Flexible TiO2 nanograss array film decorated with oxygen vacancies introduced by facile chemical reduction and their photocatalytic activity

Flexible TiO 2 nanograss array film was prepared by simple chemical oxidation of Ti wire mesh at a low temperature of 353 K. To improve its visible-light-driven photocatalytic activity, we further carried out a low-temperature chemical reduction to introduce oxygen vacancies in the solution of ethylene glycol (EG) and ammonium fluoride (NH 4 F). The results of XPS and EPR confirmed the formation of surface and bulk oxygen vacancies was confirmed, and their concentrations increased as the reduction time increased. Compared with the as-annealed TiO 2 film, the as-reduced specimens exhibited higher visible-light-driven photocatalytic activity. When reduction time was 48h, the photocatalytic activity was increased by 15.8 times compared to the as-annealed sample. The remarkable improvement in photocatalytic activity should be ascribed to the oxygen vacancies’ introduction. The most excellent photocatalytic performance was obtained when a suitable concentration ratio of surface oxygen vacancies to bulk oxygen vacancies was reached. Low-temperature chemical reduction in the solution of EG + NH 4 F is very efficient and convenient for introducing defects such as oxygen vacancies and Ti 3 + ${}^{3+}$ .