Synchronous construction of oxygen vacancies and phase junction in TiO2 hierarchical structure for enhancement of visible light photocatalytic activity

Abstract

Oxygen vacancy defect and phase junction in semiconductor oxides play crucial role in determining their electronic structure, light absorption, photocatalytic activity, etc. Herein, we reported a facile molten salt (MS) calcination strategy for synchronously constructing oxygen vacancies and phase junction in TiO2 hierarchical structure. Flower-like TiO2 hierarchical structure were firstly synthesized via solvothermal method by adjusting the volume ratio of acetic acid (HAc) to N, N-dimethyl formamide (DMF) and then were subjected to MS calcination treatment. EPR, Raman and XPS results demonstrated that large amount of oxygen vacancies was formed on the surface of TiO2 hierarchical structure after MS calcination treatment. Meanwhile, the presence of oxygen vacancies resulted in the formation of phase junction. More importantly, the flower-like hierarchical structures were well maintained in the MS calcined samples, avoiding serious sintering during the calcination process. The synergistic effect of oxygen vacancies and phase junction not only extends the visible light adsorption range, but also promotes the separation of photogenerated electrons and holes, thereby greatly increasing the visible light photocatalytic activity. The highest photocatalytic activity was achieved for the MS calcined sample at 400 °C, which was about 5.5 folds higher than that calcined in air. This work provides a facile approach for synchronously constructing oxygen vacancies and phase junction in semiconductor oxides with special morphologies.