Effects of Solvent Treatment on the Formation of Oxygen Vacancy in TiO2 via Vacuum Annealing

In this work, vacuum annealing of hydrothermally prepared titanium dioxide (TiO2) washed with water (W-TiO2) or ethanol (E-TiO2) at different temperatures was performed. Total organic carbon and Fourier transform infrared characterizations confirm the adsorption of washing solvents by TiO2. As the vacuum annealing temperature increases, W-TiO2 appears as white powders, whereas E-TiO2 shows a gradually deepening color with certain absorption of visible light due to the pyrolysis of ethanol. Electron paramagnetic resonance analyses demonstrate that the crystallization of W-TiO2 creates oxygen vacancy (Vo), and the pyrolysis of ethanol favors its formation in E-TiO2. Diffuse reflectance spectra and photocatalytic performances of all TiO2 photocatalysts suggest that Vo is not responsible for visible light absorption. Our work proves that the formation of Vo in TiO2 via vacuum annealing is influenced by the solvent treatment and gives new insights into the origin of Vo as well as its role.