Journal of Colloid and Interface Science 275 (2004) 214–224 www.elsevier.com/locate/jcis pH-dependent surface charging and points of zero charge II. Update Marek Kosmulski Department of Electrochemistry, Lublin University of Technology, Nadbystrzycka 38A, 20618 Lublin, Poland Received 3 December 2003; accepted 5 February 2004 Available online 18 March 2004 Abstract Recently published PZC (points of zero charge) of metal oxides and related materials are compiled to update the previous compilations (M. Kosmulski, Chemical Properties of Material Surfaces, Dekker, New York, 2001; J. Colloid Interface Sci. 253 (2002) 77). The elec- troacoustic method has been widely used; it has become a standard tool, and it has proved to produce IEP (isoelectric points) comparable with those obtained by means of classical electrokinetic methods. The recently published numerical values of PZC/IEP of various materials corroborate the old results, with one exception: the PZC of magnetite found at pH 8 is substantially higher than the values reported in the old literature. New approaches to the electrokinetics of sparingly soluble salts have recently been proposed; e.g., the hysteresis in electrokinetic curves of (nominally) BaTiO 3 has been interpreted in terms of changes in the surface stoichiometry caused by leaching.  2004 Elsevier Inc. All rights reserved. 1. Introduction The famous compilation by Parks [1] published in 1965 is the most frequently quoted source of the pristine points of zero charge (PZC) of metal oxides and related materi- als (Fig. 1). Recent progress in the field and demand for reliable and up-to-date pristine PZC of various materials en- couraged the present author to compile the results published over the periods 1966–1999 [2] and 2000–2001 [3]. Very re- cent results (2002–2003) and a few older results overlooked in previous searches are compiled in the present paper, in Table 1. The style of the original tables from Ref. [2] is preserved in Table 1 to facilitate combination of the present compi- lation with the previous ones. The materials are sorted into a few groups (simple metal oxides, aluminosilicates, mixed oxides, salts, and other materials) and listed by chemical formula within each group (salts are sorted by anion, and then by cation). Trade names of commercial materials and the origins of natural minerals are reported, and prepara- tion of synthetic materials is briefly described. The formula and concentration (concentration range) of the supporting E-mail address: kosmulsk@hermes.umcs.lubin.pl. electrolyte (alkali halide, chlorate VII, or nitrate V) and the temperature are also reported, when available. The results reported in Table 1 were obtained by various methods, which are sorted into a few categories (detailed de- scriptions of the methods can be found elsewhere [2]): • CIP (common intersection point of potentiometric titra- tion curves obtained at three or more ionic strengths); • Intersection (intersection point of potentiometric titra- tion curves obtained at two ionic strengths); • pH (natural pH of the dispersion); • IEP (isoelectric point obtained by classical electroki- netic methods); • Acousto (isoelectric point obtained by the electroa- coustic method). Specific adsorption induces shifts in the CIP and IEP in two opposite directions; thus matching CIP and IEP is very likely to indicate the pristine PZC. On the other hand, dis- crepancies between the CIP and IEP indicate insufficient purity of the powder [4]. “Potentiometric mass titration” [5], recently proposed as a new method to determine the PZC, can produce meaning- ful results when the powder is very pure (free from soluble acidic or basic impurities). The discrepancies between the results obtained by means of potentiometric mass titration, 0021-9797/$ – see front matter  2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2004.02.029