RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

Several heterogeneous electrolyte adsorption models are derived. The underlying assumptions for these models and their applicability are discussed. It is shown that the pristine point of zero charge (PPZC) may well be a function of the degree of surface heterogeneity. On the other hand model calculations show that the shape of the surface charge (σ₀)-pH curves is very insensitive towards the degree of heterogeneity. It thus follows that σ₀-pH curves for metal oxides, exhibiting some degree of heterogeneity, may be described with a homogeneous electrolyte adsorption model. Interestingly it appears that the titration curves of TiO₂ in KNO₃ can be described equally well using a “one-pK” model as with a “two-pK” model.