Synergistic Effects of B-F/B-S and Nitrogen Vacancy Co-Doping on g-C(3)N(4) and Photocatalytic CO(2) Reduction Mechanisms: A DFT Study

Nonmetallic co-doping and surface hole construction are simple and efficient strategies for improving the photocatalytic activity and regulating the electronic structure of g-C(3)N(4). Here, the g-C(3)N(4) catalysts with B-F or B-S co-doping combined with nitrogen vacancies (N(v)) are designed. Compared to the pristine g-C(3)N(4), the direction of the excited electron orbit for the B-F-co-doped system is more matching (N(2pz)→C(2pz)), facilitating the separation of electrons and holes. Simultaneously, the introduced nitrogen vacancy can further reduce the bandgap by generating impurity states, thus improving the utilization rate of visible light. The doped S atoms can also narrow the bandgap of the B-S-N(v)-co-doped g-C(3)N(4), which originates from the p-orbital hybridization between C, N, and S atoms, and the impurity states are generated by the introduction of N vacancies. The doping of B-F-N(v) and B-S-N(v) exhibits a better CO(2) reduction activity with a reduced barrier for the rate-determining step of around 0.2 eV compared to g-C(3)N(4). By changing F to S, the origin of the rate-determining step varies from *CO(2)→*COOH to *HCHO→*OCH(3), which eventually leads to different products of CH(3)OH and CH(4), respectively.