Density functional study of X monodoped and codoped (X = C, N, S, F) anatase TiO2

Using density-functional theory (DFT) calculations within the generalized gradient corrected approximation, the models that nonmetallic impurities X (X = C, N, S, F) substituted for O or Ti sites in anatase TiO2 were investigated. By calculating the formation energy of X-monodoped TiO2 with X substituted for O, we suggested that X dopants existed as C4−, N3−, S2− and F− ions, respectively. Meanwhile, the X dopants existed as C4+, N3+, and S6+ for X-monodoped (X = C, N, S) TiO2 with X substituted for Ti. The conclusion of the valence states of nonmetallic impurities X substituted for O or Ti sites in TiO2 is also supported by the results of optimized cell parameters and the local structures. Furthermore, an effective nonmetallic passivated codoping approach to modify the band edges of TiO2 is proposed. Based on the first-principle calculations, we suggested that nonmetallic passivated groups such as (S2− + C4+) and (C4− + S6+) could reduce the band gap largely and make less perturbation in conduction band minima (CBM), thus lead to an ideal visible-light absorption region without affecting the reducing power. This work provides some new results and is anticipated to give some inspiration and guidance for design visible-light-driven TiO2 photocatalyst with high efficiency.