The pH-dependent surface charging and points of zero charge

Journal of Colloid and Interface Science 353 (2011) 1–15

Contents lists available at ScienceDirect

Journal of Colloid and Interface Science www.elsevier.com/locate/jcis

The pH-dependent surface charging and points of zero charge V. Update Marek Kosmulski ⇑ Department of Electrochemistry, Lublin University of Technology, Nadbystrzycka 38, PL-20618 Lublin, Poland Department of Physical Chemistry, Åbo Akademi University, Porthansgatan 3-5, FIN-20500 Åbo, Finland

a r t i c l e

i n f o

Article history: Received 22 June 2010 Accepted 6 August 2010 Available online 22 August 2010 Keywords: Point of zero charge Isoelectric point Surface charge density Zeta potential Electrokinetic potential

a b s t r a c t The points of zero charge (PZC) and isoelectric points (IEP) from the recent literature are discussed. This study is an update of the previous compilation [M. Kosmulski, Surface Charging and Points of Zero Charge, CRC, Boca Raton, FL, 2009] and of its previous update [J. Colloid Interface Sci. 337 (2009) 439]. In several recent publications, the terms PZC/IEP have been used outside their usual meaning. Only the PZC/IEP obtained according to the methods recommended by the present author are reported in this paper, and the other results are ignored. PZC/IEP of albite, sepiolite, and sericite, which have not been studied before, became available over the past 2 years. Ó 2010 Elsevier Inc. All rights reserved.

1. Introduction The pH-dependent charging of various solid surfaces in aqueous solutions of 1–1 electrolytes governs the adsorption of ions, and thus it is of great theoretical and practical interest. The points of zero charge (PZC) and isoelectric points (IEP) observed in 0.0001–0.1 M aqueous solutions of alkali halides, nitrates(V), or chlorates(VII) are termed pristine PZC/IEP (to distinguish them from PZC/IEP observed in the presence of other solutes), and they are used to characterize the materials in materials engineering, catalysis, geochemistry, agriculture, wastewater management, etc. PZC/IEP from the literature have been summarized in numerous reviews. More dilute electrolyte solutions (<0.0001 M) are not suitable for studies of pH-dependent surface charging, because only a very limited pH range can be covered. More concentrated (>0.1 M) solutions of 1–1 electrolytes often show substantial ion specificity (the electrolytes are not inert), and they cause experimental difficulties (e.g., in pH measurements). The classical paper by Parks [1] is the most frequently used reference on pristine PZC. More recent, the most comprehensive compilation of pristine PZC was published by Kosmulski [2]. Due to a high activity in the field, that review was recently updated [3]. Several specialized reviews have been published, limited to certain types of materials, e.g., a recent review on IEP of viruses [4].

⇑ Address: Department of Electrochemistry, Lublin University of Technology, Nadbystrzycka 38, PL-20618 Lublin, Poland. E-mail address: [email protected] 0021-9797/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2010.08.023

The production of new results is still extensive, and the very recent results (2009–2010) and a few older results (overlooked in [2,3]) are compiled in the present paper in Table 1. The reliable and up-to-date compilation of PZC/IEP is especially valuable for those who use the concept of PZC/IEP, but who do not measure their values themselves, and using a value from a random primary source or from an outdated or incomplete review may have adverse effects. For example in a very recent paper [5] IEP of AKP50 alumina at pH 7.9 is reported, probably based on the literature. This happens to be the lowest IEP ever published for AKP-50, and it is lower by over 1 pH unit than the results reported in other sources. A correlation between IEP and electronegativity discussed in a very recent paper [6] was based on nonexistent results or substantially underestimated IEP, probably taken from a review paper. 1.1. Approach to results of insufficient quality Most studies containing PZC/IEP of insufficient quality (according to the standards defined by the present author [2], and by the others [7]) are simply ignored in the present compilation. The present approach has it pros and cons, and some readers may prefer an exhaustive list of deliberately ignored references, with an explanation why those reference were not used, as it was done, e.g., in the famous book of Dzombak and Morel [8]. A few arguments in favor of the present approach are discussed in this section. First, there is no sharp borderline between ‘‘correct” and ‘‘incorrect” results. Only a few papers totally conform to the standards settled in this review, and many papers only partially conform to those

Material

3.1. Oxides 3.1.1.1.1

Al2O3, AD101-F, from ACEa

3.1.1.1.1 3.1.1.1.1.3 3.1.1.1.1.4.1

Al2O3, AO-802 from Admatech, a, 99.8% pure Al2O3, a, CT300SG, Alcoa, original and NaOH-washed Al2O3, a, Aldrich, >99.7%, washed

3.1.1.1.1.5 3.1.1.1.1 3.1.1.1.1 3.1.1.1.1.21 3.1.1.1.1.21 3.1.1.1.1.21 3.1.1.1.1.21 3.1.1.1.1 3.1.1.1.1.29 3.1.1.1.1 3.1.1.1.1 3.1.1.1.1.50.1

Al2O3, a, 99.95% pure, from Alfa Aesar Al2O3, K10 from Alum-Earth Plantc Al2O3, a, from Antaria Al2O3, Degussa C, used as obtained Al2O3, Degussa C Al2O3, Degussa C Al2O3, Degussa C Al2O3, c, from Engelhard Al2O3, T126 from Girdler, heated at 200 °C for 16 h Al2O3, a, from Interchim, 99.99% pure, NaOH-washed Al2O3, sapphire from Kelpin or from MaTeck, 001 plane Al2O3, c, from Merck, washed

3.1.1.1.1 3.1.1.1.1.68 3.1.1.1.1.72.2

Al2O3, Shanghai Chem. Co. f Al2O3, Sigma–Aldrich, high purity a-Al2O3, AKP30, Sumitomo, original/washed

3.1.1.1.1.72 3.1.1.1.1.84 3.1.1.4.1.1.1 3.1.1.4.1.2.1.4 3.1.1.4.1.2 3.1.6.1.2 3.1.6.1.2 3.1.8.4.1

a-Al2O3, AKP-HP40, Sumitomo Commercial c-Al2O3 from unknown sourceg

3.1.9.2.1.1

CuO from Aldrich

3.1.9.4.4

Cu(OH)2l

Gibbsite, S11 from Alcoa Synthetic gibbsiteh Synthetic gibbsitei Synthetic CeO2 Synthetic cerianite, CeO2 Cr(OH)3j

Electrolyte

t, °C

Method

Instrument

pH

KOH+HCl 0.0005 M NaCl, NaBr, NaI, NaNO3 0.01 M NaCl NaClO4 0.01 M NaCl 0.001–0.1 M KNO3 0.005–0.5 M KNO3 0.01 M NaCl 0.001 M NaCl 0.001 M KCl 0.001, 0.01 M KCl, NaCl, NaNO3 0.01 M NaCl

25 25 20 25 25

25

25

HCl + NaOH 0.01 M KCl

0.001 M KCl 0.015 M NaCl 0.01–0.5 M KNO3 0.01 M KCl

25 25

0.0001–0.01 M KClO4

0.01 M KNO3 0.001–0.1 M NaCl

6.7 iep

3

9.1 iep

48 48 48 48

8.9 8.9 8.9 8.9

3

8.8

5

8. 7

(1) 21

8.6 9

iep pH iep iep cip cip iep pH iep

Malvern Nano ZS

8.2 6.5 7.7–8.3 9 8.3 8 9.2 8.6* 8.8* 9.1 4d 7.6e 8 8 7.9/8.1 9.3*/9.8

[19] [20,21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31,32]

[34] [35] [36] [37] [38] [39] [40] [41]

7

10

Coulter Delsa 440 electrophoresis Brookhaven Zeta PALS Laser Zee Meter 501

9 8* 9.1 10.1 5.7 8.5 8.1 8.4

2

iep

Otsuka

8.5k

[42,43]

2

iep

Malvern Nano ZS

10

[44]

2

7.8;8.4 iep 8.5;9.2 iep 8.5;10.3 iep

[45] [46] [47] [48]

4 –”– 4

6.7 iep –‘‘– 6.7 iep

1

7.7 iep

3

6.6

2

6.5, 9, iep

iep pH iep iep iep/cip iep iep iep iep cip iep iep iep iep

0–0.5 M NaNO3 0.005, 0.01 M NaCl

cip iep

3.1.12.2.5 3.1.12.3.1.1.2 3.1.12.3.1.2.5 3.1.12.3.1.2.5 3.1.12.3.1.2 3.1.12.3.1.2 3.1.12.2.2

Magnetite, 105 m2/g Maghemite from Alfa Aesar, 40 m2/g Synthetic maghemiteo Synthetic maghemite, from FeCl2 and FeCl3 Synthetic maghemitep Synthetic maghemiteq Hematite from Alfa Aesar

0.001–0.1 M NaCl 0.001 M NaCl

cip iep iep pH iep iep iep

0.001 M KCl 0.001 M NaCl

1

[15,16] [17] [18]

Synthetic magnetite, prepared under nitrogen Magnetite, natural, from Ward’s

25

[14]

PZC/IEP in [2,3]

8.5b 9.5 6.7

3.1.12.2.2 3.1.12.2.4

0.1 M NaNO3

8.3*

No. of entries in [2,3]

Zeta Probe Colloidal Dynamics DT 1200 Malvern Zetasizer 3000 HS

Magnetite from Prolabo Synthetic magnetitem –‘‘– Synthetic magnetiten

0.002 M NaNO3

Ref.

iep iep iep

3.1.12.2.1 3.1.12.2.2.1.3 –”– 3.1.12.2.2.1.3

25 25 25

PZC/IEP

cip iep iep iep

ZetaProbe, Colloidal Dynamics Acoustosizer 2

Zeta-Plus, Brookhaven Zeta Meter 77 Surpass, Paar Malvern Zetasizer 3000 Zeta PALS, Brookhaven Zeta-Plus, Brookhaven Matec ESA 9800, ZetaProbe, Colloidal Dynamics Zetasizer III Malvern Zeta Meter 77 Zeta Meter 3.0

*

Malvern Zetasizer 3000 HS Malvern Zetasizer 2000 Zeta PALS, Brookhaven

Coulter Delsa 440SX/ Zeta Probe,Colloidal Dynamics Malvern Zetasizer 3000 HSA Malvern Zetasizer 2000 Malvern Zetasizer Nano ZS Zeta PALS, Brookhaven Zeta Probe, Colloidal Dynamics

[33] [12] [16]

6.7 5.6 6.5 6.5 text 5.5 Fig. 1 8.2 3.8/3.8

[49] [50]

8 6.9 7.5 6.5 6.1 6.4 8.9

[25] [51] [52] [53] [54] [55] [56]

M. Kosmulski / Journal of Colloid and Interface Science 353 (2011) 1–15

Section in [2]

2

Table 1 PZC/IEP compilation: update of [2,3].

Hematite from Johnson Matthey Synthetic hematiter Hematite, 1 M FeCl3 was added to boiling waters Synthetic hematite, recipe from Matijevic and Scheiner Synthetic hematite, recipe from Breeuwsma Synthetic hematitet Synthetic hematiteu Synthetic hematitev Hematite, 19 m2/g Goethite from Aldrich Goethite from BASF

3.1.12.5.1.1 3.1.12.5.1.2.1.1 3.1.12.5.1.2.1.1 3.1.12.5.1.2.1.1 3.1.12.5.1.2.1.1 3.1.12.5.1.2.1.1 3.1.12.5.1.2.1.1 3.1.12.5.1.2.6 3.1.12.5.1.2.6 3.1.12.5.1.2.6 3.1.12.5.2.2.1.5 3.1.12.7.1.1 3.1.12.7.1 3.1.12.7.1.6 3.1.12.8 3.1.12.8 3.1.22.14.3 3.1.23.2 3.1.24.2 3.1.26.2.1 3.1.26.2.2 3.1.35.1

Goethite from Sigma–Aldrich Synthetic goethitex Synthetic goethitey Synthetic goethitez Synthetic goethiteaa Synthetic goethiteab Synthetic goethiteac Synthetic goethitead Synthetic goethiteae Synthetic goethiteaf Synthetic lepidocrociteag 2 line ferrihydriteah 6 line ferrihydriteai nitrate/sulfate precursor Synthetic ferrihydriteaj Iron hydroxideak Iron hydroxide, colloidal, origin unknown MnO2, natural, 2 specimens H4Nb6O17 hydrousal Nd hydroxide, from nitrate Pb(OH)2 from nitrate SiO2 D11-10 from BASF, heated at 200 °C for 16 h

0.001 M KCl

3.1.35.1 3.1.35.1.20.3 3.1.35.1.20.3 3.1.35.1.22.1 3.1.35.1.22.3 3.1.35.1 3.1.35.1 3.1.35.1 3.1.35.1 3.1.35.1 3.1.35.1 3.1.35.1 3.1.35.1.64 3.1.35.4.1 3.1.35.2.3 3.1.35.2.3 3.1.35.2.3

SiO2Daisogel from Daiso SiO2, Aerosil 200 from Degussa SiO2, Aerosil 200 from Degussa Ludox AM from DuPont (0.2% Al2O3) Ludox HS from DuPont SiO2 from EMS, 65 nm in diameter SiO2 from Fisher SiO2 from Fisher SiO2 SP-03 from Fuso SiO2 X-Tec 3408 from NanoX, 19 nm in diameter SiO2, commercial quartz sand from Roth, 99% pure SiO2, silica sand from Sibelco SiO2 from Sigma–Aldrich, 640 m2/g Quartz cell Stober silicaap Stober silicaaq Stober silicaar

HCl 0.001–0.1 M KNO3 None 0.001 M KCl 0.001 M KCl

HCl/NaOH 0.001–0.1 M NaCl 0.01 M NaCl 0.001–0.01 M NaClO4, KNO3 0.001 M KCl 0.001–0.1 M NaCl 0.01 M KCl

0.01–0.2 M NaCl KCl NaNO3 KNO3 HCl + NaOH 0.1 M NaNO3 0.001–0.1 M NaCl 0.001–0.1 M NaCl 0.005–0.1 M KCl HCl/NaOH 0.01 M KCl 0.01 M NaNO3 0.001–0.1 M NaCl 0.01 M KNO3 0.001–0.1 M NaCl 0.01–0.5 M KNO3 0.001–0.1 M NaCl 0.01 M NaNO3 0.001 M KCl HCl + NaOH 0.1 M

25

25

25

30

25

25

25

25

25 25 25 20 20

0.001 M NaCl 0.01 M KCl HCl 0.001–0.1 M NaCl HCl + NaOH H2SO4 + NaOH 0.0001 M KCl

0.01 M NaCl

25

pH iep cip iep cip iep cip iep cip pH cip/iep

PCD03pH, Mutek Acoustosizer 2 Zeta PALS, Brookhaven Coulter Delsa 440

Coulter Delsa 440 X

iep pH cip cip cip iep iep iep cip iep cip cip iep cip pH iep titration iep iep iep

Zeta Probe, Colloidal Dynamics

Zeta PALS Brookhaven Malvern Nano ZS Rank Brothers Mark II

iep

Zeta Meter 77

iep pH iep iep iep iep iep iep iep iep pH iep iep iep iep iep iep

Malvern Nano ZS

PCD03pH, Mutek Delsa 440 Malvern Zetasizer 3000 HSA Malvern Zetasizer 2000

Malvern Zetanano DLS

Zetaphoremeter IV

Malvern Zetasizer Nanosizer Malvern Zetasizer IIc Malvern Zetasizer IIc Zeta-Plus, Brookhaven Acoustosizer 2 Zeta-Plus, Brookhaven Colloidal Dynamics Zeta Probe Zeta Plus, Brookhaven Zeta Cad ELS-800 electrophoresisao electrophoresis DT 1200 Rank Brothers Mark II

8.1* 7 8.1 9.3 8.8 5.5 8.8* 7 7.6 6.9* 8/7.7 8.3/– 7.3/7.6 7.3/– 6.2w 7.5 7.5* 9.4 9.4 8.2 9.2 9.6 7.9 7.6*/7.2* 7.8* 8.7 8.2/7.2 8.2* 6.5 6 4.7 <3 if any 9.4* 11.5 Only negative zeta* 3.2 <5 if any 2.5am <3 if any <3 if any 2 <3 if any <3 if any <3.5 if anyan 1.5 2.6* <3 of any 1 <3 if any 3 <3 if any <3 if any

[57] [58] [59] [23] [60] [55] [45] [38] [25] [57] [61]

[62] [63] [45] [64] [65] [58] [66] [67] [59] [68] [45] [69] [70] [45] [71,72] [73] [74] [75] [76] [77]

(1)

8.1

1 23 9

7.8,8.2 iep 7.6 8.7

25 5

7.6 7.2 iep

(1)

8.8

108 108 108 108 108 108

8.5 8.5 8.5 8.5 8.5 8.5

1 1

7.7 cip 8.7 cip

1

8

1 3

>11 iep 11 iep

12 12 3 3

<3 <3 <2 <2.5

[28]

[78] [24] [79] [80] [80] [81] [82] [12] [16,83] [81] [59] [84] [85] [86] [39] [87] [88]

M. Kosmulski / Journal of Colloid and Interface Science 353 (2011) 1–15

3.1.12.3.2.1.7 3.1.12.3.2.2.1.1 3.1.12.3.2.2.2.4 3.1.12.3.2.2.2.8 3.1.12.3.2.2.3.3 3.1.12.3.2.2.7.2 3.1.12.3.2.2.2.8 3.1.12.3.2.2.3.5 3.1.12.3.2.4 3.1.12.5.1.1 3.1.12.5.1.1.2

(continued on next page)

3

4

Table 1 (continued) Material

Electrolyte

t, °C

Method

Instrument

PZC/IEP

Ref.

3.1.35.2.3 3.1.35.2 3.1.35.2.2.7 3.1.35.2.5.1 3.1.35.2.5.2 [3] [3] 3.1.35.2 3.1.35.3

Stober silica, recipe by Bogush Synthetic SiO2as Synthetic SiO2at MCM-41 made with CTMABr

0.001 M KCl 0.01 M NaNO3 0.001 M NaCl NaOH + HNO3

25 25 25

iep pH iep pH

Malvern Zetasizer II c

<3 if any 2.2 2.3 3.2

[89] [72] [90] [91]

SBA-15 made with Pluronic 123 SBA-15 made with Pluronic 123 Hollow SiO2particlesav quartz, natural, from Ward’s

HCl + NaOH HNO3 + NaOH

25 25

iep iep iep iep

[92] [93] [94] [50]

3.1.35.4.1 3.1.35 3.1.36.3.1 3.1.36.3.2 3.1.39.1.1.1.3 3.1.39.1.1.2.2 3.1.39.1.1.2.2 3.1.39.1.1.10 3.1.39.1.1.10.1 3.1.39.1.1.10.1 3.1.39.1.1.10.1 3.1.39.1.1.10.1 3.1.39.1.1.10.1 3.1.39.1.1.10.1 3.1.39.1.1.10.1 3.1.39.1.1.10.1 3.1.39.1.1.10.1 3.1.39.1.1.10.1 3.1.39.1.1.10.1 3.1.39.1.1.10.1

Quartz SiO2aw SnO2 from Alfa Aesar, 99.9% pure, cassiterite, washed Synthetic SnO2ay TiO2 from Aldrich, 99.999% pure, washed TiO2 anatase from Alfa Aesar TiO2 anatase from Alfa Aesar TiO2 P20 from Degussa, heated at 200 °C for 16 h TiO2 P25 from Degussa TiO2 P25 from Degussa TiO2 P25 from Degussa TiO2 P25 from Degussa, washed TiO2 P25 from Degussa TiO2 P25 from Degussaba TiO2 P25 from Degussa TiO2 P25 from Degussa TiO2 P25 from Degussa TiO2 P25 from Degussa TiO2 P25 from Degussa TiO2 P25 from Degussa, original/acid- and basewashed

2.5 4au 2 <2 if any/<2 if any <3 if any 2.5 4.1ax 4.1 5–6 5.5 6* 5.7* 6.5az 6.8 6.7 6.6 7 6.4 6bb 6.5* 6.5 6.6 6.5 5.5/6.1 –/6 (Table 1)

3.1.39.1.1.12 3.1.39.1.1.23 3.1.39.1.1.27.2

TiO2 pigment from DuPont (?), chloride processbc Anatase pigment from Kerr McGee, NaOH-washed Rutile from Merck, washed

0.001 M KNO3 0.01 M NaCl

3.1.39.1.1.28 3.1.39.1.1.28 3.1.39.1.1

DT51D from Millenium, anatase G5 from Millenium, anatase TiO2, used as active layer in filtration membrane from Pall Exekia TiO2 from Tioxide, washed Tronox, amorphous and anatase TiO2Sachtopore from ZirChrom TiO2from TiCl4bd TiO2from TiCl4be TiO2from TiCl4bf TiO2from propoxidebg TiO2from isopropoxidebh TiO2from isopropoxidebi

0.001–0.1 M NaCl 0.001–0.1 M NaCl None 0.05 M NaCl 0.01, 0.1 M NaCl 0.001–0.1 M NaCl HCl

25

0.01 M NaNO3

25

3.1.39.1.1.49 3.1.39.1.1 3.1.39.1.1 3.1.39.1.3.1 3.1.39.1.3.1 3.1.39.1.3.1 3.1.39.1.3.3 3.1.39.1.3.3 3.1.39.1.3.3

0.005 M NaCl

0.001, 0.01 M NaCl 0.001 M NaCl HCl 0.000001–0.1 M KCl HCl + NaOH 0.001 M NaCl 0.001 M KCl 0.001 M NaCl

25 25 25

25

0.001 M NaCl 0.0001–0.01 M NaCl

25

None 0.01 M NaCl

25

0.001–0.1 M NaCl 0.001, 0.01 M NaCl 0.005–0.5 M KNO3 0.001–0.1 M NaClO4 0.01 M NaCl

25

iep iep iep iep iep iep pH iep iep iep iep iep iep pH iep iep cip iep cip cip

iep iep iep iep cip cip iep

25

intersection cip iep pH pH iep iep iep pH

Zeta Plus

Malvern Zatasizer NanoZS Malvern Zatasizer NanoZS Malvern Nano ZS Coulter Delsa 440SX/ Zeta Probe,Colloidal Dynamics Rank Brothers Mark II Electrophoresis Electrophoresis Malvern Nano ZS Pen-Kem 3000 Malvern Nanosizer NanoZ Zeta Meter 77 Malvern Zetasizer IV Malvern Zetasizer Brookhaven Zeta PALS DT 300 Zetacompact Z8000 CAD Malvern NanoZS Delsa 440SX Zeta-Plus, Brookhaven Brookhaven Bi90

Pen-Kem 3000 Acoustosizer 2 Matec ESA 9800, ZetaProbe, Colloidal Dynamics

Malvern Nanosizer

Malvern Nano ZS

Zetacompact Z8000 CAD Malvern Nano ZS DT 1200 1 day equilibration

[77] [95] [96] [78] [97,98] [84] [27] [28] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [25] [109]

8.4* 6 6

[110] [111] [16]

5.8 6.1 4.1 4.4 5.4 5.3 5 5.7 5.5 6.5 5.6 6.7 6.5 6.3 6.1 6

[107] [107] [112] [113,114] [107] [78] [115] [116] [103] [117] [87] [118]

No. of entries in [2,3]

PZC/IEP in [2,3]

1 1

1.7 iep 3.5 iep

(1) (1)

4.2 4.2

(2) (2)

6.1 6.1

74 74 74 74 74 74 74 74 74 74 74 74

6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3 6.3

(1)

7.6

M. Kosmulski / Journal of Colloid and Interface Science 353 (2011) 1–15

Section in [2]

bj

TiO2 from butoxide TiO2 from butoxidebk TiO2 from butoxidebl TiO2, syntheticbm TiO2 nanotubesbn TiO2 nanofibersbo

3.1.39.1.3 3.1.39.1.3

TiO2 flame hydrolysis of TiCl4 bp TiO2, obtained by flame spray pyrolysis, 80% anatase, 20% rutile Y hydroxide, from nitrate ZnO from Meliorum Technologies, 99.99% pure ZnO from MK Impex, 99.9% pure ZnO, NanoX200 ZrO2 from Alfa Aesar ZrO2 from Alfa Aesar, used as received TZ-O ZrO2 from Tosoh, original/washed

3.1.44.2.7 3.1.46.1.1 3.1.46.1.1 3.1.46.1.1 3.1.47.1.1.3 3.1.47.1.1.3 3.1.47.1.1.19.1 3.1.47.1.1.19.1 3.1.47.1.2.1 3.1.47.1.2 3.1.47.2.2.2

TZ-O ZrO2 from TSK ZrO2 from propoxidebq ZrO2, obtained by flame spray pyrolysis, monoclinic and tetragonal Zr hydrous, amorphous oxide, from nitrate

0.001–0.01 M NaCl None

0.01 M NaCl

25

0.1 M

0.005–0.5 M KNO3 0.001 M NaCl 0.001, 0.01 M NaCl

25 25

0.1 M

iep iep iep iep iep iep

ZetaPALS 32 Brookhaven Zetacompact Z8000 CAD Brookhaven Zeta PALS Malvern Zetasizer Brookhaven Zeta PALS

iep iep

Malvern NanoZS Brookhaven Zeta PALS

iep iep iep cip pH iep iep

Malvern Nano ZS Zeta PALS Brookhaven Zeta PALS Brookhaven

3.2.35 3.2.35 3.2.35.18 3.2.35.18

5

5.8

1

6.7

1

5.5

<2 if any 6 6–7bs 3 <3 if any 2.5*

[125] [126] [127]

6 <2 if any/ 4.5 <3 if any 2

[130] [131]

<2 if any

[135]

3.7*

[129]

Zeta Meter 3.0+ Pen-Kem 7000

3.2.35 3.2.35 3.2.35

[124] [117] [40]

Zeta Meter 3.0

iep iep

3.2.35 3.2.35 3.2.35

6.2 6.2 5.8

[76]

0.0001–0.2 M NaCl 0.01 M KCl

3.2.30.2.1

4 4 5

8

0.01 M KCl 0.01–0.2 M NaCl

3.2.30.1

9

Malvern Nano ZS

3.2.18 3.2.29

3.2.30.1 3.2.30.1

5 6.9 6.4

1

iep iep pH pH iep iep pH

3.2.30.1 3.2.30.1

[76] [122] [122] [25] [27] [123] [16]

iep iep iep

None 0.001–0.1 M NaClO4 0.0001–0.1 M NaCl

Chlorite from Ward’s, fresh and aged dispersion Illite from Liaoning, China, H2O2 washed, and converted into Na form Albion Sperse 100, kaolin from Albion Kaolin Co. Hydrite PXN, Georgia kaolin from Dry Branch Kaolinbt

9.8* 9.3 9.1 9.2 6.7* 6.5 5.8/8.2

Malvern Zetaziser 2000 Matec ESA 9800, ZetaProbe, Colloidal Dynamics Mass transport apparatus Malvern Nano ZS Brookhaven Zeta PALS

3.2. Aluminosilicates, clay minerals (sorted by name) 3.2 NaAlSi3O8, albite, from Esan-Eczacibasi 3.2 Na-attapulgitebr 3.2 Na-attapulgite from Floridin, Florida

25 25

[105] [40]

[119] [120] [103] [101] [100] [121]

Malvern Zetasizer II Zeta-Plus, Brookhaven

Kaolinite from Evans Clay Co., Georgia, USA, washed Georgia kaolinite from Thiele Kaolin Co., original and washed Kaolinite from VE-KA, The Netherlands

0.0001–0.01 M NaCl, LiCl 0.01 M KCl

22.5 25

iep iep

Zeta Meter 3.0+ Zetasizer 4, Malvern

0–0.1 M NaCl, KCl

25

iep

Malvern Zetasizer 1000HS/3000 HS

Kaolinite from Jingde, China, H2O2 washed, and converted into Na form Acid-activated montmorilloinite from Aldrich Bara-Kade, Wyoming bentonite from Bentonite Co. Montmorillonite from Heishan, China, H2O2 washed, and converted into Na form Natural bentonite from Kholais, Saudi Arabia Natural montmorillonite from Milos, Greece Natural bentonite from Stara Kremenicka, Slovakia, washedbv K-montmorillonitebw K-montmorillonitebx Na-montmorillonite, B20 from Bromhead & Denison, purified Na-montmorillonite made from SWy-1, dialyzedbz

0.01–0.2 M NaCl

pH

[12,128] [129]

[132,133] [134]

HCl + NaOH 0.01 M KCl 0.01–0.2 M NaCl

25 25

iep iep pH

Zeta Meter 3.0+ Zetasizer 4, Malvern

<2 if any <2 if any 2.6*

[136] [134] [129]

HCl + NaOH HNO3 + NaOH

25

iep pH iep

Zeta Meter 3.0

3bu 8.8 <3 if any

[137] [138] [139]

7–8 7.4–8.1

[140] [141] [142]

0.001–0.1 M KNO3 0.03–1 M KCl 0.1 M NaCl (?)

25 25 25

pH pH iep

0.001–0.1 M NaCl

25

pH

Zeta-Plus Brookhaven

Rank Bros.

by

7.5–8.3

M. Kosmulski / Journal of Colloid and Interface Science 353 (2011) 1–15

3.1.39.1.3.3 3.1.39.1.3.3 3.1.39.1.3.3 3.1.39.1.3.3 3.1.39.1.3 3.1.39.1.3

5.9 5.7 5.5 6.4 6.5 6.6 5.3 A4 B4 C 3.9 D 6.5 2–3 6.8

[24] (continued on next page) 5

6

Table 1 (continued) Material

Electrolyte

t, °C

Method

Instrument

PZC/IEP

Ref.

3.2.35.18 3.2.35.18.4 3.2.35.18.6

Na-montmorillonite made from SWy-2, dialyzedca Na-montmorillonite from Wyoming Na-montmorillonite, from natural bentonite from Almeria (Spain) Na-montmorillonite, from natural bentonite from Clay Spur, Wyoming Muscovitecb Muscovite mica from Bihar, India, freshly cleaved Muscovite mica, ground natural material

0.001–0.1 M NaCl 0.001–0.1 M NaCl 0.002 M NaNO3

25 25 25

pH cip iep

Malvern Zetasizer 2000

6.4–7.2 8.1 <3 if any

[24] [143] [47]

0.0001–0.1 M NaCl

20

iep

Electrophoresis

<3 if any

[144]

iep iep iep

Acoustosizer 2 Electroosmosiscc Matec ESA 8000

4.5 <3 if any 3.3

[145] [146] [147]

0.001 M NaCl

3.2.43

Ruby muscovite mica, obtained from Continental Trade, freshly cleaved Na-palygorskitescd

iep

Streaming potential

<3 if any

[148]

0–0.01 M NaCl

iep

Pen-Kem Laser Zee Meter 501

[149]

22.5

iep iep

Zeta Meter 3.0+ Zeta Meter 77

0.01 M KNO3

23

iep

Acoustosizer 2 Malvern Nano ZS

A 4.1 B 4.5* <3 if any Only negative zeta* <2 if any

3.2.45 3.2

Pyrophyllite from Malatya, Turkey Sepiolite, 120 NF from Tolsa, heated at 200 °C for 16 h

0–0.01 M NaCl, KCl 0.001 M KCl

3.2

Sericitece

3.2.52

Na-smectite from Tunisia

0.001–0.1 M NaCl

25

cip

0.001 M KCl 0.01 M KNO3 0.001 M KCl

25 25

iep iep iep

Zeta Meter 77 Malvern Nano ZS Zeta PALS, Brookhaven

iep

3.3.15.4 3.3.15.7

Synthetic GaAl2O4cf Mg-Al-mixed oxidecg (Fe0.89Ni0.11)yOz (Fe0.54Ni0.46)yOzch Silica (30%)–ferrihydrite compositeci nitrate/sulfate precursor Mg-Mn mixed hydroxidecj Mg3(OH)2Si4O10 talc from Ward’s Mg3Si2O5(OH)4 serpentine from Ward’s, fresh/aged dispersion Mg3Si4O10(OH)2 Na-stevensite from Morocco Synthetic a-Zn2SiO4 TiO2, 0.2 at.% Al2O3, 0.4 at.% SiO2 pigment from Kemira, sulfate-process TiO2, 0.9 at.% Al2O3, 0.2 at.% SiO2 pigment from Kemira, chloride processcl Pb(Zr,Ti)O3cm ZrO2–TiO2mixed oxides from propoxidescn

3.3.18.3.1.7.7

TZ-3Y, ZrO2 + 3 mol% Y2O3 from TSK

3.2.35.18 3.2.38 3.2.33.4 3.2.38 3.2.38

3.3. Mixed oxides 3.3.1 3.3.1.6 3.3.6.5 3.3.6.6 3.3.8 3.3.13.5.2.4 3.3.13.5 3.3.13.5.5 3.3.13.7 3.3.15.1 3.3.15

3.4. Salts (sorted by anion) 3.4.3.1.2 SiC from IFP, original/heated at 350 °C 3.4.3.1.2 b-SiC, whisker from Tateho 3.4.3.2.2 Synthetic witherite BaCO3, two specimens 3.4.3.2.3.2 Synthetic aragonite 3.4.3.2.3.2 Synthetic calcite, 2 samples 3.4.3.2.3.2 Synthetic vaterite CaCO3 3.4.3.2.3.3 Calcite from China

0.001 M KNO3 0.001 M KCl

0.01, 0.1 M NaCl 0.01 M KCl

25 22 (?) 20

20

0.01 M KCl

3

<3 iep

(1)

7.7 salt addition

[150] [28]

[44]

[35] [151] [55]

Malvern Zetanano DLS

pH iep

1 day equlibration Zeta-Plus, Brookhaven

7 <3 if any

[152] [128]

iep

Zeta-Plus, Brookhaven

8/4

[12,128]

iep

Zetaphoremeter II, Z3000

<3 if any

[153]

1

2 iep

7.5ck 6.3*

[154] [155]

(1)

7.5

3.8*

[155] [156] [117]

1

6.6 iep

[124]

3

7.2 iep

[157] [34] [158] [158] [158] [158] [159]

0.001 M KCl

25

iep

25 25 25 25 25

<3 iep <3 iep

4.2 6.5 7.2 8. 4 6/4

pH iep

NaCl NaCl NaCl NaCl KNO3

1 1

[143]

25 25

0.001 M 0.001 M 0.001 M 0.001 M 0.001 M

PZC/IEP in [2,3]

8

0.001–0.1 M KCl, KClO3 0.001 M KCl

0.0001–0.01 M NaCl

No. of entries in [2,3]

iep iep

Malvern Zetasizer II, Coulter Delsa 440 Malvern Zetasizer II, Coulter Delsa 440 Zeta-Plus, Brookhaven Malvern Nano ZS

iep

Mass transport apparatus

7.5 5.3 5.7 6.3 7

iep iep iep iep iep iep iep

Streaming potential Zetasizer III Malvern Zeta-Plus, Brookhaven Zeta-Plus, Brookhaven Zeta-Plus, Brookhaven Zeta-Plus, Brookhaven MRK

4/3 5 <6 if any <6 if any <6 if any 7.3 10.5

[70]

M. Kosmulski / Journal of Colloid and Interface Science 353 (2011) 1–15

Section in [2]

Calcite from Las Cuevas, Mexico CaCO3, Iceland Spar from Ward’s FeCO3co Magnesite from Kosice-Bankov Dolomite from Kosice-Bankov NiCO3, gaspeite, syntheticcr

0.005 M NaCl 0.01 M NaCl 0.017 M NaCl

3.4.3.2.16 3.4.7.1.3 3.4.13.4

Synthetic strontianite SrCO3, two specimens Fluorite from China TiN from Hefei Kaier Nanotechnology Development, China HCa2Nb3O10cs b-Calcium phosphate from Fluka, heated at 200 °C for 2h Hydroxyapatite from Riedel de Haen, heated at 200 °C for 2 h Synthetic hydroxyapatitect Synthetic hydroxyapatitecu Apatite from China Natural hydroxyapatite from Bosilegrad, Serbia Fluoroapatite from Canada, 97% pure ZrP2O7cw Chalcocitecx

0.001 M NaCl 0.001 M KNO3 HCl + NaOH

25 25

HCl + NaOH None

25

3.4.12 3.4.15.3.1 3.4.15.4.1 3.4.15.4.2.1 3.4.15.4.2.2 3.4.15.4.3 3.4.15.4.3 3.4.15.6.3 3.4.15.15.2 3.4.17.1.4.1.2

iep iep iep iep iep pH iep iep iep iep

Zeta Probe, Colloidal Dynamics Surpass, Paar Malvern Nanosizer Z Zeta-Plus, Brookhaven Zeta-Plus, Brookhaven Zetaphoremeter IV 4000

cp

6.2–8.7

[50] [160] [161] [162] [162] [163]

Zeta-Plus, Brookhaven MRK Malvern Nano ZS 90

<6 if any 10.5 3.6

[158] [159] [164]

iep iep

Zeta PALS Brookhaven DT-1200

2 6.2

[165] [166]

None

iep

DT-1200

6.8

[166]

0.01, 1 M KCl 0.001 M KCl 0.001 M KNO3 None 0, 0.002 M KNO3 0.5 M NaClO4 0.01 M KNO3

intersection iep iep iep iep pH iep

[167] [168] [159] [169] [170] [171] [44]

iep iep iep iep iep iep iep iep iep iep iep iep iep iep

Acoustosizer 2 Malvern Nano ZS Malvern Zetasizer 3000 Zetaphoremeter IV Rank Brothers Mark II Zeta Probe, Colloidal Dynamics Coulter Delsa 440SX Malvern Zetasizer 3000 electrophoresis Zeta Meter Pen-Kem 7000 Malvern Zetamaster ZEM5002 Pen-Kem 3000 Pen-Kem 3000 Matec ESA 8050 MRK

7.3 6.5 3cv <5 if any 4 3.6 <2 if any 2.2 <3 if any <3 if any 2.8 6.1 2.2 <3 if any 7.2 >10 if any 3 4.5 4.7 10.2* 2

[172] [73] [77] [50] [173] [172] [174] [175] [176] [177] [178] [179] [180] [159]

0.002, 0.02 M NaCl 0.001 M KCl 0.001 M NaCl

iep iep iep

Streaming potential EKA, Paar Streaming potential

3 <3 if any <3 if any

[157] [181] [182]

0.000001–0.1 M KCl 0.000001–0.1 M KCl

iep iep pH pH pH pH/iep

Pen-Kem 3000 Pen-Kem 3000

8–9.5 2–3.8 7.2dg 5.3* 6.8* 7.5/6 4/1.2 4.7/1.3 3.9/1.3 8/7.8 6.5/3.7 3.5 7.9* 7.9*

[97,98] [97,98] [183] [184] [184] [185]

22

0.001–0.1 M NaCl

cy

3.4.17.1.10.1.1 3.4.17.1.10.3 3.4.17.1.10.3.1.2 3.4.17.1.10.1.3 3.4.17.1.10.1.3 3.4.17.1.12.1 3.4.17.1.12 3.4.17.2.1 3.4.18.1.1 3.4.18.1.1 3.4.18.1.2 3.4.18.1.2 3.4.18.1 3.4.19.1.1

Galena from Gregory, Bottley, and Lloyd Galenacz Galenada Galena from Naica, Mexicodb Galena from Naica, Mexicodc Sphalerite from Gregory, Bottley, and Lloyddd Sphalerite Alunite, natural, from Marysvale, Utah BaTiO3 from Criceram HTD BaTiO3, Tamtron X7R, 302H from TAM BaTiO3de BaTiO3df BaTiO3 Scheelite from China

3.5. Glasses 3.5 3.5 3.5.1.5

Glass beads from Sovitec, acid-washed homemade fibers Microscope slide, washed

3.6. Carbon-rich materials 3.6.4.1.1 Regal 660 from Cabot 3.6.4.1.1 Black Pearls from Cabot 3.6.4.1.2 CPG-LF from Calgon 3.6.4.1.4 Ceca AC40 3.6.4.1.4 Ceca GAC 3.6.4.1.2.6 F400 from Chemviron A B C D E Fdh 3.6.4.1 NIPex 150, carbon black, from Evonik Degussa 3.6.4.1.2.6 Filtrasorb 400 3.6.4.1.13 Merck

0.001 M KNO3 0.001 M KCl

25 22.5 23 27

0.001 M NaCl 0.001 M KNO3

25 27

0.001, 0.02 M NaNO3 HCl + KOH HCl + KOH

25

0.001 M KNO3

25

0.1 M NaCl

0.001 M KCl

iep pH pH

Malvern Zetasizer Nano ZS MRK Zeta-meter Zeta-meter

Malvern Zetasizer 3000 HSA

Malvern Zetasizer 3000

12.5 8.9 6 cq

[186] [184] [184]

4 1 2 1 1

5.3 <7; 7.2 iep <9 6.6 iep

1

8.2

2

<3 iep

1

10.3

1

<3 iep

M. Kosmulski / Journal of Colloid and Interface Science 353 (2011) 1–15

3.4.3.2.3.3 3.4.3.2.3.3.4 3.4.3.2.9.1 3.4.3.2.11.1.4 3.4.3.2.11.2.3 3.4.3.2.13

3 (1) 7.5 (continued on next page) 7

8

Table 1 (continued) Section in [2]

Material

Electrolyte

t, °C

Method

Instrument

PZC/IEP

Ref.

3.6.4.1 3.6.4.1.15

From Nan Feng Wood Processing Factorydi PKST from Noritdj

25

iep pH

Zeta Probe, Colloidal Dynamics

0.1 M NaCl

[187] [188]

3.6.4.1.15 3.6.4.1 3.6.4.1 3.6.4.1

Norit PicaChem150 from Pica Picaflo 103LB from Pica Coconut-shell-derived activated carbon from Shanghai Xinhuoli Activated Carbon Co.dk

3.6.4.1 3.6.4.1 3.6.4.1 3.6.4.1 3.6.4.1 3.6.4.2.1

C320.00A carbon fibers from SGL Sigri Carbon Group HM48.00A carbon fibers from SGL Sigri Carbon Group HM48.00B carbon fibers from SGL Sigri Carbon Group Sorbo Witco Carbon from bamboo (waste handicrafts)do

3.6.4.2.1

8 activated carbons from cherry stonesdp

3.6.4.2.1

4 activated carbons from cherry stones

dq

3.6.4.2.1.5 3.6.4.2.1.4 3.6.4.2.1

Carbon from palm stonesdr Charcoal from spruce woodds Charcoal from vine shootsdt

0.1 M NaCl 0.05 M NaNO3 0.1 M NaNO3

3.6.4.2.2

Carbon from cellulose acetatedu

3.6.4.2.2

3.6.5.1

0.1 M NaCl

iep iep iep pH pH pH

Malvern Zetasizer 3000 HSA

0.1 M NaNO3

iep pH pH

pH pH pH

2 days equilibration 1 day equilibration

None

pH

1 day equilibration

Carbon from cellulose acetatedv

None

pH

1 day equilibration

Spectracarb 2225 from Spectra Corp.

0.1 M NaNO3

pH

1 day equilibration

6.3/1.8 A7 B3 C 8.2 9.2* 2.2* 2.6* A 3.5/10.1 B 2.4/5.2 C 2.1/4.1 D 2.3/4.9 E <2/3.1 F <2/3.2 4.2dl 3.6dm <3 if anydn 9.4* 6.9* A 3.4–3.7 B 3.5 1.5–2 2–3 A 8.8* B 9.8* C 4.3* D 3.6* 6.8* 6.4* A 8.3* B 9.7* C 9.2* D 10.2* E 10* F 9.2* G 9.6* H 9.7* I 9.8* A 7.1* B 6.4* C 6.3* D 7.1* A 4.6* B 9.5* C 9* 7.4

pH

2 min equilibration

2.6

[201]

0.0001, 0.01 M KCl

iep

Zetasizer Nano ZS

<2.5 if any

[202]

0.001 M NaCl

iep

Streaming potential

3

[182]

HCl + NaOH/NaNO3

Stober silica shell with fluorescent core

3.10. Polymers, macroscopic specimens 3.10 Cellulose hydrate (Cellophan) from Kalle

25

Coulter Delsa 440 SX

EKA Paar EKA Paar EKA Paar

overnight equilibration

1 day equilibration

PZC/IEP in [2,3]

[184] [189] [189] [190]

[191] [191] [191] [184] [184] [192,193] [183] [194]

[195] [196] [197]

[198]

[198]

[199,200]

M. Kosmulski / Journal of Colloid and Interface Science 353 (2011) 1–15

0.001 M KCl 0.001 M KCl 0.001 M KCl

3.7. Other well-defined inorganic compounds 3.7 Ge-, n-, and p-type 3.8. Coatings 3.8.10

pH pH pH iep/pH

No. of entries in [2,3]

3.10 3.10.1 3.10.5 3.10.7

0.001 M 0.001 M 0.001 M 0.001 M

3.11. Latexes 3.11.1.5 3.11.1.7 3.11.1 3.11.2.4

Carboxylated, polystyrene, Estapor-Merck PL-7, from Interfacial Dynamics Nylon 12 from Toray, washed Melamine-formaldehyde latexdw

3.11.2.7

Polystyrene, Invitrogen, 800 nm nominal size

3.11.2.7

Polystyrene, synthetic, with sulfonate groups, 800 nm nominal size Polystyrenedx

3.10.9 3.10.10 3.10.10 3.10.11

3.11.2.7

a

NaCl NaCl NaCl KCl

iep iep iep iep

Streaming potential Streaming potential Streaming potential EKA, Paar

3.5 4 3 4.6*

[182] [182] [182] [203]

0.001 M KCl 0.001 M KCl HCl, 0.001 M KCl 0.001 M NaCl

iep iep iep iep

Streaming potential EKA, Paar Streaming potential Streaming potential

4 4.4* 4 4

[204] [203] [204,205] [182]

0.001 M NaNO3 0.000001–0.1 M KCl 0.0001 M KCl 0.001 M NaCl, NaBr, NaNO3, NaClO4, KBr, KI, KNO3 0.001, 0.01 M NaCl

25

iep iep iep iep

Malvern Zetasizer Nano Pen-Kem 3000 Electrophoresis Malvern, Nano ZS

<2 if any 2.5–4 5 8.5

[206] [97,98] [86] [207]

20

iep

>9 if any

[148]

20

iep

<3 if any

[148]

iep

Zeta PALS Brookhaven, Malvern Nano ZS Zeta PALS Brookhaven, Malvern Nano ZS ELS-8000 Otsuka

4.1

[208,209]

0.001, 0.01 M NaCl

4

3

1

<3 iep

1

11

3.12. Natural high-molecular-mass organic compounds 3.12.4 Cellulose

0.001 M KCl

iep

Streaming potential

4

[204]

5

<3

3.13. Microorganisms [3] Gloeocapsa

0.01, 0.1 M NaNO3

iep

Zetaphoremeter IV, Z 4000, CAD

<2 if anydy

[210]

1

<1.5

2

242 m /g. The same paper reports PZC of manganese-oxide-coated alumina (based on AD101-F alumina) at pH 7.5. The maximum in the yield stress of the dispersion matches the IEP. 250 m2/g. The same papers report PZC of iron-hydroxide-coated alumina (based on K10) at pH 6.9. d A review. The IEP was confirmed by measurement performed with a homemade streaming current device. Contact angle showed a maximum at pH about 6. e PZC at 15 and 35 °C is also reported. f 122 m2/g. Actually only 4 Pd-doped samples were studied, and the amount of Pd did not affect the IEP. g Also Ga-doped c-Al2O3 with 0.2–1.7 mass% Ga. h 4 M NaOH was added to 1 M AlCl3 under nitrogen until pH 4.6. The dispersion was aged for 2 h at 70 °C. Dialyzed at room temperature. i 0.5 M NaOH was added to 0.1 M Al(NO3)3 until pH 7. The dispersion was aged for 7 days at room temperature, and for 20 days at 65 °C. Dialyzed at room temperature, and freeze-dried. j 0.0004 M KCr(SO4)2 was heated for 1 day at 75 °C. Charging curves do not show a CIP over a pH range 4–9. k Interpolated. No data points for pH 8–10. The same studies report IEP at pH < 3, if any, for unspecified silica. l 2 M KOH was added to 1 M Cu(NO3)2. m 1 M FeCl3 and 2 M FeCl2 in 2 M HCl were added to 0.7 M ammonia at room temperature. n 250 mL of 0.005 M KOH, 100 mL of 0.2 M KNO3, and 550 mL of water were mixed under nitrogen. Then 100 mL of 0.03 M FeSO4 was added. The system was kept at 85 °C for 4 h. o A solution of 3.25 g of FeCl3 and 2 g of FeCl24H2O in a mixture of 50 mL of water and 10 ml of 1 M HCl was added dropwise to 100 mL of 1 M NaOH under stirring under argon at room temperature. The IEP was obtained by interpolation: no data points between pH 7 and pH 9. p A mixture of 0.32 mL of oleic acid and 20 mL of dioctyl ether was heated to 90 °C under argon. Then 0.1 mL of Fe(CO)5 was added, and the mixture was heated at 340 °C for 30 min, and then allowed to cool. The particles were precipitated with 40 mL ethanol, and redispersed in hexane. q Electrodeposition from 0.01 Fe(III) solution with steel sheets as the anode and the cathode at 20 °C and 1 A/cm2. r Transformation of ferrihydrite at pH 7 maintained by means of NaHCO3. Recipe from Schwertmann and Cornel. s Similar recipe was used to produce hematite coating on sand, and the CIP was at pH 7.6. t Annealing of synthetic maghemite for 10 min at 600 °C. u Solution of FeCl3 in 0.002 M HCl was aged at 98 °C for 7 days. Similar recipe was used to produce hematite coating on sand, and the CIP was at pH 4. v A solution 0.02 M in Fe(III) nitrate and 0.002 M in HNO3 was aged for 7 days at 98 °C (recipe from Schwertmann and Cornell), dialyzed, and freeze-dried. w Matches a maximum in yield stress of 42–57 mass% dispersions. x From 1 M Fe(III) nitrate and 10 M NaOH, recipe from Schwertmann and Cornell. Similar PZC is reported for Ni-doped goethite. y 0.5 L of 0.5 M Fe(NO3)3 was quickly titrated with 0.4 L of 2 M NaOH under nitrogen. Aged for 1 day at 60 °C. Similar recipe was used to produce goethite coating on sand, and the CIP was at pH 3.6. z Fe(III) nitrate was titrated with concentrated NaOH to pH 12. The precipitate was aged for 1 day at 60 °C. The synthesis was carried out under nitrogen atmosphere. aa 4 L of 0.1 M Fe(III) nitrate were titrated with 0.8 L of 5 M NaOH. The precipitate was aged for 3 days at 60 °C. The synthesis was carried out under nitrogen atmosphere. ab KOH was added to Fe(III) nitrate. The dispersion was diluted and aged for 60 h at 70 °C. Recipe from Schwertmann and Cornell. ac Fe(III) nitrate was rapidly titrated with concentrated KOH. The dispersion was diluted and aged for 60 h at 70 °C. Recipe from Schwertmann and Cornell. (continued on next page) b c

M. Kosmulski / Journal of Colloid and Interface Science 353 (2011) 1–15

Cellulose triacetate from Kalle Polyamide, Supranyl N200 from Kalle Polyethylene, Suprathen NR 200 from Kalle Poly(methyl methacrylate), Palapress from HaraeusKulzer Polystyrene Polytetrafluoroethylene Teflon from DuPont Polyurethane, SYSpur from VEB Synthesewerk Schwarzheide

9

10

Table 1 (continued) ad

Hydrolysis of Fe(NO3)3. Recipe from Schwertmann and Cornell. Contact with glass was avoided during the synthesis. FeCl2 was oxidized with NaClO3 at pH 7 (in the presence of NaHCO3). Similar recipe was used to produce goethite coating on sand, and the CIP was at pH 6.5. af Oxidative hydrolysis of FeSO4 at pH 7 in the presence of H2O2. Original/autoclaved at 120 °C and microwaved. ag A mixture of 0.228 M FeCl2 and 0.4 M NaOH was oxidized at neutral pH with oxygen. Similar recipe was used to produce lepidocrocite coating on sand, and the CIP was at pH 3.5. ah 1 M NaOH was added to 0.1 M Fe(NO3)3 to adjust the pH to 8. Aged for 2 days at 20 °C, dialyzed, and finally freeze-dried. ai Produced in a continuous reactor at 85 °C and at pH 2.65 from 0.1128 M Fe(III) nitrate or sulfate and 8 M NaOH. The effective residence time was 45 min. aj 0.2 M FeCl3 was adjusted to pH 7–8 with 1 M NaOH. Similar recipe was used to produce ferrihydrite coating on sand, and the CIP was at pH 4.6. ak 0.25 M Fe(NO3)3 was titrated to pH 7.5 with 0.75 M NaOH. The precipitate was aged for several hours, washed, and dried at 105 °C for 2 h. al K2CO3 (10% excess)-Nb2O5 mixture was heated at 1200 °C for 15 min in air. The product was treated with H2SO4 and then with TBAOH and finally with HCl or HNO3. Washed with water. A formula K4Nb6O17 was used in the original paper, but in fact K was ion-exchanged and a formula H4Nb6O17 may be more suitable. am No clear sign reversal. At higher NaCl concentrations (0.1 and 0.3 M) IEP was shifted to higher pH. an f potential was close to zero at pH 2–3.5, but no clear sign reversal. ao From a mobility profile of latex particles in a quartz cell. ap 2 mL of tetraethoxysilane were added to a mixture of 1.5 mL of water, 47 mL of ethanol, and 1.7 mL of ammonia. The mixture was stirred at 25 °C for 3 h. IEP of Ce-coated silica at pH 7.5 is also reported. aq Tetraethoxysilane was added to a mixture of ethanol and ammonia. The mixture was stirred for 3 h. ar 1.5 L of 0.74 M ethanolic tetraethoxysilane was rapidly added to a mixture of 7 L of ethanol and 0.6 L of 1.03 M ammonia. The mixture was stirred for 3 h. The sol was dialyzed. as Recipe from C.Y. Xu, R.I. Tang, Y.X. Hua, P.X. Zhang. Chin. J. Chem. Phys. 21 (2008) 596. PZC of a 1:1 Si–Fe mixed oxide at pH 5.1 is also reported. at Sodium silicate solution containing cyclohexane was mixed with HCl solution containing cyclohexane. Both emulsions were stabilized by a commercial surfactant. Hot water and acetone were used to remove the surfactant from the particles. 0.1 M NaCl induced a shift in the IEP to pH 3. au Interpolated (no data points for pH 3.5–6). av Commercial polydivinylbenzene beads were functionalized with poly(sodium 4-styrenesulfonate) and heated in 4:4:1 water:ethanol:tetraethyl orthosilicate mixture for 2 h at 60 °C. The particles were calcined in air at 500 °C for 2 h. aw The electrokinetic curves obtained for quartz are reported explicitly. Positive zeta potential at pH 2, negative zeta potential at pH 3, and no data points in between. The electrokinetic curves for vitreous silica, tridymite, and cristobalite are not explicitly reported, but they are described as similar to those of quartz. More details on the studied powders are reported in I. Bergman, J. Cartwright. Staub 24 (1964) 8. ax Interpolated (no data points near the IEP). Results obtained by homemade apparatus. Also 125–260 °C. ay Silica spherical particles were impregnated with SnCl2 solution. Then heated to 150 (3 h), 250 (3 h), and 550 °C (5 h). Finally silica was removed with 2 M NaOH at 90 °C, and the particles were washed with 0.1 M HCl. az Original sample. Grinding induces a shift in the IEP to lower values. Titration curves in 0.1 M NaNO3 are also reported for the original and ground specimens. ba PZC of WO3-loaded titanias derived from P-25 are also reported. bb interpolation from scattered data points. bc Also 5 other alumina- and/or silica-coated titania pigments, IEP at pH 4.5–8.7. bd 10 mL of TiCl4 was introduced to 100 mL of ice-cold water. After 30 min. the pH was adjusted to 5.5 with 25% ammonia and the mixture was aged at room temperature for 1 day. The powder was washed, dried, and calcined for 4 h. 500 and 700 °C calcination produced similar PZC. P-doped titanias were also studied. be 5 mL of 0.7 M TiCl4 in 3 M HCl was introduced to 30 mL of water at room temperature, and the pH was adjusted to 3 by 3 M NaOH. The volume was adjusted to 50 mL, and the dispersion was aged for 3 days at 60 °C without stirring. bf TiCl4 was slowly added to water ethanol mixture at 1:4:10 Ti:water:ethanol ratio. After 1 day the gel was dried then calcined at 500–800 °C. Similar procedure in the presence of surfactants resulted in lower IEP. bg Agarose gel template was soaked in 70 vol.% solution of Ti propoxide in 2-propanol. The hydrolysis was carried out in 1:1 by volume aqueous 2-propanol for 6 h. The template was removed by calcination at 420 °C for 5 h in air. bh 1.5 mL of hydrochloric acid was added to 150 mL of 10% solution of Ti tetraisopropoxide in ethanol. Then 150 mL of water was added. The gel was peptized with acid after 12 h, and the solvent was evaporated. Similar procedure was used to obtained titania coating on Stober silica, and the core–shell particles had similar IEP as TiO2. bi Solution of 26.7 g of Ti tetraisopropoxide in 186.6 g of absolute ethanol was stirred under nitrogen. Then 0.33 mL of 0.28 M HCl was added. Then 120 g of urea–ethanol–water mixture, 1:5:1 by mass was added. The gels were dried, extracted with water, and calcined at 100, 200, 300, 400, 500, and 600 °C (PZC listed in this order) for 2 h. Similar procedure was used to prepare W-doped materials. bj A film deposited from a 1:0.3:0.4:7 vol/vol mixture of Ti butoxide, acetylacetone, water, and 1-propanol was heated in air at 500 °C for 1 h. IEP in Table 1 is an arbitrary interpolation of the authors, not consistent with the published data points. bk 0.05 mol of Ti butoxide was mixed with 120 mL of absolute ethanol, 15 mL of acetic acid, and 5 mL of water. The mixture was aged for 1 day, dried, and then calcined at 700 °C for 2 h. IEP of 3% W-doped titania at pH 5 is also reported. bl Ti butoxide solution in ethanol at 1:10 Ti:ethanol ratio was adjusted to pH 2 with 1 M HCl. After 1 day the gel was dried and then calcined at 500–800 °C. Similar procedure in the presence of surfactants resulted in lower IEP or in complex electrokinetic curves with two sign reversal points. bm 1:1 v/v mixture of Ti ethoxide and ethanol was added to water to reach a 1:200 Ti:water mole ratio. Aged for 2 days. bn Material termed titanate nanotubes was obtained by hydrothermal treatment of P25 titania with 10 M NaOH at 130 °C for 1 day. The powder was washed with water, 1 M HCl, and water again. IEP of W-impregnated titanate nanotubes at pH 3.4 is reported in the same study. bo Material termed titanate nanofibers was obtained by hydrothermal treatment of P25 titania with 15 M NaOH at 150 °C for 2 days. The powder was washed with water. The original material (A) was heated at 400 (B) or 600 °C (C) for 4 h. Alternatively, powder A was autoclaved in HNO3 solution (initial pH 2) at 175 °C for 2 days (D). bp Three specimens obtained in hydrogen–air flame at various temperatures, flow rates, and molar ratios of reactants. bq Monoclinic. Agarose gel template was soaked in 70 vol.% solution of Zr propoxide in 2-propanol. The hydrolysis was carried out in 1:1 by volume aqueous 2-propanol for 6 h. The template was removed by calcination at 420 °C for 5 h in air. br Natural mineral from Gansu, China, converted into Na form. No CIP, but common PZC for 3 ionic strengths. bs No CIP, the PZC decreases with the ionic strength. IEP at pH 3 was obtained for 0.0001 M NaCl. At higher NaCl concentrations the f potential was negative over the entire pH range. bt Original/washed with 1 M ammonium acetate. bu The same study reports IEP of sonicated dispersions. A shift in the IEP caused by sonication is claimed, but the reported IEP of both raw and sonicated dispersions are based on arbitrary interpolations. bv The same study reports electrokinetic curves of two samples of maghemite (synthesized at 20 and 85 °C), and iron oxide-bentonite composites. ae

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bw

From bentonite from Cortijo de Archidona deposit, Almeria, Spain. No CIP, PZC decreases with the ionic strength. Also 50 and 70 °C. From SWy-1 Crook County Wyoming montmorillonite. No CIP. Only positive values at pH 3–10 are reported in Fig. 5. Very likely a missing minus sign is a typographical error. bz Substantial hysteresis. PZC obtained in the first titration are indicated in the table. In next titration cycles the PZC shifted to higher pH. ca Substantial hysteresis. PZC obtained in the first titration are indicated in the table. In next titration cycles the PZC shifted to higher pH. cb Polydispersed particles from Geological Specimen Supplies, Australia. The electrokinetic potential shows a substantial hysteresis at various solid-to-liquid ratios. The IEP at pH 4.5–5 was obtained in titration from high to low pH, while in back titrations from low to high pH, the IEP was at pH 6–7.5. The IEP matches the maximum in the yield stress. cc Determined from a parabolic profile of velocity of latex particles in a flat cell. cd A Negev, Israel, B Mt.Flinders, Australia. The IEP roughly matches the maximum in the yield stress in 3% dispersion. ce >99% pure from IKEDA, Japan, idealized formula KAl2(AlSi3O10)(OH)2. cf Rough interpolation (no data points for pH 3–5). Prepared from nitrates. Recipe from C. Arean et al., Z. Anorg. Allgem. Chem. 63 (2000) 2122, cited in [35]. cg Obtained from 1-propanolic solution of Mg ethoxide and Al isopropoxide by addition of water. Calcined for 6 h at 550 °C. Two specimens with 5 and 20 mol% of Al2O3 had similar IEP (interpolated from a few data points). ch Electrodeposition from 0.01 [Fe(III)+Ni(II)] solution with steel sheets as the anode and the cathode at 20 °C and 1 A/cm2. ci Produced in a continuous reactor at 85 °C and at pH 2.65 from 8 M NaOH and 0.1128 M (Fe + Si) solution composed of Fe(III) nitrate or sulfate and sodium metasilicate. The effective residence time was 45 min. cj Solution of MnCl2 and Mg(NO3)2 at 1:3 molar ratio was adjusted to pH 11 with LiOH. H2O2 was added and the precipitate was stirred in mother liquor for 2 h, and then dried and calcined at 450 °C for 4 h and leached with 0.5 M HCl. The PZC at pH 7.8 reported in the original manuscript was obtained by means of a nonstandard method, which is not recommended by the present author. ck No clear CIP, the charging curves merge over a wide pH range. cl Also 11 alumina-, silica-, and alumina-silica-coated pigments (chloride or sulfate-process), IEP at pH 2–8. cm Obtained by solid-state sintering of corresponding oxides. IEP obtained by arbitrary interpolation: no data points near the IEP. cn Three specimens synthesized with 20, 40, and 70 vol.% of Zr-precursor (with respect to Zr + Ti precursors), respectively. Agarose gel template was soaked in 70 vol.% solution of Zr and Ti propoxides in 2-propanol. The hydrolysis was carried out in 1:1 by volume aqueous 2-propanol for 6 h. The template was removed by calcination at 420 °C for 5 h. co Steel wool was stirred in 0.1 mass% NaCl bubbled with CO2. The zeta potential was measured in solution equilibrated with 1 bar CO2. cp The data points in Fig. 2 suggest that increase in pH results in sign reversal of f from negative to positive, but Fig. 5 reports a usual trend. cq The data points in Fig. 2 suggest that increase in pH results in sign reversal of f from negative to positive, which is opposite to the usual trend. cr Ni(II) basic carbonate hydrate was aged for 2 months at 250 °C in the presence of CO2 (40 atm). cs CaCO3–Nb2O5 mixture was heated at 1200 °C for 15 min in air. The product was treated with H2SO4, then with TBAOH, and finally with HCl or HNO3. Washed with water. ct 0.5 M Ca(OH)2 was titrated with 0.3 M H3PO4 to pH 9.2. cu A solution of 2.36 g of Ca(NO3)24H2O in 25 mL of water was titrated with ammonia to pH 10. A solution of 0.79 g (NH4)2HPO4 was then added and the mixture was stirred at 40 °C for 1 day while kept at pH 10. Dialyzed. The f potential was positive at pH 5.8–6.5, and negative outside this range. cv Determined from data points beyond the range of stability of apatite against dissolution. cw Solution of ZrCl4 in fuming HCl was dropped over H3PO4 at 130 °C. The Zr:P ratio was <1:2. The precipitate was aged for 4 h in mother liquor, washed, and then calcined at 800 °C for 6 h. cx >98% pure from Ward’s, 1.41% Cl, 0.56% Fe. No special efforts are reported to remove oxygen from the dispersions of chalcocite. cy No special measures to remove oxygen. cz From Rapid Bay in Broken Hill, Australia, different size fractions. The IEP of intermediate particles was <3 if any in nitrogen-purged dispersion and 4 in oxygen-purged dispersion. The IEP of fine particles was about 11 in nitrogen purged and in oxygen-purged dispersions. da From Missouri, purchased from Ward’s. Aging of virgin galena at various conditions may lead to sign reversal of f potential at pH > 7 to positive. db No special efforts are reported to remove oxygen from the dispersions. dc No special efforts are reported to remove oxygen from the dispersions. dd No special measures to remove oxygen. de Ti isopropoxide and 2,4-pentadione were added to methanolic solution of Ba(OH)2. Then HNO3 was added, and the mixture was heated at 150 °C for 3 h, and then at 700 °C for 6 h. Silica-coated material has IEP at pH 2. df A solution 0.005 M in Ti isopropoxide, 0.01 M in EDTA, 0.005 M in BaCl2, and 0.38 M in H2O2 was aged for 2 h at 60 °C, at pH 9.9 adjusted with ammonia. Particles dried at 100 °C and those calcined at 550 °C had the same IEP. dg Positive zeta potential at pH 3.5, negative zeta potential at pH 7, and no data points in between. The IEP reported in the original paper is based on arbitrary interpolation. dh A, original; B-D, HNO3-treated at 90 °C for 6 h, then washed with B, water; C, NaOH; sample D after HNO3 treatment was evacuated for 12 h at 307 °C; sample E was obtained by hydrogen treatment at 900 °C for 3 h. Sample F was obtained from sample E by treatment with solution of sulfuric and nitric acid in acetic anhydride followed by reduction with aqueous solution of ammonia and sodium dithionite. di Original/modified. Treatment with boiling 1:1 nitric acid for 3 h was followed by water-washing, drying, and heating at 300 °C for 1 h in air. dj A, HNO3 and HF-treated; B, A treated with 13% H2O2; C, A heated in Ar at 1400 K, and equilibrated with air at room temperature. dk A, HCl-washed; the other samples were derived from sample A: B, treated with 10 M H2O2 at room temperature for 1 day; C, treated with 10 M H2O2 at 363 K for 1 day; D, treated with 10 M HNO3 at room temperature for 1 day; E, treated with 10 M HNO3 at 363 K for 1 day; F, treated with 5 M HNO3 at 363 K for 4 h. dl Nitrogen treatment of the original specimen at 905 °C followed by exposition to air at room temperature resulted in a shift in IEP to pH 10.9. Nitrogen treatment of the original specimen at 905 °C followed by exposition to oxygen at 42 °C resulted in a shift in IEP to pH 10.1. dm Nitrogen treatment of the original specimen at 905 °C followed by exposition to oxygen at 42 °C resulted in a shift in IEP to pH 9.4. dn Nitrogen treatment of the original specimen at 905 °C followed by exposition to oxygen at 42 °C resulted in a shift in IEP to pH 11. do The precursor was soaked in phosphoric acid at 1:1 mass ratio. Samples A were carbonized in a microwave reactor (different times), and sample B was carbonized at 600 °C, both under nitrogen. Then the products were washed with water, dried, and stored in desiccator. dp Cherry stones were carbonized in nitrogen at 900 °C for 2 h. Then activated by means of CO2 (A, 2 h) or steam (B, 3 h) at 850 °C. Samples C and D were obtained from A and B, respectively, by treatment with ozone for 1 h at 25 °C. dq Cherry stones were carbonized in nitrogen at 500 °C for 2 h and then activated by means of KOH or ZnCl2 added to the char in different proportions. The activation was performed at 500 °C for 4 h in nitrogen. The material was washed with 0.1 M HCl, and then with water. The results are presented in graphical form, with many overlapping data points. dr Palm stones were carbonized at 450 °C in nitrogen, and activation was carried out in CO2 at 800 °C. (continued on next page) bx

by

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dt

Also 3 Ca-impregnated charcoals from spruce wood. Carbonized at 400 °C for 1 h under nitrogen. Activated at 700 (samples B–E) or 800 °C (samples F–I) in CO2. Burnup %: B, 16; C, 22; D, 30; E, 39; F, 21; G, 35; H, 40; I, 70. du Cellulose acetate-based organic gel was supercritically dried and pyrolyzed at 1000 °C in nitrogen for 1 h. A, original; B, oxidized for 2 days with 5 M H2O2 at room temperature; C, oxidized for 2 days with 4 M HNO3 at room temperature; D, impregnated with melamine and then heated at 750 °C in nitrogen for 1 h. dv Cellulose acetate-based organic gel was supercritically dried and pyrolyzed at 1100 °C in nitrogen for 1 h. A, original; B, heated at 400 °C in ammonia for 3 h; C, oxidized for 2 days with 4 M HNO3 at room temperature and then heated at 400 °C in ammonia for 3 h. dw 15 g of melamine was dissolved in a mixture of 419 cm3 of water and 81 cm3 of 37% formaldehyde. 2.5 cm3 of formic acid was added, and the mixture was stirred for 10 min. The particles were removed by sedimentation at room temperature and washed with water. Increase in the ionic strength to 0.01 M induced a shift in IEP to lower pH. dx Styrene was heated at 65 °C with aqueous acetate buffer under nitrogen for 20 min. Then 2,20 -azobis[N-(2-carboxylethyl)-2-methylpropionamidine] tetrahydrate was added. Magnetic particles (magnetite nanoparticles embedded in latex) had a similar IEP. dy Potentiometric titration curves are also presented. * No data points reported, only PZC/IEP value.

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Table 1 (continued)

12

standards. Thus the ‘‘best” rejected paper is only slightly superior to the ‘‘worst” included paper, and the decision (include or ignore) is based on limited information included in the original publication, and on an arbitrary judgment of the present author. For example, the papers on materials, which are very well-documented (alumina, titania) were subjected to higher standards than papers on exotic materials, for which high-quality data do not exist at all. Many scientists believe that scientific papers which obtain many citations are superior to those which obtain fewer citations. By citing ‘‘correct” and not citing ‘‘incorrect” papers, more credit is given to the former. Otherwise, both ‘‘correct” and ‘‘incorrect” papers receive the same score. Therefore, only a few examples of erroneous and/or misleading results from the recent literature are discussed in this review. 1.2. Examples of erroneous and/or misleading results reported in the recent literature A substantial fraction of recently published apparent PZC/IEP is rather indirectly related to the PZC/IEP in their usual meaning, and this is a real challenge for a reader, who is looking for the values of PZC/IEP of specific material in primary sources. Therefore a few issues are discussed, which may seem obvious, yet several recent papers show that different approaches to those apparently obvious questions are possible. It should be emphasized that the choice of the examples discussed below was arbitrary, and the issues discussed below must not be considered as the ‘‘worst” or ‘‘most important” errors in the recent PZC/IEP literature. A few results from those papers are valuable, and they are reported in Table 1. For example in a very recent paper [9] IEP is defined as a minimum in the f potential in an electrokinetic curve with only positive values. This approach is in contradiction with the usual definition, in which the f potential is positive at pH below the IEP and negative above the IEP. Thus a U- or V-shaped electrokinetic curve with a minimum at f = 0 does not imply an IEP, according to the present definition. In another recent paper [10] the IEP was obtained by means of a procedure, described in more detail in a previous paper of the same authors [11]. In that procedure the f potential was not plotted against the equilibrium pH of the dispersion, in which the electrokinetic measurement was carried out, but against a pH of a solution used in preparation of that dispersion. The particles do not ‘‘remember” the pH value of a solution once used in preparation of the dispersion, but they adjust their surface charge and f potential according to the current composition of the solution. Thus, the pH of a dispersion should be measured just before or just after the electrokinetic measurement. Many modern zeta-meters perform such a measurement automatically by means of a built-in pH-meter. Apparent PZC values of serpentine and chlorite obtained by a salt addition (Mular–Roberts) method are reported in [12]. This method is based on the assumption that the titration curves obtained at different ionic strengths have a common intersection point CIP, which is true for metal oxides, but not necessarily for serpentine or chlorite. Therefore, Mular–Roberts is not universal, and it is not recommended in materials, in which the occurrence of CIP is not certain. 2. Structure of Table 1 Table 1 is organized according the same rules as Table 1 in Ref. [3]. The organization scheme is illustrated in Fig. 1. The materials are organized into 13 categories such as metal oxides, clay minerals, and salts. An idealized chemical formula reported in Table 1 is not necessarily identical with the actual composition of the specimen. For example, the specimens referred to as magnetite [Fe(II/III)

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erably a combination of both as the most credible methods to determine the PZC of metal oxides, while with other materials (e.g., in clay minerals), CIP often does not occur, as discussed above. The surface charging is interrelated with several physical quantities as the rate of coagulation, viscosity of dispersions, contact angle, etc. The relationship between the PZC/IEP of bulk metal oxides and the properties of oxide films on passive metals was discussed in [13]. The PZC based solely on the studies of pH effect on quantities other than uptake of protons from solution or electrokinetic potential were not considered in this review, but the reported correlations, e.g., between the IEP and a maximum in the viscosity of dispersion, are indicated in the footnotes of Table 1. Along with the newly reported data, Table 1 reports the PZC/IEP of similar materials taken from [2,3] if such data are available. A median value is reported for specimens with 3 or more references in [2,3]. The numbers in brackets denote that only PZC obtained by means of less credible methods (pH, intersection) are available. The asterisk in Table 1 denotes that only the value of PZC/IEP is reported in the original paper (no data points). For all specimens, a section in [2] is indicated reporting PZC/IEP of similar (but not necessarily identical) materials. Blank cells in Table 1 denote that specific data are not available or not applicable. 3. Discussion of Table 1 3.1. Choice of specimens

Fig. 1. Organization scheme of Table 1.

oxide] are usually partially converted into maghemite [Fe(III) oxide]. Within each category the materials are sorted primarily by their chemical formulas, and then according to their source (commercial, home-synthesized, and naturally occurring materials). The details of the source (trade name, recipe, etc.) are specifically reported in the second column of Table 1. The nature of electrolyte, temperature, method, and instrument used in the surface charging measurements are reported in separate columns of Table 1. Several details reported in Table 1 are not explicitly available from the cited references, but they were taken from the references therein or obtained from the authors as personal communications. Many different experimental protocols have been used to determine the PZC/IEP, and very different terminology has been used to describe those methods. They can be sorted into the following main categories:  cip (common intersection point of potentiometric titration curves obtained at three or more ionic strengths or equivalent methods including the aforementioned Mular–Roberts method),  intersection (intersection point of potentiometric titration curves obtained at two ionic strengths),  pH (natural pH of the dispersion, e.g., mass titration and potentiometric titration at one electrolyte concentration),  iep (isoelectric point obtained by means of electrophoresis, electroosmosis, streaming potential, or electroacoustic method). These methods and their terminology were discussed in more detail in [2]. The present author recommends cip and iep, and pref-

PZC of albite, sepiolite, and sericite originally published in 2009 or 2010, and reported in Table 1, are probably the first ever published PZC of these materials. On the other hand, most other results reported in Table 1 refer to materials whose PZC is already welldocumented, and even to certain specimens (e.g., P-25 titania from Degussa), for which dozens of PZC values have been published. Thus, accumulation of data for a few materials is continued, while new data on less well-documented materials are scarce. It should be emphasized that a few apparent PZC of exotic materials published in the recent literature were deliberately not included in Table 1 due to inadequate experimental procedures, presence of strongly adsorbing species, etc. Several recent studies were carried out with specimens of apparently well-documented materials, which have been synthesized with special care. This includes avoidance of specific impurities (as silica and/or CO2), which might have affected the PZC reported previously for similar materials, recipes aimed at crystals of specific morphologies, etc. 3.2. Methods Most new data on PZC have appeared in journals devoted to colloid and interface chemistry. The recommendations of the present author [2] are based on the standards observed in those journals and described in detail by Lyklema [7]. On the other hand, a growing interest in surface charging in other parts of the scientific community is observed, and a substantial fraction of new results have appeared in other journals. Interestingly enough, some groups of scientists appear to have established their own standards, which do not match the standards observed in the colloid science community. This may be due to the reviewing system in scientific journals, which prefers referees who publish in the same journal. The concept of surface charging is frequently used by geochemists, and their studies mostly comply with the standards established in the colloid science community. In contrast the scientists interested in synthesis of catalysts often use mass titration as the sole method to establish the PZC. That method is fast and easy, but also very sensitive to minor amounts of acidic or basic impurities,

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occurring in the materials; thus the credibility of such PZC is limited. The existing knowledge is often ignored in the newly published studies. For example, most PZC were reported without the information about the temperature (cf. Table 1). The surface charging is temperature dependent, and a difference of 1 °C may induce a shift in the PZC by up to 0.03 pH unit. This is especially important in the authors who consider the second decimal place in their PZC as significant. The IEP of sulfides and nitrides is strongly affected by the redox reactions; thus the control over oxygen in the electrokinetic studies is essential, but this problem was ignored in many recent electrokinetic studies of sulfides or nitrides. 3.3. Values of PZC Most results reported in Table 1 confirm the well-established PZC reported for similar materials in older literature. This is not surprising considering that the specimens whose PZC is close to the ‘‘recommended” value for certain compound (as Degussa C alumina or P-25 titania) are studied more frequently than other specimens. The problem of biased choice was identified and discussed in more detail elsewhere [2]. References [1] G.A. Parks, Chem. Rev. 65 (1965) 177. [2] M. Kosmulski, Surface Charging and Points of Zero Charge, CRC, Boca Raton, FL, 2009. [3] M. Kosmulski, J. Colloid Interface Sci. 337 (2009) 439. [4] B. Michen, T. Graule, J. Appl. Microbiol. 109 (2010) 388. [5] L. Besra, T. Uchikoshi, T.S. Suzuki, Y. Sakka, J. Eur. Ceram. Soc. 30 (2010) 1187. [6] V. Glibin, L. Svirko, I. Bashtan-Kandybovich, D. Karamanev, Surface Sci. 604 (2010) 500. [7] J. Lyklema, Fundamentals of Interface and Colloid Science, vol. 2, Academic Press, London, 1995. [8] D.A. Dzombak, F.M.M. Morel, Surface Complexation Modeling: Hydrous Ferric Oxide, Wiley-Interscience, New York, 1990. [9] H. Xu, I.P. Shapiro, P. Xiao, J. Eur. Ceram. Soc. 30 (2010) 1105. [10] A. Vincent, T.M. Inerbaev, S. Babu, A.S. Karakoti, W.T. Self, A.E. Masunov, S. Seal, Langmuir 26 (2010) 7188. [11] S. Patil, A. Sandberg, E. Heckert, W. Self, S. Seal, Biomaterials 28 (2007) 4600. [12] M. Alvarez-Silva, A. Uribe-Salas, M. Mirnezami, J.A. Finch, Miner. Eng. 23 (2010) 383. [13] E. McCafferty, Electrochim. Acta 55 (2010) 1630. [14] S.M. Maliyekkal, L. Philip, T. Pradeep, Chem. Eng. J. 153 (2009) 101. [15] E.J. Teh, Y.K. Leong, Y. Liu, V.S.J. Craig, R.B. Walsh, S.C. Howard, Langmuir 26 (2010) 3067. [16] E.J. Teh, Y.K. Leong, Y. Liu, B.C. Ong, C.C. Berndt, S.B. Chen, Powder Technol. 198 (2010) 114. [17] S. Bertazzo, K. Rezwan, Langmuir 26 (2010) 3364. [18] M.R. Das, J.M. Borah, W. Kunz, B.W. Ninham, S. Mahiuddin, J. Colloid Interface Sci. 344 (2010) 482. [19] M. Del Nero, C. Galindo, R. Barillon, E. Halter, B. Made, J. Colloid Interface Sci. 342 (2010) 437. [20] K. Polyak, E. Racz, J. Hlavay, Mag. Kem. Fol. 101 (1995) 189. [21] J. Hlavay, K. Polyak, J. Colloid Interface Sci. 284 (2005) 71. [22] K.S. Kho, E.J. Teh, Y.K. Leong, Langmuir 25 (2009) 3418. [23] M. Kosmulski, P. Prochniak, E. Maczka, J.B. Rosenholm, J. Phys. Chem. C, in press. [24] E. Tombacz, M. Szekeres, Appl. Clay Sci. 27 (2004) 75. [25] E. Tombacz, Period. Polytech. Chem. Eng. 53 (2009) 77. [26] E.J. Elzinga, Y. Tang, J. McDonald, S. DeSitso, R.J. Reeder, J. Colloid Interface Sci. 340 (2009) 153. [27] A. Debczak, J. Ryczkowski, J. Patkowski, Appl. Surf. Sci. 256 (2010) 5449. [28] M.A. Dinamarca, C. Ibacache-Quiroga, P. Baeza, S. Galvez, M. Villarroel, P. Olivero, J. Ojeda, Bioresource Technol. 101 (2010) 2375. [29] C. Alliot, L. Bion, F. Mercier, P. Toulhoat, J. Colloid Interface Sci. 287 (2005) 444. [30] J. Lutzenkirchen, R. Zimmermann, T. Preocanin, A. Filby, T. Kupcik, D. Kuttner, A. Abdelmonem, D. Schild, T. Rabung, M. Plaschke, F. Brandenstein, C. Werner, H. Geckeis, Adv. Colloid Interface Sci. 157 (2010) 61. [31] M. Wisniewska, S. Chibowski, T. Urban, J. Colloid Interface Sci. 334 (2009) 146. [32] S. Chibowski, M. Wisniewska, T. Urban, Adsorption 16 (2010) 321. [33] H. Chen, Z. Xu, H. Wan, J. Zheng, D. Yin, S. Zheng, Appl. Catal. B 96 (2010) 307. [34] H.M. Jang, J.H. Moon, C.W. Jang, J. Am. Ceram. Soc. 75 (1992) 3369. [35] J.N. Diaz de Leon, M. Picquart, M. Villarroel, M. Vrinat, F.J. Gil Llambias, F. Murrieta, J.A. de los Reyes, J. Mol. Catal. A 323 (2010) 1.

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