On the nature of the energetic surface heterogeneity in ion adsorption at a water oxide interface: the behavior of potentiometric, electrokinetic, and radiometric data

pH-dependent surface charging of metal oxides

“…Considering the high specific surface area of alumina measured in general by means of potentiometric acid-base titration method and the endeavor of experimenters to reach equilibrium state of surface-charging by increasing the time of titration, it is highly probable to suppose that the experimental charge potential curves are disturbed by the H + /OH − consumption from dissolution, even those which were measured over the likely dissolution-free pH range. In some works, the possibility of alumina dissolution is excluded with reference to the chemical equilibrium calculation [34] or it is not mentioned [37]- [39] at all. Fitting of experimental surface-charging curves led to more and more complicated theoretical approaches with increasing number of layers for charge-compensating ions in the surface complexation models (diffuse double-, triple-, and four-layer models [38,39]) and with introducing surface site heterogeneity parameters.…”

“…Fitting of experimental surface-charging curves led to more and more complicated theoretical approaches with increasing number of layers for charge-compensating ions in the surface complexation models (diffuse double-, triple-, and four-layer models [38,39]) and with introducing surface site heterogeneity parameters. The heterogeneity of proton binding sites at oxide-solution interface is studied theoretically [40]- [42] and both theoretically and experimentally [5,34,37]- [39,43]. Based on potentiometric titration performed over a broad range of pH's (3-11), affinity distributions for four different surface sites were calculated with the aim of studying the heterogeneity of acid-base properties at aluminum oxide-solution interface [43].…”

Effects of surface heterogeneity of oxides in simple ion adsorption at oxide/electrolyte interfaces

“…2), T is the temperature, e is the elementary charge and k is the Boltzman constant. The knowledge of PZC (Point of Zero Charge) experimental value and the knowledge that in most systems the PZC value does not practically depend on salt concentration in the bulk solution, (i.e., a common intersection point (CIP) occurs at pH = PZC) Kallay et al, 1990;Sprycha, 1984) make it possible to obtain the following relations (Rudzifiski et al, 1992): Except of the two intrinsic equilibrium constants and the density of the surface sites N, as the parameters (Rudzifiski et al, 1992), the triple layer model assumes two values of the parameter cl to exist, depending on the sign of the charge of the surface (Blesa and Kallay, 1988):…”

“…A similar effect has been known for a long time in gas adsorption onto solid surfaces. In another paper, Rudzifiski et al (1992) showed that titration curves were much less sensitive to the surface heterogeneity than individual adsorption isotherms of ions measured by using radiometric methods. Titration curves probably involve a certain mutual cancellation of heterogeneity effects.…”

1pK and 2pK Protonation Models in the Theoretical Description of Simple Ion Adsorption at the Oxide/Electrolyte Interface: The Analysis of Temperature Dependence of Potentiometric Titration Curves

“…from the condition that the experimentally observed PZC is practically independent of the salt concentration (16,18,14). From the system of equations δ 0 (pH = PZC) = 0 and ∂δ 0 (pH = PZC) ∂a = 0, [15] the following relations are obtained:…”