Ab initio studies of Nb–N–S tri-doped TiO2 with enhanced visible light photocatalytic activity

The electronic and optical properties of Nb–N–S tri-doped anatase TiO2 were investigated within the frame of the density functional theory (DFT) plus U method. Results show that a significant red-shift effect and improvement of visible-light absorption for Nb–N–S tri-doped TiO2 are observed with respect to pure TiO2 and S–N codoped TiO2. At the same time, the enhanced visible-light photocatalytic activity of tri-doped TiO2 is derived from the narrowing band gap, the appearance of Nb 4d state at the bottom of conduction band and the mixture of N 2p, S 3p states forming new defect levels at the top of valance band, which is excellently consistent with the previous experiment. Moreover, S ion leads to the lattice distortion and promotes the visible-light photocatalytic activity. Furthermore, the absorbance of 1.39NbNS–TiO2 accords well with the experimental result in the visible region. It is also found that the 2.78NbNS–TiO2 can be easily grown under O-rich condition and have the strongest absorbance from 2.0 to 4.2 eV among four models.

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