Enhancing photocatalytic properties of rutile TiO2 by codoping with N and metals – Ab initio study

• Electronic and optical properties of (M = Pt, V, Sb; N) codoped TiO2 are studied.
• Codoping induces localized states within band gap of all the investigated cases.
• Improved visible light photcatalytic activity is caused by presence of these states.

Substitutional N to O and M to Ti (M = Pt, V, Sb) codoped rutile TiO2 was investigated using density functional theory (DFT) based calculations with both standard and hybrid exchange-correlation functionals. The band gaps calculated using generalized gradient approximation (GGA) exhibited narrowing compared to the pure rutile TiO2 in all the investigated cases. In contrast, the results obtained with hybrid exchange-correlation functional showed that there was no band gap narrowing, but doping induced localized states within the band gap just above the valence band, as well as below the conduction band for Pt doped TiO2. The presence of broad intermediate states (IS) in the band gap could enhance visible light absorption through a two step optical transition from the valence to the conduction band via the IS and at the same time lower recombination of the photogenerated charges.