Calorimetric Effects Accompanying Ion Adsorption at the Charged Metal Oxide/Electrolyte Interfaces:  Effects of Oxide Surface Energetic Heterogeneity

Abstract

A quantitative theoretical analysis of the enthaplic effects accompanying ion adsorption at the oxide/electrolyte interface, based on a model of energetically heterogeneous surface oxygens, is presented. The triple layer complexation model is accepted, along with the 2-pK charging mechanism. For the purpose of illustration a set of experimental data is subjected to that quantitative analysis including titration curves, radiometrically measured individual iostherms of ions, and calorimetric titration data for the alumina/NaCl electrolyte system. Two models of energetic heterogeneity were taken into consideration. One of them assumes that the binding-to-oxygen energies of the surface complexes vary but are highly correlated when going from one to another surface oxygen. The other model of surface heterogeneity assumes that these correlations are very small. Our numerical simultaneous analysis of the titration data, of the individual isotherms of Na+ and Cl- adsorption, and of the accompanying heat effects advocates strongly for the model of surface heterogeneity assuming small correlations to exist. A good simultaneous fit of all three kinds of experimental data is obtained, with a small uncertainty as for the values of the estimated adsorption parameters. A simultaneous fit of the measured enthalpic effects appears to be an especially strong criterion for a proper choice of adsorption parameters.

The influence of surface energetic heterogeneity on electrofluidic gating of a metal oxide surfaces

“…Assuming Gaussian-like distribution of adsorption energy one arrives at the following expressions for the mean surface coverage by the i-th adsorption complex (Rudzinski et al 1998),…”

“…To simplify our analysis we assumed in calculations that heterogeneity parameters of different complexes have the same value kT c . This means that we assumed that interactions between SO À groups and different monovalent ions are highly correlated (Rudzinski et al 1998).…”

“…The real surfaces are energetically heterogeneous and this fact should be considered in the theoretical description of any adsorption process. Models assuming energetic heterogeneity of surface have been successfully applied to described gas adsorption on solids (Rudzinski and Everett 1992), molecules adsorption from solution (Podkościelny and Nieszporek 2007) and ion adsorption from electrolyte solutions on metal oxides (Rudzinski et al 1998).…”

Calorimetric Effects and Temperature Dependence of Simple Ion Adsorption at Oxide/Electrolyte Interfaces: The Systems in Which PZC and CIP Do Not Coincide

“…To express ψ 0 (pH) dependence, which occurs in the equations for the individual adsorption isotherms θ i 's, and for the surface charge δ 0 , we accepted in our works (34,39 …”

“…Although more refined mechanistic models have alos been proposed (43), and other charging mechanisms considered (43)(44)(45)(46)(47)(48), the majority of the potential readers and users may still be interested in applying the adsorption model most familiar to them. That popular model has been elaborated further by Rudzinski and co-workers taking into account the energetic heterogeneity of the real oxide surfaces (33,39). This development leads to a better agreement with experiment, but does not change substantially the information deduced from experiment.…”