A combined temperature-calorimetric study of ion adsorption at the hematite-electrolyte interface: II. Models of a heterogeneous oxide surface

The two hematite/KNO3 adsorption systems investigated in Part I are now sub jected to a more refined quantitative analysis based on the models of an en ergetically heterogeneous oxide surface. The estimated parameters lead to a much more consistent, simultaneous fit of both titration isotherms and the related directly measured enthalpic effects. That quantitative analysis re veals that the differences in the preparation of these two hematite samples result in substantial differences in the heats accompanying ion adsorption . Generally, the more porous surface is, the lower are the heats of proton and cation adsorption, due probably to a deeper dehydratation of adsorbed i ons. Our quantitative analysis also reveals substantial electrostatic contr ibutions to the observed enthalpic effects, as well as contributions caused by surface energetic heterogeneity.