First-principles study on the electronic structure and optical properties of O and Ti co-doped g-C3N4

Element doping is an effective method to regulate the electronic structure and optical properties of g-C3N4. In this study, the Vienna Ab initio Simulation Package based on density functional theory was used to investigate the stability, electronic structure, and optical properties of four systems: single-layer g-C3N4, O-doped g-C3N4 (O-g-C3N4), Ti-doped g-C3N4 (Ti-g-C3N4), and O–Ti co-doped g-C3N4 (O-Ti-g-C3N4) before and after doping. The results show that the O-doped g-C3N4 system has the lowest formation energy, indicating that this system is easier to form. Electronic structure analysis reveals that the bandgap values of all doped systems are reduced compared to the intrinsic g-C3N4 system, which is attributed to the contribution of O-2p and Ti-3d orbitals to the conduction band. From the perspective of optical properties, all doped systems exhibit a redshift of the absorption edge. This redshift is caused by the reduced bandgap, which potentially broadens the light absorption range and enhances the solar light harvesting capability. Furthermore, the real part of the dielectric function shows that the O–Ti co-doped system has the highest value, suggesting that this system also possesses the optimal polarity. In the field of photocatalysis, the excellent polarity of the O–Ti co-doped system can promote the efficient separation of photogenerated carriers and accelerate the rate of catalytic reactions, such as water splitting for hydrogen production and pollutant degradation. This provides support for the practical development of clean energy production and environmental remediation technologies.