Understanding the roles of point defects in optical transitions is a key to the desirable engineering of photochemical materials. In this study, the origins of the significantly varying optical and photochemical properties of Nb-doped anatase TiO2were systematically investigated, using density functional theory (DFT) calculations and experimental verifications. We found from DFT calculations that the desirable band gap reduction of anatase TiO2by ∼0.1 eV reported in many of experimental reports and the resultant improvements of photocatalytic and photovoltaic efficiencies of Nb5+-doped anatase TiO2are due to the formation of complex (NbTi-VTi)3−as the compensator of NbTi+. Our experiments demonstrated that the O2-rich annealing, which is expected to increase the concentration of desirable (NbTi-VTi)3−complex, narrows band gap of TiO2and strongly enhances the photocatalytic activity of Nb-doped TiO2particle. On the contrary, pure TiO2showed rather worse photocatalytic performances when annealed in O2-rich atmosphere, which is due to the formation of deep level by O-interstitial defect (Oi). Theoretically obtained charge effective masses could further explain the different photocatalytic activities of undoped and Nb-doped TiO2.
All Science Journal Classification (ASJC) codes
- Environmental Science(all)
- Process Chemistry and Technology