Photocatalytic reaction and degradation of methylene blue on TiO2 films in vacuum: an X-ray photoelectron spectroscopy study

Photocatalytic reaction and degradation of methylene blue on TiO₂ films illuminated by ultraviolet light in air and in vacuum were studied by X-ray photoelectron spectroscopy (XPS). The results show that TiO₂ film has photocatalytic activity in high vacuum, while the oxygen-containing groups on TiO₂ film play a very important role in maintaining photocatalytic reaction, a certain nitrogenous group has been removed from the methylene blue molecule to make the atomic ratio of its N and S decrease from 2.83 to 2.09, and form the intermediate reaction products containing benzene ring and N, S heterocycle, which can be degraded incompletely.