Understanding electronic and optical properties of N–Sn codoped anatase TiO2

• DFT + U calculations are used to study Sn-, (N, Sn), and (2N, Sn) doped TiO2.
• (2N, Sn) codoped anatase TiO2 leads to a much more effective band gap narrowing.
• The coupling between N atoms plays a key role in the band gap narrowing.

Understanding photoelectrochemical properties of N–Sn codoped anatase TiO2 is attractive and significant for their potential applications in solar photocatalysis. In this work, we use density functional theory plus U (DFT + U) calculations to investigate the electronic structures and optical properties of Sn-, (N, Sn), and (2N, Sn) doped anatase TiO2. It is found that Sn monodoping, (N, Sn) codoping and even (2N, Sn) codoping by two non-adjacent N atoms cannot lead to an effective band gap narrowing. In contrast, (2N, Sn) codoping by two adjacent N atoms can result in a much more effective band gap narrowing, due to the appearance of the effective N–N coupling that can form two distinguishable occupied states in the forbidden gap. Our results show that the coupling between N atoms plays a key role in the enhanced visible light photocatalytic activity of N–Sn codoped anatase TiO2.