ACIDO-BASIC PROPERTIES OF SIMPLE OXIDE SURFACES .2. A SIMPLE-MODEL

We present a quasi-analytical model for the adsorption of H+ and OH- species on oxide surfaces, in order to characterize their acido-basic character. The following contributions to the adsorption energies are considered: electron delocalization effects, electrostatic energy, ion internal energies and short-range repulsion. We show that covalent interactions between the surface and the absorbates drive the adsorption, in contrast to the pure electrostatic model by Parks [Chem. Rev. 65 (1965) 177]. We stress the relevance of some microscopic parameters, such as the value of the Madelung field at oxide surface sites, the anion-cation bond length, the cation charge....,in determining the acido-basic character of oxides, and we explain which role these parameters play in the various microscopic interactions.