Role of complex defects in photocatalytic activities of nitrogen-doped anatase TiO2

Abstract

Deep impurity states associated with a substitutional nitrogen at an oxygen site (N_O) are believed to be the source of the visible-light absorption of nitrogen-doped titanium dioxide (TiO₂). Our comprehensive study using density functional theory (DFT) plus onsite Coulomb interaction (U) reveals that a titanium atom at an interstitial site (Ti_i) is highly mobile and strongly binds with N_O. Hybridizations of N p with Ti d states of Ti_i give rise to a new band at the valence band edge, eliminating the hole-trapping centers originated from the deep N_O states. The suggested mechanism explains the photocatalytic oxidation reactions as well as the visible-light absorption observed on N-doped anatase TiO₂.