The Preparation of Visible Light-Responsive TiO2 Thin Films by Applying a RF-Magnetron Sputtering Deposition Method and Their Photocatalytic Reactivity for the Decomposition of Water with a Separate Evolution of H2 and O2

TiO2 (Vis-TiO2) thin films absorbing UV and visible light in regions of 250-600nm have been successfully developed by applying a radio-frequency (RF) magnetron sputtering deposition method. SIMS depth profiles of Vis-TiO2 revealed that the O/Ti ratio gradually decreases from the top surface (O/Ti ratio : 2.00 ± 0.01) to the inside (1.93 ± 0.01). This unique declined O/Ti composition (anisotropic structure) may be the origin of the significant perturbation in the electronic structure of Vis-TiO2, enabling the absorption of visible light and their high photocatalytic performance under visible light irradiation. In fact, it was found that the separate evolution of H2 and O2 from water could be successfully achieved under visible light or solar light irradiation by applying these thin film photocatalysts in an H-type glass container separating the two aqueous solutions by a TiO2 thin film and proton-exchange membrane, having H2 evolution from Pt side and O2 evolution from TiO2 thin film side, respectively.