH0

Reference

Streaming potential

4

[2147]

Pure U3O8

TABLE 3.1101 PZC/IEP of Pure U3O8 Electrolyte

T

Method iep

a

a

Only value, data points not reported; the authors describe the experiment as “not completely successful.”

506

Surface Charging and Points of Zero Charge

3.1.41.2.5 Pitchblende from Johanngeorgenstadt, Saxony TABLE 3.1102 PZC/IEP of Pitchblende from Johanngeorgenstadt, Saxony, Two Specimens Electrolyte

T

Method iep

a

Instrument

pH0

Reference

Streaming potential

a

[2147]

3 4.5

Extrapolated.

3.1.41.3 U(VI) Oxide Precipitated In Situ TABLE 3.1103 PZC/IEP of U(VI) Oxide Electrolyte 0.0005 M NaCl

3.1.42

T

Method

Instrument

pH0

Reference

25

iep

Rank Brothers

<5.5 if any

[38]

VANADIUM (HYDR)OXIDES

Vanadium forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation (+3 to +5), degree of hydration, and crystallographic structure. They show substantial solubility in water and are beyond the scope of the present book. PZCs/IEPs of V2O5 are presented in Table 3.1104. TABLE 3.1104 PZC/IEP of V2O5 Description Merck, orthorhombic

7.1 m2/g, mean diameter 0.6 μm

Electrolyte

T

Method

Instrument

0.0005, 0.005 M KNO3 0.01 M KCl

iep

iep

Rank Brothers Malvern Zetasizer II c Electro-osmosis

HNO3 + KOH 0.01M KNO3

iep

Pen Kem 501

iep

Malvern Zetasizer 3000 HS

iep

Zm-77

Prepared by calcination 0.001 M KCl of ammonium vanadyl oxalate at 500°C in air flow

23

pH0

Reference

<1.5 if any

[830,831]

<1 if any <2 if any <3 if anya

[1217]

1.4

[911]

[2148] [2112]

continued

507

Compilation of PZCs/IEPs

TABLE 3.1104 (continued) Description

Electrolyte

V2O5 ⋅ nH2O, prepared from vanadic acid, recipe from [2149] 4.5 m2/g

a b c

T

Method

Instrument

pH0

iep

0.1 M KCl

Room Mass titration

Reference

2b

[2100]

3.1c

[1718]

IEP at pH 2 reported in text is not supported by data. Only value, no data points. Only value, data points not reported, cited in [1103] as IEP at pH 1 determined by electro-osmosis.

3.1.43

TUNGSTEN (HYDR)OXIDES

Tungsten forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of oxidation (up to +6), degree of hydration, and crystallographic structure. They are sparingly soluble in water, but soluble in dilute acids (this is important, because the PZC at strongly acidic pH is reported). PZCs/IEPs of tungsten (hydr)oxides are presented in Tables 3.1105 through 1108. 3.1.43.1 WO3 3.1.43.1.1

Commercial

3.1.43.1.1.1 WO3 from Aldrich Properties: 99.99% pure [2150], BET specific surface area 1.3 m2/g [2151], 1.1 m2/g [2150], particle size 20 μm [2150]. TABLE 3.1105 PZC/IEP of WO3 from Aldrich Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3 0.0001–0.01 M NaCl 0.001 M KNO3

23

iepa iep iep

Streaming potential Malvern Zetasizer 2000 Coulter Delsa 440 SX

4.9 <3 if any 1.5

[261] [2151] [2150]

a

25

Only value, data points not reported.

3.1.43.1.1.2 Origin Unknown, Water-Washed, and Dried at 110°C TABLE 3.1106 PZC/IEP of WO3 from Unknown Commercial Source Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M KCl

25

iep

Rank Mark II

2

[1213]

508

Surface Charging and Points of Zero Charge

3.1.43.1.2 Origin Unknown TABLE 3.1107 PZC/IEP of WO3 from Unknown Sources Electrolyte

T

Method a

iep iep iepa

0.01 M KCl 0.01 M KCl a

3.1.43.2

Instrument

pH0

Reference

Electro-osmosis 1.5 Electro-osmosis <2 if any Zeta-Meter ZM-77 0.3

[1103] [1217] [844,1005]

Only value, data points not reported.

Hydrous WO3, Origin Unknown TABLE 3.1108 PZC/IEP of Hydrous WO3 from Unknown Source Electrolyte

a

T

Method

Instrument

pH0

Reference

iepa

Electro-osmosis

<0.3

[1214]

Only value, data points not reported.

The “IEP” of WO3 cited in [1] after [53] is discussed in Chapter 2.

3.1.44

Y2O3

Yttrium has only one stable oxidation state (+3) within the electrochemical window of water, but it forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. These compounds absorb atmospheric CO2. Nominal degree of hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of hydration. PZCs/IEPs of Y2O3 (nominally) are presented in Tables 3.1109 through 3.1126. 3.1.44.1 Commercial 3.1.44.1.1 Y2O3 from Cerac Properties: 99.99% pure [284]. TABLE 3.1109 PZC/IEP of Y2O3 from Cerac Electrolyte 0.01 M NaCl a

T 26–27

Method iep

Instrument a

Malvern Zetasizer II c

pH0

Reference

8.2

[284]

From Table 1. Figure 1b suggests that the IEP at pH 9.3 was obtained by means of Chemtrac ECA 2000 (streaming current).

509

Compilation of PZCs/IEPs

3.1.44.1.2

Y2O3 from Merck

TABLE 3.1110 PZC/IEP of Y2O3 from Merck Description

Electrolyte

T

Method

Instrument

pH0

Reference

As received

0.001–0.1 M NaCl

25

cip iep

Malvern Zetasizer 2c

7.9 8.5

[1376]

3.1.44.1.3

Unocal P/N 5600 from Molycorp

TABLE 3.1111 PZC/IEP of Unocal P/N 5600 from Molycorp, 99.99% Pure Electrolyte

T

Method

Instrument

pH0

Reference

iep

Matec ESA 8000

8.5

[834]

0.001 M KNO3

3.1.44.1.4

Y2O3 from Nanotek TABLE 3.1112 PZC/IEP of Y2O3 from Nanotek Electrolyte

T

Method

Instrument

a

pH0 Reference 8.4a

iep

[2152]

Based on arbitrary interpolation.

3.1.44.1.5 Y2O3 from Nyacol Nano Technologies Particles were isolated from a commercial 14 mass% dispersion stabilized with acetate, containing 10 nm particles. They were then calcined at 550°C in air or in an 8% H2–92% N2 mixture. TABLE 3.1113 PZC/IEP of Y2O3 from Nyacol Nano Technologies Calcined

Electrolyte

In air In H2/N2

0.004 M NaCl

a

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer Nano ZS

8.2 9.8

[1930]a

Same particles (layer-deposited on silica-based material) were studied by means of streaming potential, and the IEP was 7.7 and 8.5 for particles calcined in air or in 8% H2–92% N2 mixture, respectively. The low IEP might be due to the presence of silica-based material.

510

Surface Charging and Points of Zero Charge

3.1.44.1.6 Y2O3 from Rhone Poulenc Properties: 99.99% pure, average diameter 2 μm, specific surface area 2.7 m2/g [1803]. TABLE 3.1114 PZC/IEP of Y2O3 from Rhone Poulenc Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaNO3

25

iep

Malvern Zetasizer 4

8.5

[1803]

3.1.44.1.7

99.9% Pure Y2O3 from Shin-etsu

TABLE 3.1115 PZC/IEP of Y2O3 from Shin-etsu Electrolyte

T

KOH + HCl a

Method

Instrument

pH0

Reference

iep

Pen Kem 7000a

8.3

[1041]

Solid-to-liquid ratio (0.1% by volume) was below standard level used in electroacoustic measurements (Chapter 2). Only value, data points not reported.

3.1.44.1.8 Y2O3 from Starck 3.1.44.1.8.1 Grade C Properties: >99.95% pure [1030], d10 = 280 nm, d50 = 460 nm, d50 = 740 nm, BET specific surface area 15 m2/g [476]. TABLE 3.1116 PZC/IEP of Grade C Y2O3 from Starck Electrolyte

T

Method

Instrument

pH0

Reference

iep iep

ESA ESA 8000, Matec

11.1 10

[476] [1030]

3.1.44.1.8.2 Other Properties: Particle size 836 and 360 nm (two instruments), specific surface area 13 m2/g [2153]. TABLE 3.1117 PZC/IEP of Unspecified Y2O3 from Starck Electrolyte

T

0.001 M KCl 25 a

Method

Instrument

iep

Malvern Zetasizer IIc

7.5–7.6 in aged dispersions.

pH0 Reference 8a

[2153]

511

Compilation of PZCs/IEPs

3.1.44.2 Synthetic 3.1.44.2.1 Hydrolysis of Y(NO3)3 in the Presence of Urea Solution 0.276 M in Y(NO3)3 and 50 g/dm3 in urea was heated at 95°C for 100 min (probably, YOHCO3 was obtained, then calcined). TABLE 3.1118 PZC/IEP of Y2O3 Obtained by Hydrolysis of Y(NO3)3 in Presence of Urea Electrolyte

T

Method

Instrument

pH0

Reference

iep

ZetaPlus Brookhaven

8.2

[1082]

0.001 M KNO3

3.1.44.2.2 Thermal Decomposition of YOHCO3 at 600°C A solution containing 3.3 M urea and 0.03 M Y(NO3)3 was heated at 115°C for 18 h. The product was calcined at 600°C. Properties: XRD results and TEM image available, BET specific surface area 13 m2/g [2154]. TABLE 3.1119 PZC/IEP of Y2O3 Obtained by Thermal Decomposition of YOHCO3 at 600°C Electrolyte

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa

7.6

[2154]

0.001 M NaNO3

3.1.44.2.3 Thermal Decomposition of YOHCO3 at 800°C A solution containing 1.8 M urea and 1.1–4.9 mM Y(NO3)3 was heated at 90°C for 9 h. The product was dried at 60°C and then calcined at 800°C for 3 h in air. TABLE 3.1120 PZC/IEP of Y2O3 Obtained by Thermal Decomposition of YOHCO3 at 800°C Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaCl

25

iepa

Malvern Zetasizer 2c

8.6

[2155]

a

Only value, data points not reported.

3.1.44.2.4 Thermal Decomposition of YOHCO3 at 750 or 900°C A filtered solution 0.02 M in YCl3 and 0.4 M in urea was heated to boiling. It was boiled for 1 h, and then quenched in an ice–water batch. The precipitate was washed and dried at 40°C in vacuum. It was then calcined for 3 h at 750 or 900°C.

512

Surface Charging and Points of Zero Charge

Properties: BET specific surface area 7.5 (calcination at 750°C) and 5 (at 900°C) m2/g, modal diameter 220 nm (calcination at 750°C) [597]. TABLE 3.1121 PZC/IEP of Y2O3 Obtained by Thermal Decomposition of YOHCO3 at 750 or 900°C Calcination Temperature (°C) 750 900/air 900/N2

Electrolyte

T

0.0001–0.1 M NaClO4

Method cip/iep

Instrument

pH0

Reference

Pen Kem Laser Zee Meter 501

8.4/9 8.9/9.1 9.2/9.2

[597]

3.1.44.2.5 Thermal Decomposition of YOHCO3 Properties: <0.02% of Fe, Al, Ca, Mg, and Cu, polydisperse, 35 nm–6 μm, specific surface area 14 m2/g [2156], modal diameter 300 nm [220]. TABLE 3.1122 PZC/IEP of Y2O3 Obtained by Thermal Decomposition of YOHCO3 Decomposition Temperature (°C) 800

Electrolyte

T

0.001 M NaNO3 0.1 M KCl

a

Method

Instrument

iep pH iep

Coulter Delsa Delsa 440

pH0 Reference 8.6 7a 10.2

[2157] [2156] [220]

Lowest CCC at pH 8–9 (NaNO3).

3.1.44.2.6

Thermal Decomposition of Latex Coated with Yttrium Basic Carbonate at 800°C Properties: Spherical, hollow particles, 210 nm outer and 130 nm inner diameter, TEM image and IR spectrum available [2157]. TABLE 3.1123 PZC/IEP of Y2O3 Obtained by Thermal Decomposition of Latex Coated with Yttrium Basic Carbonate Electrolyte 0.001 M NaNO3

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa

8.6

[2157]

513

Compilation of PZCs/IEPs

3.1.44.2.7

Hydrous, from Y(NO3)3 and NaOH

TABLE 3.1124 PZC/IEP of Hydrous Y2O3 Obtained from Y(NO3)3 and NaOH Electrolyte

a

T

Method

Instrument

pH0

Reference

iepa

Electrophoresis

9

[1229]

Only value, data points not reported. The same IEP is reported in [2226] for a precipitate termed hydroxide.

3.1.44.2.8 Spraying a Solution of Y(NO3)3 into Plasma Argon, ultrahigh-temperature inductively coupled plasma. Properties: 10–40 nm in diameter, cubic with unidentified admixture [2158].

TABLE 3.1125 PZC/IEP of Y2O3 Obtained by Spraying Solution of Y(NO3)3 into Plasma Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

8.8

[2158]

0.001 M NaCl

3.1.44.3

Origin Unknown

TABLE 3.1126 PZC/IEP of Y2O3 from Unknown Sources Description

Electrolyte

T

2

4.1 m /g Cubic, 1.5% CO2

a

Instrument

pH0

Reference

7.4 7.5/7.6/7.8

[1103] [1753]

iep cip

Electro-osmosis

25

Room

iepa iepa iep

9 10.6 Zeta-Meter 3.0+ 9.2

0.01–1 M NaClO4/ NaCl/KNO3 KNO3 0.001 M KCl

a

Method

[2159] [2160] [1004]

Only value, data points not reported.

3.1.45

Yb2O3

PZCs/IEPs of Yb2O3 (nominally, origin unknown) are presented in Table 3.1127.

514

Surface Charging and Points of Zero Charge

TABLE 3.1127 PZC/IEP of Yb2O3 Description

Electrolyte

T

Method a

Cubic, 0.5% CO2 a

iep cipa

0.01–1 M NaCl/KNO3 25

Instrument

pH0

Reference

Electro-osmosis

6.8 7.2

[1103] [1753]

Only value, data points not reported.

3.1.46

ZINC (HYDR)OXIDES

Zinc has only one stable oxidation state (+2) within the electrochemical window of water, but it forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. Nominal degree of hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of hydration. PZCs/ IEPs of zinc (hydr)oxides are presented in Tables 3.1128 through 3.1160. 3.1.46.1

ZnO

3.1.46.1.1

Commercial

3.1.46.1.1.1 Aldrich Properties: >99% pure [1686], BET specific surface area 6.9 m2/g [2161], specific surface area 4 m2/g [1686]. TABLE 3.1128 PZC/IEP of ZnO from Aldrich Electrolyte

T

0.005 M NaCl

a

Method

Instrument

iep pH iep

Pen Kem 500 Brookhaven ZetaPlus

pH0

Reference

7.2 7 7.5

[1686a,1688] [1263]a

Only value, data points not reported.

3.1.46.1.1.2 BASF Properties: BET specific surface area 13 m2/g, average size of primary particles 200 nm [135]. TABLE 3.1129 PZC/IEP of ZnO from BASF Description Electrolyte Original Washed a

T

Method

Instrument

Room

iep

Rank Brothers Mark II

pH0 Reference 9.2 8.3

[135]a

Immersion of ZnO in water has negligible effect on pH at pH 7–8. At pH > 8, immersion of ZnO induces decrease in pH.

515

Compilation of PZCs/IEPs

3.1.46.1.1.3 Zinkweiss Pharma A from BBU Properties: 99.9% pure, BET specific surface area 4.2 m2/g, average particle diameter 0.83 μm [2162,2163]. TABLE 3.1130 PZC/IEP of Zinkweiss Pharma A from BBU Description

Electrolyte

As received

NaOH + HCl

a

T

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee Meter 501

8.7a

[2163]

Two points of sign reversal of z potential in a supernatant solution of a 1 vol% dispersion are reported in [2162].

3.1.46.1.1.4

Fisher, 99.5% pure, 80% -25 µm

TABLE 3.1131 PZC/IEP of ZnO from Fisher Electrolyte

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

7a

[390]

0.001 M KCl a

No data points for pH 7–9. Maximum of settling velocity at pH 10.

3.1.46.1.1.5 Grillo Properties: 99.6% pure, BET specific surface area 3.6 m2/g, average particle diameter 1.9 μm [2162,2163].

TABLE 3.1132 PZC/IEP of ZnO from Grillo Description

Electrolyte

As received

NaOH + HCl

a

T

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee Meter 501

9.8a

[2162,2163]

Two points of sign reversal of z potential in a supernatant solution of a 1 vol% dispersion are reported in [2162].

3.1.46.1.1.6 Highways Properties: Specific surface area 3.8 m2/g (original), 2.1 m2/g (calcined in air at 650°C and cooled in vacuum) [2165].

516

Surface Charging and Points of Zero Charge

TABLE 3.1133 PZC/IEP of ZnO from Highways Description

Electrolyte

T

Method

As received, extrapolated to t = 0 As received, fast titration

0.001–0.1 M NaCl

20

cip

0.001–0.1 M NaCl

20

pH

Calcined in air at 650°C and cooled in vacuum

0.1 M NaCl

20

iep pH

Instrument

pH0

Reference

8.7

Electrophoresis

[2164,2165]

<8 if any

[2165]

<8 if any 9.5

[2164] [2165]

3.1.46.1.1.7 Johnson Matthey Properties: 99.99% pure, BET specific surface area 3 m2/g, average particle diameter 1.2 μm [2162,2163]. TABLE 3.1134 PZC/IEP of ZnO from Johnson Matthey Description

Electrolyte

As received

NaOH + HCl

a

T

Method

Instrument

pH0

Reference

Pen Kem Laser Zee 9.2a Meter 501

iep

[2163]

Two points of sign reversal of z potential in a supernatant solution of a 1 vol% dispersion are reported in [2162].

3.1.46.1.1.8

Probus

TABLE 3.1135 PZC/IEP of ZnO from Probus Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaCl

25

iep

Malvern Zetasizer 2c

9.2

[340]

3.1.46.1.1.9

Puratronic Grade I

TABLE 3.1136 PZC/IEP of Puratronic Grade I ZnO Electrolyte 0.005 M KCl

T

Method

Instrument

iep

Laser Zee Meter 500 Pen Kem

pH0 <8 if any

Reference [2166]

517

Compilation of PZCs/IEPs

3.1.46.1.1.10

Sakai

Properties: Average particle size 40 nm [2167].

TABLE 3.1137 PZC/IEP of ZnO from Sakai Electrolyte

a

T

Method

Instrument

iep

LEZA-600, Otsuka

pH0 Reference 9.6a

[2167]

Arbitrary interpolation.

3.1.46.1.1.11 Sigma (Sigma-Aldrich) Properties: BET specific surface area 4 m2/g [1031], XRD pattern available [2168]. TABLE 3.1138 PZC/IEP of ZnO from Sigma (Sigma-Aldrich) Description

Electrolyte

As received

0.01 M KNO3 KCl

T

Method

Instrument

pH0

Reference

iep iep

Rank Brothers II Malvern Nano ZS

9.2 9.5

[2168] [1031]

3.1.46.1.1.12 Slovak Koseca Properties: 99.78% pure, BET specific surface area 3.6 m2/g, average particle diameter 1.5 μm [2162,2163]. TABLE 3.1139 PZC/IEP of ZnO from Slovak Koseca Description

Electrolyte

As received

NaOH + HCl

a

T

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee Meter 501

8.6a

[2163]

Two points of sign reversal of z potential in a supernatant solution of a 1 vol% dispersion are reported in [2162].

3.1.46.1.1.13

Standard Labs

TABLE 3.1140 PZC/IEP of ZnO from Standard Labs Electrolyte 0–0.01 M KCl a

T

Method

Instrument

pH0

iep

Briggs-Mattson apparatus

<7.5a

Maximum coagulation at pH about 10.5.

Reference [134]

518

Surface Charging and Points of Zero Charge

3.1.46.1.1.14 [387].

Ventron 99.999%

Properties: BET specific surface area 7.5 m2/g

TABLE 3.1141 PZC/IEP of ZnO from Ventron Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep

Pen Kem S3000

9.3

[387]

3.1.46.1.1.15 Origin Unknown Washed with water. Properties: BET specific surface area 3.2 m2/g [2169]. TABLE 3.1142 PZC/IEP of ZnO from Unknown Commercial Sources Description Water-washed, and dried at 110°C >99.9% pure, 4.4 m2/g a b

Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M KCl

25

iep

Rank Mark II

6.9

[1213]

8 8.9

[2169] [1362]

0.001–0.1 M KNO3 20a KCl

cip pHb

Also 30–50°C. Only value, data points not reported.

3.1.46.1.2 Synthetic 3.1.46.1.2.1 From Chloride 3.1.46.1.2.1.1 From 1 M ZnCl2 and an Excess of 2 M NaOH The precipitate was refluxed and washed. ZnCl2 was added to adjust the pH to 7. The mixture was refluxed for 10 d and then stored for 1.5 y. Properties: Specific surface area 13.1 m2/g [549]. TABLE 3.1143 PZC/IEP of ZnO Obtained from 1 M ZnCl2 and an Excess of 2 M NaOH Electrolyte

T

Method

0.0002–0.1 M NaNO3 NaClO4 NaCl

25

cipa

a

Only value, data points not reported.

Instrument

pH0

Reference

8.8 9.1 9.2

[549]

519

Compilation of PZCs/IEPs

3.1.46.1.2.1.2 From 1 M ZnCl2 and an Excess of 8 M KOH aged at 100°C for 10 d in plastic container, stored for 1.5 y. Properties: Specific surface area 11.5 m2/g [549].

Precipitate

TABLE 3.1144 PZC/IEP of ZnO Obtained from 1 M ZnCl2 and an Excess of 8 M KOH Electrolyte 0.0002–0.1 M NaNO3

a

T

Method

Instrument

a

25

cip

pH0

Reference

9.5 10

[549]

Only value, data points not reported.

3.1.46.1.2.1.3 From 1 M ZnCl2 and an Excess of 8 M KOH, Final pH 10.5 Refluxed for 20 d. Properties: Specific surface area 16.5 m2/g [549]. TABLE 3.1145 PZC/IEP of ZnO Obtained from 1 M ZnCl2 and an Excess of 8 M KOH at Final pH 10.5 Electrolyte

T

Method

0.0002–0.1 M NaNO3 NaClO4

25

cipa

a

Instrument

pH0

Reference

8.8 8.5

[549]

Only value, data points not reported.

3.1.46.1.2.1.4 From Concentrated ZnCl2 (450 g + 400 g of Water) and an Excess of 8 M KOH at Boiling Point Washed and refluxed for 2 d. Properties: Specific surface area 6.5 m2/g [549]. Table 3.1146 PZC/IEP of ZnO Obtained from Concentrated ZnCl2 Solution and an Excess of 8 M KOH at Boiling Point Electrolyte

T

Method

0.0002–0.1 M NaNO3 NaCl NaBr NaI

25

cip

Instrument

pH0

Reference

8.6 8.8 8.7 8.7

[549]

520

Surface Charging and Points of Zero Charge

3.1.46.1.2.1.5 From ZnCl2 and NaOH at 100°C Refluxed for 10 d, washed. Properties: Structure confirmed by XRD, contains SiO2 [2170]. TABLE 3.1147 PZC/IEP of ZnO Obtained from ZnCl2 and NaOH at 100°C Electrolyte

T

Method

<0.02 M NaCl <0.02 M NaNO3 a

Instrument

pH0

Reference

9.2 8.7

[2170]a

Titration

Only values, no data points.

3.1.46.1.2.2 From Nitrate 3.1.46.1.2.2.1 From 1 M Zn(NO3)2 and 10 M NaOH in the Presence of 0.003 mol% of In Refluxed for 4 d. Calcined at 1250°C. Properties: Specific surface area 0.5 m2/g [549]. TABLE 3.1148 PZC/IEP of ZnO Obtained from 1 M Zn(NO3)2 and 10 M NaOH in Presence of 0.003 mol% In Electrolyte

T

Method

0.0002–0.1 M NaNO3

25

cipa

a

Instrument

pH0

Reference

9.5

[549]

Only value, data points not reported.

3.1.46.1.2.2.2 From Solution of 450 g Zn(NO3)2 in 1.5 dm3 of Water and Half of Stoichiometric Amount of 10 M NaOH at Boiling Point Aged for 7 d at 100°C. Properties: Specific surface area 13.5 m2/g [549]. TABLE 3.1149 PZC/IEP of ZnO Obtained from Solution of 450 g Zn(NO3)2 in 1.5 L of Water and Half of Stoichiometric Amount of 10 M NaOH at Boiling Point Electrolyte

T

Method

0.0002–0.1 M NaNO3 NaCl

25

cip

Instrument

pH0

Reference

<8 8.2

[549]

3.1.46.1.2.2.3 From Zn(NO3)2 and Urea A solution 0.1 M in Zn(NO3)2 and 0.5 M in urea was aged for 8 h at 95°C. The precipitate was calcined.

521

Compilation of PZCs/IEPs

Properties: XRD pattern, FTIR spectrum, TEM image available [387]. TABLE 3.1150 PZC/IEP of ZnO Obtained from Zn(NO3)2 and Urea Calcination Temperature (°C)/Specific Surface Area (m2/g) 300/17.9 600/10.4

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem S3000

9.8 9.3

[387]

0.001 M KNO3

3.1.46.1.2.2.4 From Zn(NO3)2 and Ammonia 40 cm3 of 1 M Zn(NO3)2 was abruptly mixed with 10 cm3 of 25% ammonia and aged for 20 min–1 d at 120 or 160°C. The precipitate was washed and dried. Properties: XRD pattern, FTIR spectrum, TEM image available [387]. TABLE 3.1151 PZC/IEP of ZnO Obtained from Zn(NO3)2 and Ammonia Aging Temperature (°C)/ Aging Time/Specific Surface Area (m2/g) Electrolyte 120/50 min/4.5 160/20 min/1.6 160/2 h/1.9 160/1 d/1.1

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep

Pen Kem S3000

9.4 9.5 9.3 9.4

[387]

3.1.46.1.2.2.5 From Zn(NO3)2 and NaOH, Washed, and Aged structure confirmed by XRD, [1088].

Properties:

TABLE 3.1152 PZC/IEP of ZnO Obtained from Zn(NO3)2 and NaOH Electrolyte

T

Method iep

a

a

Instrument

pH0

Reference

Electrophoresis

9.2–9.7

[1088]

Only range, data points not reported.

3.1.46.1.2.3 From Acetate 80 cm3 of 0.02 M NaOH in 2-propano1 was added to 1 mmol of zinc acetate in 920 cm3 of 2-propanol at 0°C, then aged for 2 h at 65°C, and for 3 d at room temperature. The solution was evaporated at 30°C at 1 Torr, and redispersed in water.

522

Surface Charging and Points of Zero Charge

Properties: Mean diameter 5 nm, TEM image available [1393]. TABLE 3.1153 PZC/IEP of ZnO Obtained from Acetate Electrolyte

T

Method

0.002 M CH3COONa

25

Inflection Coagulation

Instrument

pH0

Reference

9.3

[1393]

3.1.46.1.2.4 Calcination of Oxalate The oxalate was obtained from 1 M Zn(NO3)2 and a 10% excess of oxalic acid, washed with water, and calcined at 600°C for 6 h. The oxide was washed with water until constant conductivity. It was calcined at 800–1400°C for 6 h and washed again. Not-crushed and crushed samples produce similar IEPs. TABLE 3.1154 PZC/IEP of ZnO Obtained by Calcination of Oxalate Second Calcination Temperature (°C) None 800 1000 1200 1400 a

Electrolyte 0.001 M NaCl

T 25

Method a

pH

Instrument

pH0

Reference

Streaming potential

9.9 9.8 9.8 9.2 9.2

[33]

Only value, data points not reported.

3.1.46.1.2.5 From Zincite Reference [2171] is cited for the recipe, but no detailed recipe was found there. 10 GPa, 200°C. Properties: Tetragonal, volume-centered [2171], BET specific surface area 67.5 m2/g [2172,2173], specific density 6215 kg/m3 [2171]. TABLE 3.1155 PZC/IEP of ZnO Obtained from Zincite Electrolyte 0.001 M NaCl

a b

T

Method iep Titrationb

+19 mV at pH 8.5, −16 mV at pH 10.4. Only value, data points not reported.

Instrument Brookhaven ZetaPlus

pH0 >8.5 9.4

a

Reference [2172,2173] [2173]

523

Compilation of PZCs/IEPs

3.1.46.1.2.6 Oxidation of Metallic Zn TABLE 3.1156 PZC/IEP of ZnO Obtained by Oxidation of Metallic Zn Electrolyte

T

Method

Instrument

pH0

Reference

9

[1067]

Drifta a

Only value, data points not reported.

3.1.46.1.3 Origin Unknown TABLE 3.1157 PZC/IEP of ZnO from Unknown Sources Description

Electrolyte

T

0.01 M KCl

Amorphous

a b

0.05 M NaClO4 0.001 M KNO3 0.0175 M KNO3

25

Method

Instrument

pH0

Reference

pH iep iep

[2174]a

Electro-osmosis

9.2 9.2 9.3

iep iep

Zeta-Meter Delsa 440

9.8 9.8

[1103]a [1217] [1264] [1252b,1254]

Only value, data points not reported. Described as hydrous ZnO.

3.1.46.2

Hydrous ZnO Obtained from ZnCl2 and NaOH

TABLE 3.1158 PZC/IEP of Hydrous ZnO Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

10.3

[1229]a

Only value, no data points. The same IEP is reported in [2226] for a precipitate termed hydroxide.

3.1.46.3 Zinc Oxide–Hydroxide 12.2 g of ZnO was dissolved in HNO3 (pH 2). The pH was then brought to 8 with NaOH.

524

Surface Charging and Points of Zero Charge

TABLE 3.1159 PZC/IEP of Zinc Oxide–Hydroxide Electrolyte

T

Method

Instrument

pH0

Reference

iep

Rank Brothers II

8.1

[2168]

0.01 M KNO3

3.1.46.4 Zn(OH)2 TABLE 3.1160 PZC/IEP of Zn(OH)2 Description

Electrolyte

Precipitated ZnCl2 + 0.01 M NaOH, at 23°C, not washed Johnson Matthey Alfa a

T

Method

Instrument

0.002, 0.02 M NaCl 0.001 M NaNO3

iep iep

Riddick-type cell Delsa 440

0.005 M NaCl

iep pH

Pen Kem 500

pH0 Reference 9.6 10a

[1232] [1220]

6 7.2

[1688]

Arbitrary interpolation, IEP at pH 10.3 is reported in abstract.

3.1.47

ZIRCONIUM (HYDR)OXIDES

Zirconium has only one stable oxidation state (+4) within the electrochemical window of water, but it forms several relatively stable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. Y-modified zirconias are often referred to as “ZrO2” in the original publications, but in the present book they are discussed in Section 3.3.18.3. Nominal degree of hydration indicated by a chemical name/formula reported in the literature does not necessarily reflect the actual degree of hydration. PZCs/ IEPs of zirconium (hydr)oxides are presented in Tables 3.1161 through 3.1228. The PZCs/IEPs of ZrO2 are compiled in [284,2175–2178]. 3.1.47.1 ZrO2 3.1.47.1.1

Commercial

3.1.47.1.1.1 ZrO2 from 3 M, Eight Samples Properties: Porous spherules, particle size, surface area, pore diameter, and porosity available [1854]. TABLE 3.1161 PZC/IEP of ZrO2 from 3 M Electrolyte 20% w/v NaCl

T 30

Method Instrument pH

pH0 Reference 5.5

[1854]

525

Compilation of PZCs/IEPs

3.1.47.1.1.2 ZrO2 from Aldrich Properties: Monoclinic, 99.99% [560], monoclinic [409], BET specific surface area 1.4 m2/g [560], 32.5 (original) and 32 (washed) m2/g [2179], average diameter 300 nm [409]. TABLE 3.1162 PZC/IEP of ZrO2 from Aldrich Description

Electrolyte

T

Method

0.01 M NaCl 0.001 M KNO3 Water-washed 0.01 M 0.1 M NaOH-washed NaCl Aged in 0.001 M 0.001–0.1 M KNO3 for (h): KNO3 16 30 50 120 170

25

iep

23

iepa

25

iep/pH

20

cip/iep

a b

Instrument Malvern Zetasizer 2000 Streaming potential Malvern Zetasizer 3000 Rank Brothers Mark II

pH0

Reference

6.1

[409]

7.4

[261]

8/4.2 7b/7

[2179] [560]

9.5(merge)/9 7.2/— 7/— 6.5/— —/6.2

Only value, data points not reported. Arbitrary interpolation.

3.1.47.1.1.3 ZrO2 from Alfa Aesar Properties: 99% [260], -325 mesh [260], mean particle size 700 nm [433], (20% dispersion) particle diameter 110 nm [2117, Table 2]. ZrO2 from Alfa Aesar, Johnson Matthey: monoclinic, >99.5% pure, BET specific surface area 5 m2/g, average particle size 640 nm, SEM image available [2180]. TABLE 3.1163 PZC/IEP of ZrO2 from Alfa Aesar Electrolyte

T 25

0.0001 M KCl 0.001 M NaCl a

20

Method iep iep iep iep

Instrument

pH0

Electrophoresis Matec ESA 9800 Brookhaven ZetaPlus Malvern Zetasizer Nano ZS

a

6 6.4 8.1 4.7

Reference [260] [433] [2117] [2180]

Based on subjective interpolation, no data points at pH 5–6.5. Also 120 and 200°C.

3.1.47.1.1.4 [915,1773].

ZrO2 from Degussa

Properties: BET specific surface area 39 m2/g

526

Surface Charging and Points of Zero Charge

TABLE 3.1164 PZC/IEP of ZrO2 from Degussa Description Acid-washed a

Electrolyte

T

0.001 M NaClO4

Method iep

Instrument

pH0

Reference

a

Electrophoresis

8.2

[2181]

Matches stability minimum.

3.1.47.1.1.5 Pure Grade ZrO2 from Donetsk Plant of Chemical Reagents Properties: (acid-washed) baddeleyite, particle size 2–20 mm, BET specific surface area 20 m2/g [2182]. TABLE 3.1165 PZC/IEP of ZrO2 from Donetsk Plant of Chemical Reagents Description 1: 3 HCl-washed

Electrolyte

T

0.001–1 M KCl

Method

Instrument

pH0 Reference

cip iep

Electrophoresis

5.1 5.1

[2182]

3.1.47.1.1.6 Dynazirkon F from Dynamit Nobel Properties: Monoclinic [2183]. TABLE 3.1166 PZC/IEP of Dynazirkon F from Dynamit Nobel Electrolyte

T

HCl

Method

Instrument

pH0

Reference

iep

Micromeritics mass transport

5

[2183]

3.1.47.1.1.7 ZrO2 from Fisher Properties: Average particle size 2 μm, BET specific surface area 3 m2/g [2048]. TABLE 3.1167 PZC/IEP of ZrO2 from Fisher Electrolyte 0.1 M KCl a

T

Method a

iep

Instrument

pH0

Streaming potential

6.6

Only value, data points not reported.

Reference [2048]

527

Compilation of PZCs/IEPs

3.1.47.1.1.8 ZrO2 from Inframat Advanced Materials Properties: Purity >99.9%, specific surface area 15–40 m2/g, particle size 30–60 nm, specific density 5680 kg/m3, SEM image available [397]. TABLE 3.1168 PZC/IEP of ZrO2 from Inframat Electrolyte

T

Method

0.01 M KNO3 a

iep

Instrument Zeta-Meter 3.0+

pH0 a

5.4

Reference [397]

Arbitrary interpolation.

3.1.47.1.1.9 ZrO2 from INVAP Properties: High purity, 1.5 ppm F, baddeleyite, average diameter 0.18 mm, nonporous, nearly spherical, BET specific surface area 5.7 m2/g [1289]. TABLE 3.1169 PZC/IEP of ZrO2 from INVAP Electrolyte

T

Method

Instrument

0.001–0.1 M KNO3

30 25

cip iep

Carl Zeiss

pH0 Reference 6.4 6.5

[1289]

3.1.47.1.1.10 ZrO2 from Johnson-Matthey, Purity Grade Z See also Alfa Aesar. Properties: Mixture of monoclinic and tetragonal form, crystallite size 42 nm (monoclinic), BET specific surface area 7 m2/g [2184]. TABLE 3.1170 PZC/IEP of ZrO2 from Johnson–Matthey Electrolyte 0.01 M NaNO3 a

T

Method

Instrument

pH0

Reference

iepa

Electrophoresis

4.9

[2184]

Only value, data points not reported.

3.1.47.1.1.11 ZrO2 from Magnesium Elektron (or Magneson Electron) Properties of SC 30: 99% ZrO2, BET specific surface area 2.8 m2/g [794].

528

Surface Charging and Points of Zero Charge

Properties of SC 105: BET specific surface area 1.9 m2/g [667] (the column headings in Table 1 of [667] were probably swapped). Properties of unspecified ZrO2: BET specific surface area 21 m2/g [2185]. TABLE 3.1171 PZC/IEP of ZrO2 from Magnesium Elektron Type Unspecified SC 30 Unspecified SC 105, Soxhlet-washed a

Electrolyte

T

0.01 M KCl 0.001 M KCl

20 25

Method

Instrument

pH0 Reference

iep Zetasizer 2c Malvern iep Rank Brothers Mark II iepa Mass titration

6 6.2 6.5 6.5

[2185] [794] [2186] [667]

Only value, data points not reported.

3.1.47.1.1.12 [2187].

ZrO2 from Merck

Properties: BET specific surface area 7.4 m2/g

TABLE 3.1172 PZC/IEP of ZrO2 from Merck Description Water-washed

Electrolyte 0.001–0.1 M NaCl

Acid- and base-washed a

T

Method

Instrument

cip 20

iep

Acoustosizer Matec

pH0

Reference

3.5

[2187]a [2188] [1987,2153]

7.6

Higher values reported in text (determined as natural pH).

3.1.47.1.1.13 NZS-30A from Nissan Sol, 30% by mass. Properties: Monoclinic, average particle size 62 nm [1013].

TABLE 3.1173 PZC/IEP of NZS-30A from Nissan Description

Electrolyte 0.03 M NH4Cl

a

T

Method iep

Instrument Sugiura 2 VD

+14 mV at pH 6, −5 mV at pH 8, no data points in between.

pH0 >6

a

Reference [1013]

529

Compilation of PZCs/IEPs

3.1.47.1.1.14 ZrO2 from Norton Properties: Monoclinic [39,1921], 0.5% of impurities (TiO2, SiO2, Fe2O3, CaO) [1921], specific surface area 0.1 m2/g [39]. TABLE 3.1174 PZC/IEP of ZrO2 from Norton Electrolyte

T

Method

0.001,1 M KNO3 0.001–1 M KNO3, NaClO4

25

Intersection pH

a

Instrument

pH0

Reference

6.3 6–6.7a

[1921] [39]

Only acidic side shown.

3.1.47.1.1.15 ZrO2 from Nyacol Nano Technologies Particles were isolated from a commercial 20 mass% dispersion stabilized with acetate, containing 5–10 nm particles. They were then calcined at 250 or 400°C in air for 1 h. Properties: Particles calcined at 250 are amorphous, particles calcined at 400°C show presence of tetragonal phase, XRD pattern available [1931].

TABLE 3.1175 PZC/IEP of ZrO2 from Nyacol Nano Technologies Calcined 250 400 a

Electrolyte

T

0.004 M NaCl

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer Nano ZS

9.5 5

[1931]a

Original particles had IEP at pH 7 (acetate present). Calcined particles (layer-deposited on silica-based material) were studied by means of streaming potential, and IEP was 9 and 5.5 for particles calcined at 250 and 400°C, respectively.

3.1.47.1.1.16 Membralox Membrane from SCT

TABLE 3.1176 PZC/IEP of Membralox Membrane from SCT Description New Used and cleaned a

Electrolyte 0.001 M KCl

T 25

Confirmed by electroviscous effect.

Method iep

Instrument a

Streaming potential

pH0

Reference

>8 5.2

[995]

530

Surface Charging and Points of Zero Charge

3.1.47.1.1.17 ZrO2 from S.D. Fine Chemicals Properties: Monoclinic, mean particle size 10.5 μm, BET specific surface area 22.4 m2/g [355]. TABLE 3.1177 PZC/IEP of ZrO2 from S.D. Fine Chemicals Electrolyte

T

Method

Instrument

pH0

iep

Malvern Zetasizer 3000

6.2

0.001 M KNO3

Reference [355]

3.1.47.1.1.18 Filtration Membranes from Techsep TABLE 3.1178 PZC/IEP of Filtration Membranes from Techsep Description

Electrolyte

T

Method

Instrument

pH0

Reference

M 4, 97.7% ZrO2

0.001 M NaCl

50

iep

0.001 M NaCl

50

iep

4.2 4 6/4a 4

[2189]

M 1, 99.5% ZrO2

Rank Brothers Mark II Streaming potential Rank Brothers Mark II Streaming potential

a

[2189]

Powder used for membrane manufacturing/powder scrapped from a membrane.

3.1.47.1.1.19 ZrO2 from Tosoh 3.1.47.1.1.19.1 TZ-0 (from Tosoh or from TSK) See also Section 3.1.47.1.1.20. Properties: Monoclinic [509,801,1039,1043,2190], <0.005% Al2O3, 0.006% SiO2, 0.003% Fe2O3, 0.016% Na2O [801], BET specific surface area 14 m2/g [509,1039,2190], 14.1 m2/g [1043], specific surface area 15.2m2/g [801], particle diameter 73 nm [1043], mean diameter 300 nm [801], 0.4 mm [509], mean size 0.1 mm [1039,2190], specific density 5.7 g/cm3 [509]. TABLE 3.1179 PZC/IEP of TZ-0 from Tosoh Description As obtained

T

Method

Instrument

pH0

Reference

0.0001–0.01 M NaCl

Electrolyte

25

Rank Brothers II

25

Acoustosizer 2 DT 1200

5.5 5.8a 5.8 5.8

[1039,2190]

None

cip iep iep iep

[2191] [1043]

iep iep

AcoustoSizer Acoustosizer

6.4 8.2b

[801] [509]

Calcined at 400°C for 4 h 0.001 M KCl 25 0.01, 0.1 M NaNO3, 25 NaCl, NaClO4, NaBrO3 a b

Figure captions (Figures 2 and 3) are swapped in [1039]. Maximum in yield stress of dispersion (0.2 volume fraction) matches IEP.

531

Compilation of PZCs/IEPs

3.1.47.1.1.19.2 Monoclinic Properties: BET specific surface area 10.3 m2/g [1000], specific surface area 15.5 m2/g [284], particle size 300 nm [284], mean diameter 0.8 mm [1000].

TABLE 3.1180 PZC/IEP of Unspecified Monoclinic ZrO2 from Tosoh Electrolyte 0.01 M NaCl 0.001 M KNO3 a

T

Method

Instrument

pH0

Reference

26–27

iep pH

Malvern Zetasizer II c

5.6a 7.3

[284] [1000]

Only value, from Table 1. Figure 1a reports IEP at pH 6–6.5 (for different aging time and different solid-to-liquid ratios) obtained by streaming current.

3.1.47.1.1.20 TZ-0 (TSK) from Toyo Soda See also Section 3.1.47.1.1.19. Properties: Monoclinic [267], 99.6% ZrO2 [794], BET specific surface area 11.4 m2/g [794], average size 0.05 mm [267], TEM image available [267].

TABLE 3.1181 PZC/IEP of TZ-0 (TSK) from Toyo Soda Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

25

iep iep

Rank Brothers Mark II Mass transport

6.5 6.5

[794] [267]

NH4OH + HCl

3.1.47.1.1.21 3.3 m2/g.

ZrO2 from Unitec

Properties: BET specific surface area

TABLE 3.1182 PZC/IEP of ZrO2 from Unitec Electrolyte 0.01 M NaNO3 a

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 2.0

6a

[787]

Subjective interpolation. IEP roughly matches maximum in yield stress in a 25 vol% dispersion.

3.1.47.1.1.22 ZrO2 from Ventron Properties: Monoclinic [560,1675,1676,2192], 99.9%, [560], 99%, baddeleyite [1736], 30 ppm Na, 210 ppm Ca, 1150 ppm Ti, 2.7% Hf [1675,1676,2192], BET specific surface area 0.66 m2/g [560], 27.9 m2/g [1675,1676,2192], specific surface area 3.4 m2/g [1736], particle size 400 nm [1736].

532

Surface Charging and Points of Zero Charge

TABLE 3.1183 PZC/IEP of ZrO2 from Ventron Description

Electrolyte

As obtained

0.0001–0.01 M NaCl 0.001–0.1 M NaCl

NH3-washed

T

Method

Instrument Pen Kem S 3000

25

iep Mass titration cip

20

cip/iep

Aged in 0.001 M 0.001–0.1 M KNO3 KNO3 for (h): 16 60 10 140 150 250

pH0

Reference

7 6 7.6

[1736]

Rank Brothers Mark II 8.8/9.1 7.5/— 7.1/— —/6.5 6.7/— 6.3/—

[1675,1676, 2192] [560]

3.1.47.1.1.23 ZrO2 from Yixing Zirconium Co. Properties: BET specific surface area 11.8 m2/g [2193], average particle diameter 370 nm [2193]. TABLE 3.1184 PZC/IEP of ZrO2 from Yixing Electrolyte

T

Method iep

a

Instrument Malvern 3000 HSA

pH0 6

a

Reference [2193]

Only IEP reported, no data points.

3.1.47.1.1.24 ZrO2 from Z-Tech (ICI Z-Tech) 3.1.47.1.1.24.1 SF Ultra 0.5 from Z-Tech Properties: Monoclinic, particle size 410 nm [901]. TABLE 3.1185 PZC/IEP of SF Ultra 0.5 from Z-Tech Electrolyte KOH + HCl

T

Method

Instrument

pH0

iep

Pen Kem Acoustophoretic Titrator 7000

7

Reference [901]

3.1.47.1.1.24.2 Other Sample prepared by precipitation from sulfuric acid [508]. Properties: Monoclinic [508,2194], impurities (in ppm) SiO2 58, Fe2O3 46, CaO 23, TiO2 169, Al2O3 33, S 67 (sample calcined at 850°C for 5 h) [508], 2% HfO2 [2194,2195], other impurities (in ppm) SiO2 77, Fe2O3 75, CaO 26, TiO2 70, Al2O3 37, S 50 [2195], BET specific surface area 15.1 m2/g [2195–2197], 15.4 m2/g [436], 65, 23, and 16.7 m2/g (sample calcined at 450, 650, and 850°C) [508],

533

Compilation of PZCs/IEPs

21.6 m2/g [2194], 15.1 m2/g [2186,2198], particle diameter 300 nm [2195,2196], median particle size 250 nm [436], particle size D90 = 260 nm, D50 = 210 nm, D10 = 170 nm [2198], D90 = 580 nm, D50 = 250 nm, D10 = 130 nm [2197], D90 = 1490 nm, D50 = 530 nm, D10 = 190 nm [2194], specific density 5880 kg/m3 [2197], 5900 kg/m3 [2198]. TABLE 3.1186 PZC/IEP of Unspecified ZrO2 from Z-Tech Description Calcined at (°C): 450 650 850, Soxhlet-extracted Calcined at 850°C

Electrolyte

T

Method

Instrument

0.0001–0.01 M KNO3

25

iep

Rank Brothers Mark II

0.001 M NaNO3

25

iep

Matec Acoustosizer Rank Brothers Mark II

0.001 M NaCl

iep iep iep

a b c d e f

0.05 M KNO3 0.001–0.1 M KNO3 0.01 M KNO3

25

iep cip iep

0.1 M KCl

25

iep

Matec Acoustosizer Matec MBS-8000 Matec MBS-8000 Acoustosizer

pH0 Reference 6 5.1 7.7a 6.5b

[508]

6.7c

[2194]

7d 7e

[2199] [436]

7e

[2197]

7.3f

[2195]

7.8e

[2198]

[2196]

AFM results produce IEP at pH 7. AFM results produce IEP at pH 7.2. Matches maximum in yield stress of dispersion, 50% by mass. Only value, data points not reported. Matches the maximum in yield stress of dispersion, 57% by mass. Matches the maximum in yield stress of dispersion, 57–65% by mass.

3.1.47.1.1.25 Other Properties: Monoclinic, high purity, BET specific surface area 2.2 m2/g [1457], reagent-grade [1247]. TABLE 3.1187 PZC/IEP of Unspecified Commercial ZrO2 Electrolyte 0.001–0.1 M KCl 0.001 M KNO3 a

T

Method

Instrument

pH0 Reference

cip Electrophoresis 4 iep Titration 6.4a

Only value, data points not reported.

[1457] [1247]

534

Surface Charging and Points of Zero Charge

3.1.47.1.2 Synthetic 3.1.47.1.2.1 From Isopropoxide 3.1.47.1.2.1.1 Calcined at 750°C Zirconium propoxide was hydrolyzed in 100 (mol/mol) parts of water. The precipitate was filtered and washed, dried at 100°C, and calcined at 750°C. Properties: Monoclinic, specific surface area 66 m2/g [2178]. TABLE 3.1188 PZC/IEP of ZrO2 Obtained from Isopropoxide and Calcined at 750°C Electrolyte

T

Method

Instrument

pH0

Reference

0.0001, 0.01 M NaCl

25

iep pH

Rank Brothers Mark II

6.7 3.9

[2178]

3.1.47.1.2.1.2 Calcined at 500°C Zirconium n-propoxide was hydrolyzed in 4 (mol/mol) parts of water at room temperature. The precipitate was washed in warm water, and calcined at 500°C for 3 h. Properties: Monoclinic, specific surface area 19 m2/g [2200]. TABLE 3.1189 PZC/IEP of ZrO2 Obtained from Isopropoxide and Calcined at 500°C Electrolyte

T

Method

Instrument

pH0

Reference

iep

Matec 8050

7.3

[2200]

NaOH + HCl

3.1.47.1.2.2 From Chloride See also Section 3.1.47.1.2.6. 3.1.47.1.2.2.1 Prepared at pH 3.6 Calcined at 400°C for 5 h. Properties: Mixture of monoclinic (33%), tetragonal (33%), and cubic (33%) form, BET specific surface area 55.2 m2/g [2201]. TABLE 3.1190 PZC/IEP of ZrO2 Obtained from Chloride at pH 3.6 Electrolyte 0.001–0.1 M KNO3

T

Method Instrument cip

pH0

Reference

7.9

[2201]

3.1.47.1.2.2.2 From ZrOCl2, Prepared at pH 4 A: Washed, dried at 120°C. Properties: Amorphous, BET specific surface area 84 m2/g [2184].

535

Compilation of PZCs/IEPs

B: Sample A calcined at 1300°C. Properties: Monoclinic, crystallite size 60 nm [2184].

TABLE 3.1191 PZC/IEP of ZrO2 Obtained from ZrOCl2 at pH 4 Description

Electrolyte

A B

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

4 4

[2184]

0.01 M NaNO3

3.1.47.1.2.2.3 Prepared at pH 4.5. Calcined at 200°C for 22 h, mechanical treatment. Properties: Monoclinic, BET specific surface area 149.7 m2/g [596,2201].

TABLE 3.1192 PZC/IEP of ZrO2 Obtained from Chloride at pH 4.5 Description Aged at pH 4.4 Aged at pH 9.4

Electrolyte

T

0.001–0.1 M KNO3 0.001–0.1 M KNO3

Method

Instrument pH0 Reference

cip cip

7.9 8 7.2

[2201] [596]

3.1.47.1.2.2.4 Prepared at pH 5.7 Calcination at 400°C for 5 h. Properties: Mixture of monoclinic (50%), tetragonal (25%), and cubic (25%) form, specific surface area 117.9 m2/g [2201]. TABLE 3.1193 PZC/IEP of ZrO2 Obtained from Chloride at pH 5.7 Electrolyte 0.001–0.1 M KNO3

T

Method cip

Instrument

pH0

Reference

7.8

[2201]

3.1.47.1.2.2.5 From ZrOCl2, prepared at pH 10 A: Dialyzed. Properties: Amorphous [2184]. B: Washed. Properties: Amorphous [2184]. C: Sample B dried at 120°C. Properties: Amorphous [2184]. D: Sample C calcined at 1300°C. Properties: Monoclinic, crystallite size 65 nm [2184].

536

Surface Charging and Points of Zero Charge

TABLE 3.1194 PZC/IEP of ZrO2 Obtained from ZrOCl2 at pH 10 BET Specific Description Surface Area (m2/g) Electrolyte A B C D

T

Method iep

0.01 M NaNO3 260 1

Instrument

pH0 Reference

Electrophoresis 4.5 4.5 4.7 4.8

[2184]

3.1.47.1.2.2.6 Precipitated at final pH 14 Calcination at 200°C for 22 h. Properties: Tetragonal, specific surface area 235.9 m2/g [2201]. TABLE 3.1195 PZC/IEP of ZrO2 Obtained from Chloride at Final pH 14 Electrolyte

T

0.001–0.1 M KNO3

Method

Instrument

cip

pH0

Reference

6.2

[2201]

3.1.47.1.2.2.7 From ZrOCl2, Hydrolyzed with Aqueous Ammonia Washed, dried at 100°C, and calcined. TABLE 3.1196 PZC/IEP of ZrO2 Obtained from ZrOCl2, Hydrolyzed with Aqueous Ammonia Calcination 2

300°C, 289 m /g 500°C, 82 m2/g

Electrolyte

T

Method

0.01 M KCl

40

pH

Instrument

pH0

Reference

<2.8 <2.7

[979]

3.1.47.1.2.2.8 From 0.1 M ZrCl4 Adjusted to pH 0.5 and Aged for 20 Days at 100°C 0.1 M ZrCl4 adjusted to pH 0.5 with HCl was heated in a Pyrex reactor for 20 d at 100°C. The precipitate was washed with water. Properties: Monoclinic [2202]. TABLE 3.1197 PZC/IEP of ZrO2 Obtained from 0.1 M ZrCl4 Adjusted to pH 0.5 and Aged for 20 Days at 100°C Electrolyte 0.001–0.03 M KNO3

T

Method cip

Instrument

pH0

Reference

7.6

[2202]

3.1.47.1.2.2.9 From 1 M ZrOCl2 Adjusted to pH 2.5 and Refluxed for 44 h Filtered 1 M ZrOCl2 was adjusted to pH 2.5 by dropwise addition of 0.5 M

537

Compilation of PZCs/IEPs

ammonia and refluxed for 44 h. It was then diluted to 3 dm3, adjusted to pH 2.5 by dropwise addition of 0.5 M ammonia, and refluxed for 44 h. Properties: Monoclinic, specific surface area 143 m2/g [2203]. TABLE 3.1198 PZC/IEP of ZrO2 Obtained from 1 M ZrOCl2 Adjusted to pH 2.5 and Refluxed for 44 h Electrolyte

T

Method

0–0.1 M NaCl

Instrument

cip

pH0

Reference

8.2

[2203]

3.1.47.1.2.2.10 From ZrCl4 Solution Adjusted to pH 2 or 2.5 and Refluxed for 4 Days Recipe from [2204]: Acidic ZrCl4 solution was adjusted to different pH values with ammonia. It was then refluxed for 4 d, washed, dried, and calcined at 470°C. Properties: Monoclinic [2205]. TABLE 3.1199 PZC/IEP of ZrO2 Obtained from ZrCl4 Solution Adjusted to pH 2 or 2.5 and Refluxed for 4 Days pH of Precipitation 2 2.5

Electrolyte

T

0.001–0.1 M KNO3

Method

Instrument

cip

pH0

Reference

8.6 8.5

[2205]

3.1.47.1.2.2.11 From Boiling Acidic ZrCl4 Solution Adjusted to Different pH Values with KOH 60 drops/min were added with stirring. The precipitate was washed, dried, and calcined at 470°C. Properties: Monoclinic + tetragonal (precipitated at pH5–7.5) or tetragonal (precipitated at pH > 7.5) [2205]. TABLE 3.1200 PZC/IEP of ZrO2 Obtained from Boiling Acidic ZrCl4 Solution Adjusted to Different pH with KOH pH of Precipitation 5 6 6.2 7.3 7.8 9.5 11 12.2

Electrolyte 0.001–0.1 M KNO3

T

Method cip

Instrument

pH0

Reference

8.4 8.2 8.1 7.9 6.9 6.8 6.7 6.6

[2205]

538

Surface Charging and Points of Zero Charge

3.1.47.1.2.2.12 Addition of 0.4 M ZrOCl2 to Hot Urotropine or NH3 Solution at 70°C 0.4 M ZrOCl2 was added to hot (70°C) urotropine or NH3 solution, and heated to 100°C for 30 min. The precipitate was dried at 140°C, and treated for 2 h at various temperatures. Properties: Samples heated above 600°C are monoclinic. For specific surface area, see Table 3.1201 [2206]. TABLE 3.1201 PZC/IEP of ZrO2 Obtained by Addition of 0.4 M ZrOCl2 to Hot Urotropine or NH3 Solution at 70°C Specific Surface Area (m2/g)

Description Urotropine Urotropine, heated at 300°C Urotropine, heated at 600°C Urotropine, heated at 1200°C NH3

343 238

Electrolyte

T

0.001 M KCl

Method

Instrument

pH0

Reference

iep

Otsuka ELS 3800

5.3 3.8

[2206]

38

5.5

<2

3.2 7.2

3.1.47.1.2.2.13 Alkaline Precipitation from Acidic Solution of Chloride at Boiling Point The heating was continued for 2 h, then the product was washed, dried and calcined at 200–800°C in oxygen. Properties: Mixture of monoclinic with cubic and tetragonal (up to 400°C) or with tetragonal (>400°C). Mechanical treatment produces a pure monoclinic phase [2207]. Calcined at 200°C: Monoclinic, XRD patterns available [2208]. Not calcined: Monoclinic and tetragonal. Calcined at 800°C: Monoclinic [825]. TABLE 3.1202 PZC/IEP of ZrO2 Obtained by Alkaline Precipitation from Acidic Solution of Chloride at Boiling Point Calcination Temperature (°C)

Description, BET Specific Surface Area (m2/g)

200

Original Dried in desiccator for 8–10 months

Electrolyte 0.001–0.1 M KNO3

T

Method Instrument pH0 cip

7.7 7.3

Reference [2208]

continued

539

Compilation of PZCs/IEPs

TABLE 3.1202 (continued) Calcination Temperature (°C)

Dried powder ball-milled Original powder ball-milled 231.9

None 800 200 400 500 600 700 800 a

Description, BET Specific Surface Area (m2/g)

190 90 95 50 55 35

Electrolyte

T

Method Instrument pH0

Reference

7.3 7.7 KNO3

cipa

0.001–0.1 M KNO3

cip

7.7 7.7 8.1 8.3 8.1 8 8 8.1

[825] [2207]

Only value, data points not reported.

3.1.47.1.2.2.14 Sample Studied in [2207] (prepared at 200°C) Stored for 6 Days A: In water. B: In 0.001 M KNO3. TABLE 3.1203 PZC/IEP of Sample Studied in [2207] (Prepared at 200°C) Stored for 6 Days Description A B

Electrolyte 0.001–0.1 M KNO3

T

Method cip

Instrument

pH0

Reference

8 7.9

[2209]

Reference [2209] reports a shift in the CIPs of the other samples studied in [2207] (prepared at temperatures >200°C) induced by aging in 0.001 M KNO3. After 5 d of aging, the IEP was shifted towards pH 6.5. 3.1.47.1.2.2.15 Sample Studied in [2207] (Prepared at 800°C), Stored and Calcined A: Stored for 2 weeks. B: Stored for 1 year. C: Sample B was calcined for 2 h at 800°C in oxygen. The solid was aged in 0.001 M KNO3 solution at natural pH for 18 h before titration.

540

Surface Charging and Points of Zero Charge

TABLE 3.1204 PZC/IEP of Sample Studied in [2207] (Prepared at 800°C) Stored and Calcined Description A B C

Electrolyte

T

Method

0.001–0.1 M KNO3

Instrument

pH0

Reference

8.2 6.8 7.1

[595]

cip

3.1.47.1.2.2.16 Recipe from [2207], Then Treatment With Hydrogen in Dry State Samples prepared by means of a method described in [2207] (calcination of hydroxide at 200°C for a total of 12 h, combined with grinding) were treated with hydrogen. TABLE 3.1205 PZC/IEP of ZrO2 Obtained According to Recipe from [2207] and Treated with Hydrogen Hydrogen Treatment

Electrolyte

None 0.25–2 h at 25°C 1 h at 80°C 2 h at 80°C 0.25 h at 200°C 22 h at 25°Cb 22 h at 25°Cb 2 h at 80°C + 20 h at 25°C 3 h at 80°C 4 h at 80°C 5 h at 80°C a b

0.001–0.1 M KNO3

T

Method

Instrument

cip

pH0a

Reference

7.6–7.7 7.6–7.7 7.8–7.9 8–8.1 8–8.1 7.2–7.5 7.1–7.5 7.6–7.9 7.9–8.1 7.7–8.1 7.5–7.9

[160]

Charging curves did not produce one clear CIP. Probably one of these samples was treated with hydrogen in a wet state (typographic error in Table 3 in [160]).

3.1.47.1.2.2.17

Other

TABLE 3.1206 PZC/IEP of ZrO2 Obtained by Hydrolysis of Chloride Electrolyte 0.01 M KNO3

a

T

Method

Instrument

pH0

Reference

iep iep

Zeta PALS Brookhaven

<6.4 9

[2608]a [2214]

Detailed recipe reported in [2608].

541

Compilation of PZCs/IEPs

3.1.47.1.2.3 From Zr(NO3)4 3.1.47.1.2.3.1 Prepared at pH 9 Washed, Dried at 120°C. Properties: Amorphous, BET specific surface area 105 m2/g [2184]. TABLE 3.1207 PZC/IEP of ZrO2 Obtained from Zr(NO3)4 at pH 9 Electrolyte

T

Method

Instrument

pH0

Reference

iepa

Electrophoresis

4.1

[2184]

0.01 M NaNO3 a

Only value, data points not reported.

3.1.47.1.2.3.2 From Zr(NO3)4 and Ammonia Water-washed and aged for 15 d. Properties: BET specific surface area 4.3 m2/g [2210]. TABLE 3.1208 PZC/IEP of ZrO2 Obtained from Zr(NO3)4 and Ammonia Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.5 M NaCl

35

cip iep

Electrophoresis

6.7

[2210]

3.1.47.1.2.3.3 In the Presence of Isooctane 0.05 M Zr(NO3)4 acidified with HNO3was mixed ultrasonically with 0.15 M ammonia at nearly stoichiometric ratio (final pH7–10) in the presence of isooctane (1:1 to 1:5 organic/aqueous phase ratio) containing 0.01–0.5 M of carboxylic acid. The precipitate was centrifuged, evaporated at 150°C, and calcined at 1000°C. TABLE 3.1209 PZC/IEP of ZrO2 Obtained from Zr(NO3)4 in Presence of Isooctane Description Fresh Calcined a

Electrolyte 0.001 M KNO3

T

Method

Instrument

iep

Malvern Zetasizer IIc

pH0 Reference 9a 3

[2211]

Arbitrary interpolation.

3.1.47.1.2.4 From Sulfate 3.1.47.1.2.4.1 From ZrOCl2, K 2SO4, and HCl Solutions containing ZrOCl2 (0.005–0.046 M), K2SO4 (S:Zr ratio 2:1), and HCl (0.5–1.2 M) were aged at 65–98°C for 1–12 d. The deposit was washed with water.

542

Surface Charging and Points of Zero Charge

Properties: Amorphous, SEM images, particle size range available [2212]. TABLE 3.1210 PZC/IEP of ZrO2 Obtained from ZrOCl2, K2SO4, and HCl Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

25

iep

Zeiss Cytopherometer

5.8

[2212]

3.1.47.1.2.4.2 Hydrolysis of Zr(SO4)2, then Calcination at 700°C Properties: Monoclinic, BET specific surface area 45.7 m2/g [1678]. TABLE 3.1211 PZC/IEP of ZrO2 Obtained from Zr(SO4)2 and Calcined at 700°C Electrolyte

T

Method

Instrument

pH0

Reference

4.8

[1678]

3.1.47.1.2.5 Thermal Decomposition 3.1.47.1.2.5.1 From Isopropoxide by Flame Pyrolysis specific surface area 32 m2/g [2206].

Properties: BET

TABLE 3.1212 PZC/IEP of ZrO2 Obtained from Isopropoxide by Flame Pyrolysis Electrolyte

T

0.001 M KCl

Method

Instrument

pH0

Reference

iep

Otsuka ELS 3800

7.9

[2206]

3.1.47.1.2.5.2 Hollow Particles Calcination of polystyrene latex coated with Zr2(OH)6SO4 at 800°C for 3 h. Properties: Tetragonal and monoclinic, particle diameter outer 200 nm, inner 100 nm, TEM image, IR spectrum available [2213]. TABLE 3.1213 PZC/IEP of Hollow Particles of ZrO2 Electrolyte 0.01 M NaNO3

T

Method

Instrument

pH0

Reference

iep

Delsa 440 Coulter

4.5

[2213]

3.1.47.1.2.5.3 Calcination of Zr2O2(OH)2CO3 Properties: 95% of monoclinic form, 5% of tetragonal form, diameter 540 nm, spherical monodispersed particles, TEM image available [409].

543

Compilation of PZCs/IEPs

TABLE 3.1214 PZC/IEP of ZrO2 Obtained by Calcination of Zr2O2(OH)2CO3 Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaNO3 0.01 M NaCl

25

iep iep

Delsa Coulter Malvern Zetasizer 2000

4.5 5.6

[474] [409]a

a

“Acid sulfate” reported in [409] as the precursor of ZrO2, probably by mistake.

3.1.47.1.2.5.4 Spraying of ZrO(NO3)2 Solution into Plasma high-temperature inductively coupled plasma. Properties: Tetragonal, 10–40 nm in diameter [2158].

Argon, ultra-

TABLE 3.1215 PZC/IEP of ZrO2 Obtained by Spraying of ZrO(NO3)2 Solution into Plasma Description Refluxed in water for 170 h Original

a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

iep

Electrophoresis

5.2

[2158]

0.001 M NaCl

iep

Electrophoresis

6.5

[2158] [2215]a

Extrapolated, [2215] reports also limited number of data points for four other specimens of ZrO2.

3.1.47.1.2.6 Recipe from [2216] A solution 0.316 M in HCl, 0.7 M in KCl, and 0.1 M in ZrCl2 was aged at 100°C for 20 d. The precipitate was washed and dried at 100°C. TABLE 3.1216 PZC/IEP of ZrO2 Obtained According to Recipe from [2216] Electrolyte

T

Instrument

cipa

KNO3 a

Method

pH0

Reference

8.2

[825]

Only value, data points not reported.

3.1.47.1.2.7 Other TABLE 3.1217 PZC/IEP of Unspecified Synthetic ZrO2 Calcined at (°C) 450 650 850 a

Electrolyte

T

Method

KNO3

25

Titration iep

Only value, data points not reported.

Instrument

pH0

Reference

6 5.1 7.6–8.1

[2217]a

544

Surface Charging and Points of Zero Charge

3.1.47.1.3 Natural baddeleyite from Palabora, Transvaal

TABLE 3.1218 PZC/IEP of Natural ZrO2 Electrolyte

T

Method

Instrument

pH0

iep

Zeta-Meter

3

NaOH + HClO4

Reference [104]

3.1.47.1.4 Origin Unknown TABLE 3.1219 PZC/IEP of Unspecified ZrO2 Description

Industrial, >99.9% pure, 2.2 m2/g Washed

Electrolyte

T

0.0003, 0.001 M KCl KCl 0.01 M NaNO3 0.001–1 M NaNO3

25

Method

Instrument

Monoclinic, 3 m2/g Reactor graded 15.4 m2/g Membrane 18 m2/g D90 530 nm, D50 240 nm, D10 130 nm a b

c d

e

0.001, 0.01 M KCl 0.01 M KNO3 0.01 M NaCl 0.01 M KCl

30 25

Reference

iep

4

[1454]

pHa

4

[1362]

4.5 4.6

[2213] [1241]

Electrophoresis

≤5.5 6b 6.5c 6.5

[280] [2219] [2132]

Zeta-Meter Streaming potential Electro-osmosis

6.8 6.8 6.8

iep pHa

Delsa 440 Coulter

iepa None

pH0

iep titrationa iep merge iep iep iep

iep

Electro-osmosis

7.5a 7.8e

[2218]

[1065,1234] [811] [1102a,1103a, 1217] [2220] [2221]

Only value, data points not reported. IEP is based on three data points: -16 mV in 0.00003 M KOH, +1.6 mV in water (pH 6), and +16 mV in 0.0001 M HCl. Results from [280] were interpreted in [1] as IEP of natural mineral at pH 4, and that value was cited after [1] in several papers. In [2178], cited as IEP of commercial material. Also temperature effect. 99.9%, Hf 100 ppm, Si 35 ppm, Fe 33 ppm, Cu 30 ppm, Al 25 ppm, Ti 20 ppm, Ni 15 ppm, 6.8 m2/g. Maximum in viscosity of 56 mass% dispersion roughly matches IEP.

545

Compilation of PZCs/IEPs

3.1.47.2

Hydrous ZrO2

3.1.47.2.1 From Chloride 3.1.47.2.1.1 Precipitated from ZrOCl2 Solution with Ammonia Dried in air at 110°C. Properties: Amorphous, specific surface area 180 m2/g (Strohlein area meter). [2177] TABLE 3.1220 PZC/IEP of Hydrous ZrO2 Precipitated from ZrOCl2 Solution with Ammonia Electrolyte

T

Method

0.01–0.1 M NaCl

25

pH

Instrument

pH0

Reference

4

[2177]

3.1.47.2.1.2 Aging of a Solution 0.001 M in ZrCl4 and 0.2 M in Triethanoloamine at 95°C at pH 8 Solutions of ZrCl4 and triethanoloamine were preheated to 95°C. The solution of ZrCl4 was poured into a solution of triethanoloamine, and aged for 1 h at 95°C under agitation, then immersed into ice– water. The particles were centrifuged, washed, and dried at 60°C overnight. Properties: Amorphous, TEM and SEM images available [2222]. TABLE 3.1221 PZC/IEP of Hydrous ZrO2 Obtained by Aging of Solution 0.001 M in ZrCl4 and 0.2 M in Triethanoloamine at 95°C at pH 8 Electrolyte

T

0.01 M NaCl

Method

Instrument

pH0

Reference

iep

Delsa 440

8.2

[2222]

3.1.47.2.1.3 From ZrOCl2 Solution and 3 M KOH 1105 g of 0.71 M ZrOCl2 was mixed with 225 cm3 of 3 M KOH at room temperature. The precipitate was washed and dried at 112°C for 3 d and ground. Properties: Loss of ignition 14.1% [2175], amorphous, specific surface area 252 m2/g [2175,2223]. TABLE 3.1222 PZC/IEP of Hydrous ZrO2 Obtained from ZrOCl2 Solution and 3 M KOH Electrolyte

T

Method

0.001–0.1 M NaCl

21

pH

a b

Instrument

pH0

Reference

6.6a

[2175,2223b]

No clear CIP: charging curves obtained at various ionic strengths merge in the range 6.5–8. Only value, data points not reported.

546

Surface Charging and Points of Zero Charge

3.1.47.2.1.4 From ZrOCl2 Solution and 0.1 M NaOH A solution of 20 g of ZrOCl2 · 8 H2O in 200 cm3 of water was adjusted to pH 6.8 with 0.1 M NaOH. The precipitate was washed, and dried at room temperature for 10 h and then at 80°C for 2 h, finally at 300°C for 3 h. Properties: BET specific surface area 181 m2/g [2224]. TABLE 3.1223 PZC/IEP of Hydrous ZrO2 Obtained from ZrOCl2 Solution and 0.1 M NaOH Electrolyte

T

Method

Instrument

pH0

Reference

30

iep

Zeta-Meter 3.0+

5.5

[2224]

3.1.47.2.2 From Nitrate 3.1.47.2.2.1 From a Solution of ZrO(NO3)2 · nH2O A: Aged for a few hours at room temperature. B: Refluxed at pH 4–7 for 1 d. C: Refluxed at pH 4–7 for 11 d. D: Refluxed at pH 11 for 43 h. E: Refluxed at pH 11 for 22 d. Properties: Amorphous (A–D), E shows a diffraction pattern different from known ZrO2 minerals [2225]. TABLE 3.1224 PZC/IEP of Hydrous ZrO2 Obtained from Solution of ZrO(NO3)2 ⋅ nH2O Description A B C D E

Electrolyte

T

Method

0.001–0.1 M KNO3

31

cip

Instrument

pH0

Reference

6.6 6.6 6 6.3 6.3

[2225]

3.1.47.2.2.2 From Zr(NO3)4 or ZrO(NO3)2 and NaOH Table 3.1225 PZC/IEP of Hydrous ZrO2 Obtained from Zr(NO3)4 and NaOH Electrolyte 0.02 M

a b

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.7

[1229]a [2226]b

Only value, data points not reported. Precipitate is termed hydroxide in [2226].

547

Compilation of PZCs/IEPs

3.1.47.2.3 From Sulfate 0.005 M Zr(SO4)2 containing 5 vol% of formamide and 0.5 mass% of polyvinylpyrrolidone was aged for 2 h at 70°C. Properties: TEM image available, BET specific surface area 140 m2/g [1431]. TABLE 3.1226 PZC/IEP of Hydrous ZrO2 Obtained from Sulfate Electrolyte

T

Method

Instrument

pH0

Reference

iep

Delsa Pen Kem 3000

7.2 6.6

[1431]

0.01 M NaNO3

3.1.47.3 Zr(OH)4 See also Section 3.1.47.2.2.2. 3.1.47.3.1 From ZrO(NO3)2 and NaOH Properties: Amorphous, DSC curves available [2227]. TABLE 3.1227 PZC/IEP of Zr(OH)4 Obtained from ZrO(NO3)2 and NaOH Description

Electrolyte

Obtained at pH 10.4 Obtained at pH 7 Obtained at pH 2 pH was adjusted to 5.5–11 with NaOH pH was adjusted to 5.5–10 with NaOH Precipitate was washed and aged for 2 h in 1 M NaCl at 80°C a b

T

Method

0.001 M NaCl

iep

0.01–1 M NaCl, NaClO4, NaNO3 0.01–1 M NaCl

Instrument Pen Kem S 3000

pH0 a

[2227]

pH

6.1/5.8 7/7.7 7/6.2 3.8–11.2

pH

2.8–9.8

[678]

Original/after g irradiation. Materials obtained from Zr(SO4)2 were also studied.

3.1.47.3.2

Reference

Membrane, Deposited from Nitrate TABLE 3.1228 PZC/IEP of Zr(OH)4 Membrane, Deposited from Nitrate Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

31

iep

Streaming potential

6.1

[2229]

[2228]b

548

3.2

Surface Charging and Points of Zero Charge

ALUMINOSILICATES, PHYLLOSILICATES, CLAYS, AND CLAY MINERALS

PZCs/IEPs of aluminosilicates, phyllosilicates, clays and clay minerals are presented in Tables 3.1229 through 3.1356. Aluminosilicates, phyllosilicates, clays, and clay minerals have variable composition, and complicated classification and terminology. The same or similar specimens are named differently in different publications. In the present survey, aluminosilicates, phyllosilicates, clays, and clay minerals are sorted alphabetically according to their names used in the original publications. These names may refer to specific minerals, to groups of minerals, to clays, or to rocks. Specimens, mostly of natural origin, have been usually comminuted and/or purified. Several modified natural specimens and synthetic materials are also included.

3.2.1

ADULARIA

See Section 3.2.25.

3.2.2

AMELIA ALBITE FROM WARDS

Properties: K 0.01Na 0.98Ca 0.02Al1.01Si2.98O8 [2230]. Reference [2230] presents results of acid–base titrations of original and washed, albite at different NH4Cl concentrations.

3.2.3

(Ca,Fe)2(Ln,Al,Fe)3Si3O12OH, ALLANITE (ORTHITE) FROM K ABULAND, NORWAY TABLE 3.1229 ZC/IEP of Allanite (Orthite) from Kabuland, Norway Electrolyte NaOH + HClO4

3.2.4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

4.5

[104]

AMPHIBOLES

TABLE 3.1230 PZC/IEP of Amphiboles Name, Location

Electrolyte

Basaltic hornblende, Räderberg, Eifel NaOH + HClO4 Tremolite Hornblende, Kragerö Anthophyllite, Hermannschlag, Czech Republic

T Method Instrument pH0 Reference iep

Zeta-Meter

3.3 9.2 2.7 3

[104]

549

Compilation of PZCs/IEPs

3.2.5

ANDALUSITE

TABLE 3.1231 PZC/IEP of Andalusite Description Dolny Bory, former Czechoslovakia a

Electrolyte

T

Method pH iep

NaOH + HClO4

Instrument

pH0

Reference

Zeta-Meter

5.2–8a 10

[2231] [104]

Only range, data points not reported.

3.2.6

ANDESINE

See Section 3.2.25.

3.2.7

ANORTHITE

See Section 3.2.25.

3.2.8

ANORTHOCLASE

See Section 3.2.25.

3.2.9

ANTHOPHYLLITE

See Section 3.2.4.

3.2.10

AUGITE, (Al,Ca,Fe,Mg,Ti)2(Al,Si)2O6

Properties: SiO2 50.4%, Al2O3 7.4%, Fe2O3 2.8%, FeO 5.7%, MgO 18%, CaO 12.6%, detailed analysis available [2232]. TABLE 3.1232 PZC/IEP of Augites Description

Electrolyte

From Eglazines, France Basaltic augite from NaOH + HClO4 Firmerich, Eifel

T

Method

Instrument

iep iep

Streaming potential Zeta-Meter

pH0 2.7 3

Reference [2232] [104]

550

3.2.11

Surface Charging and Points of Zero Charge

BEIDELLITE, SBCa-1

Properties: XRD pattern available, specific surface area 61 (original) and 92 (milled) m2/g [2233]. TABLE 3.1233 PZC/IEP of SBCa-1 Description

Electrolyte

Original Milled

3.2.12

T

0.001 M NaCl

Method

Instrument

iep

Pen Kem S3000

pH0 <3 if any 3

Reference [2233,856]

BENTONITE

See Section 3.2.35.

3.2.13

Be3Al2Si6O18 BERYL FROM HOGGAR, ALGERIA

Properties: detailed analysis available [2232]. TABLE 3.1234 PZC/IEP of Beryl from Hoggar, Algeria Electrolyte

a

3.2.14

T

Method

Instrument

iep

Streaming potential

pH0 Reference 4.2a

[2232]

Arbitrary interpolation.

BIOTITE K(Mg,Fe,Mn)3(OH,F)2(Al,Fe,Ti)Si3O10

See also Section 3.2.33. 3.2.14.1 From Razes, France Properties: SiO2 34.4%, Al2O3 19.4%, Fe2O3 3.5%, FeO 20%, MgO 4.6%, TiO2 2.6%, K2O 8.8%, F 1.5%, detailed analysis available [2232]. TABLE 3.1235 PZC/IEP of Biotite from Razes, France Electrolyte

T

Method

Instrument

pH0

Reference

iep

Streaming potential

<2 if any

[2232]

551

Compilation of PZCs/IEPs

3.2.14.2 Isolated from Natural Material from Finland Reference [2234] reports titration curves of two samples of biotite (isolated from natural material from Finland, 1–4.7 m2/g) in the presence of 0.1 M NaClO4. Uncorrected charging curves indicated positive surface charge at pH < 5 and negative surface charge at pH > 7. The charging curves in graphical and in digital form are reported.

3.2.15

BLAZER FROM HUBER Na2O · Al2O3 · 2.8 SiO2 · 7 H2O

Properties: BET specific surface area 55 m2/g [851], 41 m2/g [858], particle diameter 5 mm [851].

TABLE 3.1236 PZC/IEP of Blazer from Huber Electrolyte

T

0.01 M NaClO4

a

3.2.16

Method

Instrument

pH0

Reference

iep

Laser Zee 500

iep

Electrophoresis

5.9 (table) 6.5 (figure) 8

[851] [858,899]a

Only value, data points not reported.

BRONZITE FROM KRAUBATH

TABLE 3.1237 PZC/IEP of Bronzite from Kraubath Electrolyte NaOH + HClO4 a

3.2.17

T

Method iep

Instrument Zeta-Meter

At pH 12, the z potential equals zero (two IEPs).

BYTOWNITE

See Section 3.2.25.

3.2.18

CHLORITE (Mg,Al,Fe)12(Al,Si)8O20(OH)16

Properties: specific surface area 4.8 m2/g [2235].

pH0 3

a

Reference [104]

552

Surface Charging and Points of Zero Charge

TABLE 3.1238 PZC/IEP of Chlorites Description

Electrolyte

From Ordu, Turkey, XRD pattern available Fe-ripidolite from Sandbalmhöhe, Göschenen Clinochlore from Zillertal, Tirol From France, washed with diluted H2O2 From Ward’s

a

T

Method

HCl + NaOH

iep

NaOH + HClO4

iep

Instrument Rank Brothers MK II Zeta-Meter

pH0

Reference

<3 if any

[2236]a

5

[104]

4 0.001, 0.01 M NaCl 0.001 M KCl

iep

Pen Kem S3000

5

[2235]

iep

Rank Brothers Mark II

5.5

[1768]

Same study reports electrokinetic data on natural illite and kaolinite, both containing quartz and other impurities.

3.2.19

CLEAVELANDITE

See Section 3.2.25.

3.2.20 CLINOCHLORE See Section 3.2.18.

3.2.21

CLINOPTILOLITE, ZEOLITE, UNIT CELL: Na6(AlO2)6(SiO2)30 · 24H2O

From Gordes region, Turkey. Properties: Clinoptilolite 90.5–92%, smectite 4.2–5%, cristobalite 2–3.5%, mica 1–1.3% [2237]

TABLE 3.1239 PZC/IEP of Clinoptilolite from Gordes Region, Turkey Electrolyte

T

Method

Instrument

pH0

Reference

20

iep

Zeta-Meter 3.0

<2 if any

[2237]

553

Compilation of PZCs/IEPs

3.2.22

CLINOZOISITE FROM KIRCHHAM

TABLE 3.1240 PZC/IEP of Clinozoisite from Kirchham Electrolyte

T

NaOH + HClO4

3.2.23

Method

Instrument

pH0

Reference

iep

Zeta-Meter

4.5

[104]

CORDIERITE 2MgO · 2Al2O3 · 5SiO2

Properties: Mean average diameter 800 nm, BET specific surface area 3 m2/g [1787], SEM image available [2238].

TABLE 3.1241 PZC/IEP of Cordierites Description

Electrolyte

Synthetic, from 0.001 M KCl alumina, silica, and Mg(NO3)2 Commercial, None from Baikowski

T

20

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440 SX

2

[2238]

iep Malvern Negative z at pH Coagulation Zetasizer 3 2–4.8 and >6 Positive z at pH 4.8–6

[1787]

Reference [104] reports electrokinetic curves for two natural cordierites from Norway with multiple IEPs in the pH range 2–5.

3.2.24 Ca2(Fe,Al)Al2[O/OH/SiO4/Si2O7] EPIDOTE FROM KNAPPENWAND TABLE 3.1242 PZC/IEP of Epidote from Knappenwand Electrolyte 0.001 M NaClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

4

[104]

554

Surface Charging and Points of Zero Charge

3.2.25

FELDSPAR

TABLE 3.1243 PZC/IEP of Feldspars Description

Electrolyte

Orthoclase, from Mandt HClO4 Microcline (amazonite), Evje, Norway Adularia, Uri Sanidine, Volkesfeld, Eifel Oligoclase, Aeretveit Cleavelandite, Evje Oligoclas (andesine) from Mandt Anorthoclase from rhomboporphyr, Sollihøgda, Norway Andesine–labradorite from anorthosite, Jøssingfjord, Norway Labradorite–Bytownite Washed

Argentina, 85.1 m2/g

a

b c

0.001– 0.1 M KCl

T

Method Instrument iep

pH0 Reference

Zeta-Meter <1 <1 <1 <1 <1 <1 2 1.2

[104]a

1.8

25

iepb

Malvern Zetasizer 3000 HAS

pH

1.2 <2 if any

[358]

4.1c

[576]

[104] reports also results for bytownite, Lake View, Oregon and anorthite, Yoichi, Japan (multiple IEPs). Only value, data points not reported. Common PZC for different ionic strengths, but no CIP.

3.2.26

GARNETS

3.2.26.1 From Costaboone, France Properties: SiO2 38.1%, Al2O3 10%, Fe2O3 15.1%, FeO 2.4%, MnO 1.7%, CaO 31.2%, detailed analysis available [2232,2239].

TABLE 3.1244 PZC/IEP of Garnet from Costaboone, France Description Original Washed

Electrolyte 0–0.01 M KCl

T

Method

Instrument

pH0

Reference

iep

Streaming potential

4.4 2.2

[2232] [2239]

555

Compilation of PZCs/IEPs

3.2.26.2 Garnet Group, (Mg,Fe,Mn)3(Al,Fe,Ti,V,Cr)2(SiO4)3 TABLE 3.1245 PZC/IEP of Garnet Group Minerals Description

Electrolyte

Grossular from Lago Jaco, Mexico Almandine from Lindu, West Africa Pyrop from Czech Republic Andradite from Drammen, Norway Melanite from Frascati, Italy a

T Method Instrument pH0 Reference

NaOH + HClO4

iep

Zeta-Meter

3.5 4.5 4a 3.8 4

[104]

Arbitrary interpolation from scattered data.

3.2.27

HALLOYSITE-7Å

Natural, HLY8, from Sao Vincente de Pereira, Portugal Properties: BET specific surface area 16.5 m2/g, Si:Al 0.68 [1098]. TABLE 3.1246 PZC/IEP of Halloysite-7Å Electrolyte

T

0.001 M KCl

Method

Instrument

pH0

Reference

iep

Zetasizer 4

<3 if any

[1098]

3.2.28 HORNBLENDE See Section 3.2.4.

3.2.29 ILLITE 3.2.29.1 From Clay Minerals Society’s Source Clays Repository Properties: Specific surface area 102 m2/g (EGME) [2240]. TABLE 3.1247 PZC/IEP of Illite from Clay Minerals Society’s Source Clays Repository Description Ground a

Electrolyte 0.01 M NaCl

T 25

Method a

pH

Only value, data points not reported; also 40°C.

Instrument

pH0

Reference

9.6

[2240]

556

Surface Charging and Points of Zero Charge

3.2.29.2 API No. 35 from Ward’s Properties: Electron micrograph available [598]. TABLE 3.1248 PZC/IEP of API No. 35 from Ward’s Description

Electrolyte

After 10 cycles of washing and drying

T

Method

0.001 0.01 0.1 M NaCl

Instrument

pH

pH0

Reference

7 6.3 5.8

[598]

3.2.29.3 From Argentina Properties: BET specific surface area 66.6 m2/g [576]. TABLE 3.1249 PZC/IEP of Illite from Argentina Electrolyte

T

Method

0.001–0.1 M KCl a

Instrument

pH0 a

pH

6.4

Reference [576]

Common IEP for different KCl concentrations, but no CIP.

3.2.29.4 From Muloorina, Australia Properties: SiO2 53.4%, Al2O3 14.8%, Fe2O3 15.8%, MgO 3.2%, TiO2 1.3%, CaO 1.7%, Na2O 0.9%, K2O 7.3% [623] SiO2 58%, Al2O3 18%, Fe2O3 12%, MgO 4%, K2O 7% [1508], BET specific surface area 123.3 m2/g [1508,1509,2241], 128 m2/g [623], 126 m2/g [623]. TABLE 3.1250 PZC/IEP of Illite from Muloorina, Australia Description Washed

Na-form

K-form

Cs-form

Electrolyte

T

0.001 0.01 0.1 M NaCl 0.001 0.01 0.1 M NaCl 0.001 0.01 0.1 M KCl 0.001 0.01 0.1 M CsCl 0.01 M KClO4

Method

pH0

Reference

pH

8.6 8.2 7.7

[623]

pH

5 4.4 3.8 5.6 5 4.4 7 6.5 6

[623]

pH

pH

25

Instrument

pH

>8

[623]

[623]

[1508,1509,2241]

557

Compilation of PZCs/IEPs

3.2.29.5 From Hebei Province, China Properties: 90% illite, 5% chlorite, 5% quartz, 1.4% Mg, 0.4% Na, 2% Fe, 0.2% Ti, 0.5% Ca, 3.4% K, 32.6% Si, 8.1% Al, concentrations of 12 other elements available, SEM image available, BET specific surface area 22.3 m2/g [137]. TABLE 3.1251 PZC/IEP of Illite from Hebei Province, China Electrolyte 0.001 M NaNO3 a

T

Method

25

Instrument

pH0

Reference a

iep

<2 if any

[137]

Titration results are also available.

3.2.29.6 From Zhejiang, >90% Pure TABLE 3.1252 PZC/IEP of Illite from Zhejiang Electrolyte

T

0.001 M KCl or KNO3

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

2.8

[60]

3.2.29.7 From Hungary, Washed with Diluted H2O2 Properties: Specific surface area 37 m2/g [2235]. TABLE 3.1253 PZC/IEP of Illite from Hungary Electrolyte

T

0.001–0.56 M NaCl

Method

Instrument

pH0

Reference

iep

Pen Kem S3000

<2 if any

[2235]

3.2.29.8 From Silver Hill Montana Properties: (Purified and transferred into sodium form) BET specific surface area 16.4 m2/g [2242]. TABLE 3.1254 PZC/IEP of Illite from Silver Hill Montana Electrolyte 0.2, 0.5 M NaClO4

T

Method pH

Instrument

pH0

Reference

6.3

[2242]

558

Surface Charging and Points of Zero Charge

3.2.29.9 From Fithian, Illinois Properties: traces of quartz and kaolinite [139], SiO2 47.2%, Al2O3 23.1%, Fe2O3 14.8%, MgO 4.1%, TiO2 1.7%, CaO 0.9%, Na2O 2.1%, K2O 6% [623], BET specific surface area 66.8 m2/g [139], 62 m2/g [623].

TABLE 3.1255 PZC/IEP of Illite from Fithian, Illinois Description

Electrolyte

T

Washed

0.001–0.1 M NaCl

Na-form

0.001 0.01 0.1 M NaCl 0.001–0.1 M NaNO3 25

Method

Instrument

pH merge pH

pH

pH0

Reference

<3 if any 3 5.2 4.3 3.3 6–7.5 (no CIP)

[623] [623]

[139]

3.2.29.10 Marblehead Illite Properties: K0.79Na0.02Al1.43Fe0.11Mg0.37Ti0.08Si3.55Al0.45O10(OH)2, BET specific surface area 60.1m2/g [2243].

TABLE 3.1256 PZC/IEP of Marblehead Illite Electrolyte

T

Method

1 M KCl 0.01, 0.1 M KCl

25

pH

Instrument

pH0

Reference

4 <3 if any

[2243]

3.2.29.11 Grundite Illite Cleaned and converted into Na-form [2244].

TABLE 3.1257 PZC/IEP of Na-Illite Electrolyte

T

0.01 M NaNO3 a

Also Al- and Fe-coated.

Method

Instrument

pH0

Reference

iep

Rank Mk II

<2 if any

[2245]a

559

Compilation of PZCs/IEPs

3.2.29.12 Origin Unknown TABLE 3.1258 PZC/IEP of Illite from Unknown Source Electrolyte

T

Method

Instrument

iep a

pH0

Reference

3.2

[1146]a

Only value, data points not reported.

3.2.30

KAOLINITE AND K AOLIN Si2Al2O5(OH)4

Kaolinite is a clay mineral, kaolin is clay, but these terms are often used as synonyms. The results obtained for kaolin and for kaolinite are presented together. Kaolinites converted into specific form (Na-, Ca-) are also included. Collections of PZC and/or charging curves of kaolinite from different sources can be found in [2246–2248]. 3.2.30.1

From Commercial Sources

3.2.30.1.1 From Ajax Described as “acid-washed” and/or “as received” in a series of papers presenting similar results. Properties: BET specific surface area 14 m2/g [1019] 14.4 m2/g [2254], 14.7 m2/g [1508,1509,2241,2249–2253], SEM image available [2251], face dimensions 200–1000 nm, thickness 35–65 nm, no XRD-detectable impurities [2249,2252]. TABLE 3.1259 PZC/IEP of Kaolinite from Ajax Electrolyte

T

0.01 M KNO3 0.005 M KNO3 0.01 M NaNO3, 0.01 M KClO4

25 22

3.2.30.1.2

Method

Instrument

pH0

Reference

iep pH

Acoustosizer

<4 if any 4.6

[1019] [1508] [1509,2241, 2249,2251,2254]

From Aldrich, Well-Crystallized

TABLE 3.1260 PZC/IEP of Kaolinite from Aldrich Electrolyte 0.001 M NaCl

T

Method

Instrument

pH0

Reference

iep

Pen Kem S3000

<2 if any

[856]

560

Surface Charging and Points of Zero Charge

3.2.30.1.3 From BDH Properties: Specific surface area 48.2 m2/g (EGME) [2240]. TABLE 3.1261 PZC/IEP of Kaolinite from BDH Description

Electrolyte

T

Method

As obtained

0.01 M NaCl

25

pH

3.2.30.1.4

Instrument

pH0

Reference

4.5

[2240]

From Clay Minerals Society

3.2.30.1.4.1 Well-Crystallized Kaolinite Washed with 30% H2O2, 1 M NaCl, and water. Properties: BET specific surface area 10.1 m2/g [2255]. TABLE 3.1262 PZC/IEP of Well-Crystallized Kaolinite from Clay Minerals Society Electrolyte

T

Method

Instrument

pH0

Reference

iep

JS94B, Jecheng

<3 if any

[2255]

0.001 M NaCl

3.2.30.1.4.2 Kaolinite from Clay Minerals Society Repository Properties: 48.1% SiO2, 38.9% Al2O3, 0.1% Fe2O3, 0.01% CaO, 0.03% MgO, 12.1% loss of ignition at 500°C, BET specific surface area 8.7 m2/g [2256]. TABLE 3.1263 PZC/IEP of Kaolinite from Clay Minerals Society Repository Description

Electrolyte

As supplied

0.01 M KNO3

T

Method

Instrument

pH

pH0

Reference

4.5

[2256]

3.2.30.1.5 K15GM from Commercial Minerals Properties: 99% pure, 1% of mica and quartz, specific density 2600 kg/m3, BET specific surface area 24.8 m2/g, median diameter 2.8 μm [2257]. TABLE 3.1264 PZC/IEP of K15GM from Commercial Minerals Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

22

iep

Acoustosizer

<2 if any

[2257]

561

Compilation of PZCs/IEPs

3.2.30.1.6 From ECC International Lee Moor China Clay Pit, Cornwall, UK Properties: BET specific surface area 12.2 m2/g [2258]. TABLE 3.1265 PZC/IEP of Kaolinite from ECC International Lee Moor China Clay Pit Electrolyte

T

Method

0.01–0.1 M NaNO3

25

pH

Instrument

pH0

Reference

4.7 (Table 2)

[2258]

3.2.30.1.7 From Engelhard Properties: 42.8% SiO2, 39.8% Al2O3, 0.25% Fe2O3, 0.5% TiO2, 1.2% CaO, 0.75% MgO, 0.1% K2O, 0.24% Na2O, 14% loss of ignition, specific surface area 12 m2/g [909], high iron content [1830]. TABLE 3.1266 PZC/IEP of Ultra Brite from Engelhard Description

Electrolyte

Ultra Brite, H-form

0.01–1 M KCl

T

Method Instrument iep cip

DT-300

pH0

Reference

<4 if any 2.8

[1830] [909]

3.2.30.1.8

China Clay Supreme from English Clay Lovering Pochin (or English China Clay) (St Austell kaolinite) Properties: 97% of kaolinite, 3% of muscovite [483], 46.2% SiO2, 39.2% Al2O3, 0.23% Fe2O3, 0.09% TiO2, 0.06% CaO, 0.07% MgO, 0.2% K 2O, 0.09% Na2O, 0.1% F, loss of ignition 13.8% [2259], BET specific surface area 15 m2/g [988], 10 m2/g [2260], 13.2 m2/g [140]. TABLE 3.1267 PZC/IEP of China Clay Supreme from English Clay Lovering Pochin Electrolyte 0.0001 M NaCl 0.001, 0.01 M NaCl 0.05 M NaNO3

T

Method iep

20

0.001 M NaCl 0.025 0.1 0.5 M NaClO4 0.1 M NaNO3 a b c d

Instrument Rank Brothers MK II

pH iep

25

c

pH

20

pH

pH0 4 <3 if any 4.5

Reference [483] [988]a

Rank Brothers

5b

[2259] [2260]

Equilibration time 5 min–2 d

5 4.8 4.8 7.5d

[140]

Only value, data points not reported. “PZC” at pH 4.8 cited in [2246] as a result from [2259] is a point of equal Na and Cl uptake. Also 60°C. No data points for pH > 7.5.

562

Surface Charging and Points of Zero Charge

3.2.30.1.9 Kaolin or Kaolinite from Fisher Properties: BET specific surface area 10 m2/g [2261], specific surface area originally 17 m2/g, increases to 47 m2/g after a 5 min milling [922]. TABLE 3.1268 PZC/IEP of Kaolin from Fisher Description

Electrolyte

T

Original 0.001 and Milled for (s): 0.1 M KCl 30 45 60 120 750 HCl-washed Milled for 45 s then HCl-washed Milled for 750 s then HCl-washed Acid-washed Artificial groundwater

Method

Instrument

Intersection

pH0

Reference

2.6

[922]

2.8 3.5 3.8 3.8 4 2.8 3.9 4.2 pH

Washed with HNO3

iep

Delsa 440, Coulter

s0 = 0 at pH 4.5–5.5 4.4

[2261] [2262]

3.2.30.1.10 From Georgia Kaolin Co. 3.2.30.1.10.1 Hydrite Properties: well-crystallized, axial ratio 10:1, narrow particle size distribution, equivalent spherical particle size 550 nm [2263]. TABLE 3.1269 PZC/IEP of Hydrite from Georgia Kaolin Co. Description PX, >97% pure, 15.3 m2/g (BET) PD-10 Original Salt-washed

Electrolyte 0.001–1 M KNO3

T

Method

Instrument

pH0

25

iep pH

Malvern Zetasizer 2c

3

[2280]

4.2 6.6

[2263]

pH

Reference

563

Compilation of PZCs/IEPs

3.2.30.1.10.2 Ultra White Converted into Ca-form, calcined at 550°C. Properties: Original: specific surface area 12 m2/g (based on exchange capacity) [875,910].

TABLE 3.1270 PZC/IEP of Ultra White from Georgia Kaolin Co., Converted into Ca-Form Electrolyte

T

0–1 M KCl

Method

Instrument

cip

pH0

Reference

4.1

[875]

3.2.30.1.10.3 Higlow, Converted into H-Form Properties: 44.3% SiO2, 39.5% Al2O3, 1.4% Fe2O3, 0.45% TiO2, traces of CaO, 0.1% MgO, 0.06% K 2O, 0.14% Na2O, 14% loss of ignition, specific surface area 14.5 m2/g [909], 14 m2/g (based on exchange capacity) [875,910].

TABLE 3.1271 PZC/IEP of Higlow from Georgia Kaolin Co., Converted into H-Form Electrolyte

T

0.001–1 M KCl

3.2.30.1.10.4

Method

Instrument

cip

pH0

Reference

3

[875,909]

Other Properties: specific surface area 19 m2/g [576].

TABLE 3.1272 PZC/IEP of Unspecified Kaolinite from Georgia Kaolin Electrolyte 0.001–0.1 M KCl

T

Method pH

Instrument

pH0

Reference

4.8

[576]

3.2.30.1.11 KGa-1 Properties: contains vermiculite and feldspar [866], BET specific surface area 7.5 m2/g [2264], 8.6 m2/g [904], 9.1 m2/g [2265], 10.2 m2/g [2266], 15.5 m2/g (purified sample) [761], single-point BET specific surface area 9.1 m2/g [866,870], specific surface area 10 m2/g [98].

564

Surface Charging and Points of Zero Charge

TABLE 3.1273 PZC/IEP of KGa-1 Description

Electrolyte 0.01 M NaCl 0.1 M NaCl 0.01M NaCl 0.1 M NaCl 0.01 M LiCl

As obtained As obtained 1h 3 h equilibration 14–16 h equilibration

Washed with HClO4, H2O2 and NaOH Na-form a b c d

T b

25 25c

Method

Instrument

pH0

iep pH pH

Zeta-Meter 3.0

2.9 3.9–4.3 4 <4 if any 4.7 4.7 5 <4.5 if any <4 if any

pH

0.1 M NaCl

25b

pH

0.001–0.1 M NaClO4 0.01 M NaCl

25

pH pH

4.8

Reference [866,870a] [2267] [904] [2246d,2268]

[98] [2266] [2282]

Only value, data points not reported. Also 50 and 70°C. Also 60°C. Different values reported in Table 3 are results of graphical interpolation.

3.2.30.1.12 KGa-2 Properties: >93% pure [449], contains chlorite [866,1177,1178], BET specific surface area 18.1 m2/g [449], 23 m2/g [2269,2270], 23.8 m2/g [631], single-point BET specific surface area 19.3 m2/g [866,1177,1178], 20.2 m2/g [1193], TEM image available [2270].

TABLE 3.1274 PZC/IEP of KGa-2 Description NaCl-washed

Fraction <1 μm, washed

Electrolyte

T

Method

Instrument

pH0

0.01 M NaCl 0.1 M NaCl 0.01 M NaCl

iep iep iep

Zeta-Meter 3.0 2.9 Zeta-Meter 3.0 3 Zeta-Meter 3.0 3.3

0.001–0.1 M NaCl 25 ± 3

iep merge iep

Acoustosizer

0.01 M NaClO4

25

Zetasizer 3 Malvern

3.8–4.3b 3 4.8

Reference [866] [1193] [1177] [1178]a [449] [2269, 2270] continued

565

Compilation of PZCs/IEPs

TABLE 3.1274 (continued) Description

Electrolyte

1 h equilibration

0.01 M LiCl

3 h 14–16 h equilibration

0.01–0.1 M NaNO3

a b c

T

Method

Instrument

pH 25

pH

pH0

Reference

>5.2 if any 5.4–5.8

[2246c, 2268] [631]

Only value, data points not reported. Hysteresis. Different values reported in Table 3 are a results of graphical inter- or extrapolation.

3.2.30.1.13

From Sigma (Sigma-Aldrich)

3.2.30.1.13.1 Kaolin Properties: BET specific surface area 19.3 m2/g [1868]: particle size 100–400 nm [2271].

TABLE 3.1275 PZC/IEP of Kaolin from Sigma (Sigma-Aldrich) Electrolyte

T

Method

0.01 M KCl

25

iep

0.0007–0.14 M NaCl

25

iep

a

Instrument Malvern Nano ZP DT 1200 Acoustosizer Zeta-Meter 3.0

pH0

Reference

<3.3 if any <4 if any 3.6a 3–3.5

[2271]

[1868]a

Only value, data points not reported.

3.2.30.1.13.2 Sodium Kaolinite Properties: 98%, particle diameter 0.1–4 mm, BET specific surface area 12 m2/g [2272].

TABLE 3.1276 PZC/IEP of Na-Kaolinite from Sigma Description 1 M NaCl-washed

Electrolyte

T

Method

0.005 M NaCl

25

iep

Instrument

pH0

Malvern Zetasizer II <3 if any

Reference [2272]

566

Surface Charging and Points of Zero Charge

3.2.30.1.14

From Wako

TABLE 3.1277 PZC/IEP of Kaolin Clay from Wako Description

Electrolyte

T

Method

Instrument

pH0

Reference

20

iep

BIC 90 Plus

3.2

[3118]

3.2.30.1.15 From Ward’s Properties: ground and water-washed, <74 μm fraction, BET specific surface area 10.7 m2/g [109,952], specific surface area 63 m2/g (No. 5 Lamar Pit, Bath, South Carolina, or API No.5) [598], 97% kaolinite, 3% K-feldspar, BET specific surface area 2.7 m2/g [428].

TABLE 3.1278 PZC/IEP of Kaolinites from Ward’s Description

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl Ground to pass 0.01 M 38 μm sieve NaCl No. 5, after 10 0.001 cycles of washing 0.01 and drying 0.1 M NaCl

22

iep

Brookhaven Zeta PALS

<3 if any

[3119]

iep

Zeta Probe, Colloidal Dynamics

a

pH

3

[428]a

6 5.5 5

[598]

Only value, data points not reported.; also Al- and Fe-coated kaolinite

3.2.30.1.16 From Wusi Chemical Agents Company Properties: BET specific surface area 11.2 m2/g, average particle diameter 735 nm, XRD pattern available [616].

TABLE 3.1279 PZC/IEP of Kaolinite from Wusi Chemical Agents Company Electrolyte 0.002–0.2 M NaNO3

T

Method cip

Instrument

pH0

Reference

2.2

[616]

567

Compilation of PZCs/IEPs

3.2.30.2 From Specific Locations 3.2.30.2.1 From China Properties: Detailed chemical analysis (eight elements), XRD patterns available [383].

TABLE 3.1280 PZC/IEP of Kaolinites from China Location

Electrolyte

Hunan Miluo Henan Jiaxian Henan Mianchia Henan Dayugoua Henan, >90% pure

0.001 M KCl or KNO3 HCl + NaOH

Ping ding Shan, Henan province a b

T

Method

Instrument

iep

Brookhaven ZetaPlus

iep

Brookhaven ZetaPlus Brookhaven ZetaPlus

iep

pH0

Reference

3.3 3.6 3.8 2.8 3.6

[383]

4.3b

[2273]

[60]

Contains illite. Arbitrary interpolation.

3.2.30.2.2 From Egypt, Na and Ca Form Properties: XRD patterns available [534]. TABLE 3.1281 PZC/IEP of Kaolinite from Egypt Location

Electrolyte 2

Bed selected, 10.3 m /g 0.0001–0.01 M NaCl Esila, 12.2 m2/g Kalabsha, 13.6 m2/g a

T

Method Instrument iep

Zeta-Meter

pH0

Reference a

<3 if any

[535]

Numerical values reported as PZC in [534] and in [535] are erroneous.

3.2.30.2.3 Kaolin from Charentes (France) Properties: 87% kaolinite, 3% quartz, 5.4% mica, 1.4% anatase, 1.2% iron oxide, particle size up to 10mm, specific surface area 20 m2/g [790].

568

Surface Charging and Points of Zero Charge

TABLE 3.1282 PZC/IEP of Kaolin from Charentes (France) Electrolyte

T

Method

Instrument

pH0 a

pH a

3.2

Reference [790]

Only value, data points not reported.

3.2.30.2.4 Kaolin from Zettlitz, Germany Treated with Na2CO3 at 80°C for 2 d, and then with 1 M NaCl to obtain Na-kaolinite. Properties: XRD pattern available, BET specific surface area 83 m2/g [632].

TABLE 3.1283 PZC/IEP of Kaolin from Zettlitz, Germany Electrolyte

T

Method

Instrument

pH0

Reference

0.01–1 M NaCl

25

pH iep

Malvern Zetasizer 4

5.5–7 <3 if any

[632]

3.2.30.2.5

From Sao Vincente de Pereira, Portugal

3.2.30.2.5.1 SVP7, Well-Ordered 16.7 m2/g, Si:Al 1.01 [1098].

Properties: BET specific surface area

TABLE 3.1284 PZC/IEP of SVP7 from Sao Vincente de Pereira, Portugal Electrolyte

T

0.001 M KCl

Method

Instrument

pH0

Reference

iep

Zetasizer 4

<3 if any

[1098]

3.2.30.2.5.2 SVP44, Poorly Ordered Properties: BET specific surface area 15.9 m2/g, Si:Al 0.97 [1098].

TABLE 3.1285 PZC/IEP of SVP44 from Sao Vincente de Pereira, Portugal Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Zetasizer 4

<3 if any

[1098]

569

Compilation of PZCs/IEPs

3.2.30.2.6 ECESA, from Deposits in Burela (Spain) Properties: Specific surface area by ethylene glycol monoethyl ether method: 46.7 m2/g [2274]. TABLE 3.1286 PZC/IEP of ECESA, from Deposits in Burela (Spain) Electrolyte

T

Method

0, 0.0488 M NaCl

3.2.30.2.7

Instrument

pH

pH0

Reference

6.2

[2274]

From Thailand, Washed

TABLE 3.1287 PZC/IEP of Kaolin from Thailand Location

Electrolyte

Ranong Lampang Narathiwat

T

Method

Instrument

pH0

25

iep

Malvern Zetasizer 3000 HAS

<2 if any

Reference [358]

3.2.30.2.8 From Guzelyurt (Aksaray), Turkey Properties: 53% SiO2, 26.7% Al2O3, 0.6% Na2O, 1.4% K2O, 0.6% CaO, 0.4% Fe2O3, 0.3% MgO, loss of ignition 17.2% [258,2275], XRD pattern available [258]. TABLE 3.1288 PZC/IEP of Kaolinite from Guzelyurt, Turkey Electrolyte

T

Method

Instrument

pH0

Reference

20 ± 2

iep

Zeta-Meter 3.0+

<2.3 if any

[258,2275]

3.2.30.2.9 Hydrite Flat D from Dry Branch, GA Properties: BET specific surface area 7 m2/g, EGME specific surface area 20.4 m2/g, SEM images available [2276]. TABLE 3.1289 PZC/IEP of Hydrite Flat D from Dry Branch, Georgia (USA) Electrolyte 0.001–1 M NaCl a

T

Method pH

Instrument

pH0

Reference

3.5–4.5a

[2276]

CIP at pH 2.6 is reported in text, but this result is not supported by data in Figure 2.

570

Surface Charging and Points of Zero Charge

3.2.30.2.10 From Twiggs County, Georgia (USA) Properties: Ordered kaolinite, 95%, very well-crystallized, 2.8% TiO2, 0.6% Fe2O3, traces of quartz, BET specific surface area 8.2 m2/g [627].

TABLE 3.1290 PZC/IEP of Kaolinite from Twiggs County, Georgia (USA) Electrolyte

T

Method

0.001–0.1 M KClO4

Instrument

pH

pH0

Reference

5.5

[627]

3.2.30.2.11 Astra Brite from Georgia (USA), H-form Properties: 42.5% SiO2, 38.9% Al2O3, 0.32% Fe2O3, 0.95% TiO2, 1.45% CaO, 0.67% MgO, 0.1% K2O, 0.22% Na2O, 13.7% loss of ignition, specific surface area 12 m2/g [909].

TABLE 3.1291 PZC/IEP of Astra Brite from Georgia (USA) Electrolyte

T

Method

0.001–1 M KCl

Instrument

cip

pH0

Reference

2.8

[909]

3.2.30.2.12 From Birch Pit, Macon, Georgia (USA) Properties: BET specific surface area (fraction <2 μm, Na-form) 22.4 m2/g [100], specific surface area 7.9 m2/g, from p-nitrophenol adsorption from xylene [711,1147,2277,2278].

TABLE 3.1292 PZC/IEP of Kaolinite from Birch Pit, Macon, Georgia (USA) Electrolyte 0.001–0.1 M NaNO3

T

Method pH

Instrument

pH0

Reference

4.9–6

[100]

3.2.30.2.13 Well-Crystallized, from Washington County, Georgia (USA) Properties: Platelets 200 nm thick, 400 nm–1 μm in diameter, BET specific surface area 11.2 m2/g [189].

571

Compilation of PZCs/IEPs

TABLE 3.1293 PZC/IEP of Kaolinite from Washington County, Georgia (USA) Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaNO3

25

pH iep

Pen Kem 3000

4 4.2

[189]

3.2.30.2.14 From Georgia (USA) Properties: Contains quartz, BET and EGME specific surface areas given in graphical form [125].

TABLE 3.1294 PZC/IEP of Kaolinite from Georgia (USA) Electrolyte

T

Method

Instrument

pHa a

pH0

Reference

6.3–6.7

[125]

Intersection at pH 4.

3.2.30.3 Other 3.2.30.3.1 Na-Kaolinite, Described by [2244]. Cleaned and converted into Na-form [2244].

TABLE 3.1295 PZC/IEP of Na-Kaolinite Electrolyte 0.01 M NaNO3

T

Method

Instrument

pH0

Reference

iep

Rank Mk II

<2 if any

[2245]

3.2.30.3.2 Georgia Kaolinite Properties: 46.2% SiO2, 38.5% Al2O3, 0.56% Fe2O3, 0.06% TiO2, 0.12% CaO, 0.1% MgO, 1.01% K2O, 0.22% Na2O, 0.5% water, BET specific surface area 35 m2/g [2279].

572

Surface Charging and Points of Zero Charge

TABLE 3.1296 PZC/IEP of Kaolinites from Other Sources Description

Electrolyte

Water-washed 15.6 m2/g, d50 429 nm

0.1 M NaCl 0.0001 M NaNO3

Greenbushes and Groomailling (Western Australia, two specimens)

T

Method

25

iep iep

pH0

Reference

Rank Mark I Zeta-Meter 3.0

1.8 2.5

[1933] [345]

3.4 <4

[1146] [2281]

4 3.3 4

[2279]

iepa pH

0

cip pH iep

0.001–0.1 M KNO3

a

Instrument

6 d equilibration Electrophoresis

Only value, data points not reported.

3.2.31

LABRADORITE

See Section 3.2.25.

3.2.32

LAPONITE Na0.8Mg5.4Li0.4Si8O20(OH)4 FROM LAPORTE

Properties: BET specific surface area 300 m2/g, particle size 20 nm [143]. TABLE 3.1297 PZC/IEP of Laponite from Laporte Electrolyte

T

Method

None 0.1 M KNO3

25

Mass titration

3.2.33 3.2.33.1

Instrument

pH0

Reference

9.8 9.5

[143]

MICA Muscovite Mica Sheet from Alfa Aesar

TABLE 3.1298 PZC/IEP of Muscovite Mica Sheet from Alfa Aesar Electrolyte 0.001 M KCl

T

Method iep

Instrument

pH0

Reference

Streaming potential

<3 if any

[2283]

573

Compilation of PZCs/IEPs

3.2.33.2 From Clay Minerals Society Repository Properties: 52.8% SiO2, 37.6% Al2O3, 0.03% Fe2O3, 0.01% CaO, 0.01% MgO, 9.2% loss of ignition at 500°C, BET specific surface area 125 m2/g [2256].

TABLE 3.1299 PZC/IEP of Mica from Clay Minerals Society Repository Description

Electrolyte

T

As supplied

0.01 M KNO3

Method

Instrument

pH

pH0

Reference

5.5

[2256]

3.2.33.3 From Mica Supplies Source indicated in [1762].

TABLE 3.1300 PZC/IEP of Mica from Mica Supplies Electrolyte

T

0.0001 M NaNO3 a

Method iep

Instrument Streaming potential

pH0

Reference a

<3 if any

[1761]

Data points reported for pH > 5; the line in the pH range 3–5 may be a result of interpolation.

3.2.33.4 From Bihar, India Properties: SiO2 45.7%, Al2O3 33.6%, Fe2O3 2.4%, TiO2 0.4%, MgO 1%, Na2O 0.6%, K2O 9%, ignition loss 6.8% [276], SiO2 45.7%, Al2O3 36.9%, FeO 1.1%, MgO 0.4%, Na2O 0.9%, K2O 9.9% [487]. TABLE 3.1301 PZC/IEP of Mica from Bihar, India Description

Electrolyte

Fresh 0.001 M Aged at pH 7 for 7 d KNO3 Aged at pH 3 for 1 d Aged at pH 3 for 7 d Aged at pH 10 for 1 d in glass Aged at pH 10 for 7 d in glass

T

Method

Instrument

iep

Rank Bros

pH0 <3 if any 5.5 Positive z at pH 4–6 8.2

Reference [487]

6.5 <3 if any

continued

574

Surface Charging and Points of Zero Charge

TABLE 3.1301 (continued) Description

Electrolyte

T

Method

Instrument

pH0

Aged at pH 10 for 1–4 d in Teflon

Reference

8–8.5

0.001 M KCl 20 0.001 M KCl 25

iep iep

Streaming potential Pen Kem 3000 from mobility profile (iep of basal plane)

<3.5 if any 3 <2 if any

[2284] [276]

3.2.33.5 From Madagascar Properties: SiO2 45.3%, Al2O3 31.9%, Fe2O3 5.2%, MgO 0.9%, Na2O 0.6%, K2O 10.6% [487]. TABLE 3.1302 PZC/IEP of Mica from Madagascar Description

Electrolyte

Freshly cleaved, aged at pH 5.8 for 0–4 d a

T

Method

0.001, 0.01 M KCl

iep

Instrument Streaming potential

pH0

Reference a

<3 if any

[487]

But washing at low pH may induce sign reversal to positive.

3.2.33.6

Other

TABLE 3.1303 PZC/IEP of Mica from Other Sources Description Muscovite from Rostadheia Biotite from Rostadheia Zinnwaldite Lepidolite

Electrolyte NaOH + HClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

4 2.2 1.8 1.7

[104]

3.2.34 MICROCLINE See also Section 3.2.25. 3.2.34.1 Microcline from Ward’s Reference [598], in Fig. 1.4c, reports titration results in 0.001, 0.01, and 0.1 M NaCl. The PZC is difficult to read from the figure. Also Al- and Fe-coated.

575

Compilation of PZCs/IEPs

3.2.35

MONTMORILLONITE

Montmorillonites (clay mineral) and bentonites (clay, which consists chiefly of montmorillonite), and montmorillonites converted into certain ionic forms (Na-form, etc.) are discussed in this section. 3.2.35.1

Montmorillonites from Fluka

3.2.35.1.1 K10 Properties: Specific surface area 200 m2/g,modal particle size 200 or >1000 nm (different instruments, fine fraction isolated from commercial material) [2271]. TABLE 3.1304 PZC/IEP of K10 from Fluka Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KCl

25

iep

Malvern Nano ZP DT 1200a Acoustosizera

<3 if any

[2271]

a

Only value, data points not reported.

3.2.35.1.2 K30 Properties: BET specific surface area 330 m2/g [2285]. TABLE 3.1305 PZC/IEP of K30 from Fluka Electrolyte

T

Method

Instrument

pH0

Reference

25

iep

Malvern Zetasizer 3000 HS

<1 if any

[2285]

3.2.35.1.3 Aluminum-Pillared, Analytical-Grade Properties: Specific surface area 420 m2/g [1915]. TABLE 3.1306 PZC/IEP of Al-Pillared Analytical Grade Montmorillonite from Fluka Electrolyte NaOH + HNO3 a

T

Method a

iep

Instrument

pH0

Reference

ZetaPlus 100

5.6

[1915]

Only value, data points not reported.

3.2.35.1.4 Other Properties: specific surface area 898 m2/g (EGME) [2240].

576

Surface Charging and Points of Zero Charge

TABLE 3.1307 PZC/IEP of Unspecified Montmorillonite from Fluka Description As obtained a

Electrolyte

T

0.01 M NaCl

25

Method a

Instrument

pH0

Reference

3.8

[2240]

pH

Only value, data points not reported, also 40°C.

3.2.35.2 Kunipia F from Kunimine Properties: Na-saturated, Na0.87Al3.12Fe0.2 Mg0.61Ti0.01Si7.9Al0.1O20(OH)4, particle size 200 nm [1001]. TABLE 3.1308 PZC/IEP of Kunipia F from Kunimine Electrolyte

T

Method Mass titration

a

Instrument a

pH0

Reference

10.6

[1001]

Only value, data points not reported.

3.2.35.3 STx-1 from Gonzales, Texas, in K-Form and Ca-Form Properties: BET specific surface area 83.9 m2/g, wide range of face dimensions from 0.1 to 2 μm [2286]. TABLE 3.1309 PZC/IEP of STx-1 from Gonzales, Texas Electrolyte

T

Method

0.01 M KNO3

25

pH

Instrument

pH0

Reference

6.6

[2286]

3.2.35.4 MX-80, Wyoming-Bentonite Properties: Montmorillonite 80–84%, quartz and cristoballite 6–7%, plagioclases 3.4%, phlogopite 2.5–4.3%, feldspars 1.2%, calcite 0.5–1.6%, pyrite 0.6%, phosphate 0.3%, anatase 0.2% [766]. TABLE 3.1310 PZC/IEP of MX-80 Wyoming Bentonite Description

Electrolyte

T

Method

Instrument

pH0

Reference

Mutek, PCD 03

<2 if any

[2287]

577

Compilation of PZCs/IEPs

Reference [766] reports selected parameters of a model of surface charging of MX-80 bentonite. 3.2.35.5 SWy-1 Na0.5Mg0.5Al1.5Si4O10(OH)2 Properties: Contains mica [1177,1178], BET specific surface area 14.9 m2/g [2264], 18.6 m2/g [2265], 21.4 m2/g [2288], 35 m2/g [2289], single point BET specific surface area 18.6 m2/g [1177,1178,870], EGME surface area 470 m2/g [2264], 661.5 m2/g [2288]. TABLE 3.1311 PZC/IEP of SWy-1 Description Washed with NaClO4 a

Electrolyte

T

Method

Instrument

iepa pH

Zeta-Meter 3.0 1 or 7 d equilibration

0.01 M NaCl 0.1, 0.5 M NaClO4

pH0

Reference

<2 if any [1177,1178] 7.8 [2289]

Only value, data points not reported.

3.2.35.6 SWy-2 Properties: Unit cell formula Na0.66Mg0.45Al3.07FeII0.18FeIII0.25Si7.97Al0.03O20(OH)4 [2290], BET specific surface area 15.2 m2/g [101], 27.8 m2/g [1190], 29.4 m2/g [2291], 36.4 m2/g [1511], 31.8 m2/g (K-form) [2286], EGME specific surface area 596 m2/g [1511], 697 m2/g [101], particle size < 2 μm [101]. TABLE 3.1312 PZC/IEP of SWy-2 Description Purified, Na-form

Purified K-form

Electrolyte

Method

0.01 M NaClO4

iep

0.01 M KCl

iepa

0.01 M KNO3 NaOH + HNO3 0.01 M NaCl

a

T

25 25

Titrationa pH pH Mass titration

25

iep

Instrument

pH0

Reference

Zetaphoremeter Sephy 2100 Pen Kem 501 Laser Zee Meter

<2 if any

[2290]

<2 if any

[1511]

4.2 7.6 8.3 Malvern Zetasizer 4 <3 if any

[1190] [2286] [2292] [632]

Only value, data points not reported.

3.2.35.7 From Cerro Bandera (or Cerro Banderita), Argentina Properties: Specific surface area 808 m2/g, from glycerol adsorption [711,1147, 2277,2278], 800 m2/g [2293].

578

Surface Charging and Points of Zero Charge

TABLE 3.1313 PZC/IEP of Montmorillonite from Cerro Bandera, Argentina Description

Converted into Na-form a

Electrolyte

T

Method

0.01 M NaCl 0.006 0.014 0.088 M NaCl 0.002 0.009 0.08 M NaCl 0.001–1 M NaNO3

iep pH

Mass titration

Instrument

pH0

Reference

Rank Brothers <3 if any 8.7 8.3 8 8.9 8.6 7.8 a

pH

[2293] [2293]

[2293]

[1150]

The results presented in Figure 4, curve 1 are difficult to read.

3.2.35.8 From Argentina Properties: BET specific surface area 472 m2/g [576]. TABLE 3.1314 PZC/IEP of Montmorillonite from Argentina Electrolyte

T

Method

0.001–0.1 M KCl

Instrument

pH

pH0

Reference

<3 if any

[576]

3.2.35.9 From Croatia Washed with diluted H2O2. Properties: Single-point BET specific surface area 78 m2/g [2235]. TABLE 3.1315 PZC/IEP of Montmorillonite from Croatia Electrolyte 0.0001–0.01 M NaCl

3.2.35.10

T

Method iep

Instrument

pH0

Pen Kem S3000 <2 if any

Reference [2235]

FEBEX (Full-Scale Engineered Barrier Experiment) Bentonite from Spain Properties: Smectite 93%, quartz 2%, cristobalite 2%, plagioclase 3%, total surface area 725 m2/g, BET (external) specific surface area 33 m2/g, particle radius 250 nm, specific density 2700 kg/m3 [36].

579

Compilation of PZCs/IEPs

TABLE 3.1316 PZC/IEP of Bentonite from Spain Electrolyte

T

Method

0.001–0.1 M NaClO4

iep pH

Instrument

pH0

Reference

Malvern Zetamaster

<3 if any 6.7

[36]

3.2.35.11 Bentonite from Djebel Haidoudi, Tunisia Properties: SiO2 56.7%, Al2O3 25.6%, Fe2O3 10%, MgO 2.4%, Na2O 2.7%, CaO 0.3%, K2O 1.8% [394]. TABLE 3.1317 PZC/IEP of Bentonite from Djebel Haidoudi, Tunisia Description

Electrolyte

NaCl-washed, NaOH + HCl <80 mm fraction a

T

Method

Instrument

pH0

Reference

20–30

iep

Malvern Zetasizer 5000

<2 if anya

[394]

Yield stress of a dispersion (12.5% by mass) shows the highest value at pH 4.4.

3.2.35.12 Bentonite from Berka, Tunisia Properties: SiO2 63.4%, Al2O3 20.7%, Fe2O3 8.5%, MgO 3.2%, Na2O 2.3%, CaO 0.08%, K2O 1.4% [394]. TABLE 3.1318 PZC/IEP of Bentonite from Berka, Tunisia Description NaCl-washed, <80 mm fraction a

Electrolyte

T

Method

Instrument

pH0

Reference

NaOH + HCl

20–30

iep

Malvern Zetasizer 5000

1.5a

[394]

Yield stress of a dispersion (8.5% by mass) shows the highest value at pH 5.8.

3.2.35.13 SCa-3, Otay, California TABLE 3.1319 PZC/IEP of SCa-3, Otay, California Electrolyte 0.001 M NaCl

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

<2 if any

[856]

580

Surface Charging and Points of Zero Charge

3.2.35.14 Bentonite from Black Hills Properties: Contains cristobalite and quartz, SEM image available, BET and EGME specific surface areas given in graphical form [125]. TABLE 3.1320 PZC/IEP of Bentonite from Black Hills Electrolyte

T

Method

Instrument

pHa a

pH0

Reference

>6 if any

[125]

Intersection at pH 2.7.

3.2.35.15 Bentonite from Wyoming Properties: SiO2 64%, Al2O3 24%, Fe2O3 4%, MgO 2.8%, Na2O 3.6%, CaO 0.09%, K2O 0.6% [394]. TABLE 3.1321 PZC/IEP of Bentonite from Wyoming Description

Electrolyte

NaCl-washed, NaOH + HCl <80 mm fraction a

T

Method

20–30

iep

Instrument

pH0

Malvern Zetasizer 5000

<2 if any

Reference a

[394]

Yield stress of a dispersion (5.5% by mass) shows the highest value at pH 2.3 (the lowest pH value studied).

3.2.35.16 SAz-1 BET specific surface area 95 m2/g [2294], 97.4 m2/g [1617] glycerol specific surface area 820 m2/g [2294]. TABLE 3.1322 PZC/IEP of SAz-1 Electrolyte 0.01–1 M NaCl a

T

Method

Instrument

pH

No CIP, s0 = 0 over a wide pH range.

3.2.35.17 Bentonite, Origin Unknown Properties: Detailed composition available [1310].

pH0 6.5–8

Reference a

[1617]

581

Compilation of PZCs/IEPs

TABLE 3.1323 PZC/IEP of Bentonite from Unknown Source Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta PALS

1

[1310]

3.2.35.18 Na-Montmorillonites 3.2.35.18.1

Prepared from MX-80 Bentonite from American Colloid (or from Bureau de Recherches Géologiques et Minières) The < 2 μm fraction was flocculated in 0.001 M HNO3 + 1 M NaNO3 solution. It was redispersed and centrifuged, and the washing solution was exchanged five times until the pH of the supernatant reached 3. It was then redispersed in 0.1 NaNO3 (the washing solution was exchanged five times until the pH of the supernatant reached 5.1) and finally in 0.01 NaNO3 under argon. Another Recipe ([2260]): Five washings with 1 M NaCl, and then washings with 0.025 M NaClO4. Properties: BET specific surface area 31.5 m2/g [2295], 24 m2/g [2260], d-spacing from XRD 1.245 nm [2295]. TABLE 3.1324 PZC/IEP of Na-Montmorillonite Prepared from MX-80 Bentonite from American Colloid Electrolyte 0.005 0.05 0.5 M NaNO3 0.025 0.1 0.5 M NaClO4 a

T

Method

Instrument

pH

25a

pH

pH0

Reference

8 7 6.2 8.2 7.3 6.8

[2295]

[2260]

Also 60 °C

3.2.35.18.2 Extracted from MX80 Bentonite from ANDRA, Na-Form See also Section 3.2.35.18.3. Properties: Si4(Al1.57Mg0.25Fe0.18)Na0.35O10(OH)2, specific surface area 9 m2/g [565]. TABLE 3.1325 PZC/IEP of Na-Montmorillonite from MX80 Bentonite from ANDRA Electrolyte

T

Method

0.001–0.1 M NaNO3

22

pH

a

Lower PZC at high electrolyte concentration.

Instrument

pH0

Reference

5.2–6.8a

[565]

582

Surface Charging and Points of Zero Charge

3.2.35.18.3 Na-Montmorillonite from MX80 Wyoming Bentonite from ANDRA See also Section 3.2.35.18.2. MX80 Wyoming bentonite was washed with 0.5 M NaCl and 0.1 M acetic acid, extracted with dithionite–citrate–bicarbonate, treated with 3% H2O2, and then washed with 0.5 M NaCl again. TABLE 3.1326 PZC/IEP of Na-Montmorillonite from MX80 Wyoming Bentonite Electrolyte

T

0.02 M NaCl

Method

Instrument

pH

pH0

Reference

7.4

[141,765]

3.2.35.18.4 Na-Montmorillonite Prepared from Wyoming Bentonite TABLE 3.1327 PZC/IEP of Na-Montmorillonite from Wyoming Bentonite Electrolyte

T

Method

Instrument

pH0

Reference

0.002 M NaCl 0.01 M NaCl 0.01–1 M NaCl

25

iep pH pH

Malvern Zetasizer 4

<3 if any >9 if any 6.4–7.2a

[1296]

a

25

[564]

Natural pH, no acid or base added. Acid titration to pH 4 and then base titration produced substantially higher PZC.

3.2.35.18.5 Bentonite from Weifang, China, Converted into Na-Form Properties: BET specific surface area 27.2 m2/g [2296]. TABLE 3.1328 PZC/IEP of Bentonite from Weifang, China, Converted into Na-Form Electrolyte

T

Method cip

a

Instrument

pH0 a

2.8

Reference [2296]

Only value, data points not reported.

3.2.35.18.6 Na-Montmorillonite Prepared from Bentonite from Almeria, Spain The <2 μm fraction was stirred in 1 M NaCl solution for 1 h, and then centrifuged. After five cycles of NaCl washing, the particles were washed with water and dried at 100°C.

583

Compilation of PZCs/IEPs

Properties: Detailed composition available, BET specific surface area 54.1 m2/g [994]. TABLE 3.1329 PZC/IEP of Na-Montmorillonite from Bentonite from Almeria, Spain Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaCl

25

iep

Malvern Zetasizer 2000

<3 if any

[994]

3.2.35.18.7 Bentonite from Balikesir, Turkey, Converted into Na-Form Properties: Detailed analysis, XRD pattern available [2297]. TABLE 3.1330 PZC/IEP of Bentonite from Balikesir, Turkey, Converted into Na-Form Electrolyte

T

Method

Instrument

pH0

Reference

25

iep

Malvern Nano ZS

<2 if any

[2297,2732]

3.2.35.18.8 Bentonite from Wyoming Cleaned and converted into Na-form [2244]. TABLE 3.1331 PZC/IEP of Na-Bentonite Electrolyte

T

0.01 M NaNO3

3.2.36

Method

Instrument

pH0

Reference

iep

Rank Mk II

<2 if any

[2245]

MONTMORILLONITE–ALUMINA COMPOSITE

0.2 M AlCl3 was adjusted to pH 4.2 with 0.1 M NaOH. Na-montmorillonite was aged with Al solution for different times, with or without discarding the supernatant (6 different procedures). TABLE 3.1332 PZC/IEP of Montmorillonite–Alumina Composite Electrolyte 0.001, 0.1 M NaNO3

T

Method Intersection

Instrument

pH0

Reference

4.5–5.9

[1150]

584

3.2.37

Surface Charging and Points of Zero Charge

MORDENITE (SYNTHETIC ZEOLITE) FROM HUBER NaAlSi5O12 · 3H2O

Properties: BET specific surface area 340 m2/g [851], 149 m2/g [877,858]. TABLE 3.1333 PZC/IEP of Mordenite Electrolyte

T

0.01 M NaClO4

Method

Instrument

pH0

Reference

iep

Laser Zee 500

<2 if any

[851,858a,877a] [899]a

1.3 a

Only value, data points not reported.

3.2.38

MUSCOVITE

See also Section 3.2.33. 3.2.38.1

Muscovite from Ward’s

TABLE 3.1334 PZC/IEP of Muscovite from Ward’s Description

Electrolyte

After 10 cycles of washing and drying

0.001 0.01 0.1 M NaCl

a

T

Method

Instrument

pH

pH0 6.8 6.3 5.8

Reference [598]a

Also Al- and Fe-coated.

3.2.39

Na3K(AlSiO4)4 NEPHELIN FROM SKUDESUNDSKJAER

TABLE 3.1335 PZC/IEP of Nephelin from Skudesundskjaer Description 3 min and 16 h aged

Electrolyte NaOH + HClO4

3.2.40 OLIGOCLASE See Section 3.2.25.

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

4

[104]

585

Compilation of PZCs/IEPs

3.2.41

OLIVINE FROM DREIS

TABLE 3.1336 PZC/IEP of Olivine from Dreis Electrolyte

T

NaOH + HClO4 a

Method

Instrument

pH0

Reference

iep

Zeta-Meter

3a

[104]

At pH > 11, the sign of the z potential becomes positive (two IEPs).

Reference [104] reports electrokinetic curves of other olivines with multiple IEPs.

3.2.42

ORTHOCLASE

See Section 3.2.25.

3.2.43

PALYGORSKITE (Mg,Al)2Si4O10(OH) · 4(H2O) FROM TUNISIA

TABLE 3.1337 PZC/IEP of Palygorskite from Tunisia Electrolyte

T

0.001–0.1 M NaCl

a

25

Method

Instrument

a

cip Mass titration

pH0

Reference

9.8 8.4–8.8

[2298]

Reported in text; Figure 2 reveals absence of a sharp CIP; IEP at pH 4–4.5 is also cited (Reference 12) in [2298].

3.2.44

PERLITE FROM CUMAOVASI, TURKEY (OR FROM IZMIR [2275])

Properties: SiO2 72.8%, Al2O3 13.6%, Fe2O3 0.8%, MgO 0.3%, Na2O 2.9%, CaO 1.1%, K2O 4.9%, BET specific surface area 1.2 m2/g (original), 2.3 m2/g (expanded) [257,2299,2275], SEM images available [257]. TABLE 3.1338 PZC/IEP of Perlite from Cumaovasi, Turkey Description

Electrolyte

T

Method

Instrument

pH0

Reference

Original and expanded

0–0.01 M NaCl

30

iep

Zeta-Meter 3.0

<2 if any

[257,2299] [2275]

586

3.2.45

Surface Charging and Points of Zero Charge

PYROPHYLLITE Al2(OH)2Si4O10

3.2.45.1 From Zhejiang, >90% Pure TABLE 3.1339 PZC/IEP of Pyrophyllite from Zhejiang Electrolyte

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

2.4

[60]

0.001 M KCl or KNO3

3.2.45.2 Other

TABLE 3.1340 PZC/IEP of Unspecified Pyrophyllites Electrolyte

T

HClO4 + NaOH

a

Method

Instrument

pH0

Reference

iep iepa

Zeta-Meter

2 2.3

[104] [1146]

Only value, data points not reported.

3.2.46

RHOMBOPORPHYR

See Section 3.2.25.

3.2.47

RIPIDOLITE

See also Section 3.2.18. 3.2.47.1 CCa-1 Properties: XRD pattern available, specific surface area 2.6 m2/g (original) and 32 m2/g (milled), SEM image available [2233]. TABLE 3.1341 PZC/IEP of CCa-1 Description Original Milled

Electrolyte 0.001 M NaCl

T

Method

Instrument

iep

Pen Kem S3000

pH0 <3 if any 6

Reference [856,2233]

587

Compilation of PZCs/IEPs

3.2.48

SANIDINE

See Section 3.2.25.

3.2.49

SAPONITE

3.2.49.1 From Ballarat, USA TABLE 3.1342 PZC/IEP of Saponite from Ballarat, USA Electrolyte

T

0.001 M NaCl

Method

Instrument

pH0

Reference

iep

Pen Kem S3000

<2 if any

[856]

3.2.49.2 Synthetic Saponite Recipe from [2300]: A mixture of Na2CO3, Al and Mg nitrates, and Si(EtO)4 was adjusted to pH 14. The resulting gel was dried, calcined, crushed, and heated at 400°C at 108 Pa for 28 d. Na xSi8-xAl xMg6O20(OH)4, x = 0.7–2 (five samples). TABLE 3.1343 PZC/IEP of Synthetic Saponite Electrolyte

T

0.0001–0.01 M NaClO4

Method

Instrument

pH0

Reference

iep

Zetaphoremeter Sephy 2100

<2 if any

[2290]

3.2.50 SAPPHIRINE Reference [104] reports an electrokinetic curve for natural sapphirine from Madagascar with multiple IEPs in the pH range 2–5.

3.2.51

SERPENTINE

3.2.51.1 Serpentine (Antigorite) from Morud TABLE 3.1344 PZC/IEP of Serpentine (Antigorite) from Morud Electrolyte NaOH + HClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

>12 if any

[104]

588

Surface Charging and Points of Zero Charge

3.2.51.2 Natural, Origin Unknown Mainly antigorite, with admixture of chrysotile, talc, and olivine.

TABLE 3.1345 PZC/IEP of Serpentine of Unknown Origin Electrolyte

T

Method

Instrument

pH0

Reference

iep

EMTA 1202, Micromeritics

<6 if any

[1315]

0.0006 M NaClO4

3.2.52

SMECTITE

3.2.52.1 From Clay Minerals Society Repository Properties: 56.8% SiO2, 7.3% Al2O3, 16.4% Fe2O3, 0.4% CaO, 1.1% MgO, 16.2% loss of ignition at 500°C, BET specific surface area 92.7 m2/g [2256].

TABLE 3.1346 PZC/IEP of Smectite from Clay Minerals Society Repository Electrolyte

T

Method

0.01 M KNO3

Instrument

pH

pH0

Reference

9.3

[2256]

3.2.52.2 Smectite, Isolated from Regolith from Kansas Extracted with dithionite–citrate–bicarbonate, treated with 3% H2O2. Properties: Composition Ca0.01Na0.47K0.31Al2.99Fe(iii)0.545 Mg0.277Ti0.08(Si7.74Al0.26) O20(OH)2, specific surface area 99 m2/g, EGME specific surface area 348 m2/g, mean particle diameter 0.16 μm [142].

TABLE 3.1347 PZC/IEP of Smectite, Isolated from Regolith from Kansas Electrolyte 10−2.16, 10−2.36 M

3.2.53

TREMOLITE

See Section 3.2.4.

T

Method pH

Instrument

pH0

Reference

8.5

[142]

589

Compilation of PZCs/IEPs

3.2.54

TURMALINE (DRAWITE) NaMg3Al6B3Si6O27(OH,F)4

3.2.54.1 From Cleveland Properties: Dark green, slightly magnetic, particle size 2–6 μm. TABLE 3.1348 PZC/IEP of Tourmaline from Cleveland Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep

Hamilton Stevens microelectrophoresis cell

5

[1965]

3.2.54.2 From South Australia, Distributed by Australian Mineral Supplies Ground to 50 μm. Properties: Detailed analysis available [2301]. TABLE 3.1349 PZC/IEP of Tourmaline from South Australia Electrolyte

T

Method

Instrument

pH a

pH0

Reference

6.6a

[2301]

Only value, data points not reported.

3.2.54.3 Tourmaline Group: (Ca,Na,K,Mn)(Mg,Li,Al,Mn,Fe)3 Si6O18(BO3)3 (OH,F)4 TABLE 3.1350 PZC/IEP of Tourmaline Group Minerals Description

Electrolyte

Schorl, Luolamaki, Finland Dravite, Unterdrauburg, Yugoslavia Schorl a

NaOH + HClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

4.5 4.5

[104]

7a

[2302]

Only value, data points not reported.

3.2.55

VERMICULITE FROM CLAY MINERALS SOCIETY REPOSITORY

Properties: 23.3% SiO2, 2.3% Al2O3, 0.8% Fe2O3, 25.3% CaO, 28.1% MgO, 14.1% loss of ignition at 500°C, BET specific surface area 22 m2/g [2256].

590

Surface Charging and Points of Zero Charge

TABLE 3.1351 PZC/IEP of Vermiculite from Clay Minerals Society Repository Electrolyte

T

Method

0.01 M KNO3

3.2.56

Instrument

pH

pH0

Reference

9.3

[2256]

VESUVIAN FROM SOLBERG

TABLE 3.1352 PZC/IEP of Vesuvian from Solberg Electrolyte

T

NaOH + HClO4 a

Method

Instrument

pH0

Reference

iepa

Zeta-Meter

3

[104]

Another point of sign reversal at pH 12.

3.2.57

ZEOLITES

3.2.57.1 MFI Type Zeolites from Exxon Mobil See also Section 3.2.57.3. Original materials containing organic template were calcined for 3 h at 550°C. A: Si/Al > 2000, silicalite, crystal size 370 nm. B: Si/Al 39, crystal size 650 nm. C: Si/Al 39, crystal size 800 nm. D: Si/Al 39, crystal size 3500 nm.

TABLE 3.1353 PZC/IEP of MFI-type Zeolites from Exxon Mobil Description A B C D a

Electrolyte

T

Method a

iep

Instrument

pH0

Reference

Malvern Zetasizer 3000

5.4 <2 if any <2 if any <2 if any

[2303]

Electrokinetic curves of uncalcined specimens are also reported.

3.2.57.2 Zeolite A from Huber Na12[(AlO4)2(SiO4)2]·27H2O Properties: BET specific surface area 3 m2/g, particle diameter 4 mm [851].

591

Compilation of PZCs/IEPs

TABLE 3.1354 PZC/IEP of Zeolite A from Huber Electrolyte

T

0.01 M NaClO4

a

Method

Instrument

pH0

Reference

iep

Laser Zee 500

7.2 7a

[851] [899]

Only value, data points not reported.

3.2.57.3 MFI Zeolite See also Section 3.2.57.1. Properties: SiO2:Al2O3 > 12, specific surface area 320 m2/g [847]. TABLE 3.1355 PZC/IEP of MFI Zeolite Electrolyte

T

0.1 M NaCl a

25

Method Mass titration

Instrument

pH0

Reference

4

[847]

Instrument

pH0

Reference

ZetaPlus 100

6.6

[1915]

a

Only value, data points not reported.

3.2.57.4 b-Zeolite from Zeolyst Properties: Si:Al = 20, specific surface area 505 m2/g [1915]. TABLE 3.1356 PZC/IEP of β-Zeolite from Zeolyst Electrolyte

T

NaOH + HNO3 a

Method a

iep

Only value, data points not reported.

3.2.58

ZINNWALDITE

See Section 3.2.33.6.

3.3 MIXED OXIDES PZCs/IEPs of mixed oxides and hydroxides are presented in Tables 3.1357 through 3.1567. Mixed oxides comprise stoichiometric salt-type compounds and nonstoichiometric mixtures. PZCs/IEPs of the components of these mixed oxides are

592

Surface Charging and Points of Zero Charge

reported in Section 3.1. No sharp concentration limit has been set to distinguish between simple oxides containing other oxides as impurities (Section 3.1) and mixed oxides (Section 3.3). Thus, materials of similar composition can be found in either Section 3.1 or Section 3.3. Salt-type compounds, which are composed of at least one water-soluble oxide, are discussed in Section 3.4.

3.3.1

MATERIALS CONTAINING ALUMINUM

3.3.1.1 Al–Ce mixed oxides (10% CeO2, 90% Al2O3) Evaporation and Calcination of Al(NO3)3–Ce(NO3)3– Citric Acid Solution 33.1 g Al(NO3)3 · 9H2O and 1.162 g Ce(NO3)3 · 6H2O were dissolved in 50 cm3 of water. 17.5 g of citric acid were added. The solution was evaporated to 20 cm3, and heated at 70°C for 8 h. The precipitate was heated at 120°C, and then calcined at 600°C for 4 h. Properties: a-Alumina and cubic CeO2 [2304]. 3.3.1.1.1

TABLE 3.1357 PZC/IEP of Al–Ce Mixed Oxide Obtained by Evaporation and Calcination of Al(NO3)3 –Ce(NO3)3 –Citric Acid Solution Electrolyte

T

Method

Instrument

pH

pH0

Reference

9.5

[2304]

3.3.1.1.2

Evaporation and Calcination of Al(NO3)3–Ce(NO3)3– Citric Acid–Ammonia Solution Prepared as in Section 3.3.1.1.1, but before evaporation step, pH was adjusted to 6.5 with 1:1 ammonia. Properties: a-Alumina and cubic CeO2 [2304].

TABLE 3.1358 PZC/IEP of Al–Ce Mixed Oxide Obtained by Evaporation and Calcination of Al(NO3)3 –Ce(NO3)3 –Ammonia Solution Electrolyte

T

Method

Instrument

pH

3.3.1.2

Al–Co Mixed Oxides

3.3.1.2.1 Synthetic CoAl2O4, Recipe from [2305]

pH0

Reference

9.5

[2304]

593

Compilation of PZCs/IEPs

TABLE 3.1359 PZC/IEP of Synthetic CoAl2O4 Electrolyte

T

0.001 M NaCl 0.005 M NaCl 0.01 M NaCl

Method

Instrument

pH0

Reference

pH

Streaming potential

10.5 9 8.5

[482]

3.3.1.2.2 Al–Co Mixed Oxide, Heated at 1200°C The mixed-component metal oxide was heated for 6 h at 1200°C. It was ground, reheated at the same temperature, crushed, and washed with water. TABLE 3.1360 PZC/IEP of Al–Co Mixed Oxide, Heated at 1200°C Co/(Co + Al) (mol %) 20 30 33.3 40 60 80 a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

25

iepa

Streaming potential

9.7 9.6 9.6 9.7 9.8 9.9

[33]

Only value, data points not reported.

3.3.1.3 3.3.1.3.1

Al–Cr Mixed Oxides Firing Coprecipitated Hydroxides

TABLE 3.1361 PZC/IEP of Al–Cr Mixed Oxide Obtained by Firing of Coprecipitated Hydroxides Firing Temperature % (°C) Cr2O3 600 1100 1200 1200 1200 1400 a

1.9 1.9 4.5 1.9 0.2 1.9

Electrolyte

T

Method

Instrument

pH0

Reference

iepa

Electrophoresis

9.5 6.3–9.1 7 5.5–7 5.5–7.2 3–5.4

[2306]

Aged for 1–29 days in water. Only values, data points not reported.

594

Surface Charging and Points of Zero Charge

3.3.1.3.2 Calcined at 1200°C for 3 h A mixture of nitrates was adjusted to pH 2 with HNO3, and then treated with excess of ammonia. The precipitate was washed with water, calcined at 600°C for 5 h, washed with water again, calcined at 1200°C for 3 h, and washed with water again. Properties: Rhombohedral Cr2O3-type structure, lattice spacing data available [1077]. TABLE 3.1362 PZC/IEP of Al–Cr Mixed Oxide Calcined at 1200°C for 3 h Cr2O3 (mol %) 20 40 60 80 90 a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

25

iepa

Streaming potential

9.6 9.6 9.5 9.4 9.4

[1077]

Only value, no data points.

3.3.1.3.3 Calcined for 5 h at 470°C Aluminum sec-butoxide was mixed with 100 parts of aqueous Cr(NO3)3. The mixture was heated to 75°C for 30 min, then 0.05 mole of HNO3 was added per mole of aluminum sec-butoxide at 85°C, and the mixture was stirred at this temperature for 3 h. The sol was dried at room temperature, then at 150°C, and calcined for 5 h at 470°C.

TABLE 3.1363 PZC/IEP of Al–Cr Mixed Oxide Calcined for 5 h at 470°C % Cr/Specific Surface Area (m2/g) 1/302 1.8/331 2.7/298 4/327 5.4/336 a

Electrolyte 0.001–0.1 M KNO3

Only value, no data points.

T

Method

Instrument

pH0

Reference

25

a

Matec Acustosizer

7.7 7.3 6.4 6.4 6.4/7.2

[1069]

cip /iep

595

Compilation of PZCs/IEPs

3.3.1.4 Al–Fe Mixed Oxides and Clay Mineral– Fe (Hydr)oxide Composites 3.3.1.4.1 Firing Coprecipitated Hydroxides, 1.9% Fe2O3

TABLE 3.1364 PZC/IEP of Al–Fe Mixed Oxide Obtained by Firing of Coprecipitated Hydroxides Firing Temperature (°C)

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

9.7 4.5

[2306]

600 1200

3.3.1.4.2 Calcined at 1200°C for 3 h A mixture of nitrates was adjusted to pH 2 with HNO3, and then treated with excess of ammonia. The precipitate was washed with water, calcined at 600°C for 5 h, washed with water again, calcined at 1200°C for 3 h, and washed with water again. Properties: Rhombohedral Cr2O3-type structure, lattice spacing data available [1077].

TABLE 3.1365 PZC/IEP of Al–Fe Mixed Oxide Calcined at 1200°C for 3 h Al2O3 (mol%) 10 20 40 50 70 80 a

Electrolyte 0.001 M NaCl

T 25

Method a

iep

Instrument

pH0

Reference

Streaming potential

8.6 8.8 9.6 9.6 9.6 9.6

[1077]

Only value, no data points.

3.3.1.4.3 Coprecipitation from Nitrates A solution, 0.3 M in HNO3 containing Al(NO3)3 and Fe(NO3)3, was adjusted to pH 8 by rapid addition of 3 M NaOH. The pH was maintained at 8 for 2 h. Another procedure was similar, except that Al(OH)3 and Fe(OH)3 were prepared in separate containers, aged at pH 8 for 2 h and then mixed. Properties: BET specific surface area 297 m2/g (coprecipitation), 263 m2/g (mixture) [1191,1192].

596

Surface Charging and Points of Zero Charge

TABLE 3.1366 PZC/IEP of Al–Fe Mixed Hydroxide Obtained by Coprecipitation from Nitrates Description

Electrolyte

T

Coprecipitation Mixture a

Method

Instrument

pH0

Reference

iepa

Electrophoresis

9.1 9.2

[1191,1192]

Only value, data points not reported.

3.3.1.4.4 Treated at 90–95°C in Autoclave for 6 h A solution containing a mixture of FeCl3 and AlCl3 was neutralized with 25% ammonia. The dispersion was dispersed in undecane, and small drops of the formed dispersion were added to ammonia solution. The particles were washed with water, and treated at 90–95°C in an autoclave for 6 h. Two materials were prepared: Fe2O3·Al2O3·xH2O, single-point BET specific surface area 396 m2/g, and Fe2O3·2Al2O3·xH2O, specific surface area 388 m2/g [2307].

TABLE 3.1367 PZCs/IEPs of Al–Fe Mixed Hydroxide Treated at 90–95°C in Autoclave for 6 h Electrolyte

T

Method

Instrument

pH0

Reference

HCl + NaOH

22

iepa

Rank Brothers Mark II

3.6

[2307,2308]

a

Titration curves also reported.

3.3.1.4.5 Montmorillonite–Iron (Hydr)oxide Composites 3.3.1.4.5.1 Montmorillonite–Lepidocrocite Composite A solution of 250 mg of FeSO4 in 150 cm3 of CO2-free water was neutralized with 1 M NaOH to pH 6.5–7. Montmorillonite was added (Fe:clay ratio of 0.32 by mass) and oxygen was bubbled through the dispersion, and NaOH solution was added to keep the pH at 6.5–7. The precipitate was washed with water. Properties: 9% lepidocrocite, 24% ferrihydrite (Fe2O3·2.2H2O), XRD pattern available, BET specific surface area 118 m2/g, TEM image available [1611].

597

Compilation of PZCs/IEPs

TABLE 3.1368 PZC/IEP of Montmorillonite–Lepidocrocite Composite Electrolyte

T

Method iep

a

a

Instrument

pH0

Reference

Malvern Zeta Master

4.4

[1611]

Only value, data points not reported.

3.3.1.4.5.2 Montmorillonite–Ferrihydrite Composite 1 g of montmorillonite was suspended in water, and Fe(iii) salt added at pH 2.5 (Fe:clay ratio of 0.32 by mass). The dispersion was stirred for 1 h. 1 M NaOH solution was slowly added to adjust the pH to 8, and the dispersion was stirred for 1 h. The precipitate was washed with water. Properties: 36% ferrihydrite (Fe2O3 · 2.2H2O), XRD pattern available, BET specific surface area 213 m2/g, TEM image available [1611]. TABLE 3.1369 PZC/IEP of Montmorillonite–Ferrihydrite Composite Electrolyte

T

Method a

iep a

Instrument

pH0

Reference

Malvern Zeta Master

7.7

[1611]

Only value, data points not reported.

3.3.1.5 LaAl11O18 A stoichiometric solution of anhydrous La acetate (or acetylacetonate) and Al secbutoxide in 2-methoxyethanol was refluxed at 125°C for 8 h, and hydrolyzed in a water–ethanol mixture. TABLE 3.1370 PZC/IEP of LaAl11O18 Electrolyte CH3COOH + NH4OH

3.3.1.6

T

Method

Instrument

pH0

Reference

iep

Coluler Delsa 440SX

7.5

[2309]

Al–Mg Mixed Oxide (or Hydroxide)

3.3.1.6.1 Hydroxide, from Chlorides Mixtures of Al and Mg chlorides at different ratios, total molarity 0.5, were added to ammonia solution, and the final pH was 9.5. The precipitate was aged for 5 h at room temperature and washed with water. It was peptized at 333K and washed by ultrafiltration.

598

Surface Charging and Points of Zero Charge

TABLE 3.1371 PZC/IEP of Al–Mg Mixed Hydroxide Precipitated from Chlorides Al/(Al + Mg) (molar) 0.228 0.26 0.332 0.466 a

b

Electrolyte 0.001–0.1 M NaNO3

T

Method

Instrument

pH0

Reference

25

a

3 d equilibration (cip) DXD-II

12/11.9 12.1/11.8 12.2/11.4 12.3/11

[2310,2311b, 2312]

cip /iep

Values claimed by authors. An example shown in a figure in [2310] indicates that the CIP was not very sharp. Cf. Chapter 1 for discussion about the significance of s0 at very low or very high pH. Only values, data points not reported.

3.3.1.6.2 From Nitrates A solution of 0.32 mol of Mg(NO3)2 · 6 H2O and 0.16 mol of Al(NO3)3 · 9 H2O in 1 dm3 of water was added dropwise to a solution of 1.1 mol of NaOH and 0.15 mol of NaNO3 in 1 dm3 of water. The dispersion was aged for 6 d at 20°C. The sediment was washed with water and dialyzed. Properties: [Mg2.16Al0.84(OH)6]0.84+, balanced by nitrate (60%), chloride (5%), and carbonate (35%), particle diameter 70 nm [2313].

TABLE 3.1372 PZC/IEP of PZC/IEP of Al–Mg Mixed Hydroxide Precipitated from Nitrates Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 501

>12 if any

[2313]

3.3.1.7 Si–Al Mixed Oxide 3.3.1.7.1

Commercial

3.3.1.7.1.1 Silica (3% by mass)-Modified Alumina from Akzo BET specific surface area 460 m2/g [1075].

Properties:

TABLE 3.1373 PZC/IEP of 3% Silica-Modified Alumina from Akzo Electrolyte HCl + KOH

T

Method

Instrument

pH0

Reference

iep

Rank Mark II

4.6

[1075]

599

Compilation of PZCs/IEPs

3.3.1.7.1.2 From Chlorovinyl Another series of samples studied by the same research group in described in Section 3.3.1.7.1.5. Properties: Amorphous, BET specific surface area 171 (23% Al2O3 by mass) and 180 m2/g (30% Al2O3 by mass) [836], 220, 180, 170, and 170 m2/g for 1, 3, 23, and 30% Al2O3, respectively [837], IR spectrum available [836]. TABLE 3.1374 PZC/IEP of Si–Al Mixed Oxides from Chlorovinyl % Al2O3 by Mass 1 3 23 30

Electrolyte

T

HCl + NaOH

Method

Instrument

pH0

Reference

iep

ZetaPlus Brookhaven

<2.5 if any

[836,837]

3.3.1.7.1.3 Zeolex from Huber Al2O3 · 12 SiO2 · 2H2O Properties: BET specific surface area 70 m2/g, particle diameter 6 mm [851]. TABLE 3.1375 PZC/IEP of Zeolex from Huber Electrolyte

T

0.01 M NaClO4 a

Method

Instrument

pH0

Reference

iep

Laser Zee 500

<3 if any 1

[851] [899]a

Only value, no data points.

3.3.1.7.1.4 Cracking Catalyst from Hydrocarbons Properties: SiO2, 24% Al2O3, 20% water, BET specific surface area 268 m2/g [2279]. TABLE 3.1376 PZC/IEP of Cracking Catalyst from Hydrocarbons Electrolyte 0.001–0.1 M KNO3

T

Method

Instrument

pH0

Reference

cip pH iep

4.8 6 5

[2279]

6 d equilibration Electrophoresis

3.3.1.7.1.5 From Institute of Surface Chemistry, Kalush, Ukraine Fumed. Another series of samples studied by the same research group in described in Section 3.3.1.7.1.2.

600

Surface Charging and Points of Zero Charge

TABLE 3.1377 PZC/IEP of Si–Al Mixed Oxides from Institute of Surface Chemistry, Kalush, Ukraine BET Specific Surface Area % Al2O3 (m2/g) Electrolyte 1 23

207 353

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000

<3.5 if any <3.5 if any

[926]

0.001 M NaClO4

3.3.1.7.1.6 N-631(L) from Nikki surface area 394 m2/g [979].

Properties (calcined at 500°C): BET specific

TABLE 3.1378 PZC/IEP of N-631(L) from Nikki Electrolyte

T

Method

0.01 M KCl

40

pH

Instrument

pH0

Reference

4.6

[979]

3.3.1.7.2 Synthetic 3.3.1.7.2.1 From Alkoxides 3.3.1.7.2.1.1 10% Al2O3–90% SiO2 Mixed Oxide Prepared in Water– Alcohol Medium Silica was obtained from tetraethylsilicate in a water–alcohol medium at room temperature, dried at 385K for 20 h, and calcined for 16 h at 875K. Silica was impregnated with aluminum isopropoxide solution in benzene. After 1d exposure to air, benzene was evaporated, and the product was subjected to slow hydrolysis. Properties: BET specific surface area 541 m2/g [1912]. TABLE 3.1379 PZC/IEP of 10% Al2O3–90% SiO2 Mixed Oxide Prepared in Water–Alcohol Medium Electrolyte

T

Method

Instrument a

Mass titration a

Only value, data points not reported.

pH0

Reference

5.1

[1912]

601

Compilation of PZCs/IEPs

3.3.1.7.2.1.2 Prepared in the Presence of Sulfate A dispersion 0.4 M in Al(t-BuO)3 and 0–3.2 M in Si(EtO)4 in t-butanol was prepared by ultrasonication for >1 h. This dispersion was added to an acidified (pH ⬇ 2) solution of (NH4)2SO4 at room temperature, and the system was stirred for 1 h. [Al] = 0.002 M, [SO4] = 0.003 M in aqueous dispersion. The system was then sealed and heated for 1 d at 98°C. The precipitate was washed and dried at room temperature. Properties: SEM images, XRD pattern, and results of thermal analysis available [2314].

TABLE 3.1380 PZC/IEP of Al–Si Mixed Oxide Prepared in Presence of Sulfate Description

Electrolyte

T

Si/Al 4 6 8

Method

Instrument

pH0

Reference

iep

Delsa 440

9 7.4 <3 if any

[2314]

3.3.1.7.2.2 From Ethoxide and AlCl3 Propylene oxide was added to Si(OC2H5)4 + AlCl3 solution in methanol. Methanol was removed by rinsing in diethyl ether. Diethyl ether was evaporated. Properties: For BET specific surface area, see Table 3.1381; Na and Cl concentration, and pore volume available [1090].

TABLE 3.1381 PZC/IEP of Al–Si Mixed Oxide Prepared from Ethoxide and AlCl3 Mass % Al2O3 88 77 69 26 11 0.4 a

Merge.

BET Specific Surface Area (m2/g) 437–446 402–431 315–373 405–425 524–548 378–385

Electrolyte 0.001–0.1 M NaNO3

T

Method cip

Instrument

pH0

Reference

6.7 6.3 5.9 4.8 4.4a 4.1a

[1090]

602

Surface Charging and Points of Zero Charge

3.3.1.7.2.3 From Inorganic Precursors 3.3.1.7.2.3.1 From Na2SiO3 and Al(NO3)3 1 M Na2SiO3 and 1 M Al(NO3)3 were pumped into at beaker held at pH 7. The precipitate was freeze-dried, waterwashed, and freeze-dried again. Properties: Amorphous [1187]. TABLE 3.1382 PZC/IEP of Al–Si Mixed Oxide Prepared from Na2SiO3 and Al(NO3)3 Al/(Al + Si) (molar) 0.5 0.6 0.7 0.8 a

Electrolyte

T

Method

Instrument

Salt additiona

0.01 M NaNO3

pH0

Reference

4.3 4.5 5 7

[1187]

Only value, data points not reported.

3.3.1.7.2.3.2 From Na2SiO3 and AlCl3 1 dm3 of Na2SiO3 solution was prepared by dissolving 13.5 g of silica in concentrated NaOH. The final pH was 13. This solution of Na2SiO3 and 1 dm3 of 0.22 M AlCl3 solution in HCl were added simultaneously to 100cm3 of water with stirring, and the pH ⬇ 7 was held by addition of NaOH or HCl. The dispersion was aged for 1 d at room temperature, and then washed with 1 M NaCl and then with water. The solid was dried at 100°C, and then calcined in air for 3 h at 400°C. Properties: Not calcined 1.67 SiO2 · Al2O3 · 0.04 Na2O · 1.06 H2O, calcined 1.67 SiO2 · Al2O3 · 0.04 Na2O · 0.05 H2O, specific surface area (different methods) 47–52 m2/g, 15–100 nm in diameter, irregularly shaped particles, XRD, thermal analysis, IR spectra available [144]. TABLE 3.1383 PZC/IEP of Al–Si Mixed Oxide Prepared from Na2SiO3 and AlCl3 Electrolyte 0.001–0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep pH

Rank Brothers Zeta-Meter 3.0

5.5 Merge at pH < 5

[144]

3.3.1.7.2.3.3 Synthetic Imogolite, Al:Si Molar Ratio 2.01 0.1 M Al(ClO4)3 was added to 0.002 M silicic acid at an Al/Si molar ratio of 1.613. The solution was titrated with 1 M NaOH to pH 5 and acidified with a mixture of 0.4 M CH3COOH and 0.2 M HNO3 at a CH3COOH-to-Al molar ratio of 0.818. The dispersion was aged for 8–12 h and then refluxed for 5 d.

603

Compilation of PZCs/IEPs

TABLE 3.1384 PZC/IEP of Synthetic Imogolite Electrolyte

T

Method a

0.001, 0.01 M NaClO4, NaNO3, NaCl, NaBr, NaI a b

iep

Instrument

pH0

Reference

Zeta-Meter 3.0

>11 if any

[25]b [329]

Atypical terminology is used in [25,329]. Only value, data points not reported.

3.3.1.7.2.3.4 From Sodium Aluminate

TABLE 3.1385 PZC/IEP of Al–Si Mixed Oxide Prepared from Sodium Aluminate Al/SiO2 (mass%)

Electrolyte

T

Method pHa

0.03 1 3 19 a

Instrument

pH0

Reference

2.7 3.2 4 4.5

[544]

Only value, data points not reported.

3.3.1.7.2.4 Oxidation of Alkoxides in Air Vapors of aluminum sec-butoxide and silicon ethoxide (premixed or sequentially delivered) were oxidized in air at 700–1400°C for various times (64–170ms) and different Al2O3/SiO2 ratio (mass%). Properties: 44–352 m2/g, XRD pattern available, TEM image available [1086].

TABLE 3.1386 PZC/IEP of Al–Si Mixed Oxide Prepared by Oxidation of Alkoxides in Air Description Premixed, two samples Sequential delivery (Al2O3:SiO2): 41:59 23:77 25:75

Electrolyte NaOH + HCl

T

Method iep

Instrument

pH0

Malvern Zetasizer <3 if any 3000 7.5 5.5 <3 if any

Reference [1086]

604

Surface Charging and Points of Zero Charge

3.3.1.7.2.5 Recipe from [2315,2316] Aqueous silicic acid was obtained from sodium silicate by ion exchange. AlCl3 was dissolved in aqueous silicic acid, and the solution was sprayed into dilute ammonia. The product contains 72.5% of alumina by mass. Properties: Particle size 340 nm, SEM images, XRD pattern available [488]. TABLE 3.1387 PZC/IEP of Al–Si Mixed Oxide Prepared According to Recipe from [2315,2316] Aging

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern AZ-6004

8.2 7 6.1 6.1 5.9 5.8

[488]

None 3h 7h 12 h 1d Autoclave

0.001 M NaCl

3.3.1.7.3

Natural Imogolite from Kitakami, Japan, Al2O3 · SiO2 · 2.5H2O

TABLE 3.1388 PZC/IEP of Natural Imogolite from Kitakami, Japan Description H2O2-treated

a

Electrolyte 0.001–0.1 M NaCl

T

Method

25

pH iep

Instrument Electrophoresis, Briggs cell

pH0 a

6 >11 if any

Reference [2317]

No clear CIP. Other PZC/IEP data for imogolite reported in References 3, 8, 10, and 11 in [2317].

3.3.1.8 Al2O3 –TiO2 Mixed Oxides 3.3.1.8.1 Membrane Supports, Membranes TABLE 3.1389 PZC/IEP of Membrane Supports and Membranes Made of Al2O3 –TiO2 Mixed Oxides Description TAMI Support Membrane

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl 0.001 M NaCl 0.001, 0.005 M KCl

25 25 20

iep iep iep

Streaming potential Streaming potential Streaming potential

6.4 6.5 6.5

[2318] [2319] [2322]

605

Compilation of PZCs/IEPs

3.3.1.8.2 Amperit 744.1 from Stark, 87% Al2O3, 13% TiO2 Original and plasma-sprayed. Properties: a-alumina and rutile (original), a-alumina with admixture of g (after spraying), XRD patterns available, specific surface area original: 0 .3 m2/g, after spraying: 0 .8 m2/g [1003].

TABLE 3.1390 PZC/IEP of Amperit 744.1 from Stark Description Original Original, washed Sprayed Sprayed, washed

3.3.1.9

Electrolyte

T

0.01 M NaCl

Method

Instrument

Mass titration

pH0

Reference

7.8 8.1 8.5 7.6

[1003]

Al-Si-Ti Mixed Oxides

3.3.1.9.1 Commercial 3.3.1.9.1.1 From Chlorovinyl, 50% TiO2, 22% Al2O3 by Mass Fumed. Another series of samples studied by the same research group in described in Section 3.3.1.9.1.2. Properties: Amorphous alumina and silica, anatase 88%, rutile 12%, BET specific surface area 62 m2/g, IR spectrum available [836].

TABLE 3.1391 PZC/IEP of Al–Si–Ti Mixed Oxide from Chlorovinyl Electrolyte HCl + NaOH a

T

Method iep

Instrument ZetaPlus Brookhaven

pH0 3.3

a

Reference [836]

Only one data point in the vicinity of IEP.

3.3.1.9.1.2 From Institute of Surface Chemistry, Kalush, Ukraine Fumed. Another sample studied by the same research group in described in Section 3.3.1.9.1.1

606

Surface Charging and Points of Zero Charge

TABLE 3.1392 PZC/IEP of Al–Si–Ti Mixed Oxides from Institute of Surface Chemistry, Kalush, Ukraine TiO2/ SiO2 (%) 50/28 71/8 82/6 87/4 88/8

BET Specific Surface Area (m2/g)

D (nm)

38 74 39 42 39

51 24 42 38 41

Electrolyte

T

Method Instrument

0.001 M NaCl

25

iep/pH

Malvern Zetasizer 3000

pH0

Reference

3.2 8.5/4.6 8.6/5.2 8.5/4.8 8.5/4.8

[926]

3.3.1.9.1.3 Pulverized Microporous Membrane from TAMI: 64% Al2O3, 27% TiO2, 9% SiO2 Properties: BET specific surface area 1.4 m2/g [660]. TABLE 3.1393 PZC/IEP of Pulverized Microporous Membrane from TAMI Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.05 M NaCl

20 25

iep cip Mass titration Salt addition

Electro-osmosis Streaming potential

4.7 8.2 8.2 8.2

[660,2320]

3.3.1.9.1.4 Membrane: Nominally 70% Al2O3, 30% TiO2 Properties: 10% of silica [2321]. TABLE 3.1394 PZC/IEP of a Membrane: Nominally 70% Al2O3, 30% TiO2 Electrolyte

T

Method

Instrument

pH0

Reference

0.0001–0.01 M KCl, NaCl

20

iep

Streaming potential

4.5

[2321]

3.3.1.9.1.5 Al–Si–Ti Membrane, 9% of Silica TABLE 3.1395 PZC/IEP of Al–Si–Ti Membrane, 9% Silica Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

20

iep

Streaming potential

4.5

[2322]

607

Compilation of PZCs/IEPs

3.3.1.10 Activated Bauxite from Milwhite Properties: 76.5% Al2O3, 4% Fe2O3, 3.5% TiO2, 10% SiO2, 4.5–6.5% volatile matter [808,809] HCl- and water-washed (different sequences). TABLE 3.1396 PZC/IEP of Activated Bauxite from Milwhite Electrolyte

a

T

Method

Instrument

pH0

Reference

iepa

Streaming potential

5.8

[809]

Only value, data points not reported.

3.3.1.11 Al–Y Mixed Oxide 3.3.1.11.1 From Alkoxides 37 mol% Y2O3. From Al sec-butoxide and Y isopropoxide. Different recipes were tested, and products were characterized by TEM and XRD [2323]. TABLE 3.1397 PZC/IEP of Al–Y Mixed Oxide Prepared from Alkoxides Electrolyte

T

Method

Instrument

pH0

Reference

iep

ELS-800 Otsuka

10

[2323]

NaOH + HCl

3.3.1.11.2 From Al Sec-Butoxide and Y(NO3)3 Calcined at 750°C for 6 h, recipe from [1070]. TABLE 3.1398 PZC/IEP of Al–Y Mixed Oxide Prepared from Al sec-butoxide and Y(NO3)3 Y2O3 (mass%)/BET Specific Surface Area (m2/g) 2.5/299 10/305 20 /236

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

Room

iep

Zeta-Meter 3.0+

8.4 8.6 9

[1004]

3.3.1.12 Al–Zn Mixed (Hydr)oxides 3.3.1.12.1 Al–Zn Mixed Oxides The mixed-component metal oxide was heated for 6 h at 1200°C. It was ground, reheated at the same temperature, crushed, and washed with water.

608

Surface Charging and Points of Zero Charge

TABLE 3.1399 PZC/IEP of Al–Zn Mixed Oxides Zn/(Zn + Al) (mol%) 20 30 33.3 40 60 80 a

Electrolyte

T

0.001 M NaCl

Method

25

iep

Instrument

a

Streaming potential

pH0 9.7 10 10 9.7 9.8 9.9

Reference [33]

Only value, data points not reported.

3.3.1.12.2 Zn–Al Mixed Hydroxides Obtained from Chlorides and NH3 Properties: Specific surface area 1014–1071 m2/g, lattice parameters available [2324,2325], XRD patterns available [2325]. TABLE 3.1400 PZC/IEP of Zn–Al Mixed Hydroxides Obtained from Chlorides and NH3 Composition Zn0.48Al0.52(OH)2.34Cl0.18 Zn0.59Al0.41(OH)2.24Cl0.17 Zn0.63Al0.37(OH)2.21Cl0.16 Zn0.65Al0.35(OH)2.19Cl0.16 Zn0.69Al0.31(OH)2.11Cl0.20

Electrolyte

T

0.001–0.1 M NaCl

25

Method Instrument cip/iep

pH0

Reference

10.4/11 10.5/11 10.5/11 10.7/11 11/11.2

[2324] [2325]

3.3.1.13 Zn–Al–Fe Mixed Hydroxides From chlorides (total metal cation concentration 0.5 M) and 0.25 M NH3. Properties: Specific surface area 937–972 m2/g, lattice parameters, XRD patterns available [2325]. TABLE 3.1401 PZC/IEP of Zn–Al–Fe Mixed Hydroxides Composition Zn0.47Al0.27Fe0.26(OH)2.21Cl0.32 Zn0.35Al0.38Fe0.27(OH)2.3Cl0.35 Zn0.28Al0.30Fe0.42(OH)2.66Cl0.06 Zn0.26Al0.28Fe0.46(OH)2.71Cl0.03 Zn0.18Al0.23Fe0.59(OH)2.76Cl0.06

Electrolyte 0.001–0.1 M NaCl

T

Method

25

cip

Instrument

pH0 Reference 10 9.6 9.5 9.5 9.3

[2325]

609

Compilation of PZCs/IEPs

3.3.1.14 Al–Zr Mixed Oxide 8% mol ZrO2. From Al sec-butoxide and Zr butoxide. Different recipes were tested, and products were characterized by TEM, SEM, and XRD [2323].

TABLE 3.1402 PZC/IEP of Al–Zr Mixed Oxide Electrolyte

T

NaOH + HCl

3.3.1.15

Method

Instrument

pH0

Reference

iep

ELS-800 Otsuka

10

[2323]

Red Mud

3.3.1.15.1 From Weipa Properties: BET specific surface area 22.2 m2/g [2326].

TABLE 3.1403 PZC/IEP of Red Mud from Weipa Electrolyte

T

0.01–0.5 M NaCl

Method

Instrument

pH0

Reference

pH

18 h equilibration

6.5

[2326]

3.3.1.15.2 From Claremont Properties: BET specific surface area 48.7 m2/g [2326].

TABLE 3.1404 PZC/IEP of Red Mud from Claremont Electrolyte 0.01–0.5 M NaCl

T

Method

Instrument

pH0

Reference

pH

18 h equilibration

7.8

[2326]

3.3.1.15.3 Red Mud, a By-product from Bayer Process (Etibank, Turkey) Properties: Hematite 37.3%, Al2O3 17.6%, SiO2, 16.9%, TiO2 5.6%, Na2O 8.3%, CaO 4.4%, loss of ignition 7.2%, BET specific surface area 20.7 m2/g [578,2327].

610

Surface Charging and Points of Zero Charge

TABLE 3.1405 PZC/IEP of Red Mud, a By-Product from Bayer Process (Etibank, Turkey) Electrolyte 0.001–1 M CsCl 0.001–1 M NaCl

T

Method

25

Instrument

a

cip

cipb a b

pH0

Reference

8.2 8.1 8.3

[578] [2327]

Based on subjective interpolation. Only value, data points not reported.

3.3.1.15.4 Activated Red Mud Red mud was refluxed in 20% HCl for 2 h. The solution was treated with ammonia at room temperature. The precipitate was water-washed, and dried at 110°C. Properties: Specific surface area 249 m2/g [2328]. TABLE 3.1406 PZC/IEP of Activated Red Mud Electrolyte

T

0.001–1 M KNO3

3.3.2

Method

Instrument

cip

pH0

Reference

8.5

[2329]

Bi–Th MIXED OXIDES

0.1 M Bi(NO3)3 and 0.1 M Th(NO3)4, both in 1 M HNO3, were mixed at different ratios, and then excess of NaOH was added at 97°C. The precipitate was digested for 2 h at hot conditions, aged for 1 d at room temperature, water-washed, dried, washed, and dried again. Properties: XRD pattern available; for specific surface area, see Table 3.1407 [1216]. TABLE 3.1407 PZC/IEP of Bi–Th Mixed Oxides Th/(Bi + Th) (by mass)/Specific Surface Area (m2/g) 0.05/21 0.11/27 0.28/46 0.32/30 0.36/29 a

Electrolyte 0.1 M NaClO4 NaNO3

Only value, no data points.

T

Method pH/Mass titration

Instrument

pH0

Reference

4.8/5 4.5 4.8/5.2 6.7/6.6 7.2/7.4

[1216]a

611

Compilation of PZCs/IEPs

3.3.3

MATERIALS CONTAINING Ce

3.3.3.1 Ce–Pr Mixed Oxide Obtained by calcination of Pr0.24Ce0.76OHCO3 at 600°C for 1 min. Properties: Fluorite structure, TEM image, DTA and TGA results available, d50 = 200 nm, BET specific surface area 10.7 m2/g [338, Table 3]. TABLE 3.1408 PZC/IEP of Ce–Pr Mixed Oxide Electrolyte

T

0.01 M NaCl

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer

7.6

[338]

3.3.3.2 Ce(IV)–Y Mixed Oxides Obtained by calcination of mixed basic carbonates at 650°C for 3 h. C: From Y0.75Ce0.25OHCO3 · H2O. Properties: XRD pattern between those of Y2O3 (body-centered cubic) and CeO2 (face-centered cubic), IR spectrum available, particle diameter 80 nm, specific surface area 15 m2/g [2154]. D: From Y0.25Ce0.75OHCO3 · H2O. Properties: XRD pattern of CeO2 (face-centered cubic), particle diameter 90 nm, specific surface area 12 m2/g [2154].

TABLE 3.1409 PZC/IEP of CeIV–Y Mixed Oxides Description C D a

Electrolyte

T

0.001 M NaNO3

Method

Instrument

pH0

Reference

iep

Coulter Delsa

3.9a 3.9

[2154]

Additional two IEPs at pH 5.5 and 7.3, which are probably due to dissolution of Y. Sample D had a maximum in mobility in this pH range, but without sign reversal. The dispersions were aged for 3–5 h before measurement.

3.3.4

MATERIALS CONTAINING Co

3.3.4.1 Co–Mn Mixed Oxides 0.125 M (Mn + Co)(NO3)2 acidified with concentrated HNO3 (1 cm3 per 1 dm3 of solution) was evaporated at 90°C, calcined at 250°C in air and at 400°C in oxygen for 3 d, and then quenched in liquid nitrogen. Properties: XRD patterns available, spinel structure [1240].

612

Surface Charging and Points of Zero Charge

TABLE 3.1410 PZC/IEP of Co–Mn Mixed Oxides MnxCo3−xO4, x = 0.25 0.5 0.75 1 a

Electrolyte

T

Method

Instrument

a

pH

1 M KNO3

pH0

Reference

6.6 6.2 6 6

[1240]

Only value, data points not reported.

3.3.4.2 NiCo2O4 Obtained from Co(NO3)2 · 6H2O and Ni(NO3)2 · 6H2O. TABLE 3.1411 PZC/IEP of NiCo2O4 Calcination Temperature (°C)

Electrolyte

T

Instrument

Titrationa

250 300 350 400 450 500 550 600 650 700 a

Method

pH0

Reference

8.8 8.9 9.1 9.2 9.4 9.1 9 8.9 8.7 8.8

[2330, 2355]

Only value, data points not reported. Reference [893] was also cited as a source of similar results, apparently by mistake.

3.3.5

MATERIALS CONTAINING Cr

3.3.5.1 FeCr2O4, Chromite from Kemi Mine, Outokumpu, Finland Properties: 49.6% Cr2O3, 19.4% Fe, contains MgCr2O4 and (Mg,Al)(Cr,Al)2O4, particle size distribution available, specific density 4340 kg/m3 [1443]. TABLE 3.1412 PZC/IEP of Chromite from Kemi Mine, Outokumpu, Finland Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem, Laser Zee Meter 501

6

[1443]

613

Compilation of PZCs/IEPs

3.3.5.2 (Mg,Fe)(Al,Cr)2O4, Picotite from Kapfenberg TABLE 3.1413 PZC/IEP of Picotite from Kapfenberg Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

2

[104]

NaOH + HClO4

3.3.5.3 Lanthanum Chromites from Praxair Produced by combustion spray pyrolysis, calcined at 650°C. TABLE 3.1414 PZC/IEP of Lanthanum Chromites Formula LaCr0.9Ni0.1O2.95 LaCr0.9Zn0.1O2.95 a

Electrolyte

T

Method

Instrument

0.01 M NaCl

24

iepa

Malvern Zetasizer 4

pH0 Reference 7.6 7.6

[2331]

Only one data point near IEP.

3.3.5.4 Cr–Ti Mixed Oxide Amperit 712.066 from Stark, 75% Cr2O3, 25% TiO2. Original and plasma-sprayed. Properties: Eskolaite (original and after spraying), specific surface area 0.2 m2/g (original), 1.2 m2/g (after spraying), XRD patterns available [1003]. TABLE 3.1415 PZC/IEP of Cr–Ti Mixed Oxide Description Original Original, washed Sprayed Sprayed, washed

3.3.6

Electrolyte

T

0.01 M NaCl

Method Mass titration

Instrument

pH0

Reference

8.9 8.3 4 5.8

[1003]

MATERIALS CONTAINING Fe

3.3.6.1 Fe–Co Mixed Oxides 3.3.6.1.1 Heated for 6 h at 1000°C The mixed-component metal oxide was heated for 6 h at 1000°C, ground, reheated at the same temperature, crushed, and washed with water.

614

Surface Charging and Points of Zero Charge

TABLE 3.1416 PZC/IEP of Fe–Co Mixed Oxides Heated for 6 h at 1000°C Co/(Co + Fe) (mol%) 10 20 30 33.3 40 60 80 a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

25

iepa

Streaming potential

3.8 3.7 3.4 3.1 6.2 9.5 9.8

[33]

Only value, data points not reported.

3.3.6.1.2 CoFe5.3O11.9, Cobalt Ferrite Recipe from [2332]: A solution 0.125 M in FeSO4, 0.075 M in Co(NO3)2 0.2 M in KNO3 and 0.1 M in KOH in oxygen-free water was aged for 1 d at 90°C. The dispersion contained goethite, which was removed by magnetic sedimentation. Properties: XRD pattern available [2333], TEM image available [501,2333], average diameter 850 nm [501,2333], SEM images available, also for different Co:Fe ratios [2332]. TABLE 3.1417 PZC/IEP of CoFe5.3O11.9 Electrolyte

T

Method

Instrument

pH0

Reference

0.0001–0.01 M NaNO3 0, 0.01 M NaNO3

25

iep iep

Malvern Zetasizer 2000 Malvern Zetasizer 2000

6.5a 6.5b

[2333] [501]

a b

IEP roughly matches pH of minimum stability. IEP roughly matches the maximum in the elastic modulus corresponding to the viscoelastic linear region in a 2 vol% dispersion, with or without magnetic field.

3.3.6.1.3 CoFe2O4 Precipitated from Co(NO3)2 and FeCl3 Hydrothermal coprecipitation from Co(NO3)2–FeCl3 mixture in alkaline medium, acid-washed and boiled with Fe(NO3)3. Properties: Particle size 12 nm, EM image, XRD pattern available [2334]. TABLE 3.1418 PZC/IEP of CoFe2O4 Electrolyte

T

Method pH

Instrument

pH0

Reference

6.9

[2334]

615

Compilation of PZCs/IEPs

3.3.6.1.4 CoxFe3-xO4 Precipitated from Co(NO3)2 and FeSO4 Synthetic CoxFe3-xO4 0.25 < x < 1. Solutions of Co(NO3)2 and FeSO4 were prepared and mixed in a nitrogen atmosphere, and then heated to boiling point. A mixture of KOH and KNO3 was added dropwise within 70 min, and the boiling and mixing was continued for the next 1 h. After cooling to room temperature, the precipitate was washed with degassed water and dried under reduced pressure. Properties: Spherical particles with wide size distribution: 10–200 nm, inverted spinel structure; for BET specific surface area, see Table 3.1419 [2335]. TABLE 3.1419 PZC/IEP of Cox Fe3−x O4 Precipitated from Co(NO3)2 and FeSO4 Specific Surface Co/Fe (mol%) Area (m2/g) 10 20 25 33.3 50

12 17 20 20 17

Electrolyte

T

0.001–0.1 M KNO3

25

Method

Instrument

pH0

cip/iep Rank Brothers 6.4/6.5 MK II 6.8 7/7 7.4/7.3 8.2/8.3

Reference [2335]

3.3.6.1.5 Synthetic Co-Substituted Magnetite Oxidation of mixed Fe(ii)–Co hydroxide gel with KNO3 at near-boiling conditions. Properties: Specific surface area, XRD pattern, and isotherms of water adsorption available [1284]. TABLE 3.1420 PZC/IEP of Co-Substituted Magnetite Fe (mass%) 71 68 71 53 29 12 8 3 0.4

Co (mass%)

Electrolyte

0.1 4 11 17 28 35 40 48 49

NaOH + HNO3

T

Method pH

Instrument

pH0 Reference 8.1 8.2 7.2 7.1 7.1 7.8 8 8.1 8.3

[1284]

616

Surface Charging and Points of Zero Charge

3.3.6.1.6 Co-Modified Goethite 10 M NaOH was added to 1 M Fe(NO3)3 containing Co (50–500 ppm) with stirring to adjust the pH to 11.5–12. This was followed by aging for 1 d at 70°C in a polyethylene bottle.

TABLE 3.1421 PZC/IEP of Co-, Cu-, and Ni-Modified Goethites Co (%) 0.25 0.5 1 2.2 a

Electrolyte

T

Method a

pH

0.01 M KNO3

Instrument

pH0

Reference

3 d equilibrated

7.5 7.4 7.2 6.9

[1577]

Only value, data points not reported.

3.3.6.2 Fe–Cr Mixed (Hydr)oxides 3.3.6.2.1 Fe1-xCrxOOH Obtained by aging nitrate solutions in KOH at 70°C for 153 d. Properties: a-form [1248].

TABLE 3.1422 PZC/IEP of Fe1−x Crx OOH Description

Electrolyte

T

Method

Instrument

pH0

Reference

0.04 < x < 0.13

0.01 M KCl

25

iepa

Electrophoresis

8.5

[1248]

a

Only value, data points not reported.

3.3.6.2.2 Fe–Cr Mixed Oxide A mixture of nitrates was adjusted to pH 2 with HNO3, and then treated with excess of ammonia. The precipitate was washed with water, calcined at 600°C for 5 h, washed with water again, calcined at 1200°C for 3 h, and washed with water again. Properties: Rhombohedral Cr2O3-type structure, lattice spacing data available [1077].

617

Compilation of PZCs/IEPs

TABLE 3.1423 PZC/IEP of Fe–Cr Mixed Oxide Fe2O3 (mol%) 10 20 40 60 80 a

Electrolyte

T

0.001 M NaCl

Method

25

a

iep

Instrument

pH0

Reference

Streaming potential

7.5 7 6.2 4.5 4.2

[1077]

Only values, data points not reported.

3.3.6.2.3 Synthetic Cr-Substituted Magnetite Oxidation of mixed Fe(ii)–Cr hydroxide gel with KNO3 at near-boiling conditions. Properties: Specific surface area, XRD pattern, and isotherms of water adsorption available [1284].

TABLE 3.1424 PZC/IEP of Cr-Substituted Magnetite Fe (mass%) 84 72 50 38 20 9 5 2 0.2

Cr (mass%)

Electrolyte

0.1 6 13 18 29 37 42 47 48

NaOH + HNO3

T

Method Instrument pH

pH0 Reference 7.3 7 7.3 7.2 8.5 8.5 8.5 8.5 8.7

[1284]

3.3.6.3 Fe–Cu Mixed Oxides 3.3.6.3.1 Heated for 6 h at 950°C The mixed-component metal oxide was heated for 6 h at 950°C, ground, reheated at the same temperature, crushed, and washed with water.

618

Surface Charging and Points of Zero Charge

TABLE 3.1425 PZC/IEP of Fe–Cu Mixed Oxides Heated for 6 h at 950°C Cu/(Cu + Fe) (mol%) 20 30 33.3 40 60 80 a

Electrolyte

T

0.001 M NaCl

Method

25

iep

a

Instrument

pH0 Reference

Streaming potential

8.3 6.2 7.8 8.7 9 9.1

[33]

Only value, data points not reported.

3.3.6.3.2 Cu-Modified Goethite 10 M NaOH was added to 1 M Fe(NO3)3 containing Cu (50–500 ppm) with stirring to adjust the pH to 11.5–12. This was followed by aging for 1 d at 70°C in a polyethylene bottle.

TABLE 3.1426 PZC/IEP of Cu-Modified Goethite Cu (%) 0.25 0.5 1 2.7 a

Electrolyte

T

0.01 M KNO3

Method a

pH

Instrument

pH0

Reference

3 d equilibrated

7.7 7.8 7.9 8.5

[1577]

Only value, data points not reported.

3.3.6.4 (Mn, Zn, Fe)Fe2O4 from Spang Properties: HRTEM image available [2336]. TABLE 3.1427 PZC/IEP of (Mn, Zn, Fe)Fe2O4 Electrolyte

T

Method

Instrument

pH0

Reference

iep

ZetaPALS, Brookhaven

7.2

[2336]

619

Compilation of PZCs/IEPs

3.3.6.5 Fe–Ni Mixed Oxides 3.3.6.5.1

From Electricite de France (EDF)

TABLE 3.1428 PZC/IEP of Fe–Ni Mixed Oxide from Electricité de France (EDF) Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

25

iep

Streaming potential

5.5

[295]

3.3.6.5.2 Heated for 6 h at 1000°C The mixed-component metal oxide was heated for 6 h at 1000°C, ground, reheated at the same temperature, crushed, and washed with water. TABLE 3.1429 PZC/IEP of Fe–Ni Mixed Oxide Heated for 6 h at 1000°C Ni/(Ni + Fe) (mol%) 10 20 30 33.3 40 60 80 a

Electrolyte

T

0.001 M NaCl

25

Method iep

a

Instrument Streaming potential

pH0 Reference 5.2 4.2 4.8 4.2 5 8.3 9.3

[33]

Only value, data points not reported.

3.3.6.5.3 From Ni(NO3)2 and FeSO4 Solutions of KNO3, Ni(NO3)2, FeSO4, and KOH were added to water under O2and CO2-free conditions. The gel was aged for 4 h at 90°C. Properties: Average diameter 810 nm [2337], SEM images available [2338], spherical particles, TEM image available [2337]. TABLE 3.1430 PZC/IEP of Fe–Ni Mixed Oxide Obtained from Ni(NO3)2 and FeSO4 Composition Ni0.79Fe2.21O4 Ni0.5Fe2.5O4 Ni0.18Fe2.82O4 NiFe2O4

Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

25

iep

Rank Brothers Mark II

[2338]

0.0001–0.01 M NaCl

25

iep

Malvern Zetasizer 2000

6.7 6.7 6.7 6.7

[2337]

620

Surface Charging and Points of Zero Charge

3.3.6.5.4 NiFe2O4 Obtained at 200°C Stoichiometric amounts of NiO and Fe3O4 were digested in an autoclave at 200°C for 1 d. Properties: Si 600 ppm, Al 200 ppm, Mg 100 ppm, Zr 30 ppm, Ti 800 ppm, Co 100 ppm, specific surface area 5.9 m2/g [1065]. TABLE 3.1431 PZC/IEP of NiFe2O4 Obtained at 200°C Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

30

iep

Zeta-Meter

7

[1065]

3.3.6.5.5 From Oxalates Stoichiometric amounts of Ni and Fe oxalates were decomposed at 800°C (recipe from [2339]). Properties: Si 100 ppm, Al 150 ppm, Mg 50 ppm, Zr 20 ppm, Ti 100 ppm, Co 100 ppm, specific surface area 5.1 m2/g [1065]. TABLE 3.1432 PZC/IEP of Fe–Ni Mixed Oxide Obtained from Oxalates Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

30

iep

Zeta-Meter

3.5

[1065]

3.3.6.5.6 Synthetic Ni-Substituted Magnetite Oxidation of mixed Fe(ii)–Ni hydroxide gel with KNO3 at near-boiling conditions. Properties: Specific surface area, XRD pattern and isotherms of water adsorption available [1284]. TABLE 3.1433 PZC/IEP of Ni-Substituted Magnetite Fe (mass%) 65 58 48 41 37 29 24 15 9 4

Ni (mass%) 3 12 17 20 22 28 32 39 46 52

Electrolyte NaOH + HNO3

T

Method Instrument pH

pH0

Reference

7 6 6.1 5.9 6 6.6 7 7.2 7.5 7.5

[1284]

621

Compilation of PZCs/IEPs

3.3.6.5.7 Ni-Modified Goethite 10 M NaOH was added to 1 M Fe(NO3)3 containing Ni (50–500 ppm) with stirring to adjust pH to 11.5–12. This was followed by aging for 1 d at 70°C in a polyethylene bottle.

TABLE 3.1434 PZC/IEP of Ni-Modified Goethite Ni (%) 0.25 0.5 1 2 a

Electrolyte

T

Method a

pH

0.01 M KNO3

Instrument

pH0

Reference

3 d equilibrated

7.8 7.7 7.7 7.1

[1577]

Only value, data points not reported.

3.3.6.6 Fe–Si Mixed (Hydr)oxides 3.3.6.6.1 Obtained from 1 M Na2SiO3 and 1 M Fe(NO3)3 at pH 7 1 M Na2SiO3 and 1 M Fe(NO3)3 were pumped into a beaker held at pH 7. The precipitate was freeze-dried, water-washed, and freeze-dried again Properties: Amorphous [1187].

TABLE 3.1435 PZC/IEP of Fe–Si Mixed Oxides Obtained from 1 M Na2SiO3 and 1 M Fe(NO3)3 at pH 7 Fe/(Fe + Si) (molar) 0.6 0.7 0.8 0.9 a

Electrolyte 0.01 M NaNO3

T

Method Salt addition

Instrument

pH0

Reference

3.6 4 5.1 6.5

[1187]a

Only value, data points not reported.

3.3.6.6.2 Goethite–Silica Composite Fe(OH)3 was precipitated from FeCl3 in the presence of 0.05 mol of Na2SiO3 per 1 mol of Fe. The precipitate was aged in 1 M NaOH for 2 d at 60°C. Properties: 0.9% Si, needles or laths, particles 50–100 nm long and 10 nm thick, BET specific surface area 75 m2/g [2340].

622

Surface Charging and Points of Zero Charge

TABLE 3.1436 PZC/IEP of Goethite–Silica Composite Electrolyte

T

Method

Instrument

pH0

Reference

6.4

[2340]

cipa a

Only value, data points not reported.

3.3.6.7 Fe–Sn Mixed Oxide A stoichiometric amount of 0.25 M NH3 was added to a solution 0.25 M in SnCl4 and 0.25 M in FeCl3. The precipitate was washed, filtered, and dried at 50°C. It was treated with hot water, washed with dilute ammonia and water, and dried at 50°C. Properties: DTA results available, BET specific surface area 150 m2/g [1660]. TABLE 3.1437 PZC/IEP of Fe–Sn Mixed Oxide Electrolyte

T

Method

0.001 M NaCl

25

pH

a

Instrument

pH0

Reference

6.2

[1660,1661a]

Only value, data points not reported.

3.3.6.8 FeTa2O6 Synthetic Tapiolite 0.1078 g Fe, 0.3109 g Fe2O3, and 2.5804 g Ta2O5 were mixed, pressed together, and calcined for 3 h at 750°C, and then for 45 h at 850°C in a sealed tube. The powder was ground, repressed, and calcined for 1 d at 850°C, and ground again. Properties: Tapiolite structure confirmed by XRD. BET specific surface area 3 m2/g [2341]. TABLE 3.1438 PZC/IEP of Synthetic Tapiolite Electrolyte

T

0.0001–1 M KNO3

a

Method

Instrument

pH0

Reference

cipa iep

Rank Brothers Mark II

3.8 3.9

[2341]

Confirmed by salt titration.

3.3.6.9 Fe-Ti Mixed Oxides 3.3.6.9.1 Synthetic Titanomagnetite Stoichiometric amounts of Fe, Fe2O3, and TiO2 were milled and sintered under various conditions.

623

Compilation of PZCs/IEPs

Properties: XRD patterns available [2342]. TABLE 3.1439 PZC/IEP of Synthetic Titanomagnetite Type of Mill/ Sintering Temperature (°C) High energy/1050 Low energy/1050 High energy/1400 Low energy/1400 a

Electrolyte

T

HCl + NaOH

Method

Instrument

pH0

Reference

iep

Mutek PCD 03

3.8 3.6 3.9 3.7

[2342]a

Only values, no data points.

3.3.6.9.2 Natural Titanomagnetite Primary concentrate from BHP New Zealand Steel. Properties: Fe2O3 + FeO 76.6%, TiO2 8%, SiO2 4.9%, Al2O3 4.1%, MnO 0.6%, CaO 1.7%, MgO 3.2%, detailed analysis available [2342]. TABLE 3.1440 PZC/IEP of Natural Titanomagnetite Description

Electrolyte

Water-washed 1 d aged at pH 3.5 1 d aged at pH 4.2–8.2 a

HCl + NaOH

T

Method

Instrument

pH0 Reference

iep

Mutek PCD 03

2.9 4 3.6

[2342]a

Only values, no data points.

3.3.6.10 Y3Fe5O12 Nine different recipes: A solution containing stoichiometric amounts of FeCl3 and YCl3 (concentrations in the range 0.0001–0.01 M) was filtered, 1% of PVP was added (optionally), and the solution was heated to 90°C. Then ammonia or urea (concentration 1–2 M) was added, and the solution was aged for 3 h at 90°C. The precipitate was filtered out, and calcined for 4 h at 1100°C. Properties: TEM images, DTA, and XRD patterns available [473]. TABLE 3.1441 PZC/IEP of Y3Fe5O12 Electrolyte NH3 a

T

Method iep

Instrument Electrophoresis

pH0 5–6.8

Reference a

[473]

Range of IEP for four samples (different recipes) reported in text. Owing to low absolute values of z potential, estimation of IEP is very uncertain.

624

Surface Charging and Points of Zero Charge

3.3.6.11 Fe–Zn Mixed Oxides The mixed-component metal oxide was heated for 6 h at 1000°C, ground, reheated at the same temperature, crushed, and washed with water. TABLE 3.1442 PZC/IEP of Fe–Zn Mixed Oxides Zn/(Zn + Fe) (mol%) 20 30 33.3 40 60 80

3.3.7

Electrolyte

T

Method

Instrument

pH0 Reference

0.001 M NaCl

25

iep

Streaming potential

7 3.5 4.2 6.8 8.7 9.1

[33]

In–Sn MIXED OXIDES

3.3.7.1 In2O3 (90 mass%)–SnO2 Mixed Oxide from Nanophase Technologies Properties: Average particle size 20 nm, specific density 7100 kg/m3 [2343]. TABLE 3.1443 PZC/IEP of In2O3 –SnO2 Mixed Oxide from Nanophase Technologies Electrolyte

T

Method

Instrument

iep

Malvern Zetasizer 4

0.001 M NaCl

iep a

pH0

Reference

6

[2343]

7–8

[2344]a

No data points.

3.3.7.2 From Sumitomo Properties: 90% In2O3, 10% SnO2 by mass, primary particle size <200 nm, specific surface area 3.3 m2/g [2345]. TABLE 3.1444 PZC/IEP of In2O3 –SnO2 Mixed Oxide from Sumitomo Electrolyte

T

Method a

iep a

Arbitrary interpolation.

Instrument

pH0

Reference

Zeta-Meter

2.5

[2345]

625

Compilation of PZCs/IEPs

3.3.7.3 Prepared by Co-Precipitation, Recipe from [2346,2347] References [2346] and [2347], both cited in [2348] report completely different recipes. Properties: 10% SnO2, TEM image, particle size distribution available [2348]. TABLE 3.1445 PZC/IEP of In–Sn Mixed Oxide Prepared by Coprecipitation Electrolyte

T

Method iep

a

Instrument Malvern Zetasizer 3000 HS

pH0 a

7.4

Reference [2348]

Matches minimum in colloid stability of ultrasonified dispersion measured by absorbance of dispersion at 245 nm.

3.3.7.4 Prepared by Controlled Growth Technique Properties: XRD pattern, particle size histogram available [2349]. TABLE 3.1446 PZC/IEP of In–Sn Mixed Oxide Prepared by Controlled Growth Technique Electrolyte

3.3.8

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer

8.5

[2349]

MIXED OXIDES CONTAINING Mg

3.3.8.1 Mg–Fe Mixed Hydroxides A mixed solution of Mg and Fe(iii) chlorides (molar ratio 2, 2.5, or 3) of total metal ion concentration 0.5 M was slowly titrated with 0.25 M ammonia to pH 9.5. The precipitate was aged for 2 h in the mother solution, then washed with water and peptized at 80°C for 1 d. Properties: Specific surface areas available [2350]. TABLE 3.1447 PZC/IEP of Mg–Fe Mixed Hydroxides Composition

Electrolyte

T

Mg0.64Fe0.36(OH)2Cl0.03(OH)0.33 0.001–0.1 M NaCl 25 Mg0.68Fe0.32(OH)2Cl0.05(OH)0.27 Mg0.7Fe0.3(OH)2Cl0.06(OH)0.24 Mg0.79Fe0.21(OH)2Cl0.08(OH)0.13

Method Instrument cip

pH0

Reference

10.3 10.6 10.8 10.9

[2350, 2351]

626

Surface Charging and Points of Zero Charge

3.3.8.2 Fe–Al–Mg Mixed Hydroxides A mixed solution of Mg, Al and Fe(iii) chlorides was titrated with ammonia to pH 9.5. The product was peptized at 80°C for 1 d. Properties: Specific surface areas available [2352]. TABLE 3.1448 PZC/IEP of Fe–Al–Mg Mixed Hydroxides Composition

Electrolyte T

Fe0.13Mg0.72Al0.15(OH)2Cl0.2(OH)0.07 Fe0.03Mg0.65Al0.32(OH)2Cl0.14(OH)0.21 Fe0.24Mg0.52Al0.24(OH)2Cl0.12(OH)0.36 Fe0.16Mg0.50Al0.34(OH)2Cl0.12(OH)0.38 Fe0.21Mg0.46Al0.33(OH)2Cl0.11(OH)0.43 Fe0.29Mg0.42Al0.29(OH)2Cl0.1(OH)0.48

0.001– 0.01 M NaCl

Method Instrument

25

iep/cip

DXD-II, Jiangsu

pH0

Reference

11.5/11.1 11.5/10.9 11.2/10.6 11.3/10.8 11.3/10.5 11.1/10.4

[2352, 2353]

3.3.8.3 Zn–Mg–Al Mixed Hydroxides A mixed solution of Mg, Zn, and Al chlorides (different molar ratios) of total metal ion concentration 0.5 M was slowly titrated with 0.25 M ammonia to pH 9.5. The precipitate was aged for 2 h in the mother solution, and then washed with water and peptized at 80°C for 1 d. Properties: Lattice parameters, particle size available [2354]. TABLE 3.1449 PZC/IEP of Zn–Mg–Al Mixed Hydroxides Composition

Electrolyte

Zn0.27Mg0.37Al0.36(OH)2Cl0.13(OH)0.24 0.001– Zn0.13Mg0.58Al0.29(OH)2Cl0.12(OH)0.17 0.01 M Zn0.17Mg0.54Al0.29(OH)2Cl0.16(OH)0.12 NaCl Zn0.08Mg0.67Al0.25(OH)2Cl0.17(OH)0.08 Zn0.16Mg0.6Al0.24(OH)2Cl0.16(OH)0.08 Zn0.19Mg0.6Al0.21(OH)2Cl0.15(OH)0.06

3.3.9

T 25

Method Instrument cip

pH0 Reference 9.6 9.7 9.7 10.2 10.3 10.6

[2354]

MATERIAL CONTAINING Nb

(Mn,Fe)(Nb,Ta)2O6 natural columbite from Gov. Valadares, Brasil TABLE 3.1450 PZC/IEP of Natural Columbite Electrolyte NaOH + HClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

3

[104]

627

Compilation of PZCs/IEPs

3.3.10

MATERIALS CONTAINING Ni

3.3.10.1 Ni + 1 mol% Al Mixed Oxide The components were mixed, sintered at 1275°C, ground, mixed, sintered at 1275°C, and ground again.

TABLE 3.1451 PZC/IEP of Ni + 1% Al Mixed Oxide Electrolyte

T

NaOH + HCl

Method

Instrument

pH0

Reference

iep

Zeta-Meter

9.4

[1732]

3.3.10.2 Ni + Co Mixed Oxides Thermal decomposition of the nitrates, and calcination at 400°C for 3 h in a stream of oxygen. Properties: Samples with 0–80 mol% of Ni contain spinel phase. Samples with 60–100 mol% of Ni contain cubic phase (NiO). BET specific surface area see Table 3.1452 [1237].

TABLE 3.1452 PZC/IEP of Ni + Co Mixed Oxides Specific Ni/(Ni + Co) Surface (mol%) Area (m2/g) 10 20 30 33 40 50 60 67 79 80 90

31 38 32 30 28 18 17 25 25 25 34

Electrolyte 0.005–0.1 M KNO3

T

Method Instrument cip

pH0

Reference

8.2 8.9 9.4 9.3 9.4 9.4 9.4 9.4 9.4 9.4

[1237]

628

3.3.10.3

Surface Charging and Points of Zero Charge

Ni + 1% Cr Mixed Oxide

TABLE 3.1453 PZC/IEP of Ni + 1% Cr Mixed Oxide Electrolyte

a

T

Method

Instrument

pH0

Reference

iepa

Zeta-Meter

9.4

[1732]

Only one data point in vincinity of IEP

3.3.11

MATERIALS CONTAINING Pb

3.3.11.1 Pb2Ir2O7−y Mixture of Pb(NO3)2 and Ir was heated at 850°C. TABLE 3.1454 PZC/IEP of Pb2Ir2O7−y Electrolyte

T

Method

0.4 M KCl a

Instrument

pH

pH0

Reference a

[1684]

pH0

Reference

10.7

[1684]

<3.3 if any

σ0 = 0 at pH 1.5–3.3.

3.3.11.2 Pb2Ru2O7−y A mixture of PbO and RuO2 was heated at 850°C.

TABLE 3.1455 PZC/IEP of Pb2Ru2O7−y Electrolyte

T

0.4 M KCl

3.3.12

Method pH

Instrument

MATERIALS CONTAINING Ru

3.3.12.1 RuO2–IrO2 Mixed Oxides RuCl3 and IrCl3 were mixed with 2-propanol and calcined in a stream of oxygen for 6 h at 500°C. The product was milled and calcined for 6 h, and washed with dilute KNO3. Properties: Specific surface area about 13 m2/g [2356].

629

Compilation of PZCs/IEPs

TABLE 3.1456 PZC/IEP of RuO2–IrO2 Mixed Oxides x(IrO2)

Electrolyte

10 15 20 25 30 35 a

T

Method a

0.001–0.1 M KNO3

cip /iep

Instrument

pH0

Reference

Rank Brothers Mark II

5.6 5.3 5.3/5.1 5.1 4.8/4.7 4.6

[2356]

Average of several values of CIP reported in Figure 3.

3.3.12.2

Ru0.7Rh0.3O2, Origin Unknown

TABLE 3.1457 PZC/IEP of Ru0.7Rh0.3O2 Electrolyte 0.4 M KCl

T

Method

Instrument

pH

pH0

Reference

7.9

[1684]

3.3.12.3 RuO2–TiO2 Mixed Oxide RuCl3 and TiCl4 were dissolved in 1 M HCl. The solution was gently heated to dryness, and then heated for 1 h at 450°C. The precipitate was crushed, milled, and heated again (total calcination time 3 h). It was then washed with water. Properties: Solid solution rather than mixed phase; at >40% RuO2, TiO2 was in rutile form; anatase was present at lower RuO2 concentrations; for BET specific surface area, see Table 3.1458 [1750].

TABLE 3.1458 PZC/IEP of RuO2–TiO2 Mixed Oxide RuO2 (mol%) 20; 50 m2/g 30 (550°C calcination) 40; 36 m2/g 60 80

Electrolyte

T

0.005–0.05 M KNO3

25

Method Instrument pH0 cip

5.7 5.7 5.2 5.3 5.3

Reference [1750]

630

Surface Charging and Points of Zero Charge

3.3.12.4 RuO0.3Ti0.7−x Cex O2 0.4 M solutions of RuCl3, TiCl4 and CeCl3 in 1:1 HCl were mixed to produce a certain nominal composition. This was heated at <100°C to dryness, and calcined at 550°C in an O2 stream for 1 h, crushed, milled, and calcined as above. The procedure was repeated three times. The product was then washed with water to remove chlorides. One sample was prepared at 450°C. Properties: BET specific surface area 50 m2/g for 40 mol% of CeO2 [2357].

TABLE 3.1459 PZC/IEP of RuO0.3Ti0.7−x Cex O2 CeO2 (mol%) 0 5 10 20 30 40 50 60 70

3.3.13

Electrolyte

T

Method

Instrument

cip

0.005–0.3 M KNO3

pH0

Reference

5.7 6 6.5 7.1 7.4 7.5 8.1 8.2 8.5

[2357]

SILICATES

3.3.13.1 Al Silicates 3.3.13.1.1 14SiO2·Al2O3 Tixolex from Rhone Poulenc

TABLE 3.1460 PZC/IEP of Tixolex from Rhone Poulenc Electrolyte

T

Method

0.1 M NaCl

25

Mass titration

a

Instrument

pH0

Reference

8.6–10.1a

[847]

Only range, data points not reported.

3.3.13.1.2 Kyanite Al2O3 · SiO2, Beneficated Ore from Wanapitei, Canada Properties: 60.1% Al2O3, 39.7% SiO2, 0.5% FeO, 0.3% CaO, 0.2% K2O, 0.01% MnO, 0.2% TiO2 [991].

631

Compilation of PZCs/IEPs

TABLE 3.1461 PZC/IEP of Kyanite Electrolyte

T

Method

Instrument

pH0 Reference

iep

Pen Kem 3000

5.8 [991,992]

0.01 M KCl

3.3.13.1.3 Mullite 3Al2O3 · 2SiO2 3.3.13.1.3.1 Baikalox, from Baikowski SEM image and detailed chemical analysis available, BET single-point specific surface area 19.2 m2/g [2358]. TABLE 3.1462 PZC/IEP of Baikalox, from Baikowski Description SASM a

Electrolyte 0.01 KCl

T

Method

25

titration iep

Instrument

pH0

Reference

Acoustosizer

8.5 7.3

[810]a [2358]

Only value, data points not reported.

3.3.13.1.3.2 From Pacific Rundum specific surface area 2.7 m2/g [2359].

Properties: Average particle size 3.3 μm,

TABLE 3.1463 PZC/IEP of Mullite from Pacific Rundum Electrolyte

T

Method iep

Instrument

pH0 Reference

Matec ESA 8000 7.4

[2359]

3.3.13.1.4 Natural Al2SiO5 3.3.13.1.4.1 Sillimanite from Chatrapur, India Properties: XRD pattern available, 98.5% pure, traces of Fe and Mg, BET specific surface area 1.5 m2/g [2360]. TABLE 3.1464 PZC/IEP of Sillimanite from Chatrapur, India Electrolyte

T

Method

Instrument

0.1 M NaCl

25

iep

Zeta-Meter 3.0+

pH0 Reference 8

[2360]

632

Surface Charging and Points of Zero Charge

3.3.13.1.4.2 Al2SiO5 Disthene from Nanga Ekoko, Cameroon Properties: 36.5% SiO2, 60.6 (or 60.3)% Al2O3, 1.1% Fe2O3, 0.8% TiO2, 0.2% P2O5, volatile mater 0.3% [2232,2239]. TABLE 3.1465 PZC/IEP of Disthene from Nanga Ekoko, Cameroon Description

Electrolyte

Original Washed

T

Method

Instrument

pH0

Reference

iep

Streaming potential

6.2 5.2

[2232,2239]

0–0.01 M KCl

3.3.13.1.4.3

Disthene from Frodalera

TABLE 3.1466 PZC/IEP of Disthene from Frodalera Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

10

[104]

0.001 M NaClO4

3.3.13.1.5 Synthetic Allophane 3.3.13.1.5.1 From AlCl3 and Na2SiO3 200 cm3 of 0.1 M AlCl3 was added at 5 cm3/min with stirring to 200 cm3 of 0.1 M Na2SiO3, adjusted to pH 8, aged for 5 d, then the precipitate was washed with NaCl solution. Properties: Al:Si molar ratio 1:1, single-point BET specific surface area 201 m2/g [1193].

TABLE 3.1467 PZC/IEP of Allophane Obtained from AlCl3 and Na2SiO3 Electrolyte 0.1 M NaCl a

T 25

Method iep

Instrument Zeta-Meter 3.0

pH0 7.8

a

Reference [1193]

Arbitrary interpolation.

3.3.13.1.5.2 From AlCl3 and Si(EtO)4 0.002 M silicic acid was obtained by hydrolysis of Si(EtO)4. 0.1 M aqueous AlCl3 was added to produce the desired Al:Si ratio. The solution was titrated with 0.1 M NaOH at 7.5 cm3/min until opalescence appeared. It was then aged for 2 h, and titration was continued to reach the desired final pH. It was then refluxed, flocculated and dialyzed.

633

Compilation of PZCs/IEPs

TABLE 3.1468 PZC/IEP of Allophane Obtained from AlCl3 and Si(EtO)4 Al/Si 2.02 1.64 1.26 a

Electrolyte

T

Method

0.001, 0.01 M NaClO4, NaNO3, NaCl, NaBr, NaI

iep

a

Instrument

pH0

Reference

Zeta-Meter 3.0

9.8–10.3 8.8–9 6.5–6.7

[25] [329]

Atypical terminology is used in [25], and IEP is termed PZC.

3.3.13.1.6 MCM-41 Recipe from [2361]: From Si(C2H5O)4, Al(iso-C3H7O)3, and hexadecyltrimethylammonium bromide. The precipitate was calcined at 550°C for 5 h.

TABLE 3.1469 PZC/IEP of MCM-41 Si/Al Molar Ratio/ Specific Surface Area (m2/g) 32/1126 10/1020

Electrolyte

T

0.0001–0.1 M KCl

Method

Instrument

cip

pH0

Reference

4 4.4

[625]

3.3.13.1.7 Synthetic Silica (75% by mass)–Alumina Properties: Specific surface area 440 m2/g [847].

TABLE 3.1470 PZC/IEP of Synthetic Silica (75%)–Alumina Electrolyte

T

Method

0.1 M NaCl

25

Mass titration

a

Instrument

pH0

Reference

4

[847]a

Only value, no data points.

3.3.13.1.8 Topaz Al2(F,OH)2SiO4 3.3.13.1.8.1 From Minas Gerais, Brazil, Distributed by Ward’s Natural Science Establishment, Ground to 50 µm Properties: Detailed analysis available [2301].

634

Surface Charging and Points of Zero Charge

TABLE 3.1471 PZC/IEP of Topaz from Minas Gerais, Brazil Electrolyte

T

Method pH

a

Instrument

pH0

Reference

5.6

[2301]

a

Only value, data points not reported.

3.3.13.1.8.2

Origin Unknown

TABLE 3.1472 PZC/IEP of Topaz from Unknown Source Electrolyte

T

Method

None

Instrument

iep

pH0

Reference

3.3

[1960]

3.3.13.2 Chrysocolla 3.3.13.2.1 From Inspiration Mine Properties: 44.1% CuO, 42.6% SiO2 [2362]. TABLE 3.1473 PZC/IEP of Chrysocolla from Inspiration Mine Electrolyte

T

HCl + NaOH

Method

Instrument

pH0

Reference

iep

Zeta-Meter

<3.5 if any

[2362]

3.3.13.2.2 From Exotica Mine (Chile) Properties: Amorphous, 25% Cu, 43% SiO2 [1265]. TABLE 3.1474 PZC/IEP of Chrysocolla from Exotica Mine (Chile) Electrolyte 0.001 M KClO4

T

Method pH

Instrument

pH0

Reference

6.5

[1265]

3.3.13.3 Fe silicates 3.3.13.3.1 Fe2SiO4, Fayalite Reference [104] reports electrokinetic curve with multiple IEPs.

635

Compilation of PZCs/IEPs

3.3.13.3.2 Fe–Si Mixed Oxide Equivalent amounts of Fe(NO3)3 and NaOH solutions were added dropwise to a silica dispersion. The dispersion was stirred for 30 min, and aged at 30°C for 1 h. The precipitate was washed, and dried at 105°C for 2 d. Properties: BET specific surface area 136, 200, and 91 m2/g for Fe:Si molar ratio 1:3, 1:1, and 3:1, respectively, SEM images available [573]. TABLE 3.1475 PZC/IEP of Fe–Si Mixed Oxide Electrolyte

T

0.1 M NaNO3 a

Method

20

Instrument

pH

pH

1 d equilibration

9

Reference

a

[573]

Independent of Fe:Si molar ratio. Charging curves from fast titration experiments in 0.001–0.1 M NaNO3 are also reported (also at 30–50°C), and their results are unusual (s0 decreases with ionic strength).

3.3.13.4 Fe–Mg Silicates See also Section 3.2.41. 3.3.13.4.1 (Fe,Mg)7Si8O22(OH)2, Cummingtonite Extracted from taconite from Mitchell pit near Babbitt, Minn. TABLE 3.1476 PZC/IEP of Cummingtonite Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

5.2

[1306]

3.3.13.4.2 (FeII,III,Na,Mg)7Si8O22(OH)2, Crocidolite From Coegas Mine, Cape, South Africa. TABLE 3.1477 PZC/IEP of Crocidolite Electrolyte NaOH + HCl

T

Method

Instrument

iep

Rank Brothers Streaming potential

3.3.13.4.3 (Fe,Mg)7Si8O22(OH)2, Amosite From Penge Mine, Transvaal.

pH0 Reference 3.2

[241]

636

Surface Charging and Points of Zero Charge

TABLE 3.1478 PZC/IEP of Amosite Electrolyte

T

NaOH + HCl

Method

Instrument

pH0

Reference

iep

Rank Brothers Streaming potential

3.2

[241]

3.3.13.5 Mg Silicates 3.3.13.5.1 3.3.13.5.1.1

Chrisotile (chrysotile) From Black Lake, Ontario

TABLE 3.1479 PZC/IEP of Chrisotile–Asbest from Black Lake, Ontario Electrolyte

T

NaOH + HClO4

3.3.13.5.1.2

Method

Instrument

pH0

Reference

iep

Zeta-Meter

10.5

[104]

From Lake Asbestos, Quebec

TABLE 3.1480 PZC/IEP of Chrisotile–Asbest from Lake Asbestos, Quebec Electrolyte

T

0.00001 M KCl

Method

Instrument

pH0

Reference

iep

Streaming potential

11.8

[2363]

A review with four references can be found in [2364]. 3.3.13.5.1.3 Synthetic Chrisotile Aerosil was autoclaved with aqueous MgCl2 at pH 12.5, 300°C and 65 × 105 Pa for 1 d. The precipitate was washed with saturated Mg(OH)2 and freeze-dried. Properties: Structure confirmed by XRD, TEM image available, tubular particles, inner diameter 9 nm, outer diameter 39 nm, length 1 mm, BET specific surface area 90 m2/g [2364]. TABLE 3.1481 PZC/IEP of Synthetic Chrisotile Electrolyte

T

Method

Instrument

pH0

Reference

0–1 M NaCl, NaNO3

30 22

iep pH

Mitamura Riken, Laser Zee Meter 500

12.3a 10–10.5

[2364]

a

>12 if any in 0.01 M NaCl and NaNO3.

637

Compilation of PZCs/IEPs

3.3.13.5.2

Talc, Mg6Si8O24(OH)4

3.3.13.5.2.1 From BDH Properties: No phases other than talc detected by XRD, purity 96%, Fe2O3 and Al2O3 detected as major impurities, krypton BET surface area 2 m2/g (original) and 5.2 m2/g (ground), mean diameter 21.5 μm [417].

TABLE 3.1482 PZC/IEP of Talc from BDH Electrolyte

T

0.01 M KCl a

Method

Instrument

pH0

Reference

iep

Rank Brothers Mark II

<3 if anya

[417]

Morris’ thesis cited in [417] reports IEP at pH ª 2 (probably extrapolated, MK) at various ionic strengths.

3.3.13.5.2.2 From Commercial Minerals [427].

Properties: High purity, D50 = 6 μm

TABLE 3.1483 PZC/IEP of Talc from Commercial Minerals Electrolyte

T

Method

instrument

pH0

0.01 M KNO3

22

iep

Acoustosizer

<6 if any

a

Reference a

[427]

At 5–35 % talc by mass. At 45 % talc by mass, positive z potentials are reported at pH > 10. The yield stress depends on the history of dispersion.

3.3.13.5.2.3 From Talcs de Luzenac Properties: Talc 98%, chlorite 1.5%, traces of pyrite and rutile [2290].

TABLE 3.1484 PZC/IEP of Talc from Talcs de Luzenac Electrolyte 0.01 M NaClO4

T

Method

Instrument

pH0

Reference

iep

Zetaphoremeter Sephy 2100

3

[2290]

3.3.13.5.2.4 New York Talc from Ward’s Properties: 98.5% pure, 10.3% Mg [2365], BET specific surface area 10.2 m2/g [2366].

638

Surface Charging and Points of Zero Charge

TABLE 3.1485 PZC/IEP of New York Talc from Ward’s Electrolyte

T

Method

0.01–0.1 M KCl a

Instrument

Salt addition

pH0

Reference

7.7

[2365,2366]a

Maximum in yield stress of dispersion, 0.54 volume fraction at pH 5.5.

3.3.13.5.2.5

From Ontario, Ground

TABLE 3.1486 PZC/IEP of Talc from Ontario Electrolyte

T

Method

Instrument

pH0

Reference

KOH + HNO3

22

iep

Zeta-Meter

3

[370]

3.3.13.5.2.6 From Balmat Mine, New York, from Wards Properties: 98% pure, SEM image available, BET specific surface area 7.4 m2/g [1925].

TABLE 3.1487 PZC/IEP of Talc from Balmat Mine, New York Electrolyte

T

Method

0.002 M KNO3

a b

Instrument

iep

Pen Kem Laser Zee Meter 501 Zeta-Meter

pH0

Reference

a

>2.5

[1925b,1926,2367]

+3 mV at pH 2.5, −23 mV at pH 4.2. IEP at pH 2 reported in text is not supported by data.

3.3.13.5.2.7

Other

TABLE 3.1488 PZC/IEP of Talc of Unknown Origin Electrolyte HClO4 + NaOH

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

2

[104]

639

Compilation of PZCs/IEPs

3.3.13.5.3 Mg2SiO4, Forsterite Properties: Specific surface areas available [2368].

TABLE 3.1489 PZC/IEP of Forsterites Description

Electrolyte

Twin Sisters Range, Washington San Carlos: Original Acid-reacted Dunite from Twin Sisters Range Synthetic Original Calcined at 500 and 900°C a b c

d

0.01 M NaCl

0.001 M KNO3

T

Method

Instrument

pH0

Reference

25

iep

Electrophoresis

4.1

[2369]a,b

25

iepc

Zetacad Z3000 Sephy

45

iep

25

pH

Streaming potential

[2368] 4.4 2 5.3 10

[2370]a,d [2368]

[2369] and [2370] report also IEPs of quartz and several silicates. Only value, no data points. Titration results available (different NaCl concentrations). Selective leaching of components. PZC at pH 9-10 (pH, dependent of ionic strength and sample treatment). Cited in [2368] as IEP of forsterite.

Reference [104] reports an electrokinetic curve of forsterite from Gabbs, Nevada with multiple IEPs. 3.3.13.5.4

Mg3Si2O5(OH)4 Lizardite

TABLE 3.1490 PZC/IEP of Lizardite Description Lake Asbestos, Quebec Ward’s

Electrolyte

T

Method

Instrument

pH0

0.00001 M KCl

iep

Streaming potential

9.6

0.001 M KCl

iep

Rank Brothers Mark II >10 if any

Reference [2363] [1768]

3.3.13.5.5 Natural Stevensite From Jebel Rhassoul, Morocco Properties: 57.5% SiO2, 25% MgO, 1.5% CaO, 2.2% Al2O3, 1.3% Fe2O3, loss of ignition 8.3%, BET specific surface area 134 m2/g, XRD pattern (quartz and dolomite detected) and SEM image available [2371].

640

Surface Charging and Points of Zero Charge

TABLE 3.1491 PZC/IEP of Stevensite Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Zetaphotometer II

2a

[2371]

Only value, data points not reported.

3.3.13.5.6

Mg8Si12O30(OH,F)4(H2O)4·8H2O Sepiolite

3.3.13.5.6.1 From Andrici (Serbia) Properties (original): 53% SiO2, 28.6% MgO, 0.2% CaO, 0.5% Al2O3, 0.9% Fe2O3, 0.07% K2O, loss of ignition: 15.6%, BET specific surface area 267.5 m2/g, XRD pattern, FTIR spectrum, DTA curve available [628]. Properties of acid-activated material (10 g of sepiolite equilibrated with 100 cm3 of 4 M HCl for 10 h, then washed with water) are also reported.

TABLE 3.1492 PZC/IEP of Sepiolite from Andrici (Serbia) Description Original Acid-activated

Electrolyte

T

Method

0.001–0.1 M KNO3

22

pH

Instrument

pH0

Reference

7.4 6.9

[628]

3.3.13.5.6.2 From Aktas Luletasi-Eskisehir (Turkey) Properties: 53.5% SiO2, 23.6% MgO, 0.7% CaO, 0.2% Al2O3, 0.2% Fe2O3, 0.4% NiO, loss of ignition 21.5%, BET specific surface area 342 m2/g [256,2372,2275]. TABLE 3.1493 PZC/IEP of Sepiolite from Aktas Luletasi (Turkey) Electrolyte 0.001 M NaCl a

T 20

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0+

6.6

[256, 2275]

iep

Zeta-Meter 3.0+

7.8a

[2372]

Subjective interpolation.

3.3.13.6 3.3.13.6.1

Si–Ti Mixed Oxides Ti-MCM-41

3.3.13.6.1.1 1.86% Ti by Mass Synthesis: A mixture, mole composition 1 TEOS: 0.02 Ti(OC4H9)4: 0.36 TMAOH: 110 H2O: 0.24 CTMABr, was aged at room temperature for 1 d, then filtered, washed, dried at 120°C for 2 h, and calcined at 650°C for 4 h.

641

Compilation of PZCs/IEPs

Properties: Specific surface area 1325 m2/g, average pore diameter 3.6 nm [2373]. TABLE 3.1494 PZC/IEP of Ti-MCM-41, 1.86% Ti by mass Electrolyte

T

Method

a

Instrument

pHa

NaNO3

pH0

Reference

4.5

[2373]

Only value, data points not reported.

3.3.13.6.1.2 Si/Ti Molar Ratio 12 Recipe from [2361]: From Si(C2H5O)4, Ti(iso-C3H7O)4, and hexadecyltrimethylammonium bromide. The precipitate was calcined at 550°C for 5 h. Properties: BET specific surface area 961 m2/g [625]. TABLE 3.1495 PZC/IEP of Ti-MCM-41, Si/Ti Molar Ratio 12 Electrolyte

T

Method

0.0001–0.1 M KCl

3.3.13.6.2

Instrument

cip

pH0

Reference

4.8–5.3

[625]

Commercial Si–Ti Mixed Oxides

3.3.13.6.2.1 From Chlorovinyl Fumed. Another series of samples studied by the same research group in described in Section 3.3.13.6.2.2. Properties: BET specific surface area 70, 90, 95 m2/g (21, 36, 37% TiO2) [836], 270, 215, 137, 70, 250, 60, 90 m2/g (5, 9, 14, 20, 22, 29, 36% TiO2) [837], IR spectrum available [836]. TABLE 3.1496 PZC/IEP of Si–Ti Mixed Oxides from Chlorovinyl TiO2 (%) 9 14 20 29 36

Electrolyte HCl + NaOH

T

Method

Instrument

pH0

Reference

iep

ZetaPlus Brookhaven

<3 if any

[836,837]

3.3.13.6.2.2 From Institute of Surface Chemistry, Kalush, Ukraine Fumed. Another series of samples studied by the same research group in described in Section 3.3.13.6.2.1.

642

Surface Charging and Points of Zero Charge

Properties: BET specific surface area 83, 34, 30 m2/g (63, 65, 94% TiO2), average particle diameter 22, 52, 51 nm (63, 65, 94% TiO2) [926]. TABLE 3.1497 PZC/IEP of Si–Ti Mixed Oxides from Institute of Surface Chemistry, Kalush, Ukraine TiO2 (%)

Electrolyte

T

0.001 M NaCl

63 65 94

3.3.13.6.3

Method

Instrument

pH0

Reference

iep/pH

Malvern Zetasizer 3000

4.3 2.5/<4 7/<4

[926]

Synthetic Si–Ti Mixed Oxides

3.3.13.6.3.1 Flame Hydrolysis Deposition Properties: Amorphous, 7% titania, BET specific surface area 17.7 m2/g, SEM image available [604].

TABLE 3.1498 PZC/IEP of Si–Ti Mixed Oxide Obtained by Flame Hydrolysis Deposition Electrolyte

T

Method pH

0.0001-0.1 M NaCl a

Instrument

a

pH0 2.5

Reference [604]

Charging curves merge at pH < 2.5.

3.3.13.6.3.2 From Alkoxides 3.3.13.6.3.2.1 Silica–Titania Catalyst Titanium isopropoxide (11.36 parts) was slowly added to a solution of HNO3 (1 part) in water (136.4 parts). TEOS was mixed with ethanol, water, and HCl in a volumetric ratio 2000:525:625:1. Precursor sols were mixed, dialyzed, evaporated, and sintered to 300°C. Properties: BET specific surface area 320 m2/g [2120]. TABLE 3.1499 PZC/IEP of Silica–Titania Catalyst Description

Electrolyte

Not sintered Sintered

0.01 M

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

5.2 5.2

[2120]

3.3.13.6.3.2.2 From Titanium Isopropoxide and Silicon Ethoxide in Ethanol Properties: BET specific surface area 320–357 m2/g [2030], specific surface area 380 m2/g [2374].

643

Compilation of PZCs/IEPs

TABLE 3.1500 PZC/IEP of Si–Ti Mixed Oxide Obtained from Titanium Isopropoxide and Silicon Ethoxide in Ethanol Description

Electrolyte

T

Method

Obtained in the presence of HNO3 Si:Ti molar ratio 3:1 Three different recipes, 5–20 mass% SiO2 a

Instrument

pH0

Reference

iep

Zeta Reader Mark 21

2.8

[2374]

pH

3 d equilibration

6.2–6.7a

[2030]

Specific values not reported.

3.3.13.6.3.3 From Na2SiO3 and TiCl4 1 dm3 of a solution 0.5 M in Na2SiO3 and 2 M in NaOH was added at 20 cm3/min with stirring to 1 dm3 of a solution 0.5 M in TiCl4 and 1 M in HCl. Then the pH was adjusted to 7, and the precipitate was aged for 2 d in mother liquor, filtered, water-washed, and dried for 3 d at 70°C. It was then immersed in water, dried, and then crushed, water-washed, and dried again. TABLE 3.1501 PZC/IEP of Si–Ti Mixed Oxide Obtained from Na2SiO3 and TiCl4 Electrolyte

T

Method

a

Instrument

pHa

0.05 M NaNO3

pH0

Reference

4.2

[2375]

Only acidity constants, data points not reported.

3.3.13.7 Zn2SiO4 The stoichiometric amount of Si(C2H5O)4 was added to a saturated solution of Zn(NO3)2 · 6H2O in a 5:1 ethanol–water mixture. The mixture was aged for 2 h at 50°C, and calcined at 400°C, and then for 30 h at 1250°C. Properties: a-Zn2SiO4, specific surface area 1.6 m2/g [2376]. TABLE 3.1502 PZC/IEP of Zn2SiO4 Electrolyte

T

Method

0.001–0.1 M KNO3

25

pHa

a

Charging curves merge at pH < 7.7.

Instrument

pH0

Reference

7.4

[2376]

644

Surface Charging and Points of Zero Charge

3.3.13.8 Zr Silicates 3.3.13.8.1

Commercial ZrSiO4

3.3.13.8.1.1 From Aldrich Properties: 2% Hf, specific surface area 3.2 m2/g, mean diameter 1.2 μm [2377].

TABLE 3.1503 PZC/IEP of ZrSiO4 from Aldrich Description

Electrolyte

T

Method

Instrument

pH0 Reference

Water-washed

0.0001–0.1 M NaCl

25

cip iep

Malvern Zetasizer 3000

3.3.13.8.1.2

From Richards Bay Minerals

7.2 5.5

[2377]

TABLE 3.1504 PZC/IEP of ZrSiO4 from Richards Bay Minerals Electrolyte

T

0.01–0.1 M KCl a

Method

Instrument

pH0 a

Salt addition

6.5

Reference [2365]

Maximum in yield stress of dispersion, 0.54 volume fraction at pH 6.

3.3.13.8.2

Synthetic Silica–Zirconia Composites

3.3.13.8.2.1 From ZrOCl2 and Si(OC2H5)4 Aqueous ammonia was added to a solution of ZrOCl2 and Si(OC2H5)4 (3:7 molar ratio) in 2-propanol. The precipitate was washed, dried at 120°C, and calcined at 500°C. Properties: BET specific surface area 265 m2/g [979].

TABLE 3.1505 PZC/IEP of Si–Zr Mixed Oxide Obtained from ZrOCl2 and Si(OC2H5)4 Electrolyte

T

Method

0.01 M KCl

40

pH

Instrument

pH0

Reference

3.8

[979]

3.3.13.8.2.2 From Ethoxides A mixture of tetramethyl orthosilicate and zirconium n-propoxide was hydrolyzed in 4 (mol water/mol Zr + Si) parts of water at room temperature. The precipitate was washed in warm water and calcined at 500°C for 3 h. Properties: Amorphous, specific surface area 148 m2/g (Zr0.75Si0.25O2) and 346 m2/g (Zr0.25Si0.75O2) [2200].

645

Compilation of PZCs/IEPs

TABLE 3.1506 PZC/IEP of Si–Zr Mixed Oxide Obtained from Ethoxides Formula

Electrolyte

Zr0.75Si0.25O2 Zr0.25Si0.75O2

T

Method

Instrument

pH0

Reference

iep

Matec 8050

4.7 3.2

[2200]

NaOH + HCl

3.3.13.8.2.3 Obtained in Microemulsion Ammonium hydroxide was added to a solution containing Igepal Co520 (surfactant) and cyclohexane, and the mixture was shaken to obtain a microemulsion. Solutions of zirconium n-propoxide in acetylacetone and n-butanol (1:0.5:3) and of tetraethyl orthosilicate in water and ethanol (1:1:4) were mixed for 3 h, and the mixture was added to the microemulsion with stirring, and hydrolyzed for 3 d. The final concentrations of alkoxides were 0.0075 M, the water:surfactant molar ratio was 0.8, and the water:alkoxide molar ratio was 10. The powder was washed with acetone and heated at 900°C for 2 h. Properties: Zr:Si ratio 1:1, XRD pattern and IR spectrum available [2378].

TABLE 3.1507 PZC/IEP of Si–Zr Mixed Oxide Obtained in Microemulsion Electrolyte

T

Method

Instrument

pH0

Reference

iep

Delsa 440, Coulter

2.8

[2378]

NaCl

3.3.13.8.3

Natural Zircon

3.3.13.8.3.1 From Mudd Tank, Northern Territory, Australia Properties: 64.9% ZrO2, 32.8% SiO2, 0.01% Fe2O3, 0.02% TiO2, 0.1% Al2O3, 0.01% P2O5, 1% HfO2, 1% ThO2, 0.005% U3O8, 0.02% CaO, 0.09% MgO, 0.02% Y2O3, 0.01% CeO2 structure confirmed by XRD [2379], krypton BET specific surface area 1.7 m2/g [2379,2380], XPS surface analysis available [2379], particle diameter 6.1 μm [2380].

TABLE 3.1508 PZC/IEP of Zircon from Mudd Tank, Northern Territory, Australia Electrolyte

T

Method

Instrument

pH0

Reference

0.0001–0.1 M KNO3

25

iep cip, salt addition

Rank Brothers Mark II

5.7 5.9

[2379,2380]

3.3.13.8.3.2 From Westralian Sands Properties (dithionite- and acid-washed): 63.9% ZrO2, 32.7% SiO2, 0.07% Fe2O3, 1.2% TiO2, 0.7% Al2O3, 0.09% P2O5, 1%

646

Surface Charging and Points of Zero Charge

HfO2, 0.02% ThO2, 0.03% U3O8, 0.03% CaO, 0.04% MgO, 0.1% Y2O3, 0.02%, CeO2 structure confirmed by XRD, krypton BET specific surface area 2 m2/g, XPS surface analysis available [2379].

TABLE 3.1509 PZC/IEP of Zircon from Westralian Sands Electrolyte

T

Method

Instrument

pH0

Reference

0.0001–0.1 M KNO3

25

iep cip, salt addition

Rank Brothers Mark II

5.5 6.1

[2379]

3.3.13.8.3.3 From Antete, Madagascar Properties: 63.3% ZrO2, 32.1% SiO2, 0.2% Fe2O3, 0.3% TiO2, 0.1% P2O5, volatile matter 0.2% [2232,2239].

TABLE 3.1510 PZC/IEP of Zircon from Antete, Madagascar Description Original Washed a

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Streaming potential

5.8a 4.7

[2232,2239]

pH0

Reference

4 4b 5.8a 4.7 6 9c

[2381]a [2382]

0–0.01 M KCl

Arbitrary interpolation.

3.3.13.8.3.4

Other

TABLE 3.1511 PZC/IEP of Zircons from Other Sources Description Pitinga Mine, Brazil

Australia a b c

Electrolyte

T

0.01 M NaCl

NaOH + HClO4

Only value, data points not reported. Arbitrary interpolation. Curve I in Figure 54, arbitrary interpolation.

Method iep iep Salt addition iep iep iep

Instrument Rank Brothers

Zeta-Meter

[2383]a [2384]a [104]

647

Compilation of PZCs/IEPs

3.3.14 MATERIALS CONTAINING SNO2 3.3.14.1 Doped with Different Oxides Original SnO2 (0.1–0.5% Al, 0.01% Si, 0.02% Fe by mass) doped with different oxides (1 mol%) and sintered at different temperatures. Wet grinding. With Fe and Cr solution doping (nitrates).

TABLE 3.1512 PZC/IEP of SnO2 Doped with Different Oxides Dopant 1050°C: WO3 Sb2O5, vacuum Sb2O5 Fe2O3 Cr2O3 1400°C: Nb2O5 Sb2O5 or Sb2O3 Fe2O3 Cr2O3

Electrolyte

T

Method

Instrument

iep

Zeta-Meter

NaOH + HCl

pH0 Reference [1958] 2.2 2.5 2.9 7.1 6.9 5.5 6.8 6.9 7

3.3.14.2 Sn–Mg and Sn–Fe Mixed Oxides Tin citrate solution in ethylene glycol containing HNO3 and MgO or Fe(NO3)3 was heated at 180–200°C. Then the product was heated at 450°C for 4 h and at 500°C for 15 h. Properties: For BET specific surface area, see Table 3.1513 [1957].

TABLE 3.1513 PZC/IEP of Sn–Mg and Sn–Fe Mixed Oxides Additive (mol%)/Specific Surface Area (m2/g) 2% Fe/38.3 5% Fe/48.9 10% Fe/61.1 2% Mg/42.5 5% Mg/61.5 10% Mg/73.7 a

Electrolyte

T

Method

KOH + HNO3

At pH 12, sign of z potential is reversed to positive.

iep

Instrument Matec ESA 8000

pH0

Reference

4.6 5.2 6.6 5.7 9.4 10.5a

[1957]

648

Surface Charging and Points of Zero Charge

3.3.14.3 Sn–Sb Mixed Oxides 3.3.14.3.1 Commercial Sb3O4 (10 mass%)–SnO2 mixed oxide from Nanophase Technologies. Properties: Average particle size 15 nm, specific density 6800 kg/m3 [2343].

TABLE 3.1514 PZC/IEP of Sn–Sb Mixed Oxide from Nanophase Technologies Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 4

<1 if any

[2343]

0.001 M NaCl

3.3.14.3.2 Prepared by Controlled Growth Technique Properties: XRD pattern, particle size histogram available [2349].

TABLE 3.1515 PZC/IEP of Sn–Sb Mixed Oxide Prepared by Controlled Growth Technique Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer

3.7

[2349]

3.3.15 MATERIALS CONTAINING TiO2 3.3.15.1 Ti–Al Mixed Oxides 3.3.15.1.1

Al-Doped Commercial Rutile Pigment, Prepared Using Chloride Process Properties: 0.91% Al2O3 by mass, particle diameter 270 nm, BET specific surface area 5.1 m2/g, TEM image available [903].

TABLE 3.1516 PZC/IEP of Al-Doped Commercial Rutile Pigment, Prepared Using Chloride Process Description

Electrolyte

T

Method

Instrument

pH0

Reference

Water-washed

0.001 M KNO3

25

iep

Malvern Zetasizer 2 c

7.8a

[903]

a

IEP matches maximum in yield stress of 10 vol% dispersion.

649

Compilation of PZCs/IEPs

3.3.15.1.2 Flame Oxidation of TiCl4 in the Presence of AlCl3 and PCl3 Properties: 0.55% Al, 0.16% P, and 0.1% Cl, detailed chemical analysis (bulk and surface) available, BET specific surface area 6.1 m2/g [2385].

TABLE 3.1517 PZC/IEP of Ti–Al Mixed Oxide Obtained by Flame Oxidation of TiCl4 in Presence of AlCl3 and PCl3 Electrolyte

T

0.001 M KNO3

a

Method

Instrument

pH0

Reference

iep pH

Pen Kem Zeta 3000

6.5 6–7

[2385]a

Only value, data points not reported.

3.3.15.1.3 From Propoxides Aluminum propoxide was dissolved in titanium propoxide at 60°C, and a 30-fold excess of water was added dropwise. The powder was calcined at 550°C. Properties: 5 mol% alumina, anatase, specific surface area 190 m2/g, XRD pattern available [342].

TABLE 3.1518 PZC/IEP of Ti–Al Mixed Oxide Obtained from Propoxides Electrolyte

T

Method

Instrument

0.01 M KNO3

25

iep

Malvern Zetasizer 3000

pH0 Reference 4.9

[342]

3.3.15.2 Bi4Ti3O12 Obtained from Ti butoxide and Bi nitrate. Calcined at 750∞C.

TABLE 3.1519 PZC/IEP of Bi4Ti3O12 Electrolyte

T

0.001 M KCl

3.3.15.3 3.3.15.3.1

Method

Instrument

iep

Brookhaven ZetaPlus

pH0 Reference 4

[2386]

Ti–Fe Mixed Oxides Commercial

3.3.15.3.1.1 Ilmenite from Alfa Aesar Properties: 99.9% pure, specific surface area 1.3 m2/g [2387].

650

Surface Charging and Points of Zero Charge

TABLE 3.1520 PZC/IEP of Illmenite from Alfa Aesar Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaCl

25

cip iep

Malvern Zetasizer 3000

7.2 4.5

[2387]

3.3.15.3.1.2 [1031].

PF2 from Degussa

Properties: BET specific surface area 23 m2/g

TABLE 3.1521 PZC/IEP of PF2 from Degussa Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Nano ZS

6.7a

[1031]

KCl a

Arbitrary interpolation.

3.3.15.3.1.3

Other

TABLE 3.1522 PZC/IEP of Unspecified Commercial Ilmenite Description

Electrolyte

T

Method

Instrument

pH0

Reference

Fresh Leached

0.01 M KCl

25

iep

Electrophoresis

3.5 3.8

[1248]

3.3.15.3.2 Synthetic Cold (-20°C), freshly distilled TiCl4 was added to cold (0°C), fresh FeCl3 solution, aged for several hours below 5°C, then dialyzed against water. Properties: Diameter 5 nm, at 50% Fe(iii)—pseudobrookite (Mossbauer) [1393]. TABLE 3.1523 PZC/IEP of Synthetic Ti–FeIII Mixed Oxide Description 2.9% Fe 50% Fe a

Electrolyte

T

Method

25

Inflection Coagulation

Only value, data points not reported.

Instrument

pH0

Reference

5.5 7

[1393]a

651

Compilation of PZCs/IEPs

3.3.15.3.3

Natural Ilmenites

TABLE 3.1524 PZC/IEP of Natural Ilmenites Description

Electrolyte

From Yang Yang mine, Korea, distributed by Rare Minerals, Korea, 35.2% Fe, 32.2% Ti, washed in warm 0.1 M HCl From Egersund, Norway

a

T

NaOH + HClO4

Method

Instrument

pH0

Reference

iep

Electrophoresis, flat cell

5.6

[2388]

iep

Zeta-Meter

8a

[104]

Arbitrary interpolation.

3.3.15.4 Pbx Zr0.52Ti0.48O3 50 g of a mixture of oxides (commercial reagents) was homogenized with 25 cm3 of acetone in a 50 cm3 container loaded up to 30% with zirconia balls. The mixture was dried at 100°C, and calcined at 900°C for 2 h. Properties: Specific surface area 0.3 m2/g, particle size 1 μm, tetragonal and rhombohedral forms (x = 1) [1736]. TABLE 3.1525 PZC/IEP of PbxZr0.52Ti0.48O3 x

Electrolyte

1 1.025a 0.99a a

T

0.0001 M NaCl

Method

Instrument

pH0

Reference

iep/mass titration

Pen Kem S 3000

6.6/6.3 6.6 6.6

[1736]

Few data points near IEP.

3.3.15.5 Titania–Pt Composites Titania was impregnated with H2PtCl6 and reduced in hydrogen at 480°C. TABLE 3.1526 PZC/IEP of Titania–Pt Composites Pt (%) 0.5 1 5 10

Electrolyte

T

Method

Instrument

0.001 M NaCl

25

iep/titration

Rank Brothers Mark II

pH0 5.9/— —/6.7 5.1/5.6 4.6/<4

Reference [255]

652

Surface Charging and Points of Zero Charge

3.3.15.6 V-Doped Titanias A 1:1 (by volume) mixture of Ti(EtO)4 and ethanol containing V(v) triisopropoxide oxide was mixed with 0.15 M HNO3 at a H2O:Ti:H+ molar ratio of 200:1:0.5. The alcohol was boiled off at 80°C and the mixture was stirred for 2 d. The dispersion was dialyzed against water, and calcined at 350°C. Properties: XRD pattern available, anatase [2112].

TABLE 3.1527 PZC/IEP of V-doped Titanias V/Ti Mole Ratio (%)

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000 HS

6 6.4 6 5.7 5.5

[2112]

0.5 1 1.5 2.5 5

0.01 M KNO3

3.3.15.7

Zirconia–Titania Composites

3.3.15.7.1 Zirconia–Titania Catalyst Titanium isopropoxide (11.36 parts) was slowly added to a solution HNO3 (1 part) in water (136.4 parts). Zironium propoxide (3.65 parts) was slowly added to a solution HNO3 (1 part) in water (50 parts). The precursor sols were mixed, dialyzed, evaporated, and sintered to 400°C (experimental, or to 300°C, Fig. 12). Properties: BET specific surface area 220 m2/g [2120].

TABLE 3.1528 PZC/IEP of Zirconia–Titania Catalyst Description

Electrolyte

Not sintered Sintered

0.01 M

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

5.9 6.3

[2120]

3.3.15.7.2 From TiCl4 and ZrO(NO3)2 TiO2–ZrO2 mixed oxide, 79.4–20.6% by mass. A mixture of aqueous TiCl4 and ZrO(NO3)2 was treated with aqueous NH3. The hydroxide was thermally decomposed at different temperatures for 3 h. Properties: Anatase (decomposed at 500°C), rutile and ZrTiO4 (decomposed at 1000°C) [2389].

653

Compilation of PZCs/IEPs

TABLE 3.1529 PZC/IEP of TiO2–ZrO2 Mixed Oxide Obtained from TiCl4 and ZrO(NO3)2 Decomposition Temperature (°C) 500 1000 a

Electrolyte

T

Method

0.001–0.1 M KNO3

40

cip

Instrument

pH0

Reference

7 10.1

[2389]a

Only value, no data points.

3.3.15.7.3 From Propoxides A mixture of Ti isopropoxide and Zr n-propoxide was hydrolysed in water. The hydroxide was thermally decomposed at different temperatures for 3 h. Properties: Anatase (decomposed at 500°C), rutile and ZrTiO4 (decomposed at 1000°C) [2389]. TABLE 3.1530 PZC/IEP of TiO2–ZrO2 Mixed Oxide Obtained from Propoxides Decomposition at 500°C 1000°C a

Electrolyte

T

Method

0.001–0.1 M KNO3

30a 40

cip

Instrument

pH0 Reference 5.9 6.2

[2389]

Also 40–60°C

3.3.15.7.4 From Zr n-Propoxide and Rutile Zr n-propoxide was hydrolysed in a dispersion containing pure rutile (from National Lead). The hydroxide was thermally decomposed at 500°C for 3 h. Properties: Rutile [2389]. TABLE 3.1531 PZC/IEP of Titania–Zirconia Composite Obtained from Zr n-Propoxide and Rutile Electrolyte

T

Method

0.001–0.1 M KNO3

40

cip

a

Instrument

pH0

Reference

4.4

[2389]a

Only value, no data points.

3.3.15.7.5 From Ti Isopropoxide and Monoclinic Zirconia Ti isopropoxide was hydrolysed in a dispersion containing pure monoclinic zirconia (from Riedel-de-Haen). The hydroxide was thermally decomposed at 500°C for 3 h. Properties: Anatase, monoclinic zirconia [2389].

654

Surface Charging and Points of Zero Charge

TABLE 3.1532 PZC/IEP of Titania–Zirconia Composite Obtained from Ti Isopropoxide and Monoclinic Zirconia Electrolyte

T

Method

0.001–0.1 M KNO3

40

cip

a

Instrument

pH0

Reference

6.3

[2389]a

Only value, no data points.

3.3.15.7.6 From Chlorides Aqueous ammonia was added to a solution of ZrOCl2 and TiCl4 (37:63 molar ratio) in 2-propanol. The precipitate was washed, dried at 120°C, and calcined at 500°C. Properties: BET specific surface area 280 m2/g [979]. TABLE 3.1533 PZC/IEP of Titania–Zirconia Composite Obtained from Chlorides Electrolyte 0.01 M KCl a

T

Method

Instrument

a

40

pH

pH0

Reference

5

[979]

Only value, data points not reported.

3.3.16 MATERIALS CONTAINING WO3 3.3.16.1 Ferberite Natural: 76.4% WO3, 2.5% MnO, 21.1% FeO, from Da Minyun, China. TABLE 3.1534 PZC/IEP of Ferberite Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep

MRK

2.1

[2390]

3.3.16.2 Huebnerite Natural: 75.8% WO3, 19.3% MnO, 3.8% FeO, from Fukan, China. TABLE 3.1535 PZC/IEP of Huebnerite Electrolyte 0.001 M KNO3

T

Method

Instrument

pH0

Reference

iep

MRK

2.8

[2390]

655

Compilation of PZCs/IEPs

3.3.16.3 Tungstosilicates 3.3.16.3.1 ThSiW12O40 · xH2O A solution 8 × 10-5 M in H4SiW12O40 and 0.005 M in Th(NO3)4 was aged at pH 3 for 4 h at 70°C. Properties: Monodispersed, spherical particles of diameter of 300 nm, SEM image and XRD pattern available [2391]. TABLE 3.1536 PZC/IEP of ThSiW12O40 ⋅ xH2O Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

3.4

[2391]

3.3.16.3.2 ZrSiW12O40 ·26ZrO2 · xH2O A solution 8 × 10-5 M in H4SiW12O40 and 0.0005 M in ZrCl4 was aged at pH 2 for 2.5 h at 60°C. Properties: Monodispersed, spherical particles of diameter of 500 nm, SEM image and XRD pattern available [2391]. TABLE 3.1537 PZC/IEP of ZrSiW12O40 ·26ZrO2· xH2O Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

3

[2391]

3.3.17 MATERIALS CONTAINING Zn Zn–Cr layered hydroxide. 200 cm3 of solution 0.2 M in ZnCl2 and 0.1 M in CrCl3 was added dropwise to 100 cm3 of 0.1 M NaCl and the pH was adjusted to 5 with 0.1 M KOH. Once addition of reactants was complete, the mixture was stirred for 2 h at room temperature, and then refluxed for 1 d. The precipitate was then washed with 0.1 M NaCl and with water. Properties: Zn:Cr 1.99, 0.5% C by mass, XRD pattern available [2392]. TABLE 3.1538 PZC/IEP of Zn–Cr Layered Hydroxide Electrolyte 0.003–0.1 M NaCl

T

Method

Instrument

pH0

Reference

Room

cip iep Salt addition

Rank Brothers Mark II

>11 if any >11 if any 11.9

[2392]

656

Surface Charging and Points of Zero Charge

3.3.18 MATERIALS CONTAINING ZIRCONIA 3.3.18.1

Ce-Modified Zirconias

3.3.18.1.1 12Ce-TZP from Tosoh Properties: 12 mol % CeO2, specific surface area 7.7 m2/g, average particle size 400 nm [2393].

TABLE 3.1539 PZC/IEP of 12Ce-TZP from Tosoh Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer ZET 5004

8

[2393]

HCl + NaOH

3.3.18.1.2 CEZ-10 from Zirconia Sales Properties: ZrO2 + HfO2 87 mol%, CeO2 13 mol%, specific density 6200 kg/m3, particle size 400 nm, BET specific surface area 21.4 m2/g [444].

TABLE 3.1540 PZC/IEP of CEZ-10 from Zirconia Sales Electrolyte

T

0.005, 0.01 M NaCl a

Method

Instrument

pH0

Reference

iep

Acoustosizer, Matec

7.9a

[444]

Roughly matches maximum in viscosity of 10 and 25 vol% dispersions, and maximum in flocculation rate. Malvern Zetasizer 4 produced substantially lower, but unspecified, IEP.

3.3.18.2 Zr–Ti Mixed Oxides Filtration membranes from Techsep. TABLE 3.1541 PZC/IEP of Filtration Membranes from Techsep Type: Composition

Electrolyte

T

Method

M 14: 90.5% ZrO2, 8% TiO2

0.001 M NaCl

50

iep

M 5: 97.8% ZrO2, 2.2% TiO2

0.001 M NaCl

50

iep

a

Instrument Rank Brothers Mark II Streaming potential Rank Brothers Mark II Streaming potential

Powder used for membrane manufacturing/powder scraped from membrane.

pH0

Reference

a

5/4 4

[2189]

7/5a 5

[2189]

657

Compilation of PZCs/IEPs

3.3.18.3 Zr–Y Mixed Oxides Zr–Y mixed oxides are often referred to as “zirconia” in scientific publications. Their PZCs are reviewed in [284]. 3.3.18.3.1

Commercial Y-Modified Zirconias

3.3.18.3.1.1 From Aldrich Properties: 3 mol% Y2O3, specific surface area 37.9 m2/g [2394], average particle size 50–75 nm [2395], 75 nm [2394], SEM image available [2394].

TABLE 3.1542 PZC/IEP of Y-Modified Zirconia from Aldrich Electrolyte

T

HCl + NaOH

Method

Instrument

pH0

Reference

iep

Nihon Rufuto model 502

7

[2395,2394]

3.3.18.3.1.2 From Daichi Properties: 8 mol % Y2O3, detailed chemical analysis available, single-point BET specific surface area 7.4 m2/g [493].

TABLE 3.1543 PZC/IEP of Y-Modified Zirconia from Daichi Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KCl

25

iep

AcoustoSizer

6.5

[493]

3.3.18.3.1.3 DZF 5Y-1100 from Dynamit Nobel Properties: 4.8 mass % Y2O3, detailed chemical analysis available, tetragonal:monoclinic ratio 40:60, BET specific surface area 8 m2/g, average grain size 300 nm [2183].

TABLE 3.1544 PZC/IEP of DZF 5Y-1100 from Dynamit Nobel Electrolyte HCl

T

Method

Instrument

pH0

Reference

iep

Micromeritics, mass transport

6

[2183]

3.3.18.3.1.4 Y-Modified Zirconias from Mandoval 3.3.18.3.1.4.1 YSZ Properties: 8 mol% Y2O3, 0.25% Al2O3, 0.1% SiO2, 0.1% TiO2 (by mass), specific surface area 7 m2/g, d50 = 400 nm [2396].

658

Surface Charging and Points of Zero Charge

TABLE 3.1545 PZC/IEP of YSZ from Mandoval Electrolyte

T

0.001 M NaCl a

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 2000

6a

[2396]

Viscosity of 35 and 40 mass% slurries peaks at pH 7.

3.3.18.3.1.4.2 HSY-3 Properties: 76% tetragonal, 26% monoclinic, 5.3% Y2O3, 0.11% SiO2, 0.01% Na2O, 0.01% CaO by mass, specific surface area 8.2 m2/g, particle diameter 410 nm [801].

TABLE 3.1546 PZC/IEP of HSY-3 from Mandoval Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

25

iep

AcoustoSizer

6.6

[801]

3.3.18.3.1.5 From MEL Properties: 8 mol % Y2O3, detailed chemical analysis available, single-point BET specific surface area 2.3 m2/g [493].

TABLE 3.1547 PZC/IEP of Y-Modified Zirconia from MEL Electrolyte 0.01 M KCl a

T

Method

25

iep

Instrument AcoustoSizer

pH0 a

6.5

Reference [493]

Acid titration; 7.5 in base titration.

3.3.18.3.1.6 3YTZP from Shenzen Nanbo Properties: Composition (mass%) ZrO2 93.6, Y2O3 1.9, HfO2 1.8, SiO2 0.29, SO3 0.16, Cl 0.13, Fe2O3 0.12, NiO 0.09, ZnO 0.03 [408], >5.1 mass% Y2O3 [514], specific surface area 28.6 m2/g [408], 15 m2/g [514], average particle size 25 nm [514]. TABLE 3.1548 PZC/IEP of 3YTZP from Shenzen Nanbo Electrolyte 0.001–0.1 M KCl 0.001–0.1 M NaCl

T

Method

Instrument

pH0

Reference

iep iep

Brookhaven ZetaPlus Brookhaven ZetaPlus

6.4 6.8

[408] [514]

659

Compilation of PZCs/IEPs

3.3.18.3.1.7 From Tosoh 3.3.18.3.1.7.1 TZP, 2.8 mol % Y2O3 Not directly addressed as Tosoh product. See also Section 3.3.18.3.3. Properties: >99.9% purity [1109], specific surface area 40.4 m2/g, particle size 20 nm [1109], TEM image available [1109].

TABLE 3.1549 PZC/IEP of TZP, 2.8 mol % Y2O3 from Tosoh Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 4

6.5

[1109]

3.3.18.3.1.7.2 3Y-TZP Properties: 3 mol% Y2O3 [284,2393], specific surface area 15.7 m2/g [284], 7.2 m2/g [2393], particle size 300 nm [284], average particle size 500 nm [2393].

TABLE 3.1550 PZC/IEP of 3Y-TZP from Tosoh Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

26–27

iep

Malvern Zetasizer II c ECA 2000 Chemtrac Zetasizer ZET 5004 Malvern

6.8 6.6 7.9

[284]

HCl + NaOH

iep

[2393]

3.3.18.3.1.7.3 4Y-TZP Properties: 4 mol % Y2O3, specific surface area 17.9 m2/g, particle size 300 nm [284].

TABLE 3.1551 PZC/IEP of 4Y-TZP from Tosoh Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

26–27

iep

Malvern Zetasizer II c

7.2

[284]

3.3.18.3.1.7.4 6Y-TZP Properties: 6 mol % Y2O3, specific surface area 19 m2/g, particle size 300 nm [284]. TABLE 3.1552 PZC/IEP of 6Y-TZP from Tosoh Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

26–27

iep

Malvern Zetasizer II c

7.2

[284]

660

Surface Charging and Points of Zero Charge

3.3.18.3.1.7.5 8Y-TZP Properties: 8 mol% Y2O3, detailed chemical analysis available, single-point BET specific surface area 14.3 m2/g [493].

TABLE 3.1553 PZC/IEP of 8Y-TZP from Tosoh Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KCl

25

iep

AcoustoSizer

9.3a

[493]

a

Acid titration; 9.6 in base titration.

3.3.18.3.1.7.6 TZ-3YS Properties: 3 mol% Y2O3, specific surface area 6.9 m2/g [2397] 6.1–6.6 m2/g [2153].

TABLE 3.1554 PZC/IEP of TZ-3YS from Tosoh Electrolyte

T

0.001 M NH4NO3 0.01 M (CH3)4NCl a

b

25

Method iep iep

Instrument Malvern Zetasizer IIc Zeta-Meter 3.0

pH0 a

6.5 7.5b

Reference [2153] [2397]

IEP determined in aged dispersions ranged from 3.9 to 6.8 for dispersions prepared in different ways. As-received powder, arbitrary interpolation.

3.3.18.3.1.7.7 TZ-3Y Properties: 5.2 mass% Y2O3 [422,441], >94.1% ZrO2, loss of ignition 0.7% [441], BET specific surface area 16 m2/g [422], 15.4 m2/g [441], particle size 40 nm [422], D10 = 5 μm, D50 = 700 nm, D 90 = 200 nm [441], density 6050 kg/m3 [441]. TABLE 3.1555 PZC/IEP of TZ-3Y from Tosoh Electrolyte 0.001 M KCl HCl + NaOH a b

T

Method

Instrument

pH0

Reference

25

iep iep iep

Zeta PALS Brookhaven Brookhaven ZetaPlus Acoustosizer

6 7.2a 9.8b

[2398] [422] [441]

Maximum in sediment volume roughly matches IEP. Arbitrary interpolation.

661

Compilation of PZCs/IEPs

3.3.18.3.1.8 Y-Modified Zirconias from Toyo Soda 3.3.18.3.1.8.1 TZ-2Y Properties: 95.6% ZrO2, 3.5% Y2O3 by mass, BET specific surface area 16.1 m2/g [794].

TABLE 3.1556 PZC/IEP of TZ-2Y from Toyo Soda Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

25

iep

Rank Brothers Mark II

7.4

[794]

3.3.18.3.1.8.2 TZ-3Y Properties: Tetragonal [267], 3 mol % Y2O3 [267], average size 0.06 mm [267], TEM image available [267]. The IEP at pH 6.5 reported in [267] is a result of subjective interpolation. 3.3.18.3.1.9 Z-Tech 3.3.18.3.1.9.1 SY 5.2 from Z-Tech Properties: 5% Y2O3 [784,2194], 51% Y2O3 by mass (probably a typographic error), impurities (in ppm) Fe2O3 21, SiO2 12, TiO2 75, Al2O3 8, S 85, CaO 9 [2399], BET specific surface area 13.1 m2/g [2399], 14.3 m2/g [2194], 14.9 m2/g [784,786], average particle size 0.21 mm [786], 0.27 μm [2399], D 90 = 700 nm [2194], 580 nm [2399], D50 = 340 nm [2194], D10 = 130 nm [2194].

TABLE 3.1557 PZC/IEP of SY 5.2 from Z-Tech Electrolyte 0.001 M NaNO3 0.01 M NaNO3

a

b

T

Method

Instrument

pH0

Reference

Room

iep iepa iep

ESA 8000 Zeta-Meter 2.0 ESA 8000

6.7 6.9 7.7

[786] [784] [2399]b

Only value, data points not reported.. Maximum in yield stress and minimum in stability roughly match IEP from electrophoretic measurements. SY 5.2 Ultra.

Reference [2194] reports a maximum in the yield stress of 65 mass% dispersion at pH 8.1. 3.3.18.3.1.9.2 Extracted from SYP 5.2 from Z-Tech SYP 5.2 contains 4% of organic binder. Properties: BET specific surface area 14.9 m2/g, d50 = 166 nm [785].

662

Surface Charging and Points of Zero Charge

Table 3.1558 PZC/IEP of Y-Modified Zirconia Extracted from SYP 5.2 from Z-Tech Electrolyte

T

Method a

0.01 M NaNO3 a

iep

Instrument

pH0

Reference

Zeta-Meter 2.0

6.7

[785]

Only value, data points not reported.

3.3.18.3.1.10

Y-Modified Zirconia, 8YSZ, Origin Unknown

TABLE 3.1559 PZC/IEP of Y-Modified Zirconia from Unknown Commercial Source Electrolyte

T

HCl + NaOH

3.3.18.3.2

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000 HS

8

[2400]

Synthetic

3.3.18.3.2.1 ZrY0.8O3.2 Obtained by Calcination of ZrY0.8(OH)3.8(CO3)1.3 for 3 h at 800°C

TABLE 3.1560 PZC/IEP of ZrY0.8O3.2 Obtained by Calcination of ZrY0.8(OH)3.8(CO3)1.3 Electrolyte

T

Method iep

0.01 M NaNO3 a

Instrument Delsa Coulter

pH0

Reference

a

5.3

[474]

Three IEPs: at pH 5.3, 6, and 7.

3.3.18.3.2.2 From Zirconium Isopropoxide and Yttrium Acetylacetonate by Flame Pyrolysis Properties: 9 mol% yttria, BET specific surface area 68 m2/g [2206]. TABLE 3.1561 PZC/IEP of Zr–Y Mixed Oxide Obtained from Zr Isopropoxide and Y Acetylacetonate Electrolyte 0.001 M KCl a

T

Method

Instrument

pH0

Reference

iepa

Otsuka ELS 3800

8

[2206]

Only value, data points not reported.

663

Compilation of PZCs/IEPs

3.3.18.3.2.3 Spraying a Solution of ZrO(NO3)2 and Y(NO3)3 into Plasma Argon, ultrahigh-temperature inductively coupled plasma. Properties: 10–40 nm in diameter, tetragonal [2158].

TABLE 3.1562 PZC/IEP of Zr–Y Mixed Oxide Obtained by Spraying a Solution of ZrO(NO3)2 and Y(NO3)3 into Plasma Description Refluxed in water for 170 h Original a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

iep

Electrophoresis

5.5

[2158]

0.001 M NaCl

iep

Electrophoresis

7.7a

[2158]

Arbitrary interpolation.

3.3.18.3.2.4 From ZrOCl2 and Y2O3 1 M ZrOCl2 and Y2O3 were added to hot (70°C) urotropine or KOH solution, and heated to 100°C for 30 min. The precipitate was dried at 140°C, and treated for 2 h at various temperatures. Properties: 9 mol% yttria, samples heated above 600°C are cubic; for BET specific surface area, see Table 3.1563 [2206].

TABLE 3.1563 PZC/IEP of Zr–Y Mixed Oxide Obtained from ZrOCl2 and Y2O3

Description Urotropine Urotropine, heated at 300°C Urotropine, heated at 600°C Urotropine, heated at 1200°C KOH KOH, heated at 300°C KOH, heated at 600°C KOH, heated at 1200°C

Specific Surface Area (m2/g) Electrolyte 295 171

0.001 M KCl

T

Method Instrument iep

Otsuka ELS 3800

pH0 Reference 5.7 4.4

58

4.9

<1

3

[2206]

5.5 5.5 5.4 4.2

3.3.18.3.2.5 From ZrOCl2–YCl3 Solution Acidified with HCl Reference [2401] is cited in [2403] for the recipe, but no detailed recipe was found there. Addition of ammonia to ZrOCl2–YCl3 solution acidified with HCl.

664

Surface Charging and Points of Zero Charge

Properties: 90% ZrO2, 6% Y2O3, 0.5% Na2O, 0.3% Nd2O3, 0.07% Fe2O3 [2402], BET specific surface area 31.5 or 31.6 m2/g [411,2403], 1.05 m2/g [2402], mean particle size 30 nm or 40 nm, [411,2403], particle size 600 nm [2402], TEM image available [2403]. TABLE 3.1564 PZC/IEP of Zr–Y Mixed Oxide Obtained by Addition of Ammonia to ZrOCl2–YCl3 Solution Acidified with HCl Electrolyte 0.001 M KCl a

T

Method

25

iep

Instrument ZetaPlus Brookhaven

pH0 5.8

a

Reference [411,2402,2403]

Arbitrary interpolation

3.3.18.3.2.6 From ZrOCl2 and Y(NO3)3 Nanosized synthetic Y-modified zirconia, 8 mol% Y2O3 · ZrOCl2 · 8H2O, and Y(NO3)3 · 6H2O were dissolved in a water–ethanol 1:5 (volume ratio) mixture. Polyethylene glycol was added, and the mixture was heated at 75°C for 2 h. Then the pH was adjusted to 9 with ammonia. The gel was washed with water and freeze-dried. Finally, it was calcined under different conditions. Properties: Specific surface area 117 m2/g, average particle size 8.5 nm [2400], XRD patterns, FTIR spectra, crystallite sizes, TEM images available [2404]. TABLE 3.1565 PZC/IEP of Zr–Y Mixed Oxide Obtained from ZrOCl2 and Y(NO3)3 Electrolyte

T

HCl + NaOH

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000 HS

7.2

[2400]

3.3.18.3.2.7 Synthetic Y-Modified Zirconia, 3 mol% Y2O3 Properties (powder prepared by chemical coprecipitation): specific surface area 34 m2/g, average particle size 340 nm, TEM image available [405]. TABLE 3.1566 PZC/IEP of Unspecified Synthetic Zr–Y Mixed Oxide Electrolyte 0.0001 M NaCl

T

Method

Instrument

pH0

Reference

iep

ZetaPlus Brookhaven

6

[405]

3.3.18.3.3 Y-Modified Zirconia, Origin Unknown See also Section 3.3.18.3.1.7.1. Properties: 2.8 mol% Y2O3, impurities <0.1%, BET specific surface area 40.4 m2/g, average grain size 20 nm, TEM image available [2405].

665

Compilation of PZCs/IEPs

TABLE 3.1567 PZC/IEP of Unspecified Zr–Y Mixed Oxide Electrolyte

T

None

3.4

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer IV

6.4

[2405]

SALTS

PZCs/IEPs of sparingly soluble salts (other than combination of two or more sparingly soluble oxides) are presented in Tables 3.1568 through 3.1910. PZCs/IEPs of silicon carbide and nitride are also presented in this section. Salt-type compounds composed entirely of sparingly soluble oxides are discussed in Section 3.3. In the studies devoted to the effect of water-soluble salts with an anion or cation in common with the sparingly soluble salt of interest, the IEP has been defined in terms of concentration of these salts (ions) in addition to (or rather than) pH.

3.4.1

ALUMINATES AND HALOALUMINATES

3.4.1.1 Ba-β-Alumina Hot Ba(NO3)2 solution (330K) was acidified with HNO3 to pH 1, and mixed with Al(NO3)3. The mixture was poured with stirring at 330K into (NH4)2CO3 solution. The final pH was 7.5–8. The precipitate was aged for 3 h at 330K, then washed and dried. It was then calcined for 10 h at 1670K. Properties: Ba:Al ratio 1:12, specific surface area 15 m2/g. TEM image and FTIR spectra available [672].

TABLE 3.1568 PZC/IEP of Ba-β-alumina Electrolyte

T

Method

1 M KCl

3.4.1.2

Instrument

pH

pH0

Reference

9.5

[672]

Natural Cryolite from Ivigtut

TABLE 3.1569 PZC/IEP of Natural Cryolite Electrolyte NaOH + HClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

1.5

[104]

666

Surface Charging and Points of Zero Charge

3.4.2

BORIDES AND BORATES

3.4.2.1 ZrB2, Grade B from Starck Properties: 0.9% of oxygen (manufacturer), specific surface area 1.4 m2/g, average particle size 2–3 μm (manufacturer), SEM image available [401]. TABLE 3.1570 PZC/IEP of ZrB2 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

4.7

[401]

KCl

3.4.2.2

Natural Borates from Bigadic, Turkey

TABLE 3.1571 PZC/IEP of Natural Borates Formula

Electrolyte

Boraxa from Kirka, Turkey 0.11 M borax Colemanite Ca2B6O11 ⋅ 5H2Oa HCl + NaOH Ulexite NaCaB5O9 ⋅ 8H2Oa Inderite Tunellite a

T

Method

22–26

iep iep

Instrument

pH0 Reference

PALS <8 Zeta-Meter 3.0 10.5 <7 >11 >12

[2406] [2407]

These materials show relatively high solubility.

3.4.3

CARBIDES, CARBONATES, AND SALTS OF ORGANIC ACIDS

3.4.3.1 Carbides Carbides are easily oxidized; thus, the composition of the external layer is often different from the bulk composition. In a few studies, the problem of oxidation has been taken into account; for example, the external oxidized layer was removed, and/or the experiments were carried out under controlled redox conditions. 3.4.3.1.1 NbC, Synthetic, Plasma Chemical Method Properties: Particle size 10–20 nm, specific surface area 30 m2/g [2408]. TABLE 3.1572 PZC/IEP of NbC Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M KNO3

22

pH

1 d equilibration

3.6

[2408]

667

Compilation of PZCs/IEPs

3.4.3.1.2 SiC Compilations of PZC of SiC can be found in [2409,2410]. 3.4.3.1.2.1 Commercial 3.4.3.1.2.1.1 From Aldrich Properties: a-form, BET specific surface area 0.26 m2/g, mean particle size 8.4 μm [362].

TABLE 3.1573 PZC/IEP of SiC from Aldrich Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000

3

[362]

3.4.3.1.2.1.2 From Grindwell Norton, Bangalore, India Properties: a-form [403].

Table 3.1574 PZC/IEP of SiC from Grindwell Norton, Bangalore, India Type G800 G1000 G1200 a

Electrolyte

T

Method a

HNO3 + NH3

iep

Instrument

pH0

Reference

Micromeritics model 1202

4.8 4.2 3.3

[403]

Arbitrary interpolation

3.4.3.1.2.1.3 RS 07 from Huamei, China Manufactured by carbothermic reduction method. Properties: Composition (mass%) SiC >98, free Si 0.5, O 0.5, free C 0.7, Fe2O3 <0.5, BET specific surface area 4.2 m2/g, d50 = 1.5 μm [2411].

TABLE 3.1575 PZC/IEP of RS 07 from Huamei, China Electrolyte None

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

3.3

[2411]

668

Surface Charging and Points of Zero Charge

3.4.3.1.2.1.4 RP-2 from Japan Fine Ceramics Center ( JFCC) Properties: BET specific surface area 20.5 m2/g, d10 = 0.2 μm, d50 = 0.62 μm, d90 = 2 μm [935].

TABLE 3.1576 PZC/IEP of RP-2 from Japan Fine Ceramics Center (JFCC) Electrolyte

T

0.001 M NH4NO3 a

Method

Instrument

iep

Matec ESA 8000, Mutek PCD

pH0 Reference 6.1a

[935]

Different solid-to-liquid ratios

3.4.3.1.2.1.5 From Impaco Industrial Minerals Processing, USA Properties: Composition by mass: SiC 98.5%, SiO2 0.5%, Si 0.3%, Al 0.1%, Fe 0.08%, C 0.3%, average particle size 6 μm [2412].

TABLE 3.1577 PZC/IEP of SiC from Impaco Industrial Minerals Processing, USA Electrolyte

T

NH3 + HCl

Method

Instrument

pH0

Reference

iep

Coulter

<1.5 if any

[2412]

3.4.3.1.2.1.6 From Lonza 3.4.3.1.2.1.6.1 UF 10 Properties: a-form [357], >97% SiC, <0.7% O, specific surface area 10 m2/g [624], particle size 1.8 μm [357].

TABLE 3.1578 PZC/IEP of UF 10 from Lonza Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KNO3

iep

Pen Kem 3000 Matec ESA 8000

[357]

0.001–1 M KNO3

pH

2.5 <4 if any 3–4

[624]

3.4.3.1.2.1.6.2 UF 15 (Carbogran) Properties: a-form [371,624], >96% SiC [624], <1% O, [624], 0.39% free C, 0.12% free Si, 0.05% Al, 0.04% Fe, 0.01% Ti (according to the manufacturer) [371], BET specific surface area 15 m2/g [371,1100], specific surface area 15 m2/g [624,2413], 50 mass% of particles have size <700 nm [371], average and median size 600 nm [624].

669

Compilation of PZCs/IEPs

TABLE 3.1579 PZC/IEP of UF 15 (Carbogran) from Lonza Description

Electrolyte

T

Method

0.001–1 M KNO3 0.01 M NaCl 0.01 M NaCl

pH iep 20

pH0

Reference

<3 if any Zetasizer MKII, 2.9 Malvern Zetasizer MKII, 3.8 (text) Malvern <2.6 if any (figure) <3 if any

iep pH

Well-cleaned 0.01, 0.1 M KNO3

Instrument

[624] [371] [1100] [2413]

3.4.3.1.2.1.6.3 UF 45 from Lonza, France Properties: a-form [1017], BET specific surface area 45 m2/g [1017], average size 150 nm [1017]. TABLE 3.1580 PZC/IEP of UF 45 from Lonza Electrolyte

T

0.01 M NaCl

Method

Instrument

pH0

Reference

iep

ESA 8000 Matec

<2 if any

[1017]

3.4.3.1.2.1.7 From MarkeTech Properties: b-form, specific surface area 75 m2/g, particle size 20 nm [2408]. TABLE 3.1581 PZC/IEP of SiC from MarkeTech Description

Electrolyte

T

Method

Instrument

pH0

Reference

Original Washed

0.001–0.1 M KNO3

22

pH

1 d equilibration

4.9 4.4

[2408]

3.4.3.1.2.1.8 MSC-20 from Mitsui Toatsu Properties: b-form, 0.1% SiO2, specific surface area 21.3 m2/g, particle size 150 nm, TEM image available [1029]. TABLE 3.1582 PZC/IEP of MSC-20 from Mitsui Toatsu Electrolyte

T

0.01 M KCl or NaCl a

Arbitrary interpolation.

Method

Instrument

pH0

Reference

iep

Otsuka ELS-800 or Bel Japan Zetasizer 4

5.8a

[1029]

670

Surface Charging and Points of Zero Charge

3.4.3.1.2.1.9 From Norton Properties: a-form [2414,2415], free SiO2 0.6/1.6%, free Si 0.4/0.3%, total O 0.6/0.5% [2415] (powder A/powder B), specific surface area 10 m2/g, medium particle size 900 nm [2414,2415] (powder A), a-form, 7 m2/g, d50 = 2 μm [2415] (powder B). TABLE 3.1583 PZC/IEP of SiC from Norton Description

Electrolyte

T

Two powders None

Method

Instrument

pH0

Reference

iep

Matec ESA 8050

[2415]

iep

Zeta-Meter 3.0+

2.5 2 3.6

[782]

3.4.3.1.2.1.10 PJ-PL from PlasmaChem Properties: TEM image, particle size distribution available [2416]. TABLE 3.1584 PZC/IEP of PJ-PL from PlasmaChem Electrolyte

T

Method

Instrument

pH0

Reference

HCl + NaOH

25

iep

Laser Zee 501, Pen Kem ECA 2000, Chemtrac

2.6 3

[2416]

3.4.3.1.2.1.11 b-SiC from Sanxin Industries, China Properties: 98% SiC, 0.2% free C, 0.9% O, 0.05% Ca, 0.05% Al, 0.04% Mg, 0.03% Fe, 0.04% Na by mass, BET specific surface area 6.5 m2/g, d10 = 366 nm, d50 = 1.6 μm, d90 = 3.9 μm [399]. TABLE 3.1585 PZC/IEP of β-SiC from Sanxin Industries, China Description Original (NH4)2CO3-washed a

Electrolyte 0.001 M NaCl

T

Method iep

Instrument Brookhaven ZetaPlus

pH0 a

3.5 3.5a

Reference [399]

Arbitrary interpolation, no data points at pH 3.2–4.5.

3.4.3.1.2.1.12 HSC059 from Superior Graphite Properties: b-form, 0.8% C, 0.03% Si, 0.2% N, 0.8% O, specific surface area 15 m2/g, particle size 560 nm, TEM image available [1029].

671

Compilation of PZCs/IEPs

TABLE 3.1586 PZC/IEP of HSC059 from Superior Graphite Electrolyte

T

0.01 M KCl or NaCl

Method

Instrument

pH0

Reference

iep

Otsuka ELS-800 or Bel Japan Zetasizer 4

4

[1029]

3.4.3.1.2.1.13 TWS-400 from Tokai Carbon Properties: b-form, detailed analysis (nine elements) available, whiskers, length 15–60 μm, diameter 500– 1000 nm [2417].

TABLE 3.1587 PZC/IEP of TWS-400 from Tokai Carbon Electrolyte

T

Method

Instrument

iep a

pH0 4

a

Reference [2417]

Arbitrary interpolation. 8 mV at pH 3 and −15 mV at pH 5.

3.4.3.1.2.1.14 From Yakashima Electric Industry, Japan Properties: a-form, 11% of 4H and 89% of 6H type (hexagonal), composition by mass SiC 97.5%, SiO2 1.7%, Al 0.02%, Fe 0.03%, specific surface area 13.4 m2/g, equivalent spherical particle diameter 140 nm [2418].

TABLE 3.1588 PZC/IEP of SiC from Yakashima Electric Industry, Japan Electrolyte 0.01 M NH4NO3

T

Method

Instrument

pH0

Reference

iep

Rank Mark II

2.5

[2418]

3.4.3.1.2.1.15 Commercial SiC from China, Origin Unknown Properties: 28.7% C, 69.4% Si, 0.8% O, BET specific surface area 10 m2/g, mean particle size 880 nm [406].

672

Surface Charging and Points of Zero Charge

TABLE 3.1589 PZC/IEP of SiC from Unknown Commercial Source in China Description

Electrolyte

Original HF-washed

NaCl

T

Method

Instrument

pH0

Reference

Brookhaven ZetaPlus

2 4.7

[406]

3.4.3.1.2.1.16 Commercial SiC, Origin Unknown, Washed with Hot HCl and Water Properties: a-form, 97.5% SiC, 0.2% free C, 0.2% Fe, 1.5% SiO2, BET specific surface area 0.02 m2/g [2419].

TABLE 3.1590 PZC/IEP of SiC from Unknown Commercial Source Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee 501

<2.7 if any

[2419]

0.002 M

3.4.3.1.2.2 Synthetic 3.4.3.1.2.2.1 From Silica, Sucrose, and Boric Acid Recipe from [2420]. A sol containing silica, sucrose (C:Si mole ratio 4:1) and boric acid (0–13.5% by mass) was dried and heated in argon at 1550°C for 3 h. Properties: b-form [2408,2420], specific surface area 7 m2/g [2408], 12.8 m2/g [2410], particle size <50 nm [2408], XRD pattern available [2420].

TABLE 3.1591 PZC/IEP of SiC Obtained from Silica, Sucrose, and Boric Acid Description Original Washed

Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M KNO3

22

pH

1 d equilibration

8.5 4.7 8.5a

[2408]

0.01 M KNO3 a

pH

[2410]

Also CIP (extrapolated). PZC (pH) shifts to low pH on acid washing.

3.4.3.1.2.2.2 From SiH4 and C2H4, Inductively Coupled Plasma Recipe from [2421]. Properties: C/Si molar ratio 1.14, cubic, XRD pattern, IR spectra, TEM images available [272]

673

Compilation of PZCs/IEPs

A: original B: heated at 650°C for 30 min. C: B leached with 5% HF TABLE 3.1592 PZC/IEP of SiC Obtained from SiH4 and C2H4, Inductively Coupled Plasma Description

Electrolyte

T

Method

A B C a

iep

Instrument

pH0

Reference

a

Coulter Delsa 440

4.6 2.7 6a

[272]

In dispersions aged for 6 h. Aging for 4 d induced a shift in the IEP to pH 5.6 (C) and 3.7 (A).

3.4.3.1.2.3

Origin Unknown

TABLE 3.1593 PZC/IEP of SiC from Unknown Sources Description

Electrolyte

T

a, 11 m2/g, 1.5 μm 0.01, 0.05 M NaCl b Mean size 80 nm a

HCl + NaOH

Method

Instrument

Salt additiona pH Streaming potential iep iepa iep

Brookhaven ZetaPlus

pH0

Reference

<2 if any 2.2

[2422] [2423]

3

[2159]

3.4

[1096]

Only value, data points not reported.

3.4.3.1.3

TiC

3.4.3.1.3.1 Commercial 3.4.3.1.3.1.1 From Starck Properties: Specific surface area 17 m2/g [2408]. TABLE 3.1594 PZC/IEP of TiC from Starck Electrolyte

T

Method

Instrument

0.001–0.1 M KNO3

22

pH

1 d equilibration

pH0 Reference 5

[2408]

3.4.3.1.3.1.2 From Zhuzhou Hard Alloy Plant Original and acid- and base-treated.

674

Surface Charging and Points of Zero Charge

Properties: 98.7% pure, main impurities Cr2O3 0.8%, Fe2O3 0.3%, Al2O3 0.1% by mass, particle diameter 900 nm, specific surface area 14.5 m2/g, XRD pattern available [2424]. TABLE 3.1595 PZC/IEP of TiC from Zhuzhou Hard Alloy Plant Electrolyte

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

3.4

[2424]

0.001 M KCl

3.4.3.1.3.2

Origin Unknown

TABLE 3.1596 PZC/IEP of TiC from Unknown Source Electrolyte

T

Method

Instrument

a

iep a

pH0

Reference

2

[2425]

Only value, data points not reported.

3.4.3.1.4

WC

3.4.3.1.4.1 Commercial, from Voksal, Electrochemically Prepared Properties: Particle size 750 nm, specific surface area 6 m2/g [2408]. TABLE 3.1597 PZC/IEP of WC from Voksal Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M KNO3

22

pH

1 d equilibration

3.9

[2408]

3.4.3.1.4.2 Nanonyne Grade, Nanocarb Original commercial material containing Co was leached to remove Co according to a procedure described in [2426]. TABLE 3.1598 PZC/IEP of WC, Nanonyne Grade, Nanocarb Electrolyte

a

T

Method

Only value, no data points.

Instrument

pH0

Reference

4.4

[2426]a

675

Compilation of PZCs/IEPs

3.4.3.1.4.3 Synthetic, Plasma Chemical Method, Original and Water-Washed Properties: Particle size 100–520 nm, specific surface area 6 m2/g [2408].

TABLE 3.1599 PZC/IEP of WC Obtained by Means of Plasma Chemical Method Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M KNO3

22

pH

1 d equilibration

3.2

[2408]

3.4.3.2

Carbonates

3.4.3.2.1

Aluminum Hydroxycarbonate

3.4.3.2.1.1 Commercial, from Barcroft Properties: Amorphous, TEM image available [308].

TABLE 3.1600 PZC/IEP of Aluminum Hydroxycarbonate from Barcroft Electrolyte KCl 0.01 M KCl a b

T

Method

25 25

iep iepb

Instrument Delsa 440 Delsa 440

pH0

Reference a

7–8.2 7.5–>9a

[2427] [308]

Depends on dilution. Only values, data points not reported.

3.4.3.2.1.2

Commercial Gels, Origin Unknown

TABLE 3.1601 PZC/IEP of Aluminum Hydroxycarbonate Gels from Unspecified Commercial Sources Electrolyte

T

0.0005–0.6 M KCl 0.0005–0.6 M KCl 0.0005–0.6 M KCl 0.0005–0.6 M KCl 0.0005–0.6 M KCl 0.0005–0.6 M KCl 0.0005–0.6 M KCl 0.0005–0.6 M KCl 0.0005–0.6 M KCl a

Only value, no data points.

Method cip cip cip cip cip cip cip cip cip

Instrument

pH0

Reference

6.3 6.5 6.5 6.6 6.7 6.9 6.9 7 7.3

[1194]a [1194]a [1194]a [1194]a [1194]a [1194]a [1194]a [1194]a [1194]a

676

Surface Charging and Points of Zero Charge

3.4.3.2.1.3 Synthetic 0.5 M AlCl3 was added to a solution 0.5 M in NaHCO3 and 0.23 M in Na2CO3 until pH 6.6, it was then allowed to stand for 1 d and washed. TABLE 3.1602 PZC/IEP of Synthetic Aluminum Hydroxycarbonate Electrolyte

T

Method

0.0005–0.6 M KCl a

Instrument

cip

pH0

Reference

6.6

[1194]a

Only value, no data points.

3.4.3.2.2

BaCO3

3.4.3.2.2.1 Synthesized at 25°C TABLE 3.1603 PZC/IEP of Synthetic BaCO3 Electrolyte a

0.01 M NaNO3 a

T

Method

Instrument

pH0

Reference

25

iep

Sephy Z3000

8.7

[200]

Total concentrations of metal cations and of CO2 are reported.

3.4.3.2.2.2

Origin Unknown

TABLE 3.1604 PZC/IEP of BaCO3 from Unspecified Source Electrolyte 0.0005–0.6 M KCl

T

Method

Instrument

pH0

Reference

iep

ELS 8000 Otsuka

8.2

[2138]

3.4.3.2.3 CaCO3 The PZCs/IEPs of CaCO3 are reviewed in [291,2428]. 3.4.3.2.3.1 Commercial 3.4.3.2.3.1.1 From Omya Properties: 98.8% pure [2429], 0.4% MgCO3 [2430], BET specific surface area 8.5 m2/g [432], specific surface area 7.1 m2/g [2430], 8.3 m2/g [2429], particle diameter 2 mm [2430], average particle size 900 nm [2429], 1.1 μm [432]. See also [2449].

677

Compilation of PZCs/IEPs

TABLE 3.1605 PZC/IEP of CaCO3 from Omya Description Original Washed Washed, in N2 Extra CL HC-90 a b

Electrolyte

T

Method

Instrument

pH0

Reference

0–0.01 M NaCl

25

iep

Rank Brothers, Mark II

[2430]a

25 25

iep iep

Acoustosizer Acoustosizer

9.6 8.4 <7 if any >10 if any >11 if any

[2429] [432]b

Natural. Potentiometric titrations at 0–0.1 M NaCl produced apparent PZC (pH) at pH 8–9 and no clear CIP.

3.4.3.2.3.1.2 Precipitated, Albaglos M, from Pfizer Properties: Prismatic calcite, >99% pure, BET specific surface area 8.6 m2/g, particle diameter 0.7 mm, 2 and 2.7 nm micropores [2431]. Only positive z potentials (Matec, 23°C) are reported at pH 9.3–9.9 and [Ca2+] 6 × 10-5-7 × 10-3 M [2431]. 3.4.3.2.3.1.3 Multifex from Pfizer surface area 22 m2/g [1177].

Properties: Single point BET specific

TABLE 3.1606 PZC/IEP of Multifex from Pfizer Electrolyte

T

0.001 M NaCl a

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

>11.8a

[1177]

Only value, data points not reported.

3.4.3.2.3.1.4 Polycarb Properties: Traces of Mn, Fe, and organic matter, particle size 2.8 μm, specific surface area 6.6 m2/g [2432].

TABLE 3.1607 PZC/IEP of Polycarb CaCO3 Electrolyte

T

0.001 M NaCl

3.4.3.2.3.1.5 Socal area 17 m2/g [2432].

Method

Instrument

pH0

Reference

iep

Pen Kem S3000

<6 if any

[2432]

Properties: Pure, particle size 2.2 μm, specific surface

678

Surface Charging and Points of Zero Charge

TABLE 3.1608 PZC/IEP of Socal CaCO3 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem S3000

9.5

[2432]

0.001 M NaCl

3.4.3.2.3.1.6 From Solvay, Synthetic Properties: Specific surface area 22.3 m2/g, particle diameter 0.75 mm [2430].

TABLE 3.1609 PZC/IEP of CaCO3 from Solvay Electrolyte

T

Method

Instrument

pH0

Reference

iep

Rank Brothers, Mark II

9.6

[2430]

0, 0.01 M NaCl 25

3.4.3.2.3.1.7 From Ward’s XRD pattern available [2433].

Properties: BET specific surface area 1.5 m2/g,

TABLE 3.1610 PZC/IEP of CaCO3 from Ward’s Electrolyte

T

0.001 M KClO4

Method

Instrument

iep

pH0

Reference

<6.5

[2433]

3.4.3.2.3.2 Synthetic 3.4.3.2.3.2.1 Exposure of CaCl2 Solution Containing NH4Cl to Vapor of Ammonium Carbonate Recipe from [2434]. Properties: SEM images available [2435]. See also [2449].

TABLE 3.1611 PZC/IEP of CaCO3 Obtained by Exposure of CaCl2 Solution to Ammonium Carbonate Vapor Electrolyte 0.005 M NaCl a

T

Method iep

Instrument Streaming potential

pH0 <7 if any

Reference a

PZC as pCa 3.4–4 for different electrolytes containing calcium and/or carbonates.

[2435]

679

Compilation of PZCs/IEPs

3.4.3.2.3.2.2 Recipe from [2436,2437] Properties: 10 mm size, BET specific surface area 0.7 m2/g [2438]. TABLE 3.1612 PZC/IEP of CaCO3 Obtained According to Recipe from [2436,2437] Electrolyte

T

Method

0, 0.002 M KNO3

a

iep

Instrument

pH0

Laser Zee Meter, Pen Kem Zeta-Meter

a

10.5

Reference [2438]

Arbitrary interpolation.

3.4.3.2.3.3 Natural 3.4.3.2.3.3.1 Biogenic, from Laguna de Mar Chiquita, Argentina

TABLE 3.1613 PZC/IEP of CaCO3 from Laguna de Mar Chiquita, Argentina Electrolyte

T

Method

Instrument

pH0

Reference

0.03 M KCl

25

iep

Rank Brothers, Mark II

<8.5 if any

[2428]

3.4.3.2.3.3.2 From Broken Hill, Australia Properties: Analysis (15 elements) available [489].

TABLE 3.1614 PZC/IEP of CaCO3 from Broken Hill, Australia Electrolyte

T

Method

Instrument

pH0

Reference

0.002 M NaClO4

25

iep

Abramson cell

8.2

[489]

3.4.3.2.3.3.3 From Changsha, China area 0.9 m2/g [2439].

Properties: BET specific surface

TABLE 3.1615 PZC/IEP of CaCO3 from Changsha, China Electrolyte 0.001 M KNO3

T

Method

Instrument

pH0

Reference

25 ± 2

iep

MRK

11

[2439]

680

Surface Charging and Points of Zero Charge

3.4.3.2.3.3.4 Iceland Spar TABLE 3.1616 PZC/IEP of Iceland Spar Description

Electrolyte

T

Method

0–0.01 M 25 NaOH, NaCl 0.023 or 0.23 atm CO2

Very pure No mixing, or 1 week or 2 months mixing

a b

Instrument

pH0 Negative ζa

Reference

iep

Electro-osmosis

[281]

iep

Streaming potential <5 if any

[291]

iep

Streaming potential ∼10b

[695]

iep

Streaming potential 10.8

[2440]

pH was not controlled. Values in text are based on subjective interpolation.

3.4.3.2.3.3.5 Carrara Marble TABLE 3.1617 PZC/IEP of Carrara Marble Electrolyte

T

Method

Instrument

pH0

Reference

0.1 M NaCl

25

iep

Malvern Zetasizer 5000

<7 if any

[388]

3.4.3.2.3.3.6 From Morocco Properties: >92% pure, contains quartz and apatite [2441]. TABLE 3.1618 PZC/IEP of CaCO3 from Morocco Electrolyte

T

0, 0.01 M KCl a

Method

Instrument

pH0

Reference

iep

Streaming potential

<6.2a

[2441]

Addition of up to 0.1 M of CaCl2 at pH 8.5 and 10 has not induced sign reversal.

3.4.3.2.3.3.7 From Kansas TABLE 3.1619 PZC/IEP of CaCO3 from Kansas Electrolyte 0.001 M NaNO3

T

Method

Instrument

pH0

Reference

iep

Riddick Zeta-Meter

>10.5

[2442]

681

Compilation of PZCs/IEPs

3.4.3.2.3.3.8 Other TABLE 3.1620 PZC/IEP of Natural CaCO3 from Different Sources Description

Electrolyte

Aragonite “Bohmen” Calcite from Brilon Calcite from Iceland

3.4.3.2.3.4

T

HClO4 + NaOH

Method

Instrument

pH0

Reference

iep

Zeta-Meter

<6 >12 >12

[104]

Origin Unknown

TABLE 3.1621 PZC/IEP of CaCO3 from Unspecified Sources Description Reagent grade precipitated

Electrolyte

T

Method

Instrument

pH0

0.03 M KCl

25

iep

NaCl + CaCl2

25

iep

<8.5 if any pCa 2.7 pCa>4

NaCl

25

iep

Rank Brothers, Mark II Rank Brothers, Mark II Streaming potential

One specimen Two specimens (natural)

[2428] [2443]

Positive ζa

[2444]

iep

Positive ζ

[2445]

iep

Negative ζ >11 if any <7 if any

[2448]

iep

iep iep a

Reference

ELS 8000 Otsuka

8 9.5

[2446,2447]

[2138] [2139]

pH not measured or controlled.

Five calcite samples (most of them characterized by purity, chemical composition, specific surface area, etc.) were studied in [2449] by electrophoresis (Laser Zee, Model 500, Pen Kem). One of these calcites showed the following behavior. In the presence of 0.01 M NaCl, in dispersions containing less than 30 mg of calcite per 100 cm3, the z potential was negative at pH 8–11. In dispersions containing more than 100 mg of calcite per 100 cm3, the z potential was positive at pH 8–11. In dispersions containing 50–70 mg of calcite per 100 cm3, an IEP was observed (particle-concentration-dependent). Synthetic calcite and aragonite were studied in [2450] by electrophoresis. Samples with CaCl2 added (0.0005–0.05 M, different pH) were positively charged and samples with Na2CO3 added (0.0005–0.05 M, different pH) were negatively charged. At pH 9.1, in the presence of 0.01 M NaCl, both minerals were positively charged.

682

Surface Charging and Points of Zero Charge

3.4.3.2.4 CdCO3, Synthesized at 250°C Properties: Specific surface area 0.2 m2/g [200]. TABLE 3.1622 PZC/IEP of CdCO3 Electrolyte a 3

0.01 M NaNO a

T

Method

Instrument

pH0

Reference

25

iep

Sephy Z3000

9

[200]

Total concentrations of metal cations and of CO2 are reported.

3.4.3.2.5 Ce Basic Carbonates 3.4.3.2.5.1 CeOHCO3 A solution containing 0.5 M urea and 0.013 M Ce(NO3)3 was heated at 100°C for 2 h. Properties: BET specific surface area 16.8 m2/g, elongated and spherical particles, DTA analysis and TEM image available [338].

TABLE 3.1623 PZC/IEP of CeOHCO3 Electrolyte

T

0.01 M NaCl

Method

Instrument

pH0

Reference

iep

Malvern Zetamaster

8.8

[338]

3.4.3.2.5.2 Pr0.24Ce0.76OHCO3 A solution containing 0.5 M urea, 0.003 M Pr(NO3)3, and 0.01 M Ce(NO3)3 was heated at 100°C for 2 h. Properties: BET specific surface area 6.7 m2/g, particle diameter 300 nm, spherical, DTA analysis and TEM image available [338].

TABLE 3.1624 PZC/IEP of Pr0.24Ce0.76OHCO3 Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep

Malvern Zetamaster

8.8

[338]

3.4.3.2.5.3 Y0.25Ce0.75OHCO3 · H2O A solution containing 0.5 M urea, 0.005 M Y(NO3)3 and 0.015 M Ce(NO3)3 was heated at 90°C for 2 h. Properties: Specific surface area 17 m2/g, particle diameter 90 nm (Table 3) or 100 nm (Table 5), spherical particles, DTA analysis and TEM image available [2154].

683

Compilation of PZCs/IEPs

TABLE 3.1625 PZC/IEP of Y0.25Ce0.75OHCO3 ⋅ H2O Electrolyte

T

Method

Instrument

pH0

iep

Coulter Delsa

7.1

0.001 M NaNO3

Reference [2154]

3.4.3.2.6 CoCO3, Synthesized at 250°C Properties: Specific surface area 9 m2/g [200].

TABLE 3.1626 PZC/IEP of CoCO3 Electrolyte a 3

0.01 M NaNO a

T

Method

Instrument

pH0

Reference

25

iep

Sephy Z3000

5.8

[200]

Total concentrations of metal cations and of CO2 are reported.

3.4.3.2.7

Cu Basic Carbonates

3.4.3.2.7.1 Cu(OH)2 · CuCO3 Fresh, filtered 0.016 M Cu(NO3)2 containing 0.4 M of urea was heated at 85°C for 1 h under CO2. The precipitate was then quenched to room temperature, washed with water, and dried in a desiccator. Properties: TEM image, TGA and DTA results available [1802].

TABLE 3.1627 PZC/IEP of Cu(OH)2 ⋅ CuCO3 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Delsa 44, Coulter

8.2

[1802]

3.4.3.2.7.2 Cu2CO3(OH)2, Origin Unknown contains Fe2O3, Al2O3, SiO2 [1265].

Properties: 95% malachite,

TABLE 3.1628 PZC/IEP of Cu2CO3(OH)2 Electrolyte 0.001 M KClO4

T

Method pH

Instrument

pH0

Reference

7.6

[1265]

684

Surface Charging and Points of Zero Charge

3.4.3.2.8 EuOHCO3 Several recipes are reported in [2451]. The IEP is then reported for one of these products (it is not indicated which). Properties: TEM image, particle diameters available [2451]. TABLE 3.1629 PZC/IEP of EuOHCO3 Electrolyte

T

0.001 M NaNO3

3.4.3.2.9

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

7.6

[2451]

FeCO3

3.4.3.2.9.1 Synthetic

Properties: BET specific surface area 2.2 m2/g [145].

TABLE 3.1630 PZC/IEP of Synthetic FeCO3 Electrolyte

T

Method

0.1 M NaCl, 5 × 104 Pa CO2

25

pH

3.4.3.2.9.2

Instrument

pH0

Reference

5.3

[145]

Natural Siderites

TABLE 3.1631 PZC/IEP of Natural Siderites Description

Electrolyte 2

From Mexico, 0.1 m /g From Flinders Ranges, South Australia, 7.4% Mg, 0.6% Mn, 0.1% Ca by mass, BET specific surface area 2.7 m2/g From Siegerland From China a b c

a

0.01 M NaNO3 0.0001–0.01 M KNO3

HClO4 + NaOH 0.01 M NaCl

T

Method

Instrument

25 25

iep iep

Sephy Z3000 Rank Brothers Mark II

iep iepc

Zeta-Meter Pen Kem 300

pH0 7.4 7.9

11.2b >12 if any

Reference [200] [1953]

[104] [1317]

Total concentrations of metal cations and of CO2 are reported. Arbitrary interpolation. Only value, data points not reported.

3.4.3.2.10 GdOHCO3 Several recipes are reported in [2451]. The IEP is then reported for one of these products (it is not indicated which).

685

Compilation of PZCs/IEPs

Properties: TEM images, particle diameters available [2451]. TABLE 3.1632 PZC/IEP of GdOHCO3 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

7.6

[2451]

0.001 M NaNO3

3.4.3.2.11

Mg Carbonates

3.4.3.2.11.1 Magnesite 3.4.3.2.11.1.1 From Ward’s XRD pattern available [2433].

Properties: BET specific surface area 1.1 m2/g,

TABLE 3.1633 PZC/IEP of Magnesite from Ward’s Electrolyte

T

0.001 M KClO4

Method

Instrument

iep

pH0

Reference

<7.8

[2433]

3.4.3.2.11.1.2 From Montner, Pyrenees, France Properties: 0.6% Si, 1.2% Ca, 1% Fe, detailed analysis available, BET specific surface area 3.6 m2/g [2452]. TABLE 3.1634 PZC/IEP of Magnesite from Montner, Pyrenees, France Electrolyte 3

0.1 M NaCl, 10 Pa CO2/ 0.015–0.5 M NaCl, 101.5 Pa CO2

T

Method

Instrument

25 23

pH iep

Zetacad Zetaphoremetre II, Model Z3000, Sephy

pH0 8/8.7 8.5

Reference [2452]

3.4.3.2.11.1.3 From Satka, Russia Properties: 0.4% Si, 0.6% Ca, detailed analysis available, BET specific surface area 3.8 m2/g [2452]. TABLE 3.1635 PZC/IEP of Magnesite from Satka, Russia Electrolyte 3

0.1 M NaCl, 10 Pa CO2/ 0.015–0.5 M NaCl, 101.5 Pa CO2

T

Method

Instrument

pH0

Reference

25 23

pH iep

Zetacad Zetaphoremetre II, Model Z3000, Sephy

8/8.7 8.5

[2452]

686

Surface Charging and Points of Zero Charge

3.4.3.2.11.1.4 From Kosice, Slovakia Properties: 45.3% MgO, 0.42% CaO, 0.88% SiO2, 1.85% FeO, 51.1% CO2, solubility data available [2453].

TABLE 3.1636 PZC/IEP of Magnesite from Kosice, Slovakia Electrolyte

T

Method

Instrument

pH0

Reference

0–0.01 M KCl 0.001–0.1 M NaNO3

25 22

iep iep

Streaming potential Zeta-Meter

<7 if any 7.2a

[2453] [372]

a

The range of data points also covers the pH range in which magnesite is dissolved. Results of mass titration are also reported.

3.4.3.2.11.1.5 From Konya-Argit (Turkey) CaO, 1.5% SiO2, 0.3% FeO, 49.8% CO2 [402].

Properties: 46.9% MgO, 1.1%

TABLE 3.1637 PZC/IEP of Magnesite from Konya-Argit (Turkey) Electrolyte

T

Method

Instrument

pH0

Reference

iep

Rank Brothers

6.8 6.2

[402]

None 0.01 M NaCl

3.4.3.2.11.1.6 Magnesite, Origin Unknown

TABLE 3.1638 PZC/IEP of Natural Magnesite from Unknown Source Electrolyte 0.0006 M NaClO4 HClO4 + NaOH a b

T

Method

Instrument

pH0

Reference

iepa iep

EMTA 1202, Micromeritics Zeta-Meter

8.3 >12b

[1315] [104]

Arbitrary interpolation. The results (positive ζ potentials at pH 6–12) for two other minerals (ankerite and synthetic nesquehonite) are presented in the same figure in [104].

3.4.3.2.11.2 Dolomite 3.4.3.2.11.2.1 From Ward’s Properties: BET specific surface area 1.4 m2/g, XRD pattern available [2433].

687

Compilation of PZCs/IEPs

TABLE 3.1639 PZC/IEP of Dolomite from Ward’s Electrolyte

T

Method

0.001 M KClO4

Instrument

iep

pH0

Reference

<7.8

[2433]

3.4.3.2.11.2.2 From Cap de Bouc, Aude, France Properties: BET specific surface area 2.8 m2/g [203].

TABLE 3.1640 PZC/IEP of Dolomite from Cap de Bouc, Aude, France Electrolyte

T

Method

Instrument

pH0

Reference

0.01–0.5 M NaCl, 101.5 Pa CO2

25

pH iep

Zetacad Zetaphoremetre II, model Z3000, Sephy

8

[203]

3.4.3.2.11.2.3 From Kosice Properties: 21.32% MgO, 29.54% CaO, 0.76% SiO2, 1.02% FeO, 47% CO2, solubility data available [2453].

TABLE 3.1641 PZC/IEP of Dolomite from Kosice Electrolyte

T

Method

Instrument

pH0

Reference

0–0.01 M KCl

25

iep

Streaming potential

<9 if any

[2453]

3.4.3.2.11.2.4 From Granada Properties: BET specific surface area 0.3 m2/g [1868].

TABLE 3.1642 PZC/IEP of Dolomite from Granada Electrolyte

T

Method

Instrument

pH0

Reference

0.0007–0.14 M NaCl

25

iepa

Zeta-Meter 3.0

12.3

[1868]

a

Only value, data points not reported.

688

Surface Charging and Points of Zero Charge

3.4.3.2.11.2.5 From Konya-Argit (Turkey) Properties: 21.2% MgO, 30% CaO, 0.8% SiO2, 1% FeO, 46.1% CO2 [402]. TABLE 3.1643 PZC/IEP of Dolomite from Konya-Argit (Turkey) Electrolyte

T

Method

Instrument

pH0

Reference

iep

Rank Brothers

6.3 5.5

[402]

None 0.01 M NaCl

3.4.3.2.11.2.6 Origin Unknown TABLE 3.1644 PZC/IEP of Dolomite from Unspecified Source Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

>12

[104]

HClO4 + NaOH

3.4.3.2.11.3 Hunite Mg3Ca(CO3)4 from Egirdir Lake, Turkey elemental composition, XRD pattern available [325].

Properties:

TABLE 3.1645 PZC/IEP of Hunite Electrolyte

T

0–0.01 M NaCl

3.4.3.2.12

Method iep

Instrument Zeta-Meter 3.0

pH0 Reference 8

[325]

Mn Carbonates

3.4.3.2.12.1 Rhodochrosite from Ventrom Alpha surface area 22 m2/g [145].

Properties: BET specific

TABLE 3.1646 PZC/IEP of Rhodochrosite from Ventrom Alpha Electrolyte 0.0032, 1 M NaCl, 5 × 102 Pa CO2 a

T 25

Method

Instrument

pH

Intersection at pH 5.5 with 5 ¥ 104 Pa CO2.

pH0

Reference

a

[145,2454]

6.8

689

Compilation of PZCs/IEPs

3.4.3.2.12.2 Synthetic, from MnSO4 and Urea Properties: SEM images and XRD patterns available [1427,2455].

TABLE 3.1647 PZC/IEP of Synthetic Mn Carbonates Recipe

Electrolyte

Method

Instrument

pH0

Reference

0.16 M MnSO4 and 0.4 M urea aged for 25 min at 85°C (A) Mother liquor of A separated and aged for 90 min at 85°C 0.02 M MnSO4 and 0.4 M urea aged for 20 min at 90°C

0.001 M

T

iep

Pen Kem 3000

5.8

[2455]

0.001 M

iep

Pen Kem 3000

5.8

[2455]

iep

Electrophoresis

6

[1427]

NaOH + HCl

3.4.3.2.12.3 Natural Rhodochrosites

TABLE 3.1648 PZC/IEP of Natural Rhodochrosites Description

Electrolyte

From Pyrenees, France, 0.05 m2/g From Argentina a

0.01 M NaNO3

a

HClO4 + NaOH

T

Method

Instrument

pH0

Reference

25

iep

Sephy Z3000

7.8

[200]

iep

Zeta-Meter

10.5

[104]

Total concentrations of metal cations and of CO2 are reported.

3.4.3.2.13 NiCO3, Synthesized at 250°C Properties: Specific surface area 0.05 m2/g [200].

TABLE 3.1649 PZC/IEP of NiCO3 Electrolyte a

0.01 M NaNO3 a

T

Method

Instrument

pH0

Reference

25

iep

Sephy Z3000

6.6

[200]

Total concentrations of metal cations and of CO2 are reported.

690

Surface Charging and Points of Zero Charge

3.4.3.2.14

Pb Carbonates

3.4.3.2.14.1 Synthetic 3.4.3.2.14.1.1 Addition of KOH to Air-Saturated Pb(NO3)2 Solution The solid was washed and dried at room temperature. Properties: identity confirmed by IR spectroscopy [1920].

TABLE 3.1650 PZC/IEP of PbCO3 Obtained from KOH and Air-Saturated Pb(NO3)2 Solution Electrolyte

T

Method

Instrument

pH0

Reference

Air-saturated 0.001 M KNO3

22

iep

Zeta-Meter 3.0

12

[1920]

3.4.3.2.14.1.2 0.08 m2/g [200].

Synthesized at 250°C

Properties: Specific surface area

TABLE 3.1651 PZC/IEP of PbCO3 Synthesized at 250°C Electrolyte a

0.01 M NaNO3 a

T

Method

25

iep

Instrument

pH0

Reference

Sephy Z3000

6.2

[200]

Total concentrations of metal cations and of CO2 are reported.

3.4.3.2.14.2 Natural Cerussite TABLE 3.1652 PZC/IEP of Natural Cerussites Origin Tsumeb, Namibia Tiger I, Arizona Mammoth Mine, Arizona Tiger II, Arizona

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

3.8 <5 <5 <5

[475]

3.4.3.2.15 PrOHCO3 A solution containing 0.5 M urea and 0.013 M Pr(NO3)3 was heated at 100°C for 2 h.

691

Compilation of PZCs/IEPs

Properties: Specific surface area 7.2 m2/g, elongated particles, DTA analysis and TEM image available [338].

TABLE 3.1653 PZC/IEP of PrOHCO3 Electrolyte

T

Method

0.01 M NaCl

iep

Instrument

pH0

Reference

8.8

[338]

Malvern Zetamaster

3.4.3.2.16 SrCO3, Synthesized at 250°C Properties: Specific surface area 0.5 m2/g [200].

TABLE 3.1654 PZC/IEP of SrCO3 Electrolyte a

0.01 M NaNO3 a

T

Method

Instrument

pH0

Reference

25

iep

Sephy Z3000

8.2

[200]

Total concentrations of metal cations and of CO2 are reported.

3.4.3.2.17 TbOHCO3 Several recipes are reported in [2451]. The IEP is then reported for one of these products (it is not indicated which). Properties: TEM image, particle diameters available [2451].

TABLE 3.1655 PZC/IEP of TbOHCO3 Electrolyte 0.001 M NaNO3

3.4.3.2.18

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

7.6

[2451]

Y Carbonates

3.4.3.2.18.1 Y2O(CO3)2 A solution containing 3.3 M urea and 0.03 M Y(NO3)3 was heated at 115°C for 18 h. Properties: Composition Y2(CO3)3 · NH3 · 3H2O (original), Y2O(CO3)2 (calcined), specific surface area 4.1 m2/g and 6.5 m2/g (calcined at 300°C), rod-like particles, IR spectrum, XRD pattern, and TEM images available [2154].

692

Surface Charging and Points of Zero Charge

TABLE 3.1656 PZC/IEP of Y2O(CO3)2 Description

Electrolyte

Original Calcined at 300°C

3.4.3.2.18.2

T

0.01 M NaNO3

Method

Instrument

pH0

iep

Coulter Delsa

7.6

Reference [2154]

Synthetic YOHCO3

3.4.3.2.18.2.1 From 0.33 M urea and 0.015 M Y(NO3)3 A solution containing 0.33 M urea and 0.015 M Y(NO3)3 was heated at 85°C for 2 h. Properties: Composition YOHCO3 · H2O, specific surface area 6.1 m2/g, particle diameter 310 nm, IR spectrum and TEM image available [2154]. TABLE 3.1657 PZC/IEP of YOHCO3 Obtained from 0.33 M Urea and 0.015 M Y(NO3)3 Electrolyte

T

0.001 M NaNO3

Method

Instrument

pH0

Reference

iep

Coulter Delsa

7.5

[2154]

3.4.3.2.18.2.2 From 1.8 M Urea and 1.1–4.9 mM Y(NO3)3 A solution containing 1.8 M urea and 1.1–4.9 mM Y(NO3)3 was heated at 90°C for 2–15 h. Properties: IR spectrum and TEM image available [2456]. TABLE 3.1658 PZC/IEP of YOHCO3 Obtained from 1.8 M Urea and 1.1–4.9 10 −3 M Y(NO3)3 Description

Electrolyte

T

Method a

0.02 M Y(NO3)3 additionally 1.2% by mass of polyvinylpyrrolidone, MW 360,000 a b

0.001–0.1 M 25 iep NaCl 0.001 M NaNO3 iepb

Instrument Malvern Zetasizer 2c Delsa

pH0

Reference

8

[2155]

7.6

[2456]

Only value, data points not reported. Arbitrary interpolation.

3.4.3.2.18.2.3 From 0.02 M YCl3 and 0.4 M Urea A filtered solution 0.02 M in YCl3 and 0.4 M in urea was heated to boiling. It was boiled for 1 h, then quenched in an ice–water batch. The precipitate was washed, and dried at 40°C in vacuum. Properties: BET specific surface area 6.5 m2/g, modal diameter 330 nm [597].

693

Compilation of PZCs/IEPs

TABLE 3.1659 PZC/IEP of YOHCO3 Obtained from 0.02 M YCl3 and 0.4 M Urea Electrolyte

T

Method

Instrument

pH0

Reference

cip iep

Pen Kem Laser Zee Meter 501

7.7 8.7

[597]

0.0001–0.1 M NaClO4

3.4.3.2.18.3 Y0.75Ce0.25OHCO3 · H2O A solution containing 0.5 M urea, 0.015 M Y(NO3)3 and 0.005 M Ce(NO3)3 was heated at 90°C for 2 h. Properties: specific surface area 19 m2/g, particle diameter 120 nm (Table 3) or 90 nm (Table 5), spherical particles, IR spectrum and TEM image available [2154]. TABLE 3.1660 PZC/IEP of Y0.75Ce0.25OHCO3 ⋅ H2O Electrolyte

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa

7.1

[2154]

0.001 M NaNO3

3.4.3.2.19 Zinc Carbonates 3.4.3.2.19.1 ZnCO3 3.4.3.2.19.1.1 Natural Smithsonite from Ural, Russia or Synthesized at 25°C. Properties: Specific surface area 0.2 or 0.3 m2/g [200]. TABLE 3.1661 PZC/IEP of ZnCO3 from Ural, Russia, or Synthetic Electrolyte

T a 3

25

0.01 M NaNO a

Method iep

Instrument Sephy Z3000

pH0 a

7.6

Reference [200]

Arbitrary interpolation. Total concentrations of metal cations and of CO2 are reported.

3.4.3.2.19.1.2

Synthetic, Origin Unknown

TABLE 3.1662 PZC/IEP of Unspecified Synthetic ZnCO3 Electrolyte 0.01 M KCl

T

Method pH

Instrument

pH0

Reference

8

[2457]

694

Surface Charging and Points of Zero Charge

3.4.3.2.19.2

Zn5(OH)6(CO3)2, Synthetic Origin Unknown

TABLE 3.1663 PZC/IEP of Unspecified Synthetic Zn5(OH)6(CO3)2 Electrolyte

T

Method

0.001–0.1 M KClO4

Instrument

cip

pH0

Reference

7.6

[2457]

3.4.3.2.19.3 Zinc Hydroxycarbonate Precipitated at pH 8 17.1 g of ZnCO3· 3H2O was dissolved in 1 dm3 of HNO3 (pH 3). The pH was then brought to 8 with NaHCO3. Properties: XRD pattern, SEM image available [2168].

TABLE 3.1664 PZC/IEP of Zinc Hydroxycarbonate Precipitated at pH 8 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Rank Brothers II

<2 if any

[2168]

0.01 M KNO3

3.4.3.2.20

Zr Carbonates

3.4.3.2.20.1 Zr2O2(OH)2CO3 Obtained at 70°C A solution 0.001 M in Zr(SO4)2, 0.72 M in urea, and 1.5 M in formamide containing 0.9% of poly(vinylpyrrolidone) by mass was aged for 8 h at 70°C.

TABLE 3.1665 PZC/IEP of Zr2O2(OH)2CO3 Obtained at 70°C Electrolyte 0.01 M NaNO3

T

Method

Instrument

pH0

Reference

iep

Delsa 440 Coulter

3

[2213]

3.4.3.2.20.2 Zr2O2(OH)2CO3 Obtained at 80°C A solution 0.005 M in Zr(SO4)2, 1.8 M in urea, and 0.05 M in HNO3 containing 3% of poly(vinylpyrrolidone) by mass was aged for 5 h at 80°C. Properties: Particle diameter 460 nm, TEM image available [474].

695

Compilation of PZCs/IEPs

TABLE 3.1666 PZC/IEP of Zr2O2(OH)2CO3 Obtained at 80°C Electrolyte

T

Method

Instrument

iep

Delsa 440 Coulter

0.01 M NaNO3

pH0 Reference 3.2

[474]

3.4.3.2.20.3 ZrY0.8(OH)3.8(CO3)1.3 A solution 0.005 M in Zr(SO4)2, 0.004 M in Y(NO3)2, 1.8 M in urea, and 0.005 M in HNO3 containing 3% of poly(vinylpyrrolidone) by mass was aged for 5 h at 80°C. Properties: particle diameter 550 nm, TEM image available [474].

TABLE 3.1667 PZC/IEP of ZrY0.8(OH)3.8(CO3)1.3 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Delsa 440 Coulter

3

[474]

0.01 M NaNO3

3.4.3.3 Ca Dodecylsulfonate Precipitated from sodium dodecylsulfonate and concentrated CaNO3)2 solution. TABLE 3.1668 PZC/IEP of Ca Dodecylsulfonate Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

<4 if any

[2458]

0.002 M NaNO3

3.4.3.4

Oleates

3.4.3.4.1 Ba, Ca, and Fe oleates Obtained from sodium oleate and Ba(NO3)2, CaCl2, and FeCl3 solutions. TABLE 3.1669 PZC/IEP of Ba, Ca, and Fe Oleates Electrolyte

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

<3 if any

[2459]

696

Surface Charging and Points of Zero Charge

3.4.3.4.2 Ca Oleate Precipitated from sodium oleate and concentrated Ca(NO3)2 solution. TABLE 3.1670 PZC/IEP of Ca Oleate Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

<4 if any

[2458]

0.002 M NaNO3

3.4.3.5 Ca Tridecanoate Precipitated from sodium tridecanoate and concentrated Ca(NO3)2 solution. TABLE 3.1671 PZC/IEP of Ca Tridecanoate Electrolyte

T

Method

0.002 M NaNO3

3.4.4

iep

Instrument

pH0

Zeta-Meter < 5.5 if any

Reference [2458]

CHLORIDES

3.4.4.1 AgCl Precipitated from stoichiometric amounts of 1 M AgNO3 and NaCl, washed with water. TABLE 3.1672 PZC/IEP of AgCl Electrolyte

T

pH 5.4–5.8

Method

Instrument

iep

Malvern Zetasizer III

pCl0 Reference 6

[2460]

3.4.4.2 Zn5(OH)8Cl2 · H2O 12.2 g of ZnO was dissolved in 1 dm3 of HCl (pH 2). The pH was then brought to 6.5 with NaOH. Properties: XRD pattern, SEM image available [2168]. TABLE 3.1673 PZC/IEP of Zn5(OH)8Cl2 · H2O Electrolyte 0.01 M KNO3

T

Method

Instrument

pH0

Reference

iep

Rank Brothers II

9.2

[2168]

697

Compilation of PZCs/IEPs

3.4.5 3.4.5.1

CHROMATES Natural Chromites

TABLE 3.1674 PZC/IEP of Natural Chromites Origin

Composition

Transvaal Albania

Cuba

Russia

Electrolyte

T

Method

NaOH + HClO4 0.01 M KCl

1.1% SiO2, 11% Al2O3, 55.9% Cr2O3, 11% FeO, 4.3% Fe2O3, 15.1% MgO, 2.1% CaO 1.1% SiO2, 25.4% 0.01 M KCl Al2O3, 39.3% Cr2O3, 11% FeO, 4.3% Fe2O3, 16.7% MgO, 2.3% CaO 0.01 M KCl 1.2% SiO2, 23.8% Al2O3, 41.8% Cr2O3, 12.5% FeO, 3.5% Fe2O3, 15.1% MgO, 2% CaO

Instrument

pH0 Reference

Zeta-Meter

5

[104]

Salt addition

7.2

[664]

Salt addition

7.4

[664]

7.7

[664]

iep

Salt addition

3.4.5.2 Ca- and Sr-Doped Lanthanum Chromites, Praxair Produced by combustion spray pyrolysis, calcined at different temperatures.

TABLE 3.1675 PZC/IEP of Ca- and Sr-Doped Lanthanum Chromites, Praxair Composition (calcination T )

Electrolyte

T

Method

Instrument

pH0 Reference

LaCa0.2CrO2.9 (650°C) LaCa0.15CrO2.93 (650°C) LaCa0.2CrO2.9 (1150°C) LaSr0.1Cr0.9Ni0.1O2.9 (1000°C) LaSr0.1Cr0.9Cu0.1O2.9 (1000°C) LaSr0.1Cr0.9Mg0.1O2.9 (1000°C)

0.01 M NaCl

24

iep

Malvern Zetasizer 4

5.6 6.8 3.7 4.1 3.7 3.7

[2331]

698

Surface Charging and Points of Zero Charge

3.4.5.3 Ca-Doped Lanthanum Chromite, Pyrox Produced by solid-state reaction (yttria added as sintering aid), calcined at 1200°C. TABLE 3.1676 PZC/IEP of Ca-Doped Lanthanum Chromite, Pyrox Composition

Electrolyte

T

Method

Instrument

pH0

Reference

LaCa0.2CrO2.9

0.01 M NaCl

24

iep

Malvern Zetasizer 4

5.6

[2331]

3.4.6

LICOO2

L106 from LICO, Taiwan. Properties: High purity, median size 8 μm [426]. TABLE 3.1677 PZC/IEP of LiCoO2 Electrolyte

T

Method

Instrument

pH0

Reference

iep

DT 1200

6

[426]

None

3.4.7

FLUORIDES

3.4.7.1

CaF2

3.4.7.1.1

Commercial

3.4.7.1.1.1

From Aldrich

Properties: 99.9% pure, particle size 38 μm [2460].

TABLE 3.1678 PZC/IEP of CaF2 from Aldrich Electrolyte

T

None

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer III

>11 if any

[2460]

3.4.7.1.1.2 Optical Window from Harrick TABLE 3.1679 PZC/IEP of CaF2, Optical Window from Harrick Electrolyte 0.001 M NaNO3

T

Method AFM

Instrument

pH0

Reference

9.2

[2461]

699

Compilation of PZCs/IEPs

3.4.7.1.2

Synthetic, Origin Unknown

TABLE 3.1680 PZC/IEP of Synthetic CaF2 Electrolyte

T

Method

Instrument

iep a

3.4.7.1.3

pH0

Electrophoresis

9.5

a

Reference [2462]

Only value, data points not reported.

Natural

TABLE 3.1681 PZC/IEP of Natural CaF2 Source, Properties

Electrolyte

T

Method iep

Fluorspar Mines, Kadipani, India 98.3% pure, 0.9 m2/g Criciuma, Santa Catarina, Brazil Erongo Mountains, South West Africa and from Utah (almost identical results), elemental analysis available Dongfeng, China 0.6 m2/g Finstergrund, Schwarzland a b

a

Instrument

pH0

Reference

Electrophoresis

6.2–8.8

[2462]

0.1 M NaCl

iep

Laser Zee Meter 501

9b

[957]

0.001 M NaNO3

iep

Rank Brothers

10

[2463]

0, 0.001 M NaCl

iep

Riddick Zeta-Meter

10.2

[2464]

iep

MRK

10.5

[2439]

iep

Zeta-Meter

11

[104]

0.001 M KNO3 NaOH + HClO4

25 ± 2

Only value, data points not reported. Arbitrary interpolation.

3.4.7.1.4 Master Curve, 16 Specimens from Different Sources Natural and reagent-grade, also doped with various elements.

700

Surface Charging and Points of Zero Charge

TABLE 3.1682 PZC/IEP of CaF2 Derived from a Master Curve Obtained for 16 Specimens Electrolyte

3.4.7.1.5

T

Method

Instrument

pH0

Reference

iep

Riddick Zeta-Meter

10

[2465]

Origin Unknown

TABLE 3.1683 PZC/IEP of Unspecified Samples of CaF2 Description

Electrolyte

T

Method

Flat plate, (111) surface

Streaming potential NaOH+HCl

a b

Instrument

pH0

Reference

<4 if any [2283,2465]

Electrophoresis

7a

[2466]

iep iep

8.5b 10

[2467] [2440]

Zeta-Meter

Only value, data points not reported. Quartz was also studied.

3.4.7.2

MgF2

3.4.7.2.1 Commercial from Aldrich Properties: 99.9% pure, 3–6 mm [2460]. TABLE 3.1684 PZC/IEP of MgF2 from Aldrich Electrolyte

T

Method

None

3.4.7.2.2

iep

Instrument

pH0

Malvern Zetasizer III >11 if any

Reference [2460]

Synthetic Sellaite

TABLE 3.1685 PZC/IEP of Synthetic Sellaite Electrolyte NaOH + HClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

12

[104]

701

Compilation of PZCs/IEPs

3.4.8

Ba FERRITE FROM ALDRICH

Properties: Specific surface area 2.6 m2/g (as received) [2468].

TABLE 3.1686 PZC/IEP of Ba Ferrite from Aldrich Description Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta Probe Colloidal Dynamics

6.5a 8.9

[2468]

As received Milled a

3.4.9

Two other IEPs at pH about 11.

AgI

TABLE 3.1687 PZC/IEP of AgI Electrolyte

T

Method iep iepb

0.012 M KNO3

a b

Instrument

pI

Reference

Electrophoresis

10.7a 10.7

[2469] [240]

Arbitrary interpolation. Compilation of results from different sources.

3.4.10

MANGANATES

3.4.10.1 δ-MnO2 The “d-MnO2” is referred to as oxide in many publications. The actual composition deviates from the idealized formula. A review of PZCs of “d-MnO2” can be found in [2470]. 3.4.10.1.1 Commercial, Origin Unknown Water-washed, and dried at 110°C.

TABLE 3.1688 PZC/IEP of Commercial “δ-MnO2” Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M KCl

25

iep

Rank Mark II

1.9

[1213]

702

3.4.10.1.2

Surface Charging and Points of Zero Charge

Synthetic

3.4.10.1.2.1 Obtained from KMnO4 and HCl 3.4.10.1.2.1.1 By Reduction of KMnO4 with Hot 6 M HCl Recipe from [1712]: 500 cm3 of 1:1 (by volume) HCl was slowly added to 1 dm3 of solution containing 90 g of KMnO4 preheated to 80–90°C. Recipe from [2471]: 6 M HCl was added dropwise to hot 1 M KMnO4 under agitation until the color disappeared. Recipe from [1709]: 2 mol of concentrated HCl was added dropwise to a boiling solution of 1 mol of KMnO4 in 2.5 dm3 of water. This was boiled for a further 10 min. Modified method from [1709] reported in [1713]: A solution of 35 cm3 of concentrated HCl in 15 cm3 of water was added dropwise at 0.7 dm3/min to 500 cm3 of boiling 0.4 M KMnO4. The dispersion was boiled for a further 30 min, then aged at 60°C for 12 h. The precipitate was washed with water and freeze-dried. Properties: poorly crystallized birnessite [2472], MnO1.81 [2472], Mn oxidation state 3.44 [1694], 3.96 [1713], O:Mn 1.88 [2471], 4.05% K2O [2472], K0.05MnO2.01(H2O)0.65 [1713], 1.18% K2O [2471], 21.1% water [2472], 4.1% water [2471], detailed analysis available [1712], BET specific surface area 35.4 m2/g [332,1417], 40 m2/g [1694], 83.8 m2/g [1511], 93 m2/g [1714], specific surface area 43.6 m2/g [2471], 48.3 m2/g [1713], 49 m2/g [2472], 71.1 m2/g [121], SEM image available [332,1417], XRD and ED pattern, TEM image available [1713]. TABLE 3.1689 PZC/IEP of “δ-MnO2” Obtained by Reduction of KMnO4 with Hot 6 M HCl Description

Washed with 0.001 M HCl

Electrolyte 0.01 M NaNO3, KNO3 0.01 M KCl

T

Method iepa

iepa

0–1 M NaCl pH 0.01–0.5 M pH NaNO3 30 Salt addition 0.001–1 M pH NaCl, KNO3 iep 0.001–0.5 M pH NaNO3 iepa

LiNO3 a b

pH 27 Salt addition

Instrument

pH0

Malvern <2 Zetasizer 3000HSa Pen Kem 501 <2 if any Laser Zee Meter 3 d equilibration <2 if any <2.5 if any Rank Brothers Rank II

Electrophoresis

<2.5 if any <2.5 if any 2.8 <2.5 if any

Reference [332,1417]

[1511] [2471] [2473] [2472]

[1714]

1.8 [1694] (extrapolated) 1.8b [1713] 2.2a [121]

Only value, data points not reported. Obtained by fast titration, only PZC reported. The charging curve reported in [1713] (only negative charge at pH > 2.5) was obtained by back titration.

703

Compilation of PZCs/IEPs

3.4.10.1.2.1.2 Reduction of KMnO4 (excess) with HCl Properties: O:Mn >1.9, BET specific surface area 300 m2/g [481], low degree of crystallinity (d-spacings of 0.73, 0.245, and 0.141 nm), O:Mn 1.92, specific surface area 160 m2/g (BET), 350 m2/g (glycol retention method) [2474], 223 m2/g (ethylene glycol monoethyl ester method) [2475].

TABLE 3.1690 PZC/IEP of “δ-MnO2” Obtained by Reduction of KMnO4 (Excess) with HCl Description

Electrolyte

Washed with 0.05 M HClO4 Washed, dried at 60°C

a

T

None

Method

Instrument

pH0

iep Coagulation Titration iep

Electrophoresis

1.4 1.5 Electrophoresis 2.7a <3 if any

Reference [2474]a [2475]

Only value, data points not reported.

3.4.10.1.2.2 Oxidation of Mn(OH)2 with Oxygen at 20–25°C Detailed recipe in [1714,2476]. Properties: MnO1.88 highly crystallized birnessite, 13.5% Na2O, 6.6% water [2472], BET specific surface area 105 m 2/g [1714], specific surface area 10 m 2/g [2472].

TABLE 3.1691 PZC/IEP of “δ-MnO2” Obtained by Oxidation of Mn(OH)2 with Oxygen at 20–25°C Electrolyte

T

0.001–0.5 M NaNO3 0.001–1 M NaCl

30

a

Method pH Salt addition pH iepa

Instrument Rank Brothers Rank II

pH0

Reference

<4 if any 2.9 <3.3 if any <3.5 if any

[1714] [2472]

The significance of data points in upper part of Fig. 8b is difficult to access.

3.4.10.1.2.3 Slow Addition of KMnO4 to H2O2 + NaOH Solution at 70°C The precipitate was washed with water, and dried at 44°C. Properties: d-form [1704], 74.3% MnO1.98, 12.1% H2O, 14.3% K [185,2477], BET specific surface area 4 m2/g [185,1704,2477], XRD pattern available, TGA and DTA results available [1704].

704

Surface Charging and Points of Zero Charge

TABLE 3.1692 PZC/IEP of “δ-MnO2” Obtained by Slow Addition of KMnO4 to H2O2 + NaOH Solution Electrolyte

T

Method

0.001–0.1 M KCl 0.5, 1 M KCl

25

pH Sedimentation

a

Instrument

pH0

Reference

Merge at pH < 6 3.8

[1704]a

PZC at pH 3.3 is reported in the text of [1704] and cited in [2477] after [1704]. The same value is reported in [185] without literature reference.

3.4.10.1.2.4 From KMnO4 and Mn(II) Salts 3.4.10.1.2.4.1 From Sulfate A solution of 60 g of hydrous MnSO4 in 500 cm3 of in 0.05 M H2SO4 was added to an equal volume of solution containing 40 g of KMnO4. Properties: O:Mn molar ratio 1.82, nearly amorphous, 1.6% K 2O, 17.1% water [2472], detailed analysis available [1712], specific surface area 150 m 2/g [2472], 94.2 m 2/g [121].

TABLE 3.1693 PZC/IEP of “δ-MnO2” Obtained from MnSO4 and KMnO4 Electrolyte

T

Method

0.001–1 M NaCl, KNO3

30

LiNO3

27

Salt addition iep Salt addition

a

Instrument

pH0

Rank Brothers Rank II <2.5 if any 3.3 1.5a

Reference [2472] [121]

Extrapolated. Only value, no data points.

3.4.10.1.2.4.2 From Chloride at pH 8–8.5 MnCl2 was oxidized with KMnO4 in the presence of NaOH (pH 8–8.5). Washed, but not dried, the dispersion was stored in a polyethylene bottle. Properties: low crystallinity [2470], nearly amorphous [2471,2472], O:Mn molar ratio 1.87[2472], 1.9 [2471], 1.96 [2470], 0.3% K, 0.06% Na by mass [2470], 10.2% K2O, 0.22% Na2O, 19.6% water [2471], 3.8% Na2O, 31% water [2472], BET specific surface area 74 m2/g [2470], 130 m2/g [1575], specific surface area 57.9 m2/g [2471], 15 m2/g [2472].

705

Compilation of PZCs/IEPs

TABLE 3.1694 PZC/IEP of “δ-MnO2” Obtained from MnCl2 and KMnO4 at pH 8–8.5 Electrolyte

T a

0.015–1 M NaCl 0.001–1 M NaCl

30

0–1 M NaCl 0.001–0.1 M NaNO3 25 a b c

Method pH Salt addition pH iep pH pH Merge

Instrument Rank Brothers Rank II

2 min and 3 d equilibration

pH0

Reference

<2 if any <3 if any <2.5 if any 2.7 1.7b <2 if any 2.3

[2470] [2472]

[1575] [2471] [1722]c

0.015 M NaCl contained 0.001 M KCl. Only value, data points not reported. pH of precipitation not reported. BET specific surface area 290 m2/g.

3.4.10.1.2.4.3 From Chloride at pH 9–10 0.75 M MnCl2 was slowly added to 0.1 M KMnO4, and the pH was maintained at 9–10 with 1 M KOH. Properties: O:Mn molar ratio 1.93, low crystallinity [1647].

TABLE 3.1695 PZC/IEP of “δ-MnO2” Obtained from MnCl2 and KMnO4 at pH 9–10 Electrolyte

T

Method

Instrument

Salt titrationa a

pI

Reference

<1.5 if any

[1647]

Only value, data points not reported.

3.4.10.1.2.4.4 From Nitrate 100 cm3 of a solution containing 2.2 g of KMnO4 and 1.6 g of KOH was added to 900 cm3 of a solution containing 5.2 g of Mn(NO3)2 · 4H2O. The precipitate was aged for 1 h in the mother solution, and then washed. Properties: BET specific surface area 331 m2/g, XRD pattern available [2478]. TABLE 3.1696 PZC/IEP of “δ-MnO2” Obtained from Nitrate Electrolyte

T

Method

Instrument

pH0

Reference

0.1 M KNO3

25

pH

<20 min equilibration

<3 if any

[2478]

706

Surface Charging and Points of Zero Charge

3.4.10.1.2.4.5 From Nitrate at pH 7.5 100 cm3 of a solution 0.04 M in KMnO4 and 0.08 M in KOH was added dropwise with stirring to 900 cm3 of 0.0067 M Mn(NO3)2. The dispersion was adjusted to pH 7.5 and stirred for 30 min. The precipitate was washed with water. Properties: MnO1.96, BET specific surface area 296 m2/g, XRD pattern available [2479].

TABLE 3.1697 PZC/IEP of “δ-MnO2” Obtained from Nitrate at pH 7.5 Electrolyte

T

Method

0.001–0.1 M NaNO3

25

pH

Instrument

pH0

Reference

<4 if any

[2479]

3.4.10.1.2.4.6 Other Properties: Hydrous manganese dioxide [2480], d-form [2481], stoichiometry MnO1.93 [2480], MnO1.92 [2481], BET specific surface area 260 m2/g [2480], 263 m2/g [2481], TEM image available [2481].

TABLE 3.1698 PZC/IEP of “δ-MnO2” Obtained from KMnO4 and Unspecified Mn(II) Salt Electrolyte

T

0.001 M NaCl 0.0001 M NaCl

Method

Instrument

pH0

Reference

iep iep pH

Briggs flat cell Briggs electrophoresis cell

<3 if any <3 if any

[2482] [2481]

3.4.10.1.2.5 Recipe from [2486] [2483–2485] are also cited in [85], but no recipe for hexagonal birnessite could be found there. Properties: Hexagonal, XRD pattern available [85].

TABLE 3.1699 PZC/IEP of “δ-MnO2” Obtained According to Recipe from [2486] Electrolyte

T

Method

0.1 M NaNO3

25

pH

Instrument

pH0

Reference

2.9

[85]

3.4.10.1.2.6 From Mn(OH)2 and Persulfate Recipe from [1712]: 230 g of (NH4)2S2O8 were added with stirring to a precipitate obtained from a solution of 169 g of hydrous MnSO4 in 3 dm3 of water and ammonia. The dispersion was agitated for 1 h.

707

Compilation of PZCs/IEPs

TABLE 3.1700 PZC/IEP of MnO2 Obtained from Mn(OH)2 and Persulfate Description Electrolyte 2

77.7 m /g

LiNO3

T

Method

27

Salt addition

Instrument

pH0

Reference

2.1

[121]

3.4.10.1.2.7 Oxidation of MnSO4 with NaClO Recipe from [1712]: A solution of 109 g of hydrous MnSO4 in 200 cm3 of water was titrated with 1 dm3 of NaClO solution containing 80 g of active chlorine. The dispersion was agitated for 1 h. The precipitate was washed with 0.5 M H2SO4 and with water. TABLE 3.1701 PZC/IEP of MnO2 Obtained by Oxidation of MnSO4 with NaClO Description 2

60.4 m /g

Electrolyte

T

Method

LiNO3

27

Salt addition

Instrument

pH0

Reference

2

[121]

3.4.10.2 Todorokite Recipe from [2487]. Synthetic birnessite was treated by excess of 1 M MgCl2 for 12 h. The product was washed and refluxed for 8–24 h, then washed again and freeze-dried. Properties: Composition Mg0.17MnO2.1(H2O)0.88, Mn oxidation state 3.82, specific surface area 98.5 m2/g, XRD pattern available [1713].

TABLE 3.1702 PZC/IEP of Todorokite Electrolyte

T

Method pH

a

Instrument

pH0 3.8a

Reference [1713]

Obtained by fast titration; only PZC reported. Charging curve reported in [1713] (only negative charge at pH > 2.5) was obtained by back titration.

PZC of todorokite at pH1–1.8 is reported in [2488].

3.4.11 MOLYBDATES 3.4.11.1 Zirconium Molybdate 1 M solution of alkali molybdate was prepared by dissolution of MnO3 in alkali hydroxide and adjusted to pH 4. A 1 M solution of ZrO(NO3)2 was adjusted to pH 1

708

Surface Charging and Points of Zero Charge

with HNO3. The solutions were mixed. The composition of the gels is given in Table 3.1703. Properties: Thermogravimetric data available [2489].

TABLE 3.1703 PZC/IEP of Zirconium Molybdate Composition (Mass%)

Electrolyte

Mo 18.6, Zr 19.2, Li 1.9, H2O 18.7 Mo 23.3, Zr 20.2, Na 3.4, H2O 11.1 Mo 22.5, Zr 24.6, Na 3.3, K 3.4, H2O 8.3 Mo 19.6, Zr 17.7, K 4.99, H2O 15.2

0.005–0.5 M nitrate

T

Method Instrument cip

pH0 Reference 3.6 3.2 3.2

[2489]

2.9

3.4.11.2 Zirconium–Cerium Molybdate 1 M solution of alkali molybdate was prepared by dissolution of MnO3 in alkali hydroxide and adjusted to pH 4. A solution of ZrO(NO3)2 and (NH4)2Ce(NO3)6 (total metal concentration 1 M) was adjusted to pH 1 with HNO3. The solutions were mixed. The composition of the gel was Mo 23.4, Zr 19.4, Ce 4.7, Na 2.4, H2O 9.3% by mass. Properties: Thermogravimetric data available [2489].

TABLE 3.1704 PZC/IEP of Zirconium–Cerium Molybdate Electrolyte

T

Method

0.005–0.5 M NaNO3

Instrument

cip

pH0

Reference

3.8

[2489]

3.4.12 Sr1-X NbO3- d A mixture of SrCO3 and Nb2O5 was heated in air. The product was mixed with Nb powder and heated in vacuum for 2 d at 1200°C.

TABLE 3.1705 PZC/IEP of Sr1−x NbO3−d Description

Electrolyte

x = 0.05 0.2 0.3

0.4 M KCl

T

Method pH

Instrument

pH0

Reference

5.6 5.8 6.3

[1684]

709

Compilation of PZCs/IEPs

3.4.13 NITRIDES Nitrides are easily oxidized; thus, the composition of the external layer is often different from the bulk composition. In a few studies, the problem of oxidation has been taken into account; for example, the external oxidized layer was removed, and/or the experiments were carried out under controlled redox conditions. 3.4.13.1 BN from Sigma-Aldrich Properties: Hexagonal, average size 943 nm, XRD pattern, particle size distribution, SEM image available [987].

TABLE 3.1706 PZC/IEP of BN from Sigma-Aldrich Electrolyte

T

Method

Instrument

pH0

None

25

iep

Malvern NanoZS

3.3

Reference [987]

3.4.13.2 Si3N4 Compilation of PZC of Si3N4 from literature can be found in [2409,2490]. 3.4.13.2.1 Commercial 3.4.13.2.1.1 From Aldrich Properties: a-form, >99.9% pure, BET specific surface area 10.7 m2/g [2491].

TABLE 3.1707 PZC/IEP of Si3N4 from Aldrich Description

Electrolyte

T

Washed with 0.2 M 0.001, 0.01 M NaCl NaOH for 1 h

Method

Instrument

Intersection

pH0

Reference

7.1

[2491]

3.4.13.2.1.2 From Denka 3.4.13.2.1.2.1 P21B Obtained by nitridation of Si. Properties: 82% a-phase, 0.4% O, 0.2% C, 0.004% Fe, 0.009% Al, BET specific surface area 6.8 m2/g [435].

TABLE 3.1708 PZC/IEP of P21B from Denka Description Original Acid- or base-washed

Electrolyte None

T

Method

Instrument

pH0

Reference

iep

ESA 8000 Matec

8.9 8.9

[435]

710

Surface Charging and Points of Zero Charge

3.4.13.2.1.2.2 P21C3

Properties: Average size 700 nm [2492].

TABLE 3.1709 PZC/IEP of P21C3 from Denka Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

6.2

[2492]

3.4.13.2.1.2.3 9FW Properties: >90% a-form [2493], 90–93% a-phase [624], 1% O [2493], 1.7% O, 0.2% C, detailed analysis available [624], specific surface area 12 m2/g [624,2493], median size 700 nm [624], TEM image available [2493].

TABLE 3.1710 PZC/IEP of 9FW from Denka Electrolyte

T

Method

0.001–1 M KNO3 HNO3 + NH4OH a

Instrument

cip iep

pH0

Reference

8.6 9a

[624] [2493]

Matches maximum in viscosity of 20 mass% dispersion.

3.4.13.2.1.2.4 9S Properties: >90% a-form, 1.8% O, specific surface area 7 m2/g, TEM image available [2493].

TABLE 3.1711 PZC/IEP of 9S from Denka Electrolyte HNO3 + NH4OH a

T

Method iep

Instrument

pH0

Reference

3a

[2493]

20 mass% dispersion shows a broad maximum in pH range 3–7.

3.4.13.2.1.3 From Founder High Technology Ceramics, Beijing Properties: d50 = 0.98 μm, 93.1% a-phase, 2.2% O, 1.4% Si + SiO2, 1300 ppm Al, 190 ppm Ca, 7 ppm Fe [1082].

711

Compilation of PZCs/IEPs

TABLE 3.1712 PZC/IEP of Si3N4 from Founder High Technology Ceramics, Beijing Electrolyte

T

Method

Instrument

pH0

Reference

iep

ZetaPlus Brookhaven

3.8

[1082]

0.001 M KNO3

3.4.13.2.1.4 SN 502 from GTE Properties: 91.4% a-phase, 8.4% b-phase, median and average size 400 nm, 2.4% O, detailed analysis available, specific surface area 5 m2/g [624].

TABLE 3.1713 PZC/IEP of SN 502 from GTE Electrolyte

T

Method

0.001–1 M KNO3

Instrument

cip

pH0

Reference

6.5

[624]

3.4.13.2.1.5 RP-4 from Japan Fine Ceramics Center ( JFCC) Properties: BET specific surface area 9.9 m2/g, d10 = 0.23 μm, d50 = 0.61 μm, d90 = 1.7 μm [935]. TABLE 3.1714 PZC/IEP of RP-4 from Japan Fine Ceramics Center (JFCC) Electrolyte

T

Method

0.001 M NH4NO3

a

iep

Instrument Matec ESA 8000 Mutek PCD

pH0 a

7.2

Reference [935]

Different solid-to-liquid ratios.

3.4.13.2.1.6 Johnson Matthey Properties: a-form, specific surface area 3 m2/g [490]. TABLE 3.1715 PZC/IEP of Si3N4 from Johnson Matthey Dispersion

Electrolyte

Fresh 14 d aged Acid-washed Base-washed

0.01 M NaNO3

T

Method

Instrument

iep

Rank Brothers Mark II

pH0 4 <3 if any 4 <3 if any

Reference [490]

712

Surface Charging and Points of Zero Charge

3.4.13.2.1.7 From Kema Nord 3.4.13.2.1.7.1 P 95 Properties: In [386]. TABLE 3.1716 PZC/IEP of P 95 from Kema Nord Description

Dry-milled Wet-milled Dry and Wet-milled a

Electrolyte

T

Method

Instrument

0.01 M NaCl

20

0.01 M NaCl

20

iep iep iep

Zetasizer MKII, Malvern ESA Zetasizer MKII, Malvern

0.01 M NaCl

20

iep

Zetasizer MKII, Malvern

pH0

Reference

4 4.3 4.7 6.7 5

[1100] [2494] [386]a [386]

Y-modfied Si3N4 was also studied.

3.4.13.2.1.7.2 P95 M from Kema Nord Obtained by nitridation of Si Properties: 91% a-phase [435], a:b 91:9 [42,43], 0.9% O, 0.3% C, 0.05% Fe, 0.03% Al [435], detailed chemical analysis available [42,43], BET specific surface area 6.6 m2/g [435], single-point BET specific surface area 8.3 m2/g [42], specific surface area 7.8 m2/g, [43] d90 = 3500 nm, d50 = 750 nm, d10 = 150 nm [42,43]. TABLE 3.1717 PZC/IEP of P95 M from Kema Nord Description 20 min aged 28 d aged at pH 9 Original Acid- or base-washed a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaCl

20

iep

Zetasizer MKII

[42,43]

iep

ESA 8000 Matec

4.2 6.8a 5 6

None

[435]

Arbitrary interpolation.

3.4.13.2.1.7.3 Other Properties: Surface composition (ESCA) available [88]. TABLE 3.1718 PZC/IEP of Unspecified Si3N4 from Kema Nord Etched by Original HCl HF KOH a

Electrolyte

T

0.01 M KCl

Acoustosizer/Malvern/titration.

Method pH iep

Instrument Malvern Zetasizer 4 Acoustosizer

pH0 6/7/7.2 6/6.5 9/9.5/9 6.3/7

Reference a

[88]

713

Compilation of PZCs/IEPs

3.4.13.2.1.8 MI Properties: Specific surface area 92 m2/g, 54% Si, 38% N, 8% O by mass [2409,2490].

TABLE 3.1719 PZC/IEP of MI Si3N4 Description

Electrolyte

Washed Original

0.001–0.1 M KNO3

T

Method

Instrument

pH

pH0

Reference

6.8 7.6

[2409, 2490]

3.4.13.2.1.9 NSNC 300 from Norton Obtained by nitridation of Si. 90% a-phase, 1.1% O, 0.1% C, 0.02% Fe, 0.02% Al, BET specific surface area 5.9 m2/g [435].

TABLE 3.1720 PZC/IEP of NSNC 300 from Norton Electrolyte Original Acid-washed Base-washed

T

None

Method

Instrument

pH0

Reference

iep

ESA 8000 Matec

5.9 6.5 6.8

[435]

3.4.13.2.1.10 From Shenhai Nitride Ceramics, Nantong Properties: Specific surface area 11 m2/g, mean particle diameter 420 nm, 99.5% pure [410].

TABLE 3.1721 PZC/IEP of Si3N4 from Shenhai Electrolyte 0.001 M KCl a

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

4.6a

[410]

Viscosity of 30 vol.% dispersion decreases as pH increases (no maximum at IEP).

3.4.13.2.1.11 From Starck 3.4.13.2.1.11.1 LC 10 Obtained by nitridation of Si. Properties: a:b-form 94:6 [42], 95% a-phase [435], detailed chemical analysis available [42], 1.9% O, 0.2% C, 0.01% Fe, 0.03% Al [435], BET specific surface area 12.6 m2/g [435], single-point BET specific surface area 13.5 m2/g [42], d10 = 230 nm, d50 = 720 nm, d90 = 2200 nm [42].

714

Surface Charging and Points of Zero Charge

TABLE 3.1722 PZC/IEP of LC 10 from Starck Description As received 1 month aged Original Acid-washed Base-washed

Electrolyte

T

Method

0.001–0.1 M NaCl None

0.01 M NaCl

20

Instrument

iep iep

ESA Malvern Zetasizer II

iep

ESA 8000 Matec

iep

Zetasizer MKII, Malvern

pH0

Reference

5.5 6.5–8 6.8 7.5 7.5 7.5 8

[2494] [42] [435]

[1100]

3.4.13.2.1.11.2 LC 10-N Properties: 95% a-form, BET specific surface area 13.4 m2/g, d10 = 210 nm, d50 = 420 nm, d90 = 870 nm, [476].

TABLE 3.1723 PZC/IEP of LC 10-N from Starck Electrolyte

T

Method

Instrument

pH0

Reference

iep

ESA

7.1

[476]

HCl + NaOH

3.4.13.2.1.11.3 LC 12 Properties: 0.2% C, 2% O, metals 0.05% [438], 1.3% O [2495] a-form [438], a/b-form ratio >18 [2495], BET specific surface area 17 m2/g [438], specific surface area 20.3 m2/g [2495], mean grain size 450 nm [438].

TABLE 3.1724 PZC/IEP of LC 12 from Starck Description

Electrolyte KCl

Original Washed

HCl + NaOH 0.01–0.045 M KCl

a b

T

Method

Instrument

pH0

Reference

iep iep

Electrophoresis Malvern Zetasizer II

[2496]a [2495]b

iep iep

Pen Kem 7000 ESA

4.4–8 4.5 3.2 7.4 8.3

[438] [2494]

Only value, data points not reported. Arbitrary interpolation.

3.4.13.2.1.11.4 M11 Properties: 93.3% a-form [2497], 94.5% a-form [2498], 1.3% O [2497], 1% O, 0.2% C by mass, Fe 23 ppm, Al 527 ppm, Ca 37 ppm [2498],

715

Compilation of PZCs/IEPs

BET specific surface area 13.3 m2/g [834], 11.2 m2/g [2497], 12.8 m2/g [2498], average particle size 630 nm [2497], 300 nm [834], d10 = 340 nm, d50 = 740 nm, d90 = 1230 nm [2498].

TABLE 3.1725 PZC/IEP of M11 from Starck Description

Electrolyte

As received

0.01 M NaCl 0.001 M KNO3

T

Method

Instrument

pH0

Reference

iep iep

Malvern Zetamaster Matec ESA 8000

4.4 4.8

[2498] [834]

3.4.13.2.1.12 From Toshiba Properties: 99% a-phase, 1.9% O, 0.9% C, detailed analysis available, specific surface area 11 m2/g, median size 4 μm, average size 800 nm [624].

TABLE 3.1726 PZC/IEP of Si3N4 from Toshiba Electrolyte

T

0.001–1 M KNO3 a

Method

Instrument

pH0

Reference

Merge/iep

MBS 800 Matec

3.2a/<2 if any

[624]

Reported as CIP in figure caption. In fact, there is no clear CIP.

3.4.13.2.1.13 From Toyo Soda Properties: Specific surface area 11 m2/g [2413].

TABLE 3.1727 PZC/IEP of Si3N4 from Toyo Soda Description

Electrolyte

Well-cleaned

0.1, 1 M KNO3

a

T

Method Merge

Instrument

pH0

Reference

3a

[2413]

No data points at pH < 3.

3.4.13.2.1.14 From UBE See also Section 3.4.13.2.3. 3.4.13.2.1.14.1 E03 (or E3) Properties: BET specific surface area 3.4 m2/g [2499], specific surface area 3.6 m2/g, TEM image available [1123], mean diameter 600 nm [2499].

716

Surface Charging and Points of Zero Charge

TABLE 3.1728 PZC/IEP of E03 (or E3) from UBE Description

Electrolyte

As received

0.01 M KNO3

T

Method

Instrument

pH0

Reference

iep iep

Pen Kem 3000 Zeta-Meter 3.0

4.8 5.4

[1123] [2499]

3.4.13.2.1.14.2 E-10 from UBE, Yamaguchi Obtained by decomposition of diimide. Properties: a-form [357,2500], a:b 97:3 [42,43], 96.4% a-phase, 3.6% b phase [624], >95% a-phase [322,435], purity >97% [2417], 1.2% O [435], 1.3% O [322], detailed chemical analysis available [42,43], 38.6% N, 1.4% O [624], BET specific surface area 10.1 m2/g [322,786,2501], 10.7 m2/g [435], 10.6 m2/g [2502], singlepoint BET specific surface area 10 m2/g [2500], 9.8 m2/g [1100], 10.3 m2/g [42], specific surface area 8.3 m2/g [671,2503], 9.7 m2/g [43], 10.4 m2/g [2504], 13 m2/g [624,2413], mean particle diameter 0.4 mm [322], 0.5 mm [2504], 0.6 mm [2500], particle size 500 nm [357], 100–300 nm [2417], average particle size 0.4 mm [786], minimum (?) particle diameter 0.4 mm [2501], median size 1.6 mm [624], mean particle size 300 nm [2502], d90 = 840 nm, d50 = 500 nm, d10 = 240 nm [42,43]. TABLE 3.1729 PZC/IEP of E-10 from UBE, Yamaguchi Description

Electrolyte

Well-cleaned

0.1 M KNO3 1 M KNO3 0.01 M KCl

Original Washed Washed Evacuated Evacuatedd

20 min aged 35 d aged at pH 9

HCl 0.001, 0.1 M NaCl 0.001–0.1 M NaCl

None

Method pH

25

0.001–1 M KNO3

0.01 M NaCl Original Acid-washed Base-washed

T

iep Mass titration cip/iep

25

iep iep

20

iepe

20

iep iep

Instrument

pH0

3 <3 if anya 4c Short equilibration 4.2 Equilibration for >20 d 8.2b MBS 800 Matec 5.5/6.4 6.2 7 6.8 6.2 Acoustosizer 5.8 ESA 6.1 (Fig. 8) 6.9 (Fig.7) Zetasizer MKII 6.1 7 Zetasizer MKII, Malvern ESA 8000 Matec

Reference [2413] [2417] [671] [624]

[2504] [2494] [42,43]

6.2

[1100]

6.2 7.2 7.5

[435]

continued

717

Compilation of PZCs/IEPs

TABLE 3.1729 (continued) Description

Electrolyte

T

Method

0.01 M NaNO3 0.0025–0.05 M 20 NaNO3, 0.01 M KNO3, NH4NO3, KI, KBr, KCl HNO3 + KOH 0.001 M KNO3

Heated at (°C): 260 350 450 a

b c d e

f

Room

0.01 M NaCl

20

pH0

Reference

iep iep

Acoustosizer Matec ESA 8000

6.3 6.4

[2501] [322]

iep iep

Matec ESA 8000 Pen Kem 3000 Matec ESA 8000 Electrophoresis

6.4 6.4 6.5 6.5 7 6.5

[2500] [357]

6.7

[2502] [43]

iep Titration iep

KNO3 0.001 M NaNO3

Instrument

iep iep

ESA 8000 Matec ESA 8000 Zetasizer MKII

[2505]f [786]

7.5 6.8 6.2

No intersection point. Charging curve for 0.001 M KNO3 is also reported. [2413] reports also results of titration of as-received powder, and of powders cleaned by different methods. PZC at pH 5.5–7 is mentioned in text without clear statement how these results were obtained. Confirmed in [2503] by a study of particle attachment. Arbitrary interpolation. 6 mV at pH 3 and −10 mV at pH 5. Different washing procedures and combination of washing and evacuation. [42] reports also results of titration at two ionic strengths. Titration curves with supporting electrolyte used as blank merge at pH 7.5. Titration curves with supernatant used as blank intersect at pH 10.2. Only value, no data points.

3.4.13.2.2 Synthetic 3.4.13.2.2.1 From Silica and Sucrose Silica sol and sucrose, C:SiO2 mole ratio 3.5, were heated at 1450°C in nitrogen (20 dm3/h). Properties: a- and b-form (80:20) specific surface area 104 m2/g [2409,2490]. TABLE 3.1730 PZC/IEP of Si3N4 Obtained from Silica and Sucrose Description

Electrolyte

Washed Original

0.001–0.1 M KNO3

T

Method pH

Instrument

pH0

Reference

6.5 5.7

[2409,2490]

718

Surface Charging and Points of Zero Charge

3.4.13.2.2.2 Obtained in Low-Temperature Plasma Properties: Mixture of amorphous material, a- and b-form, 2% elementary Si, specific surface area 60 m2/g, average diameter 30 nm [2506].

TABLE 3.1731 PZC/IEP of Si3N4 Obtained in Low Temperature Plasma Electrolyte

T

NaNO3 a

Method

Instrument

pH0

Reference

iep

Electrophoresis

3.5a

[2506]

z potential = 0 also at pH 1.5; charging curves are also reported, but the data points are only available for pH < 4 and > 8.

3.4.13.2.3 Origin Unknown

TABLE 3.1732 PZC/IEP of Si3N4 from Unspecified Sources Description

Electrolyte

T

Method

pH0

Reference

b, from UBE

iep

Zeta-Meter

3.3

[2507]

Electrophoresis

b

iepa iepa

5.9 6

[2508] [2509]

6.2 6.5 4.2 6.2 7.5

[681] [2510] [2159]b [2511] [2159]b

0.001 M KNO3

AFM iep iep iepa iepa

Pure Oxidized

a b

Instrument

Only value, data points not reported. Same original reference but different IEP.

3.4.13.3 Si2N2O From Chalmers University of Technology, Sweden.

TABLE 3.1733 PZC/IEP of Si2N2O Description 1 or 24 d aged at pH 9

Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaCl

20

iep

Zetasizer MKII

<2 if any

[43]

719

Compilation of PZCs/IEPs

3.4.13.4

TiN

3.4.13.4.1 From Sanhe Yanjiao Xinyu Properties: Average particle size 2.3 μm, specific surface area 1.6 m2/g [420].

TABLE 3.1734 PZC/IEP of TiN from Sanhe Yanjiao Xinyu Electrolyte

T

0.001 M KCl

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

2.2

[420]

3.4.13.4.2 From H.C. Starck Properties: Detailed analysis available, 50% of particles by mass have size <1.2 μm [2512,2513].

TABLE 3.1735 PZC/IEP of TiN from H.C. Starck Electrolyte

T

0.01 M NaCl

a

b

Method iep iepb

Instrument

pH0 a

Zeta-Meter 3.0

4 4

Reference [2512,2513] [2514]

Roughly matches the viscosity maximum of 10 vol.% dispersion at a shear rate of 100 s−1. Only value, data points not reported.

3.4.13.4.3 From Tioxide Properties: Contains 7.1% O and 0.5% Cl by mass, specific surface area 36 m2/g, mean grain size 15–30 nm, XRD pattern, TEM image available [2515].

TABLE 3.1736 PZC/IEP of TiN from Tioxide Electrolyte

T 25

a

Method iep

Probably a typographical error.

Instrument a

PCD 02 Malvern

pH0

Reference

3.7

[2515]

720

Surface Charging and Points of Zero Charge

3.4.14 NIOBATES 3.4.14.1 (Na,Ca,U)2(Nb,Ti,Ta)2O6(OH,F,O) Koppite, natural pyrochlore from Schelingen, Kaiserstuhl.

TABLE 3.1737 PZC/IEP of Koppite Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

3

[104]

NaOH + HClO4

3.4.14.2 PbMg1/3Nb2/3O3 from Praxair Specialty Ceramics Properties: 99.9% pure (manufacturer), BET specific surface area 1.2 m2/g, specific density 7967 kg/m3 [147]. TABLE 3.1738 PZC/IEP of PbMg1/3Nb2/3O3 Electrolyte

T

Method iep

a

Instrument Malvern 3000 HS ESA 9800 Matec

pH0

Reference

4.4–10a

[147]

IEP shifts to high pH as solid-to-liquid ratio increases.

3.4.15 PHOSPHATES AND APATITES Phosphates usually occur as nonstoichiometic compounds, and their composition often deviates from specific chemical formulas reported in scientific papers. 3.4.15.1 3.4.15.1.1

AlPO4 Adju-Phos from Superfos Biosector

TABLE 3.1739 PZC/IEP of Adju-Phos from Superfos Biosector Electrolyte

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440

5

[1169]

3.4.15.1.2 Synthetic 3.4.15.1.2.1 From AlCl3 250 cm3 of 0.1 M AlCl3 was mixed with equal volume of 1 M NaH2PO4. The mixture was titrated with 500 cm3 of 1 M NaOH at 5 cm3/min. Properties: Amorphous, TEM image available [329].

721

Compilation of PZCs/IEPs

TABLE 3.1740 PZC/IEP of AIPO4 Obtained from Chloride Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

5.6

[329]

0.001 M NaCl

3.4.15.1.2.2 From Al(NO3)3 0.5 M Al(NO3)3 was stirred at 40°C for 1 h. Then 0.5 M Na3PO4 was added dropwise until the pH reached 5. The mixture was dialyzed for 10 d, filtered and washed with water for the next 6 d. The precipitate was then dried at 105°C and ground. A portion of the powder was calcined for 1 d at 400°C. Properties: BET specific surface area 95.2 m2/g (uncalcined), 127.5 m2/g (calcined) [1097]. TABLE 3.1741 PZC/IEP of AlPO4 Obtained from Nitrate Description

Electrolyte

Uncalcined Calcined

T

Method

30

Salt addition

Instrument

pH0

Reference

3.5 5.1

[1097]

3.4.15.1.2.3 Other TABLE 3.1742 PZC/IEP of Unspecified Precipitated AlPO4 Electrolyte

T

Method

Instrument

Titrationa a

pH0

Reference

4

[810]

pH0

Reference

4

[810]

Only value, data points not reported.

3.4.15.1.3

Natural Variscite

TABLE 3.1743 PZC/IEP of Natural Variscite Electrolyte

T

Method a

Titration a

Only value, data points not reported.

Instrument

722

Surface Charging and Points of Zero Charge

3.4.15.2 Synthetic Ba-Apatites 3.4.15.2.1 From Ba(OH)2 and H3PO4 Ba(OH)2 was titrated with H3PO4 at 1 cm3/min in a CO2-free atmosphere at a final Ba:P ratio of 1.67. The product was aged at 100°C for 2 d, washed with water, and dried at 70°C. Properties: Ba:P ratio 1.59, BET specific surface area 34.3 m2/g, IR spectrum, XRD pattern available [2516].

TABLE 3.1744 PZC/IEP of Ba-Apatite Obtained from Ba(OH)2 and H3PO4 Electrolyte

T

Method pH

a

Instrument

a

pH0

Reference

6.3

[2516]

Only value, data points not reported.

3.4.15.2.2 From BaCl2 and K2HPO4 Stoichiometric amounts of KOH, BaCl2 and K2HPO4 were added to a large volume of boiling water. Properties: Mixture of chloroapatite (78%) and hydroxyapatite, specific surface area 14.5 m2/g, particle length 500 nm, radius 20 nm [20].

TABLE 3.1745 PZC/IEP of Ba-Apatite Obtained from BaCl2 and K2HPO4 Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

25

iep

Zeta-Meter

>11a

[20]

a

Value reported in [20] was obtained by extrapolation.

3.4.15.3 Calcium Phosphates 3.4.15.3.1

Precipitated Ca3(PO4)2

TABLE 3.1746 PZC/IEP of Unspecified Precipitated Ca3(PO4)2 Electrolyte

T

Method

Instrument

pH0

Reference

NaCl + CaCl2

25

iep

Rank Brothers, Mark II

pCa 3.3

[2443]

723

Compilation of PZCs/IEPs

3.4.15.3.2 Ca5(PO4)2.88(OH)1.36

TABLE 3.1747 PZC/IEP of Unspecified Ca5(PO4)2.88(OH)1.36 Electrolyte

T

HCl + NaOH a

Method

Instrument

pH0

Reference

iep

Electrophoresis

7.6

[2517]a

Also aluminum and iron basic phosphates.

3.4.15.4 Hydroxyapatite PZCs of apatites are reviewed in [653] and [2441] (also fluoroapatites). 3.4.15.4.1 Commercial 3.4.15.4.1.1 From Alfa Aesar Properties: 38.3% Ca, 16.8% P, 0.3% Mg, 0.3% Si, 1 ppm Cd, 4 ppm Cu, 5 ppm Zn, 1 ppm Pb, BET specific surface area 50 m2/g, SEM image, FTIR spectrum available [2518].

TABLE 3.1748 PZC/IEP of Apatite from Alfa Aesar Electrolyte

T

Method

Instrument

a

pH a

pH0

Reference

7.4

[2518]

Only value, data points not reported.

3.4.15.4.1.2 Apafill from Center of Biomaterials, University of Havana, Two Samples Properties: FTIR spectrum available [349]; see also Table 3.1749.

TABLE 3.1749 PZC/IEP of Apafill from Center of Biomaterials, University of Havana BET Specific Ca/P Surface Area (mol/mol) (m2/g) 1.6 1.81

1.7 4.3

Electrolyte 0.01 M KNO3

T

Method

Instrument

pH0

Reference

iep

Rank Brothers

<5 if any <5 if any

[349]

724

Surface Charging and Points of Zero Charge

3.4.15.4.1.3 From Merck Properties: 63.5% Ca, 35.9% P (reported in [2519], probably these figures refer to oxides), single-point BET specific surface area 52 m2/g, particle size distribution available [2519]. TABLE 3.1750 PZC/IEP of Apatite from Merck Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

<5 if any

[2519]

3.4.15.4.1.4 From Sigma TABLE 3.1751 PZC/IEP of Apatite from Sigma Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Nano ZS

2.9

[1031]

KNO3

3.4.15.4.1.5 From Taihei

Properties: XRD pattern available [2520].

TABLE 3.1752 PZC/IEP of Apatite from Taihei Electrolyte

T

Method

Instrument

pH0

Reference

pH

1 d equilibration

8.4a

[2520]

0.005 M KNO3 a

[2520] reports also PZC (the same method and conditions) of two synthetic hydroxyapatites at pH 7.2 and 9.8.

3.4.15.4.1.6 From Urodelia, 99% Pure Properties: (not sintered/sintered at 600°C/sintered at 1180°C) mean size 3.2/2.9/3 μm, specific surface area 38/26.7/6.1 m2/g, SEM image available [2521]. TABLE 3.1753 PZC/IEP of Apatite from Urodelia Sintering Temperature (°C) None 600 1180 a

Electrolyte

T

NaCl

Only values, data points not reported.

Method

Instrument

pH0

Reference

iepa

Sephy

4.4 4.8 5.2

[2521]

725

Compilation of PZCs/IEPs

3.4.15.4.2 Synthetic 3.4.15.4.2.1 From Ca(OH)2 and H3PO4 3.4.15.4.2.1.1 Titration at 95°C to pH 7 0.5 M Ca(OH)2 was slowly titrated with 0.5 M H3PO4 in a nitrogen atmosphere at 95°C to pH 7. The product was aged at 95°C for 1 d, washed with water, and dried at 105°C. Properties: Ca:P molar ratio 1.6 [2522], BET specific surface area 21 m2/g [653], 67 m2/g [2522], XRD pattern available [653,2522], SEM image available [653].

TABLE 3.1754 PZC/IEP of Apatite Obtained by Titration of Ca(OH)2 with H3PO4 at 95°C to pH 7 Electrolyte 0.1 M KNO3 0.1 M KNO3 a

T

Method

25

pH pH

Instrument 1 d equilibration

pH0

Reference

4.1–6.1 6.1

a

[653] [2522]

Depends on solid-to-liquid ratio.

3.4.15.4.2.1.2 Titration to Final Ca:P Ratio of 1.67 Ca(OH)2 was titrated with H3PO4 at 1 cm3/min in a CO2-free atmosphere at final Ca:P ratio of 1.67. The product was aged at 100°C for 2 d, washed with water, and dried at 70°C. Properties: Ca:P ratio 1.65, BET specific surface area 76.6 m2/g, IR spectrum, XRD pattern available [2516].

TABLE 3.1755 PZC/IEP of Apatite Obtained by Titration of Ca(OH)2 with H3PO4 to Final Ca:P Ratio of 1.67 Electrolyte

T

Method pHa

a

Instrument

pH0

Reference

6.8

[2516]

Only value, data points not reported.

3.4.15.4.2.1.3 Precipitated at Room Temperature A solution of 0.405 mol of Ca(OH)2 in 20 dm3 of CO2-free water was stirred for 1 d. 0.226 mol of H3PO4 was added, and the mixture was stirred for 1 d at room temperature and then aged for 2 d at 100°C. The precipitate was washed with water, and dried for 1 d at 70°C. Properties: Ca/P ratio 1.64, specific surface area 93.1 m2/g [2523].

726

Surface Charging and Points of Zero Charge

TABLE 3.1756 PZC/IEP of Apatite Precipitated from Ca(OH)2 and H3PO4 at Room Temperature Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

<5 if any

[2523]

3.4.15.4.2.2 From Ca(NO3)2 and (NH4)2HPO4 3.4.15.4.2.2.1 Obtained at 70°C Recipe from [2524]: 1 dm3 of 0.5 M Ca(NO3)2 and 1 dm3 of 0.3 M (NH4)2HPO4 were added simultaneously to 150 cm3 of CO2-free water at 70°C over 2 h. The pH was maintained at 10 with NH3. The precipitate was water-washed and refluxed at 70°C. Properties: Primary crystallites 50–150 nm, BET specific surface area 23 m2/g [618,2524].

TABLE 3.1757 PZC/IEP of Apatite Precipitated from Ca(NO3)2 and (NH4)2HPO4 at 70°C Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.03 M NaNO3

25

cip iep Mass titration

Malvern Zetasizer 5000

6.5 6.2 6.5

[618]

3.4.15.4.2.2.2 Obtained at 80°C Ca(NO3)2, (NH4)2HPO4, and ammonia solutions were mixed (final pH 10) and stirred at 80°C for 3h. The precipitate was water-washed and freeze-dried. Properties: Three specimens: Ca:P ratios 1.58, 1.65, and 1.5, BET specific surface area 123, 38, and 80 m2/g [271].

TABLE 3.1758 PZC/IEP of Apatite Precipitated from Ca(NO3)2 and (NH4)2HPO4 at 80°C Electrolyte

T

Method

0.001 M KNO3

20

iep

a b

Instrument Pen Kem Laser Zee Meter 500

Extrapolated. IEP of synthetic fluoroapatite at pH 6.2 is also reported.

pH0

Reference

7.2 6.9 5.5a

[271]b

727

Compilation of PZCs/IEPs

3.4.15.4.2.2.3 Boiled for 10 minutes 0.5 M Ca(NO3)2 was titrated with 0.25 M (NH4)2HPO4 at pH 12 (adjusted with ammonia) to a Ca/P ratio of 1.67 with stirring. The dispersion was boiled for 10 min. and aged for 1 d. The precipitate was washed, and calcined at 200–400°C. Properties: BET specific surface area 158.4 m2/g, XRD pattern available [2525]. TABLE 3.1759 PZC/IEP of Apatite Precipitated from Ca(OH)2 and (NH4)2HPO4 and Boiled for 10 minutes Electrolyte

T

Method

Instrument

pH0

Reference

iep pH

Malvern Zetasizer 3000

<5 if any <8 if any

[2525]

0.001–0.1 M NaClO4

3.4.15.4.2.3 From CaHPO4 and Ca(OH)2 Solutions of 0.5162 g of CaHPO4· 2H2O in 40 cm3 of water and of 0.1482 g of Ca(OH)2 in 40 cm3 of water were mixed at pH 9 (adjusted with acetic acid). The dispersion was aged for 1 d at 120°C. The precipitate was washed, and dried at 60–100°C. Properties: Ca:P ratio 1.67, BET specific surface area 16.2 m2/g, XRD pattern available [2525]. TABLE 3.1760 PZC/IEP of Apatite Precipitated from Ca(OH)2 and CaHPO4 Electrolyte

T

Method

Instrument

pH0

Reference

iep pH

Malvern Zetasizer 3000

<5 if any <7 if any

[2525]

0.001–0.1 M NaClO4

3.4.15.4.2.4 From Ca(OH)2 and Ca(H2PO4)2 Solutions of CO2-free Ca(OH)2 and Ca(H2PO4)2 were added to water at 100°C under a nitrogen atmosphere. The precipitate was washed with hot CO2-free water or with acetone, and dried at 105°C. Different flow rates and volumes of water produce different particle sizes. Properties: Detailed analysis (Ca, P, F, Na, CO3, Cl, As, Mg, K, Fe, Zn, S) available, TEM image available; for specific surface area, see Table 3.1761 [617]. TABLE 3.1761 PZC/IEP of Hydroxyapatite Obtained from Ca(OH)2 and Ca(H2PO4)2 Specific Surface Area (m2/g) 9.1 26.6 26.6

Electrolyte

T

Method

Instrument pH0 Reference

0.01–1 M KCl, (CH3)4NCl 0.01, 0.1 M KClO4 0.01–1 M NaCl

20

cip, intersection

8.5 8.5 7.6

[617]

728

Surface Charging and Points of Zero Charge

3.4.15.4.2.5 Grown on Hydroxyapatite Seeds Stoichiometric amounts of Ca(NO3)2 and ammonium phosphate solutions were added to a boiling dispersion containing hydroxyapatite as seeds. The pH was maintained at 10 with gaseous NH3. The precipitate was water-washed and freeze-dried. Properties: Structure confirmed by XRD, Ca/P ratio 1.61, 0.12% SiO2, krypton BET specific surface area 11.9 m2/g, specific density 2960 kg/m3 [2458].

TABLE 3.1762 PZC/IEP of Apatite Grown on Hydroxyapatite Seeds Electrolyte

T

0.002 M NaNO3 a

Method

Instrument

pH0

Reference

iep

Zeta-Meter

6.5a

[2458]

Arbitrary interpolation.

3.4.15.4.2.6 Hydrothermal Reaction of Urea, Ca-EDTA, and Phosphate Recipe from [2527–2529]. Properties: BET specific surface area 67 m2/g [2530].

TABLE 3.1763 PZC/IEP of Apatite Obtained by Hydrothermal Reaction of Urea, Ca-EDTA and Phosphate Electrolyte

T

0.001–0.1 M KCl

Method

Instrument

pH

pH0

Reference

6.8

[2530]

3.4.15.4.2.7 Precipitation from Ammoniacal Solution at pH 12 at Room Temperature Properties: Specific surface area 57.7 m2/g, particle length 100 nm, radius 10 nm [20].

TABLE 3.1764 PZC/IEP of Apatite Precipitated at pH 12 at Room Temperature Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

25

iep

Zeta-Meter

7

[20]

729

Compilation of PZCs/IEPs

3.4.15.4.2.8 Recipes from [2531–2534] Four synthetic hydroxyapatites. Properties: FTIR spectra, SEM images available [349]; see also Table 3.1765.

TABLE 3.1765 PZC/IEP of Apatites Obtained According to Recipes from [2531–2534] Ca/P (mol/mol)

BET Specific Surface Area (m2/g)

1.82 1.81 1.7 1.82

16.5 0.1 23.5 143.4

Electrolyte

T

Method iep

0.01 M KNO3

Instrument

pH0

Reference

Rank Brothers <5 if any <5 if any <5 if any 9

[349]

3.4.15.4.2.9 Recipe from [2436,2437] K2HPO4 + KOH solution was mixed with aqueous Ca(NO3)2 under nitrogen and boiled. Properties: BET specific surface area 30.3 m2/g [2438].

TABLE 3.1766 PZC/IEP of Apatites Obtained According to Recipe from [2436,2437] Electrolyte

T

0, 0.002 M KNO3

Method

Instrument

pH0

Reference

iep

Laser Zee Meter from Pen Kem Zeta-Meter

7.4

[2438]

3.4.15.4.2.10 Other

TABLE 3.1767 PZC/IEP of Other Synthetic Apatites Electrolyte

T

Method

Instrument

pH0

Reference

0–0.01 M KNO3 NaCl

23

iep titrationb

Zeta-Meter

6.8 7.6

[2526]a [2536]

a b

Recipe in Reference 1 in [2526], properties in [2526]. Only value, data points not reported.

Reference [2535] reports z potentials obtained at pH 7.4 in the presence of a pH buffer. A positive z potential (probably at natural pH) is reported in [2542].

730

Surface Charging and Points of Zero Charge

3.4.15.4.3 Natural TABLE 3.1768 PZC/IEP of Natural Apatites Source

Electrolyte

T

Method Instrument

Wangji, China, BET specific 0.001 M KNO3 25 ± 2 surface area 2.1 m2/g NaOH + HClO4 Oedegardena Durango a

pH0

Reference

iep

MRK

3

[2439]

iep iep

Zeta-Meter Zeta-Meter

3.2 6.4

[104] [2440]

Two other apatites, from Durango and from Risör, showed multiple IEPs.

3.4.15.4.4

Origin Unknown

TABLE 3.1769 PZC/IEP of Unspecified Apatites Electrolyte

T

Method

Instrument

a

iep a

pH0

Reference

<2

[2537]

Only value, data points not reported.

3.4.15.5 Chloroapatites

TABLE 3.1770 PZC/IEP of Natural Chloroapatites Description

Electrolyte

T

From Madagascar, 0–0.01 M KCl detailed analysis available From Broken Hill, Australiaa 0.002 M NaClO4 25 a

Method

Instrument

pH0 Reference

iep

Streaming potential

4.1

iep

Abramson cell 6.7

[2441]

[489]

Crushed, ground, deslimed in tap water, run through magnetic separator, washed in 0.5 M HCl, and in cold and hot water, crystalline, analysis (15 elements) available.

3.4.15.6 Fluoroapatite 3.4.15.6.1 From Gregory, Bottley, and Lloyd Properties: 2–3% of impurities, 39.95% Ca, 17.63% P, 2.7% F [2538], 97% pure, BET specific surface area, 1.5 m2/g [957], 9.3 m2/g (<5 μm fraction) [2538].

731

Compilation of PZCs/IEPs

TABLE 3.1771 PZC/IEP of Fluoroapatite from Gregory, Bottley & Lloyd Description Ground pure crystals of Canadian fluoroapatite a b

Electrolyte 0.1 M NaCl 0.1 M NaCl

T

Method

Instrument

pH0 Reference

25

iep pH

Laser Zee Meter 501 3 d equilibration before titration

5.2a 8.1b

[957] [2538]

Arbitrary interpolation. PZC at pH 8.1 in nitrogen atmosphere, at pH 7.1 in air.

3.4.15.6.2 Synthetic 3.4.15.6.2.1 From KF and Ca8H2(PO4)6 Solutions of CO2-free KF and Ca8H2(PO4)6 were mixed at 40°C for 21 d. The precipitate was washed with hot CO2-free water, and dried at 105°C. Properties: Detailed analysis (Ca, P, F, Na, CO3, Cl, As, Mg, K, Fe, Zn, S) available, specific surface area 35.3 m2/g [617]. TABLE 3.1772 PZC/IEP of Fluoroapatite Obtained from KF and Ca8H2(PO4)6 Electrolyte

T

Method

0.01–1 M KCl, 0.01, 0.1 M KClO4

20

cip, intersection

Instrument

pH0

Reference

6.8

[617]

3.4.15.6.2.2 From Ca(NO3)2, (NH4)2HPO4, and NH4F Recipe from [2539]: A solution of 94.47 g of Ca(NO3)2 · 4H2O in 1 dm3 of water was added dropwise with stirring to a boiling solution of 31.69 g of (NH4)2HPO4 and 5.93 g of NH4F in 1 dm3 of water. The pH was adjusted to 9 with 25% NH3. The product was aged for 1 h at 80°C with stirring, then washed and dried at room temperature and stored in a desiccator. Properties: BET specific surface area 17.7 m2/g, XRD pattern, SEM image, FTIR spectrum available [2540].

TABLE 3.1773 PZC/IEP of Fluoroapatite Obtained from Ca(NO3)2, (NH4)2HPO4, and NH4F Electrolyte

T

Method

Instrument

pH0

Reference

0.1 M NaNO3

25

pH iep

Malvern Zetasizer 4

5.7 <6 if any

[2540]

732

Surface Charging and Points of Zero Charge

3.4.15.6.2.3 From Ca(NO3)2, KF and K2HPO4 Stoichiometric amounts of KF, Ca(NO3)2, and K2HPO4 were added to a large volume of boiling water. Properties: Specific surface area 6.7 m2/g, particle length 1 μm, radius 50 nm [20].

TABLE 3.1774 PZC/IEP of Fluoroapatite Obtained from Ca(NO3)2, KF, and K2HPO4 Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

25

iep

Zeta-Meter

6.5

[20]

3.4.15.6.3 Natural TABLE 3.1775 PZC/IEP of Natural Fluoroapatites Origin Paraiba, Brasila

Electrolyte

T

Method

0.01–0.5 M NaCl, KCl 0–0.01 M KCl

25

iep pH iep

Mera el Arech, Moroccob Ayata, Tunisiab Djebel Onk, Algeriab Durango, Mexico, 0.002 M crystallinec NaClO4 Christmas Island, amorphousc a b

c

25

iep

Instrument

pH0

Zetaphoremeter <1 if any IV 7.7 Streaming 4.7 potential 4.9 3.9 Abramson cell 5.5

Reference [2541] [2441]

[489]

3.5

Elemental analysis available; BET specific surface area 3.5 m2/g. Detailed analysis available; referred to as phosphates and carbonate–apatites in the original publication. Crushed, ground, deslimed in tap water, run through magnetic separator, washed in 0.5 M HCl, and in cold and hot water. Analysis (15 elements) available.

3.4.15.6.4 Origin Unknown TABLE 3.1776 PZC/IEP of Fluoroapatites from Unknown Sources Description Acid-washed to remove calcite Acid-washed to remove calcite

Electrolyte

T

Method

0.01 M KNO3

iep

0.0001–0.01 M KNO3

iep

Instrument

pH0

Streaming potential 4 (fresh) 6 (14 d aged) Streaming potential 5.6

Reference [24] [2543]

733

Compilation of PZCs/IEPs

3.4.15.7

Carbonate Fluoroapatite

3.4.15.7.1 Synthetic Ca10(PO4)5CO3F2.72(OH)0.28 Recipe from [2544,2545]. 1 M Ca(NO3)2 and a solution 0.5 M in K2HPO4, 0.1 M in KHCO3, and 0.3 M in KF were slowly added to 0.1 M KNO3 at 70ºC. The precipitate was aged for 5 h in mother liquor, washed and dried at room temperature. Properties: XRD pattern, IR spectrum available, BET specific surface area 8.8 m2/g [505].

TABLE 3.1777 PZC/IEP of Synthetic Ca10(PO4)5CO3F2.72(OH)0.28 Electrolyte

T

Method

Instrument

pH0

Reference

0.01–0.5 M KNO3

25

iep Intersection

Delsa 440

6.4

[505]

3.4.15.7.2 Natural Francolite Ca10(PO4)4.68(CO3)1.32F1.87(OH)1.45 from Oulad Abdoun, Morocco Properties: Detailed chemical analysis available, BET specific surface area 13.9 m2/g [505].

TABLE 3.1778 PZC/IEP of Natural Francolite Electrolyte

T

Method

Instrument

pH0

Reference

0.01–0.5 M KNO3

25

iep Intersection

Delsa 440

4.8 8.4

[505]

3.4.15.7.3 Other

TABLE 3.1779 PZC/IEP of Francolites from Unidentified Sources Electrolyte KCl

T

Method

Instrument

pH0

Reference

iep

Streaming potential

2.8–4.9

[2546]

3.4.15.8 CePO4 A compilation [2547] reports PZCs, mostly published in conference proceedings, which are very scattered (pH 1.1–9). A few results for YPO4 are also given.

734

Surface Charging and Points of Zero Charge

3.4.15.8.1 Natural Monacite

TABLE 3.1780 PZC/IEP of Monacite Origin

Electrolyte

T

Method

Australia Iveland, Norway NaOH + HClO4 a

iep iep

Instrument Malvern Zetasizer II c Zeta-Meter

pH0

Reference

a

5.3 9.5

[2554] [104]

Arbitrary interpolation.

3.4.15.9 Co(II) Phosphate A solution 0.005 M in CoSO4, 0.005 M in NaH2PO4, 0.01 M in SDS and 1 M in urea was heated at 80°C for 3 h. Properties: Spherical particles, radius 190 nm [31]. Reference [31] reports an extensive study by electrophoresis and an electroacoustic method at pH 7–10. The particles were negatively charged, but when sufficient amounts of Co(ii) and then NaOH were added, an IEP at pH ⬇ 9.8 was observed, probably owing to formation of hydroxide. 3.4.15.10 CrPO4 Na3PO4 was added to Cr(NO3)3 solution dropwise at 40°C until the pH reached 5. The precipitate was washed for 6 d, and dried at 105°C for 2 d. Properties: Specific surface area 48 m2/g, SEM image available [2548].

TABLE 3.1781 PZC/IEP of CrPO4 Electrolyte

T

Method

Instrument

pH0

Reference

0.1 M KCl

30

pH

1 d equilibration

2.5

[2548]

3.4.15.11

La Phosphates

3.4.15.11.1 LaPO4 LaCl3 and NH4H2PO4 solutions were mixed at a La:P molar ratio of 1:1. The precipitate was dried at 120°C, and calcined for 2 h at 600°C under argon, and at 1200°C for 8 h. The product was ground, and washed with water. Properties: BET specific surface area 10.4 m2/g [400,2549].

735

Compilation of PZCs/IEPs

TABLE 3.1782 PZC/IEP of LaPO4 Electrolyte

T

0.05 and 0.1 M KNO3

a b

Method

Instrument

pH0

Reference

iep iep

Delsa 440

3.5a 4

[400] [2549]b

[400] reports also the results of potentiometric titration, but not PZC. Only value, no data points; submitted paper cited in [2549], which was finally not published.

3.4.15.11.2 LaPO4 · H2O 3.4.15.11.2.1 Obtained from La(NO3)3 and H3PO4 Properties: Rod-like particles, crystalline (rhabdophane), TEM image available [2550].

TABLE 3.1783 PZC/IEP of LaPO4 · H2O Obtained from La(NO3)3 and H3PO4 Electrolyte

T

HNO3 + NH4OH

Method

Instrument

pH0

Reference

iep

Matec ESA 8000

5.4

[2550]

3.4.15.11.2.2 Obtained from La(NO3)3, H3PO4, and Citric Acid A solution of La(NO3)3 was aged with citric acid (5 mol per mole of La). The pH was then adjusted to 1, H3PO4 was added, and the solution was heated to 30°C. Properties: Spherical particles, crystalline (rhabdophane), SEM image available [2550].

TABLE 3.1784 PZC/IEP of LaPO4 · H2O Obtained from La(NO3)3, H3PO4, and Citric Acid Electrolyte HNO3 + NH4OH

T

Method

Instrument

pH0

Reference

iep

Matec ESA 8000

4.3

[2550]

3.4.15.11.3 La(PO3)3 LaCl3 and NH4H2PO4 solutions were mixed at a La:P molar ratio of 1:3. The precipitate was dried at 120°C, and calcined for 2 h at 600°C under argon, and at 800°C for 2 h. The product was ground and washed with water.

736

Surface Charging and Points of Zero Charge

Properties: BET specific surface area 3.8 m2/g [2549].

TABLE 3.1785 PZC/IEP of La(PO3)3 Electrolyte

T

Method

Instrument

iep a

pH0

Reference

3

[2549]a

Only value, no data points; submitted paper cited in [2549], which was finally not published.

3.4.15.12 Sr-Apatite Precipitation from ammoniacal solution at pH 12 at room temperature. Properties: Specific surface area 36.3 m2/g, particle length 250 nm, radius 15 nm [20].

TABLE 3.1786 PZC/IEP of Sr-Apatite Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

25

iep

Zeta-Meter

9.8

[20]

3.4.15.13 Thorium Phosphates 3.4.15.13.1 Th3(PO4)4 Recipe from [2551]: Stoichiometric amounts of Th(NO3)4 and H3PO4 solutions were rapidly mixed, dried, and calcined for 2 h at 200°C, 2 h at 500°C, 6 h at 850°C, and 1 h at 1400°C.

TABLE 3.1787 PZC/IEP of Th3(PO4)4 Electrolyte

T

Method

Instrument

pH0

Reference

0.005–0.2 M LiClO4

25

iep

Delsa 440

2.3

[230]

3.4.15.13.2 Th4(PO4)4P2O7 Th(NO3)4 and NH4H2PO4 solutions were mixed at a P:Th molar ratio 3:2. The precipitate was dried at 120°C, and heated at 400°C and then at 1250°C. Properties: BET specific surface area 1.2 m2/g [2552,2553].

737

Compilation of PZCs/IEPs

TABLE 3.1788 PZC/IEP of Th4(PO4)4P2O7 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Delsa 440

6.8

[2552a,2553]

0.05 M KNO3 a

Only value, no data points.

3.4.15.14

YPO4

3.4.15.14.1 Natural Xenotime from Pitinga Mine, Brazil

TABLE 3.1789 PZC/IEP of Xenotime from Pitinga Mine, Brazil Electrolyte

T

0.01 M NaCl

a

Method

Instrument

pH0

Reference

iep Salt additiona

Rank Brothers

2.3 3

[2382]

Only value, no data points.

3.4.15.14.2

Other

TABLE 3.1790 PZC/IEP of YPO4 from Other Sources Origin

Electrolyte

T

Australia

a

Method

Instrument

pH0

Reference

iep iepa iepa

Malvern Zetasizer II c

<3 if any 4 5

[2554] [2383] [2384]

Only value, no data points.

3.4.15.15

Zr Phosphates

3.4.15.15.1 Zr2O(PO4)2 3.4.15.15.1.1 Calcined at 1280°C ZrOCl2 and NH4H2PO4 solutions were mixed at a P:Zr molar ratio 1:1. The precipitate was dried at 120°C, and heated at 400°C and then at 1280°C. Properties: BET specific surface area 0.9 m2/g [2552,2553], 1.2 m2/g [2555].

738

Surface Charging and Points of Zero Charge

TABLE 3.1791 PZC/IEP of Zr2O(PO4)2 Calcined at 1280°C Electrolyte

T

0.05 M KNO3 0.1 M NaClO4 a b

b

25

Method

Instrument

pH0

Reference

iep Mass titration

Delsa 440

4 4.8

[2552]a [2553] [2555]a

Only value, no data points. Also 50–90°C.

3.4.15.15.1.2 Calcined at 500°C A solution containing 12.8 mmol of Zr(SO4)2 · 4 H2O was added dropwise to solution of 6.87 mmol of octadecyltrimethylammonium bromide. The mixture containing 50 g of water was stirred for 2 h at room temperature and then aged for 2 d at 90°C. The precipitate was filtered out and aged for 1 d with 85% H3PO3 solution containing 0.5 mol of H3PO3. The product was filtered out, washed with water, dried for 2 d at room temperature, and calcined for 5 h at 500°C in air. Properties: BET specific surface area 468.1 m2/g, XRD pattern, TGA and IR results available [2556]. TABLE 3.1792 PZC/IEP of Zr2O(PO4)2 Calcined at 500°C Electrolyte

T

Method pH

0.1 M NaNO3

3.4.15.15.2

Instrument

pH0

Reference

2.6

[2556]

ZrP2O7

3.4.15.15.2.1 Calcined at 950°C ZrOCl2 and NH4H2PO4 solutions were mixed at a P:Zr molar ratio 2:1. the precipitate was dried at 120°C, and heated at 400°C and then at 950°C. Properties: BET specific surface area 5.5 m2/g [2552,2553], 13.4 m2/g [2557], average grain size 75% of particles <1.7 μm, 90% of particles <2.3 μm [2557]. TABLE 3.1793 PZC/IEP of ZrP2O7 Calcined at 950°C Electrolyte 0.05 M KNO3 0.5 M KNO3

a b

T 25

b

Method

Instrument

pH0

Reference

iep pH Mass titration

Delsa 440

3.6 2.6

[2552a,2553] [2557]

Only value, no data points. Also 50–90°C.

739

Compilation of PZCs/IEPs

3.4.15.15.2.2 Calcination of Zr(HPO4)2-x(C6H5PO3)x, x = 0 or 0.48 at 500°C Properties: a-form [2558].

TABLE 3.1794 PZC/IEP of ZrP2O7 Calcined at 500°C Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KCl

25

iep

Rank Brothers Mark II

2.8

[2558]

3.4.15.15.3 Zr(HPO4)2-x(C6H5PO3)x A mixture of H3PO4 and H2C6H5PO3 in 1-propanol (different ratios, total P concentration of 2 M) was slowly added to 1 M Zr propoxide in 1-propanol. The mixture was aged for 2 h. Then a mixture of concentrated H3PO4 and H2C6H5PO3 was added, and the mixture was refluxed for 20 h. The solid was washed with 1-propanol, resuspended in 1:1 aqueous H3PO4 and refluxed for 5 d. The precipitate was then washed with water, and dried at 60°C. Properties: a-form, IR spectra available [2558].

TABLE 3.1795 PZC/IEP of Zr(HPO4)2−x(C6H5PO3)x x

Electrolyte

T

Method

Instrument

pH0

Reference

0 0.48–0.91

0.01 M KCl

25

iep

Rank Brothers Mark II

1.7 <1.7 if any

[2558]

3.4.16 SILICATES 3.4.16.1

CaSiO3, Natural Wollastonite

TABLE 3.1796 PZC/IEP of Natural Wollastonites Source Pargas Rajasthan, Indiaa a

Electrolyte NaOH + HClO4

T

Method

Instrument

pH0

Reference

iep Titration

Zeta-Meter

2 2.6

[104] [2559]

Chemical analysis available, mean particle size 100 μm, specific surface area 1.2 m2/g. Only value, no data points.

740

Surface Charging and Points of Zero Charge

3.4.16.2 Synthetic Hydrous Calcium Silicate, Ca/Si Molar Ratio of 0.66 Aerosil 200 from Degussa and freshly decarbonated Ca(OH)2 were added to water (water:solid = 50:1), and the dispersion was aged for 21 d. TABLE 3.1797 PZC/IEP of Synthetic Hydrous Calcium Silicate, Ca/Si Molar Ratio 0.66 Electrolyte

T

Method

0–0.1 M NaCl, LiCl, CsCl a

iep

Instrument Coulter Delsa 440

pCa0 2.7

a

Reference [2560]

Low ionic strength limit. pCa0 shifts to lower values as ionic strength increases. Experiments were carried out at pH 11–12.

3.4.16.3

CaMgSi2O6, Natural Diopside

TABLE 3.1798 PZC/IEP of Natural Diopsides Source

Electrolyte

Kärnten Transbaikal regiona a

T

NaOH + HClO4 0.01–0.1 M NaCl 25

Method

Instrument

iep iep

Zeta-Meter Zetaphoremeter IV, CAD

pH0 Reference 3 3.4

[104] [2561]

Ca0.99Mg0.98Fe0.02Cr0.01Si2O6, BET specific surface area 0.1 m2/g (original), 2.2 m2/g (ground).

3.4.17 SULFIDES AND SULFATES 3.4.17.1 Sulfides Sulfides are easily oxidized; thus, the composition of the external layer is often different from the bulk composition. In a many studies, the problem of oxidation has been taken into account; for example, the external oxidized layer was removed, and/or the experiments were carried out under controlled redox conditions. Storage of dispersions in darkness was also suggested to avoid the danger of photo-oxidation. IEPs of sulfides obtained under oxygen-free conditions are compiled in [2562]. PZCs/IEPs of sulfides are compiled in [1264]. 3.4.17.1.1

As2S3

3.4.17.1.1.1 Synthetic As2O3 was dissolved in 0.2 M NaOH and the solution was saturated with H2S. The pH was then adjusted to 1.5. Excess of H2S was removed from the dispersion by passing air for 1 h. The precipitate was washed with water. Then the dispersion was saturated with nitrogen and stored under nitrogen.

741

Compilation of PZCs/IEPs

Properties: Specific surface area 50 m2/g [2563].

TABLE 3.1799 PZC/IEP of Synthetic As2S3 Description

Electrolyte

N2 saturated water a

T

0.05 or 0.1 M NaCl

Method

25

Instrument

pH0

Reference

a

pH

3

[2563]

Claimed in Table 5. Charging curves in Figure 3 have an atypical course. Also 45–90°C.

3.4.17.1.1.2

Origin Unknown

Properties: Orpiment [1264].

TABLE 3.1800 PZC/IEP of As2S3 from Unspecified Source Description

Electrolyte

HCl-washed, conditioned in N2-saturated water a

T

Method

Instrument

pH0

Reference

iepa

Zeta-Meter

<3 if any

[1264]

NaClO4

Only value, no data points.

3.4.17.1.2 CdS 3.4.17.1.2.1 Commercial 3.4.17.1.2.1.1. From Aldrich or from Fisher >99%, specific surface area 14 m2/g [1264].

Properties: Hawleyite, purity

TABLE 3.1801 PZC/IEP of CdS from Aldrich or Fisher Description HCl-washed, conditioned in N2-saturated water

Electrolyte 0.005–0.1 M NaClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

5.5 (Figs. 1, 3c) 7 (Table 1)

[1264]

3.4.17.1.2.1.2 From Atomergic Chemetals Properties: Pure hexagonal phase, BET specific surface area 0.9 m2/g, mean grain size 6.6 μm [2564].

742

Surface Charging and Points of Zero Charge

TABLE 3.1802 PZC/IEP of CdS from Atomergic Chemetals Description

Electrolyte

T

Method

N2-flushed glove box

0.01 M KCl

20

iep

Instrument

pH0 Reference

Pen Kem Laser Zee Meter 501

1.5

[2564]

3.4.17.1.2.1.3 From Fisher Properties: Wurzite-type structure, confirmed by XRD, BET specific surface area 14 m2/g, particle diameter 4 μm [318, 1221]. TABLE 3.1803 PZC/IEP of CdS from Fisher Description N2-saturated water

Electrolyte

T

Method

Instrument

pH0

Reference

iep cip

Laser Zee 500

7.5 7.5

[318,1221]

0.005–0.5 M NaClO4

3.4.17.1.2.2 Synthetic 20 cm3 of a solution 0.0012 M in Cd(NO3)2, 0.24 M in HNO3, and 0.005 M in thioacetamide was aged at 26°C for 14.5 h. Then 0.25–1 cm3 of 0.05 M thioacetamide was added, and the dispersion was maintained at 26°C for up to 100 min. Properties: BET specific surface area 3.2 m2/g, modal radius 400 nm, monodispersed spherical particles, particle size distribution, TEM and SEM images available [2565]. TABLE 3.1804 PZC/IEP of Synthetic CdS Description No control over oxygen

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Rank Brothers

3.7

[2565]

0.01 M KNO3

3.4.17.1.3 CoS from Aldrich or from Fisher, Synthetic Properties: Purity >99% [1264]. TABLE 3.1805 PZC/IEP of CoS from Aldrich or Fisher Description HCl-washed, conditioned in N2-saturated water a

Only value, no data points.

Electrolyte NaClO4

T

Method a

iep

Instrument

pH0

Reference

Zeta-Meter

<3 if any

[1264]

743

Compilation of PZCs/IEPs

3.4.17.1.4 Cu Sulfides 3.4.17.1.4.1 Cu2S 3.4.17.1.4.1.1 From J. Roy Gordon Research Laboratory, Mississuaga, Ontario Properties: Chalcocite, 79.6% Cu, 19.7% S, BET specific surface area 0.9 m2/g (ground sample) [391].

TABLE 3.1806 PZC/IEP of Cu2S from J. Roy Gordon Research Laboratory, Mississuaga, Ontario Description a

Freshly exposed surface a

Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

25

iep

Zeta-Meter

<3.5 if any

[391]

Aging in aerated water for 1 h at pH 3.5 or 10.8 produced negative z potentials at high and low pH and positive z potentials at neutral pH (5–10 in sample aged at pH 3.5 and 4.5–8 in sample aged at pH 10.8).

3.4.17.1.4.1.2 From Ward’s Natural Science Establishment Properties: Chalcocite, 74.3% Cu, 0.3% Fe, 19.5% S, 0.01% Zn [2566].

TABLE 3.1807 PZC/IEP of Cu2S from Ward’s Natural Science Establishment Description Aged in N2-saturated water Aged in O2-saturated water a

Electrolyte

T

Method

0.01 M KNO3

21

iep

Instrument

pH0

Rank Brothers <5 if any Mark II 9–10.5a

Reference [2566]

Hysteresis.

3.4.17.1.4.1.3 From Messina, Transvaal, Supplied by Ward’s Natural Museum Properties: Chalcocite [1264].

TABLE 3.1808 PZC/IEP of Chalcocite from Messina, Transvaal, Supplied by Ward’s Natural Museum Description HCl-washed, conditioned in N2-saturated water a

Electrolyte 0.05 M NaClO4

T

Method

Instrument

iep

Zeta-Meter

Scattered, low in absolute value z potentials over a pH range 3–10, no clear IEP.

pH0 Reference a

[1264]

744

Surface Charging and Points of Zero Charge

3.4.17.1.4.2 CuS 3.4.17.1.4.2.1 From Aldrich or Fisher, Synthetic Properties: Covellite, purity >99%, specific surface area 4.6 m2/g [1264]. TABLE 3.1809 PZC/IEP of CuS from Aldrich or Fisher Description

Electrolyte

HCl-washed, conditioned in N2-saturated water

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

<3 if any

[1264]

0.05 M NaClO4

3.4.17.1.4.2.2 From Morton Thiokol, Alfa Products specific surface area 2.7 m2/g [2567].

Properties: Covellite,

TABLE 3.1810 PZC/IEP of CuS from Morton Thiokol, Alfa Products Description No control over oxygen a

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

multiplea

[2567]

0.03 M NaCl

z potential is positive at pH 6.5–9, and negative at pH < 6.5 or > 9.

3.4.17.1.4.2.3 From Ward’s Natural Science Establishment (or Ward’s Natural Museum) Properties: Covellite [2566,1264], 67% Cu, 0.5% Fe, 33.5% S, 0.01% Zn [2566].

TABLE 3.1811 PZC/IEP of CuS from Ward’s Description

Electrolyte

From Montana, NaClO4 HCl-washed, conditioned in N2-saturated water Aged in N2-saturated water 0.01 M KNO3 Aged in O2-saturated water a

T

21

Method

Instrument

pH0

Reference

iep

Zeta-Meter

<3 if any

[1264]

iep

Rank Brothers <5 if any Mark II <5 if anya

[2566]

Hysteresis: No IEP when pH changes from high to low, when pH changes from low to high, the z potential is positive at pH 7.2–9.5, and negative at pH < 7.2 or > 9.5.

745

Compilation of PZCs/IEPs

3.4.17.1.4.2.4 Origin Unknown TABLE 3.1812 PZC/IEP of Unspecified CuS Description

Electrolyte

N2-saturated water

T

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee Meter 500

<3 if any

[1221]

0.05 M NaClO4

3.4.17.1.4.3 CuFeS2 3.4.17.1.4.3.1 From Chitradurga Copper Mines, Supplied by Alminrock Indscer Fabriks Properties: Chalcopyrite [348].

TABLE 3.1813 PZC/IEP of Chalcopyrite from Chitradurga Copper Mines, Supplied by Alminrock Indscer Fabriks Description

Electrolyte a

T

Freshly ground 0.001 M NaNO3, no Ground and stored in control over oxygen air for 3 y a

b

25

Method Instrument iep

Zeta-Meter 3.0

pH0

Reference

<3 Multipleb

[348]

IEP depends on solid-to-liquid ratio. Only negative z potentials were obtained with solid-to-liquid ratio of 1:10000. With solid-to-liquid ratios of 1:4000–1:1000, the z potential was positive at pH 3–5.5 and negative at pH < 3 or > 5.5. z potential was positive at pH 3–9 and negative at pH < 3 or > 9. Treatment with 1% H2O2 produced positive z potential at pH 4.5–10 and negative at pH < 4.5 or > 10.

3.4.17.1.4.3.2 Natural Chalcopyrite from Gregory, Bottley, and Lloyd Properties: BET specific surface area 1.6 m2/g (ground sample) [2568].

TABLE 3.1814 PZC/IEP of Natural Chalcopyrite from Gregory, Bottley, and Lloyd Description No control over oxygen

Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000

<3 if any

[2568]

746

Surface Charging and Points of Zero Charge

3.4.17.1.4.3.3 From Malanjkhand Copper Mines, supplied by Hindustan Copper Ltd, India Properties: Chalcopyrite [348].

TABLE 3.1815 PZC/IEP of Chalcopyrite from Malanjkhand Copper Mines, Supplied by Hindustan Copper Ltd, India Description Fresh Tarnished

Electrolyte 0.001 M NaNO3, no control over oxygen

T

Method

Instrument

pH0

Reference

25

iep

Zeta-Meter 3.0

<3 <3

[348]

3.4.17.1.4.3.4 From Rouyn, Quebec, Obtained from Ward’s Natural Science Establishment Properties: Chalcopyrite, purity 97.4% [2569].

TABLE 3.1816 PZC/IEP of Chalcopyrite from Quebec, Obtained from Ward’s Natural Science Establishment Description

Electrolyte

T

Method

Instrument

pH0 Reference

No control over oxygen

HCl + KOH

25

iep

Rank Brothers Mark II

2.2

[2570]

3.4.17.1.4.3.5 From Messina, South Africa, Supplied by Ward’s Natural Science Establishment Properties: Chalcopyrite [348].

TABLE 3.1817 PZC/IEP of Chalcopyrite from Messina, South Africa, Supplied by Ward’s Natural Science Establishment Description Freshly ground Ground and stored in air for 3 y a

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaNO3, no control over oxygen

25

iep

Zeta-Meter 3.0

<3 8–10a

[348]

IEP depends on solid-to-liquid ratio. H2O2 treatment (different concentrations) induced a sign reversal of z potential to positive in neutral pH range. Negative ζ potential at pH < 3.5.

3.4.17.1.4.3.6 From Ward’s Natural Science Establishment Properties: Chalcopyrite, 35.5% Cu, 26.3% Fe, 35.8% S, 0.07% Pb, 700 ppm Zn [2566].

747

Compilation of PZCs/IEPs

TABLE 3.1818 PZC/IEP of Chalcopyrite from Ward’s Natural Science Establishment Description Aged in N2-saturated water Aged in O2-saturated water Treated with H2O2 a

Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

21

iep

Rank Brothers Mark II

<5 if any <5 if any 6.5–8.5a

[2566]

Hysteresis.

3.4.17.1.4.3.7 Chalcopyrite, from Fusseberg TABLE 3.1819 PZC/IEP of Chalcopyrite from Fusseberg Description No control over oxygen

Electrolyte

T

NaOH + HClO4

Method

Instrument

pH0

Reference

iep

Zeta-Meter

1.8

[104]

3.4.17.1.4.4 Bornite, Cu5FeS4 from Ward’s Natural Science Establishment Properties: Bornite, 60.6% Cu, 10.9% Fe, 23.4% S, 0.01% Pb, 0.06% Zn [2566]. TABLE 3.1820 PZC/IEP of Bornite Description

Electrolyte

T

Aged in N2-saturated water 0.01 M KNO3 21 Aged in O2-saturated water a

Method

Instrument

pH0

Reference

iep

Rank Brothers Mark II

<5 if any <5 if anya

[2566]

Hysteresis: No IEP when pH changes from high to low; when pH changes from low to high, z potential is positive at pH 6.5–9 and negative at pH < 6.5 or > 9.

3.4.17.1.4.5 Enargite, Cu3AsS4 from Continental Minerals Properties: Enargite, 57.2% Cu, 3% Fe, 28.3% S, 11.7% As, 0.02% Pb, 0.2% Zn [2566]. TABLE 3.1821 PZC/IEP of Enargite Description Aged in N2-saturated water Aged in O2-saturated water a

Electrolyte

T

Method

0.01 M KNO3

21

iep

Instrument

pH0

Rank Brothers <5 if any Mark II <5 if anya

Reference [2566]

Hysteresis: No IEP when pH changes from high to low; when pH changes from low to high, z potential is positive at pH 6.5–10 and negative at pH < 6.5 or > 10.

748

Surface Charging and Points of Zero Charge

3.4.17.1.4.6 Tennantite, Cu12As4S13 From Continental Minerals Properties: Tennantite, 45.7% Cu, 4.5% Fe, 23.6% S, 13.4% As, 0.03% Pb, 0.04% Zn [2566].

TABLE 3.1822 PZC/IEP of Tennantite Description

Electrolyte

T

Method

Aged in N2-saturated water 0.01 M KNO3 21 Aged in O2-saturated water a

iep

Instrument

pH0

Rank Brothers <5 if any Mark II Hysteresisa

Reference [2566]

When pH changes from high to low, z potential is positive at pH ª 8, and negative at pH < 7.5 or > 8.5; when pH changes from low to high, z potential is positive at pH 6–10, and negative at pH < 6 or > 10.

3.4.17.1.5 Iron Sulfides 3.4.17.1.5.1 FeS2 3.4.17.1.5.1.1 Synthetic 3.4.17.1.5.1.1.1 From Sulfate A solution containing 1:1 molar mixture of S and Na2S and FeNH4(SO4)2 solution were mixed at 200°C and aged at 200°C for 1 d.

TABLE 3.1823 PZC/IEP of Pyrite Obtained from Sulfate Description N2 atmosphere

Electrolyte

T

Method

0.005 M NaCl

25 26

iep

Instrument

pH0 Reference

Pen Kem Zee Meter 501

2.2

[2571]

3.4.17.1.5.1.1.2 From Chloride 0.067 M NaHS and 0.034 M FeCl3 in deoxygenated water were mixed at 80°C. The pH was adjusted to 3.5, and the system was equilibrated for 36 h. Then the precipitate was washed with 1 M HCl. Properties: Pyrite, XRD pattern available [675].

TABLE 3.1824 PZC/IEP of Pyrite Obtained from Chloride Description N2 atmosphere

Electrolyte

T

Method

None

25

Inflection

Instrument

pH0

Reference

2

[675]

749

Compilation of PZCs/IEPs

3.4.17.1.5.1.2 Natural Pyrites and Marcasite 3.4.17.1.5.1.2.1 Pyrite from Alminrock Indser Fabricks, Bangalore ties: BET specific surface area 1.3 m2/g (ground sample) [2568].

Proper-

TABLE 3.1825 PZC/IEP of Pyrite from Alminrock Indser Fabricks, Bangalore Description No control over oxygen

Electrolyte

T

Method

0.001 M KCl

iep

Instrument Malvern Zetasizer 3000

pH0

Reference

3.2

[2568]

3.4.17.1.5.1.2.2 Pyrite from East Khasi Hills of Meghalaya, India Properties: BET specific surface area 0.24 m2/g (150 mesh fraction), XRD pattern available [2572].

TABLE 3.1826 PZC/IEP of Pyrite from East Khasi Hills of Meghalaya, India Description a

No control over oxygen a

Electrolyte

T

Method

Instrument

0.1 M NaNO3

30

pH

6 h equilibration

pH0 Reference 6.4

[2572]

Original mineral was acid-washed and stored under nitrogen, but no control over oxygen in solution is reported.

3.4.17.1.5.1.2.3 Pyrite from Elba

TABLE 3.1827 PZC/IEP of Pyrite from Elba Description No control over oxygen

Electrolyte NaOH + HClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

2

[104]

3.4.17.1.5.1.2.4 Pyrite from Huanzala, Peru, Obtained from Ward’s Natural Science Establishment Properties: Structure confirmed by XRD [2573], 43.3% Fe, 51.5% S, 0.07% Cu, 0.3% Pb, 3% SiO2 [2573,2574], BET specific surface area 4.5 m2/g [675], specific surface area 1 m2/g [2573].

750

Surface Charging and Points of Zero Charge

TABLE 3.1828 PZC/IEP of Pyrite from Huanzala, Peru Description

Electrolyte

T

Method

Instrument

Aged at pH 5: 19 h in N2 0.5 h in Ar 0.5 h in air 2 h in air 19 h in air 0.5 h in O2 19 h in O2 0.5 h in O2, pH 6 0.5 h in O2, pH 7 0.5 h in O2, pH 9

0.005 M KNO3

25

iep

Rank Brothers Mark II

Crushed and washed with 0.005–0.1 M HCl, N2 atmosphere NaClO4 HCl-washed, N2 atmosphere

0.01 m NaCl

HCl-washed, conditioned in N2-saturated water

NaClO4

HCl-washed, N2 atmosphere

0.005 M NaCl

a b c

pH Inflection

24

iepb

Zeta-Meter

iep

Pen Kem Zee Meter 501

pH0

Reference [2574]

<3 <3 <3 4.6 6 6.5 6.5 5.5 <3 <3 1.5a

[2573]

2.4

[675]

2.5

[1264]

10

[2571]c

Merge. Only value, no data points. [2571] reports IEP of pyrite and of many other sulfides obtained in the presence of Na2SO3 (as a scavenger of oxygen).

3.4.17.1.5.1.2.5 Marcasite from Indiana, Supplied by Ward’s Natural Museum

TABLE 3.1829 PZC/IEP of Marcasite from Indiana, Supplied by Ward’s Natural Museum Description

Electrolyte

HCl-washed, conditioned in N2-saturated water a

Only value, no data points.

NaClO4

T

Method

Instrument

pH0

Reference

iepa

Zeta-Meter

<3 if any

[1264]

751

Compilation of PZCs/IEPs

3.4.17.1.5.1.3 Pyrite Origin Unknown, Pure TABLE 3.1830 PZC/IEP of Pure Pyrite from Unspecified Source Description

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

6.2/6.9a

[2575]

No control over oxygen a

5/15 min conditioning.

3.4.17.1.5.2 FeS from Aldrich or from Fisher, Synthetic >99% [1264].

Properties: Purity

TABLE 3.1831 PZC/IEP of FeS from Aldrich or Fisher Description

Electrolyte

HCl-washed, conditioned in N2-saturated water a

T

Method a

NaClO4

iep

Instrument

pH0

Reference

Zeta-Meter

5.7

[1264]

Only value, no data points.

3.4.17.1.5.3 Fe5S6 3.4.17.1.5.3.1 Commercial, from Fisher Properties: Pyrrhotite, structure confirmed by XRD, specific surface area 0.7 m2/g [2567].

TABLE 3.1832 PZC/IEP of Pyrrhotite from Fisher Description Ground, no control over oxygen a

Electrolyte 0.03 M NaCl

T

Method

Instrument

pH0 Reference

iep

Zeta-Meter

5.8a

[2567]

Arbitrary interpolation; z potential is positive at pH < 4 and negative at pH > 6.5.

3.4.17.1.5.3.2 Synthetic 3.4.17.1.5.3.2.1 Obtained at 245°C 0.1 M Na2S solution was mixed with 0.4 M Fe(NH4)2(SO4)2 (both solutions prepared with fresh boiled water to minimize

752

Surface Charging and Points of Zero Charge

concentration of oxygen) at 245°C in a specially designed reactor and aged for 30 min. The mixture was then quenched, filtered, and dried under a nitrogen atmosphere. Properties: Pyrrhotite, structure confirmed by XRD [2562].

TABLE 3.1833 PZC/IEP of Pyrrhotite Obtained at 245°C Description

Electrolyte

T Method

Solutions prepared with 0.001–0.011 M NaCl N2-saturated water

Instrument

iep

pH0 Reference

Pen Kem Laser Zee 501

2

[2562]

3.4.17.1.5.3.2.2 Obtained at 230°C 0.3 M NaHS containing 0.05 M KH2PO4 and 0.01 M Na2HPO4 was heated to 230°C at 107 Pa. 1.1 M FeSO4 · (NH4)2SO4 was injected and the system was equilibrated for 10 h. Properties: Pyrrhotite, BET specific surface area 16.8 m2/g, XRD pattern available [675].

TABLE 3.1834 PZC/IEP of Pyrrhotite Obtained at 230°C Description N2 atmosphere

Electrolyte

T

Method

None

25

Inflection

Instrument

pH0

Reference

2.7

[675]

3.4.17.1.5.3.3 Origin Unknown

TABLE 3.1835 PZC/IEP of Pyrrhotite from Unspecified Source Description No control over oxygen

Electrolyte NaOH + HClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

<2 if any

[104]

3.4.17.1.5.4 Fe3S4 0.1 M Na2S solution was mixed with S (3:1 molar ratio) at 180°C. After complete dissolution of S, the solution was mixed at 140°C with 0.4 M Fe(NH4)2(SO4)2 (both solutions prepared with fresh boiled water to minimize concentration of oxygen) in a specially designed reactor and aged for 30 min. The mixture was then quenched, filtered, and dried under a nitrogen atmosphere.

753

Compilation of PZCs/IEPs

Properties: Greigite, structure confirmed by XRD [2562].

TABLE 3.1836 PZC/IEP of Greigite Description Solutions prepared with N2-saturated water

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee 501

3

[2562]

0.001–0.011 M NaCl

3.4.17.1.5.5 Synthetic Mackinawite Oxygen-free 0.3 M NaHS containing 0.05 M KH2PO4 and 0.01 M Na2HPO4 was heated to 130°C at 107 Pa. 1.1 M FeSO4 · (NH4)2SO4 was injected, and the system was equilibrated for 20 h. Properties: BET specific surface area 80 m2/g, XRD pattern available [675].

TABLE 3.1837 PZC/IEP of Mackinawite Description N2 atmosphere

Electrolyte

T

Method

None

25

Inflection

Instrument

pH0

Reference

2.9

[675]

3.4.17.1.6 Commercial HgS 3.4.17.1.6.1 From Aldrich or from Fisher, Synthetic Properties: Cinnabar and metacinnabar (two samples), purity >99% [1264]. TABLE 3.1838 PZC/IEP of HgS from Aldrich or Fisher Description HCl-washed, conditioned in N2-saturated water a

Electrolyte NaClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

<3 if any 5.1a

[1264]

Table 1 in [1264] reports IEP at pH < 3 and 5.1 for synthetic cinnabar and metacinnabar, respectively (only IEP, no data points). The experimental section refers to cinnabar from Idria, Yugoslavia, but no results for that material are reported.

3.4.17.1.6.2 From Alfa Products 4 m2/g [317].

Properties: Black, BET specific surface area

754

Surface Charging and Points of Zero Charge

TABLE 3.1839 PZC/IEP of HgS from Alfa Products Description

Electrolyte

T

Ground under N2

0.005–0.2 M NaClO4 in N2-saturated water, stored in darkness

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee Meter 500

7

[317]

3.4.17.1.6.3 From Fisher Properties: a-form (cinnabar), structure confirmed by XRD [395,341], purity 99.5% [395], >99.5% [341], BET specific surface area 0.9 m2/g [395], 1 m2/g [341], SEM images available [395]. TABLE 3.1840 PZC/IEP of HgS from Fisher Description Not sonified Sonified for 3 h HCl-washed a

Electrolyte

T

Method a

Instrument

pH0

Reference

3.9 4.6 4

[395] [341]

No control over oxygen

iep

BIC 90 plus

No control over oxygen

iep

Brookhaven

Only values, data points not reported.

3.4.17.1.6.4 Origin Unknown TABLE 3.1841 PZC/IEP of HgS from Unspecified Source Description N2-saturated water

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee Meter 500

6.5

[1221]

Instrument

pH0

Reference

Zeta-Meter

<3 if any

[1264]

0.05 M NaClO4

3.4.17.1.7 MnS from Aldrich or from Fisher, Synthetic Properties: Purity >99% [1264]. TABLE 3.1842 PZC/IEP of MnS Description HCl-washed, conditioned in N2-saturated water a

Electrolyte NaClO4

Only value, data points not reported.

T

Method iep

a

755

Compilation of PZCs/IEPs

3.4.17.1.8 MoS2, Origin Unknown Properties: Molybdenite [104,1264].

TABLE 3.1843 PZC/IEP of MoS2 Description HCl-washed, conditioned in N2-saturated water No control over oxygen

Method

Instrument

pH0

Reference

NaClO4

Electrolyte

T

iep

Zeta-Meter

<3 if any

[1264]

NaOH + HClO4

iep

Zeta-Meter

<1 if any

[104]

3.4.17.1.9 Nickel Sulfides 3.4.17.1.9.1 Ni3S2 from J.Roy Gordon Research Laboratory, Mississuaga, Ontario Properties: Heazlewoodite, 73.2% Ni, 27.3% S, BET specific surface area 0.7 m2/g (ground sample) [391].

TABLE 3.1844 PZC/IEP of Ni3S2 Description Conditioned at pH 9.5 in N2-saturated watera a

Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KNO3

25

iep

Zeta-Meter

>12 if any

[391]

Aging at pH 9.5 or 11 in aerated water produced IEP at pH 11.5; aging at pH 3 produced an atypical electrokinetic curve: z potential is negative at pH < 4 and positive at pH > 5.

3.4.17.1.9.2 NiS 3.4.17.1.9.2.1 From Aldrich or from Fisher, Synthetic >99% [1264].

Properties: Purity

TABLE 3.1845 PZC/IEP of NiS from Aldrich or Fisher Description HCl-washed, conditioned in N2-saturated water a

Electrolyte NaClO4

Only value, data points not reported.

T

Method a

iep

Instrument

pH0

Reference

Zeta-Meter

<3 if any

[1264]

756

Surface Charging and Points of Zero Charge

3.4.17.1.9.2.2 From Morton Thiokol, Alfa Products Properties: Millerite, structure confirmed by XRD, 99.9% pure, specific surface area 0.7 m2/g [2567].

TABLE 3.1846 PZC/IEP of NiS from Morton Thiokol, Alfa Products Description

Electrolyte

Ground, no control over oxygen a

T

0.03 M NaCl

Method

Instrument

pH0

Reference

iep

Zeta-Meter

Multiplea

[2567]

z potential is positive at pH 8–11, and negative at pH < 8 or > 11.

3.4.17.1.10

PbS

3.4.17.1.10.1 Commercial 3.4.17.1.10.1.1 From Aldrich or Fisher, Synthetic Properties: Galena, purity >99% [1264].

TABLE 3.1847 PZC/IEP of PbS from Aldrich or Fisher Description

Electrolyte

HCl-washed, conditioned in N2-saturated water a

T

Method

Instrument

iepa

Zeta-Meter

NaClO4

pH0 <3 if any

Reference [1264]

Only value, data points not reported.

3.4.17.1.10.1.2 From Merck, Synthetic Properties: Galena [2576], 0.6–1% SiO2, 0.4–0.6% CaO, 0.1% Fe2O3, 0.1–0.2% MgO, 0.2% MnO, BET specific surface area 1 m2/g [2576].

TABLE 3.1848 PZC/IEP of PbS from Merck Description No control over oxygen

Electrolyte

T

Method

Instrument

pH0

Reference

0.002 M NaNO3

20

iep

Rank Brothers Mark II

5.5

[2576]

757

Compilation of PZCs/IEPs

3.4.17.1.10.2 Synthetic Pb(NO3)2 solution was titrated with the stoichiometric amount of Na2S solution in inert gas atmosphere. The precipitate was washed with 0.1 M NaNO3 or NaClO4. TABLE 3.1849 PZC/IEP of Synthetic PbS Description Stored and handled under nitrogen

Electrolyte

T

Method

0.1 M NaClO4 or NaNO3

25

pH

Instrument

pH0

Reference

8.6

[13]

3.4.17.1.10.3 Natural 3.4.17.1.10.3.1 From Ward’s Natural Science Establishment 3.4.17.1.10.3.1.1 From Kansas, obtained from Ward’s Natural Science Establishment Properties: Galena, purity 99.6% [2569].

TABLE 3.1850 PZC/IEP of PbS from Kansas, Obtained from Ward’s Natural Science Establishment Description Ground under water Dry ground NH4Cl-treated Dry ground and aged a

Electrolyte

T

HCl + KOH, no control over oxygen

25

Method iep

Instrument Rank Brothers Mark II

pH0 a

6.8 5.2 4.2 2.2

Reference [2570]

Interpolated from scattered results.

3.4.17.1.10.3.1.2 From Missouri, Supplied by Ward’s Natural Museum Properties: Galena [1264].

TABLE 3.1851 PZC/IEP of PbS from Missouri, Supplied by Ward’s Natural Museum Description HCl-washed, conditioned in N2-saturated water a

Electrolyte NaClO4

Only value, data points not reported.

T

Method a

iep

Instrument Zeta-Meter

pH0 <3 if any

Reference [1264]

758

Surface Charging and Points of Zero Charge

3.4.17.1.10.3.1.3 Other Properties: Galena, 99.9% pure [957], BET specific surface area 0.6 m2/g [13,2577], 0.5 m2/g [957].

TABLE 3.1852 PZC/IEP of PbS from Ward’s Natural Science Establishment Description

Electrolyte

T

No control over oxygen

0.1 M NaCl

Stored and handled under nitrogen

0.1 M NaClO4 or NaNO3

Method

Instrument

pH0

Reference

iep

Laser Zee Meter 501

<3 if any

[957]

25

pH

8.7

[13]

3.4.17.1.10.3.2 From Sweden, Supplied by Boliden Mineral Properties: Galena [2576], 4–6% SiO2, 0.1% CaO, 0.5% Fe2O3, 1.2–1.5% MgO, 0.1% MnO, BET specific surface area 0.4 m2/g [2576].

TABLE 3.1853 PZC/IEP of Galena from Sweden Description No control over oxygen

Electrolyte

T

Method

Instrument

pH0

Reference

0.002 M NaNO3

20

iep

Rank Brothers Mark II

<3 if any

[2576]

3.4.17.1.10.3.3 Origin Unknown

TABLE 3.1854 PZC/IEP of Galena from Unspecified Sources Description Ground and stored without contact with air Galenite, freshly ground a

Electrolyte

T

Method

Instrument

pH0

HCl

iep

Electrophoresis <2.5 if any

NaOH + HClO4

iep

Zeta-Meter

z potential close to 0 at pH 6–9.

9a

Reference [227]

[104]

759

Compilation of PZCs/IEPs

3.4.17.1.11

Sb2S3

3.4.17.1.11.1 Synthetic 0.05 M KSbO · C4H4O6 (tartrate complex) was saturated with H2S. The pH was then adjusted to 1.5. Excess H2S was removed from the dispersion by passing air for 1 h. The precipitate was washed with water. Then the dispersion was saturated with nitrogen and stored under nitrogen. Properties: BET specific surface area 108 m2/g [2563].

TABLE 3.1855 PZC/IEP of Synthetic Sb2S3 Description

Electrolyte

T

N2-saturated water 0.05 or 0.1 M NaCl a

25

Method a

Instrument

pH0 Reference

pH

3.4

[2563]

Unusual course of apparent charging curves; also 45–90°C.

3.4.17.1.11.2

Origin Unknown

Properties: Stibnite [1264].

TABLE 3.1856 PZC/IEP of Unspecified Stibnite Description

Electrolyte

HCl-washed, conditioned in N2-saturated water a

T

Method a

NaClO4

iep

Instrument

pH0

Reference

Zeta-Meter

<3 if any

[1264]

Only value, data points not reported.

3.4.17.1.12

ZnS

3.4.17.1.12.1 Commercial 3.4.17.1.12.1.1 From Aldrich or from Fisher Properties: Wurzite, purity >99%, specific surface area 9 m2/g [1264]. TABLE 3.1857 PZC/IEP of ZnS from Aldrich or Fisher Description HCl-washed, conditioned in N2-saturated water

Electrolyte 0.005–0.1 M NaClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

8.5

[1264]

760

Surface Charging and Points of Zero Charge

3.4.17.1.12.1.2 From Atomergic Chemetals Properties: Pure hexagonal phase, BET specific surface area 0.5 m2/g, mean grain size 10.8 μm [2564].

TABLE 3.1858 PZC/IEP of ZnS from Atomergic Chemetals Description

Electrolyte

T

Method

Instrument

N2-flushed glove box

0.01 M KCla

20

iep

Pen Kem Laser Zee Meter 501

a

pH0 Reference 2.4

[2564]

Similar IEP was obtained with 0.01 M NaHCOO.

3.4.17.1.12.1.3 From BDH Laboratories, Synthetic Properties: 0.01–0.1% Al, Ba, Ca, Si, Sr, krypton BET specific surface area 7.6 m2/g [1269].

TABLE 3.1859 PZC/IEP of ZnS from BDH Laboratories Description HCl-washed, stored under N2

Electrolyte

T

0.002 M NaCl

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer II

8

[1269]

3.4.17.1.12.1.4 From Koch Light, Precipitated with H2S or (NH4)2S Properties: 99.99% pure [2578]. TABLE 3.1860 PZC/IEP of ZnS from Koch Light Description

Electrolyte

T Method

Deoxygenated water 0.001, 0.01 M KNO3 25

iep

Instrument

pH0 Reference

Rank Brothers Mark II 6.8

[2578]

3.4.17.1.12.1.5 From KEBO Properties: Sphalerite and wurzite, BET specific surface area 6.4 m2/g [772,2577].

TABLE 3.1861 PZC/IEP of ZnS from KEBO Description Argon-saturated water

Electrolyte

T

Method

0.1 M NaClO4

25

pH

Instrument

pH0 Reference 8.6

[772]

761

Compilation of PZCs/IEPs

3.4.17.1.12.1.6 From Merck, Patinal TABLE 3.1862 PZC/IEP of ZnS from Merck Description No control over oxygen Treated with 3% H2O2 Treated with 15% H2O2

Electrolyte

T

Method

Instrument

0.01 M NaCl

25

iep

Malvern Zetasizer 2c

pH0 Reference 3.3 4.5 6.5

[340]

3.4.17.1.12.2 Synthetic 3.4.17.1.12.2.1 Obtained at 60°C Seeds 80 nm in radius were grown in a solution 0.11 M in thiacetamide, 0.024 M in Zn(NO3)2, and 0.062 M in HNO3 at 26°C for 5 h and then at 60°C for 1.5 h. Properties: Sphalerite, structure confirmed by XRD [2579,2580], specific surface area 43.7 m2/g [340],modal radius 230 nm [2579], average diameter 320 nm [340,2580], spherical particles [2580], particle size distribution [2579], electron micrographs available [2580] (also for samples grown at 60°C for longer times) [2579].

TABLE 3.1863 PZC/IEP of Synthetic ZnS Obtained at 60°C Description No control over oxygen No control over oxygen

Electrolyte

T

Method

Instrument

pH0 Reference

0.01 M KNO3

iep

Rank Brothers

3

[2579]

0.0001–0.01 M NaCl 25 0.01 M KNO3

iep

Malvern Zetasizer 2c

5.5

[340,2580]

3.4.17.1.12.2.2 Dissolution of ZnO in H2SO4 –Thioacetamide Solution, and Heating to 75°C TABLE 3.1864 PZC/IEP of Synthetic ZnS Obtained at 75°C Description No control over oxygen a

Electrolyte 0.005 M KCl

T

Method iep

Instrument Pen Kem Laser Zee Meter 500

Similar IEP is reported for ZnS from other (unspecified) sources.

pH0 a

3

Reference [2166]

762

Surface Charging and Points of Zero Charge

3.4.17.1.12.2.3 Dissolution of ZnO in HCl-Thioacetamide Solution and Heating to 80°C for 1 h Washed with dilute ammonia and with water. Properties: BET specific surface area 56 m2/g [2581], spherical particles, 2–8 μm in diameter [1945], SEM image available [2581].

TABLE 3.1865 PZC/IEP of Synthetic ZnS Obtained at 80°C Description Particles stored in nitrogen at 4°C

Electrolyte

T

0.0002 M NaCl or 0.001 M

Method

Instrument

pH0

Reference

iep

Rank Brothers Mark II

7.3

[1945] [2581]

3.4.17.1.12.3 Natural 3.4.17.1.12.3.1 Supplied by Ward’s Natural Museum 3.4.17.1.12.3.1.1 From Tennessee, Supplied by Ward’s Natural Museum Properties: Sphalerite [1264].

TABLE 3.1866 PZC/IEP of Sphalerite from Tennessee Description

Electrolyte

HCl-washed, conditioned in N2-saturated water

T

0.05 M NaClO4

Method

Instrument

pH0

Reference

iep

Zeta-Meter

<3

[1264]

3.4.17.1.12.3.1.2 From Ward’s Natural Science Establishment Sphalerite, 65% Zn, 0.3% Fe, 0.1% Cu [390].

Properties:

TABLE 3.1867 PZC/IEP of Unspecified Sphalerite from Ward’s Natural Science Establishment Description Ground, before and after settling

Electrolyte

T

0.001 M KCl, no control over oxygen,

3.4.17.1.12.3.2 From Hudson Bay Fe, 1.2% Cu, 0.1% Pb [390].

Method

Instrument

pH0

Reference

iep

Laser Zee Meter 501

4.5 3

[390]

Properties: Sphalerite, 48% Zn, 12.4%

763

Compilation of PZCs/IEPs

TABLE 3.1868 PZC/IEP of Sphalerite from Hudson Bay Description

Electrolyte

Ground, before and after settling

T

0.001 M KCl, no control over oxygen

Method iep

Instrument

pH0

Reference

6 6

[390]

Laser Zee Meter 501

3.4.17.1.12.3.3 From Selbaie Mines Properties: Sphalerite, 51% Zn, 8.2% Fe, 1.3% Cu, 0.1% Pb [390]. TABLE 3.1869 PZC/IEP of Sphalerite from Selbaie Mines Description Ground

a

Electrolyte

T

Method

0.001 M KCl, no control over oxygen

iep

Instrument Laser Zee Meter 501

pH0 <2

a

Reference [390]

One data point (pH 3.3) represents a positive z potential.

3.4.17.1.12.3.4 From Sweden, Supplied by Boliden Minerals Properties: Sphalerite [1269], purity 99.1% [772], 0.1–1% Ca, Mg, Mn, 7.9% Fe, 3.3% Si, 1.9% Pb, 0.01–0.1% Al, Cu, K, and P, krypton BET specific surface area 0.5 m2/g [1269], BET specific surface area 0.7 m2/g [772,2577]. TABLE 3.1870 PZC/IEP of Sphalerite from Sweden Description

Electrolyte

HCl-washed, conditioned 0.002 M NaCl in N2-saturated water Argon-saturated water 0.1 M NaClO4 a

T

Method iep

25

Instrument Malvern Zetasizer II

pHa

pH0

Reference

<3 if any

[1269]

8.7

[772]

Only value, data points not reported.

3.4.17.1.12.3.5 From Ammeberg and from Selbecke (Two Different Samples) TABLE 3.1871 PZC/IEP of Sphalerite from Ammeberg and Selbecke Description No control over oxygen

Electrolyte NaOH + HClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

2

[104]

764

Surface Charging and Points of Zero Charge

3.4.17.1.13

Zn0.95Cd0.05S Phosphor, Origin Unknown

TABLE 3.1872 PZC/IEP of Zn0.95Cd0.05S Phosphor Description

Electrolyte

No control over oxygen

T

Method

0.005 M KCl

iep

Instrument Pen Kem Laser Zee Meter 500

pH0

Reference

2.5

[2166]

3.4.17.2 Sulfates 3.4.17.2.1 KAl3(OH)6(SO4)2, Natural Alunite from Tolfa

TABLE 3.1873 PZC/IEP of Alunite Electrolyte

T

NaOH + HClO4

Method

Instrument

pH0 Reference

iep

Zeta-Meter

10.3

[104]

3.4.17.2.2 BaSO4 3.4.17.2.2.1 From Aldrich Properties: 99%, specific surface area 3 m2/g [2582].

TABLE 3.1874 PZC/IEP of BaSO4 from Aldrich Electrolyte

T

Method

Instrument

pH0

Reference

25

iep

Rank Brothers

5

[2582]

3.4.17.2.2.2 From Ward’s Properties: BET specific surface area 1.3 m2/g, XRD pattern available [2433].

TABLE 3.1875 PZC/IEP of BaSO4 from Ward’s Electrolyte 0.001 M KClO4

T

Method iep

Instrument

pH0

Reference

6

[2433]

765

Compilation of PZCs/IEPs

3.4.17.2.2.3 Synthetic A solution 0.01 M in BaCl2, 0.01 M in EDTA, and 0.01 M in Na2SO4 in 16 vol. % aqueous ethanol containing 5 vol. % of ammonia-ammonium chloride buffer (pH 10) was aged for 1 d at room temperature. Properties: Ellipsoidal particles, length 200 nm, width 160 nm, SEM image available [2583].

TABLE 3.1876 PZC/IEP of Synthetic BaSO4 Electrolyte

T

Method iep

a

Instrument Delsa 440 Pen Ken 3000

pH0 a

6.5

Reference [2583]

Arbitrary interpolation. IEP of glass beads is also reported.

3.4.17.2.2.4 Natural Barites

Table 3.1877 PZC/IEP of Natural Barites Location Dreislar Clarashall Meggena

a

Electrolyte

T

Method

Instrument

pH0

Reference

NaOH + HClO4

iep

Zeta-Meter

[104]

HCl + NaOH

iep

11.5 11.5 2.5 3.3

[2467]

95% pure, 2% SrSO4, contains quartz.

3.4.17.2.2.5 Nanoparticles Obtained by Wet Grinding of 1.5 µm Barite Properties: 1.6% Na2O, 29.7% SO3, 0.02% Cl, 1% SrO, 0.03% Y2O3, 0.5% ZrO2, 67.2% BaO by mass, BET specific surface area 36.7 m2/g, bimodal particle size distribution with 96% of 31 nm particles and 4% of 128 nm particles, particle size distribution, TEM image available [398].

TABLE 3.1878 PZC/IEP of Nanoparticles Obtained by Wet Grinding of 1.5 µm Barite Electrolyte

T

Method

Instrument

NaOH + HCl

25

iep

Malvern Zetasizer 3000 HS

pH0 Reference 7.8

[398]

766

Surface Charging and Points of Zero Charge

3.4.17.2.3 CaSO4

TABLE 3.1879 PZC/IEP of CaSO4 Electrolyte

T

Method

Instrument

pH0

Reference

12

[1218]

a

iep a

Only value, data points not reported.

Reference [104] reports electrokinetic curves for gyps and anhydrite in their saturated solutions. These curves show multiple IEPs (positive z potential at very high and at very low pH). 3.4.17.2.4 Iron Basic Sulfates precipitated 3.4.17.2.4.1 Fe8O8(OH)5.02(SO4)1.49 · 0.5H2O Schwertmannite from acid mine drainage of Kristineberg mine (Sweden). Properties: Elemental analysis available, BET specific surface area 42.9 m2/g, XRD pattern, SEM image available [484].

TABLE 3.1880 PZC/IEP of Fe8O8(OH)5.02(SO4)1.49 ⋅ 0.5H2O Electrolyte 0.1 M NaNO3 a

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 4

7.2a

[484]

Samples aged for 1, 4, and 14 days.

3.4.17.2.4.2 Fe3(OH)5(SO4)2 · 2 H2O A solution 0.18 M in Fe(NO3)3 and 0.53 M in Na2SO4 was aged for 90 min at 80°C. Properties: TEM image available [2584].

TABLE 3.1881 PZC/IEP of Synthetic Fe3(OH)5(SO4)2 ⋅ 2H2O Electrolyte 0.01 M KNO3

T

Method

Instrument

iep

Rank Brothers

pH0 Reference 6.2

[2584]

767

Compilation of PZCs/IEPs

3.4.17.2.5 Ni(OH)1.4(SO4)0.3 A solution 0.6 M in Ni(NO3)2, 0.012 M in NiSO4 and 0.6 M in Ni(CH3COO)2 was aged at 100°C for 2 d. Properties: TEM image, XRD, TGA, DTA and IR spectrum available [2585].

TABLE 3.1882 PZC/IEP of Synthetic Ni(OH)1.4(SO4)0.3 Electrolyte

T

Method

Instrument

iep

Malvern Mastersizer

0.01 M NaCl

pH0 Reference 12.5

[2585]

3.4.17.2.6 PbSO4 3.4.17.2.6.1

Commercial from Aldrich, 98%

TABLE 3.1883 PZC/IEP of PbSO4 from Aldrich Electrolyte 0.001 M KNO3

T

Method iep

Instrument

pH0

Reference

Laser Zee Meter 501 Negative z at pH 3–4 Positive z at pH 7–10

[472]

3.4.17.2.6.2 PbSO4 Natural Anglesite

TABLE 3.1884 PZC/IEP of Natural Anglesites Origin Globe Mine, Arizona Los Lamentos, Chih, Mexico Standard Consolidated Mine, Utah Exception Mine, Chih, Mexico a

Electrolyte

T

Method Instrument iep

Zeta-Meter

pH0

Reference

11a

[475]

Sign of z potential reverses from positive to negative at pH 4, back to positive at pH 6, and again to negative at pH 11.

768

Surface Charging and Points of Zero Charge

3.4.17.2.7 SrSO4, Natural Celestite

TABLE 3.1885 PZC/IEP of Natural Celestites Source Obergembeck

Electrolyte NaOH + HClO4

Montevives, Granada, Spain, 99% celestite in acid-washed material a

T

Method

Instrument

pH0 Reference

iep

Zeta-Meter

iep

Streaming potential 3a

2.5

[104] [2586]

10 min and 24 h aged dispersions.

3.4.17.2.8 3 Zn(OH)2 · ZnSO4 · 5H2O 43.1 g of ZnSO4 · 5 H2O was dissolved in H2SO4 (pH3). The pH was then brought to 6.5 with NaOH. Properties: XRD pattern, SEM image available [2168].

TABLE 3.1886 PZC/IEP of Synthetic 3 Zn(OH)2 ⋅ ZnSO4 ⋅ 5H2O Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

iep

Rank Brothers II

<7 if any

Reference [2168]

3.4.17.2.9 Zr2(OH)6SO4 3.4.17.2.9.1 From Zr(SO4)2 and Formamide A solution 0.005 M in Zr(SO4)2 and 1 M in formamide containing 0.9% of poly(vinylpyrrolidone) by mass was aged for 5 h at 70°C. Properties: TEM image available [2213].

TABLE 3.1887 PZC/IEP of Zr2(OH)6SO4 Obtained from Zr(SO4)2 and Formamide Electrolyte 0.01 M NaNO3

T

Method

Instrument

pH0

Reference

iep

Delsa 440 Coulter

4.8

[2213]

3.4.17.2.9.2 From Zr(SO4)2 and Urea A solution 0.005 M in Zr(SO4)2, 1.8 M in urea, and 0.05 M in HNO3 containing 3% of poly(vinylpyrrolidone) by mass was aged for 5 h at 50°C.

769

Compilation of PZCs/IEPs

Properties: TEM image available, particle diameter 560 nm [474]. TABLE 3.1888 PZC/IEP of Zr2(OH)6SO4 Obtained from Zr(SO4)2 and Urea Electrolyte

T

Method

Instrument

pH0

Reference

iep

Delsa Coulter

4.8

[474]

0.01 M NaNO3

3.4.18 TITANATES Titanates of alkaline earth metals undergo selective leaching of alkaline earth metal cations at acidic pH. The composition of commercial products is usually different from the idealized formula. 3.4.18.1 BaTiO3 Compilations of IEPs from the literature can be found in [149,412]. 3.4.18.1.1

Commercial

3.4.18.1.1.1 BT-05 from Sakai Properties: Ba:Ti 1.00 [148,149], median diameter 500 nm, specific surface area 2.4 m2/g [148,149,2587]. TABLE 3.1889 PZC/IEP of BT-05 from Sakai Electrolyte

Method

Instrument

pH0

0.01 M NaNO3

iep

0.01 M NaNO3 0.01 M NaNO3

iep iep

Brookhaven Matec ESA 8000 Matec ESA 9800 Matec ESA 8000

3.6–4.4 4.4–>10a >10b >10b

a

b

T

Reference [149] [148] [2587]

IEP increases when solid-to-liquid ratio increases, owing to selective leaching of Ba. Multiple IEPs are observed over a limited range of solid-to-liquid ratios. Acid treatment (Ba-containing supernatant removed) gives a product with IEP similar to that of TiO2.

3.4.18.1.1.2 From TAM 3.4.18.1.1.2.1 TICON HPB Properties: BET specific surface area 3.1 m2/g, Ba + Sr/Ti molar ratio 0.989 [2588]. TABLE 3.1890 PZC/IEP of TICON HPB from TAM Electrolyte

T

Method

Instrument

pH0

Reference

iep

ESA 8000

9.8

[2588]

770

Surface Charging and Points of Zero Charge

3.4.18.1.1.2.2 HPB-MBB Oxalate route. Properties: Ti:Ba ratio 1.05, mean particle size 500 nm [412], 1.8% BaCO3 [2589].

TABLE 3.1891 PZC/IEP of HPB-MBB from TAM Electrolyte

T

0.001 M KCl a

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 4

6a

[412]

Broad maximum in yield stress of 20 vol% dispersion at pH 9–11. IEP in supernatant obtained from 20 vol% dispersion at pH > 10.5. Results obtained for a powder calcined at 800°C are also reported, but without data points near IEP.

3.4.18.1.1.3 From Transelco Ferro Obtained by solid-state reaction between BaCO3 and TiO2. Properties: Ti:Ba ratio 1.05, contains 0.5% SrO and Nb2O5, mean particle size 1.5 μm [412] 0.6–0.9% BaCO3 [2589]. TABLE 3.1892 PZC/IEP of BaTiO3 from Transelco Ferro Electrolyte

T

0.001 M KCl a

Method

Instrument

pH0

Reference

iep

Malvern Zeta Master 4

6.5a

[412]

Maximum in yield stress of 20 vol% dispersion at pH 11. IEP in supernatant obtained from 20 vol% dispersion at pH > 10.5.

3.4.18.1.2 Synthetic 3.4.18.1.2.1 Oxalate Route, Calcined at 700°C Properties: Ti:Ba ratio 1.11, mean particle size 10 μm [412]. TABLE 3.1893 PZC/IEP of BaTiO3 Calcined at 700°C Aged for

Electrolyte

1d 3 months 6 months

0.001 M KCl

a

Arbitrary interpolation.

T

Method

Instrument

pH0

Reference

iep

Malvern Zeta Master 4

4a 5.5 5.5

[412]

771

Compilation of PZCs/IEPs

3.4.18.1.2.2 High-Gravity Reactive Precipitation Recipe from [2590]. A mixed TiCl4 + BaCl2 solution, Ba: Ti 1.07, total molarity 1, was treated with excess of NaOH solution at 85ºC for 15 min. Properties: Ba/Ti 0.997, contains BaCO3, average particle size 60 nm, TEM image available, BET specific surface area 22.1 m2/g [2591].

TABLE 3.1894 PZC/IEP of BaTiO3 Obtained by High-Gravity Reactive Precipitation Electrolyte

T

Method

0.001 M NaCl

iep

Instrument Malvern Zetasizer 3000 HS

pH0

Reference

2.5

[2591]

3.4.18.1.3 Origin Unknown Properties: Cubic, BET specific surface area 10.3 m2/g, particle size 100 nm, detailed analysis available [2592].

Table 3.1895 PZC/IEP of BaTiO3 from Unspecified Sources Ba/Ti

Electrolyte

0.998 0.99 1.07,-

0.001 M KCl

a

T

Method iep iepa iepa

Instrument

pH0

Brookhaven ZetaPlus Electrophoresis Electrophoresis

Reference

<3 if any [2592] 7.7 [2593] 8.5 [2593,2594]

Only value, data points not reported.

3.4.18.2

Ba–Ca Titanates and Titanozirconates

3.4.18.2.1 (Ba0.98Ca0.02)1.002TiO3 Synthesized from TiO2, BaCO3, and CaCO3.

TABLE 3.1896 PZC/IEP of (Ba0.98Ca0.02)1.002TiO3 Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

ELS 8000 Otsuka

6.7a

[2138]

Arbitrary interpolation.

772

Surface Charging and Points of Zero Charge

3.4.18.2.2

(Ba,Ca) (Ti,Zr) O3 from Kyorix

TABLE 3.1897 PZC/IEP of (Ba, Ca)(Ti, Zr)O3 from Kyorix Electrolyte

T

Method

0.01 M NaNO3 a

Instrument

iep

Matec ESA 9800

pH0

Reference

a

8.6

[2595]

In acid titration started at pH 9.2. Base titration from pH 3 produced positive z potentials at pH up to 10.

3.4.18.2.3 Synthetic (Ba, Ca)(Ti, Zr)O3 Reagent-grade BaCO3, CaCO3, TiO2, and ZrO2 were calcined at 1200°C. Properties: 0.16% Hf [2595].

TABLE 3.1898 PZC/IEP of Synthetic (Ba, Ca)(Ti, Zr)O3 (Ba + Ca)/(Ti + Zr) 0.995 1 1.005 a

Electrolyte

T

0.01 M NaNO3

Method

Instrument

pH0a

Reference

iep

Matec ESA 9800

>10 if any 8.7 9.2

[2595]

In acid titration started at pH 10. Base titration from pH 3 produced positive z potentials at pH up to 10.

3.4.18.2.4 Ba0.86Ca0.14Ti0.85Zr0.14Mn0.01O3 Reagent-grade BaCO3, CaCO3, TiO2, ZrO2, and MnCO3 were ball-milled in an aqueous dispersion, and calcined in air at 900–1200°C for 12 h.

TABLE 3.1899 PZC/IEP of Ba0.86Ca0.14Ti0.85Zr0.14Mn0.01O3 Calcined at (°C) 900 1000 1100 1200

Electrolyte HCl + NaOH

T

Method

Instrument

iep

Laser Zee Meter

pH0 10 8.5 7.8 7.6

Reference [2596]

773

Compilation of PZCs/IEPs

3.4.18.3

CaTiO3

3.4.18.3.1 From Alfa Aesar Properties: Perovskite, structure confirmed by XRD, purity >99%, 325 mesh [2597]. TABLE 3.1900 PZC/IEP of CaTiO3 from Alfa Aesar Electrolyte

T

None

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000 HSA

3

[2597]

3.4.18.3.2 Perovskite from High Pure Chemicals, Sakado Properties: Specific surface area 6.2 m2/g, particle size 1.2 μm [2088]. TABLE 3.1901 PZC/IEP of Perovskite from High Pure Chemicals, Sakado Electrolyte

T

Method

NaOH + HNO3

Instrument

pH0

Reference

8.1

[2088]

pH

3.4.18.3.3 Solid-State Reaction, Various Samples TABLE 3.1902 PZC/IEP of Synthetic “Perovskites” Electrolyte

T

Method

25 a

Instrument

pH

pH0 5.7–9.2

Reference a

[2598]

Only values, data points not reported. The name “perovskite,” which usually denotes calcium titanate, was used in [2598] for LaNiO3 and a series of its analogs with Ni replaced by Co, Fe, Mn, Cr, or V, and La partially replaced by Sr, Ca, Gd, or Nd.

3.4.18.3.4

Natural from Lagen-Tal, Norway

TABLE 3.1903 PZC/IEP of Natural Perovskite Electrolyte NaOH + HClO4 a

T

Method iep

Instrument Zeta-Meter

Arbitrary interpolation of scattered data points.

pH0 a

4

Reference [104]

774

Surface Charging and Points of Zero Charge

3.4.18.4 CaTiO(SiO4), Titanite

TABLE 3.1904 PZC/IEP of CaTiO(SiO4) Origin

Electrolyte

Gjerstad, Norway Chibina, former Soviet Union

T

Method

Instrument

pH0

Reference

iep iep

Zeta-Meter Zeta-Meter

3.5 3.5

[104] [104]

0.001 M NaClO4 NaOH + HClO4

3.4.18.5 Pb(Zr, Ti)O3 Synthetic, PbO:TiO2:ZrO2 = 68.3:20.7:11.2.

TABLE 3.1905 PZC/IEP of Pb(Zr, Ti)O3 Electrolyte

T

Method

Instrument

iep a

pH0

Pen Kem Laser Zee Meter 501

Reference

a

5

[123]

Arbitrary interpolation.

3.4.19 TUNGSTATES AND TUNGSTOPHOSPHATES 3.4.19.1

CaWO4

3.4.19.1.1

Natural Scheelite from King Island, Australia, Leached in Dilute HCl, then Ground Properties: 77.2% WO3, 1.04% MoO3, 21.2% CaO, 0.25% SiO2, 0.11% Fe2O3, 0.1% As, 0.02% TiO2, 0.02% MgO [2601].

TABLE 3.1906 PZC/IEP of Natural Scheelite Electrolyte 0.01 M NaCl

T

Method

Instrument

pH0

Reference

20–25

iep

Electrophoresis

<2 if any

[2601]

775

Compilation of PZCs/IEPs

3.4.19.1.2 Origin Unknown

TABLE 3.1907 PZC/IEP of CaWO4 from Unspecified Sources Electrolyte

T

NaOH + HClO4

3.4.19.2

Method

Instrument

pH0

Reference

iep iep

Zeta-Meter Zeta-Meter

<3.5 if any <1.5 if any

[2440] [104]

Tungstophosphates

3.4.19.2.1 Cs3PW12O40 CsCl solution (0.02 M) was introduced into a mixture of H3PW12O40 (0.08 mM). The mixture was heated at 90°C for 1 h. Properties: Monodispersed spherical, 900 nm in diameter. XRD pattern, and SEM images available [2602].

TABLE 3.1908 PZC/IEP of Cs3PW12O40 Electrolyte

T

HNO3 + KOH

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

1.5

[2602]

3.4.19.2.2 Th Tungstophosphate A solution containing Th(NO3)4 (2.5 mM), H3PW12O40 (0.08 mM), and AVANEL S-150 anionic surfactant (0.2 g/dm3) was heated at 90°C for 1 h. Properties: Amorphous, 500 nm in diameter, monodispersed spherical particles, SEM images available [2602].

TABLE 3.1909 PZC/IEP of Th Tungstophosphate Electrolyte HNO3 + KOH

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

5.4

[2602]

3.4.20 BaZrO3 Commercial, from Alfa Aesar. Obtained from BaCO3 and ZrO2.

776

Surface Charging and Points of Zero Charge

Properties: Purity: 99%, BET specific surface area 3.5 m2/g (original material) [2600]. TABLE 3.1910 PZC/IEP of BaZrO3 Description Original Calcined a

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3.0

5.4a 4

[2600]

0.001 M KCl

Arbitrary interpolation.

3.5 GLASSES 3.5.1

COMMERCIAL

PZCs/IEPs of glasses are presented in Tables 3.1911–3.1920. 3.5.1.1 Controlled Pore Glass from Cormay Properties: BET specific surface area 66 m2/g [2603]. TABLE 3.1911 PZC/IEP of Controlled Pore Glass from Cormay Electrolyte

T

Method

0.001–0.1 M NaCl

a

Mergea iep

Instrument

pH0

Reference

Pen Kem 501

<3 if any

[2603]

Uncorrected charging curves suggest PZC at pH about 7.

3.5.1.2 Glasses from Corning 3.5.1.2.1 Vycor from Corning No. 7900 Cleaned with boiling concentrated HNO3. Properties: 96% SiO2 [1818]. TABLE 3.1912 PZC/IEP of Vycor Glass from Corning No. 7900 Description

Electrolyte

60–80 mesh

0–0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep

Streaming potential

<3 if any

[1818]

777

Compilation of PZCs/IEPs

3.5.1.2.2 Pyrex, Borosilicate Glass from Corning No. 7740 Cleaned with boiling concentrated HNO3. TABLE 3.1913 PZC/IEP of Pyrex Glass from Corning No. 7740 Description

Electrolyte

60–80 mesh

0–0.01 M NaCl

3.5.1.3

T

Method

Instrument

iep

Streaming potential

pH0 Reference 2.5

[1818]

From Duke

TABLE 3.1914 PZC/IEP of Glasses from Duke Description

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee Meter 500

1.8

[902]

iep

Brookhaven ZetaPlus

>2.5a

[413]

Glass or SiO2, high 0.01 M KCl purity, mean particle diameter 2 μm Particle size 2 μm 0.001–0.01 M NaCl

a

+10 mV at pH 2.5; −40 mV at pH 5.8.

3.5.1.4

From Electrofact

3.5.1.4.1 Na-Responsive Glass from Electrofact Properties: SiO2 66%, GeO2 2%, Al2O3 2%, B2O3 13%, Na2O 17% by mass, 7.6 m2/g [626].

TABLE 3.1915 PZC/IEP of Na-Responsive Glass from Electrofact Electrolyte 0.001–0.1 M NaCl, LiCl, KCl, CsCl, (C2H5)4NCl

T

Method Instrument pH

pH0 Reference 6

[626]

3.5.1.4.2 K-Responsive Glass from Electrofact Properties: SiO2 66%, GeO2 2%, Al2O3 2%, B2O3 13%, K2O 17% by mass, 3.5 m2/g [626].

778

Surface Charging and Points of Zero Charge

TABLE 3.1916 PZC/IEP of K-Responsive Glass from Electrofact Electrolyte

T

0.1 M NaCl, LiCl, KCl, CsCl, (C2H5)4NCl

Method

Instrument

pH0

Reference

6

[626]

pH

3.5.1.5 Standard Microscope Glass Slides from Fisher

TABLE 3.1917 PZC/IEP of Standard Microscope Glass Slides from Fisher Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KCl

22–24

iep

Brookhaven EKA with cell from Anton Paar

<3 if any

[2604]

3.5.1.6

Pyrex Glasses

TABLE 3.1918 PZC/IEP of Pyrex Glasses Description

Electrolyte

NaCl + HCl, ionic strength 0.05 M Capillary, steamed and 0.01 M KCl aged, then heated at 500°C for 19 h Capillary, g -irradiated, 0.01 M KCl different doses Capillary, annealed at 0.001, 0.01 M 450°C, then aged and KCl steamed Capillary, annealed at 0.0001–0.01 M 450°C KCl Ground capillary

a

Only value, data points not reported.

T

Method

Instrument

pH0

Reference

iep

Electrophoresis, flat cell

<1.5 if any

[2605]

Room

iep

Electro-osmosis

<3 if any

[1941]

Room

iep

Electro-osmosis

<3 if any

[1941]

Room

iep

Electro-osmosis

3

[1941]

Room

iep

Electro-osmosis

4

[1941]

iepa

Streaming potential

4.4

[825]

779

Compilation of PZCs/IEPs

3.5.1.7 Schott Glass Powder Properties: SEM image available [2238].

TABLE 3.1919 PZC/IEP of Schott Glass Powder Electrolyte 0.001 M KCl

3.5.2

T

Method

Instrument

iep

Coulter Delsa 440 SX

pH0 Reference 2

[2238]

OTHER

TABLE 3.1920 PZC/IEP of Glasses from Different Sources Description

Electrolyte

T

25 mol% Na2O, 4 mol% HCl Al2O3 Nano- and ultraporous 0.001–0.1 M glass membranes NaCl prepared from sodium borosilicate glass Nine macroporous glass 0.001–1 M membranes NaCl 24 mol% Li2O, 10 mol% HCl Fe2O3 C glass fibers, 60–65% 0.001 M KCl SiO2, 2–7% B2O3, 7.5–12% Na2O, 13–16% CaO, 2–6% Al2O3 by mass 0.0005– 25 0.01 M NaCl NaOH + HCl Four porous glasses

0.001–0.1 M NaCl Four porous glasses. 0.001, 0.01 M Initial composition 55% NaCl SiO2, 35% B2O3, 10% Na2O, specific surface area 56.6–410 m2/g

Method iep iep

iep pH iep iep

iep iep Merge pH

Instrument

pH0

Reference

Streaming potential Streaming potential

<1 if any

[1936]

<2 if anya

[1816]

Electrophoresis, Streaming potential Streaming potential EKA Anton Paar

<2 if any <4 if any

[2606]

<2.5 if any <3 if any

[1936]

Streaming potential Streaming potential

<3 if any

[294]

<3 if any

[2607]

<3 if anyb <3.5–6

[523]

[1878]

[2609]

continued

780

Surface Charging and Points of Zero Charge

TABLE 3.1920 (continued) Description Six porous glasses. Initial composition 97.8% SiO2, 2% B2O3, 0.2% Na2O, specific surface area 107–189 m2/g Seven porous glasses. Initial composition 96.3% SiO2, 3.2% B2O3, 0.5% Na2O, specific surface area 41–75 m2/g 24 mol% Li2O, 10 mol% Fe2O3, subjected to thermal treatment E glass fibers, 53–60% SiO2, 20–25% CaO, 11–15.5% Al2O3 by mass 74% SiO2, 10% CaO, 15% Na2O, 1% Al2O3 Ingold, proton-responsive membrane S2 glass fibers, 65% SiO2, 10% MgO, 25% Al2O3 by mass Porous glasses. Initial composition 70 mol% SiO2, 23 mol% B2O3, 7 mol% Na2O Porous glass. Initial composition 68.4% SiO2, 25.6% B2O3, 6% Na2O, specific surface area 141 m2/g 10.4% Fe2O3, 28% CaO, 5.2% Na2O, 1.4% K2O, 55% Al2O3 1.8% Fe2O3, 30.9% CaO, 9.7% Na2O, 2.2% K2O, 55.4% Al2O3 8.1% SiO2, 52.5% CaO, 0.2% Na2O, 39.2% Al2O3 a b c

Electrolyte

T

Method

Instrument

pH0

Reference

0.1 M NaCl

pH

<3.5–6.5

[1834]

0.1 M NaCl

pH

<4–6.5

[1834]

HCl

iep

Streaming potential

<4.5 if any

[1936]

0.001 M KCl

iep

EKA Anton Paar

3.3

[1878]

iep

EKA

3.4

[2610]

iepc

Streaming potential EKA Anton Paar

3.8

[825]

4

[1878]

0.01 M KCl

25

0.001 M KCl

iep

0.1 M NaCl

pH

4–7.2

[2611]

0.01 M NaCl 0.001 M NaCl

pH

4.8–6.2 3.8–5.2

[2609]

8

[2610]

0.01 M KCl

25

iep

EKA

IEP shifts to high pH in the presence of 0.1 M CsCl. Uncorrected charging curves shown in figures suggest PZC at pH 4–7. Only value, data points not reported.

9.3

>8 if any

781

Compilation of PZCs/IEPs

3.6 CARBON AND CARBON-RICH MATERIALS The PZCs/IEPs of elementary carbon are presented in Tables 3.1921–3.1923.

3.6.1

DIAMOND

TABLE 3.1921 PZC/IEP of Diamond Description

Electrolyte

H-terminated O-terminated Particles 500 nm in diameter, 1 d aged PA 0.5/0, BET specific surface area 20.7 m2/g

3.6.2

0.0001– 0.01 M KCl 0.001–0.03 M KCl 0.001–0.1 M KCl, LiCl, CsCl, KNO3

T

Method

Instrument

pH0

Reference

iep

Streaming current Electrophoresis

3.5 <2.5 if any <2 if any

[466]

<3.5 if any

[2613]

iep 20

pH

[2612]

GRAPHITE

TABLE 3.1922 PZC/IEP of Graphite Location Ceylon Borrowdale

3.6.3

Electrolyte NaOH + HClO4

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

2 4

[104]

FULLERENE C60

From MER, clusters prepared from solution in toluene.

TABLE 3.1923 PZC/IEP of Fullerene C60 Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

25

iep

Malvern Zetasizer Nano ZS

<3 if any

[2614]

782

Surface Charging and Points of Zero Charge

3.6.4 CARBON BLACK, ACTIVATED CARBONS, AND RELATED PRODUCTS The PZCs/IEPs of carbon black, activated carbons, and related products are presented in Tables 3.1924–3.1999. Activated carbons are complex, ill-defined materials, and their surface composition may be different from their bulk composition. The surface properties of carbons can easily be modified. Numerous studies have been devoted to series of activated carbons obtained by modification of the same commercial product by different methods. A compilation of PZCs/IEPs of activated carbons can be found in [620]. 3.6.4.1 Commercial 3.6.4.1.1 Monarch 700, Furnace Carbon Black from Cabot Properties: <2% of ash, BET specific surface area (original) 200 m2/g [339]. A: original, 202 m2/g B: heated in argon at 1800°C, 116 m2/g C: heated in argon at 2500°C, 113 m2/g D: oxidized in boiling HNO3 for 1 h, then washed with water, 246 m2/g E: C oxidized in boiling HNO3 for 1 h, then washed with water, 131 m2/g F: C stored in air for 1 h, then heated in nitrogen at 1200°C, and exposed to air at room temperature for 1 h

TABLE 3.1924 PZC/IEP of Monarch 700 from Cabot Code A B C D E F

Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep/pH

Zeta-Meter

6.2/7 —/6.5 7.5/7.4 <2/2.6 3/5.6 8.8/7.9

[339]

3.6.4.1.2 From Calgon 3.6.4.1.2.1 BD, from Wood, Steam-Activated TABLE 3.1925 PZC/IEP of BD from Calgon Electrolyte None a

T

Method

Instrument

pH0

Reference

pHa

3 d equilibration

5.7

[2615]

Only value, data points not reported.

783

Compilation of PZCs/IEPs

3.6.4.1.2.2 BPL, from Bituminous Coal Properties: 8% ash [2616], BET specific surface area (original) 927 m2/g [2616], 1200 m2/g [2617], (ammonia-modified for 3 h at 600°C) 950 m2/g [2616], (HNO3 oxidized) 878 m2/g [2616]; a detailed analysis of each sample is available [2616].

TABLE 3.1926 PZC/IEP of BPL from Calgon Description Original NH3-modified Oxidized Original a

Electrolyte

T

0.001 M KNO3

25

Method iep/mass titration

Instrument Zeta-Meter 3.0 +

Mass titrationa

pH0

Reference

3.4/7.5 4.2/9.4 <2/2.4 9.5

[2616]

[2617]

Only value, data points not reported.

3.6.4.1.2.3 Filtrasorb 100 (or FS-100) From bituminous coal. Properties: Detailed analysis available [619], specific surface area 524 m2/g [619,2618], BET specific surface area 751 m2/g [2617].

TABLE 3.1927 PZC/IEP of Filtrasorb 100 (or FS-100) from Calgon Description Original NaOH-washed

Electrolyte

T

0.005–0.5 M NaClO4

Original a

Method

Instrument

pH0

iep Laser Zee 500 <2 if any iep <2 if any cip 9 Mass titrationa 9.2

Reference [619,2618]a

[2617]

Only value, data points not reported.

3.6.4.1.2.4 Filtrasorb 200 A: washed with water, 648 m2/g [527,2619] B: A washed with 1 M NaOH and water, 664 m2/g C: A washed with 37% HCl and water, 659 m2/g D: B washed with 1 M NaOH and water, 662 m2/g E: A washed with concentrated HNO3 and water, 636 m2/g F: E washed with 1 M NaOH and water, 647 m2/g [527] G: A washed with 1 M citric acid and water, 431 m2/g [2619] Properties: Detailed analysis available [619], specific surface area 482 m2/g [619,2618], 1008.8 m2/g [622], SEM images available [527].

784

Surface Charging and Points of Zero Charge

TABLE 3.1928 PZC/IEP of Filtrasorb 200 from Calgon Code Original NaOH washed A B C D E F A G Water-washed a b

Electrolyte

T

Method

0.005–0.5 M NaClO4

Instrument

0.1 M NaNO3

iep iep cip pH

2 d equilibration

0.1 M NaNO3

pH

2 d equilibration

0.005, 0.05 M NaClb

Laser Zee 500

Intersection

pH0

Reference

<2 if any <2 if any 8.2 6.9 10.7 5.7 8.5 3.7 7.5 7.1 6.5 7.2

[619,2618]a

[527]

[2619] [622]

Only value, data points not reported. Titration curves in 0.05 M NaClO4 and NaNO3 are also reported.

3.6.4.1.2.5 Filtrasorb 300 (or F-300), Raw Material Coal Properties: Detailed analysis available [619], 2% moisture, 9% ash [654], BET specific surface area 950–1050 m2/g [808,809] (manufacturer’s data), 850–950 m2/g [654], specific surface area 600 m2/g [619,2618], 820 m2/g [2620], mean particle diameter 1.5–1.7 mm [808,809].

TABLE 3.1929 PZC/IEP of Filtrasorb 300 (or F-300) from Calgon Description

Electrolyte

iep

Soxhlet-extracted 0.01, 0.1 M with water NaCl

a b

Method a

HCl-washed

NaOH-washed

T

0.005–0.5 M NaClO4 0.1 M NaCl

Instrument Streaming potential Rank Brothers

pH Salt addition iep iep Laser Zee 500 cip pHa 1 d equilibration

pH0 2.6 6 6 <3.2 if any <2 if anyb >10 if any 10.2

Reference [809] [654]

[619,2618]a [2620]

Only value, data points not reported. CIP reported in [619,2618] is based on arbitrary extrapolation. Unwashed material showed a mixture of positive and negative z potentials with multiple IEPs.

785

Compilation of PZCs/IEPs

3.6.4.1.2.6 Filtrasorb 400 (or F-400) from Calgon (or from Chemviron) Manufactured from bituminous coal. Properties: Detailed analysis available [619], 67 ppm Ca, 58 ppm Fe [2621], 2% moisture [207], BET specific surface area 1050–1200 m2/g [2622], 902 m2/g [2623], 930 m2/g [2621], 948 m2/g [2617], specific surface area 890 m2/g [2620] 1100 m2/g [207], 1236 m2/g (measured), 1203 m2/g (manufacturer) [619,2618], 941 m2/g [2624].

TABLE 3.1930 PZC/IEP of Filtrasorb 400 (or F-400) from Calgon Description Unwashed NaOH-washeda

Electrolyte 0.005–0.5 M NaClO4 None 0.01 M

As received

0.001–0.1 M NaCl

Water-washed Original

Acid-washed

a

b

0.1 M NaCl 0.1 M NaCl 0.01, 0.1 M NaCl

T

Method

Instrument

iep iep cip pHb pH pHb iep cip Titrationb Mass titrationb 25 pH pHb Titrationb

Laser Zee 500

3 d equilibration

Electrophoresis

1 d equilibration 1 d equilibration 12 h equilibration

pH0

Reference

2.3 <2 if any 10 5.6 6.5 7 7.1 6.8 7.2 9.2 9.8 10 11

[619,2618]a

[2615] [2599]b [2622] [2624] [207] [2617] [2623] [2620] [2621]

[619] reports also a series of electrokinetic curves (IEP at pH from <2 if any to 7) of different lots of Filtrasorb 400 treated with H2O2 or HClO, and aged under various conditions. Only value, data points not reported.

3.6.4.1.2.7 PCB, from Coconut

TABLE 3.1931 PZC/IEP of PCB from Calgon Electrolyte None a

T

Method

Instrument

pH0

Reference

pHa

3 d equilibration

9.4

[2615]

Only value, data points not reported.

786

Surface Charging and Points of Zero Charge

3.6.4.1.2.8 WPLL Manufactured from bituminous coal, used as received. Properties: BET specific surface area 294 m2/g [2617].

TABLE 3.1932 PZC/IEP of WPLL from Calgon Electrolyte

T

Method

Instrument

Mass titration

3.6.4.1.2.9

pH0

Reference

9.2

[2617]

WSIV, from Wood, Chemically Activated

TABLE 3.1933 PZC/IEP of WSIV from Calgon Electrolyte

T

Method

Instrument

pH0

Reference

pHa

3 d equilibration

9

[2615]

None a

Only value, data points not reported.

3.6.4.1.2.10 Unspecified Activated Carbon from Calgon Made from Coal Original and treated with 15 M HNO3 for 2 h at different temperatures. Properties: BET specific surface area 1300 m2/g [2625].

TABLE 3.1934 PZC/IEP of Unspecified Activated Carbon from Calgon Made from Coal Treatment Original At 25°C At 50°C At 78°C a

Electrolyte

T

0.001–0.1 M NaNO3

Method

Instrument

pH0

Reference

Mass titrationa

1 d aged

9.7 6.2 4.2 2.3

[2625]

Only values, data points not reported.

3.6.4.1.2.11 Other Properties: 86.5% C, 6.5% O, 1.2% H, BET specific surface area 820 m2/g [2626].

787

Compilation of PZCs/IEPs

TABLE 3.1935 PZC/IEP of Unspecified Activated Carbon from Calgon Electrolyte

T

Method

Instrument

pH

pH0

Reference

9

[2626]

3.6.4.1.3 D43/1 from Carbo-Tech A: de-ashed with concentrated HF and HCl B: A evacuated at 1000 K for 3 h C: B annealed in NH3 for 2 h at 1170K, cooled in NH3, and evacuated at 400 K for 3 h D: A treated with concentrated HNO3 for 3h at 80°C E: D annealed in NH3 for 2 h at 1070 K, cooled in NH3, and evacuated at 400 K for 3 h.

TABLE 3.1936 PZC/IEP of D43/1 from Carbo-Tech Code/Specific Surface Area (m2/g) A/1131 B/1133 C/1178 D/1071 E/1153

Electrolyte

T

Method

Instrument

pH

2 d equilibration

0.1 M NaCl

pH0 6.7 10.1 10.4 3.1 10.2

Reference [2627]

3.6.4.1.4 From CECA Properties: Specific surface area 1460 and 1265 m2/g (CET and CFT) [2620].

TABLE 3.1937 PZC/IEP of Activated Carbons from CECA Type CET CFT a

Electrolyte 0.1 M NaCl

T

Method pH

a

Only value, data points not reported.

Instrument

pH0

Reference

1 d equilibration

9.6 9.3

[2620]

788

Surface Charging and Points of Zero Charge

3.6.4.1.5 From Chemviron See Section 3.6.4.1.2.6. 3.6.4.1.6 Grade 12X40 from Darco

TABLE 3.1938 PZC/IEP of grade 12X40 Activated Carbon from Darco Electrolyte

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

6.2

[2624]

0.01 M NaCl

3.6.4.1.7 From Elf-Atochem 3.6.4.1.7.1 Type 1240, from Bituminous Carbon Properties: BET specific surface area 818 m2/g (original) [2615]. A: original B: acid-washed C: outgased in Ar for 16 h at 500°C D: outgased in Ar for 16 h at 900°C E: outgased in Ar for 16 h at 1200°C F: D oxidized G: E oxidized

TABLE 3.1939 PZC/IEP of Activated Carbon, Type1240 from Elf-Atochem Code Electrolyte A B C D E F G a

None

T

Method a

pH

Only value, data points not reported.

Instrument 3 d equilibration

pH0 Reference 7.2 7 9.8 11 11.1 6.2 6.7

[2615]

789

Compilation of PZCs/IEPs

3.6.4.1.7.2 BGP from Elf-Atochem, from Wood, Steam-Activated TABLE 3.1940 PZC/IEP of BGP from Elf-Atochem Electrolyte

T

a

None a

Method pH

Instrument

pH0

Reference

3 d equilibration

8.1

[2615]

Only value, data points not reported.

3.6.4.1.8 Monolith Tubes from Fractal Carbon Properties: BET specific surface area 150 m2/g [2628].

TABLE 3.1941 PZC/IEP of Activated Carbon from Fractal Carbon Electrolyte

T

0.1 M KCl a

Method

Instrument

Mass titrationa

pH0

Reference

9.5

[2628]

Only value, data points not reported.

3.6.4.1.9 From ICI 3.6.4.1.9.1 Darco G60 (from ICI or from Norit) Properties: Detailed analysis available [619,2629], BET specific surface area 761.6 m2/g [2629], specific surface area 410 m2/g [619,2618], SEM image available [2629].

TABLE 3.1942 PZC/IEP of Darco G60 from ICI Description Original NaOH-washed

Electrolyte

T

0.005–0.5 M NaClO4 0.01 M NaNO3

a

Only value, data points not reported.

Method iep iep cip iep

Instrument Laser Zee 500

Malvern Zetamaster

pH0

Reference

<2 if any <2 if any 6.2 8.1

[619] [2618]a [2629]

790

Surface Charging and Points of Zero Charge

3.6.4.1.9.2 Darco HDC Properties: Detailed analysis available [619], specific surface area 556 m2/g [619,2618]. TABLE 3.1943 PZC/IEP of Darco HDC from ICI Description NaOH-washed

a

b

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Laser Zee 500

4a

[619] [2618]b

0.05 M NaClO4

Unwashed material showed multiple IEPs. Titration curves obtained at various ionic strengths did not show a clear CIP. Only value, data points not reported.

3.6.4.1.9.3 Darco HD3000 (see also Hydro Darco 3000) Properties: Detailed analysis available [619], specific surface area 927 m2/g (measured) 714 m2/g (manufacturer) [619,2618]. TABLE 3.1944 PZC/IEP of Darco HD3000 from ICI Description Original NaOH-washed a b

Electrolyte

T

0.05 M NaClO4

Method

Instrument

pH0

Reference

iepa

Laser Zee 500

<2 if any <2 if any

[619] [2618]b

Titration curves obtained at various ionic strengths did not show a clear CIP. Only value, data points not reported.

3.6.4.1.9.4 Darco KB Properties: Detailed analysis available [619], specific surface area 2162 m2/g [619,2618] 1500 m2/g [2630].

TABLE 3.1945 PZC/IEP of Darco KB from ICI Description Original NaOH-washed

a

Electrolyte 0.005–0.5 M NaClO4

Only value, data points not reported.

T

Method

Instrument

pH0

Reference

iep iep cip pH

Laser Zee 500

<2 if any <2 if any 5.2 4.2

[619] [2618]a [2630]

791

Compilation of PZCs/IEPs

3.6.4.1.9.5 Darco S51 (or S51 RL) Properties: Detailed analysis available [619], specific surface area 520 m2/g [619,2618], 650 m2/g [2630].

TABLE 3.1946 PZC/IEP of Darco S51 (or S51 RL) from ICI Description NaOH-washed

Electrolyte

T

Method

0.05 M NaClO4

iep

S 51 RL a

b

Instrument Laser Zee 500

pH0

Reference a

<2 if any

pH

6.2

[619] [2618]b [2630]

Unwashed material showed multiple IEPs. Titration curves obtained at various ionic strengths did not show a clear CIP. Only value, data points not reported.

3.6.4.1.9.6 Hydro Darco 3000 (see also HD 3000), Raw Material: Lignite Properties: BET specific surface area 600–650 m2/g, mean particle diameter 1.6 mm [808,809].

TABLE 3.1947 PZC/IEP of Hydro Darco 3000 from ICI Description

Electrolyte

T

Method

Instrument

pH0

Reference

iepa

Streaming potential

4.8

[809]

HCl washed a

Only value, data points not reported.

3.6.4.1.10 LP from Kureha, Made of Petroleum Pitch Conditioned under different conditions: Boiled in water for 1 h, then dried at 110°C for 1 d Oxygenated in a flow of air for 1 h at 350°C Deoxygenated in a flow of nitrogen for 1 h at 850°C, and then cooled and stored in nitrogen. Properties: BET specific surface area 1112 (water-treated), 1465 (air-treated), and 1032 (nitrogen-treated) m2/g [2631,2632].

792

Surface Charging and Points of Zero Charge

TABLE 3.1948 PZC/IEP of LP Activated Carbon from Kureha Treatment

Electrolyte

Water Air Nitrogen

0.1 M NaCl

a

T

Method

Instrument

pH0

Reference

pHa

1 d equilibration

7.2 2.8 9.2

[2631,2632]

Only value, data points not reported.

3.6.4.1.11 HSAG 16 from Lonza Tar-derived, graphitic. Properties: 0.3% of ash, BET specific surface area original: 227 m2/g [339].

TABLE 3.1949 PZC/IEP of HSAG 16 from Lonza Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep/pH

Zeta-Meter

2.4/4.4

[339]

3.6.4.1.12 From Mallinckrodt Properties: Specific surface area 899.7 m2/g (o-phenanthroline adsorption) [2633].

TABLE 3.1950 PZC/IEP of Activated Carbon from Mallinckrodt Electrolyte 0.001, 0.1 M NaNO3

T

Method Intersection

Instrument

pH0

Reference

7.5

[2633]

3.6.4.1.13 From Merck, Modified A: ash discharging B: A, oxidation with 13% H2O2, removal of humic acids C: A, outgasing at 1127°C in argon, equilibrated with air at room temperature Properties: Detailed analysis available [2634] BET specific surface area 1089 m2/g [2634].

793

Compilation of PZCs/IEPs

TABLE 3.1951 PZC/IEP of Activated Carbon from Merck Code

Electrolyte

T

Method

A B C Original

0.1 M NaCl

25

pH

0.01 M NaCl

25

pH

Instrument

pH0

Reference

3.8 <2.2 if any >10 if any 7.5

[2635]

[2634]

3.6.4.1.14 MA 100 from Mitsubishi Chemicals, Japan Carbon black, original and refluxed in 20% H2SO4 at 110°C for 90 min. Properties: BET specific surface area 59.4 m2/g (original) and 62.1 m2/g (acidtreated) [2636]. TABLE 3.1952 PZC/IEP of 100 from Mitsubishi Chemicals Treatment None 20% H2SO4 at 110°C for 90 min

Electrolyte

T

Method

Instrument

pH0

Reference

0.1 M NaNO3

20

pH

6 h equilibration

6.4 3.5

[2636]

3.6.4.1.15 From Norit 3.6.4.1.15.1

Norit C Properties: BET specific surface area 1380 m2/g [2637].

TABLE 3.1953 PZC/IEP of Norit C Treatment A: Original B: 3 h in air at 250°C C: 3 h in nitrogen at 950°C D: C 7 min in air at 250°C E: 3 h in hydrogen at 950°C F: E in air for 1 d G: E in air for 7 d H: E in air for 20 d I: E in air for 30 d J: E in boiling 70% HNO3 for 15 min K: E in boiling 70% HNO3 for 30 min L: E in 18% HNO3 for 16 h at 60°C a

Electrolyte T Method 0.001 M KNO3

Instrument

iep/ Zeta-Meter mass 3.0+ titration

pH0a

Reference

2.6/2.5 2.2/2.2 3.5/5.2 2.9/4.2 4.9/9 4.2/8.9 4.2/9 3.7/8.6 3.3/8.4 1.6/3.3 1.4/2.8 3.5/3.9

[2637]

Figure 1 indicates that IEPs at pH < 2.5 reported in Table 1 of Reference [2637] were obtained by extrapolation.

794

Surface Charging and Points of Zero Charge

3.6.4.1.15.2 RX3 Extra Peat-derived, steam-activated. A: original B: oxidized by nitric acid (probably boiling, 6 M) Properties: 4% of ash, BET specific surface area (original) 1200–1300 m2/g [339].

TABLE 3.1954 PZC/IEP of RX3 Extra from Norit Code A B

Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep/pH

Zeta-Meter

2.7/6.6 —/3.4

[339]

3.6.4.1.15.3 SX PLUS Properties: BET specific surface area 900 m2/g (original), 750 m2/g (refluxed in 2.5 M HNO3 for 1 d), particle size 50–100 μm [419].

TABLE 3.1955 PZC/IEP of SX PLUS from Norit Treatment Original Refluxed in 2.5 M HNO3 for 1 d

Electrolyte 0.001 M KNO3

T

Method

Instrument

pH0

Reference

pH/iep

Pen Kem Laser Zee Meter 500

8.3/3.5 2.4/<2 if any

[419]

3.6.4.1.15.4 GAC 1240 PLUS from Norit A: original, 972 m2/g [2638] B: refluxed with 6 M HNO3, washed with water, dried for 1 d at 110°C, and stored in a desiccator, 909 m2/g C: treated with 10 M H2O2 at room temperature (until complete degradation of H2O2), washed with water, dried for 1 d at 110°C, and stored in a desiccator, 949 m2/g [2638] D: B heated in hydrogen to 700°C at 10°C/min, then 1 h at 700°C; cooled in hydrogen, equilibrated with air for 1 h at room temperature, and stored in a desiccator, 972 m2/g [2638] E: B heated in nitrogen to 700°C at 10°C/min, then 1 h at 700°C; cooled in nitrogen, equilibrated with air for 1 h at room temperature, and stored in adesiccator, 946 m2/g [2638]

795

Compilation of PZCs/IEPs

TABLE 3.1956 PZC/IEP of GAC 1240 PLUS from Norit Treatment A B C D E a

Electrolyte 0.01 M NaCl

T

Method a

Room

pH

Instrument

pH0

Reference

2 d equilibration

9.7 2.7 5.4 10.8 9.9

[2638]

Only value, data points not reported.

3.6.4.1.15.5 Sorbo-Norit Properties: Detailed analysis available [2634], BET specific surface area 1182 m2/g (original), 1237 m2/g ( HCl-washed) [2634].

TABLE 3.1957 PZC/IEP of Sorbo-Norit Treatment

Electrolyte

T

Method

Original HCl-washed

0.01 M NaCl

25

pH

Instrument

pH0

Reference

12.1 9.7

[2634]

3.6.4.1.15.6 Other From peat moss, original and treated with 15 M HNO3 for 2 h at different temperatures. Properties: BET specific surface area 1300 m2/g [2625].

TABLE 3.1958 PZC/IEP of Unspecified Activated Carbon from Norit Treatment Original At 25°C At 78°C a

Electrolyte

T

0.001–0.1 M NaNO3

Method a

Mass titration

Instrument

pH0

Reference

1 d aged

10.2 4.7 2.8

[2625]

Only value, data points not reported.

3.6.4.1.16 From North American 3.6.4.1.16.1 G-21 Boiled with HNO3 (different concentrations) for 18 h. Properties: Ash 0.6–1.1%, BET specific surface area 1015–1150 m2/g [2639].

796

Surface Charging and Points of Zero Charge

TABLE 3.1959 PZC/IEP of G-21 from North American [HNO3] (M)

Electrolyte

None 0.2 0.4 1 2 a

T

Method

Instrument a

NaNO3

Mass titration

pH0

Reference

10 7.8 6 5.5 3.5

[2639]

Only value, data points not reported.

3.6.4.1.16.2 Other From coconuts, original and treated with 15 M HNO3 for 2 h at different temperatures. Properties: BET specific surface area 1500 m2/g [2625].

TABLE 3.1960 PZC/IEP of Unspecified Activated Carbon from North American Treatment Original At 25°C At 50°C At 78°C

Electrolyte

T

0.001–0.1 M NaNO3

Method

Instrument

pH0

Reference

Mass titration

1 d aged

10.3 4.6 3.4 2.2

[2625]

3.6.4.1.17 From Nuchar See also Section 3.6.4.1.25. 3.6.4.1.17.1 Nuchar C-190-N Properties: Specific surface area 890 m2/g [2624].

TABLE 3.1961 PZC/IEP of Nuchar C-190-N Electrolyte 0.001–0.1 M NaCl

T

Method

Instrument

pH0

Reference

iep cip

Electrophoresis

4.8 4.5

[2624]

797

Compilation of PZCs/IEPs

3.6.4.1.17.2 Nuchar N-722 Properties: Specific surface area (original) 849 m2/g [2624]. TABLE 3.1962 PZC/IEP of Nuchar N-722 Electrolyte

T

Method

Instrument

iep cip

Electrophoresis

0.001–0.1 M NaCl

pH0

Reference

5.7 6

[2624]

3.6.4.1.18 Grade HGR from Pittsburgh TABLE 3.1963 PZC/IEP of HGR Activated Carbon from Pittsburgh Electrolyte

T

0.01–0.1 M NaCl

Method

Instrument

pH0

iep

Electrophoresis

Reference

6.7

[2624]

3.6.4.1.19 From Prolabo Properties: 5.6% ash, BET specific surface area 929 m2/g [2640]. TABLE 3.1964 PZC/IEP of Activated Carbon from Prolabo Electrolyte

T

Method

Instrument

pHa a

pH0

Reference

4.1

[2640, 2641]

Only value, data points not reported.

3.6.4.1.20

From Rohm and Haas

3.6.4.1.20.1 Ambersorb XE-340 Polymer-derived. Properties: <0.5% ash, BET specific surface area (original) 400 m2/g [339]. TABLE 3.1965 PZC/IEP of Ambersorb XE-340 from Rohm and Haas Electrolyte 0.001 M KNO3 a

Extrapolated.

T

Method

Instrument

pH0

Reference

iep/pH

Zeta-Meter

1.7a/3.4

[339]

798

Surface Charging and Points of Zero Charge

3.6.4.1.20.2 Ambersorb XE-348 from Rohm and Haas Polymer-derived. A: original B: original, cited after [2642] C: treated with ammonia for 1.5 h at 600°C, cited after [2642] Properties: <0.5% of ash, BET specific surface area (original) 500 m2/g [339]. TABLE 3.1966 PZC/IEP of Ambersorb XE-348 from Rohm and Haas Code A B C a

Electrolyte

T

0.001 M KNO3

Method

Instrument

pH0

Reference

iep/pH

Zeta-Meter

2.3/9.4 2a/7.8 5.7/8.6

[339]

Extrapolated.

3.6.4.1.21 Ca 346 from Scharlau Properties: BET specific surface area 838 m2/g [2643]. TABLE 3.1967 PZC/IEP of Ca 346 from Scharlau Electrolyte

T

Method

0.001–0.2 M NaCl a

Instrument

pH0

Reference

a

cip

7.5

[2643]

From TLM parameters, based on subjective extrapolation.

3.6.4.1.22 From S.D. Fine Chem., India Properties: Moisture 5%, ash 2.5%, specific surface area 492 m2/g, particle size 0.2–40 μm, peak at 25 mm, pore volume 0.231 cm3/g [2644].

TABLE 3.1968 PZC/IEP of Activated Carbon from S.D. Fine Chem. Electrolyte

T

Method

Instrument

pH0

Reference

0.1 M KNO3

25

pH

1 d equilibration

6.6

[2644]

799

Compilation of PZCs/IEPs

3.6.4.1.23 KRF from Trayal Properties: BET specific surface area 960 m2/g [2628]. TABLE 3.1969 PZC/IEP of KRF Activated Carbon from Trayal Electrolyte

T

0.1 M KCl a

Method

Instrument

Mass titration

pH0

Reference

9.3

[2628]a

Only value, no data points.

3.6.4.1.24 Ultracarb from USFilter Westates Properties: Specific surface area 870 m2/g [2645].

TABLE 3.1970 PZC/IEP of Ultracarb from USFilter Westates Electrolyte

a

T

Method

Instrument

25a

Mass titration

pH0 9.5

Reference [2645]

Only value, data points not reported. Also 5–37°C.

3.6.4.1.25 From Westvaco See also Section 3.6.4.1.17. 3.6.4.1.25.1 Nuchar SA Properties: Detailed analysis available [619], specific surface area 1251 or 1351 m2/g (measured), 1219 m2/g (manufacturer) [619,2618].

TABLE 3.1971 PZC/IEP of Nuchar SA from Westvaco Description

Electrolyte

T

NaOH-washeda 0.005–0.5 M NaClO4

a b

Unwashed material showed IEP at pH 2. Only value, data points not reported.

Method

Instrument

pH0

Reference

iep cip

Laser Zee 500

<2 if any 4

[619,2618]b

800

Surface Charging and Points of Zero Charge

3.6.4.1.25.2 Nuchar SN Properties: Detailed analysis available [619], specific surface area 1430 m2/g [619,2618].

TABLE 3.1972 PZC/IEP of Nuchar SN from Westvaco Description

Electrolyte

T

Method

Instrument

pH0

Reference

iep iep cip

Laser Zee 500

<2 if any <2 if any 3

[619a,2618b]

Original 0.005–0.5 M NaClO4 NaOH-washed

a b

From Fig. 5. Table 6 reports CIP at pH 4. Only value, data points not reported.

3.6.4.1.25.3 Nuchar WVG Properties: Detailed analysis available [619], specific surface area 1607 m2/g (measured and manufacturer) [619,2618].

TABLE 3.1973 PZC/IEP of Nuchar WVG from Westvaco Description

Electrolyte

T

Method

Instrument

pH0

Reference

iep cip

Laser Zee 500

<2 if anya 9

[619,2618]b

NaOH-washed 0.005–0.5 M NaClO4

a b

Original material showed multiple IEPs. Only value, data points not reported.

3.6.4.1.25.4 Nuchar WVL Properties: Detailed analysis available [619], specific surface area 1912 m2/g [619,2618].

TABLE 3.1974 PZC/IEP of Nuchar WVL from Westvaco Description

Electrolyte

Original 0.005–0.5 M NaClO4 NaOH-washed

a b

T

Method

Instrument

pH0

Reference

iep iep cip

Laser Zee 500

<2 if any <2 if any 7.2

[619a,2618b]

From Figure 5. Table 6 reports CIP at pH 7.9. Only value, data points not reported.

801

Compilation of PZCs/IEPs

3.6.4.1.25.5 Nuchar WVW Properties: Detailed analysis available [619], specific surface area 1215 m2/g [619,2618].

TABLE 3.1975 PZC/IEP of WVW from Westvaco Description

Electrolyte

T

Original 0.005–0.5 M NaClO4 NaOH-washed

a b

Method

Instrument

pH0

Reference

iep iep cip

Laser Zee 500

<2 if any 2.3 8a

[619] [2618]b

From Figure 5 in [619]. Table 6 in [619] reports CIP at pH 7.25. Only value, data points not reported.

3.6.4.1.25.6

WV-B

Properties: Specific surface area 1343 m2/g [2620].

TABLE 3.1976 PZC/IEP of WV-B from Westvaco Electrolyte

T

Method

0.1 M NaCl a

pH

a

Instrument 1 d equilibration

pH0 5

Reference [2620]

Only value, data points not reported.

3.6.4.1.25.7 Micro, Meso, and Macro from Westvaco Manufactured from wood, used as received. Properties: BET specific surface area Micro 1594, Meso 1664, and Macro 1644 m2/g [2617]. TABLE 3.1977 PZC/IEP of Activated Carbons Micro, Meso and Macro from Westvaco Type Micro Meso Macro

Electrolyte

T

Method Mass titration

Instrument

pH0 5.4 5 3.4

Reference [2617]

3.6.4.1.25.8 Other From wood, original and treated with 15 M HNO3 for 2 h at different temperatures. Properties: BET specific surface area 1700 m2/g [2625].

802

Surface Charging and Points of Zero Charge

TABLE 3.1978 PZC/IEP of Unspecified Activated Carbon from Westvaco Treatment Original At 25°C At 50°C At 78°C a

Electrolyte

T

Method a

Mass titration

0.001–0.1 M NaNO3

Instrument

pH0

Reference

1 d aged

4.3 2.4 2.2 1.9

[2625]

Only values, data points not reported.

3.6.4.1.26 Other

Table 3.1979 PZC/IEP of Other Commercial Activated Carbons Product/Specific Surface Area (m2/g)/ Mean Size (nm)

Electrolyte

0.01 M NaCl Derived from coal by steam activation, oxidized with H2O2 or with (NH4)2S2O8, [O] =2.21 mmol/g Ketjenblack/950 /30 Monarcha 900/230/15 Regal 660 R/112/24 Vulcan XC72R/254/30 Monarcha 1300/560/13 Mogul L/138/24 Regal 400 R/96/25 a

T

Method

Instrument

25

pH

2 d equilibration

pH

pH0 6.5

9.8 6.3 4.5 8.5 <2.5 if any <2.5 if any <2.5 if any

Reference [2646]

[2630]

See also Cabot.

Reference [2630] also reports charging curves for Elftex 495 and 285, which showed double PZCs.

803

Compilation of PZCs/IEPs

3.6.4.2 Home-Synthesized Activated Carbons 3.6.4.2.1 Obtained by Carbonization of Plant Material 3.6.4.2.1.1 From Almond Shells Almond shells were pyrolyzed in nitrogen at 900°C for 1 h and steam-activated at 850°C for 1–8 h. A few samples were oxidized using the following procedures: A: 1 g of original carbon was treated with 10 cm3 of concentrated HNO3 at 80°C until dryness, and the material was washed with water. B: 1 g of original carbon was treated with 10 cm3 of concentrated H2O2 at 25°C for 2 d. C: 1 g of original carbon was treated with 10 cm3 of a saturated solution of (NH4) S2O8 in 1 M H2SO4 at 25°C for 2 d, and the material was washed with water. TABLE 3.1980 PZC/IEP of Activated Carbons Obtained from Almond Shells BET Specific Steam Surface Activation Area (h) Oxidation (m2/g) Electrolyte 1 1 1 2.5 2.5 2.5 2.5 5 5 5 5 8 8 8 a

None A B None A B C None A B C None A B

785 650 750 825 660 800 800 1290 740 1200 1060 1600 820 1400

HCl/ NaOH

T Method a

25 pH /iep

Instrument

pH0

Reference

1 or 2 d equilibration Malvern Zetasizer IIe

9.9/1.8 2.4/— 4.8/— 10.4/2.4 2.3/<2 4.8/2.3 1.4/<2 10.6/3.4 2.4/<2 4.9/2.1 1.3/<2 11.1/4.1 2.3/— 4.7/—

[2647]

Only values, data points not reported.

3.6.4.2.1.2 From Cork A: A 1:1 mixture of cork powder and K2CO3 was calcined for 1 h at 700°C in nitrogen, and then washed with water. Properties: 4.1% ash, BET specific surface area 891 m2/g [2648]. B: A was steam-activated in the presence of nitrogen for 1 h at 750°C. Properties: 12.8% ash, BET specific surface area 1060 m2/g [2648].

804

Surface Charging and Points of Zero Charge

TABLE 3.1981 PZC/IEP of Activated Carbons Obtained from Cork Description A B a

Electrolyte

T

Method a

None

Mass titration

Instrument

pH0

Reference

>1 d equilibration

7.5 9.9

[2648]

Only values, data points not reported.

3.6.4.2.1.3 From Olive Stones 3.6.4.2.1.3.1 Steam-Activated for Different Times at 850°C Washed with 10% H2SO4 and with water, carbonized in nitrogen at 1000°C for 1 h, steamactivated for different times at 850°C; then a few samples were oxidized with HNO3, H2O2 or (NH4)2S2O8, then washed with water.

TABLE 3.1982 PZC/IEP of Activated Carbons Obtained from Olive Stones, Steam-Activated for Different Times at 850°C % Burn-Off during Steam Activation/ Oxidizer 5/none 5/H2O2 5/(NH4)2S2O8 15/none 15/H2O2 15/(NH4)2S2O8 29/none 29/H2O2 29/(NH4)2S2O8 29/HNO3 a

Specific Surface Area (m2/g)

Electrolyte

467 425 497 716 651 646 928 769 780 738

T

Method a

pH

Instrument

pH0 Reference

2 d equilibrated 10 6.5 3.1 9.9 4.7 2.6 9.8 4.1 2.7 3.8

[2649]

Only values, data points not reported.

3.6.4.2.1.3.2 Steam-Activated at 850°C for 7.5 h Carbonization in nitrogen at 1000°C for 1 h, followed by activation in steam at 850°C for 7.5 h. A: original B: A oxidized with H2O2 or with (NH4)2S2O8

805

Compilation of PZCs/IEPs

Table 3.1983 PZC/IEP of Activated Carbons Obtained from Olive Stones, Steam-Activated for 7.5 hours at 850°C Sample/[O] (mmol/g) A/0.32 B/3.26

Electrolyte

T

Method

0.01 M NaCl

25

pH

Instrument

pH0 Reference

2 d equilibration 10.1 4.2

[2646]

3.6.4.2.1.3.3 Recipe from [2650,2651] References [2650,2651] cited in [2646] do not report a detailed recipe, but refer to other papers. A: original B: A oxidized with H2O2 or with (NH4)2S2O8 C: original, another sample D: C oxidized with (NH4)2S2O8 for 3 h E: C oxidized with (NH4)2S2O8 for 1 d TABLE 3.1984 PZC/IEP of Activated Carbons Obtained from Olive Stones According to Recipe from [2650,2651] Sample/[O] (mmol/g) A/0.53 B/2.11 C/0.81 D/4.5 E/7

Electrolyte

T

Method

Instrument

0.01 M NaCl

25

pH

2 d equilibration

pH0 9.9 6.7 10.9 2.6 2.2

Reference [2646]

3.6.4.2.1.4 From Wood Properties: Elemental composition available, BET specific surface area 387 m2/g [2652].

TABLE 3.1985 PZC/IEP of Activated Carbon Obtained from Wood Electrolyte

T

Method

Instrument a

Mass titration pH a

Only value, data points not reported.

pH0

Reference

8.5 2.9

[2652] [2599]a

806

Surface Charging and Points of Zero Charge

3.6.4.2.1.5 Various Table 3.1986 PZC/IEP of Activated Carbon Obtained from Various Plant Precursors Precursor/Specific Surface Area (m2/g)

Electrolyte

T

Method

African palm stone/274 0.1 M NaCl 25 Mass titration Coconut peel/292 Pine wood/423 Peach seed/323 Husk of sugar cane/385 Rice/133 0.01 M NaNO3 iep Wheat/128.1 a

a

Instrument

pH0

Reference

2 d equilibration

8.9 7.8 7.4 9.7 9.2 2.6 3.2

[2653]

Malvern Zetamaster

[2629]

Only value, data points not reported.

3.6.4.2.2

Carbon Materials Obtained from Different Precursors

3.6.4.2.2.1 Glassy Carbon Carbonization of polyfurfuryl alcohol in nitrogen at 1000°C. Properties: BET specific surface area <5 m2/g (all samples) [2628]. TABLE 3.1987 PZC/IEP of Glassy Carbon Obtained by Carbonization of Polyfurfuryl Alcohol Description

Electrolyte

Plates Broken plates Powder

0.1 M KCl

a

T

Method

Instrument

Mass titration

pH0

Reference

8.4 7.4 8.7

[2628]a

Only value, no data points.

3.6.4.2.2.2 From Poly(ethylene Terephthalate) Recipe from [2654]. Pyrolysis at 700ºC in inert atmosphere for 30 min followed by activation at 900ºC in equimolar steam-nitrogen mixture for 30 min. Properties: BET specific surface area 1750 m2/g [566]. TABLE 3.1988 PZC/IEP of Activated Carbon Obtained from Poly(Ethylene Terephthalate) Electrolyte

T

Method pH

a

Instrument

pH0

Reference

9.8a

[566]

From drift method. Titration in 0.01 M NaCl starting at natural pH produced similar PZC.

807

Compilation of PZCs/IEPs

3.6.4.2.2.3 Carbon Nanotubes 3.6.4.2.2.3.1 Generated by Pyrolysis of Methane on Ni A: original B: 65% HNO3-modified, 1.5 d at 25°C C: 60% NaClO-modified for 3 h at 85°C The modified samples were then water-washed. Properties: Length 5–15 μm, TEM images available [2655].

TABLE 3.1989 PZC/IEP of Carbon Nanotubes Obtained by Pyrolysis of Methane on Ni Product/Specific Surface Area (m2/g)

Electrolyte

A/82.2 B/64.3 C/94.9

T

Method iep

Instrument Zeta-Meter 3.0

pH0

Reference

4.9 2.9 <2 if any

[2655]

3.6.4.2.2.3.2 Refluxed with HNO3 for 1–10 hours, then Washed with Water Properties: BET specific surface area 224.8, 237.3, 243.2, and 195.5 m2/g (refluxed for 1, 2, 6, and 10 h) [385].

TABLE 3.1990 PZC/IEP of Carbon Nanotubes Refluxed with HNO3 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer ZEN 2010

<2 if any

[385]

None

3.6.5

ACTIVATED CARBON CLOTHS AND FIBRES

3.6.5.1 Commercial 3.6.5.1.1 CS-1501, Ex-Rayon, from Actitex Properties: BET specific surface area 1680 m2/g [2656].

808

Surface Charging and Points of Zero Charge

TABLE 3.1991 PZC/IEP of CS 1501 from Actitex Electrolyte

T

Method

0.1 M NaCl

20

pH

Instrument

pH0

Reference

7.5

[2656]

3.6.5.1.2 RS-1301, Ex-Rayon, from Actitex Properties: BET specific surface area 1460 m2/g [2656].

TABLE 3.1992 PZC/IEP of RS-1301 from Actitex Electrolyte

T

Method

0.1 M NaCl

20

pH

Instrument

pH0

Reference

9.5

[2656]

3.6.5.1.3 Zorflex FM 10 from Charcoal Cloth International Based on viscose rayon. A: washed with 5% HCl B: A electrochemically oxidized at 1.1A for 6 h C: A electrochemically oxidized at 2.2A for 3 h Properties: Elemental analysis available [2657,2658], SEM images available [2657].

TABLE 3.1993 PZC/IEP of Zorflex FM 10 from Charcoal Cloth International Code A B C

Electrolyte 0.1 M NaCl

T

Method

Instrument

pH/iep

Malvern Zetamaster 3000 HSA

pH0 6.8/3 2.8/<1.3 2.7/<1.3

Reference [2657,2658]

809

Compilation of PZCs/IEPs

3.6.5.1.4 From Kynol

TABLE 3.1994 PZC/IEP of Activated Carbon Cloth and Fiber from Kynol: Original and Oxidized with Saturated Solution of (NH4)2S2O8 in H2SO4 Description/BET Specific Surface Area (m2/g) Electrolyte Cloth, original/2128 Cloth, oxidized/1636 Fiber, original/1709 Fiber, oxidized/1315 a

0.01 M NaCl

T 15

a

Method

Instrument

pH

3 min equilibration

pH0 Reference 9.1 3.7 6.6 3.7

[2659]

Also 25–45°C. Similar results are reported for granular activated carbon from Sutcliffe.

3.6.5.2 Home Made 3.6.5.2.1

Carbonization of Viscose Rayon Cloth in Nitrogen and Activation in a CO2 Flow at 850°C for 1 h Water-washed. Properties: BET specific surface area 1125 m2/g [620,2660].

TABLE 3.1995 PZC/IEP of Material Obtained by Carbonization of Viscose Rayon Cloth Electrolyte

T

Method

0.001–0.1 M KNO3

25

cip

a

Instrument

pH0

Reference

7a

[620]

PZC at pH 7 reported in [2660] was obtained by “bath equilibration” method.

3.6.5.2.2 Carbon Nanofibers Ni–hydrotalcite catalyst was reduced at 600°C for 4h in a hydrogen–nitrogen mixture in a fixed-bed reactor. A methane–hydrogen mixture was pumped through that reactor at 600°C. Carbon nanofibers were washed in concentrated HNO3 for 1 h, then washed with water and dried. The washing procedure was repeated twice. Properties: BET specific surface area 75 m2/g [2098].

810

Surface Charging and Points of Zero Charge

TABLE 3.1996 PZC/IEP of Carbon Nanofibers Obtained by Decomposition of Methane Treatment

Electrolyte

T

0.01 M NaCl None 0.01 M NaCl HNO3 H2O plasma a

Method iep iep

Instrument

pH0

Reference a

Malvern Zetasizer 3000HS Malvern Zetasizer 3000HS

<2 if any <2 if any <2 if any 4.6

Only value, data points not reported.

3.6.5.3

Other

3.6.5.3.1 Activated Fiber Properties: [O] 1.59 mmol/g [2646]. TABLE 3.1997 PZC/IEP of Activated Fiber from Unspecified Source Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaCl

25

pH

2 d equilibration

7.4

[2646]

3.6.5.3.2 Carbon Felt Properties: BET specific surface area 831 m2/g [2628]. TABLE 3.1998 PZC/IEP of Carbon Felt Electrolyte

T

Method

0.1 M KCl a

3.6.5.3.3

Instrument

Mass titration

pH0

Reference

5.9

[2628]a

Only value, no data points.

Thermotreated High Tensile Carbon Fibers

TABLE 3.1999 PZC/IEP of Thermo-Treated High-Tensile Carbon Fibers Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

EKA, Anton Paar

10

[2662]

[2098] [2661]

811

Compilation of PZCs/IEPs

3.6.6

COMPOSITE MATERIAL

Reference [2663] reports an electrokinetic study of three types of carbonencapsulated iron–iron oxide particles. Their potentials were negative at pH 2–10.

3.7 OTHER INORGANIC MATERIALS The PZCs/IEPs of other inorganic materials (elements, ice, gas bubbles, and a few complex natural materials) are presented in Tables 3.2000–3.2008.

3.7.1

SILICON, >99.6% HQ SILGRAIN FROM ELKEM MATERIALS

Properties: Elemental analysis, size distribution available [1030]. TABLE 3.2000 PZC/IEP of Silicon Description Fresh and 7 d aged

3.7.2 3.7.2.1

Electrolyte

T

Method Instrument

0.01, 0.02 M NaNO3 or NH4NO3

iep

ESA 8000, Matec

pH0

Reference

<2 if any

[1030]

SULFUR From Aldrich or Fisher, Synthetic

TABLE 3.2001 PZC/IEP of Sulfur from Aldrich or Fisher Description

Electrolyte

HCl-washed, conditioned in N2-saturated water

NaClO4

a

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

<3 if any

[1264]a

Only value, no data points.

3.7.2.2

Liberated from Galena

TABLE 3.2002 PZC/IEP of Sulfur Liberated from Galena Description No control over oxygen

Electrolyte

T

Method

Instrument

pH0

Reference

HCl + KOH

25

iep

Rank Brothers Mark II

2.2

[2570]

812

Surface Charging and Points of Zero Charge

3.7.2.3

Origin Unknown

TABLE 3.2003 PZC/IEP of Sulfur from Unspecified Sources Electrolyte

T

Method

Instrument

NaOH + HClO4

0

iep

Zeta-Meter

iep

3.7.3

pH0

Reference

2

[104] [2664]

<2

ICE TABLE 3.2004 PZC/IEP of Ice

3.7.4

Electrolyte

T

Method

Instrument

pH0

Reference

0, 0.001 M NaNO3

0

iep

ZetaPlus Brookhaven

3.4

[209]

D2O ICE

TABLE 3.2005 PZC/IEP of D2O Ice Electrolyte 0–0.001 M NaCl a

3.7.5

T 3.5

Method iep

Instrument ZetaPlus Brookhaven

pH0 3

a

Reference [2665]

Reported z potentials increase with ionic strengths. The shifts in pH induced by introduction of D2O or H2O ice are also reported. The authors claim PZC at pH 7, but, in the unbuffered system, a shift of the order of 0.1 pH unit does not allow one to draw any conclusions.

GAS BUBBLES

Properties: 60–90 μm in diameter [212].

813

Compilation of PZCs/IEPs

TABLE 3.2006 PZC/IEP of Gas Bubbles Gas

Electrolyte

T

Method

Instrument

pH0

Reference [210]

N2

0.00001–0.1 M NaCl

iep

Laser Zee Meter

<2 if any

O2

0.00001–0.001 M NaClO4

22

iep

Electrophoresis

<3 if any

[212]

0.001 M KCl (text), NaOH + HCl (figure caption) 0.0001–0.01 M NaCl

25

iep

ZetaPlus Brookhaven

>2a

[2666]

22

iep

Rank Brothers

3b

[269]

iep

Electrophoresis

4.5

[263]

H2 O2 Air a b

HCl + NaOH

+8 mV at pH 2, −9 mV at pH 4.5. <2 if any in 0.1 M NaCl.

3.7.6

NATURAL INORGANIC MATERIALS

3.7.6.1 Ottawa Sand TABLE 3.2007 PZC/IEP of Ottawa Sand Description Original Crushed

Electrolyte

T

Method

Instrument

0.001–0.1 M NaCl

25

iep

Electrophoresis Streaming potential

0.001 M NaCl

3.7.6.2

iep

pH0

Reference

<2 if any 4

[574]

<2 if any

[1060]

Berea Sandstone

TABLE 3.2008 PZC/IEP of Berea Sandstone Description

Electrolyte

T

Method

Instrument

Original Baked Crushed Baked then crushed Baked then acid-leached

0.001–0.1 M NaCl

25

iep pH

Electrophoresis Streaming potential

pH0 <2 if any 3.5 4–5 5 <2 if any

Reference [574]

814

Surface Charging and Points of Zero Charge

3.8 COATINGS The PZCs/IEPs of materials composed of a thick external layer of a different chemical nature from the core are presented in Tables 3.2009–3.2076.

3.8.1

ALUMINA COATINGS

3.8.1.1

Alumina on Silica

3.8.1.1.1

Commercial

3.8.1.1.1.1 130 M sol from Du Pont Properties: 26% SiO2, 4% Al2O3, 1.4% Cl, 0.2% Mg by mass, according to the manufacturer, spherical particles, average diameter 29 nm [2667]. TABLE 3.2009 PZC/IEP of 130 M Sol from Du Pont Description

Electrolyte

Supernatant after centrifugation of the original dispersion at 35,000 g for 10 min

a

LiOH

T

Method

Instrument

pH0 a

iep

van Gils cell

9

iep

Delsa 44, Coulter

8.4

Reference [2667]

[1802]

Aged for 10 min–30 d.

3.8.1.1.1.2 Ludox CL from Dupont (Commercial Alumina-Coated Silica) Properties: Alumina: silica mass ratio 4:26 [1799]. The z potential (0.001 M KCl, 20°C, Malvern Zetasizer II c) was positive at pH 3–8 and negative outside that range. [1799]. 3.8.1.1.1.3 From EKA Nobel Al-modified silicas with 1–16% surface silicon atoms substituted by aluminum. Washed by ultrafiltration using salt solutions. TABLE 3.2010 PZC/IEP of Al-Modified Silicas from EKA Nobel % Substitution/ Specific Surface Area (m2/g) 9/540 7/890 7/850 1/900 2/900 4/900 8/890 16/890

Electrolyte 0.002–0.05 M NaCl

T

Method

Instrument

pH0

Reference

iep pH

ESA 8000 Matec

<3 if any

[1807]

815

Compilation of PZCs/IEPs

3.8.1.1.2 Synthetic 3.8.1.1.2.1 Alumina on Ludox Silica Acidified Al(NO3)3 solution and an equivalent amount of NaOH solution were added to a dispersion of Ludox silica. The procedure was repeated several times. Properties: BET specific surface area 103 m2/g (less than original Ludox) [1192].

TABLE 3.2011 PZC/IEP of Alumina-Coated Ludox Silica Electrolyte

a

T

Method

Instrument

pH0

Reference

iep

Electrophoresis

9.1

[1192]a

Only value, no data points.

3.8.1.1.2.2 Alumina on Stober Silica Recipe from [1927]. A dispersion of silica was heated in a solution containing AlK(SO4)2, Al(NO3)3, and urea. TABLE 3.2012 PZC/IEP of Alumina-Coated Stober Silica Electrolyte

T

Method

0.001 M KCl a

iep

Instrument Delsa 440

pH0

Reference

3; 5.5; 6.5a

[1211]

Particles had three points of sign reversal.

3.8.1.1.2.3 AlOOH on Snowtex ZL Silica A Snowtex ZL silica dispersion adjusted to pH 9 with ammonia was heated to 85°C. Then different amounts of aluminum sec-butoxide were mixed with water and added to the dispersion, which was then kept at 85°C for 2 h. The particles were acid-washed. Properties: SEM images, particle size distribution available [1849].

TABLE 3.2013 PZC/IEP of AlOOH-Coated Snowtex ZL Silica Al-Sec-ButoxideSilica Mass Ratio Electrolyte 0.36 0.54 0.72 1.15

HNO3 + KOH

T

Method

Instrument

pH0

Reference

iep

DT 1200

7.5 8.5 8.2 8.7

[1849]

816

Surface Charging and Points of Zero Charge

3.8.1.2

Alumina on Titania

3.8.1.2.1 Alumina on P-25 from Degussa 5 g of titania (Degussa, P-25) was mixed with 20 cm3 of aluminum isopropoxide solution in toluene (different concentrations). The precipitate was dried overnight, and calcined at 823 K for 16 h. TABLE 3.2014 PZC/IEP of Alumina-Coated P-25 from Degussa Alumina (Mass%)

Electrolyte

0.5 0.9 1.4 2.7 5.3 7.8 a

T

None

Method

Instrument

Mass titration

pH0

Reference

6.9 7.3 7.7 7.7 7.9 8.1

[669]a

Only values, no data points.

3.8.1.2.2 Alumina on Rutile from Dupont With small areas of silicon oxide on top. Properties: Specific surface area 30 m2/g, 230 nm in diameter [2668]. TABLE 3.2015 PZC/IEP of Alumina-Coated Rutile from Dupont Electrolyte

a

T

Method

Instrument

pH0

Reference

20

iep

Moving boundary

6.2a

[2668]

Based on arbitrary interpolation.

3.8.1.2.3 Alumina on Rutile Pigment from Kronos Properties: Specific surface area 15 m2/g [375]. TABLE 3.2016 PZC/IEP of Alumina-Coated Rutile from Kronos Electrolyte 0.001 M KNO3

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000 HSA

6.7

[375]

817

Compilation of PZCs/IEPs

3.8.1.2.4

Alumina on Rutile from Laporte

3.8.1.2.4.1 Precipitated from Al2(SO4)3 Solution with NaOH at pH 3 (Initial) to 8.5 (Final) TABLE 3.2017 PZC/IEP of Alumina-Coated Rutile from Laporte Obtained at pH 8.5 Al2O3 (Mass%) 8 8 0.5 3 3 a

Specific Surface Area (m2/g) 14.1 9.5 8.8 10.3 9.3

Electrolyte

T

Method

0.01–1 M KNO3

Instrument

cip

pH0 Reference [45]a

5 5 5.6 5.2 5

Only values, no data points.

3.8.1.2.4.2 Precipitated from Al2(SO4)3 AlCl3, or Al(NO3)3 Solution with Gaseous NH3 or from NaAlO2 Solution with Gaseous CO2 at pH 8 TABLE 3.2018 PZC/IEP of Alumina-Coated Rutile from Laporte Obtained at pH 8 Al2O3 Specific Surface (Mass%) Area (m2/g) 3 3 a

11.5 19

Electrolyte

T

0.01–1 M KNO3/KCl

Method

Instrument

cip

pH0

Reference

6.8 6.5/7.2

[45]a

Only values, no data points.

3.8.1.2.4.3 Al2(SO4)3 Added to Alkaline Dispersion at pH 12 (Initial) to 7 (Final) TABLE 3.2019 PZC/IEP of Alumina-Coated Rutile from Laporte Obtained at pH 7 Al2O3 Specific Surface (Mass%) Area (m2/g) 2.5

a

15

Electrolyte 0.01–1 M KNO3

T

Method cip

Instrument

pH0

Reference

7.5

[45]a

Only values, no data points.

3.8.1.2.4.4 Alumina on Rutile (from Laporte) Al2(SO4)3 or AlCl3 was added to an alkaline dispersion at pH 12 (initial) to 4 (final), then adjusted to pH 8.5 with NaOH.

818

Surface Charging and Points of Zero Charge

TABLE 3.2020 PZC/IEP of Alumina-Coated Rutile from Laporte Obtained at pH 4 Al2O3 Specific Surface (Mass%) Area (m2/g) 3 2.8

19.8 11

Electrolyte

T

0.01–1 M KNO3

Method

Instrument

cip

pH0

Reference

7.5 7.3

[45]

3.8.1.2.5 Alumina on Anatase from Tioxide 2–3 nm layer deposited from aluminum sulfate. TABLE 3.2021 PZC/IEP of Alumina-Coated Anatase from Tioxide Electrolyte

T

0.001 M NH4CH3COO

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

8.1

[404]

3.8.1.3 Alumina on Kaolin A dispersion containing 50 g of kaolin (ECESA, from deposits in Burela, Spain) in 200 cm3 of AlCl3 solution (different concentrations) was aged for 30 min, and then the dispersion was adjusted to pH 7.5 with 0.5 M NaOH. The solids were separated and washed (non-aged precipitate). The product was dispersed in water and aged for 17 d at 70°C (aged precipitate). Properties: Specific surface area determined by ethylene glycol monoethyl ether method available [2274]. TABLE 3.2022 PZC/IEP of Alumina-Coated Kaolin Description Non-aged (%Al): 0.4 1 2 4 6 Aged (%Al): 0.4 1 2 4 6

Electrolyte 0, 0.0488 M NaCl

T

Method

Instrument

pH0

Intersection

Reference [2274]

6.2 5.5 7.6 7.3 7.6 5 5.5 7 7.2 7.2

819

Compilation of PZCs/IEPs

3.8.1.4 Hydrous Alumina on Montmorillonite Al(NO3)3 was added dropwise to a montmorillonite dispersion, then the pH was adjusted to 7 with 0.5 M NaOH. The dispersion was mixed for 2 h, washed, and freeze-dried. Properties: BET specific surface area 10.1 m2/g [1190].

TABLE 3.2023 PZC/IEP of Hydrous-Alumina-Coated Montmorillonite Electrolyte

T

Method

25 a

Titration

Instrument

a

pH0

Reference

5

[1190]

Only value, data points not reported.

3.8.1.5 Alumina on Glass and on Cordierite Dispersion of glass (cordierite) was adjusted to pH 9 with urea. Then Al(NO3)3 was added (alumina: glass/cordierite ratio 1:9), and the dispersion was heated to 90°C for 4 h. The precipitate was washed with water, then with ethanol, dried at 60°C for 2 d, and calcined at 500°C for 1 h. Properties: SEM images available [2238].

TABLE 3.2024 PZC/IEP of Alumina-Coated Glass and Cordierite Description

Electrolyte

On glass On cordierite

0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440 SX

7.6 6.5

[2238]

3.8.1.6 Al(OH)3 on SiC SiC was etched with HF. Al(NO3)3 was added dropwise to a SiC dispersion at pH 4.5. Then the pH was raised above 7 with ammonia. Properties: TEM image available [1096].

TABLE 3.2025 PZC/IEP of Al(OH)3-Coated SiC Electrolyte NaOH + HCl

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

7.3

[1096]

820

Surface Charging and Points of Zero Charge

3.8.1.7

Aluminas on Si3N4

3.8.1.7.1 Pseudoboehmite and Bayerite on Si3N4 Detailed recipe available, 3% Al2O3 by mass [2500]. TABLE 3.2026 PZC/IEP of Pseudoboehmite- and Bayerite-Coated Si3N4 Coating

Electrolyte

Pseudoboehmite Bayerite

T

Method

Instrument

pH0

Reference

iep

Matec ESA 8000

8.1 8

[2500]

HNO3 + KOH

3.8.1.7.2 Boehmite on Si3N4 A 6 vol% dispersion of Si3N4 was ultrasonified and heated to 90°C. Then aluminum sec-butoxide was added with stirring. The solution was adjusted to pH 3 with HCl. Properties: 16–50 nm layer, TEM image available [1123].

TABLE 3.2027 PZC/IEP of Boehmite-Coated Si3N4 Electrolyte

3.8.2

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

9.2

[1123]

HYDROUS CHROMIA ON HEMATITE

Spindle-like hematite particles were aged in 0.0002 M chrome alum at 85°C for 6 h. Properties: SEM image available [1251].

TABLE 3.2028 PZC/IEP of Hydrous-Chromia-Coated Hematite Electrolyte 0.01 M

3.8.3

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

7.3

[1251]

CO OXIDE ON STOBER SILICA

Silica was ultrasonically suspended in 0.005 M Co(ii) acetate solution containing 0.02 M SDS, and aged for 6 h at 90°C, then the solid particles were water-washed and dried at 50°C.

821

Compilation of PZCs/IEPs

Properties: Co/Si atomic ratio 0.69 (XPS), TEM image and XRD pattern available [1904].

TABLE 3.2029 PZC/IEP of Co Oxide-Coated Stober Silica Electrolyte

T

0.01 M NaCl

Method

Instrument

pH0

Reference

iep

Malvern Zetamaster

6

[1904]

3.8.4 IRON (HYDR)OXIDE COATINGS 3.8.4.1

Iron (Hydr)oxide on Silica

3.8.4.1.1 Iron Hydroxide on Quartz FeCl3 was added to a quartz dispersion, then NaOH was added. Properties: Contains akageneite [1756].

TABLE 3.2030 PZC/IEP of Fe Hydroxide-Coated Quartz Electrolyte

T

Method

Instrument

Inert

25

iep

ZetaPlus Brookhaven

pH0 Reference 5.1

[1756]

3.8.4.1.2 Iron Hydroxide on Ludox Acidified Fe(NO3)3 solution and an equivalent amount of NaOH solution were added to a dispersion of Ludox silica. The procedure was repeated several times. Properties: Specific surface area 144 m2/g (more than original Ludox) [1192].

TABLE 3.2031 PZC/IEP of Fe Hydroxide-Coated Ludox Silica Electrolyte

T

Method Salt addition

Instrument

pH0 Reference 7.2

[1192]

3.8.4.1.3 Iron Hydroxide on Sand The sand (Ottawa, 99.5% SiO2) was acid-washed and dried. 20 g of Fe(NO3)3·9H2O dissolved in 50 cm3 of water was poured over 200 g of sand and stirred. The mixture was heated at 110°C for 16 h, and then washed. Properties: 0.74% Fe by mass, BET specific surface area 68 m2/g [2669].

822

Surface Charging and Points of Zero Charge

TABLE 3.2032 PZC/IEP of Fe Hydroxide-Coated Ottawa Sand Electrolyte

T

Method

0.05–1 M NaNO3

25

cip

Instrument

pH0 Reference 8.2

[2669]

3.8.4.1.4 Iron Hydroxide-Coated Stober Silica A dispersion of Stober silica (0.18% by mass) was added to 0.002 M Fe(acac)3 in 1:1 (vol) aqueous ethanol containing SDS (SDS:Fe mole ratio of 15). The dispersion was aged for 1 d at 85°C. Then the particles were washed with water. Properties: TEM image available [1899].

TABLE 3.2033 PZC/IEP of Fe Hydroxide-Coated Stober Silica Electrolyte

T

Method

Instrument

iep

Malvern Zetamaster

0.01 M KNO3

pH0 Reference 6.6

[1899]

3.8.4.1.5 Goethite on Silica, Two Recipes Properties: XRD patterns, SEM images, specific surface areas available [602].

TABLE 3.2034 PZC/IEP of Goethite-Coated Silica Recipe

Electrolyte

[2670], 1.8% Fe [717], 0.3% Fe

T

0.001–0.1 M NaNO3

Method

Instrument

Intersection cip

pH0

Reference

3.1 4.4

[602]

3.8.4.2 Hematite on Anatase Spherical monodispersed anatase particles, 35 mg/dm3, were aged for 1 d at 100°C in a solution 0.0002 M in FeCl3 and 0.01 M in HCl. Properties: TEM image available [1382].

TABLE 3.2035 PZC/IEP of Hematite-Coated Anatase Electrolyte

T

Method

Instrument

0.01 M HCl (?)

25

iep

Rank Brothers

pH0 Reference 7.3

[1382]

823

Compilation of PZCs/IEPs

3.8.4.3 Iron Hydroxide on Kaolin A dispersion containing 50 g of kaolin (ECESA, from deposits in Burela, Spain) in 200 cm3 of Fe(NO3)3 solution (different concentrations) was aged for 30 min, and then the dispersion was adjusted to pH 7.5 with 30% ammonia. The solids were separated and washed (non-aged precipitate). Properties: Specific surface area determined by ethylene glycol monoethyl ether method available [2274].

TABLE 3.2036 PZC/IEP of Fe Hydroxide-Coated Kaolin Description (% Fe) 2 4 7

Electrolyte

T

0, 0.0488 M NaCl

Method

Instrument

Intersection

pH0

Reference

5.2 6.8 7.8

[2274]

3.8.4.4

Corrosion Products on Iron Ultrafine Particles from Vacuum Metallurgical Prepared by gas evaporation method. Properties: XRD pattern available, specific surface area 28 m2/g [1282].

TABLE 3.2037 PZC/IEP of Corrosion Products on Iron Electrolyte

T

Method

0.1 M NaCl, NaClO4, NaNO3

25

pH

3.8.4.5

Instrument

pH0 Reference 6.6

[1282]

HFO on Shewanella putrefaciens Strain CN 32

TABLE 3.2038 PZC/IEP of HFO-Coated Shewanella putrefaciens

3.8.5

Electrolyte

T

Method

0.1 M KNO3

25

pH

Instrument

GERMANIA ON SILICA

Properties: Particle size data available [1774].

pH0 Reference 6.5

[1635]

824

Surface Charging and Points of Zero Charge

TABLE 3.2039 PZC/IEP of Germania-Coated Silica GeO2 (Mass%) 1.5 3 6 11 20

Electrolyte

T

Method

Instrument

pH0

Reference

iep

ZetaPlus Brookhaven

3 3.2 3.4 2.6 2.6

[1774]

0.02 M NaCl

3.8.6

IrO2 ON STOBER SILICA

1.5% IrCl3 · H2O solution in 2-propanol was dropped on silica, the solvent was evaporated at 120°C, and the deposit was thermolyzed in an oxygen atmosphere for 20 min at 400°C. The sequence was repeated 18 times. Properties: Rutile structure [582].

TABLE 3.2040 PZC/IEP of IrO2-coated Stober Silica Electrolyte

T

Method

0.001–0.1 M KNO3

20

iep pH

3.8.7

Instrument Malvern Zetasizer III

pH0

Reference

2.6 <3 if any

[582]

Mn COMPOUNDS ON HEMATITE

Properties: Recipes, SEM images and XRD patterns available [1427], also XRD patterns after calcination.

TABLE 3.2041 PZC/IEP of Mn Oxide-Coated Hematite Compound Amorphous Mn(OH)2 MnO + MnO2 MnCO3

3.8.8

Electrolyte

T

Method

Instrument

iep

Electrophoresis

NaOH + HCl

pH0 Reference 4.2 4.9 6

[1427]

NICKEL (HYDR)OXIDE COATINGS

3.8.8.1 Nickel Oxide on Stober Silica Silica was ultrasonically suspended in 0.001 M NiSO4 solution containing 0.1 M urea, aged for 5 h at 85°C, and then the solid particles were water-washed, and dried at 50°C.

825

Compilation of PZCs/IEPs

Properties: Ni/Si atomic ratio 0.89 (XPS), TEM image and XRD pattern available [1904]. TABLE 3.2042 PZC/IEP of Ni Oxide-Coated Stober Silica Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetamaster

7

[1904]

0.01 M NaCl

3.8.8.2

Corrosion Products on Nickel Ultrafine Particles from Vacuum Metallurgical Prepared by gas evaporation method. Properties: XRD pattern available, specific surface area 19 m2/g [1282]. TABLE 3.2043 PZC/IEP of Corrosion Products on Ultrafine Nickel Particles

3.8.9

Electrolyte

T

Method

0.1 M NaCl, NaClO4, NaNO3

25

pH

Instrument

pH0

Reference

8.8

[1282]

RuO2 ON SILICA

Thermal decomposition of RuCl3 · nH2O at different temperatures in a stream of oxygen in the presence of Spherosil (silica beads 100 mm in diameter). Silica beads, 100 μm in diameter, were calcined at 900°C. They were then dipped in 2 mass% RuCl3 solution in 2-propanol, and calcined in an oxygen stream at 300–700°C. Properties: Very compact layer (no cracks), BET specific surface area 1.7 m2/g (decomposition at 300°C) [1744].

TABLE 3.2044 PZC/IEP of RuO2-Coated Silica Beads Calcination Temperature (°C) 300 400 500 600 650 700 a b

Electrolyte 0.005–0.2 M KNO3

T

Method cip

Longer calcination time. Only values (400–700°C), data points not reported.

Instrument

pH0

Reference

5.6–5.8 6.1 6.4 6.3 5.7 5.3; 4.5a

[1744,1749]b

826

3.8.10

Surface Charging and Points of Zero Charge

SILICA COATINGS

3.8.10.1 Silica on Hematite A dispersion of elongated, monodispersed hematite particles, 72.7 mg/dm3, in 2-propanolic solution 0.45 M in ammonia, 3.05 M in water was brought to 40°C and 0.004 M Si(EtO)4 was added after 30 min. Aging at 40°C continued for 4 h. Then the particles were filtered out and dried in vacuum for 1 d. Properties: TEM images available (also for different aging times) [1432]. TABLE 3.2045 PZC/IEP of Silica-Coated Hematite Electrolyte

T

Method

0.01 M KNO3

iep

Instrument

pH0

Reference

3

[1432]

Delsa 440

3.8.10.2 Silica on Titania 3.8.10.2.1 RLP from WKP, Stuttgart Properties: BET specific surface area 12.1 m2/g, average size 300 nm [2050]. TABLE 3.2046 PZC/IEP of RLP from WKP Electrolyte

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440

<4 if any

[2050]

0.001 M KCl

3.8.10.2.2 Concurrent Addition of NaSiO3 Solution and 3 M H2SO4 to Dispersion of Titania The IEP (Rank Brothers, 0.001 M KNO3) shifts to low pH as the silica content increases from 0.62% (negligible shift) to 5% (shift from pH 5.5 to 3). The electrokinetic curves of particles with 1–2% silica show a hysteresis (base titration produces a higher IEP). The IEP is also sensitive to storage for 3 weeks at pH 2, but is insensitive to storage for 3 weeks at pH 7 [2101]. 3.8.10.2.3 Silica on Anatase from Tioxide 2–3 nm layer deposited from sodium silicate. TABLE 3.2047 PZC/IEP of Silica-Coated Anatase from Tioxide Electrolyte 0.001 M NH4CH3COO

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

2.3

[404]

827

Compilation of PZCs/IEPs

3.8.10.2.4 Silica Coating Deposited from Ethoxide Synthetic titania was dispersed in a mixture of 100 cm3 of ethanol and 1 cm3 of 2% ammonia. Three additions of silicon ethoxide, 0.6 cm3 each, were made in 15 min intervals. The suspension was stirred for a further 12 h, and the particles were washed. Properties: Silica 3.4–13 vol%, coating thickness 6–25 nm [2117] (different methods).

TABLE 3.2048 PZC/IEP of Silica Coating Deposited on Titania from Ethoxide Electrolyte

T

0.0001 M KCl

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

<3 if any

[2117]

3.8.10.2.5 Silica and Alumina on Titania Silica was deposited at pH 9 at 80°C from NaSiO3. Alumina was deposited at pH 8 at 25°C from AlCl3. Properties: Elemental analysis available (five different samples) [2121].

TABLE 3.2049 PZC/IEP of Silica- and Alumina-Coated Titania Description

Electrolyte

Silica, then alumina Alumina, then silica

0.01 M NaCl

T

Method

Instrument

pH0

Reference

iep

Pen Kem Laser Zee Meter

8 3 2.8 6.5 7.2

[2121]

3.8.10.3 Silica on Zirconia Commercial zirconia was dispersed in a mixture of 100 cm3 of ethanol and 1 cm3 of 2% ammonia. Three additions of silicon ethoxide, 0.6 cm3 each, were made in 15 min intervals. The suspension was stirred for a further 12 h, and the particles were washed. Properties: Silica 21–39 vol%, coating thickness 5–10 nm [2117] (different methods).

TABLE 3.2050 PZC/IEP of Silica-Coated Zirconia Electrolyte 0.0001 M KCl

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

<2.5 if any

[2117]

828

Surface Charging and Points of Zero Charge

3.8.10.4 Two Types of Silica on Cu(OH)2 · CuCO3 A dispersion of Cu(OH)2 · CuCO3 (20 g/dm3) containing 0.05–1 g/dm3 of Ludox was adjusted to pH 6–8, and the coated particles were allowed to settle. The supernatant was removed, and the particles were washed. Properties: TEM images available. TABLE 3.2051 PZC/IEP of Silica-Coated Cu(OH)2 ⋅ CuCO3 External Layer

Electrolyte

T

Method

Ludox HS Ludox 130 M a

iep

Instrument

pH0 a

Delsa 44, Coulter

7.5 8.2

Reference [1802]

At low pH the sign is reversed to negative due to dissolution of Cu(OH)2 ⋅ CuCO3.

3.8.10.5 Two Types of Silica on Cu A dispersion of Cu containing 0.05–1 g/dm3 of Ludox was adjusted to pH 6–8, and the coated particles were allowed to settle. The supernatant was removed, and the particles were washed. Properties: TEM images, DTA results, XRD pattern available [1802]. TABLE 3.2052 PZC/IEP of Silica-Coated Cu External Layer

Electrolyte

T

Ludox HS Ludox 130 M

3.8.10.6

Method iep

Instrument

pH0

Reference

Delsa 44, Coulter

4 8.2

[1802]

Stober Silica on Silver TABLE 3.2053 PZC/IEP of Silica-Coated Ag Electrolyte 0.001 M KNO3

3.8.11

T

Method

Instrument

pH0

Reference

iep

Delsa 440 SX

<3 if any

[1906]

Sn(OH)4 ON HEMATITE

A dispersion of hematite, 0.2 g/dm3 in a solution 0.0037 M in SnSO4, 0.34 M in HCl, and 1.48 M in urea was heated for 1 h at 80°C with stirring. Properties: XRD pattern, SEM image, TGA, and DTA curve available [1428].

829

Compilation of PZCs/IEPs

TABLE 3.2054 PZC/IEP of Sn(OH)4-Coated Hematite Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

4.5

[1428]

0.001 M

3.8.12

TITANIA COATINGS

3.8.12.1 Titania on Alumina Alumina (Cyanamid, g) was mixed with titanium isopropoxide solution in toluene (different concentrations). The product was dried overnight, and calcined at 823 K for 16 h. TABLE 3.2055 PZC/IEP of Titania-Coated Alumina Titania (Mass%)

Electrolyte

2 5 8 11.4 b

T

None

Method

Instrument

Mass titration

pH0

Reference

8.1 7.9 7.7 7.3

[669]a

Only values, no data points.

3.8.12.2 Titania on Silica 3.8.12.2.1 XWG (Commercial Material) Properties: BET specific surface area 5.3 m2/g, average size 900 nm [2050]. TABLE 3.2056 PZC/IEP of XWG Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440

4.5

[2050]

3.8.12.2.2 Deposition of Pre-Existing Titania Particles A dispersion of Stober silica was mixed with a dispersion of titania in HNO3 solution (different concentrations). Then NaOH was added and the mixture was stirred for 3 h. Properties: SEM images available [1909].

830

Surface Charging and Points of Zero Charge

TABLE 3.2057 PZC/IEP of Titania Coating on Silica Deposited from Pre-Existing Titania Particles Electrolyte

3.8.12.2.3

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000

4.7

[1909]

Deposition from Inorganic Precursors

3.8.12.2.3.1 From Sulfate 0.2 M TiOSO4 in 1 M H2SO4 was added (dropwise in [1903]) to a dispersion of Stober silica at 90°C. In [1903], the product of hydrolysis is termed “titanyl sulfate.” Properties: 30% titania [1901]. TABLE 3.2058 PZC/IEP of PZC/IEP of Titania Coating on Silica Deposited from Sulfate Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

iep

Delsa 440

4.4

[1901]

0.001 M KBr

iep

Malvern Zetasizer 3000 HSA

4.5

[1903]

3.8.12.2.3.2 Deposited from TiCl4 Solution 0.5 M TiCl4 in ice-cold water was added to a dispersion of spherical silica particles in 0.01 M HCl solution heated to 80°C. Ammonia was added simultaneously to keep the pH at 7.5. The reagents were added within 1 h, and the reaction conditions were maintained for 1 h more. The particles were washed with water, dried at 120°C, and calcined for 1 h at 500°C. Properties: SEM and TEM images, XRD pattern available [1951]. TABLE 3.2059 PZC/IEP of PZC/IEP of Titania Coating on Silica Deposited from TiCl4 Solution Electrolyte

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

3.3

[1951]

3.8.12.2.3.3 Deposited from TiCl4 Vapor Fumed silica was dried at 150°C, and then reacted with TiCl4 vapor at 150°C for 30 min, and then with water vapor at 150°C.

831

Compilation of PZCs/IEPs

Properties: 0.6–32.4% TiO2 by mass, specific surface area 154–269 m2/g [1775]. TABLE 3.2060 PZC/IEP of PZC/IEP of Titania Coating on Silica Deposited from TiCl4 Vapor Electrolyte

T

Method

Instrument

pH0

Reference

iep

Brookhaven Zetaplus

2.7–3.3

[1775]

HCl + NaOH

3.8.12.2.4

Deposition from Alkoxides

3.8.12.2.4.1 From Isopropoxide A solution of titanium isopropoxide in ethanol was added dropwise to a dispersion of silica in a water–ethanol mixture at room temperature with stirring. The particles were washed three times with ethanol and three times with water, dried in vacuum at 60°C for 2 d, and calcined at 700°C for 2 h. Properties: 17–29% TiO2 by mass, anatase or amorphous, BET specific surface area 16–54 m2/g (calcined), 42–92 m2/g (before calcination), XRD patterns and TEM images available [1902]. TABLE 3.2061 PZC/IEP of PZC/IEP of Titania Coating on Silica Deposited from Isopropoxide Electrolyte

T

0.001 M HCl + KOH

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440

4.3

[1902]

3.8.12.2.4.2 From (Di-isopropoxide) Bis-2,4-Pentadionate 1.5% solution of Ti (di-isopropoxide) bis-2,4-pentadionate in isopropanol was dropped on silica, the solvent was evaporated at 120°C, and the deposit was thermolysed in oxygen atmosphere for 20 min at 400 or 500°C. The sequence was repeated 30 times. Properties: Anatase structure, SEM images and particle size at various number of coating cycles available [582]. TABLE 3.2062 PZC/IEP of PZC/IEP of Titania Coating on Silica Deposited from (Di-Isopropoxide) Bis-2,4-Pentanedionate Electrolyte

T

Method

0.001–0.1 M KNO3

20

iep pH

a

Instrument

pH0

Malvern Zetasizer III 3.9/4.1a merge

Reference [582]

400/500°C heated samples. Charging curves obtained for 500°C heated sample merge at pH < 4.

832

Surface Charging and Points of Zero Charge

3.8.12.2.4.3 From Butoxide, in One Step A solution of titanium butoxide in ethanol, final concentration 0.0016 M (sample A) or 0.0025 M (sample B) was slowly added under nitrogen to a dispersion of Stober silica in ethanol containing water, final concentration 0.25 M (sample A) or 0.36 M (sample B) at room temperature. Sample C was prepared with final concentrations of titanium butoxide of 0.0091 M, and of water of 0.3 M. The reagents were mixed rapidly, and refluxed for 3 h in the presence of 0.005 mass% of hydroxypropylcellulose. Properties: SEM and TEM images available [233].

TABLE 3.2063 PZC/IEP of PZC/IEP of Titania Coating on Silica Deposited from Butoxide in One Step Recipe A B C

Electrolyte

T

0.001 M KCl

Method

Instrument

iep

Malvern Zetasizer

pH0

Reference

3.4 3.8 4

[233]

3.8.12.2.4.4 From Butoxide, Multistep Recipe from [2671]: A dispersion of silica in alcohol was mixed with titanium n-butoxide (0.0091 M) and water (0.32 M). The mixture was refluxed and stirred for 1.5 h, and then washed with ethanol. This procedure was repeated several times. Properties: TEM images, particle size distributions available [1895].

TABLE 3.2064 PZC/IEP of PZC/IEP of Titania Coating on Silica Deposited from Butoxide in Many Steps Description

Electrolyte

Two samples

0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Powereach JS94E

3.5

[1895]

3.8.12.2.4.5 From Butoxide, in the Presence of Hydroxypropylcellulose 1 g of Stober silica was dispersed in 100 cm3 of ethanol in an ultrasonic bath. Water and hydroxypropylcellulose (100,000 g/mol) were added, respectively. Then a solution of titanium butoxide in ethanol was slowly added, and the mixture was refluxed in ethanol for 90 min at 85°C. Final concentrations of water, titanium butoxide, and hydroxypropylcellulose were 0.45 M, 0.12 M, and 3 g/dm3, respectively. The particles were washed in an ultrasonic bath. The above procedure was repeated one to five times.

833

Compilation of PZCs/IEPs

Properties: Specific surface area, SEM images, FTIR spectra, XRD patterns, particle size, and coating thickness available [1905].

TABLE 3.2065 PZC/IEP of PZC/IEP of Titania Coating on Silica Deposited from Butoxide in Presence of Hydroxypropylcellulose Electrolyte

T

Method

0.001 M KCl

3.8.12.3

iep

Instrument ELS 8000 Otsuka

pH0

Reference

4.2–4.5

[1905]

Passive Layer on Metallic Ti

TABLE 3.2066 PZC/IEP of Passive Layer on Metallic Ti Electrolyte

T

Method

0.001 M KCl

iep

Instrument

pH0

Reference

EKA, Paar

4.4

[2672]

3.8.12.4 Titania on Silicon Wafer from Phillips Properties: Peak-to-valley height 1.5 nm [1821], 25 nm layer, pure and stoichiometric TiO2 [1821,2673]. TABLE 3.2067 PZC/IEP of Titania-Coated Silicon Wafer from Phillips Description Original and treated at 1050°C

3.8.13

Electrolyte 0.0001, 0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Streaming potential

4.5

[1821,2673]

YTTRIA ON HEMATITE

A dispersion of hematite containing 1.8 M urea and 1.1–4.9 mM Y(NO3)3 was heated at 90°C for 9 h. The product was dried at 60°C, and then calcined at 800°C for 3 h in air. Properties: Specific surface area 10–18.8 m2/g, particle diameter 110–150 nm [1376].

834

Surface Charging and Points of Zero Charge

TABLE 3.2068 PZC/IEP of Yttria-Coated Hematite Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.01 M NaCl

25

iep

Malvern Zetasizer 2c

[2155]

0.001–0.1 M NaCl

25

cip/iep

Malvern Zetasizer 2c

7.8 8.5 8.1 7.6/8 7.7/8 7.8/8

3.8.14

[1376]

Zr (HYDR)OXIDE COATINGS

3.8.14.1 Hydrous Zirconia on Hematite A dispersion of hematite (prepared according to [1430]) in 0.005 M Zr(SO4)2 containing 5 vol% of formamide and 0.5 mass% of polyvinylpyrrolidone was aged for 2 h at 70°C. Properties: BET specific surface area 58 m2/g, TEM image available [1431].

TABLE 3.2069 PZC/IEP of Hydrous-Zirconia-Coated Hematite Electrolyte

T

Method iep

0.01 M NaNO3

Instrument Delsa

pH0

Reference

5

[1431]

3.8.14.2 Zirconia on NiO NiO was dispersed in a 0.2 M solution of ZrO(NO3)2 in a 2-propanol–water mixture (4:1 molar ratio). The temperature was slowly raised to 80°C within 1 h while stirring. The temperature was kept at 80°C for 1 h. The powder was washed with 2-propanol, dried, and calcined at 900°C for 3 h. Properties: Tetragonal ZrO2, SEM and TEM image available [1729]. TABLE 3.2070 PZC/IEP of Zirconia-Coated NiO Electrolyte

T

Method

Instrument

pH0

Reference

iep

Brookhaven ZetaPlus

6.2

[1729]

835

Compilation of PZCs/IEPs

3.8.15

PASSIVE LAYER ON Ti6Al4V ALLOY TABLE 3.2071 PZC/IEP of Passive Layer on Ti6Al4V Alloy Electrolyte

T

Method

Instrument

pH0

Reference

iep

EKA, Paar

4.4

[2672]

0.001 M KCl

3.8.16

PASSIVE FILMS ON STAINLESS STEELS

TABLE 3.2072 PZC/IEP of Passive Films on Stainless Steels Composition (Mass%) Cr 18.18, Ni 8.65, Si 0.49, Mn 0.82 Cr 17.18, Ni 8.32, Si 0.49, Mn 1.32 a

Electrolyte 0.01 M NaCl

T Method iep

Instrument

pH0

Reference

Streaming potential

4

[2674]a

4

IEP was measured after one of the following cleaning procedures: (i) soaking in 95% ethanol for 10 min; (ii) soaking in commercial surfactant for 10 min followed by water washing at 50°C; or (iii) soaking in 0.5 M NaOH, water washing, soaking in 0.2 M HNO3 at 70°C, followed by waterwashing. The effect of the cleaning procedure on the observed IEP was rather insignificant.

3.8.17 NiCO3 · Ni(OH)2 · H2O ON MnCO3 A dispersion of MnCO3, 0.26 M NiSO4, and 0.4 M urea was aged for 2 h at 85°C. Properties: SEM image and XRD pattern available [2455]. TABLE 3.2073 PZC/IEP of NiCO3 ⋅ Ni(OH)2 ⋅ H2O-Coated MnCO3 Electrolyte

T

Method

Instrument

pH0

Reference

iep

Pen Kem 3000

10

[2455]

0.001 M

3.8.18

YOHCO3 COATINGS

3.8.18.1 YOHCO3 on Hematite A dispersion of hematite containing 1.8 M urea and 1.1–4.9 mM Y(NO3)3 was heated at 90°C for 2–15 h. 11 specimens.

836

Surface Charging and Points of Zero Charge

Properties: TEM images, TGA, XPS, and particle size data available [2155].

TABLE 3.2074 PZC/IEP of YOHCO3-Coated Hematite Specific Surface Area (m2/g)

Electrolyte

T

Method

Instrument

pH0

0.001–0.1 M NaCl

25

iep

20.5

Malvern Zetasizer 2c

8 7.7 8 7.7 8.1 8.1 7.9 7.9 8.3 8 8

26.8

13.2

Reference [2155]

3.8.18.2 YOHCO3 on Polystyrene A dispersion containing polystyrene latex (100 mg/dm3), 1.8 M urea, 1.2% by mass of polyvinylpyrrolidone (MW 360,000), and 5 mM Y(NO3)3 was heated at 90°C for 2 h. Properties: Diameter 0.26 mm, IR spectrum and TEM images available [2456]. TABLE 3.2075 PZC/IEP of YOHCO3-Coated Polystyrene Electrolyte 0.001 M NaNO3 a

3.8.19

T

Method

Instrument

pH0

Reference

iep

Delsa

8a

[2456]

Subjective interpolation.

Zr2O2(OH)2CO3 AND Zr2(OH)6SO4 ON POLYSTYRENE

A solution was prepared by the addition of reagents to water to obtain the following concentrations (Zr2O2(OH)2CO3/Zr2(OH)6SO4): 0.72/0.18 M in urea, 1/0.5 M in formamide, and 0.9% of poly(vinylpyrrolidone) by mass. Then polystyrene latex was added (the order of addition of reagents is important). The dispersion was sonified, and Zr(SO4)2 solution was gradually added to produce a concentration of 0.0005/0.001 M. The product was aged for 5 h at 70°C and water-washed.

837

Compilation of PZCs/IEPs

Properties: Particle diameter 190/250 nm, TEM image, IR spectrum avalable [2213].

TABLE 3.2076 PZC/IEP of Zr2O2(OH)2CO3 and Zr2(OH)6SO4-Coated Polystyrene Coating

Electrolyte

Zr2O2(OH)2CO3 Zr2(OH)6SO4

3.9

T

0.01 M NaNO3 0.01 M NaNO3

Method

Instrument

pH0

Reference

iep iep

Delsa 440 Coulter Delsa 440 Coulter

3.5 4.8

[2213] [2213]

WELL-DEFINED LOW-MOLECULAR-WEIGHT ORGANIC COMPOUNDS

The PZCs/IEPs of well-defined low-molecular-weight organic compounds and their mixtures are presented in Tables 3.2077–3.2090.

3.9.1 3.9.1.1

HYDROCARBONS n-Heptane TABLE 3.2077 PZC/IEP of n-Heptane Electrolyte

T

HCl + NaOH 0.001 M KCl

Method

Instrument

pH0

Reference

iep iep

Brookhaven ZetaPlus

3 3.8

[2459] [2433]

3.9.1.2 Octadecane A 2.5% by mass emulsion was stirred at 80°C, ultrasonified for 10 min, and cooled to room temperature. Properties: 303 nm in diameter [2676].

TABLE 3.2078 PZC/IEP of Octadecane Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaCl

25

pH iep

Malvern Zetasizer 3000

<3 if any

[2676]

838

Surface Charging and Points of Zero Charge

3.9.1.3 Nonadecane A 2.5% by mass emulsion was stirred at 80°C, ultrasonified for 10 min, and cooled to room temperature. TABLE 3.2079 PZC/IEP of Nonadecane Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3000

<3 if any

[2677]

0.001 M NaCl

3.9.1.4 Pharmaceutical Paraffin Wax Mixture of n-alkanes C19–C40, mostly C26, particles about 700 nm in diameter, 40 min–1 d equilibrated. TABLE 3.2080 PZC/IEP of Pharmaceutical Paraffin Wax Electrolyte

T

Method

Instrument

pH0

Reference

0–0.001 M NaCl

25

iep

Zeta PALS, Brookhaven

<4 if anya

[2678]

a

Values of z potential at pH 4, 6.6, and 10 were high, negative, and relatively insensitive to pH.

3.9.1.5

n-Alkanes: C6 –C14 and C16 TABLE 3.2081 PZC/IEP of n-Alkanes: C6 –C14 and C16 Electrolyte 0.001 M NaCl

T

Method

23–25

iep

Instrument Electrophoresis

pH0

Reference

<3 if any

[2679]

3.9.1.6 Xylene TABLE 3.2082 PZC/IEP of Xylene Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

22

iep

Malvern Zetasizer IIc

<3.5 if any

[2680]

839

Compilation of PZCs/IEPs

3.9.2

BROMODODECANE FROM SIGMA-ALDRICH

TABLE 3.2083 PZC/IEP of Bromododecane Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer

<3 if any

[2681]

0.01 M NaCl

3.9.3

FULLEROL

From MER, 20–24 hydroxyl groups per C60 molecule. TABLE 3.2084 PZC/IEP of Fullerol Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

25

iep

Malvern Zetasizer Nano ZS

<3 if anya

[2614]

a

Extrapolation of charging curves suggests CIP at pH ª 3.

3.9.4

ACIDS

3.9.4.1 Stearic Acid A 2.5% by mass emulsion was stirred at 80°C, ultrasonified for 10 min, and cooled to room temperature. Properties: 673 nm in diameter [2676].

TABLE 3.2085 PZC/IEP of Stearic Acid Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaCl

25

pH iep

Malvern Zetasizer 3000

<3 if any

[2676,2677]a

a

20°C.

3.9.4.2 Carboxylic Acids Precipitates obtained in 0.0002–0.001 M solutions of carboxylic acids and their sodium salts.

840

Surface Charging and Points of Zero Charge

TABLE 3.2086 PZC/IEP of Carboxylic Acids (or Their Salts) Acid or Salt

Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter

<3 if any 3.1 3.3 2.9

[2682]

C17H33COONa C13H27COOH C11H23COONa C9H19COOH

3.9.4.3

Oleic Acid Droplets

TABLE 3.2087 PZC/IEP of Oleic Acid Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

20

iep

Electrophoresis

2a

[2683]

a

Two literature references report negative z potential at pH 3–8.

3.9.4.4 Octadecane: Stearic Acid (95:5) A 2.5% by mass emulsion was stirred at 80°C, ultrasonified for 10 min, and cooled to room temperature. Properties: 336 nm in diameter [2676].

TABLE 3.2088 PZC/IEP of Octadecane/Stearic Acid Mixture Electrolyte

T

Method

Instrument

pH0

Reference

0.001–0.1 M NaCl

25

pH iep

Malvern Zetasizer 3000

<3 if any

[2676]

3.9.4.5 Nonadecane: Stearic Acid (95:5 and 99:1) A 2.5% by mass emulsion was stirred at 80°C, ultrasonified for 10 min, and cooled to room temperature. Properties: 350–650 nm in diameter [2677].

841

Compilation of PZCs/IEPs

TABLE 3.2089 PZC/IEP of Nonadecane/Stearic Acid Mixture Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M NaCl

20

pH iep

Malvern Zetasizer 3000

<3 if any

[2677]

3.9.5

CHOLESTEROL, 99+%, ALFA AESAR

Particles were precipitated from propanolic solution by the addition of water, and the solvent was then evaporated.

TABLE 3.2090 PZC/IEP of Cholesterol Electrolyte

T

HCl + KOH

3.10

Method

Instrument

pH0

iep

Brookhaven ZetaPlus

2

Reference [2684]

POLYMERS (MACROSCOPIC SPECIMENS)

The surface charging of polymers depends on the nature and concentration of additives used in the production process. Thus, the same monomeric material can produce polymers with very different surface properties. The PZCs/IEPs of polymers are presented in Tables 3.2091–3.2103.

3.10.1

POLYAMIDES

TABLE 3.2091 PZC/IEP of Polyamides Type Polyamide 12

Electrolyte 0.0001 M KCl 0.001 M KCl HCl + NaOH

T

Nylon 6, Teijin Co.; extracted with ethanol, then with water Nylon 66, Nyltech, St 0.001 M NaCl 23–27 Fons, France

Method

Instrument

iep

EKA, Anton Paar

iep

Streaming potential

iep

Electrophoresis Electro-osmosis

pH0

Reference

3.5 4.2 4.4

[2662]

4.8

[2686]

[2685]

842

3.10.2

Surface Charging and Points of Zero Charge

POLYCARBONATES

TABLE 3.2092 PZC/IEP of Polycarbonates Type

Electrolyte

T

Method

Instrument

pH0

Reference

a

0.001 M KCl

25

iep

Streaming potential

[2687]

0.001 M KCl

25

iep iep

Electrophoresis Streaming potential

iep

EKA, Anton Paar

<3 if any <3 if any >3b >3b <4c <4 if any <4 if any <4 if any 4.2 4.5 4

15 50 100 200 Membrane 10d 30 50 100 200 (two types) Molecular mass 39 300 Da a b c d

0.0001– 0.001 M KCl

[2688] [2689]

[2662]

Track-etched membranes, from Nucleopore, different pore diameters (in nm) +3 mV at pH 3; negative z potential at pH 4. +18 mV at pH 3, −7 mV at pH 4. From Poretics, different pore diameters (in nm).

3.10.3

POLYETHERETHERKETONE, VICTREX, LITE K, FROM LIPP-TERLER

TABLE 3.2093 PZC/IEP of Polyetheretherketone Electrolyte

T

0.001 M KCl

3.10.4

Method

Instrument

pH0

iep

EKA, Anton Paar

4.5

Reference [2662]

POLYETHERIMIDE, MOLECULAR MASS 89 100, FROM LIPP-TERLER

TABLE 3.2094 PZC/IEP of Polyetherimide Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

iep

EKA, Anton Paar

4.2

Reference [2662]

843

Compilation of PZCs/IEPs

3.10.5

POLYETHYLENE

TABLE 3.2095 PZC/IEP of Polyethylene Electrolyte

T

0.001 M KCl a

Method

25

Instrument

iep

pH0

ELS-600 Otsuka

Reference

a

[275]

4

From mobility profile.

3.10.6

POLY(ETHYLENE IMINE) FROM POLYSCIENCES

TABLE 3.2096 PZC/IEP of Poly(ethylene imine) Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Nano ZS Zetasizer

>10 if any

[2690]

0.001, 0.01 M NaCl

3.10.7 PMMA TABLE 3.2097 PZC/IEP of PMMA Electrolyte

T 20

0.01 M KCl 0.01 M KCl

a

22–24

Method iep iep iep

Instrument a

Laser Zee Meter 500 Streaming potential Brookhaven EKA with a cell from Anton Paar

pH0

Reference

4 4.2 4.2

[273] [2283] [2604]

The measurement cell provided with the Laser Zee Meter 500 (Pen Kem) is made of PMMA.

3.10.8

POLYPROPYLENE FROM E-PLAS

TABLE 3.2098 PZC/IEP of Polypropylene Electrolyte

T

Method

Instrument

pH0

0.001 M KCl

20

iep

Streaming potential

<4 if any

Reference [299]

844

3.10.9

Surface Charging and Points of Zero Charge

POLYSTYRENE

TABLE 3.2099 PZC/IEP of Polystyrene Initiator

Electrolyte

T Method

Free-radical 0.001 M KCl polymerization, molecular mass 198 000 Da AIBAa 0.001 M KCl Persulfate a

Instrument

pH0

Reference

iep

EKA, Anton Paar

4.2

[2662]

iep

Malvern Zetasizer 7 Nano ZS <3 if any

[232]

900 cm3 of methanol and 100 cm3 of purified styrene were heated under nitrogen to 60°C. A solution of 909 mg of initiator (2,2¢-azobis(isobutyramidine) dihydrochloride (AIBA) or ammonium persulfate) in 150 cm3 of methanol was added, and stirring was continued for 1 day under nitrogen. The latex was washed with methanol and then with water. Properties: SEM images, particle size distributions available.

3.10.10 PTFE TABLE 3.2100 PZC/IEP of PTFE Source

Electrolyte

T

From ICI 0.001 M NaCl Petrochemicals and Plastics Division From Du Pont 0.001 M KCl 20 0.01 M NaCl 0.001 M NaCl 20–25 0.001 M KCl 25 a b

Method

Instrument

pH0

Reference

iep

Electrophoresis

<3 if any

[268]a

iep iep iep iep

Streaming potential <4 if any Electro-osmosis 3 Electro-osmosis 3 ELS-600 Otsuka 4b

[299] [1822] [278] [275]

Dimensions of particles reported. From mobility profile.

3.10.11

POLYURETHANE

Table 3.2101 PZC/IEP of Polyurethane Electrolyte

T

Method

Instrument

pH0

Reference

iep

Streaming potential

5

[289]

845

Compilation of PZCs/IEPs

3.10.12

POLYMERS, FIBERS

Standard fabrics from SDC; for properties, see [286].

TABLE 3.2102 PZC/IEP of Different Polymers in Fiber Form Description Cotton Wool Viscose rayon Polyamide 6.6 Polyester Acrylic

3.10.13

Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

28

iep

EKA Brookhaven-Paar

2.9 4.7 2.8 6.9 <2.5 if any 3

[286]

POLYMERS, POWDERS

TABLE 3.2103 PZC/IEP of Different Polymers in Powder Form Description Polybenzamidine Polyformamidine Polyacetamidine

3.11

Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 3

7 7 7.8

[1939]

LATEXES

The surface charging of latexes depends on the nature and concentration of their surface groups, which are usually provided by the initiator used in the polymerization process. Thus, the same monomeric material can produce latexes with very different surface properties. The PZCs/IEPs of latexes are presented in Tables 3.2104–3.2123.

3.11.1

COMMERCIAL

3.11.1.1 Flexbond 325 from Air Products Poly(vinyl acetate–co-acrylic), stabilized by nonionic surfactant. Properties: Volume-average particle size 333 nm, number-average particle size 60 nm, density 1200 kg/m3 [2343].

846

Surface Charging and Points of Zero Charge

TABLE 3.2104 PZC/IEP of Flexbond 325 from Air Products Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer 4

<2 if any

[2343]

0.001 M NaCl

3.11.1.2 Carboxylated Latex from BASF Properties: Average diameter 190 nm [2691].

TABLE 3.2105 PZC/IEP of Carboxylated Latex from BASF Electrolyte

T

Method

0.01–0.1 M KCl

25

pH

3.11.1.3

Instrument

pH0

Reference

<4 if any

[2691]

Eudragit from Degussa

TABLE 3.2106 PZC/IEP of Eudragit from Degussa Type/Diameter (nm) L30D-55/102 RL30D/171 NE30D/149 a

Electrolyte

T

Method

0.01 M NaCl

25

iep

Instrument Malvern Zetasizer ZEN3600

pH0

Reference

2.5a >11 if any 3a

[1453]

Subjective interpolation.

3.11.1.4

From Dow

3.11.1.4.1 Polystyrene Properties: 960 nm in diameter [2675], particle size 357 nm [2692], monodispersed [2692], electron micrographs available [2675]. TABLE 3.2107 PZC/IEP of Polystyrene Latexes from Dow Description Original Hydrolized for 5 d at 90°C

Electrolyte

T

Method

0.002 M NaCl

25

iep

Original 0.001 M NaNO3 O2 plasma-etched

iep

Instrument Rank

Coulter Delsa 440

pH0

Reference

<2 if any <1.5 if any

[2692]

3.3 3.5

[2675]

847

Compilation of PZCs/IEPs

3.11.1.4.2 Polyvinyltoluene Properties: 1.37 μm in diameter, electron micrographs available [2675].

TABLE 3.2108 PZC/IEP of Polyvinyltoluene Latex from Dow Description Original O2 plasma-etched CF4/O2 plasma-etched

Electrolyte

T

0.001 M NaNO3

Method

Instrument

pH0

Reference

iep

Coulter Delsa 440

3.6 3.6 3.6

[2675]

3.11.1.5 Polystyrene Latex, Estapor-Merck Properties: Spheres, 200–300 nm [334].

TABLE 3.2109 PZC/IEP of Estapor-Merck Polystyrene Latexes Type

Electrolyte

K1, carboxylate groups 0.01 M KCl K6, quarternary ammonium/ amine groups a b

T

Method

Instrument

iep

Malvern Zetasizer Nano

pH0 Reference <3a 6b

[334]

Only value, data points not reported. Subjective interpolation.

3.11.1.6 Aquacoat Latex from FMC Manufactured by etherification of cellulose with ethyl chloride. Properties: Spherical particles, average diameter 340 nm [2693].

TABLE 3.2110 PZC/IEP of Aquacoat Latex from FMC Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaCl

25

iep

Malvern Zetasizer 2c

<2 if any

[2693]

848

Surface Charging and Points of Zero Charge

3.11.1.7 Latexes from Interfacial Dynamics TABLE 3.2111 PZC/IEP of Latexes from Interfacial Dynamics Type/Mean Diameter (nm) Sulfate/248 Carboxyl/245

Electrolyte

T

Method Instrument

0.01 M NaCl 0.01 M NaCl

pH0

iep iep

Reference

<2 if any <4 if any

3.11.1.8 PS, Soap-Free Latexes from IDC, Portland TABLE 3.2112 PZC/IEP of Latexes from IDC Type/Size (nm) Sulfate/81 Amidine/76

3.11.2

Electrolyte

T

Method

Instrument

pH0

Reference

0.001, 0.01 M KCl 0.001, 0.01 M KCl

25 25

iep iep

Delsa 440 Delsa 440

<3 if any >10 if any

[2694] [2694]

SYNTHETIC

3.11.2.1 N,N-Dimethylaminoethyl Methacrylate Polymerized in the Presence of Poly(vinylpyrollidone) A 0.5 M solution of N,N-dimethylaminoethyl methacrylate in a 1:9 ethanol–water mixture containing 2–10% by mass of poly(vinylpyrollidone) (PVP, molecular mass of 30,000 or of 360,000), 0.5% by mass of N,N¢-methylenebisacrylamide (both with respect to N,N-dimethylaminoethyl methacrylate), and 0.2 g/dm3 of N,N¢-azobisisobutyronitrile was bubbled with nitrogen for 10 min and then heated at 65°C for 3 h. The product was then purified by microfiltration. Properties: Hydrodynamic diameter as a function of pH reported, optical micrographs, TEM images available [421].

TABLE 3.2113 PZC/IEP of N,N¢-Dimethylamino Ethyl Methacrylate Polymerized in Presence of Poly(vinylpyrollidone) Description 10% PVP 30 000 2% PVP 360 000 5% PVP 360 000

Electrolyte

T

Method

Instrument

pH0

Reference

0.005 M NaCl

25

iep

Malvern Zetasizer Nano ZS

6 6 6

[421]

849

Compilation of PZCs/IEPs

3.11.2.2 Ethylcellulose Latex 18.75 g of ethylcellulose was dissolved in 106.25 g of an 85:15 benzene–ethanol mixture. The solution was mixed with 375 cm3 of water containing 2 g of SDS. The organic solvent was evaporated from the emulsion by stirring at room temperature, and the dispersion was cleaned by dialysis. Properties: SEM image available, two populations of particles: 2.3 and 15 μm in diameter [2695]. TABLE 3.2114 PZC/IEP of Ethylcellulose Latex Electrolyte

T

Method

Instrument

pH0

Reference

25

iep

Malvern Zetasizer 2000

<2 if any

[2695]

3.11.2.3 Cross-Linked Poly(N-Isopropylmetacrylamide) Latex A solution of N-isopropylmetacrylamide (20 g/dm3), methylenebisacrylamide (8% by mass), and potassium persulfate (2% by mass) was agitated for 6 h at 70°C. Water-washed. Properties: The hydrodynamic diameter: 830 nm at 20°C and 530 nm at 50°C [2696]. TABLE 3.2115 PZC/IEP of Cross-Linked Poly(N-Isopropylmetacrylamide) Latex Electrolyte 0.001 M NaCl a

T

Method

Instrument

pH0

Reference

20a

iep

Malvern Zetasizer III

<3 if any

[2696]

Also 50°C.

3.11.2.4 Melamine–Formaldehyde Melamine was dissolved in aqueous formaldehyde at 80°C, and formic acid was added to induce polycondensation. Properties: Specific density 1410 kg/m3, particle size 100–1000 nm [2697].

TABLE 3.2116 PZC/IEP of Melamine–Formaldehyde Latex Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M KCl, LiNO3

25

iep

Malvern Nano ZP DT 1200 Acoustosizer

11

[2697]

850

Surface Charging and Points of Zero Charge

3.11.2.5 95% Methyl Methacrylate–5% Methacrylic Acid–Latex Obtained in the presence of SDS. Properties: Average diameter 25 nm [2698].

TABLE 3.2117 PZC/IEP of 95% Methyl Methacrylate–5% Methacrylic Acid Latex Electrolyte

T

Method

Instrument

pH0

pH iep

Coulter Delsa 440

<4 if any <2.5 if anya

None, 0.001 M NaNO3 a

Reference [2698]

Only value, no data points.

3.11.2.6 Methacrylic Acid–1,3-Butadiene–Latex Obtained in the presence of sodium persulfate, dialyzed, 6 or 20 mass% of methacrylic acid.

TABLE 3.2118 PZC/IEP of Methacrylic Acid–1,3-Butadiene Latex Electrolyte

T

Method

Instrument

pH0

Reference

iep

Malvern Zetasizer Nano ZS90

<2.5 if any

[2699]

3.11.2.7 Polystyrene Latex, Potassium Persulfate Initiator Properties: 900 nm in diameter, specific surface area 6.4 m2/g [817,2700].

TABLE 3.2119 PZC/IEP of Polystyrene Latex Obtained with Potassium Persulfate Initiator Electrolyte 0.001 M NaCl

3.11.2.8

T

Method

Instrument

pH0

iep

Pen Kem 501

<2.5 if any

Reference [2086]

Styrene–N,N-Diethylaminoethyl Methacrylate–Methacrylic Acid–Latex 10 cm3 of styrene, 1 g of N,N-diethylaminoethyl methacrylate (DEAM), 0.5 g of methacrylic acid (MA), 0.2 g of K2S2O8, and 100 g of water adjusted to pH 1.2 were heated to 70°C under nitrogen. The latex was carefully washed.

851

Compilation of PZCs/IEPs

Properties: Specific surface area confirmed by TEM images 31 m2/g, 185 nm in diameter [455], monodispersed, spherical [455,2701].

TABLE 3.2120 PZC/IEP of Styrene–N,N-Diethylaminoethyl Methacrylate–Methacrylic Acid Latex MA:DEAM

Electrolyte

1 0 1.1 2.2 5.5

T

Method

Instrument

pH0

Reference

iep iep

Rank Brothers Rank Brothers

6.9 8 6.5 5.7 4.2

[455] [2701]

0.001 M KNO3 0.01 M NaCl

Extensive study of the effects of storage and purification on the iep was carried out [455]. 3.11.2.9

Styrene–Methyl Methacrylate Latexes Obtained in the Presence of Different Initiators A 10 mass% dispersion of monomers (styrene:methyl methacrylate = 6.8/0.7 by mass) containing 0.16 mass% of initiator, pH 3, ionic strength 0.0052 mol/dm3, was stirred at 70°C at 200 rpm. The product was washed and dialyzed for 2 d. Properties: Monodispersed spherical particles; for particle diameter, see Table 2121 [2702].

TABLE 3.2121 PZC/IEP of Styrene–Methyl Methacrylate Latexes Obtained in Presence of Different Initiators Initiator/d (nm)

Electrolyte

2,2¢-Azobis[N-(2-carboxyethyl)2-methylpropionamidine]/358 2,2¢-Azobis[N-(1-carboxyethyl)2-methylpropionamidine]/539

3.11.3

T

Method

Instrument

iep

Zeecom, Microtec

pH0 Reference 3.5

[2702]

4

ORIGIN UNKNOWN

3.11.3.1 Polystyrene Properties: Particle diameter 180 nm [1008], median diameter 640 nm [499].

852

Surface Charging and Points of Zero Charge

TABLE 3.2122 PZC/IEP of Polystyrene Latex from Unspecified Source Electrolyte

T

Method

0.0001–0.01 M NH4NO3

iep

0.001 M KNO3

25

iep

Instrument Electrophoresis Rank Brothers Mark II

pH0

Reference

<3 if any

[499]

<3 if any

[1008]

3.11.3.2 Poly(vinylchloride)

TABLE 3.2123 PZC/IEP of Poly(vinylchloride) Latex from Unspecified Source Electrolyte

T

Method

Instrument

pH0

Reference

iep

Rank Brothers Mark II

<3 if any

[2703]

0.01 M NaNO3

3.12

NATURAL HIGH-MOLECULAR-WEIGHT ORGANIC SUBSTANCES

Natural organic colloids have variable composition, and the surface properties of various specimens of nominally the same material can vary substantially. The PZCs/IEPs of natural high-molecular-weight organic substances are presented in Tables 3.2124–3.2147.

3.12.1

HUMIC AND FULVIC ACID

3.12.1.1

Commercial

3.12.1.1.1 From Aldrich TABLE 3.2124 PZC/IEP of Humic Acid from Aldrich Description Sodium humate, technical grade Purified

Electrolyte

T

Method iep

0.005–0.1 M KNO3

pH iep

Instrument Malvern Zetamaster S Brookhaven ZetaPlus 4

pH0

Reference

<1 if any

[883]

<3 if any 1.6

[629,630] [2704]

853

Compilation of PZCs/IEPs

3.12.1.1.2 From Fluka Properties: Elemental analysis available [2705].

TABLE 3.2125 PZC/IEP of Humic Acid from Fluka Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl HNO3 + NaOH

20

iep pH

Milton Roy, Pryde

<3 if any 6a

[299] [2705]

a

Natural pH. In text, the authors report PZC at pH 4.7, obtained from acidity constants.

3.12.1.1.3

From International Humic Substances Society

TABLE 3.2126 PZC/IEP of Humic Substances from International Humic Substances Society Description

Electrolyte

T

Fulvic acid 0.005–0.04 M 25 Aquatic humic acid CH3COONa + NaCl Peat humic acid

Method

Instrument

pH0

Reference

iep

Capillary electrophoresis

<4 if any

[2706]

3.12.1.2 Isolated from Natural Materials 3.12.1.2.1 Fulvic Acid Isolated from Soil According to the procedure recommended by the International Humic Substances Society.

TABLE 3.2127 PZC/IEP of Fulvic Acid Isolated from Soil Electrolyte 0.01–0.1 M NaCl

T

Method pH

Instrument

pH0

Reference

<3.5 if any

[634,1547]

3.12.1.2.2 Fulvic Acid Isolated from Surface Water Purified according to [2707].

854

Surface Charging and Points of Zero Charge

TABLE 3.2128 PZC/IEP of Fulvic Acid Isolated from Surface Water Electrolyte

T

Method

Instrument

pH

pH0

Reference

<3 if any

[1442]

3.12.1.2.3 Fulvic Acid Extracted from Gleysol from Northern Switzerland

TABLE 3.2129 PZC/IEP of Fulvic Acid Extracted from Gleysol from Northern Switzerland Electrolyte

T

Method

0.01–0.3 M NaNO3

25

pH

Instrument

pH0

Reference

<3 if any

[633,2708]

3.12.1.2.4 Humic Acid Extracted from Gleysol from Northern Switzerland Separated into four molecular mass fractions: 10,000–30,000, 30,000–100,000, 100,000–300,000, and >300,000. TABLE 3.2130 PZC/IEP of Humic Acid Extracted from Gleysol from Northern Switzerland Electrolyte

T

Method

0.01–0.3 M NaNO3

25

pH

Instrument

pH0

Reference

<3 if any

[633]

3.12.1.2.5 Humic Acid from Brown Coal from Dudar, Hungary

TABLE 3.2131 PZC/IEP of Humic Acid from Brown Coal from Dudar, Hungary Electrolyte

T

Method

0.001–0.1 M NaCl 0.005–0.5 M NaCl

25

pH pH

Instrument

pH0

Reference

<4 if any <4 if any

[1121] [1297]

3.12.1.2.6 Humic Acid Extracted from Boom Clay Samples Properties: ash 10.7%, C/N ratio 12.8 [853].

855

Compilation of PZCs/IEPs

TABLE 3.2132 PZC/IEP of Humic Acid Extracted from Boom Clay Samples Electrolyte

T

Method

Instrument

pH0

Reference

0.1 M NaClO4

25

iep

Zeta-Meter

<5 if any

[853]

3.12.1.2.7

Suwannee River

TABLE 3.2133 PZC/IEP of Humic Acid from Suwannee River Electrolyte

T

Method

0.02, 0.2 M NaClO4

25

pH

3.12.1.2.8

Instrument

pH0

Reference

3.3

[1397]

Peat Humic Acid

TABLE 3.2134 PZC/IEP of Peat Humic Acid Electrolyte

T

0.001–0.3 M KNO3

Method

Instrument

pH

pH0

Reference

<3 if any

[594]

Reference [2709] reports experimental and calculated charging curves of nine humic and nine fulvic acids at two to five ionic strengths. Reference [2710] reports experimental and calculated charging curves of eight humic acids (Higashiyama L; Kinshozan P, F, and OH, Shitara Black; purified Aldrich; prepared from commercial peat; and from forest soil; elemental analysis and molecular mass are reported for each specimen) and one fulvic acid (Laurentian) at three concentrations of KNO3 (in the range 0.003–0.12 M, withdifferent concentrations for different samples) at 22°C. The sign of the surface charge was negative over the pH range 3–10.

3.12.2

MARINE COLLOIDAL ORGANIC MATTER

Isolated from Gulf of Mexico surface waters. TABLE 3.2135 PZC/IEP of Marine Colloidal Organic Matter Electrolyte

T

Method

0.1 M NaClO4

25

pH

Instrument

pH0

Reference

5.4

[1397]

856

Surface Charging and Points of Zero Charge

3.12.3 SUSPENDED PARTICULATE MATTER FROM RIVER MERSEY IN NW ENGLAND TABLE 3.2136 PZC/IEP of Suspended Particulate Matter from River Mersey in NW England Size (μm) >1 0.5–1 0.05–0.5

3.12.4

Electrolyte

T

Method

0.01 M NaNO3

25

pH

Instrument

pH0

Reference

5.4 6.2 7.2

[2711]

CELLULOSE

3.12.4.1 Cellulose from Arjomari Properties: SEM image available [2121]. TABLE 3.2137 PZC/IEP of Cellulose from Arjomari Electrolyte

T

Method

Instrument

pH0

Reference

0.01 M NaCl

25

iep

Pen Kem Laser Zee 500

3

[2121]

3.12.4.2 Cellulose Film on Glass Deposited from solution in N-methylmorpholine-N-oxide, original and crosslinked with a hydroxyl group reactive cross-linker.

TABLE 3.2138 PZC/IEP of Cellulose Film on Glass Electrolyte

T

Method

Instrument

pH0

Reference

iep

Streaming current

<2 if any

[2712]

0.0001, 0.001 M KCl

3.12.4.3

Origin Unknown

TABLE 3.2139 PZC/IEP of Unspecified Samples of Cellulose Electrolyte 0.001 M KCl

T

Method

Instrument

pH0

Reference

25

iep iep

Electrophoresis Coulter Delsa 440

<3 if any <4 if any

[1160] [2050]

857

Compilation of PZCs/IEPs

3.12.5 3.12.5.1

DEXTRIN From Aldrich

TABLE 3.2140 PZC/IEP of Dextrin from Aldrich Electrolyte

T

0.1 M NaCl

3.12.5.2

Method

Instrument

pH0

Reference

iep

Laser Zee meter 501

5

[2713]

Origin Unknown

TABLE 3.2141 PZC/IEP of Unspecified Sample of Dextrin Electrolyte

T

Method

Instrument

a

Reference

3.5

iep a

pH0

[957]

Only value, data points not reported.

3.12.6 b-CASEIN Micelar solution of b-casein (Sigma). TABLE 3.2142 PZC/IEP of β-Casein Electrolyte

T

<0.001 M

Method

Instrument

pH0

Reference

iep

Malvern Nano ZS90

5

[22]

3.12.7 LYSOZYME Aggregates obtained by heating lysozyme (from Sino-American Biotechnology Co.) solution at 80°C for 30 min. TABLE 3.2143 PZC/IEP of Lysozyme Electrolyte <0.001 M

T

Method

Instrument

pH0

Reference

iep

Malvern Nano ZS90

10

[22]

858

3.12.8

Surface Charging and Points of Zero Charge

CHITOSAN

Nanofiber fabric prepared by electrospray deposition. Properties: See [2714].

TABLE 3.2144 PZC/IEP of Chitosan Electrolyte

T

Method

Instrument

pH0

Reference

iep

Anton Paar

8.1

[2714]

0.001 M KCl

3.12.9

CHITOSAN–POLYMETHACRYLIC ACID COMPOSITES

Obtained by polymerisation of methacrylic acid in the presence of K 2S2O8 in chitosan solution.

TABLE 3.2145 PZC/IEP of Chitosan–Polymethacrylic Acid Composites Chitosan (Mass%) 0.2 0.5 0.8

3.12.10 3.12.10.1

Electrolyte

T

Method

NaOH + HCl

25

iep

Instrument

pH0

Reference

4.6 5.8 7.7

[2715]

ASPHALTENE Extracted from Alberta Crude Oil

TABLE 3.2146 PZC/IEP of Asphaltene Extracted from Alberta Crude Oil Electrolyte

T

Method

Instrument

pH0

Reference

0.001 M KCl

22

iep AFM

Zetaphoremeter III from Sephy

<4.5 if any

[1764]

3.12.10.2 Extracted from Crude Oil from Swidnik, Poland Properties: Mean particle diameter 776 nm [513].

859

Compilation of PZCs/IEPs

TABLE 3.2147 PZC/IEP of Asphaltene Extracted from Crude Oil from Swidnik, Poland Electrolyte

T

Method

Instrument

pH0

Reference

0.0001–0.1 M NaCl

22

Intersection iep

Malvern Zetasizer 3000

7 <4a

[513]

a

Positive ζ potential at pH 2, negative ζ potential at pH 4, no data points between pH 2 and 4.

3.13

MICROORGANISMS

PZCs/IEPs of microorganisms are presented in Tables 3.2148–3.2153.

3.13.1

BACTERIUM BACILLUS SUBTILIS

TABLE 3.2148 PZC/IEP of Bacterium Bacillus subtilis Electrolyte

T

Method

Instrument

pH0

Reference

0.1 M NaCl

25

Malvern Zetasizer 4

25

<1.5 if any 3.4 (text) <2 if any 3.7a

[2716]

0.1 M NaClO4

iep pH iep pH

a

Malvern Zetamaster

[635]

Acid-washed bacteria. Non-acid-washed bacteria have PZC at pH 6.5–8 in 0.01–0.3 M NaClO4 and no clear CIP.

3.13.2

BACTERIUM CORYNEBACTERIUM XEROSIS

TABLE 3.2149 PZC/IEP of Bacterium Corynebacterium xerosis Description

Electrolyte

Washed with water

0.001 M NaNO3

T

Method

Instrument

pH0

Reference

iep

Rank Brothers

<2 if any

[2463]

860

3.13.3

Surface Charging and Points of Zero Charge

CELL WALLS OF BACTERIUM RHODOCOCCUS ERYTHROPOLIS

TABLE 3.2150 PZC/IEP of Cell Walls of Bacterium Rhodococcus erythropolis Electrolyte

T

Method

0.01–1 M NaNO3

25

cip

Instrument

pH0

Reference

4.5

[621]

3.13.4 BACTERIUM RHODOCOCCUS OPACUS FROM FUNDACAO TROPICAL DE PESQUISAS E TECNOLOGIA ANDRE TOSELLO, SAO PAULO TABLE 3.2151 PZC/IEP of Bacterium Rhodococcus opacus Electrolyte

T

Method

Instrument

pH0

Reference

iep

Zeta-Meter 3

3.2a

[2717]

0.01 M NaCl a

Arbitrary interpolation.

3.13.5

BACTERIUM SHEWANELLA PUTREFACIENS

TABLE 3.2152 PZC/IEP of Bacterium Shewanella putrefaciens Description

Electrolyte

T

Method

Live, strain CN 32 Live Autoclaved

0.1 M KNO3

25

pH iep/pH

Instrument

pH0

Reference

5.2 3.8/6.8 4.5/6.8

[1635] [2718]

3.13.6 MS2 BACTERIOPHAGES TABLE 3.2153 PZC/IEP of MS2 Bacteriophages Electrolyte

T

Method iep

a

Only value, no data points.

Instrument

pH0

Reference

3.9a

[2719]

Compilation of PZCs/IEPs

3.14

861

METALS

In principle, metal surfaces are outside the scope of the present book. An electrophoretic study of water on silver has been published [1906]. The contact angle of silver film was studied as a function of pH [693], and the maximum was identified with the IEP. Copper was studied by means of electrophoresis [1802]. The streaming potential of Au and Al is reported in [294]. Nickel was studied by means of electrophoresis [122], and by means of electroacoustic method in [2721]. An adhesion method was used to estimate the IEPs of eight metals [689] and of Cu [2720]. A correlation between IEPs of metals and the corresponding metal oxides was found in [689]. Reference [306] reports IEP of alleged elemental iron nanoparticles, but the formation of elemental iron under the conditions described in that paper is very unlikely.

3.15 LITERATURE INTENTIONALLY IGNORED The set of PZCs/IEPs reported in Tables 3.1 through 3.2153 is a result of selection according to criteria discussed in Chapter 1. The search strategies described in Chapter 1 led to many publications that were then analyzed and finally intentionally ignored in the present compilation. A few examples of such “rejected” publications are given below. The rejection does not imply that these publications are inferior or erroneous.

3.15.1 PZCS/IEPS NOT REPORTED OR NOT FOUND This category comprises papers cited by others as sources of PZCs/IEPs data (but where PZCs/IEPs were not reported in the original papers) and papers in which PZCs/IEPs fell beyond the range of experimental data. Reference [2723] reports calculated concentrations of ⬅SiOH- surface groups. In [228,2724], silica was studied only in the neutral and alkaline range. Reference [2725] reports model parameters for silica. Fluorspar and calcite were studied in the neutral and alkaline range in [226]. The pH was adjusted by NaOH or KOH, but not reported. Charging curves of AlPO4, FePO4, and CrPO4 are reported in [2726], but not a PZC. Reference [2727] reports calculated IEPs of mixed oxides based on IEPs of their components. Surface charging of Ti/IrOx was studied in [2728], but no specific PZC was found. Reference [2577] reports model parameters obtained in a surface charging study of ZnS. The titration data of montmorillonite and model parameters are reported in [2291], but not a PZC. Negative z potentials of six minerals at pH 4, 7, and 11, and of a further two minerals at pH 7 and 11 were found in [2729].

3.15.2

SECONDARY SOURCES

Acidity constants from the literature are reported in [928,1461,1489,1503,2730, 2731,2733–2740,2833,2837]. Acidity constants and model parameters from previous

862

Surface Charging and Points of Zero Charge

studies by the same authors are reported in [1537] and [2741], respectively. Acidity constants based on experimental results taken from the literature are reported in [889, 2742,2743]. The acidity constants reported in [2744] were obtained by re-analysis of results from previous papers by the same authors. Reference [2053] reports acidity constants derived from results published in [2049]. References [2745,2746] report PZCs and acidity constants from the literature. References [2747,2748] report model parameters from the literature. Reference [2749] reports results from [1472], and [2750] reports results from [951]. The IEP of alumina at pH 7.3 is reported in [2751] without any specific information about the source of material or about experimental conditions (probably from the literature). The IEP of titania at pH 5.6 is reported in [2752] without experimental conditions (probably from the literature). The IEP of mica at pH 3–3.5 is reported in [2753] without experimental conditions (probably from the literature). Reference [2754] reports charging curves of titania, obtained under unspecified experimental conditions, probably from previous paper. Reference [2755] reports IEPs from the literature and estimated from X-ray photoelectron spectroscopy. The PZCs reported in [2756] are probably from the literature (no experimental details are provided). IEPs from the literature are reported in [2757– 2765,2767–2792,2794–2804,2842,2852,2894,2900,2905]. IEPs and PZCs from the literature are reported in [169,2805–2807]. The IEPs/PZCs reported in [2808] are also probably from the literature. Charging and electrokinetic curves from the literature are reported in [2809]. Electrokinetic curves from the literature are reported in [2810–2812]. PZCs from previous papers by the same authors are reported in [1165,2813–2821]. IEPs from previous papers by the same authors are reported in [111,2009,2822–2825]. Electrokinetic curves from previous papers by the same authors are reported in [2826,2827]. Reference [2828] reports PZC for an ill-defined material, and PZC from the literature. Reference [2829] reports calculated charging curves based on results from the literature. References [222, 1784,2830,2831] report surface charging data from the literature. Reference [2832] reports surface charging curves and PZCs from the literature. The PZCs in Table 1 of [947] are probably taken from the literature. References [2835,2836] probably report PZCs from the literature and [2838,2839] probably report IEPs from the literature. Reference [2840] reports PZCs from the literature that were confirmed by a nonstandard method. PZCs from the literature are also reported in [84,87,92, 114,118,188,723,780,945,968,1115,1162,1505,1533,1699,1766,1773,1975,1976,1996, 2035,2708,2766,2793,2841,2843–2845,2847–2851,2853–2893,2895–2899,2901– 2904,2906–2917]. Reference [2846] reports a result of coagulation study from the literature.

3.15.3

THE ELECTROLYTE IS NOT INERT

In several studies, non-inert electrolytes were purposely added to the studied system. Ca(ClO4)2 was used as a supporting electrolyte in [2288]. CaCl2 was used as a supporting electrolyte or as one of its components in [2918–2921]. The PZC reported in [2922] was determined in the presence of sulfate. Buffers were used

Compilation of PZCs/IEPs

863

in [2923] (IEP in acetate and phosphate buffers), [2924] (IEP in acetate, borate, and Tris buffers), [2925] (acetate, phosphate, and carbonate buffers), and [296, 2926,2927] (phosphate buffer). The IEP reported in [1287] was obtained in the presence of NaHCO3, and the IEP reported in [2928] was probably obtained in the presence of phosphates. Most likely, the IEP reported in [50] was obtained in the presence of dispersant (phosphate). The IEP of alumina was determined in [35] in the presence of Al(iii) in solution. Reference [47] reports an electrokinetic study in the presence of different pH buffers, and titration in the presence of CaCl2. Also, the solid particles may contain water-soluble substances, which undergo leaching and specific adsorption. Reference [1865] reports the IEP of phosphatecontaining goethite. One sample studied in [32] contained sulfate and phosphate, and its IEP and PZC differed significantly. The silica studied in [2929] was prepared in the presence of a nonionic surfactant. No attempt was made to remove that surfactant from the final product. Phosphate-doped titania was studied in [2930] and polymer-stabilized latex was studied in [2931]. A few results presented above have been cited by others as pristine PZCs/IEPs.

3.15.4

MECHANICAL MIXTURES AND COMPLEX AND ILL-DEFINED MATERIALS

Mixtures that show a high degree of homogeneity were discussed in Section 3.3. Materials consisting of a core made of one material and an external layer (coating) made of another were discussed in Section 3.8. In contrast to those two categories of materials, in which the role of particular components in the surface charging process can be relatively easily understood, several studies have been devoted to complex materials consisting of large grains of different components or to materials whose composition is not known or not reported. Such results are outside the scope of the present book. There is no sharp boundary between homogeneous and heterogeneous materials or between well-defined and ill-defined materials. The selection in this book of certain data and rejection of other data was based on a subjective assessment of the available information by the present author. A few results presented below have been cited by others as pristine PZCs/IEPs of the main component. For example, the system studied in [2932] can be interpreted as silica in the presence of adsorbed lanthanum. Commercial titanias were studied in [516,2933] (surface-modified with alumina, silica, and organic groups), [32] (surface-modified with alumina, silica, and other compounds), [2900] (surfacemodified with alumina and silica), and [1021] (probably with a surface-active additive). Particles containing surfactants were studied in [2934]. A commercial pigment with multilayer coating of unknown thickness was studied in [425], and commercial materials of unknown composition in [2935]. Complex commercial composite materials were studied in [2936,2937]. The commercial materials studied in [2938] were probably surface-treated. Surface charging of complex and/or ill-defined natural materials was studied in [2939] (anthracites), [2940,2941] (coal), [531,662,2942–2948] (soils), [2949] (china clay), [2950,2951] (complex clays), [2952] (chromite mine overburden), [2953] (sawdust and sawdust-derived ion exchanger), [2954] (natural red earth),

864

Surface Charging and Points of Zero Charge

[2955] (sand), [2956] (cork powder), [2957] (cork powder, original and after Fisher esterification), [2959] (live diatom cells and frustules), [2958,2960,2961] (complex natural materials), and [2962] (subsurface mineral materials). Multicomponent films were studied in [2963], and multilayer membranes in [279,2964–2967]. The polymeric membranes studied in [2968] were modified by post-treatment. Also, a-alumina identical to the material in Membralox membrane from SCT, studied in [1851], probably underwent surface treatment. The IEPs obtained in [2969] probably represent metal oxide–dextrin precipitates rather than pure metal oxides. Activated carbons studied in [2970] had very high ash content. Water treatment residual was studied in [2971]. The material studied in [2972] was impure. Other examples of surface charging studies carried out in complex, ill-defined materials can be found in [2722,2834,2973–2978].

3.15.5 NONSTANDARD, INCORRECT, OR UNDEFINED METHOD, AND NONSTANDARD TERMINOLOGY The following results were intentionally ignored in Tables 3.1 through 3.2153 because the method used is not recommended by the present author or not clearly described, or because experimental conditions were not reported. A few nonrecommended methods were briefly outlined in Chapter 2. The terms “PZC” and “IEP” have been used in the literature for different quantities, not necessarily related to surface charging. Several results presented below have cited as PZCs/ IEPs in the literature. Scattered results are reported in [2979], and there are too few data points near the IEP. Also, in [2980,2981], too few data points are available near the IEP to make a reliable estimate. In [2982], z at one pH value is reported. In [2983], z potentials were measured only at pH 1, 4, and 12. The IEP was obtained in [2984] from ESA measurements for two titanias (source or characterization of the powers or experimental details were not reported). The unusually high IEP reported in [2984] may be due to experimental errors: the solid concentration was too low, and the electrolyte background was not subtracted. Among the results from [1726], only the IEP for Nd(OH)3 was used. The other IEPs are based on arbitrary interpolations. The pH reported in the z (pH) plot in [208] was not the pH of the dispersion. A home-made apparatus was used in [267], atypical shapes of electrokinetic curves were reported, and the IEP was based on arbitrary interpolation. In [351,2985–2990], the data points are too far from the PZC to make a reliable estimate. The PZC of hydrous zirconia at pH 2.9 reported in [2991] is probably due to occluded HNO3. The apparent PZC found for silica by titration in [2992] is probably due to occluded acid. The dependence of the apparent PZC on the pH of precipitation reported in [2993] is chiefly due to acid or base occluded in the precipitate. The charging curves in [2994] were set off to fit ion adsorption results. Most likely, surface charging of Y(OH)2.5(NO3)0.5 studied in [2995] was not the main process governing acid–base titrations of that compound. The equilibrium pH in water and 1 M KCl at low and unknown solid-to-liquid ratio reported in [172] and the equilibrium pH at low solid-to-liquid ratio reported in [175] are not

Compilation of PZCs/IEPs

865

necessarily reliable as the PZCs. Reference [206] reports a PZC obtained as the intersection of curves representing adsorption of H+ and OH- ions. Positive adsorption of both H+ and OH- ions at the PZC is claimed. Such an approach is unusual. Normally, positive adsorption of protons is treated as equivalent to negative adsorption of OH- ions, and vice versa. Gran plots were used in [138], but the present author does not recommend such a method to determine the PZC. The results reported in [2997–2999] were obtained by subjective extrapolation, and those in [262] by subjective interpolation. Reference [3000] reports unusual results for common materials. The PZC was determined in [3001] from the difference between anion and cation exchange capacity. The “IEP” reported in [3002] is the point of equal uptake of Na and sulfate (expressed in equivalents). The PZC reported in [2022] is based on uptake of anions and cations and on nonstandard assumptions. Na and Cl uptake were studied in [3003,3004]. Reference [676] cites a submitted paper by the same authors, in which the pH of onset of uptake of Na by niobia is reported, and reports an inflection point in the titration curve. Only a CCC-based IEP is reported in [3005]. The pH of minimum stability is termed the IEP in [3006]. References [3007–3009] report PZCs derived from AFM results. A nonstandard method (second-harmonic generation) was used in [651], and the purity of the surface was problematic. The inflection point-based PZC obtained in the presence of acetate is reported in [3010]. The EMF method was used in [3011] and the ISFET method in [3012,3013]. The rate of dissolution was used to determine the PZC in [3014,3015]. The point of minimum solubility is reported in [3016]. The quantity termed “PZC” in [3017] is derived solely from ionic equilibria in solution. The calculated IEP reported in [2547] is entirely based on solution chemistry. The term “isoelectric point” used in [1258] is not related to electrophoresis. The authors studied the colors of the solution and of the sediment in a system containing alumina and a pH indicator (e.g., fuchsine) adjusted to different pH values by NaOH or H2SO4. Reference [1258] was quoted in [1] and then by a few other authors as an authoritative source of the IEP of alumina ([1258] was published in German, but was translated into German by someone other than one of the authors). A method based on a shift in pH induced by addition of BaCl2 was used in [663]. Certainly, such a method does not produce a pristine PZC. A boehmite layer on aluminum was studied in [3018] by means of the streaming potential, which is not a suitable method for such a system. In [125], an intersection point of charging curves is reported for composites containing Fe and Al oxides and clay minerals. Intersection of two charging curves is generally not recommended as a method to determine the PZC, especially for clay minerals, which usually do not show a CIP of charging curves (see Chapter 2). The results reported in [933] refer to very basic pH, without adequate CO2 protection. The powder used in [3019] reacts with the solution. Sources or characterization of powers or experimental details are not reported in [168]. The IEP is reported in [3020] without experimental details. A rough and

866

Surface Charging and Points of Zero Charge

unsupported estimate of the PZC was published in [3021]. The method and conditions are not specified in [3022]. The method is not specified in [3023]. The IEP is reported in the abstract of [3024], but not in the text. The PZCs are reported in [915] without experimental details. The IEP reported in [3025] is not supported by data. The method is not specified in [3026]. It is not clear how the surface acidity constants were obtained in [2265]. The technique of pCu adjustment and/or control is not reported in [3027]. The term “IEP” is used outside its usual meaning in [3028]. The methods used in [3029,3030] are not clearly described. Two nonstandard methods used in [3031] produced very different results for the same material. Nonstandard methods were also used in [649,3032–3038].

3.15.6

WRONG CITATIONS

A few frequently cited values of PZCs/IEPs have actually never been published. Namely, they have been cited after secondary sources, without checking the primary source, which reports different PZCs/IEPs than that in a secondary source, a result of limited significance, or no PZCs/IEPs at all. Reference [2469] is quoted in [1] and then by a few other authors (probably after [1]) as an authoritative source of the IEP of hematite. Actually, no specific IEP is reported in [2469]. The authors mention that pH 2.4–4.2 is far from the IEP, but they do not specify how far. References [3039,3040] are cited in [1] as a source of PZC of silica. Actually it is only speculated in [3040] that a maximum in gelation time may coincide with the point of zero charge, and in [3039] PZC is not mentioned at all. Reference [3041] is cited in [1] as a source of the PZC of iron oxide. Actually, [3041] reports previously published data on anion- and cation-exchange capacities of various oxides. The results from [3042] are cited in [1] as IEP at pH < 3 obtained by electrophoresis. Actually, the streaming potential was used in [3042], and the pH was not controlled or reported. All samples of quartz, also acid-treated, showed negative z potentials in the presence of various electrolytes. Results from [3043] were cited in [1], and then quoted after [1] in numerous papers. Inspection of the original paper reveals that the quality of pristine PZCs/ IEPs derived from the results presented in [3043] is limited. Table 1 reports equilibrium pH of aqueous suspensions of four oxides, apparently containing occluded acid or base and/or multivalent ions. Figure 1 shows a titration curve with no data points between pH 5 and 9. Figure 2 shows uptake of monovalent ions by two oxides as a function of pH. The uptake is not a monotonic function of pH, and there are very few data points in the vicinity of the “PZC.” A PZC of g-Fe2O3 at pH 7.3 is cited in [3044] after [3045], but the original paper reports PZC at pH 7.5.

3.16

TEMPERATURE EFFECT

Numerous PZCs/IEPs reported in the literature were obtained without temperature control, or at least the temperature was not reported. On the other hand,

Compilation of PZCs/IEPs

867

a few authors undertook systematic studies of the effect of the temperature on PZCs/IEPs. Reviews of such studies and/or compilation of the results from literature can be found in [7,3046–3051]. Studies of surface charging at two or more different temperatures are indicated in footnotes in the tables in this chapter. Specific results for alumina can be found in [793,795] (Table 3.7), [743,843] (Table 3.42), [846] (Table 3.44), [904] (Table 3.49), [907] (Table 3.50), [580] (Table 3.62), [940] (Table 3.73), [703] (Table 3.77), [666,964,965] (Table 3.88), [967] (Table 3.90), [1842] (Table 3.94), [793] (Table 3.130), [1046] (Table 3.136), [1057] (Table 3.147), and [533] (Table 3.179). Specific results for Co3O4 can be found in [1233] (Table 3.303). Specific results for magnetite can be found in [1274] (Table 3.347), [907] (Table 3.353), and [1290] (Table 3.356). Specific results for iron(iii) (hydr)oxides can be found in [1334] (Table 3.395), [1336,1339] (Table 3.396), [727,1358–1360] (Table 3.412), [1388] (Table 3.426), [1409] (Table 3.431), [119,1347] (Table 3.434), [1456] (Table 3.467), and [1507,1518,1529] (Table 3.477). Specific results for HfO2, niobia, and tantalia can be found in [1677] (Tables 3.586, 3.685, and 3.941). Specific results for manganese oxides can be found in [1704] (Table 3.649), and [1715] (Table 3.665). Specific results for NiO and Ni(OH)2 can be found in [1233] (Tables 3.705 and 3.713). Specific results for silicas can be found in [1782] (Table 3.788), [1842] (Table 3.818), [1867] (Table 3.839), and [288] (Table 3.898). Specific results for hydrous ThO2 can be found in [1972] (Table 3.954). Specific results for titania can be found in [666] (Table 3.957), [1987] (Table 3.958), [1997] (Table 3.969), [843,921,2015,2024] (Table 3.973), [259] (Table 3.993), [1988] (Table 3.997), [2076–2079,2081] (Table 3.1030), and [183,1409] (Table 3.1047). Specific results for UO2 can be found in [2144] (Table 3.1094). Specific results for ZnO can be found in [2169] (Table 3.1142). Specific results for zirconia can be found in [260] (Table 3.1163) and [2219] (Table 3.1219). Specific results for illite can be found in [2240] (Table 3.1247). Specific results for kaolinite can be found in [2260] (Table 3.1267) and [98,904,2267] (Table 3.1273). Specific results for montrorillonite can be found in [2260] (Table 3.1324). Specific results for mixed oxides can be found in [573] (Table 3.1475) and [2389] (Table 3.1530). Specific results for AgI can be found in [3052]. Specific results for zirconium phosphates can be found in [2555] (Table 3.1791) and [2557] (Table 3.1793). Specific results for As2S3 can be found in [2563] (Table 3.1799). Specific results for activated carbon can be found in [2645] (Table 3.1970) and [2659] (Table 3.1994). Specific results for a latex can be found in [2696] (Table 3.2115). The electrophoretic mobility of cross linked poly(Nisopropylmetacrylamide) latex was rather insensitive to pH, but it increased in absolute value by a factor of 10 as the temperature increased from 20 to 50°C [2696]. This effect is due to a hydrophilic–hydrophobic transition (lowest critical solubility temperature of 32°C). The PZCs of metal oxides shift to low pH as the temperature increases, and dpH0/dT is usually in the range 0 to -0.03 K-1. This means that the shift in the PZC induced by a change in temperature below 5 K is negligible, but more substantial changes in T may induce a substantial shift in the PZC. The ionic product of water increases with temperature, and pKw - PZC is nearly constant for metal oxides.

868

Surface Charging and Points of Zero Charge

The relationship DHads = RT 2 ln(10)

dpH 0 dT

(3.1)

between the enthalpy of proton adsorption and the temperature effect on pH0 (derived in terms of the 1 - pK model) makes it possible to use the results of calorimetric measurements to predict the temperature effect on pH0. The interpretation of calorimetric measurements is difficult, because the surface charging is always accompanied by other phenomena, which also produce a substantial calorimetric effect. Schemes of calorimeters used in adsorption studies can be found in [3053,3054]. Results of calorimetric measurements are available for alumina [938,3055,3056], hematite [1408], goethite [1534], and titania [1408, 2016,2024,3053]. A hysteresis in the electrokinetic behavior of alumina and hematite was found in [288]: the absolute value of the z potential at constant pH increased with T, but no return to lower z potential on cooling was observed. An increase in the absolute value of the z potential at constant pH with T was reported in [2370]. Uptake of cations from a 1-1 electrolyte by silica and alumina at constant s0 was rather insensitive to temperature [1842]. The surface potential of alumina was studied in [3057] as a function of temperature (ISFET response). The temperature effect on the streaming potential is reviewed in [3058]. The PZCs at very high temperatures reported in [3047] were obtained by extrapolation of experimental results obtained at moderate temperatures.

3.17 PRESSURE EFFECT Direct studies of the effect of pressure on surface charging are rare. The conductance of an anatase dispersion in HCl increased with pressure [179]. This suggests a release of pre-adsorbed HCl from the surface at elevated pressure. On the other hand, the pressure effect was negligible in anatase dispersions in water or in NaCl. The experimental setup was designed to study desorption kinetics, and only the sign of the pressure effect could be determined. A similar method was used to study the pressure effect on proton adsorption on alumina dispersions in water [2928,3059], and in NaCl [2928], HNO3, and NaNO3 [927] solutions, and the effect was negligible for a pressure of about 107 Pa. On the other hand, the same pressure had a substantial effect on uptake of heavy-metal cations [927] and of anions [2928,3059] on alumina. The effect of pressure on surface charging may be studied indirectly on the basis of the relationship DVads = -RT

d ln K ads dT

(3.2)

Compilation of PZCs/IEPs

869

between the volume of reaction (which can be measured at atmospheric pressure by means of a dilatometer) and the pressure effect on the equilibrium constant. A DVprotonation of 6 cm3/mol was found for amorphous iron (hydr)oxide [3060]. Substitution of this value into Equation 3.2 indicates that the pressure effect on PZC is negligible for pressures up to 107 Pa. More substantial dilatometric effects (up to 40 cm3/mol) were observed in studies of the adsorption of anions [1668,3060] and metal cations [3061,3062] on iron (hydr)oxides. These values are in a range of typical specific volumes of solution reactions [3063]. The pressure also affects the ionic product and other physical properties of water [3064], but, for pressures up to 107 Pa, the effect is rather insignificant.

3.18

COMPILATIONS OF PZC OF VARIOUS MATERIALS

Compilations are frequently cited as the sources of PZCs/IEPs data. Parks [1] compiled the PZCs/IEPs of (hydr)oxides published up to 1965. PZCs/IEPs of (hydr)oxides and other materials published over the period 1966–1999 were compiled by the present author [2], and the updates [3065–3067] cover the period 2000–2005. The above five publications report a vast majority of reliable PZC/ IEP values published up to 2005. Several other reviews of PZCs/IEPs have been published. The reviews of PZCs limited to particular materials (e.g., iron oxides and silicon nitride) are cited in this book in the sections devoted to those materials. Many reviews report only one value (range) of PZC for a given material. These “recommended” values are close to the median of the values cited for those materials in this book, with a few exceptions. Typically, the PZC values are referenced (original literature or secondary sources). The compilations [57,3068–3071] are entirely or almost entirely based on [1]. Reference [3071] reports an unusually low PZC for Fe2O3. Numerous compilations (e.g., [240,3072,3073]) are based on older compilations. The compilation in [2367] is based on a previous compilation by the same author. The compilation in [3074] (only oxides) reports unusual PZCs for titania and goethite. The compilation of IEPs in [3075] is based on two older compilations, and it reports an unusually high IEP for Si3N4. Reference [1677] compares PZCs of oxides “recommended” in different compilations. Several compilations of PZCs [102,641,3035,3076–3081] report only PZCs/ IEPs of (hydr)oxides. Reference [641] additionally reports charging curves. Reference [3082] reports an unusual PZC for aluminum hydroxide. In [2141], the original literature is not specified. Reference [714] reports surface acidity constants rather than PZCs. In [3083], PZCs of oxides are reported, but only the metal is indicated, without oxidation or hydration state. A compilation of PZCs is a part of a World Wide Web database [3084]. The compilation in [3085] covers nonpolar substances including gas bubbles. IEPs of monodispersed colloids (oxides and other) are reviewed in [311]. PZCs of oxides and silver halides are summarized in [3086]. PZCs of oxides, metals, apatites, and silver halides are summarized in [7].

870

Surface Charging and Points of Zero Charge

IEPs of selected oxides (also mixed oxides) are reviewed in [3087]. PZCs of oxides and other materials are reviewed in [3088] (original literature not reported). IEPs of radiocolloids are reviewed in [3089]. Other reviews of PZC were published in [3090] (selected materials), [3091, 3092]. [3093] reports also TLM parameters and charging curves.

3.19

CORRELATIONS

Two types of correlation have been investigated: between a pH-dependent property of a certain material and the surface charging behavior of that material (based on authors’ own measurements with the same sample of material), and between a pH-independent property in a series of materials and the PZCs in that series of materials. The second type of correlation was studied using authors’ own experimental data, data from the literature, or a mixture of both. In many dispersions, the maximum in the viscosity and/or in the yield stress matches the IEP. Several examples of such a correlation can be found in footnotes in the tables in this chapter. Specific results for aluminas can be found in [784,785] (Table 3.6), [320] (Table 3.7), [437] (Table 3.44), [998] (Table 3.117), [1010] (Tables 3.128–3.131), [1016] (Table 3.130), [509] (Table 3.131), and [1159] (Table 3.217). The yield stress of 25 vol% alumina dispersions (alkali nitrates, various concentrations) had a maximum at pH 9.2. A shift in that maximum to high pH was observed at [Li] > 0.1 M [3095], and the IEP shifted accordingly. PZCs of alumina and of iron(iii) oxide were correlated with the maximum in the friction coefficient (high-frequency friction machine) [1354]. The measurements were carried out in the presence of sulfate (possible specific adsorption). Specific results for ceria can be found in [1224] (Table 3.278). Specific results for iron (hydr)oxides can be found in [1322] (Table 3.383), and [431] (Table 3.403). Specific results for titania can be found in [1977] (Table 3.957), [384,1978,1980,1986] (Table 3.958), [437] (Table 3.973), [1980] (Table 3.982), and [2075] (Table 3.1029). Specific results for zirconia can be found in [509] (Table 3.1179), [787] (Table 3.1182), [436,2194,2195,2197,2198] (Table 3.1186), and [2221] (Table 3.1219). Specific results for ZrSiO 4 can be found in [2365] (Table 3.1504). Specific results for Y-modified zirconia can be found in [2396] (Table 3.1545). Specific results for Si3N4 can be found in [2493] (Tables 3.1710 and 3.1711) and [410] (Table 3.1721). In all these materials, the maximum in the viscosity or in the yield stress matched (at least roughly) the IEP. In contrast to metal oxides, the IEP of silica nearly matched the minimum in the viscosity [1884]. The relationship between IEPs and mechanical properties of dispersions of clay minerals is more complex than for oxides. Specific results for bentonites can be found in [394] (Tables 3.1317, 3.1318, and 3.1321). For kaolin, the maximum in the yield stress was at pH 5.3, while the z potential was negative at pH > 4. This lack of coincidence of the IEP and the maximum in the yield stress is due to different charges of faces and edges [1019].

871

Compilation of PZCs/IEPs

The speciation of vanadium [915] and molybdenium [1723] on oxide surfaces was studied by Raman spectroscopy. It was similar to the speciation in solution at a pH equal to the PZC of the given oxide. The polishing rate of silicate glass at neutral pH is high for materials with PZC at pH ⬇ 7 and low for materials with PZC at low or high pH [3073]; that is, the polishing rate of a given material is high near its PZC. Maximum polishing at the IEP of the abrasive is reported in [1228]. The PZC of the corrosion product on aluminum matched the maximum in scattered results representing the contact angle at a hexadecane/aqueous solution interface [3080]. A maximum extent of coating of silica by goethite (from 0.001–1 M NaNO3) at the PZC of goethite is reported in [1465]. The maximum was sharper at high ionic strength. The PZC of goethite matched the pH of the maximum filtration rate (minimum filtration time) [699]. A limited correlation was found between the pH of zero net charge of metal species in a saturated solution of a metal oxide and the PZC of that oxide [1208,1248,3082]. Correlation between the PZC and the pH of a saturated solution was also studied in [3096]. PZC was found to be linearly correlated with DO + DM, where DO and DM are oxygen and metal chemical shifts derived from XPS spectra of metal oxides [825,3097]. The following correlation was found in [3071]: PZC = 12.2 - 1.34(DO + DM)

(3.3)

where DO is the O 1s binding energy minus 530 eV (in eV) and DM is the difference between the cation binding energy and the metal binding energy (in eV, from XPS). Correlation between the chemical shift from XPS spectra and the PZC was also studied in [3087]. The following correlation was found [3068] in a series of metal oxides: PZC = 18.43 - 53.12

u 1 2 -u - log L 2 u

(3.4)

where v = Z/CN (with CN the coordination number). The coefficients in Equation 3.4 are based on PZCs of alumina (9.1) and magnesia (12.4). Most calculated PZCs were >9, and an unusual result (PZC at pH 12) was obtained for ZrO2. Correction for crystal field stabilization energy produces the following correlation: 2 -u Êu ˆ 1 PZC = 18.43 - 53.12 Á + 5.61 ¥ 10 -4 C ˜ - log u ËL ¯ 2

(3.5)

where C is the crystal field stabilization energy (in kcal/mol). The following correlation was found [3098,3099] in a series of metal oxides and silicates: 21.1 PZC = ____ e - 42.9 s/r M–OH + 14.7

(3.6)

872

Surface Charging and Points of Zero Charge

where e is the permittivity of the solid phase, s is the Pauling bond strength, and the average s/r M–OH over all cation sites was used for silicates. The relatively high PZC for silica (2.9 for the a-form) was used to calculate the coefficients in Equation 3.6. The latter equation produces relatively high PZCs for precipitated silica (3.9) and SnO2 (7.7). The following correlation was found in a series of metal oxides: PZC = 12.72 - 0.24b(M–M)

(3.7)

[3083] (only the metal was indicated, without oxidation state). Here b(M–M) is the metal–metal bond energy in solid metal, and is equal to 2DHs/CN, where DHs is the molar heat of sublimation of the metal and CN is its coordination number. The same author studied the correlation of the PZC with partial negative charge per oxygen atom in the oxide on the one hand and with the a parameter on the other (tendency of an oxide to accept O2- [3100]). The former correlation was rather poor, but the latter correlation was good (except for Cr). A correlation between volume field strength and IEP was found [481] in a series of Mn oxides. A correlation of the PZC with electronegativity was found in a series of metal oxides [3087,3090]. An analogous correlation was found in a series of IEPs of metal oxides and sulfides [2571]. Most IEPs of sulfides were extrapolated. The following correlation is reported in [3035]: PZC = -8.48c + 57.3

(3.8)

where c is electronegativity in eV in a series of metal oxides and titanates. The following correlation was found for metal oxides [830]: PZC = 14.43 - 0.58Xi

(3.9)

where Xi = (1 + 2z)X0, with z the metal charge and X0 the electronegativity of neutral atom reported in [3101]. A rather unusual PZC of Fe2O3 (6.8) was used to obtain the coefficients in Equation 3.9. Correlations of PZC with electronegativity, bandgap width, electron affinity, and flatband potential in a series of oxides were studied [3080]. In a series of silicas, the PZC was lower for materials with higher crystallinity, and higher for materials with low surface site density (pyrogenic silica) [544]. The PZC was correlated with partial charge on oxygen in a series of metal oxides [3081]. Unusual PZCs were obtained for zirconia (10), Fe2O3 (5.7), and quartz (3.7). A correlation between PZC and Certhledge ionic potential (see [3102]) is reported in [3096]. A correlation between average volume of unit cell per metal atom and PZC is reported in [3103]. A linear correlation between the PZC and decomposition temperature of CaSO4 in the presence of given oxide is reported in [3104]. An unusual PZC was obtained for ZrO2. Different approaches were used in studies of correlation between PZC and heat of immersion in water. Correlations between PZC and heat of immersion for a series of different oxides are reported in [1311,3090,3092]. The heat of immersion of

Compilation of PZCs/IEPs

873

rutile and of a series of silica-coated rutiles was studied in [3105]. The heat of immersion of various silicas and chromias was studied in [3106]. In the above studies, one pH-independent heat of immersion was used for a given material. In contrast, the heat of immersion of maghemite was studied as a function of pH, and a minimum was found at pH 6.8 [601]. The heat of immersion of silica in acids increased with acid concentration [1797].

3.20 MIXED WATER–ORGANIC SOLVENTS The present book is devoted in principle to aqueous solutions of 1-1 electrolytes. However, admixture of nonelectrolytes often has an insignificant effect on pHdependent surface charging, and the principles outlined in Chapters 1 and 2 and in the preceding sections of this chapter, as well as the PZCs/IEPs reported in this chapter, apply also to systems containing small amounts of certain nonelectrolytes. Larger amounts of nonelectrolytes may induce shifts in PZCs/IEPs. Several studies of surface charging have been carried out in mixed water–organic solvents. The term “mixed solvents” is used in this section for mixtures in which the molar fraction of water is greater than one-half, to distinguish them from nonaqueous solvents (where the molar fraction of water is very much less than one-half; see Section 3.21). In mixed solvents, a similar approach and similar methods can be used as in studies in water; first of all, the pH can be measured. Ions and electrolytes that are inert in a purely aqueous system are also inert in water-rich mixed solvents, and ions that adsorb specifically from water adsorb specifically from water-rich mixed solvents. pH measurements in mixed solvents require special procedures, which may be tedious but at least are well established [3107,3108]. Activity coefficients of ions and salts in mixed solvents are summarized in [3109]. A typical approach, in which the ionic strength is established by a 1-1 salt, and the pH is adjusted by an acid or base that has an ion in common with the inert electrolyte and is measured by means of a glass electrode, was used to study the following systems by titration, electrophoresis, and electroacoustics. A purely aqueous system was usually studied as a reference. The physical properties of solvents relevant to the interpretation of electrokinetic data (viscosity and permittivity) may be very different from those of water, and they have to be taken into account in the interpretation of results. Alumina was studied in aqueous alcohols [925], aqueous dioxane [666,963], aqueous dimethylsulfoxide (DMSO), aqueous glycerol, and aqueous heavy water [963]. Fe2O3 was studied in aqueous alcohols [1375,1386,1434,1456], aqueous dioxane [1388], and aqueous DMSO [1411]. Goethite was studied in aqueous acetone and aqueous methanol [1521]. Silica was studied in aqueous alcohols [1838, 1910,1911] and in other water–organic mixtures [1838]. Silica capillary was studied by electro-osmosis in 50:50 mixtures of organic solvents with water in the presence of a phosphate buffer [2927]. Surface charging of silica in mixed solvents is reviewed in [3110]. Titania was studied in aqueous alcohols [220,550,1986, 1988,2059,2115], aqueous dioxane [666,963], aqueous DMSO, aqueous glycerol, and aqueous heavy water [963]. Yttria was studied in aqueous alcohols [220].

874

Surface Charging and Points of Zero Charge

Different oxides were studied in aqueous 1-propanol [350]. Controlled pore glass was studied in aqueous alcohols [2603]. In another series of publications, the solids were dispersed in “pure” mixed solvents or the concentrations of various inorganic components (which may include acid or base) was adjusted, but the pH was not measured. Hematite was studied in a 50:50 ethanol-water mixture at different concentrations of NaOH and HNO3 [3111]. Silica was studied in aqueous acetone (0–100%) at constant NaI concentration [3112]. Quartz was studied in ethanol–water mixtures in the presence of alkali bromides [3113]. Anatase was studied in 25% and 50% methanol [1984] at different NaCl concentrations. Glass was studied in a 50:50 ethanolwater mixture at different concentrations of NaOH and HNO3 [3111]. Polystyrene latex was studied in water–alcohol mixtures in the presence of 0.0001–0.1 M KBr [3114], in aqueous ethanol and aqueous 1-propanol in the absence of electrolyte [3115], and in aqueous methanol and ethanol in the absence of electrolyte [3116]. AgI was studied in aqueous butanol and glycol [3117], and the surface charge was adjusted by addition of potential-determining ions (Ag+ and I-) rather than acid or base.

3.21

NONAQUEOUS SOLVENTS

The solution chemistry of nonaqueous solvents is very different from that of water-rich mixed solvents. pH measurement in nonaqueous solvents is difficult or impossible. Salts often show a limited degree of dissociation and limited solubility (see [132] for solubility of salts in organic solvents). Ions that adsorb nonspecifically from water may adsorb specifically from nonaqueous solvents, and vice versa. Therefore, the approach used for water and water-rich mixed solvents is not applicable for nonaqueous solvents, with a few exceptions (heavy water and short-chain alcohols). The z potential is practically the only experimentally accessible quantity characterizing surface charging behavior. The physical properties of solvents may be very different from those of water, and have to be taken into account in the interpretation of results. For example, the Smoluchowski equation, which is often valid for aqueous systems, is not recommended for estimation of the z potential in a pure nonaqueous solvent. Surface charging and related phenomena in nonaqueous solvents are reviewed in [3120–3127]. Low-temperature ionic liquids are very different from other nonaqueous solvents, in that they consist of ions. Surface charging in low-temperature ionic liquids was studied in [3128–3132]. Studies of surface charging in nonaqueous solvents can be divided into three categories. Many studies were carried out in allegedly pure solvents without the addition of any solutes. In several studies, a possible correlation between the value of the z potential and the parameters characterizing the acid–base properties and the polarity of the solvent was investigated. Detailed discussion of these solvent scales can be found elsewhere [3133–3135]. Basically, the solvent scales apply to pure solvents, but the effect of solutes has also been studied [3136]. In fact, the

Compilation of PZCs/IEPs

875

z potentials of various powders in allegedly pure nonaqueous solvents are very sensitive to impurities; the latter are omnipresent, and their nature and concentrations are usually unknown and difficult to control. Therefore, the z potential of a given powder in a given solvent is likely to change from one lot of the solvent to another, and the significance of such results is limited. Typical impurities in nonaqueous solvents and their effect on the properties of the solvent have been discussed in the literature [3137,3138]. In the second category of studies, the effect of a certain solute was investigated; that is, the z potential was studied at various concentrations of that solute under conditions that were otherwise the same. The z potential in such studies is also influenced by impurities, but the levels of the latter are independent of the concentration of the studied solute, and the observed qualitative trend (increase or decrease in the z potential and sign reversal) may be correct. Water is among the most often studied solutes, and is also a typical impurity, even in dried solvents. In the third category of studies, a similar approach was used as in aqueous system (pH adjusted and measured). Such an approach is limited to relatively polar solvents.

3.21.1

ALLEGEDLY PURE SOLVENTS

Alumina and titania in different solvents were studied in [822]. MgO and ZnO in seven organic liquids were studied in [1686]. Silica in a series of nonaqueous solvents and in acetonitrile–water and methanol–water mixtures was studied in [3139,3140]. Only positive z potentials are reported, probably by mistake. Silica in decane was studied in [3141]. ZnO in absolute methanol, ethanol, and propanol was studied in [3142]. Montmorillonite in 2-propanol was studied in [3143]. Silicon in a 99% 1-butanol–1% water mixture was studied in [3145]. In [3146], 11 solids (oxides and inorganic salts) in 9 solvents were studied.

3.21.2

EFFECT OF WATER

Addition of water induced a reversal of sign of electrokinetic potential of a-alumina in alcohols from negative to positive [975]. Alumina, magnesia, titania, and glass in 14 solvents (wet and dry) were studied in [902,3147]. CrO2 in tetrahydrofuran (THF) was studied in [3148]. Silica in 17 organic solvents (14 solvents in wet state and 3 solvents in wet and dry state) was studied in [3149]. Titania in n-alcohols (dry and wet) was studied in [3150]. Titania in n-alcohols, pure and containing water (up to 15%) was studied in [2032]. Titania in pentanol was studied in [2003]. A different approach to the effect of water was used in [404]: titania and silica- and alumina-coated titania in ethylene glycol (up to 13% of water) were studied at constant pH (rather than in allegedly pure solvent). Addition of water induced a reversal of sign from positive to negative in the z potentials of titania (pH 7) and alumina-coated titania (pH 9), and the z potential of silica-coated titania (pH 6.5) was negative, and rather insensitive to water addition.

876

3.21.3

Surface Charging and Points of Zero Charge

EFFECT OF INORGANIC ELECTROLYTES

Alumina in 93% ethanol in the presence of NaBr and HBr was studied in [3151]. Alumina in ethanol was studied in [3152]. The positive z potential was depressed when the HCl concentration increased. The sign of the z potential was reversed from positive to negative at a KOH concentration of about 0.0002 M. Alumina, silica, and quartz in 1-butanol in the presence of various 1-1 electrolytes were studied in [3153]. Alumina and titania in different solvents, also in the presence of different amines were studied in [3154]. Silica in 80–95% dioxane in the presence of HCl, KOH, and different 1:1 salts was studied in [314]. Silica in nonaqueous solvents containing 1 mass% of water in the presence of CsCl was studied in [3155]. Silica in methanol in the presence of KCl was studied in [282]. Quartz in DMSO in the presence of various 1-1 electrolytes was studied in [3156]. Quartz in ethanol in the presence of various 1-1 electrolytes was studied in [3157,3158]. Quartz in DMSO, acetone, and 1-butanol in the presence of NaBr or LiBr was studied in [3151]. Silica in methanol, acetonitrile, and methanol-water mixtures, with or without NaCl was studied in [1853]. Silica in 99.7% acetone in the presence of NaI and Bu4NI was studied in [1908]. Titania in different 99% organic–1% water mixtures in the presence of CsCl and other 1-1 salts was studied in [3160]. Anatase in different organic solvents in the presence of CsOH and HClO4 was studied in [3161].Titania in n-alcohols in the presence of different salts was studied in [2037]. LiF, CaF2, and MgF2 in methanol, acetone, and nitroethane in the presence of NaF were studied in [3162]. AgI in ethanol at concentrations of LiNO3 up to 0.01 M was studied in [3163]. CaSiO3 in DMSO at different concentrations of NaBr and CaBr2 was studied in [3144]. Diamond in 96% ethanol in the presence of various 1-1 salts was studied in [3164]. Typically, acids induced more positive z potentials and bases induced more negative z potentials, as expected from the behavior of aqueous systems. Interestingly, 1-1 salts, especially Cs salts, often induced a sign reversal of the z potential from negative to positive.

3.21.4

EFFECT OF PH

Alumina in ethanol was studied in [1026,1027]. Alumina, titania, and SiC in absolute ethanol were studied in [1045]. Silica in ethylene glycol was studied in [3165,3166]. Quartz in D2O was studied in [1938]. SiO2, NiTiO3, and SiO2-coated NiTiO3 in ethanol were studied in [3167]. SiO2, SiC, Si3N4, and MoSi2 in ethanol were studied in [2497]. Ta2O5·nH2O in ethanol was studied in [1970]. Titania and silica- and alumina-coated titania in ethylene glycol were studied in [404]. The studies reported here resulted in similar charging and electrokinetic curves as those observed in aqueous systems.

3.22 CONCLUSION A reader of this book might have expected that the compilation of the PZCs would be followed by a statistical analysis similar to that in [2]. Indeed, the original plan

Compilation of PZCs/IEPs

877

was to calculate average and median PZCs, and the standard deviations in the PZCs of various categories of materials. This plan was changed when it became clear that, for most common materials, the collection of PZCs was dominated by studies conducted with a few specimens, while the other specimens were seldom studied. For example, among 147 PZCs/IEPs reported for synthetic goethite (see Section 3.1.12.5.1.2), 106 were obtained for goethites synthesized according to Atkinson’s method (different versions, but the same basic principle), and only 41 were obtained for goethites synthesized according to 25 other recipes. Only eight PZCs/IEPs are reported for seven specimens of commercially available goethites. Thus, one type of material (Atkinson’s goethite) is severely overrepresented, and the contribution of the other types of goethite to the average in a set representing synthetic goethites or in a set representing all goethites (commercial and synthetic) is small. Similar trends are expected in the future; that is, the choice of specimens to be studied is biased. The fact that a certain specimen was studied by others or that it has a PZC at a certain pH (which is the value “recommended” in review papers) is an argument to select this particular specimen rather than look for another. Similar examples of biased choice were observed in materials other than goethite, although the dominance of one specimen was not that striking. Among 243 PZCs/IEPs of commercial titanias, 62 are reported for P25 from Degussa, and 181 are reported for 80 other commercial materials. Thus, over one-quarter of all PZCs/IEPs of commercial titania were obtained for one material. On the other hand, 117 PZCs/IEPs are reported for materials synthesized according to 46 recipes. Therefore, the average PZC in a set representing all titanias (commercial and synthetic) is dominated by commercial materials. The preference of commercial over synthetic materials was even more substantial for alumina: 316 PZCs/ IEPs are reported for 147 different commercial specimens, and only 59 PZCs/ IEPs are reported for 31 different synthetic specimens. Thus, the contribution of synthetic aluminas to the average in a set representing all aluminas (commercial and synthetic) is small, and it is comparable to the contribution of one type of commercial material (Degussa C, 47 entries). It may very well be that, indeed, the most frequently studied specimens in each category of materials are representative of the “best” PZC, but critical, fundamental studies in this direction are rare. In view of the tendency to study only a few selected specimens, the average over all values of PZCs/IEPs found in the literature may be misleading.

4

Ion Specificity

Inert electrolytes show ion specificity, as discussed in Chapter 2 and illustrated in Figures 2.4, 2.5, 2.9, and 2.10. The anions affect the positive branches of the charging and electrokinetic curves, and the cations affect the negative branches. The affinity to particular monovalent anions and cations depends on the character of the surface, and follows the hard–soft acid–base principle; that is, hard surfaces prefer to adsorb hard ions, and soft surfaces prefer to adsorb soft ions. The effects of ion specificity on the charging and electrokinetic curves are usually minor. The affinity series observed in coagulation behavior are termed Hoffmeister series. Affinity series for various hydrous oxides are compiled in [3089]. The compilation of affinity series in [3168] also includes AgI and Hg. A review of affinity series of metal cations is presented in [2981]. Increasing affinity in a series from Li to Cs is reported for materials with PZCs at pH < 4, and decreasing affinity in a series from Li to Cs is reported for materials with PZCs at pH > 5. An analytical expression for stability constants of ⬅SOMe and ⬅SOH2X complexes (TLM) as a function of the dielectric constant of the solid and the ionic radii was proposed in [3169]. The results for common oxides and common anions and cations are tabulated. Examples of ion specificity in different phenomena, not directly related to surface charging, are presented in [3170].

4.1 AFFINITY SERIES Specific examples of affinity series are presented in this section. The “>,” “=,” and “≥” symbols between the chemical symbols of elements denote the order in affinity to a certain surface. “A > B” means that the ion “A” has a higher affinity; that is, the s0 and uptake of counterions are higher and the absolute value of the z potential and the stability are lower in the presence of “A” than in the presence of “B” under conditions that are otherwise the same. The valency of the ions is not indicated (only monovalent anions and cations). The measured quantities, namely, s0, z, uptake of counterions, and critical coagulant concentration (CCC), are usually compared at constant concentration of ions (salts). In very concentrated solutions, the activities of different ions in salt solutions of equal concentrations can be very different (see Section 4.3). 879

880

4.1.1

Surface Charging and Points of Zero Charge

ALUMINAS

4.1.1.1 Al2O3 Uptake at pH 4, ionic strength 0.06 M: F >> IO4 > IO3 >> BrO3 >> Cl > Br > ClO3 > I > ClO4 [968]. Titration, 0.005–0.5 M K salts: Cl > NO3 [559]. A difference in CIP between KCl and KNO3 is reported. Electroacoustics, 0.01 M sodium salts: BrO3 > Cl苷NO3苷ClO4. In 0.1 M sodium salts: BrO3 > Cl苷NO3 > ClO4 [509]. Ion specificity in yield stress was also observed. Radiotracer, at constant s0: Na > Cs [1842]. Radiotracer, 0.01 M chlorides: Li > Cs [1841]. Titration, 0.1 M chlorides: Li > Na > Cs [963], also in the presence of organic co-solvents. Titration, 0.1 M chlorides: Na > K > Cs and 0.1 M Na salts: Cl苷Br > I [985]. Electrophoresis, coagulation, 0.001 M potassium salts: NO3苷Cl > ClO4 [944]. 4.1.1.2 Boehmite Titration, 0.001–0.25 M potassium salts: Br > I > NO3 > Cl; but at 1 M: I > Br > NO3 > Cl [1132]. Coagulation, potassium salts: NO3苷Cl > I [1133]. Titration, 0.001-1 M chlorides: Na ≥ Li > K, 0.001–1 M Na salts: NO3苷Cl苷I [548]. 4.1.1.3 Alumina Coating on Titania ICP spectrometry, 0.002 and 0.01 M chlorides: Li > Na > TMA [3171].

4.1.2

IRON (HYDR)OXIDES

4.1.2.1 Magnetite Titration, 0.25 M chlorides: Na > K > Li [117]. This unusual series may be due to the high silica contents (8%) in magnetite. 4.1.2.2 Hematite Titration, 0.001–1 M chlorides: Li > K苷Cs [1406]. Coagulation, at pH > 11.5: Li > Na > K苷Cs. No clear cation sequence at pH < 11.5. At pH < 7: IO3 > F > CH3COO > CH2ClCOO > BrO3 > SCN > CHCl2COO > Br > NO3 > ClO3 > Cl > ClO4苷I [2981,3172]. Coagulation: Li > Na > K; F > BrO3 > Br > NO3 > ClO3 > Cl > ClO4 [2846]. Urea (up to 10 M) stabilized positively charged hematite (CCC increased), but destabilized negatively charged hematite (CCC decreased). The anion affinity series was preserved in the presence of urea, and cation affinity series was reversed at [urea] > 5 M.

Ion Specificity

881

The effect of the nature of the salt (NaCl, KCl, KBr) on the z potential at pH 3 and 10 was rather insignificant over a broad range of salt concentrations [1377]. Titration, z potential: NO3 > ClO4 > Cl. In 0.1 M solution, the anion effect on the electrokinetic curves was insignificant. Coagulation: IO3 > SCN > F > NO3苷I > ClO4苷Br > Cl [328]. Titration, NO3 > ClO4 [1349]. In another sample of hematite, the CIP in the presence of perchlorate was lower by 0.3 pH units than in the presence of nitrate [1349]. 4.1.2.3 Goethite Titration, 0.02, 0.1 M Na salts: Cl > NO3 > ClO4 [1552]. Titration, 0.01 M Na salts: Cl > NO3 > ClO4 [44]. Titration, 0.01− 0.1 M Na salts: Cl > NO3 [1526]. Titration, 0.2 M salts: Li > Na > K > Cs, Cl > NO3. Anion specificity was observed also in the basic range and cation specificity was observed also in the acidic range [537,1557]. 4.1.2.4 Akageneite Titration, 0.001–0.1 M nitrates and potassium salts: Na > K > Li (figures) or Li ≥ Na ≥ K (text), Cl >> NO3 [613].

4.1.3

MnO2

Titration, 0.1 M nitrates: Li > Na > K苷Cs [932]. l-MnO2, titration, uptake, 0.1 M chlorides: Li >> Na > K, Rb, Cs [1715]; uptake: Li >> Cs > Rb > K > Na [1716].

4.1.4

HYDROUS NIOBIA

KD in 0.1 M NaCl, pH 3–7, radiotracer, AAS, initial concentration of 0.0001 M: Cs >> K >> Li [676].

4.1.5

SILICA

Titration, 0.1 M: K > Na > Li [1886]. Titration, 0.1 M chlorides: Cs > K > Na > Li [1867]. Titration, 0.001–0.1 M chlorides: Cs > Rb > K > Na > Li [1881]. Titration, 0.005–0.3 M chlorides: Cs > Rb > K > Na > Li [591]. Pyrogenic silica, titration, 0.01 M nitrates, pH 4–9: K > Li (text), Li > K (Fig. 3); stober silica, titration, 0.01 M nitrates, pH 4–9: K > Li >> Bu4N > Me4N [363]. Three types of silica, titration, 0.7 M chlorides: K > Na [1924]. Titration, 0.1 M perchlorates, at low pH: K > Na > Li; at pH > 10.5, the affinity series is reversed [3173]. Titration, 0.1 M chlorides: Cs > K > Li > (C2H5)4N [127].

882

Surface Charging and Points of Zero Charge

Titration, 0.1 M chlorides: Cs > K > Li [1772]. Titration, chlorides: K > Na [610]. Titration, 0.04 M: Cs > Rb > K > Na > Li [1754,1755,1916]. Titration, 0.067 and 0.2 M chlorides, pH 3–8.5: K > Na > Li, small differences [561]. Titration, 1 M chlorides: Rb > K > Na > Li [1795]. Titration, 0.01 M chlorides, s0 determined coulometrically: Rb > K > Li [1781]. Titration: Cs > K > Li [1943]. Titration, pH < 3 (positive charge): Cl苷NO3 [1797]. Titration, 0.001–1 M chlorides: no clear affinity series of Group 1 cations [1890]. Titration, 0.01–4 M chlorides: no clear affinity series of Group 1 cations [1891]. Apparently, Cs > Li at low salt concentration, but Li > Cs at higher salt concentrations. Titration and competition with Mg (uptake of Mg in the presence of different salts at otherwise the same conditions), 0.01 M chlorides: K > Na > Li [1782]. Titration, radiotracer, 0.01 M chlorides: Cs > Li [1841]. Radiotracer, at constant s0: Na ≥ Cs [1842]. Uptake: Cs > K > Na > Li [544]. Uptake, pH 6.7, selectivity coefficients defined as KNa苷[CR][Na +]/[NaR] [C+]: Li 0.65, Na 1, K 1.8, Rb 2.4, Cs 3.2 [3174]. Uptake, pH 3–4.4, 0.01–0.6 M, 5, 20, 35, and 50°C: K苷Na > Li [3175]. Uptake, no pH control, at sufficiently high concentration: K > Na [3176]. Uptake, AAS and ion-selective electrodes, 0.1 M: Cs > Rb > K > Na > Li [3177]. Radiotracer, pH 4-9: Cs > Rb苷K > Na [3178]. A series of chromatographic silicas, radiotracer: Cs > Na; the selectivity increases when a pore diameter decreases [3179]. This result suggests a size-exclusion effect, which may also be responsible for the cation selectivity in other silicas. Dynamic method, 0.0001 M Cs, 0.001–0.1 M NaClO4: Cs >> Na [1929]. Electrocoustics, 0.1 M chlorides: Cs > Li [1870]. Two types of silica, z potential, 0.001–0.4 M chlorides: Cs > K > Na > Li [1813]. z potential, 0.01 M chlorides, pH 3–11: Cs > K > Na > Li [429]. The coagulation behavior of silica (see [3180,3181]) is very different from that of metal oxides, and the CCC is not directly correlated with the affnity series.

4.1.6 SnO2 Titration, 1 M K-salts: Cl > NO3 [583]. Electrophoresis, 0.1 or 0.01 M nitrates: Li > K > Cs, unusual sequence in the positive branch [520]. Titration, 1 M chlorides: K > Na, small difference [546].

Ion Specificity

4.1.7

883

THORIA

Titration, 0.1 M chlorides: Li > Na > K > Cs > NH4, and Cl > NO3 > Br > CNS [3182].

4.1.8

TITANIA

Titration, 0.001 and 0.1 M nitrates: Li > Na > Cs; 0.001 and 0.1 M sodium salts: Cl苷ClO4苷NO3 > I [545]. Titration, 0.1 M chlorides: Li > Na > K > Cs; 0.1 M sodium salts Cl苷Br > I [2061]. Titration, 0.1 M: Li > K苷(CH3)4N; 1 M LiNO3 induced a shift in the PZC [2102]. Titration: in NaCl, |s0| was lower than in NaClO4 on both sides of the PZC; z potential, 0.001 M Na salts: ClO4苷Cl [615]. Titration, electrokinetics, coagulation, 0.01, 0.1 M chlorides: Li > K > Cs; titration, 0.01, 0.1 M K salts: Cl > NO3 > ClO4 [327]. Titration, electrokinetics, based on selected literature: Cl > NO3 > ClO4 > I; Li > Na > K > Cs [734]. Electrokinetics: Na salts, various concentrations, pH 4 and 5.5: Cl > NO3 [3183]. Coagulation: One sample (PZC at pH 5.9): Li > Na > K > Cs and IO3 > BrO3 > NO3 > ClO3 > Cl > Br苷I苷ClO4; three other samples (PZC at pH < 5) showed a reversed cation affinity series, and the anion affinity series were similar, although in two samples the difference between NO3, ClO3, Cl, and Br was insignificant [3005].

4.1.9

UO2

Electrokinetic potential, 0.001 M K salts: NO3 > Cl > ClO4 [2145]. A coagulation study was also carried out.

4.1.10 WO3 Coagulation, wide pH range: Cs > Rb > K > Na > Li [2997].

4.1.11 ZIRCONIA Titration, 0.1–1 M chlorides: Li > Na > K (high pH); K > Na > Li (low pH) [2177]. Titration, 0.1 M chlorides: Li苷Na苷K苷Cs [2182]. Uptake, dynamic method, 0.1 M hydroxides: Li > Na > K [3184]. Electroacoustics, 0.01 M sodium salts: BrO3苷Cl > NO3苷ClO4; 0.1 M sodium salts: BrO3 > Cl苷NO3 > ClO4 [509]. Ion specificity in the yield stress was also studied.

884

Surface Charging and Points of Zero Charge

4.1.12 MICA Streaming potential, chlorides, pH 5.8: Cs > K > Na苷Li [487,2284]. The difference is significant at concentrations > 10-3 M.

4.1.13 Na-MONTMORILLONITE Uptake: Cs > Na [3185]. Also a literature review.

4.1.14 RED MUD Titration, 0.1 and 1 M chlorides: Na > Cs [578].

4.1.15 ALKALI METAL-SUBSTITUTED MANGANESE OXIDES Uptake, different sequences [3186], Li > Na > K [3187].

4.1.16

δ -MnO2

Uptake: Na > K [2481].

4.1.17 SI3N4 Electroacoustics, 0.01 M: Na苷K > NH4; 0.01 M K salts: Cl苷Br苷I [322].

4.1.18 CHRISOTILE z potential, 0.001–0.01 M, pH 9: I > Br苷Cl [2364].

4.1.19 CONTROLLED PORE GLASSES Uptake (flame photometer): K > Na > Li [3188]. Uptake: K > Li; Cs > Na [3179]. Uptake: Cs > Na [3189].

4.1.20 DIAMOND Titration, 0.001–1 M chlorides, pH 3.5–10, LiCl, KCl, KNO3, CsCl: pH- and ionic strength-dependent affinity series, but the differences are rather insignificant [2613].

4.2 UPTAKE OF 1-1 ELECTROLYTE IONS AT OR NEAR THE PZC The present author does not recommend the measurement of uptake of ions of inert electrolyte as a method to determine the s0 or the PZC, although such a method has been used and recommended by others. The measurement of uptake

Ion Specificity

885

of ions of an inert electrolyte provides valuable complementary information, which can be used to test adsorption models and model parameters (see Section 2.9), and a few experimental results are presented in this section. Different models may produce similar s0 values but very different concentrations of particular surface species. In particular, a zero charge at the PZC is a result of cancellation of contributions of positively and negatively charged species. These contributions may be relatively large in absolute value in certain models, and very low in absolute value in other models. Models with binding of ions of the inert electrolyte (e.g., TLM) can be tested by direct comparison of the measured and predicted adsorption of co- and counterions, and these models predict a substantial uptake of inert-electrolyte ions at the PZC. Models without such binding predict negligible or negative adsorption of inert-electrolyte ions at the PZC. The experimental results are contradictory and do not clearly support either type of models. The uptake of inert-electrolyte ions is characterized using the following terminology. The uptake at the PZC is considered substantial when it is higher than 0.1 of the maximum uptake observed in the range PZC ± 3 pH units; it is considered moderate, when it is about 0.1 of the maximum uptake observed in the range PZC ± 3 pH units; and it is considered negligible when it is lower than 0.1 of the maximum uptake observed in the range PZC ± 3 pH units. The valence of ions was omitted (only monovalent ions).

4.2.1

ALUMINA

Negative uptake of the following inert-electrolyte ions has been reported: • Of Cl, no salt, only HCl added to adjust the pH; the negative adsorption was low in NaOH-washed alumina and substantial in water-washed alumina, and it was interpreted as leaching of the Cl originally present in the sample [872] • Of Na (negligible or negative uptake at pH < 8), 0.1 M NaCl [969] Negligible uptake of the following inert-electrolyte ions has been reported: Of Li, Na and Cs from 0.1 M chlorides at pH < 7 [3190] Of Cl from 0.01 M NaCl at pH > 8 [1841] Of Na and Cl, at various concentrations [3191] Of Na (AAS) and Cl (ion selective electrode) from 0.001 M NaCl [848] Of Na and Br (radiotracer method, 0.0001–0.1 M) [905] Of Na and Cl (radiotracer method, 0.01 M solution in water and in 10% aqueous propanol), two types of alumina [925] • Of Cs from 0.0001 and 0.001 M solution [926] • • • • • •

Substantial uptake of the following inert-electrolyte ions has been reported: • Of K and Cl (0.01 M, radiotracer method), two types of alumina [884,1209] • Of Na and Br (radiotracer method, 0.01 and 0.1 M) [984]

886

Surface Charging and Points of Zero Charge

• Of Na, Cs, I, and Cl (radiotracer method, 0.0001–1 M) [3192] • Of Na and Cl (radiotracer method, 0.001 and 0.01 M) [789] • Of Na and Cl (0.001, 0.1 M, radiotracer method) [518] Moderate uptake of Na and Cl by alumina-coated titania (ICP, no salt, only acid or base added to adjust pH) is reported in [2022].

4.2.2

GIBBSITE

Substantial uptake of Na and Cl was reported in [3193]. The Na:Cl ratio at a gibbsite surface was studied by XPS in [1759]. It was pH-independent over the range 4–11 and close to 1 in 0.1 M NaCl; in 0.01 M NaCl it was more sensitive to pH.

4.2.3

CdO

Substantial uptake of Na, Cl, and ClO4 was reported in [152].

4.2.4

CO3O4

Substantial uptake of Cs and Cl was reported in [1242].

4.2.5

MAGNETITE (CONTAINING 2.4% OF SILICA)

Substantial uptake of Cs, initial concentration 2–8 ¥ 10-5 M, was reported in [1275].

4.2.6

HEMATITE

Negative uptake of Cl from 0.001 M NaCl was reported in [1375]. Negligible uptake of Cl from 0.001 M NaCl was reported in [1411]. Substantial uptake of the following inert-electrolyte ions has been reported: • Of Na from 0.001 M and 0.01 M NaCl and of Cl from 0.01 M NaCl [1375] • Of Cs from 0.001–0.1 M CsCl, radiotracer method [1352]

4.2.7

GOETHITE

Negligible uptake of Na at the PZC and negative adsorption below the PZC (radiotracer, 0.005, 0.016 M perchlorate) was reported in [1528]. The Na:Cl ratio at a goethite surface was about 1, and it was rather insensitive to pH over the range 5–10 (XPS, 0.1 M NaCl) [1759].

4.2.8

HfO2

Negative adsorption of Cl from 0.001 M NaCl and substantial uptake of Na from 0.001–0.1 M NaCl was found by a radiotracer method [1675].

Ion Specificity

4.2.9

887

NIOBIA

Moderate uptake of Na and Cl (0.1 M solution) was found in [3194].

4.2.10 SILICA Silica often does not show any PZC at all. The results presented here refer to the pH range 2–4. Negligible or negative uptake of Na from 0.001–0.1 M NaCl was found in [969]. Negligible uptake of Na (AAS) and negative uptake of Cl from 0.1 M NaCl was found in [1186]. Negligible uptake of the following inert-electrolyte ions has been reported: • Of Li, Na and Cs from 0.1 M chlorides [3190] Substantial uptake of the following inert-electrolyte ions has been reported: • • • •

Of Na (radiotracer) from 0.1 M perchlorate at pH 3.5 [1793] Of K and Cl at pH 3.8 (XPS) [2994] Of Na at pH 2 (XPS, 0.02 M chloride) [1757–1759] Of Na and Cl (0.001–0.1 M NaCl, radiotracer method) [1835]

4.2.11 HYDROUS TIN OXIDE Moderate uptake of Na and Cl (0.1 M solution) was found in [3194]. Substantial uptake of Na and Cl was found in [3195].

4.2.12 ThO2 Negligible uptake of Li and Cl was found in [1972].

4.2.13 TITANIA Negative uptake of Na and negligible uptake of Cs (radiotracer, 0.001–0.01 M chlorides) is reported in [612]. Negligible uptake of the following inert-electrolyte ions has been reported: • Of Na and Cl (radiotracer, 0.01 M solution, washed titania) [2010] • Of Na and Cl (radiotracer, 0.01 and 0.001 M solution) [2115] • Of K, Na, Li, and Cl (negligible to moderate, five specimens of titania) [3196] • Of TMA and ClO4 (internal reflection spectroscopy in the infrared range) [3198]; no data points are available at the PZC, and negligible uptake was obtained by extrapolation

888

Surface Charging and Points of Zero Charge

Moderate uptake of the following inert-electrolyte ions has been reported: • Of Na and Cl (radiotracer, 0.01 M solution) [255] Substantial uptake of Cl and moderate uptake of Na was found in [3197]. Substantial uptake of the following inert-electrolyte ions has been reported: • • • •

Of Na and Cl (0.001, 0.01 M, radiotracer) [518] Of Na, Cs, Cl, and I (radiotracer, 0.01 and 0.1 M) [2061] Of Na and Cl (radiotracer, 0.01 and 0.1 M) [581,2054] Of Na and Cl (ICP, no salt, only acid or base added to adjust pH) [2022]

4.2.14 ZIRCONIA Moderate uptake of Na and Cl (13 different samples) at pH 6.5 was reported in [3199] (point of equal uptake, no independent estimation of PZC). Substantial uptake of the following inert-electrolyte ions has been reported: • Of Na (radiotracer, 0.001–0.1 M chloride) [1675] • Of Na and Cl (radiotracer, 0.001–0.1 M) [2187,2188,2192] • Of Na and Cl at pH 7 (point of equal uptake, no independent estimation of PZC) [3200]

4.2.15 ALUMINA–SILICA MIXED OXIDES Substantial uptake of Na and Cl is reported in [1186,3003] (at point of equal uptake, no independent estimation of PZC).

4.2.16 SILICA–TITANIA AND ALUMINA–SILICA–TITANIA MIXED OXIDES Substantial uptake of Cs from 0.0001 and 0.001 M solution is reported in [926].

4.2.17 TITANIA–ZIRCONIA MIXED OXIDES Negligible uptake of Na and Cl is reported in [3201] (at point of equal uptake, no independent estimation of PZC).

4.2.18

δ-MnO2

Negligible to moderate uptake of Na and K is reported in [2470].

Ion Specificity

889

4.2.19 POROUS GLASSES Substantial uptake of Na (radiotracer, 0.001, 0.01 M chloride) is reported in [2609,2611]. The results reviewed in this section are often scattered, the uptake curves are not monotonic, and the uptake of the anions and of the cations is not symmetrical with respect to the point of equal uptake. The points of equal uptake are often different from the PZC/IEP of the same type of material. The point of equal uptake is not recommended as a method to determine the PZC, although theoretically it should fall at the PZC.

4.3

HIGH IONIC STRENGTH

The approach to pH-dependent surface charging presented in Chapters 1–3 and in the preceding sections of this chapter applies to dilute and moderately concentrated electrolyte solutions (up to about 0.1 M), but it fails for more concentrated electrolyte solutions. The differences between dilute and concentrated electrolyte solutions with respect to pH dependent surface charging are briefly discussed in this section. A more detailed discussion can be found in [3202].

4.3.1

IONS IN SOLUTION

The ions in diluted solutions of 1-1 electrolytes are fully hydrated (owing to a high water-to-salt molar ratio), and they interact with other species (including surface species) chiefly via electrostatic forces. Therefore, the properties of solutions of different 1-1 electrolytes show a low degree of ion specificity. The activities of anions and cations are equal in a neutral solution. The ion specificity in surface charging discussed in Section 4.1 is due to partial dehydration, and it is more significant at higher salt concentrations and disappears at low salt concentrations. In concentrated solutions of 1-1 electrolytes, the ions are not fully hydrated, and the anions and cations compete for the limited number of water molecules. The properties of solutions of different 1-1 electrolytes become more and more ion-specific as the salt concentration increases. The activities of anions and cations are not equal in a neutral solution, although their concentrations are equal. Different activities of anions and cations imply different driving forces for ion adsorption. Nonsymmetrical adsorption of counterions may indirectly affect surface protonation/deprotonation. Solutions of different 1-1 salts of equal concentrations may show very different activities of individual ions [3203–3205]. Thus, comparison between two different salts is not as simple as with dilute solutions (solutions of equal concentrations have different activities, and vice versa; see Section 1.10.1). pH measurements at high ionic strengths require standardization with special pH buffers (because of the liquid junction potential in typical reference electrodes, which is nearly constant at low ionic strengths but variable at high ionic strengths). Other difficulties in pH measurements at high ionic strengths and in their interpretation are discussed in Sections 1.10.4 and 1.10.6. The limitations encountered

890

Surface Charging and Points of Zero Charge

in pH measurements at high ionic strengths are independent of the presence of solid particles.

4.3.2

EXPERIMENTAL METHODS

The problems with the pH measurements discussed in Section 4.3.1 make the determination of PZC by titration much more difficult than at low ionic strengths. Special procedures related to pH measurements at high ionic strengths are seldom addressed in publications reporting PZCs obtained by titration. Very likely, most titration results available in the literature were obtained by means of standard procedures recommended only for low ionic strengths. Other standard experimental methods used in studies of pH-dependent surface charging must also be combined with a reliable pH measurement, but potentiometric titration is more sensitive to problems with pH measurements than are other methods. Instant coagulation and sedimentation at sufficiently high ionic strength makes coagulation useless as a method to determine the IEP. Namely, the stability ratio is equal to 1 over a broad pH range around the IEP. Most studies of colloid stability have been carried out for electrolyte concentrations less than 0.1 M. The turbidity of titania at pH 6.2 was found to increase sharply when the NaCl concentration exceeded 1 M [503]. This result may suggest restabilization of the dispersion at very high ionic strength, but experimental results obtained by others, together with DLVO calculations, do not confirm this result. Instant coagulation also excludes methods that require a stable dispersion, such as electrophoresis. The manufacturers of certain types of zetameters claim that their instruments are suitable to perform measurements in electrolyte solutions up to about 1 M. However, in order to use a zetameter, one has to prepare a stable dispersion first, and this may be problematic. Electro-osmosis does not require stability against sedimentation, but other problems, such as low absolute values of the z potential (which may be smaller than the scatter of results) and the production of heat, convective currents, or electrolysis products (acids, bases, and gases), severely limit the application of classical electrokinetic methods (including electrophoresis) in measurements at ionic strengths greater than 0.1 M. Very few publications report z potentials obtained by classical electrokinetic methods at higher electrolyte concentrations, and the results are controversial. The z potential of titania at pH 8.2 in the presence of NaCl, CH3COONa, and C2H5COONa (up to 0.5 M) was studied by electrophoresis [49]. The z potential was found to tend asymptotically to zero as the electrolyte concentration increased. z potentials of magnetite at pH 8.3 at NaCl concentrations up to 5 M obtained by electrophoresis are reported in [1298]. The z potential tended asymptotically to 0 as the NaCl concentration increased. The IEP of that magnetite at low ionic strength was unusually low (pH 3.6). On the other hand, [1412] reports a shift in the IEPs (electrophoresis, in 0.1 M KNO3) of hematite and rutile to high pH by 0.6 and 0.5 pH units, respectively, with respect to the pristine value. A substantial shift in the IEP of hematite to high pH in 1 M LiNO3 and NaNO3 is reported [337]. The same study reports an incredibly high z potential of +180 mV in 3 M NaNO3.

Ion Specificity

891

Thus, a few results indicate that the electrokinetic behavior of metal oxides at high concentrations of 1-1 electrolytes is similar to that at low ionic strengths; that is, the increase in electrolyte concentration depresses the absolute value of the z potential, and the IEP remains unaffected. In a few other studies, a shift in the IEP to high pH was observed at concentrations of 1-1 electrolytes of about 0.1 M. Such a shift suggests specific adsorption of cations. The classical electrokinetic studies of silica in the presence of about 0.1 M sodium and potassium salts produced controversial results. IEPs of silica obtained by means of electrophoresis [610,1117] shifted from pH < 2 (if any) in 0.001 M KNO3 to 3 in 0.01 M KNO3 and to 4 in 0.1 M KNO3. However, Na (up to 0.1 M) did not induce a shift in the IEP of quartz [1117]. Absence of a shift in the IEP in the presence of 0.1 and 0.5 M KNO3 is reported in [1769]. In contrast, a substantial shift in the IEP to high pH in the presence of 0.08 M KCl is reported in [266]. A shift in the IEP of quartz to high pH was observed in 0.1 M NaCl by electrophoresis, but no shift was observed by means of streaming potential [241]. NaCl induced a shift in the IEP from 2.3 (low ionic strength) to 3.3 (0.14 M NaCl) [1868], and from 2.3 (0.001 M NaCl) to 3.1 (0.1 M NaCl) [511]. In contrast to the above contradictory results for Na and K, there is strong evidence that Rb and Cs salts at concentrations of about 0.1 M induce a substantial shift in the IEP of silica to high pH [1816] (also porous glasses) [1910,1937]. A substantial shift in the IEP of silica to high pH in the presence of Cs and the absence of such a shift in the presence of Na [1937] is in line with the affinity series observed by other methods (Section 4.1.5).

4.3.3

ELECTROACOUSTIC METHOD

The electroacoustic method (see Section 2.1.5) is more suitable for measurements of the electrokinetic potential at high ionic strengths than are classical electrokinetic methods. This method is relatively new, and commercial instruments have only been available since the 1990s. Many results obtained by the electroacoustic method suggest a shift in the IEP at high concentrations of 1-1 electrolytes. The direction of the shift depends on the nature of the solid phase, and is salt-specific. Moreover, z potentials obtained by means of the electroacoustic method at high ionic strengths are higher in absolute value than might be expected from extrapolation of the results obtained at low ionic strengths. For example, a z potential (Acoustosizer, ESA) of alumina in 1 M CsNO3 in excess of 20 mV is reported in [304]. Titration of alumina (initial pH 4, DT-1200, CVI) with KCl was studied in [3206]. The z potential dropped to 10 mV in 1 M KCl, but a further increase in KCl concentration to 2 M had an insignificant effect on the z potential. A shift in the IEPs of the following metal oxides to high pH was induced by concentrated solutions of Li and Na salts: alumina [492] (electroacoustic method and electrophoresis), [494,1018] (only Li induced a shift in the IEP; Na did not), ceria [1224], hematite [430], india and niobia [1674], rutile [430], anatase [495] (multi-instrument, multilaboratory study), [1985], [1986] (the shift in the IEP was accompanied by a shift in the maximum of viscosity), [1987,1988], and zirconia

892

Surface Charging and Points of Zero Charge

[1987,2153]. Metal oxides showed the following common pattern: at ionic strengths up to about 0.1 M, the shift in the IEP was insignificant. At higher electrolyte concentrations, the shift in the IEP to high pH was more significant. Finally, at sufficiently high electrolyte concentration (about 1 M), there was no IEP at all, and the z potential was positive even at very high pH. The shifts in the IEP induced by K, Rb, and Cs salts were much less significant than those induced by the same concentration of Li and Na salts. This result is in line with the cation specificity series for metal oxides reported in Section 4.1. In contrast with metal oxides, a shift in the IEP to low pH at high ionic strengths was observed for melamine–formaldehyde latex [2697]. Electroacoustic studies of silica at high ionic strengths produced controversial results similar to those discussed in Section 4.3.2. Amorphous materials [1813,1870] showed a shift in the IEP to high pH at 1-1 electrolyte concentrations of 0.1 M or higher. The shift was more substantial in the presence of Cs than in the presence of other monovalent cations. This result is in line with the cation specificity series reported in Section 4.1.5. However, the IEP of quartz [1813] was not shifted in the presence of 1-1 electrolytes. Montmorillonite and kaolinite [2271] showed shifts in the IEP and similar cation affinity series as amorphous silica. Contradictory results are reported for goethite [76,1318]. The shifts in the IEP observed at high electrolyte concentrations are due to high activity and low degree of hydration of the ions of the 1-1 electrolyte. These ions may contribute to the surface charge at high concentrations, while at low concentrations their role is limited to neutralization of the surface charge in the diffuse layer. The affinity of the surface to anions and cations is governed by the hard–soft acid–base character of the ions and the surface [1987]. The results presented in this section indicate that “inert electrolytes” are actually inert only at low concentrations. The specific adsorption of counterions at high electrolyte concentrations is one of the factors responsible for the discrepancies in the “pristine” IEPs reported in the literature, especially for silica.

Appendix Complex terminology was used in Chapters 1 through 4 to describe various materials. For example, various names were used for the same material, according to the names used in the original publications. These names are systematized in Tables A1 and A2, which report thermochemical and crystallographic data, respectively. Various spellings were used for names of some minerals of foreign origin in the original publications. Only the most common spelling is used in Tables A1 and A2, and it may be different from the spelling used in Chapters 1 through 4. Tables A1 and A2 report data for pure phases that are directly addressed in the preceding chapters or that may be components of materials addressed there. The relevant sections in Chapter 3 are indicated in Tables A1 and A2. Thermochemical and/or crystallographic data were found for a limited number of relevant materials; for other materials, such data were not available. The thermochemical and crystallographic data reported in various publications were not always consistent. The thermochemical data summarized in Table A1 were taken directly from [3207–3213] or calculated from the results reported there. The sources of the data are indicated in the table. The preference for certain sources in cases where different data were reported in different sources was the same as in [2]. Not all decimal digits before the decimal point in the numbers reported in Table A1 are significant. The crystallographic data in Table A2 are based on [3214]. Densities d from a few other sources were also used, and these sources are explicitly indicated in Table A2. Densities of the same phase reported in different sources show a substantial scatter. A few densities reported for specific specimens are reported in Chapter 3 as “properties.” The density at 25°C is expressed in Table A2 in kg/m3. Other temperatures (also in °C) are specified in parentheses after the density. Space groups 1 and 2 belong to the triclinic system, 3–15 to the monoclinic system, 16–74 to the orthorhombic system, 75–142 to the tetragonal system, 143–167 to the trigonal system, 168–194 to the hexagonal system, and 194–230 to the cubic system. The names of the crystallographic systems are not explicitly reported in Table A2, with exception of materials for which the space group number was not available. The following abbreviations are used: P, primitive; F, face-centered; R, rhombohedral. The meaning of blank entries in Table A2 is as follows: for axial angles, blank entries denote 90°; for cell axes, blank entries for b and c denote b = a and c = a; the other blank entries denote that the data were not available.

893

g

d

k Boehmite

Diaspore

Hydrargilite

Bayerite

Amorphous

a

b

a

Al2O3

Al2O3

Al2O3

Al2O3

AlOOH

AlOOH

Al(OH)3

Al(OH)3

Al(OH)3

BeO

Be(OH)2

Be(OH)2

97.064

Co(OH)2

62.543 42.25

Cu2O

CuO

Cr(OH)3

114.26

97.06

Co(OH)2

Crystalline

123.42

Co3O4

Cr2O3

55.22

CoO

CeO2

-118.8 61.52

44.16

CdO

Cd(OH)2

113.52

65.674

65.64

24.98

93.149

93.08

52.76

60.42

80.73

81.362

Bi2O3

Precipitated

78.83

Corundum

Water 82.706

Cp (J mol-1K-1) 75.79

TABLE A.1 Thermochemical Data

-156,059

-170,707

-1,140,558

-539,698

-541,338

-918,680

-237,944

-1,090,350

-560,702

-258,362

-573,208

-902,907

-905,798

-608,399

-1,276,120

-1,288,250

-1,293,274

-1,002,068

-985,265

-1,666,487

-1,666,487

-1,656,864

-1,675,692

-285,829

Ho = DHof (J mol-1)

-128,287

-147,886

-848,056

-1,058,917

-454,168

-460,067

-802,056

-214,190

-1,027,054

-473,753

-228,678

-492,790

-815,933

-817,811

-579,092

-1,138,706

-1,149,000

-1,155,552

-923,491

-910,162

-1,573,847

-1,572,947

-1,563,850

-1,582,276

-237,142

DGof (J mol-1)

-168,756

-198,245

-1,164,759

-563,251

-569,156

-951,276

-253,736

-1,108,925

-589,324

-274,703

-618,366

-918,874

-920,767

-612,505

-1,297,327

-1,307,645

-1,314,169

-1,012,565

-999,236

-1,682,454

-1,681,581

-1,672,457

-1,690,882

-306,685

Go (J mol-1)

[3207]

[3211]

[3210]

[3207]

[3208]

[3207]

[3207]

[3207]

[3207]

[3208]

[3207]

[3207]

[3208]

[3207]

[3207]

[3208]

[3209]

[3207]

[3207]

[3207]

[3208]

[3208]

[3208]

[3207]

Ref. [3207]

3.1.9.2

3.1.9.1

3.1.8.4

3.1.8.1

3.1.7.1

3.1.7.1

3.1.7.2

3.1.7

3.1.6.1

3.1.5.3, 3.1.5.4

3.1.5.2

3.1.3

3.1.2.3

3.1.2.3

3.1.2.1

3.1.1.4.3

3.1.1.4.2

3.1.1.4.1

3.1.2.2.1-3.1.1.2.3 3.1.1.2.4

3.1.1.1

3.1.1.1

3.1.1.1

3.1.1.1

Section

894 Surface Charging and Points of Zero Charge

151.78

Magnetite

Hematite

Goethite

Er2O3

Fe3O4

Fe2O3

FeOOH 93.86

Ga2O3

37.26

Periclase

Microcrystalline

MgO

MgO

Manganite

Birnessite

Nsutite

Pyrolusite

MnOOH

MnO2

MnO2

MnO2 57.452 132.13 111.33 44.29

NbO2

Nb2O5

Nd2O3

NiO

54.41

Bixbyite

Mn2O3

77.51

MnO2

Hausmanite

Mn3O4

Mg(OH)2

108.77

La2O3 38.48

55.64

IrO2

43.89 100.39

HgO

In2O3

60.27

HfO2

Ga(OH)3

92.58

74.32

Fe(OH)3

Red

108.5

Dy2O3

104.77

87.85 116.26

Cu(OH)2 -443,086

-239,743

-1,807,906

-1,899,536

-794,960

-522,054

-924,998

-597,981

-601,701

-1,794,936

-249,366

-925,919

-90,830

-1,117,546

-964,400

-1,089,095

-832,616

-558,145

-823,411

-1,115,479

-1,897,900

-1,862,716

-359,018

-211,582

-1,721,051

-1,765,821

-739,175

-467,190

-466,347

-457,129

-453,777

-558,527

-879,271

-1,282,978

-833,987

-565,979

-569,409

-1,707,220

-192,836

-830,756

-58,565

-999,946

-831,300

-998,328

-705,482

-487,369

-741,471

-1,012,351

-1,808,700

-1,770,971

-469,033

-251,070

-1,855,185

-1,940,471

-811,211

-537,897

-943,854

-606,303

-609,733

-1,832,896

-264,585

-956,980

-111,775

-1,135,260

-994,215

-1,114,418

-863,802

-576,146

-849,483

-1,159,078

-1,944,292

-1,907,375

[3207]

[3207]

[3207]

[3211]

[3207]

[3210]

[3210]

[3210]

[3210]

[3210]

[3210]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3212]

[3207]

[3207]

[3207]

[3207]

[3207]

[3212]

[3207]

[3208]

3.1.25.1

3.1.24.1

3.1.23.2

3.1.23.1

3.1.22.14

3.1.22.14

3.1.22.14

3.4.10.1

3.1.22.6

3.1.22.5

3.1.22.3

3.1.21.2

3.1.21.1

3.1.21.1

3.1.20

3.1.18

3.1.17.1

3.1.16

3.1.15

3.1.14

3.1.14

3.1.12.8

3.1.12.5.1

3.1.12.3.2

3.1.12.2

3.1.11

3.1.10

3.1.9.4

continued

Appendix 895

Tridimite a

Cristobalite a

SiO2

SiO2

61.81 55.1

Rutile

Anatase

ThO2

TiO2

TiO2 63.58 292.14 127.34 68.283

UO2

U4O9

V2O5

WO2.72

54.02

52.6 131.48

-781,153

-1,550,172

-4,510,398

-1,084,994

-941,400

-944,747

-1,226,414

-2,045,976

-580,822

-1,827,403

115.82

Sm2O3

Ta2O5

-1,481,100

H4SiO4

SnO2

-1,188,700

-908,346

-910,053

-910,856

-1,908,322

-1,417,539

-305,013

-1,055,832

-1,809,664

-282,784

-730,672

H2SiO3

44.95

44.71

93.94 44.43

Sb4O6

Quartz a

202.77

RuO2

SiO2

52.69

PuO2

Sc2O3

66.25

Pr2O3

Valentinite

60.99 117.98

PbO2

154.94

Pb3O4

-217,300

-220,007

45.8

Massicot

PbO

45.74

Red

PbO

Ho = DHof (J mol-1) -529,700

Cp (J mol-1K-1)

Ni(OH)2

TABLE A.1 (continued)

-708,632

-1,418,928

-4,274,804

-1,031,802

-885,947

-889,506

-1,168,781

-1,911,035

-520,001

-1,737,380

-1,332,900

-1,092,400

-854,508

-856,200

-856,442

-1,818,873

-1,253,109

-252,807

-999,041

-1,720,237

-224,509

-615,467

-187,900

-189,633

-447,200

DGof (J mol-1)

-801,554

-1,589,092

-4,610,018

-1,107,960

-956,282

-959,841

-1,245,862

-2,088,693

-596,428

-1,870,566

-1,538,345

-1,228,653

-921,285

-922,977

-923,219

-1,931,275

-1,490,889

-322,478

-1,075,548

-1,856,069

-304,988

-795,740

-237,783

-239,530

-555,938

Go (J mol-1)

[3211]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3212]

[3212]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3208]

[3207]

[3207]

[3212]

[3207]

Ref. [3212]

3.1.34.1

3.1.42

3.1.41

3.1.41.1

3.1.39.1

3.1.39.1

3.1.38.1

3.1.37.1

3.1.36.3

3.1.34

3.1.35

3.1.35

3.1.35

3.1.35

3.1.35

3.1.33

3.1.32

3.1.31.1

3.1.30

3.1.28

3.1.26.3

3.1.26

3.1.26.1

3.1.26.1

Section 3.1.25.2

896 Surface Charging and Points of Zero Charge

115.3 41.06

Yb2O3

ZnO

Clinochlorite

Cordierite

Fe-cordierite Hydrous cordierite

Halloysite

Kaolinite

Muscovite

Fe-sapphirine Sapphirine (442)

Sapphirine (793)

Mg5Al2Si3O10(OH)8

Al4Mg2Si5O18

Fe2Al4Si5O18

Mg2Al4Si5O18 · H2O

Al2Si2O7 · 2H2O

Al2O3 · 2SiO2 · 2H2O

KAl3Si3O10(OH)2

Fe3.5Al9Si1.5O20

Mg3.5Al9Si1.5O20 132.23 123.48 115.96 131.57 119.36 133.8 126.79 148.8 143.36

FeO · Al2O3

MgO · Al2O3

NiO · Al2O3

ZnO · Al2O3

FeO · Cr2O3

MgO · Cr2O3

NiO · Cr2O3

ZnO · Cr2O3

544.7

546.6

575.2

326

245.26

246.26

506.9

464.4

452.31

517.4

CoO · Al2O3

Mg4Al8Si2O20

Beryl

Be3Al2Si6O18

ZrO2

56.21

102.51

Zn(OH)2

104.09

Y2O3

72.8

WO3

H2WO4

72.383

WO2.96

a

71.379

WO2.9

-1,553,937

-1,392,435

-1,777,781

-1,458,605

-2,071,289

-1,921,497

-2,299,108

-1,969,471

-1,947,108

-11,067,020

-11,014,080

-9,834,000

-5,976,300

-4,095,843

-4,101,199

-9,430,320

-8,436,510

-9,161,701

-8,928,250

-9,006,520

-1,100,559

-641,900

-350,619

-1,814,517

-1,905,309

-1,131,893

-842,908

-834,959

-820,064

-1,439,781

-1,285,776

-1,663,176

-1,357,833

-1,945,636

-1,802,719

-2176624

-1853836

-1828645

-10,469,450

-10,415,770

-9,273,620

-5,600,298

-3,775,099

-3,780,565

-8,811,292

-7,949,440

-8,651,336

-8,265,042

-8,500,360

-1,042,788

-553,500

-320,636

-1,726,764

-1,816,620

-1,004,029

-764,054

-757,027

-743,513

-1,588,617

-1,431,106

-1,809,342

-1,502,390

-2,097,236

-1,950,813

-2,325,554

-2,001,157

-1,976,797

-11,199,697

-11,145,266

-9,998,281

-6,067,653

-4,156,345

-4,161,813

-9,512,580

-8,578,132

-9,283,079

-9,053,771

-9,109,889

-1,115,578

-666,110

-363,630

-1,854,186

-1,934,862

-1,175,055

-865,537

-857,289

-841,940

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3213]

[3213]

[3213]

[3211]

[3207]

[3208]

[3211]

[3213]

[3208]

[3211]

[3209]

[3207]

[3212]

[3207]

[3207]

[3207]

[3207]

[3207]

[3211]

[3211]

3.3.17

3.3.10.3

3.3.5.2

continued

3.3.5.1, 3.3.6.2

3.3.1.12

3.3.10.1

3.3.1.6

3.3.1.4

3.3.1.2

3.2.50

3.2.50

3.2.50

3.2.38

3.2.30

3.2.27

3.2.23

3.2.23

3.2.23

3.2.18

3.2.13

3.1.47.1

3.1.46.4

3.1.46.1

3.1.45

3.1.44.1

3.1.34.2

3.1.34.1

3.1.34.1

3.1.34.1

Appendix 897

Sillimanite

Kyanite

Metakaolinite

Hydroxy-topaz Pyrophyllite

Imogolite

Fayalite

g-Fayalite

b-Fayalite

Al2O3 · SiO2

Al2O3 · SiO2

Al2O3 · 2SiO2

Al2SiO4(OH)2

Al2Si4O10(OH)2

HOSiO3Al2(OH)3

2FeO · SiO2

Fe2SiO4

Fe2SiO4

Fe-anthophyllite

Fe-talc Grunerite

Fe7Si8O22(OH)2

Fe3Si4O10(OH)2

2MgO · SiO2

Fe7Si8O22(OH)2

Deerite

Fe18Si12O40(OH)10

FeSiO3

Andalusite

Al2O3 · SiO2

118.42

694.3

340

692.8

1552

89.454

136.1

130.2

132.9

292

159.1

224.09

120.01

121.93

122.44

137.33 322.2

Mullite

3Al2O3 · 2SiO2

159.17

NiO · Fe2O3

ZnO · Fe2O3

149.22

MnO · Fe2O3

137.78

MgO · Fe2O3

Magnesioferrite

79.996 148.8

CuO · Fe2O3

Cp (J mol-1K-1) 152.58

CuFeO2

CoO · Fe2O3

TABLE A.1 (continued)

-2,176,935

-9,631,500

-4,799,030

-9,627,760

-18,348,400

-1,194,950

-1,468,000

-1,471,500

-1,477,073

-3,192,100

-5,640,960

-2,905,000

-3,341,154

-2,594,080

-2,587,804

-2,590,314

-6,819,208

-1,179,051

-1,084,492

-1,228,840

-1,440,132

-966,504

-512,958

-1,088,676

Ho = DHof (J mol-1)

-2,057,890

-8,969,794

-4,451,060

-8,968,900

-16,902,080

-1,117,463

-1,366,071

-1,369,332

-1,376,153

-2,929,200

-5,267,080

-2,689,970

-3,139,676

-2,443,880

-2,441,070

-2,442,890

-6,441,794

-1,073,752

-974,541

-1,126,610

-1,328,721

-861,778

-460,268

-983,657

DGof (J mol-1)

-2,205,315

-9,844,558

-4,903,979

-9,843,919

-18,840,348

-1,222,954

-1,510,278

-1,513,539

-1,520,360

-3,243,710

-5,712,337

-2,934,965

-3,381,836

-2,619,263

-2,616,453

-2,618,273

-6,901,166

-1,224,758

-1,122,041

-1,274,747

-1,477,057

-1,010,259

-539,454

-1,131,215

Go (J mol-1)

[3207]

[3211]

[3213]

[3213]

[3213]

[3208]

[3211]

[3211]

[3207]

[3209]

[3211]

[3213]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3207]

[3208]

Ref. [3207]

3.3.13.5

3.3.13.3, 3.3.6.6

3.3.13.3, 3.3.6.6

3.3.13.3, 3.3.6.6

3.3.13.3, 3.3.6.6

3.3.13.3, 3.3.6.6

3.3.13.3.1

3.3.13.3.1

3.3.13.3.1

3.3.1.7.3

3.2.45

3.3.13.1.8

3.3.13.1, 3.3.1.7

3.3.13.1.2

3.3.13.1.4.1

3.2.5

3.3.13.1.3

3.3.6.11

3.3.6.5

3.3.6.4

3.3.8.1

3.3.6.3

3.3.6.3

Section 3.3.6.1

898 Surface Charging and Points of Zero Charge

g-Forsterite Low clinoenstatite

Ilmenite–Mg

Perovskite–Mg

Anthophyllite

Talc

Chrisotile

PhaseA

Al-free chlorite Clinohumite

Antigorite

Cummingtonite

Willemite

MgSiO3

MgSiO3

Mg7Si8O22(OH)2

Mg3Si4O10(OH)2

Mg3Si2O5(OH)2

Mg7Si2O8(OH)6

Mg6Si4O10(OH)8

Mg48Si34O85(OH)62

Mg7Si8O22(OH)2

2ZnO·SiO2

104.4 114.37 124.08 215.03

FeO · WO3

MnO · WO3

Y2Zr2O7

99.5

FeO · TiO2 142.3

136.4

Al2O3 · TiO2

PbO · TiO2

98.57

ZrO · 2SiO2

Fe2TiO4

84.762

121.83

428.9

4435

549.2

521.3

462.4

273.68

321.7

628.99

79.8

75.1

79.9

82.2

81.9

81.8

106.6

110.7

ZnSiO3

Ilmenite

Garnet–Mg

Mg9Si4O16(OH)2

Orthoenstatite

MgSiO3

MgSiO3

MgO·SiO2

MgSiO3

b-Forsterite

Mg2SiO4

Mg2SiO4

-4,121,993

-1,305,826

-1,184,176

-1,194,741

-1,515,236

-1,239,229

-2,607,046

-2,035,700

-1,262,572

-1,644,730

-12,217,100

-71,377,000

-9,637,840

-8,744,200

-7,129,870

-4,365,598

-5,922,498

-12,086,405

-1,450,000

-1,489,500

-1,513,000

-1,546,290

-1,548,498

-1,548,715

-2,133,200

-2,142,000

-3,917,872

-1,206,133

-1,083,211

-1,107,878

-1,417,863

-1,161,740

-2,460,788

-1,921,186

-1,179,479

-1,531,135

-11,475,109

-66,110,242

-9,062,780

-8,078,470

-6,609,650

-4,037,962

-5,542,603

-11,367,041

-1,360,639

-1,400,199

-1,423,490

-1,458,956

-1,461,631

-1,460,457

-2,012,310

-2,022,303

-4,181,622

-1,347,741

-1,223,409

-1,228,110

-1,565,633

-1,270,790

-2,639,729

-2,060,753

-1,289,268

-1,683,900

-12,361,136

-72,472,045

-9,762,467

-8,865,846

-7,234,223

-4,431,577

-6,000,225

-12,253,066

-1,467,740

-1,507,300

-1,530,591

-1,566,057

-1,568,732

-1,567,558

-2,159,735

-2,169,728

[3208]

[3207]

[3207]

[3207]

[3208]

[3207]

[3207]

[3207]

[3208]

[3207]

[3211]

[3211]

[3213]

[3213]

[3213]

[3208]

[3208]

[3208]

[3211]

[3211]

[3211]

[3211]

[3207]

[3211]

[3211]

[3211]

3.3.18.3

3.3.16.2

3.3.16.1

3.3.15.4

3.3.15.3.1, 3.3.15.3.3 3.3.6.9, 3.3.15.3

3.3.1.8, 3.3.15.1

3.3.13.8

3.3.13.7

3.3.13.7

3.3.13.5

3.2.51.2

3.3.13.5

3.3.13.5

3.3.13.5

3.3.13.5.1

3.3.13.5.2

3.3.13.5

3.3.13.5

3.3.13.5

3.2.26.2

3.3.13.5

3.3.13.5

3.3.13.5

3.3.13.5.3

3.3.13.5.3

Appendix 899

14

Bismite

Sillenite, g

b

Monteponite

b

g

Bi2O3

Bi2O3

Bi2O3

CdO

Cd(OH)2

Cd(OH)2

P21/c I23 P(-4)b2 Fm3 m

T3

D2d7

Oh5

225

164 P(-3)m1 Im Fm3 m Fm3 m

D3d3

Cs3

Oh5

Oh5

8

225

225

CeO2(-x)

CoO

117

197

C2 h5

P212121

Tetragonal

a (metastable)

Be(OH)2

19

D24

Behoite, b

P63mc

C6v4

Be(OH)2

186

I(-1)

Bromellite

P21/a

BeO

2

14

Ci1

Nordstrandite

C2 h5

Bayerite, b

Al(OH)3

P21/n

Al(OH)3

14

C2 h5

Gibbsite, Hydrargillite, g

Cmcm

Al(OH)3

63

D2 h17

Boehmite, g

Pbnm

AlOOH

62

D2 h16

Diaspore, a

AlOOH

178

P6122

Akdalaite

4Al2O3 · H2O

186

D62

Tohdite

5Al2O3 · H2O

186

Hexagonal P63mc

k¢

Al2O3

C6v4

k

Al2O3 P63mc

d

C6v4

Fd3 m

Oh7

Tetragonal

227

g

Al2O3

Al2O3

Al2O3 R(-3)c

Hermann– Schoenflies Mauguin

D3d6

Number

167

Name

Corundum, a

Formula

TABLE A.2 Crystallographic Data Z

4

4

4

1

4

8

12

4

16

4

2

8

4

8

4

4

18

1

16/3

28

16

32/3

6

d

6470

7132 (23)

4814 (20)

4790 (15)

8150

9195

8400..9200

9200

1924

3015 (0)

2430

2529 (20)

2420 (20)

2977; 3020

3400

3680

3720

3680

3250

3420

3619

3990

a

0.42581

0.5409

0.567

0.3500

0.46951

1.095

1.0268

0.58486

1.088

0.4620

0.26979

0.8752

0.5062

0.8676

0.2868

0.4401

1.287

0.5575

0.5544

0.971

0.796

0.7911

0.47589

c

0.783

0.4535

0.43772

1.0244

0.4713

0.9721

0.3700

0.2845

1.497

0.8761

0.9024

1.786

1.170

1.2991

1.025

0.341

0.4710

0.563

0.81661 0.75097

0.7039

0.5069

0.8671

0.5070

1.2227

0.9421

b

109.326

a

91.4

113.00

97.662

90.27

94.57

b

88.340

g

Section

3.1.7.1

3.1.6.1

3.1.5.3, 3.1.5.4

3.1.5.3, 3.1.5.4

3.1.5.2

3.1.3

3.1.3

3.1.3

3.1.2.3

3.1.2.3

3.1.2.1

3.1.1.4.4

3.1.1.4.2

3.1.14.1

3.1.12.1– 3.1.1.2.3

3.1.12.5

3.1.1.3

3.1.1.3

3.1.1.1

3.1.1.1

3.1.1.1

3.1.1.1

3.1.1.1

900 Surface Charging and Points of Zero Charge

C2/c I41/amd Cmcm Ia3 C2/m P21/m P(-4)21/m P63/m Ia3 P21/m P(-4)21/m P63/m Fd3 m R(-3)c Ia3 P213

D4 h19

D2 h17

Th7

C2 h3

C2 h2

D2d3

C6 h2

Th7

C2 h2

D2d3

C6 h2

Oh7

D3d6

Th7

T4

Paratenorit(Ger)

CuO

C2 h6

Tenorite

CuO

Pn3 m

Oh4

Cuprite

R(-3)m

Cu2O

Pnnm

D3d5

Grimaldiite

CrOOH

D2 h12

Guyanaite

CrOOH

Pbnm

D2 h16

Bracewellite

CrOOH

R(-3)c

D3d6

20

Monoclinic

b

Maghemite, g

d

e

Goethite, a

Fe2O3

Fe2O3

Fe2O3

Fe2O3

FeOOH

62

198

206

Pbnm

Hexagonal

Hematite, a

Fe2O3

D2 h16

2

227

Magnetite

Fe3O4

167

176

4

32/3

16

6

8

2

4

2

Er(OH)3

16

2

113

176

Dy(OH)3

4

ErOOH

113

DyOOH

2

206

11

DyOOH

6

11

12

Dy2O3

16

4

16

4

2

3

2

4

6

3

8

1

ErOOH

206

Dy2O3

2 1

Er2O3

63

Cu(OH)2

141

15

224

166

58

62

167

Eskolaite

R(-3)m

Cr2O3

Fd3 m

Oh7

D3d5

227

166

Co3O4

CoOOH

Heterogenite

P(-3)1 m

D3d1

162

a

P(-3)m1

3Co(OH)2 · 2H2O

C2/m

D3d3

164

b

Co(OH)2

C2 h3

12

CoO

3800..4400

4780

4590

5200..5300

5128

5800

7590

8640

5780

7170

8120

3850

6040

6450

6000

4110

5215

4720

6070

2890

3597 (15)

0.462

1.297

0.509

0.8339

0.940

0.50340

0.83940

0.6232

0.5517

0.594

1.0550

0.6280

0.5573

0.598

1.397

1.0667

1.059

0.584

0.46837

0.4268

0.2984

0.4861

0.449

0.495762

0.2855

0.80835

0.540

0.3173

0.5183

1.3157

0.807

0.4640

0.3017

1.340

0.2960

0.297

0.995

1.021

0.362

0.364

0.3519

0.2949

0.301

0.844

0.441

1.3752

0.3518

0.5383

0.430

0.3569

0.5446

0.429

0.8661

0.5256

0.990

0.34226 0.51288

0.4292

0.986

1.35874 0.27407

0.3015

95.33

109.3

109

100.00

95.54

125.55

continued

3.1.12.5.1

3.1.12.3.4

3.1.12.3.4

3.1.12.3.1

3.1.12.3.4

3.1.12.3.2

3.1.12.2

3.1.11

3.1.11

3.1.11

3.1.11

3.1.10

3.1.10

3.1.10

3.1.10

3.1.10

3.1.9.4

3.1.9.2

3.1.9.2

3.1.9.1

3.1.8.3

3.1.8.3

3.1.8.3

3.1.8.1

3.1.7.4

3.1.7.2

3.1.7.1

3.1.7.1

3.1.7.1

Appendix 901

a

Sohngeite

GaOOH

Ga(OH)3

P21/m P63/m Fm3 m P(-3)m1

C2 h2

C6 h2

Oh5

D3d3

176

225

Periclase

Brucite

La(OH)3

MgO

Mg(OH)2

141

Hausmannite

Groutite, a

Mn3O4

MnOOH

62

Orthorhombic

Mg(OH)2

164

11

LaOOH

Pbnm

P63/mmc

D6 h4

194

La2O3

I41/amd

Ia3

Th7

206

La2O3

D2 h16

P42/mnm

D4 h14

136

IrO2

D4 h19

Im3

Th5

204

In(OH)3

Djalindite (Dzhalindite)

31

InOOH P21nm

152,154

206

HgO

In2O3

C2v7

P21/c

Ia3

Pmn21

C2v7

C2 h5 P31,221

Pbnm

D2 h16

D34,6

R(-3)c

D3d6

Th7

C2/m

C2 h3

Pnma

P21/n

C2 h5

D2 h16

P312

D31

62

Amam

D2 h17

HgO

I4/m

C4 h5

Hermann– Schoenflies Mauguin

14

31

62

Number

HfO2

Montroydite

a

Ga2O3

167

12

b

Ga2O3

149

63

14

d

FeOOH

87

Fe(OH)3

Akaganeite, b

Lepidocrocite, g

FeOOH

Name

FeOOH

Formula

TABLE A.2 (continued)

4

4

1

4

2

2

1

16

2

8

2

16

3

4

4

8

4

6

4

8

1

4

8

Z

d

4140

4720; 4800

2360 (15)

3576

4453

5360

6510

11700 [3212]

4410

7000

7040

11000

11080 (28)

10050

3840

6480

5950

3120

3950

3950

3100

a

0.4560

0.5763

0.3792

0.3142

0.42117

0.6531

0.6572

0.39373

1.136

0.44983

0.7939

0.526

1.0117

0.3577

0.66129

0.51156

0.74865

0.451

0.49825

1.223

0.899

0.295

0.387

1.048

c

0.2965

1.3433

0.580

0.992

0.453

0.307

0.3023

1.0700

1.016

0.3929

0.456

0.2870

0.9456

0.2842

0.4766

0.3853

0.4417

0.61299

0.31544

0.327

0.8681

0.55208 0.35219

0.51722 0.52948

0.74379 0.74963

0.975

0.304

0.512

1.252

b

a

112.5

99.18

103.7

93.43

b

g

Section

3.1.22.6

3.1.22.3

3.1.21.2

3.1.21.2

3.1.21.1

3.1.20

3.1.20

3.1.20

3.1.20

3.1.18

3.1.17.2

3.1.17.1

3.1.17.1

3.1.16

3.1.16

3.1.15

3.1.14

3.1.14

3.1.14

3.1.14

3.1.12.8

3.1.12.5.4

3.1.12.5.2

3.1.12.5.3

902 Surface Charging and Points of Zero Charge

194

Nsutite, g

e

Ramsdellite, r

MnO2

MnO2

MnO2

57

Massicot, b

Litharge, a

NiOOH

PbO

PbO

135

Plattnerite, b

Pb3O4

PbO2

136

Hexagonal

Minium

Pb(OH)2

129

Cubic-F

164

Ni2O3

Hexagonal

Ni3O2(OH)4

P42/mnm

D4 h14

P4/nmm

D4 h7 P42/mbc

Pbma

D2 h11

D4 h13

P(-3)m1

D3d3

2

4

2

4

1

1

1

1

P(-3)1 m

162

P(-3)m1

3

2

D3d1

P63/m

C6 h2

2

16

a

P21/m

C2 h2

3Ni(OH)2 · 2H2O

Hexagonal-R

NiO

Ia3

Th7

16

16

D3d3

176

Nd(OH)3

164

11

NdOOH

Ia3

Th7

b

206

Nd2O3 · 2/3H2O

Ia3

Th7

0.5

48

Ni(OH)2

206

Nd2O3 · 1/3H2O

Pna21

C2v9

1 4

3/4

206

Nd2O3

Pbnm

4

2

8

3

2

8

Hexagonal

Hexagonal

Nb2O5

P63/mmc

D2 h16

P42/mnm

D4 h14

D6 h4

I4/m

B21/d

C4 h5

C2 h5

4Ni(OH)2 · NiOOH

33

62

136

Nb2O5

Bunsenite

Orthorhombic

Pyrolusite, b

MnO2

87

Hexagonal P

“d-MnO2”

Cryptomelane, a

Orthorhombic

Mn7O13·5H2O

Groutellit(Ger)

Mn2O3OH

Tetragonal(?)

14

MnO2

Feitknechtite, b

Manganite, g

MnOOH

MnOOH

9390..9490

9100

7590 [3212]

9280

9520

4150 (20)

3330

2520

3850; 3650

2950

6700..6900

4920

5840

6490

4860

4600 [3212]

4830

5120

4230

3660 (20)

4300

0.86

0.4955

0.8815

0.526

0.39759

0.5489

0.281

0.4186

0.304

0.534

0.3126

0.3071

0.29549

0.6425

0.6242

1.1518

1.1080

1.1078

0.3607

1.470

0.4533

0.2786

0.443

0.4388

0.9815

0.284

0.461

0.886

0.4755

0.3809

0.9376

0.927

0.936

0.954

0.524

0.93

0.3383

0.6565

1.47

0.5023

0.5891

0.484

1.460

0.750

0.4605

2.32

0.7227

0.3739

0.4391

0.3925

3.136

0.2866

0.4412

0.285

0.2865

0.2847

0.727

0.288

0.570

108.18

90

continued

3.1.26.3

3.1.26

3.1.26.2

3.1.26.1

3.1.26.1

3.1.25

3.1.25

3.1.25

3.1.25.2

3.1.25.2

3.1.25

3.1.25.1

3.1.24

3.1.24

3.1.24

3.1.24

3.1.24

3.1.23.2

3.1.23.2

3.1.22.14

3.1.22.14

3.1.22.14

3.1.22.14

3.1.22.14

3.4.10.1

3.1.22

3.1.22.6

3.1.22.6

Appendix 903

11

176

225

136

56

Valentinite

Senarmontite

PrOOH

Pr(OH)3

PuO2

RuO2

Sb2O3

Sb2O3

152,154

Quartz a

Tridymite a

Cristobalite a

SiO2

SiO2

SiO2

46

37

62

13

130

206

12

11

113

176

Hexagonal

H2Si2O5

H2Si2O5

H2Si2O5

H2Si2O5

H4Si4O10 · 0.5H2O

Sm2O3

Sm2O3

SmOOH

SmOOH

Sm(OH)3

Sm(OH)3 · H2O

92,96

15

204

63

ScOOH

Number

Sc(OH)3

206

Sc2O3

g

206

227

164

60

Pr2O3(+x)

a (metastable)

Name

Pr2O3

PbO2

Formula

TABLE A.2 (continued)

Pbcn P(-3)m1 Ia3 P21/m P63/m Fm3 m P42/mnm Pccn Fd3 m Ia3 Cmcm Im3 P31,221 C2/c P41,3211 Ibm2 Ccc2 Pmnb P2/c P4/ncc Ia3 C2/m P21/m P(-4)21/m P63/m

D2 h14

D3d3

Th7

C2 h2

C6 h2

Oh5

D4 h14

D2 h10

Oh7

Th7

D2 h17

Th5

D34,6

C2 h6

D44,8

C2v22

C2v13

D2 h16

C2 h4

D4 h8

Th7

C2 h3

C2 h2

D2d3

C6 h2

Hermann– Schoenflies Mauguin

2

2

4

2

6

16

4

8

4

24

4

4

48

3

8

4

16

16

4

2

4

2

2

16

1

4

Z

d

5210

7680

7310

2050

2060

2331

2270

2650

2650

3020

3860

5190

5780 (20)

7200

11500 [3212]

4730

6870..7070

9530

a

0.636

0.636

0.5710

0.613

1.4177

1.0927

0.764

1.1286

0.747

0.57

0.612

0.4971

1.854

0.49138

0.7898

0.324

0.9849

1.1152

0.4914

0.44910

0.53960

0.6454

0.6287

1.1152

0.3859

0.4988

b

0.377

0.3633

0.9905

1.194

1.46

1.540

0.501

1.301

1.2468

0.3861

0.5958

c

0.366

0.366

0.5599

0.438

0.8847

1.510

0.8377

0.491

2.976

0.496

0.6918

2.579

0.54052

0.401

0.5421

0.31064

0.3772

0.4397

0.6008

0.5465

a

108.6

99.96

103.78

117.67

107.81

b

g

Section

3.1.34

3.1.34

3.1.34

3.1.34

3.1.34

3.1.34

3.1.35

3.1.35

3.1.35

3.1.35

3.1.35

3.1.35

3.1.35

3.1.35

3.1.33

3.1.33

3.1.33

3.1.32

3.1.32

3.1.31.1

3.1.30

3.1.28

3.1.28

3.1.28

3.1.28

3.1.26.3

904 Surface Charging and Points of Zero Charge

Cassiterite

136

Brookite

Anatase

Rutile

Uraninite

TiO2

TiO2

TiO2

UO2

224

206

11

176

14

206

11

113

H8W12O40 · 5H2O

Y2O3

YOOH

Y(OH)3

Y(OH)3

Yb2O3

YbOOH

YbOOH

10

WO2(OH)2 · H2O

Hydrotungstite

14

WO3

13

a-WO3

W25O74

10

3

b-WO3

W20O58

10

Monoclinic

59

12

W20O59

Navajoite

Vanadinocker (Ger)

V2O5

g-WO3

Doloresite

V3O4(OH)4

W18O49

Montroseite

VOOH

V2O5 · 3H2O

167

Karelianite

V2O3

62

220

U4O9

225

136

141

61

227

225

Thorianite

H2Ta2O6 · H2O

ThO2

Orthorhombic

SnO2

Ta2O5

P2/m Pn3 m Ia3 P21/m P63/m P21/c Ia3 P21/m P(-4)21/m

C2 h1

Oh4

Th7

C2 h2

C6 h2

C2 h5

Th7

C2 h2

D2d3

Pmnm

D2 h13

P21/n

C2/m

C2 h3

C2 h5

Pbnm

D2 h16

P2/c

R(-3)c

D3d6

C2 h4

I(-4)3d

Td6

P2

Fm3 m

Oh5

C21

P42/mnm

D4 h14

P2/m

I41/amd

D4 h19

C2 h1

Pbca

D2 h15

P2/m

Fm3 m

C2 h1

Fd3 m

Oh7

P42/mnm

Oh5

D4 h14 2

4

2

16

2

2

16

2

2

8

2

2

1

1

6

2

2

4

6

64

4

2

4

8

4

8

11

7270

9170

3810

4620

5010

7286

7126

7140

7150

7720

2560

3357

3270..3330

4090

4720..4780

11159 (20)

10730..10820

4249.3

4060

4130

9870

5380

6720

0.47374

0.5482

0.587

1.04342

0.625

0.6241

0.595

1.0604

1.215

0.745

0.7306

1.190

1.19

1.205

1.832

1.743

1.1510

1.964

0.454

0.49515

2.17632

0.54690

0.4593659

0.37852

0.91819

0.55972

1.0580

0.6198

0.318638 0.3888

0.483

0.303

0.358

0.601

0.365

0.692

0.7540

0.3826

0.3815

0.3767

0.379

0.365

0.5326

0.427

1.540

0.3539

0.430

0.372

0.7692

5.964

4.94

2.359

1.404

1.225

0.43763 0.35677

0.299

0.997

1.4003

0.2958682

0.95139

0.54558 0.51429

4.0290

109.3

97.5

109.1

90

90.881

98.4

106.07

95.72

115.03

97

103.92

3.1.36.3

3.1.45

3.1.45

3.1.45

3.1.44

3.1.44

3.1.44

3.1.44

continued

3.1.43.2

3.1.43.2

3.1.43.1

3.1.43

3.1.43

3.1.43

3.1.43

3.1.42

3.1.42

3.1.42

3.1.42

3.1.42

3.1.41

3.1.41.1

3.1.39.1

3.1.39.1

3.1.39.1

3.1.38.1

3.1.37.2

3.1.37.1

Appendix 905

Montmorillonite

Sapphirine

Dickite

Metahalloysite

Nacrite

Chrysocola

Na0.33Mg0.33Al1.67 Si4O10(OH)2 · 4H2O

Mg3.5Al9Si1.5O20

Al2Si2O5(OH)4

Al4Si4O10(OH)8

Al2Si2O5(OH)4

Cu4H4(Si4O10) (OH)8

CeAlO3

Kaolinite

Cordierite

Mg2Al4Si5O18 · 0.5H2O

Kaolinite

Cordierite

Mg2Al4Si5O18

Al2Si2O5(OH)4

Fe-Cordierite

Fe2Al4Si5O18

Al2Si2O5(OH)4

Beryl

Be3Al2Si6O18

Mn-Cordierite

Baddeleyite

ZrO2

Halloysite

e

Zn(OH)2

Al4Si4O10(OH)8 · 4H2O

g

Zn(OH)2

Mn2Al4Si5O18

b

Zn(OH)2

Number

167

Orthorhombic

9

8

9

14

12

9

2

8

66

66

66

66

192

14

19

44

Orthorhombic

176

186

Zincite

Yb(OH)3

Name

ZnO

Formula

TABLE A.2 (continued)

P63/m P63mc

C6v4

P21/c P6/mcc Cccm Cccm Cccm Cccm Cm P(-1) Cc C2/m

P21/a Cc Cm Cc

C2 h5

D6 h2

D2 h20

D2 h20

D2 h20

D2 h20

Cs3

Ci1

Cs4

C2 h3

C2 h5

Cs4

Cs3

Cs4

R(-3)c

P212121

D24

D3d6

Imm2

C2v20

C6 h

2

Hermann– Schoenflies Mauguin 2

6

4

1

4

4

2

6

2

1

4

4

4

4

2

4

4

12

42

2

Z

6170

2100..2600

3490

2500 [3212]

2100..2600

2632

2781

5820;5730

3030

3234 (20)

3354 (20)

5642

d

0.5348

0.57

0.8909

0.515

0.5150

1.1266

0.517

0.513

0.514

0.520

1.728

1.7079

1.7083

1.7065

0.9212

0.5138

0.5170

2.307

1.317

0.3249858

0.620

a

0.885

0.5146

0.89

0.8940

1.4401

0.894

0.890

0.893

0.892

0.995

0.9730

0.9738

0.9726

0.5204

0.8547

0.804

0.642

b

1.3021

0.67

1.5697

0.757

1.4424

0.9929

1.52

2.15

0.737

1.025

0.928

0.9356

0.9335

0.9287

0.9236

0.5313

0.4930

0.330

2.41

0.5206619

0.346

c

91.8

a

113.7

100

96.73

125.46

90

90

104.5..105 90

100.2

99.2

b

g

3.3.1.1

3.3.13.2

3.3.1.7

3.3.1.7

3.3.1.7

3.2.50

3.2.35

3.2.30

3.2.30

3.2.27

3.2.23

3.2.23

3.2.23

3.2.23

3.2.13

3.1.47.1

3.1.46.4

3.1.46.4

3.1.46.4

3.1.46.1

3.1.45

Section

906 Surface Charging and Points of Zero Charge

141

227

MgFe2O4

FeMg4(OH)11

Magnesioferrite

Hexagonal

Co4Fe(OH)11

CuFe2O4

Hexagonal

I41/amd Fd3 m

D4 h19

Oh7

Fd3 m

Oh7

227

CoFe2O4

Pc21n

C2v9

33

Fd3 m

AlFeO3

I41/amd

Oh7

227

ZnCr2O4

D4 h19

141

NiCr2O4

Fd3 m

Oh7

227

Fd3 m

Oh7

NiCr2O4

Pbnm

D2 h16

62

Magnesiochromite 227

LaCrO3

MgCr2O4

Fd3 m

Oh7

227

Chromite

FeCr2O4

Fd3 m

Oh7

227

Gahnite

ZnAl2O4

R(-3)m

D3d5

166

P63/mmc

Zn8Al2O11 · 11H2O

Ia3d

D6 h4

194

Oh10

230

Y4Al4O12

P21/c

YAlO3

Fd3 m

Ia3d

14

Y4Al2O9

R(-3)m

D3d5

Oh7

C2 h5

230

Y3Al5O12

R(-3)m

D3d5

Fd3 m

R(-3)c

Oh7

Fd3 m

D3d6

Fd3 m

Oh7

Oh7

Oh10

Hexagonal

Ni4Al(OH)11

Hexagonal

AlMg4(OH)11

227

Spinel

MgAl2O4

NiAl2O4

166

227

Mg6Al2O9 · 13H2O Meixnerite

166

Hydrotalcite

Mg4Al2(OH)12 CO3 · 3H2O

227

167

Hercynite

FeAl2O4

227

LaAlO3

Hexagonal

CoAl2O4

Co4Al(OH)11

8

1

8

8

1

8

8

8

8

8

8

4

8

8

3/10

2

8

4

8

1

8

1

8

3/8

1/2

6

8

1

0.8160

0.83275

a√2 = .8253

0.8328

0.8333

0.5477

0.8377

0.80848

0.311

0.3678

1.1989

0.7373

1.2008

0.306

0.8061

0.310

0.80831

0.30463

0.3054

0.5365

0.8150

0.313

4436

5190

0.314

0.8380

a√2 = .8222

0.311

0.83919

4410..4450 (27) 0.860

5290 (13)

4415

5100

4602 (20)

4530

4650

3570

1900

2090

5840

4370 (18)

0.925

0.5514

1.0467

2.34

0.872

2.31

0.497

0.8441

0.7755

2.34

1.052

1.1121

2.34

2.37

2.293

2.281

1.311

2.37

108.53

3.3.1.2

continued

3.3.8.1

3.3.8.1

3.3.6.3

3.3.6.1

3.3.6.1

3.3.1.4

3.3.17

3.3.10.2

3.3.10.2

3.3.5.2

3.3.5.3

3.3.5.1, 3.3.6.2.2.

3.3.1.12

3.3.1.12

3.3.1.11

3.3.1.11

3.3.1.11

3.3.1.11

3.3.10.1

3.3.10.1

3.3.1.6

3.3.1.6

3.3.1.6

3.3.1.6

3.3.1.5

3.3.1.4

3.3.1.2

Appendix 907

15

Pyrophyllite

Pyrophyllite

Al2Si4O10(OH)2

Al2Si4O10(OH)2

62

Sillimanite

andalusite

Kyanite, Disthene

Piezotite

Mullite

H-Faujasite

Shattuckite

Dioptase

Orthoferrosilite

Clinoferrosilite

Fayalite

Al2SiO5

Al2SiO5

Al2SiO5

Al3Si2O7(OH)3

Al6Si2O13

H59Al59Si133O384

Cu5(SiO3)4(OH)2

Cu6Si6O18 · 6H2O

Fe2Si2O6

Fe2Si2O6

Fe2SiO4

Fe7SiO10

Triclinic

11

62

14

61

148

61

227

55

2

2

58

Monoclinic

Al2Si4O11

Al2Si4O11

2

141

FeMn2O4

227

ZnFe2O4

141

62

YFeO3

CoMn2O4

230

Y3Fe5O12

Franklinite

Trevorite

NiFe2O4

227

227

Jacobsite

MnFe2O4

Number

Hexagonal

Name

FeMn4(OH)11

Formula

TABLE A.2 (continued)

P(-1) Pbam Fd3 m Pcab R(-3) Pbca P21/c Pbnm P21/m

Oh7

D2 h15

C3i2

D2 h15

C2 h5

D2 h16

C2 h2

P(-1)

Ci1

D2 h9

C2/c

C2 h6

Ci1

I41/amd

D4 h19

P(-1)

I41/amd

D4 h19

Ci1

Fd3 m

Oh7

Pnnm

Pbnm

D2 h16

D2 h12

Ia3d

Oh10

Pbnm

Fd3 m

Oh7

D2 h16

Fd3 m

Oh7

Hermann– Schoenflies Mauguin Z

2

4

4

8

3

4

1

3/4

2

4

4

4

2

4

2

4

8

8

8

4

8

8

8

1

5020

4296(18)

3280

4110

3160

3560..3670

3140..3150

3230..3240

2650..2900

5268

4760

d

a

__

2.14

0.4818

0.97085

1.8418

1.4566

0.9885

2.4756

0.7583

0.7287

0.71192

0.77942

0.74856

0.5140

0.5173

0.51614

0.5172

a√ 2 = .8402

__

a√ 2 = .804

0.84411

0.5283

1.2376

0.8339

0.85050

0.321

c

1.8676

0.8799

0.904

0.7603

2.37

0.9504

1.8995

0.52366

0.7778

0.53825

0.28854

0.9729

0.306

1.0471

0.588

0.6086

0.90872 0.52284

0.9078

1.9832

0.7681

0.7720

0.78473 0.55724

0.78985 0.5559

0.76738 0.57698

0.9116

0.9114

0.89576 0.93511

0.8958

0.5592

b

70.32

89.977

91.2

91.03

a

98

108.432

128.7

101.121

100.2

100.0

100.37

100.0

b

Section

3.2.5

3.3.13.1.4.1

3.3.1.7

3.3.1.7

3.2.45

3.2.45

3.3.6.4

3.3.4.1

3.3.6.11

3.3.6.10

3.3.6.10

3.3.6.5

3.3.6.4

3.3.6.4

115.72

3.3.13.3

3.3.13.3.1

3.3.13.3

3.3.13.3

3.3.13.2

3.3.13.2

3.3.1.7

3.3.13.1.3

3.3.1.7

106.006 3.3.13.1.4.2, 3.3.13.1.4.3, 3.3.13.1.2

90.0

89.75

g

908 Surface Charging and Points of Zero Charge

Clinoenstatite

Willemite

Zn2SiO4

Tialite

Al2TiO5

197

42

197

Bi12TiO20

Bi4Ti3O12

Bi8TiO14

63

61

141

Zircon

ZrSiO4

44

Zn4Si2O7(OH)2 ·H2O

ZnSiO3

44

148

14

Monoclinic

Zn4Si2O7(OH)2

Hemimorphite

Chrysotile

Mg6Si4O10(OH)8

Monoclinic Pseudohexagonal

185

MgSiO3

52

Lizardite

Sepiolite

Mg4Si6O15(OH)2 ·6H2O

14

Mg6Si4O10(OH)8

Sepiolite anhydride

Mg4Si6O15(OH)2 ·2H2O

2

Antigorite

Talc

Mg3Si4O10(OH)2

15

Mg6Si4O10(OH)8

Talc

Mg3Si4O10(OH)2

62

8

Forsterite

Mg2SiO4

14

Antigorite

Deerite

Fe9Si6O20(OH)5

9

Mg6Si4O10(OH)8

Cronstedtite

Fe8Si2O10(OH)8

157

8

Hexagonal

Cronstedtite

Mg6Si2O6(OH)12 ·11H2O

Cronstedtite

Fe8Si2O10(OH)8

Fe8Si2O10(OH)8

Pbnm C2/c P(-1) P21/n Pncn

D2 h16

C2 h6

Ci1

C2 h5

D2 h6

P21/c R(-3) Imm2 Imm2 Pbca I41/amd Cmcm I23 Fm2 m I23

C2 h5

C3i2

C2v20

C2v20

D2 h15

D4 h19

D2 h17

T3

C2v18

T3

P63cm

P21/a

C2 h5

Cm

Cc

Cs4

C6v3

P31 m

C3v2

Cs3

Cm

Cs3

3

4

2

4

4

16

2

2

18

8

2

1

2

1

4

4

2

4

4

4

2

1/2

1

8930

7850

9074

3770

4706 (22)

3450

4250 (20)

2560

2080

2600..2800

3220..3260

3837

1.019

0.5408

1.01760

0.35875

0.66164

1.8204

0.8367

0.817

1.3948

0.96065

0.534

0.5301

0.5322

0.530

0.895

0.5255

1.09

0.5293

0.5287

0.47535

1.0786

0.549

0.549

0.549

0.9564

1.429

0.7085

0.732

1.465

0.7281

1.453

0.746

0.810

1.350

0.528

0.9469

1.895

0.60150

0.5278

0.5115

0.508

0.5444

3.2840

0.94237 0.96291

0.9087

1.0730

1.075

0.9315

0.88146 0.51688

0.92

0.9186

0.9219

0.920

2.697

2.33

0.5299

0.9158

1.01943 0.59807

1.888

0.951

0.951

86.06

108.335

93.27

91.40

90

98.91

99.5

107.45

97.37

104.52

119.99

continued

3.3.15.2

3.3.15.2

3.3.15.2

3.3.1.8, 3.3.15.1

3.3.13.8

3.3.13.7

3.3.13.7

3.3.13.7

3.3.13.7

3.3.13.5

3.3.13.5.1

3.3.13.5.4

3.3.13.5

3.3.13.5

3.3.13.5

3.3.13.5.6

3.3.13.5.6

3.3.13.5.2

3.3.13.5.2

3.3.13.5.3

3.3.13.3, 3.3.3.6

3.3.13.3, 3.3.3.6

3.3.13.3, 3.3.3.6

3.3.13.3, 3.3.3.6

Appendix 909

99

Macedonite

Ferberite

Hubnerite

PbTiO3

FeWO4

MnWO4

Azurite

Cu2(OH)2(CO3)

Cu3(OH)2(CO3)2

Hydrozincite

19

Hexagonal

12

Zn5(OH)6(CO3)2

Orthorhombic

Tb4O(CO3)5 · 7H2O

YOHCO3

190

Zn4(OH)2(CO3)3 · 4H2O

194

Pr2O2CO3

Orthorhombic

PrOHCO3

Pr2O(CO3)2 · 2H2O

12

Mg2(OH)2CO3 · 3H2O

14

Hexagonal

Fe6(OH)12(CO3) · 3H2O

Artinite

Malachite

Al14(OH)36(CO3)3

14

227

Triclinic

Scarbroite

Y2Zr2O7

227

Ce2Zr2O7

13

13

Monoclinic

Number

PbTi3O7

148

Ilmenite

63

FeTiO3

Pseudobrookite

Fe2TiO5

227

63

Ulvaspinel

Fe2TiO4

FeTi2O5

Pseudorutile

Name

Fe2Ti3O9

Formula

TABLE A.2 (continued)

Fd3 m

Oh7

C2 h3 C2/m

P212121

P(-6)2c

D24

P63/mmc

D3 h4

C2/m

D6 h4

C2 h3

P21/c

Fd3 m

Oh7

C2 h5

P2/c

C2 h4

P21/a

P2/c

C2 h4

C2 h5

P4 mm

C4v1

R(-3)

C3i2

2

4

1

2

4

3/8

2

4

4

8

8

2

2

1

2

6

4

4000

2040 (16)

3773

4050

2170

5530

6180

7200 [3212]

7510 [3212]

7520

5790

4500..5000

Cmcm

1.3479

1.332

0.4809

0.928

0.4146

0.4012

0.816

1.6561

0.317

0.500

0.9502

0.994

1.0426

1.0750

0.4829

0.4730

0.38985

1.0732

0.5082

0.3741

0.37385

D2 h17

4390

0.8529

4

Cmcm

8

Fd3 m

D2 h17

a

Oh7

d 0.2872

Z

Hexagonal

Hermann– Schoenflies Mauguin c 0.4594

0.6320

0.6957

1.142

0.860

0.6298

0.585

1.1974

1.488

0.5759

0.5703

0.3812

0.9798

0.5368

0.7537

0.8466

0.769

0.4986

1.5693

0.743

0.6220

2.28

1.035

0.3240

2.647

0.4998

0.4952

0.41511

0.6578

1.4027

1.0041

0.97954 0.99853

b

98.7

a

95.5

99.15

92.33

98.75

96.5

91.16

90

98.08

b

89

g Section

3.4.3.2.19

3.4.3.2.19

3.4.3.2.18

3.4.3.2.17

3.4.3.2.15

3.4.3.2.15

3.4.3.2.15

3.4.3.2.11

3.4.3.2.9

3.4.3.2.7

3.4.3.2.7

3.4.3.2.1

3.3.18.3

3.3.18.1

3.3.16.2

3.3.16.1

3.3.15.4

3.3.15.4

3.3.15.3.1

3.3.6.9

3.3.6.9

3.3.6.9

3.3.6.9

910 Surface Charging and Points of Zero Charge

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Index A Abramson cell, 43 Adhesion method, 88 AFM, See Atomic force microscopy Aging, in electrokinetic measurements, 56, 61–62 Air, See Gas bubbles Akageneite affinity series, 881 crystallographic data, 902 properties, 296–298 PZC/IEP, 296–299 transformation of magnetite into, 24 Akdalaite, crystallographic data, 900 Allanite, PZC/IEP, 548 Allophane, PZC/IEP, 632, 633 Almandine, PZC/IEP, 555 Alunite, PZC/IEP, 764 Amazonite, PZC/IEP, 554 Ammonium alum, calcination, alumina produced by, 129 Amosite, PZC/IEP, 636 Anatase crystallographic data, 905 electrokinetic behavior at high ionic strengths, 891 properties, 446, 449–454, 460–475, 479, 480, 483, 484, 486, 488–494, 496–499 PZC/IEP, 447, 448, 450–453, 455–475, 477, 479, 481, 483, 484, 486, 489–499, 501, 502 thermochemical data, 896 Andalusite crystallographic data, 908 PZC/IEP, 549 thermochemical data, 898 Andesine, PZC/IEP, 554 Andradite, PZC/IEP, 555 Andularia, PZC/IEP, 554 Anglesite, PZC/IEP, 767 Anhydrite, electrokinetic behavior, 766 Anorthite, PZC/IEP, 554 Anorthoclase, PZC/IEP, 554 Anorthosite, PZC/IEP, 554

Anthophyllite, PZC/IEP, 548 thermochemical data, 898, 899 Antigorite crystallographic data, 909 thermochemical data, 899 Apatite properties, 723–730 PZC/IEP, 723–730 Aragonite, PZC/IEP, 681 Artinite, crystallographic data, 910 Asphaltene, PZC/IEP, 858 Atomic force microscopy, 87 Augite, PZC/IEP, 549 Avicennite, PZC/IEP, 503 Azurite, crystallographic data, 910

B Back-titration method, 85, 86 Baddeleyite crystallographic data, 906 properties, 531 PZC/IEP, 532 Ball, models, 17–20 Ball-and-stick, models, 17–21 Barite, PZC/IEP, 765 Basal plane, in clay minerals, 100 Batch equilibration method, 83 Bauxite, activated, PZC/IEP, 607 Bayer process, alumina produced by, 103–105 Bayerite crystallographic data, 900 properties, 182, 184–187 PZC/IEP, 182, 184–187 thermochemical data, 894 transformation of alumina into, 24 Behoite, crystallographic data, 900 Beidellite, PZC/IEP, 550 Bentonite, See Montmorrilonite Beryl crystallographic data, 906 PZC/IEP, 550 thermochemical data, 897 BET, 90 Biotite, PZC/IEP, 550

1057

1058 Birnessite PZC/IEP, 702–706 thermochemical data, 895 Bismite, crystallographic data, 900 Bixbyite, thermochemical data, 895 Blazer, PZC/IEP, 551 Boehmite affinity series, 880 crystallographic data, 900 properties, 167–174 PZC/IEP, 167–174 thermochemical data, 894 Borax, PZC/IEP, 666 Bornite, PZC/IEP, 747 Bracewellite, crystallographic data, 901 Briggs cell, 43 Briggs-Mattson cell, 43 Bromellite, crystallographic data, 903 Bromododecane, PZC/IEP, 839 Bronzite, PZC/IEP, 551 Brookite, crystallographic data, 905 Brownian motion, 42 Brucite, crystallographic data, 902 Buffer capacity, 15 pH, 14, 33 Bunsenite, crystallographic data, 903 Bytownite, PZC/IEP, 554

C Calcite, PZC/IEP, 681 Carbon dioxide, effect on surface charging, 55 Carbonate adsorption, effect on surface charging, 6 transformation of oxide into, 24 Casein, PZC/IEP, 857 Cassiterite crystallographic data, 905 properties, 435–437 PZC/IEP, 434–437 Celestite, PZC/IEP, 768 Cellulose, PZC/IEP, 856 Cerussite, PZC/IEP, 690 Chalcocite, PZC/IEP, 743 Chalcopyrite, PZC/IEP, 745–747 Chitosan, PZC/IEP, 858 Chlorite PZC/IEP, 552 thermochemical data, 899 Chloroapatite, PZC/IEP, 730 Cholesterol, PZC/IEP, 841 Chrisotile affinity series, 884 PZC/IEP, 636 thermochemical data, 899

Index Chromatographic method, 88 Chromite crystallographic data, 907 PZC/IEP, 612, 697 Chrysocola crystallographic data, 906 PZC/IEP, 634 Chrysotile, crystallographic data, 909 Cinnabar, PZC/IEP, 753, 754 CIP, See Common intersection point Cleavelandite, PZC/IEP, 554 Clinochlorite, thermochemical data, 897 Clinoenstatite crystallographic data, 909 thermochemical data, 899 Clinoferrosilite, crystallographic data, 908 Clinohumite, thermochemical data, 899 Clinoptilolite, PZC/IEP, 552 Clinozoisite, PZC/IEP, 553 Coagulation, 87 Colemanite, 666 Colloid vibration current, 50 Combined method, 72 Common intersection point, 1, 69–70 presence or absence of, 80 Constant capacitance model, 94 Contact angle, 88 Cordierite crystallographic data, 906 PZC/IEP, 553 thermochemical data, 897 Corundum, crystallographic data, 900 Corundum, thermochemical data, 894 Covellite, PZC/IEP, 744 Cristobalite crystallographic data, 904 thermochemical data, 896 Crocidolite, PZC/IEP, 635 Cronstedtite, crystallographic data, 909 Cryolite, PZC/IEP, 665 Cryptomelane crystallographic data, 903 properties, 348, 351 PZC/IEP, 348, 351 Cummingtonite PZC/IEP, 635 thermochemical data, 899 Cuprite, crystallographic data, 901 CVI, See Colloid vibration current

D Debye-Huckel equation, 94 Deerite crystallographic data, 909 thermochemical data, 898

1059

Index Dextrin, PZC/IEP, 857 Diamond affinity series, 884 PZC/IEP, 781 Diaspore, crystallographic data, 900 properties, 174, 175 PZC/IEP, 174, 175 thermochemical data, 894 Dickite, crystallographic data, 906 Diffuse layer model, 94–95 Diopside, PZC/IEP, 740 Dioptase, crystallographic data, 908 Dissolution, kinetics of, 29–30 Disthene crystallographic data, 908 PZC/IEP, 632 Djalindite, crystallographic data, 902 DLVO theory, 87 Dolomite, PZC/IEP, 687, 688 Doloresite, crystallographic data, 905 Doppler shift, 44 Dravite, PZC/IEP, 589 Drift method, 83 Dukhin-Semenikhin equation, 65

E Edges, in clay minerals, 100 EGME, 90 Electric sonic amplitude O’Brian equation, 49 of 1-1 electrolyte, 49 Electroacoustic method commercial instruments, 50 mass fraction of solid particles, 57 volume fraction of solid particles, 57 Electrokinetic curves, shape, 60–61 potential, See Zeta potential Electronegatvity, correlation with PZC/IEP, 872 Electroosmosis, instruments, 47 Electrophoresis aging of dispersion, 56 commercial instruments, 43–44 mass fraction of solid particles, 54 ultrasonication of dispersion, 56 volume fraction of solid particles, 55 Enargite, PZC/IEP, 747 Epidote, PZC/IEP, 553 ESA, See Electric sonic amplitude Esin-Markov coefficient, 79 Eskolaite crystallographic data, 901 properties, 207 PZC/IEP, 207

F Faujasite, crystallographic data, 908 Fayalite crystallographic data, 908 electrokinetic behavior, 634 thermochemical data, 898 Feitknechtite, crystallographic data, 903 Feldspar, PZC/IEP, 554 Ferberite crystallographic data, 910 PZC/IEP, 654 Ferrihydrite properties, 301–305 PZC/IEP, 301–305 transformation into goethite, 24 transformation into hematite, 24 Ferroxyhite properties, 299, 300 PZC/IEP, 299, 300 FITEQL, 98 Flame hydrolysis of AlCl3, alumina produced by, 116, 126 Fluoroapatite, PZC/IEP, 731, 732 Forsterite PZC/IEP, 639 thermochemical data, 899 Francolite, PZC/IEP, 733 Franklinite, crystallographic data, 908 Fullerene, PZC/IEP, 781 Fullerol, PZC/IEP, 839 Fulvic acid PZC/IEP, 853, 854

G Gahnite, crystallographic data, 907 Galena, PZC/IEP, 756–758 Garnet PZC/IEP, 554 thermochemical data, 899 Gas bubbles electrophoresis of, 44 PZC/IEP, 813 Gelation rate, 89 Gibbsite crystallographic data, 900 properties, 177–184 PZC/IEP, 177–184 thermochemical data, 894 uptake of monovalent ions at PZC, 886 Goethite affinity series, 881 crystallographic data, 901 electrokinetic behavior at high ionic strengths, 892 properties, 270–291

1060 Goethite (Continued ) PZC/IEP, 270–291 thermochemical data, 895 transformation into hematite, 24 transformation of ferrihydrite into, 24 uptake of monovalent ions at PZC, 886 Graphite, PZC/IEP, 781 Greigite, PZC/IEP, 753 Grimaldiite, crystallographic data, 901 Gringard method, 91 Grossular, PZC/IEP, 555 Groutellit, crystallographic data, 903 Groutite, crystallographic data, 902 Grunerite, thermochemical data, 898 Guyanaite, crystallographic data, 901 Gyps, electrokinetic behavior, 766

H Halloysite crystallographic data, 906 PZC/IEP, 555 thermochemical data, 897 Hamilton–Stevens cell, 43 Hausmannite crystallographic data, 902 properties, 334 PZC/IEP, 334 thermochemical data, 895 Heazlewoodite, PZC/IEP, 755 Hematite affinity series, 880 crystallographic data, 901 electrokinetic behavior at high ionic strengths, 891 properties, 236–268 PZC/IEP, 236–268 thermochemical data, 895 transformation of ferrihydrite into, 24 transformation of goethite into, 24 uptake of monovalent ions at PZC, 886 Hemimorphite, crystallographic data, 909 Heptane, PZC/IEP, 837 Hercynite, crystallographic data, 907 Heterogeneity, of surface, 99 Heterogenite, crystallographic data, 901 Hg electrode, See Mercury electrode Hornblende, PZC/IEP, 548 Hubnerite crystallographic data, 910 PZC/IEP, 654 Humic acid, PZC/IEP, 852–855 Hunite, PZC/IEP, 688 Hydrargillite, See Gibbsite Hydrogen, See Gas bubbles Hydrotalcite, crystallographic data, 907

Index Hydrotungstite, crystallographic data, 905 Hydroxyapatite, See Apatite Hydroxy-topaz, thermochemical data, 898 Hydrozincite, crystallographic data, 910 Hysteresis, 6 in electrokinetic measurements, 61–62 in titration, 76

I Ice, PZC/IEP, 812 IEP, See Isoelectric point Illite properties, 555–558 PZC/IEP, 555–559 Ilmenite crystallographic data, 910 PZC/IEP, 650, 651 thermochemical data, 899 Imogolite PZC/IEP, 604 thermochemical data, 898 Inderite, PZC/IEP, 666 Inert electrolyte, 12–14 Inflection point method, 85 Isoelectric point, effect of the nature of electrolyte, 61 Isotope exchange, kinetics of, 28 IUPAC recommendations, nomenclature, 9

J Jacobsite, crystallographic data, 908

K Kaolin, See kaolinite Kaolinite crystallographic data, 906 electrokinetic behavior at high ionic strengths, 892 properties, 559–572 PZC/IEP, 559–572 thermochemical data, 897 Karelianite, crystallographic data, 905 Keggin polymer, 101 Koppite, PZC/IEP, 720 Kyanite crystallographic data, 908 PZC/IEP, 631 thermochemical data, 898

L Labradorite, PZC/IEP, 554 Laponite, PZC/IEP, 572

1061

Index Lepidocricite crystallographic data, 902 properties, 291–296 PZC/IEP, 291–296 Limonite, PZC/IEP, 301 Litharge, crystallographic data, 903 Lizardite crystallographic data, 909 PZC/IEP, 639 Lysozyme, PZC/IEP, 857

M Macedonite, crystallographic data, 910 Mackinawite, PZC/IEP, 753 Maghemite crystallographic data, 901 properties, 233–236 PZC/IEP, 233–236 transformation of magnetite into, 24 Magnesiochromite, crystallographic data, 907 Magnesioferrite crystallographic data, 907 thermochemical data, 898 Magnesite, PZC/IEP, 685, 686 Magnetite affinity series, 880 crystallographic data, 901 properties, 222–232, 255 PZC/IEP, 222–232, 255 thermochemical data, 895 transformation into akageneite, 24 transformation into maghemite, 24 uptake of monovalent ions at PZC, 886 Malachite, crystallographic data, 910 Manganite crystallographic data, 903 properties, 335, 336, 339 PZC/IEP, 335, 336, 340 thermochemical data, 895 Marcasite, PZC/IEP, 750 Mass titration method, 83, 85 Massicot crystallographic data, 903 thermochemical data, 896 Mass-transport electrophoresis, commercial instruments, 44–45 Mattson cell, 43 MCM-41 properties, 422, 423 PZC/IEP, 422, 423, 633 Ti-substituted, PZC/IEP, 641 Meixnerite, crystallographic data, 907 Melanite, PZC/IEP, 555 Mercury electrode, 12

Metacinnabar, PZC/IEP, 753 Metahalloysite, crystallographic data, 906 Metakaolinite, thermochemical data, 898 Metals, PZC/IEP, 861 Mica affinity series, 884 PZC/IEP, 572–4 Microcline, PZC/IEP, 554 Millerite, PZC/IEP, 756 Minium, crystallographic data, 903 Mixed solvents, surface charging in, 873, 874 Molybdenite, PZC/IEP, 755 Monacite, PZC/IEP, 734 Monodispersed colloids, 53 Monoliths, versus powders, discrepancies in IEP, 58–59 Monteponite, crystallographic data, 900 Montmorillonite affinity series, 884 crystallographic data, 906 electrokinetic behavior at high ionic strengths, 892 properties, 575–583 PZC/IEP, 575–583 Montroseite, crystallographic data, 905 Montroydite, crystallographic data, 902 Mordenite, PZC/IEP, 584 Moving-boundary cell, 43 Mullite crystallographic data, 908 PZC/IEP, 631 thermochemical data, 898 Muscovite PZC/IEP, 572, 584 thermochemical data, 897 MUSIC model, 97, 98

N Nacrite, crystallographic data, 906 Navajoite, crystallographic data, 905 Nephelin, PZC/IEP, 584 Nernst equation, 93 Nitrogen, See Gas bubbles Nonadecane, PZC/IEP, 838 Nonstrandite, crystallographic data, 900 Nsutite crystallographic data, 903 thermochemical data, 895

O O’Brien-White theory, 64 Obsidian, PZC/IEP, 426 Octadecane, PZC/IEP, 837 Octahedral models, 17–20

1062 Oleic acid, PZC/IEP, 840 Oligoclase, PZC/IEP, 554 Olivine, PZC/IEP, 585 Opal properties, 425 PZC/IEP, 425 Organic solvents, surface charging in, 874–876 Orthite, PZC/IEP, 548 Orthoclase, PZC/IEP, 554 Orthoenstatite, thermochemical data, 899 Orthoferrosilite, crystallographic data, 908 Oxides, transformation into carbonates, 24 Oxygen, See Gas bubbles

P Palygorskite, PZC/IEP, 585 Parabola method, 46 Paraffin wax, PZC/IEP, 838 Paratenorite, crystallographic data, 901 Parks’ review, 15–16 Particle size average, 52 definitions, 52 Periclase crystallographic data, 902 thermochemical data, 895 Perlite, PZC/IEP, 585 Permittivity, correlation with PZC/IEP, 872 Peroviskite thermochemical data, 899 type materials, PZC/IEP, 773 PZC/IEP, 773 Phase A, thermochemical data, 899 pH-drift method, 83 pH-measurements sodium effect, 33 suspension effect, 33 typical errors, 31 pH-scale, 30 ionic strength effect, 34 pressure effect, 34 temperature effect, 34 Picotite, PZC/IEP, 613 Piezotite, crystallographic data, 908 1-pK model, 96 2-pK model, 96, 97 crystallographic data, 909 PZC/IEP, 637, 638 thermochemical data, 898, 899 Plattnerite, crystallographic data, 903 Polishing rate, correlation with surface charging, 871 Potentiometric mass titration method, 83 Powder addition method, 83

Index Powders, versus monoliths, discrepancies in IEP, 58–59 Pressure effect on PZC/IEP, 868, 869 Proton adsorption, kinetics of, 27–28 Pseudoboehmite properties, 171 PZC/IEP, 171 Pseudorutile, crystallographic data, 910 Pyrex glass, PZC/IEP, 778 Pyrite, PZC/IEP, 748–751 Pyrolusite crystallographic data, 903 properties, 342 PZC/IEP, 341 thermochemical data, 895 Pyrop, PZC/IEP, 555 Pyrophyllite crystallographic data, 908 PZC/IEP, 586 thermochemical data, 898 Pyrrhotite, PZC/IEP, 751, 752

Q Quartz crystallographic data, 904 from specific locations, properties, 424, 426 from specific locations, PZC/IEP, 425–427 properties, 375, 376, 390, 401, 402, 406, 408, 409, 429 PZC/IEP, 375, 377, 378, 390, 401, 403, 404, 406, 408–410, 429, 430 thermochemical data, 896

R Ramsdellite crystallographic data, 903 properties, 348 PZC/IEP, 348 Red mud affinity series, 884 PZC/IEP, 609, 610 Rhodochrosite, PZC/IEP, 688, 689 Riddick cell, 43 Ripidolite, PZC/IEP, 586 Rotation disk, zeta potential of, 48 Rutile crystallographic data, 905 electrokinetic behavior at high ionic strengths, 891 properties, 446, 449, 451–453, 460, 461, 463–465, 467, 468, 471, 473, 474, 476–479, 481, 482, 485, 487, 495, 498–501

1063

Index PZC/IEP, 446, 449, 452, 453, 460, 463–468, 470, 471, 473, 474, 476–483, 485, 487, 488, 495, 498–501 thermochemical data, 896

S Salt addition method, 83, 84 Salt titration method, 84 Sanidine, PZC/IEP, 554 Saponite, PZC/IEP, 587 Sapphirine crystallographic data, 906 thermochemical data, 897 Scarbroite, crystallographic data, 910 Scheelite, PZC/IEP, 774 Schorl, PZC/IEP, 589 Schwertmannite, PZC/IEP, 766 Second-harmonic generation, 82 Sedimentation potential, 48 Sellaite, PZC/IEP, 700 Senarmontite, crystallographic data, 904 Sepiolite crystallographic data, 909 PZC/IEP, 640 Serpentine, PZC/IEP, 587, 588 Shattuckite, crystallographic data, 908 SHG, See Second-harmonic generation Siderite, PZC/IEP, 684 Silica biogenic properties, 428 PZC/IEP, 428 effect on surface charging of other materials, 57–58 speciation in solution, 37–38 Silicate adsorption, effect on surface charging, 6 Silicon, PZC/IEP, 811 Sillenite, crystallographic data, 900 Sillimanite crystallographic data, 908 PZC/IEP, 631 thermochemical data, 898 Smectite, PZC/IEP, 588 Smithsonite, PZC/IEP, 693 Smoluchowski equation, 41, 60, 64 Sohngeite, crystallographic data, 902 Solubility, of sparingly soluble materials, 21–24 Specific adsorption, 12 Sphalerite, PZC/IEP, 760–763 Spinel, crystallographic data, 907 Stannic acid properties, 439 PZC/IEP, 439 Stearic acid, PZC/IEP, 839

Stern model, 95 Stevensite, PZC/IEP, 640 Stibnite, PZC/IEP, 759 Stöber silicas affinity series, 881 properties, 414–420 silicas, PZC/IEP, 414–420 Streaming potential, instruments commercial, 47 home-made, 48 Sulfur, PZC/IEP, 811 Sum frequency generation, 82 Surface groups, protonable, 89–90

T Talc Tapiolite, PZC/IEP, 622 Temperature, effect on PZC/IEP, 866–868 Tennantite, PZC/IEP, 748 Tenorite, crystallographic data, 901 TGA (thermogravimetric analysis), 91 Thorianite, crystallographic data, 905 Tialite, crystallographic data, 909 Titanite, PZC/IEP, 774 Titanomagnetite, PZC/IEP, 623 Titration blank, 67 curves, of silica, 78 equilibration time, 73 hysteresis, 76 merging curves, 75 solid-to-liquid ratio, 72 TLM, See Triple layer model Todorokite, PZC/IEP, 707 Tohdite, crystallographic data, 900 Topaz, PZC/IEP, 634 Tremolite, PZC/IEP, 548 Trevorite, crystallographic data, 908 Tridymite crystallographic data, 904 thermochemical data, 896 Triple layer model, 98, 99 Tunellite, PZC/IEP, 666 Turmaline, PZC/IEP, 589

U Ulexite, PZC/IEP, 666 Ulva spinel, crystallographic data, 910 Uraninite, crystallographic data, 905

V Valentinite crystallographic data, 904 thermochemical data, 896

1064 Van Gills cell, 43 Vanadinocker, crystallographic data, 905 Variscite, PZC/IEP, 721 Velocity profile, in flat cell, 45 Vermiculite, PZC/IEP, 590 Vesuvian, PZC/IEP, 590 Viscosity, correlation with surface charging, 870 Vycor glass, PZC/IEP, 776

Index X Xenotime, PZC/IEP, 737 Xylene, PZC/IEP, 838

Y Yield stress, correlation with surface charging, 870

Z W Willemite crystallographic data, 909 thermochemical data, 899 Wollastonite, PZC/IEP, 739 Wurzite, PZC/IEP, 759, 760

Zeolite, PZC/IEP, 552, 590, 591 Zeta potential, numerical values, 59–60 Zincite, crystallographic data, 906 Zipf’s law, 35–37 Zircon crystallographic data, 909 PZC/IEP, 645, 646