Preparation and Photocatalytic Activities of Black TiO₂ in Vacuum and Ambient Temperature Environment.

Abstract

The preparation conditions are important for the structure and properties of black TiO₂. In this paper, the black rutile TiO₂ with a particle size of approximately 5 nm was prepared in vacuum by the infrared nano-second laser sputtering deposition method. The study results indicated that the prepared black TiO₂ exhibited high light absorption from UV to near-infrared region. The lattice distortion and Ti3+ were responsible for the upward shift in the valance band, and the oxygen vacancy states were determined to be located about 0.7-1.18 eV under the conduction band, narrowing the band gap of TiO₂ from 3.2 eV to 2.1 eV. Although the black TiO₂ exhibited strong adsorption effects within the full spectrum and had a higher free carrier density, the presence of excess oxygen defects resulted in a higher recombination rate of the photo electron-hole pairs, which induced a poor photocatalytic performance of the black TiO₂. This work facilitates the understanding of the mechanisms mechanism of black TiO₂ formation via laser ablation, and emphasized the need for the controllability and quantification of oxygen vacancies.