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



A novel dopant-free TiO2 photocatalyst (Vo.-TiO2), 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 TiO2 precursor, imidazole, and hydrochloric acid at elevated temperature (450 °C) in air. Control experiments demonstrate that the porous TiO2 precursor, imidazole, and hydrochloric acid are all necessary for the formation of Vo.-TiO2. Although the synthesis of Vo.-TiO2 originates from such a multicomponent system, this synthetic approach is facile, controllable, and reproducible. X-ray diffraction, XPS, and EPR spectroscopy reveal that the Vo.-TiO2 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 Vo.-TiO2 is a stable visible-light-responsive material with photogenerated charge separation efficiency higher than N-TiO2 and P25 under visible-light irradiation. The Vo.-TiO2 material exhibits not only satisfactory thermal- and photostability, but also superior photocatalytic activity for H2 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:TiO2 precursor) and calcination time on the photocatalytic activity and the microstructure of Vo.-TiO2 were elucidated.