Effect of heat treatment under vacuum on structure and visible-light photocatalytic activity of nano-TiO2

Abstract

Nano-TiO₂ is known as a photocatalyst with high catalytic activity. However, it should be emphasized that the bandgap of nano-TiO₂ is wide, which limits its photocatalytic efficiency in response to visible light and thus hinders its potential application. Improving the photocatalytic activity of nano-TiO₂ under visible light by the strategy of heat treatment under vacuum was investigated in this study. The structure and photocatalytic activity of nano-TiO₂ before and after heat treatment under vacuum were compared and analyzed by XRD, TEM, HRTEM, XPS and UV-Vis-NIR, respectively. The results show that oxygen vacancies were introduced into the crystal structure of nano-TiO₂ to change its inherent energy band structure. Particularly, the samples after heat treatment under vacuum exhibited high photocatalytic activity under visible light. In addition, the formation mechanism of non-stoichiometric compound TiO_2−x and the mechanism of oxygen vacancy defects to expand the wavelength of light that nano-TiO₂ absorbs to the visible portion of the spectrum have also been addressed in this paper.