Synthesis, characterization, and nitrogen concentration depended visible-light photoactivity of nitrogen-doped TiO₂ nanosheets with dominant (001) facets

Anatase TiO₂ nanosheets with dominant (001) facets were prepared by a simple hydrothermal method. Nitrogen-doped TiO₂ nanosheets (TiO₂-N) with different nitrogen concentration were successfully synthesized by annealing TiO₂ nanosheets in NH₃ atmosphere with different NH₃ flow rate at 400 °C for 3 h. The morphology, nanostructures, and properties of TiO₂-N were characterized by X-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy, ultraviolet-visible diffuse reflection spectroscopy, X-ray photoelectron spectroscopy, and photoluminescence. The effects of NH₃ flow rate on the nanostructures, properties, and visible-light photoactivity in the degradation of rhodamine B (RhB) aqueous solution under visible light (λ > 400 nm) irradiation of the prepared photocatalysts were investigated. Among all the prepared photocatalysts including nitrogen modified P25 (Degussa), TiO₂-N prepared with a NH₃ flow rate of 40 ml/min gave the highest visible-light photoactivity because of the dominant (001) facets, visible light responsibility, the slowest photogenerated electron (e^-) and hole (h⁺) pairs recombination rate, and the highest hydroxyl radicle (•OH) generation ability. Based on these experiments and analysis, the mechanisms of how the nitrogen concentration affects the visible-light photoactivity of TiO₂-N were proposed.