Visible light-induced photobleaching of methylene blue aqueous solution using (Sr1−xLax)TiO3+δ–TiO2 composite powder

We have investigated the charge flow through heterojunction, which consists of two semiconductors possessing the equivalent energies of the conduction band edges as well as the valence band edges. The composite powders possessing heterogeneous microjunctions prepared by precipitating anatase-type TiO2 layers on perovskite-type (Sr0.95La0.05)TiO3+δ particles from TiOSO4 aqueous solution; the (Sr0.95La0.05)TiO3+δ powder absorbed light with λ < 550 nm. Under visible light irradiation with λ > 420 nm of Xe discharge, the photobleaching of methylene blue aqueous solution sensitized using the composite proceeded several times faster than that using TiO2 alone. The change in the absorption spectrum shape of methylene blue aqueous solution with irradiation time differed significantly from that obtained using TiO2 alone. The results have revealed that the uphill energy band bending in the composite was steeper than that in TiO2 alone, and the photogenerated hole was predominantly supplied to methylene blue ions.