Electronic properties of F/Zr co-doped anatase TiO2 photocatalysts from GGAÂ +Â U calculations

► F-doping leads to the formation of reduced Ti3+ ions, and Ti orbitals slightly below the conduction band, leading to band gap narrowing. ► Zr-doping promotes Zr 4d orbitals residing well into the conduction band, with essentially no band gap change. ► F/Zr-codoping results in electronic structure similar to F-monodoping, other than Ti3+ gap state positions. ► The influence of oxygen vacancies indicates that interplay between the dopants and oxygen vacancies is key for the improvement of photocatalytic activity. ► The theoretical findings present a reasonable explanation of recent experimental results.