A study on the band gap and the doping level of V-doped TiO2 with respect to the visible-light photocatalytic activity.

The visible-light response is a necessary but not a sufficient condition for semiconductor photocatalyst to function as a visible-light active photocatalyst. To shed more light on the issue of visible-light response of semiconductor photocatalysts, the band-gaps and the doping levels of multivalency vanadium-doped TiO2 were investigated from sonochemically prepared samples. Sonochemical doping, which relies on acoustic cavitation phenomena, is a one step process excluding chemical synthesis, and three types of vanadium doped TiO2 nanopowder were prepared using such vanadium oxides as V2O3, V2O4, and V2O5. The band-gaps of as-prepared samples were obtained from the diffuse reflectance measurement, and the doping levels of vanadium in these samples were measured using electron probe micro analyzer. In addition, X-ray photoelectron spectrometer was introduced to complement electron probe micro analyzer. Furthermore, quantum-chemical calculations on simple cluster models for TiO2 and V-doped TiO2 were performed, and the resulting computational results in conjunction with experimental findings provided valuable information on oxygen vacancy and doping mechanism.