Density functional study of adsorption of Agn (n = 2, 4, 8) on partially reduced TiO2 (1 1 0) surface

The adsorption of Agn (n = 2, 4, 8) clusters on the partially reduced rutile (1 1 0) surface have been studied using DFT slab calculations. The geometry and electronic structure of silver clusters adsorbed near the oxygen vacancy as well as binding mechanism have been investigated. It has been found that the binding occurs through two types of interaction. Firstly, it is the interaction between cluster's HOMO and surface eigenstates located on hollow-Ti atoms and, secondly, the overlap of MOs of the cluster with bridging oxygen atoms. The first type leads to charge transfer from the adsorbed cluster to the surface, therefore silver particles become positively charged upon adsorption. The second type leads to the deformation of adsorbed silver cluster, thereby increasing the overlap. The interaction between molecular orbitals of the cluster and orbitals of atoms lying at the vacancy is unlikely. It has been shown that the adsorption energy of Agn clusters on stoichiometric surface are higher than those for reduced surface. Thus, the adsorption of silver clusters occurs preferably on stoichiometric surface far from oxygen vacancies.