Photocatalytic water splitting using Pt-loaded visible light-responsive TiO2 thin film photocatalysts

Visible light-responsive TiO2 (Vis-TiO2) thin films which exhibit a unique declined O/Ti composition from the surface to the deep inside bulk have been successfully developed under a substrate temperature of 873 K by applying a radio-frequency magnetron sputtering deposition (RF-MS) method. By controlling the Ar gas pressure during the deposition procedure, it was possible to control the optical properties of the TiO2 thin films. These Pt-loaded Vis-TiO2 thin films were found to decompose water involving methanol (H2 production reaction from H2O) or 0.05 M silver nitrate solution (O2 production reaction from H2O) under visible light (λ ≥ 420 nm) irradiation. In particular, the photo-oxidation of water to produce O2 proceeds under visible light of wavelengths longer than 550 nm. The conduction and valence bands of Vis-TiO2 thin film photocatalysts were, thus, seen to have enough potential for the decomposition of water into H2 and O2 under visible light irradiation. These thin films were found to be stable and the declined composition could be retained even after the reaction and calcination treatment at 723 K in O2 atmosphere. Moreover, the stoichiometric and separate evolution of H2 and O2 from H2O could be successfully achieved using an H-type glass container even under visible light.