Nitrogen-doped titanium dioxide visible light photocatalyst: Spectroscopic identification of photoactive centers

This paper focuses on the photoactive centers of nitrogen-doped TiO2 visible light photocatalyst. A series of N-doped TiO2 materials were prepared by a post-nitridation route at the temperature range of 400–800 °C. The photocatalytic oxidation of acetone as a model reaction was used to evaluate the photocatalytic properties of the materials. The chemical states of doped nitrogen species were characterized by near-edge X-ray absorption fine structure, X-ray photoelectron, and electron paramagnetic resonance spectroscopies. The results reveal that four types of N species exist alone or together in TiO2 depending on nitridation temperature. The photoactive centers of the materials are a diamagnetic [O–Ti4+–N3−–Ti4+–image] cluster containing an oxygen vacancy and a nitrogen anion. The visible light photocatalysis of N-doped TiO2 is proposed to be initiated by an excited state of the surface [Ti4+–N3−] unit.