Defect Evolution Enhanced Visible-Light Photocatalytic Activity in Nitrogen-Doped Anatase TiO₂ Thin Films

Abstract

Doping nitrogen (N) into TiO2 is one of the promising ways to extend the photocatalytic activity into the visible-light range, enabling to harvest more solar energy. In this study, we realize a high concentration of N incorporated into the anatase TiO2 films on indium tin oxide substrates. The band gap of TiO2 with a high N substitutional doping is reduced to 1.91 eV, showing a much improved photocatalytic reactivity, as supported by the degrading methyl orange solution radiated with visible light. First-principles calculations further suggest that the form of dominant defects evolves from the substitution of N (NO) to the coexistence of NO and oxygen vacancies (OV) when the N-doping concentration is increased, which leads to the reduction of band gap in the visible-light range and more delocalized charge distribution. Our results demonstrate a novel synthesis route that can realize a high concentration of N substitutional doping in TiO2 films and provide an improved understanding of enhanced visible-light photocatalytic performance of N-doped TiO2.