Effect of intervalence charge transfer on photocatalytic performance of cobalt- and vanadium-codoped TiO2 thin films. (14th December 2015) - Chen, Wen-Fan
Abstract: Co- and V-codoped TiO2 thin films were prepared by sol–gel, spin coated on glass substrates, and annealed at 450 °C for 2 h. The data suggest substitutional solid solution formation in the anatase films. Macroscopic roughening at the highest dopant levels was attributed to oversaturation, precipitation, and grain boundary pinning. Methylene blue decomposition correlated directly with the grain size and this was attributed to the associated changes in surface area and number of active sites as well as partial amorphisation. X-ray photoelectron spectroscopy data revealed the presence of Ti 4+, Co 2+, possibly Co 3+, V 3+, and V 4+, where the three clearly detected dopant valences were present as thermodynamically non-equilibrium valences under the annealing conditions used. The present work introduces the concept of intervalence charge transfer to explain the presence of these non-equilibrium species. The present work also considers briefly the potential roles of crystal field stabilization and defect equilibria relative to intervalence charge transfer. Highlights: Three key mechanisms influenced the photocatalytic properties of codoped TiO2 films. Intervalence charge transfer was the dominant mechanism at high dopant levels. Modification of band gap improved performance at the lowest dopant level. Effect of contaminants that diffused from the glass to the film was minimal.