Facile Synthesis of Thermal‐ and Photostable Titania with Paramagnetic Oxygen Vacancies for Visible‐Light Photocatalysis

A novel dopant‐free TiO 2 photocatalyst (V o . ‐TiO 2 ), which is self‐modified by a large number of paramagnetic (single‐electron‐trapped) oxygen vacancies, was prepared by calcining a mixture of a porous amorphous TiO 2 precursor, imidazole, and hydrochloric acid at elevated temperature (450 °C) in air. Control experiments demonstrate that the porous TiO 2 precursor, imidazole, and hydrochloric acid are all necessary for the formation of V o . ‐TiO 2 . Although the synthesis of V o . ‐TiO 2 originates from such a multicomponent system, this synthetic approach is facile, controllable, and reproducible. X‐ray diffraction, XPS, and EPR spectroscopy reveal that the V o . ‐TiO 2 material with a high crystallinity embodies a mass of paramagnetic oxygen vacancies, and is free of other dopant species such as nitrogen and carbon. UV/Vis diffuse‐reflectance spectroscopy and photoelectrochemical measurement demonstrate that V o . ‐TiO 2 is a stable visible‐light‐responsive material with photogenerated charge separation efficiency higher than N‐TiO 2 and P25 under visible‐light irradiation. The V o . ‐TiO 2 material exhibits not only satisfactory thermal‐ and photostability, but also superior photocatalytic activity for H 2 evolution (115 μmol h −1  g −1 ) from water with methanol as sacrificial reagent under visible light ( λ >400 nm) irradiation. Furthermore, the effects of reaction temperature, ratio of starting materials (imidazole:TiO 2 precursor) and calcination time on the photocatalytic activity and the microstructure of V o . ‐TiO 2 were elucidated.