Bandgap engineering of oxygen-rich TiO2+x for photocatalyst with enhanced visible-light photocatalytic ability

TiO2, as a photocatalyst, has attracted substantial attention since the discovery of water splitting property on the TiO2 electrodes. However, its efficiency of water splitting is limited by its wide bandgap (similar to 3.0 eV). Here, we predict its bandgap can be efficiently reduced by incorporating excess oxygen atoms on the basis of first-principles calculations. We show that the excess oxygen is more stable to bond to Ti atom and to form ordered structure. The narrowing of bandgap in oxygen-rich TiO2 originates from the ordered excess oxygen because the coupling between them shifts the conduction band bottom down. The bandgap of TiO2+x decreases with the increase of the density of excess oxygen (x). A bandgap of 1.3 eV can be achieved at x = 0.5. The oxygen-rich TiO2 shows intrinsic semiconducting characteristic without localized states within the bandgap, indicating lower trapping centers. The enhancement of visible-light absorption due to the narrowed bandgap and the intrinsic semiconductor characteristic result in the improvement of the photocatalytic performance in oxygen-rich TiO2+x.