Low-temperature S-doping on N-doped TiO2 films and remarkable enhancement on visible-light performance

Sulfur doping of nitrogen-doped TiO₂ nanograss array films was realized through facile thiourea solution immersion at a low temperature of 353 K. Doped nitrogen and sulfur atoms were found mainly in the interstitial form. Nitrogen doping (N-doping) and sulfur doping (S-doping) enhanced visible light absorption and decreased the band gap of undoped TiO₂ films from 3.10 to 3.01 and 2.81 eV, respectively. Furthermore, N-doped and N, S co-doping made the water absorbed on TiO₂ was easier to chemically dissociate and generate hydroxide groups. N-doping favored to produce more ${\text{O}}_2^{•-}$ radicals and S-doping benefit to generate more $\text{O}{\text{H}}^{•}$ radicals. Both $\text{O}{\text{H}}^{•}$ and ${\text{O}}_2^{•-}$ active radicals played a significant role in the degradation of RhB. The photocatalytic activity of undoped TiO₂ films was increased by 2.5 times by N-doping through urea treatment. By further S-doping, the photocatalytic performance of N-doped TiO₂ films was enhanced by 4.0 times again.