Effect of Nitrogen Doping on Optoelectronic Properties of TiO2 Anatase Model for Solar Hydrogen Production: A DFT + U Approach

Abstract

To deal with the energy crisis and environmental challenges, solar hydrogen generation via photocatalytic water-splitting technique is clean and green energy technology. Titanium dioxide (TiO2) plays a significant role as a photocatalyst to absorb solar energy for photocatalytic H2 production. However, the development of TiO2 as an efficient photocatalyst is always a challenging task due to its wide bandgap (TiO2 anatase ~3.2 eV) and meager visible light absorption. Herein, this work presents the computationally designed nitrogen (N)-doped TiO2 anatase models simulated via periodic density functional theory (DFT) calculations over large supercells. Hubbard’s modified DFT calculations were adopted through Perdew–Burke–Ernzerhof supported generalized gradient approximation (GGA + PBE + U) functional to simulate the optoelectronic properties of the designed models. The results reveal that N-doped TiO2 anatase model exhibits a substantial bandgap reduction up to 2.34 eV as endorsed by the electronic structure analysis. The bandgap reduction commences from the provision of N 2p states to the O 2p and Ti 3d states of TiO2 in VB region and their presence as induced mid-gap states in the bandgap. The reduction in bandgap energy of the TiO2 significantly boosts the visible light absorption under solar irradiation. Thus overall, the N-doping could be a promising non-metal doping approach for TiO2 anatase photocatalyst for the solar H2 production process.