Synthesis of black TiO2 with efficient visible-light photocatalytic activity by ultraviolet light irradiation and low temperature annealing

Highlights: • In this work, we have prepared black titanium dioxide (B-TiO₂) nanoparticals in combination with ultraviolet light and low temperature annealing. This method is simple, efficient and environmentally friendly. • The synthesis mechanism of the black B-TiO₂ nanomaterials was analyzed by combining the different characterization data with the first-principles calculation results. • The Ti-O lattice and structure of the B-TiO₂ sample did not change after low-temperature annealing. • The process of H-doping results in a reduction of the localized Ti³⁺ states, that are also the recombination centers of excited electrons and holes. • These nanoparticles can absorb a amount of visible light and degrade the organic pollution. - Abstract: Herein, a simple, efficient, and environmentally friendly strategy to prepare black TiO₂ nanoparticles has been reported; the procedure combines the ultraviolet light irradiation and low-temperature annealing (300 °C) with continuous N₂ flow under atmospheric pressure. The samples were characterized by the various techniques, such as X-ray diffraction, high resolution transmission electron microcopy, Raman spectroscopy, X-ray photoelectron spectroscopy. The photocatalytic degradation of the organic contaminant Rhodamine B was investigated when black TiO₂ nanoparticles was irradiaed with ultraviolet light and visible light. The black TiO₂ material possesses an anatase phase and is able to absorb a high amount of photon energy in the visible light region, effectively driving photochemical degradation reactions. The enhancement of the photocatalytic activity can be attributed to the following: first, the hydrogen ions decrease the localized Ti³⁺ states (which are also the e⁻-h⁺ recombination centers) leading to a more efficient separation of the electron-hole pairs; secondly, the conduction band electrons in black TiO₂ nanoparticles are responsible for strong absorption of visible light. Consequently, the photocatalytic degradation of Rhodamine B can be significantly enhanced using black TiO₂ nanoparticles. This work proves that hydrogenated black TiO₂ promotes the absorption of the entire electromagnetic spectrum and exhibits high photocatalytic activity under solar light irradiation.