Revealing the Relationship between Photocatalytic Properties and Structure Characteristics of TiO2 Reduced by Hydrogen and Carbon Monoxide Treatment

Reduction is considered to be an effective method to improve the photocatalytic activity of TiO2; however, the underlying relationship between structure and photocatalytic performance has not been adequately unveiled to date. To obtain insights into the effect of structure on photocatalytic activity, two types of reduced TiO2 were prepared from CO (CO-TiO2) and H-2 (H-TiO2). For H-TiO2, Ti-H bonds and oxygen vacancies are formed on the surface of H-TiO2, which results in a more disordered surface lattice. However, for CO-TiO2, more Ti-OH bonds are formed on the surface and more bulk oxygen vacancies are introduced; the disorder layer of CO-TiO2 is relatively thin, owing to most surface vacancies being filled by Ti-OH bonds. Under simulated solar irradiation, the photocatalytic H-2 evolution rate of CO-TiO2 reaches 7.17mmolg(-1)h(-1), which is 4.14 and 1.50times those of TiO2 and H-TiO2, respectively. The photocatalytic degradation rate constant of methyl orange on CO-TiO2 is 2.45 and 6.39times those on H-TiO2 and TiO2. The superior photocatalytic activity of CO-TiO2 is attributed to the effective separation and transfer of photogenerated electron-hole pairs, due to the synergistic effects of oxygen vacancies and surface Ti-OH bonds. This study reveals the relationship between the photocatalytic properties and structure, and provides a new method to prepare highly active TiO2 for H-2 production and environmental treatment.