Comparative study of photocatalytic deactivation of pure and black titania thin films

Thin film black titania (H-TiO2-x) was obtained in hydrogen plasma in an MPCVD system. The photocurrent and the methylene blue (MB) photodegradation rate of the black titania increased drastically compared to the pure anatase sample. A major difference between pristine and black titania films in photocatalytic deactivation by MB was found. Pristine TiO2 thin films were not deactivated after a series of MB degradation measurements followed by rinsing with DI-water, while the photocatalytic activity of H-TiO2-x dropped by 50%. It was shown that the deactivated sample can be regenerated with a process that consists of exposure of the deactivated sample to UV-VIS light in DI-water. It was found that due to the presence of hydroxyl groups on the surface, as well as an upward band bending on the surface of the black photocatalyst, the products of MB degradation during the photocatalytic reaction are being chemically bonded to the surface of H-TiO2-x but not pristine TiO2. Based on the new results, a new description of thin film black titania is provided.