ABSTRACT
The high reactivity of freshly cleaved metal oxide surfaces toward water shows itself through the strong chemisorption of water vapor at very low partial pressures. At low degrees of coverage, dissociative chemisorption takes place through the interaction with acidic and basic surface sites. Hydroxylated sites formed by water adsorption on very reactive sites do not dehydroxylate reversibly. High temperatures are required and surface reconstruction results in the passivation of the surface. Hydrophobic surfaces may result, as in the case of quartz, with very low densities of sites characterized by a high Lewis acidity or basicity. Many minerals and ceramic materials are of this type. The diffuse-layer model of the metal oxide/solution interface was first proposed by Stumm and co-workers and is perhaps the simplest representation of the metal oxide/solution double layer. Metal ions form mixed complexes in solution, in which different ligands complete the metal ion coordination sphere.
