Facile preparation of anatase–brookite–rutile mixed-phase N-doped TiO2 with high visible-light photocatalytic activity

Solvent-based ambient condition sol process with N,N-dimethyl formamide (DMF) as the solvent, is a post-processing method utilized to modify mixed-phase titania nanoparticles using polyethylene glycol (PEG) as a structure directing agent prepared by self-assembly process. Photocatalytic activity, evaluated by the photocatalytic degradation of methylene blue (MB) under visible-light irradiation, demonstrated that all the samples were more active than Degussa P25. The high photocatalytic activity was explained by the presence of a ternary mixture of anatase, brookite, and rutile and the electron-deficient nitrogen atoms in O–Ti–N nitrides that could inhibit the recombination of electron–hole pairs by capturing the photoinduced electrons. From the experimental results, it was observed that the high efficiency seems to depend on the ternary (anatase, brookite, and rutile) phase effect, the chemical states of the Ti, O, and N species on the surface, the atomic content of nitrogen and BET surface area. The activity of the N-doped TiO2 first increased and then decreased with the increase of the N-content.