Mo + N Codoped TiO2 sheets with dominant {001} facets for enhancing visible-light photocatalytic activity

Abstract

The photocatalytic activity of TiO₂ can be mainly improved from three approaches: (1) enhancing surface energy, (2) increasing availability of visible light and (3) improving the separation efficiency of photo-induced electrons and holes. Here, we report a one-step route to obtain Mo + N codoped TiO₂ sheets with dominant {001} facets by a hydrothermal process using TiN, MoO₃, HF and HNO₃ as precursor. The XRD patterns confirmed Mo and N doping into the lattice of anatase TiO₂ and the XPS survey spectrum shows nitrogen (N) acting as interstitial N or an O–Ti–N structure and molybdenum (Mo) existed as Mo⁶⁺ in TiO₂ sheets. All Mo + N codoped TiO₂ sheets can absorb visible light, but compared with N-doped TiO₂ sheets, further Mo-doping elevates the conduction band edge and expands the band gap of anatase TiO₂ slightly. The separation efficiencies of photo-induced electrons and holes of Mo + N codoped TiO₂ sheets were enhanced compared with that of N-doped TiO₂ sheets, as confirmed by detecting the production of hydroxyl radicals (˙OH), and their photocatalytic activities on decomposition of methylene blue and methyl violet was improved. The Mo + N codoped TiO₂ sheets showed the highest photocatalyst activity when the Mo-doping ratio reached 1%, indicating an appropriate codoping ratio is necessary for synergistic effect between doped metal and nonmetal elements.