Ab initio study on the effects of dopant–defect cluster on the electronic properties of TiO2-based photocatalysts

We present a first-principles study on the electronic properties of TiO2 containing both dopants and defects on the basis of density-functional theory. We show that the formation energies of defects can be reduced by up to 80% in N-doped TiO2 (N substitutes O), as compared to those in perfect TiO2, but the H-doping (H substitutes O) has less effect on the defect formation. We predict that dopant-interstitial Ti cluster plays an important role in the narrowing of band gap of N-doped anatase and brookite TiO2, and H-doped rutile TiO2. Importantly, the defect bands within the band gaps can enhance the visible-light absorption and improve the photocatalytic performance of the systems due to the reduced gap between the bands. The dopant–defect cluster in the doped TiO2 may be responsible for the observed visible-light absorption in experiments. The present study provides a new route to enhance the performance of photocatalyst.