Adsorption of Ag4 cluster on stoichiometric TiO2 (1Â 1Â 0) surface: Quantum chemical study

Titanium dioxide with silver nanoparticles deposited on the surface is known to exhibit higher photocatalytic activity than the uncovered TiO2. A study of the electronic structure of such systems is necessary to understand this effect. A quantum chemical study of silver tetramers adsorption on stoichiometric rutile (1 1 0) surface has been carried out using periodic DFT calculations. A number of adsorption positions, which correspond to two basic adsorption sites on TiO2 (i.e. bridging oxygen rows and hollow sites) have been considered. The hollow sites turned out to be preferable for Ag4 adsorption. The population analysis has been performed to study mechanism of interaction between Ag4 and TiO2 surface. The binding has been shown to occur mainly through the interaction between cluster HOMO and rutile conduction band eigenstates. A significant overlap between Ag4 HOMO and titanium orbitals has been found in the case of hollow site adsorption, in contrast to adsorption over bridging oxygen rows, where there is only weak binding towards oxygen atoms. The adsorbed cluster has been found to have a significant positive charge, which is a result of a charge transfer into conduction band.