The electronic structure and photoactivity of TiO2 modified by hybridization with monolayer g-C3N4

In this work, first-principles calculation based on density functional theory (DFT) was used to study the enhanced photocatalytic mechanism of TiO2 hybridized with pristine and defective g-C3N4 systematically. The theoretical investigations on both geometry structure and electronic properties, involving band structure, density of states, electron population and charge density difference, were carried out to characterize the improved property of TiO2. It was found that the combination TiO2 with g-C3N4 could be verified for high thermodynamic stability. The interaction between TiO2 and g-C3N4 led to form a built-in electric field at the interface, which facilitated the separation of electron-hole pairs and restrained photo-generated carrier recombination. Furthermore, electrons transiting from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) promoted the separation of electrons and holes. The effective separation of electron hole pairs prolonged the lifetime of carries and enhanced the photocatalytic activity of TiO2/g-C3N4. The theoretical investigations could verify the experimental observation results [Chem. Sci., 5(2014), 3946-3951, Phys. Chem. Chem. Phys., 17(2015), 17406-17412] and illustrate the mechanisms of photocatalytic enhancement of TiO2/g-C3N4 composite photocatalysts. Furthermore, the calculated optical absorption curves demonstrated that the absorption edge of TiO2/g-C3N4 composites shifted to visible-light region and its photocatalytic activity increased under visible-light irradiation. The theoretical investigation might provide referable and valuable information for understanding the observed enhanced photocatalytic mechanism in experiments.