Preparation of the visible light responsive TiO2 thin film photocatalysts by the RF magnetron sputtering deposition method

TiO2 thin film photocatalysts which could induce photoreactions under visible light irradiation were successfully developed in a single process by applying an ion engineering technique, i.e., the radio frequency (RF) magnetron sputtering deposition method. The TiO2 thin films prepared at temperatures greater than 773 K showed the efficient absorption of visible light; on the other hand, the TiO2 thin films prepared at around 573 K were highly transparent. This clearly means that the optical properties of TiO2 thin films, which absorb not only UV but also visible light, can be controlled by the preparation temperatures of the RF magnetron sputtering deposition method. These visible light responsive TiO2 thin films were found to exhibit effective photocatalytic reactivity under visible light irradiation (lambda > 450 nm) at 275 K for the reductive decomposition of NO into N-2 and N2O. From various characterizations, the orderly aligned columnar TiO2 crystals could be observed only for the visible light responsive TiO2 thin films. This unique structural factor is expected to modify the electronic properties of a TiO2 semiconductor, enabling the efficient absorption of visible light.