How does the B,F-monodoping and B/F-codoping affect the photocatalytic water-splitting performance of g-C3N4?

By means of density functional theory (DFT) computations, we investigated the electronic and optical properties of B,F-monodoped and B/F-codoped graphitic carbon nitride (g-C3N4) to explore the doping effects on the photocatalytic performance of g-C3N4. It is found that F atom addition plays a key role in stabilizing the surface of g-C3N4 and facilitating B atom substitution into g-C3N4. Among the different doping strategies, only B/F-codoping does not have localized states in the midgap, which act as recombination centers for the photogenerated electron-hole pairs. All the doping strategies in this study can improve the utilization ratio of visible light for the g-C3N4 photocatalyst. Considering the relationship of overpotential of water redox reaction over g-C3N4 and band edge positions with respect to the water redox potentials, only the F-doped and B/F-codoped g-C3N4 satisfy the criterion for overall water splitting. In other words, the B/F-codoping strategy not only meets the demands of no recombination centers and enhances the visible light utilization ratio, but also satisfies the need of overpotential. Thus, B/F-codoped g-C3N4 is expected to be a promising photocatalyst for overall water splitting under visible light.