Ab-initio Simulations ofCopper Oxide Nanowires and Clusters on TiO2(101)Anatase Surface

Abstract

Copper oxides deposited at titania surfaces have a beneficial effect on the photocatalytic activity of TiO2, but their role is not fully understood. In this work, possible nanostructures of copper oxide on TiO2 (101) have been investigated by simulations based on density functional theory. Various stoichiometries, from Cu2O to CuO, and morphologies, from clusters to nanowires, have been considered. Nanowire structures were consistently more stable than isolated clusters. In these structures, a Cu2O stoichiometry was found to be thermodynamically more stable than CuO at room conditions, in contrast to what happens in bulk copper. Occupied Cu 3d and O 2p states extend well into the band gap of titania, whereas the nature of the lowest-lying empty states depend on the stoichiometry: for Cu2O they consist mostly of Ti 3d orbitals, while in CuO unoccupied Cu 3d orbital ∼0.8 eV above the Fermi level are present. Thus, both oxides reduce the band gap of the system with respect to pure titania, but only Cu2O should be effective in separating photogenerated electrons and holes. These results provide insight into the role of copper oxides in the photocatalytic process.