On derivatives of surface charge curves of minerals

Surface charge characterization of metal oxides by potentiometric acid–base titration, revisited theory and experiment

“…Numerous weaknesses of seemingly well-established practices became evident for us, the discussion of which may contribute to clear up the chemical nonsense of widely scattered PZCs in literature. Our efforts to solve these problems are in line with those of Lützenkirchen and co-workers (see for example in [22,54,57]), who have also found that "true" surface charge values cannot be obtained from the titrations mainly because of impurities, data imprecision and side effects. The careful survey of possible errors in titrations presented here is based on our experience of decades' standing; the conclusion is a comprehensive method to assess pure surface protonation/deprotonation equilibria of metal oxides established theoretically and proven in practice.…”

“…Unfortunately, similar changes are frequently assigned in the literature to surface sites with pK at the inflection point of the abrupt increase [53]. Critical analysis can help to justify or rule out the possibility of additional new pKs at the inflection points [54]. Surface charging is ionic strength dependent by virtue [55], thus the "opening" of the net proton consumption vs. pH curves at different ionic strengths is a prerequisite to consider net proton consumption as net specific surface proton excess.…”

Defining reactive sites on hydrated mineral surfaces: Rhombohedral carbonate minerals

“…Nevertheless, the quantitative characterization of the reactivity of individual primary surface sites is far from trivial because the proper calibration of these multi-site, multi-reaction models requires: (i) uniform and/or well-characterized mineral surfaces in terms of chemical composition and microtopography (Barrow et al, 1993;Piasecki et al, 2001), (ii) suitable and sufficient experimental data arising from various independent sources and carrying sufficient information to properly resolve the energetic contributions of individual surface sites (Rudziń ski et al, 1992(Rudziń ski et al, , 1998Piasecki et al, 2001), and (iii) the application of sophisticated mathematical treatments (Chandler, 1987;Jäger, 1991;Borkovec and Koper, 1994). For instance, it is well known that, because of compensating effects, the composite adsorption (or surface charge) isotherms obtained from titration experiments that are typically used for the calibration of adsorption chemical models, are largely insensitive to surface energetic heterogeneity, and therefore, additional data (e.g., potentiometric, electrokinetic, radiometric, calorimetric) are required to properly discriminate among potential heterogeneity models and prevent misleading over-interpretations of available data (van Riemsdijk et al, 1987;Blesa and Kallay, 1988;Cerník et al, 1995;Rudziń ski et al, 1992Rudziń ski et al, , 1998Lü tzenkirchen, 2005). Furthermore, the presence of surface irregularities (e.g., steps, kinks and dislocations), chemical micro-heterogeneities, and multi-domain crystal surfaces, difficult to characterize experimentally, add to the complexity of multi-site models, so that the physical-chemical significance of the derived model parameters and their application to natural systems is seriously questioned (Lü tzenkirchen, 1997).…”

Physico-Chemical Characterization and Interfacial Electrochemical Properties of Nanoparticles of Anatase-TiO2 Prepared by the Sol-Gel Method

“…The experimental measures of this charge are obtained by the potentiometric titrations of the solid suspensions prepared in the presence of a known constant concentration in electrolyte 16 .…”