B&F Codoping in g-C3N4/CoN4 Transforms Type I to Z-scheme Photocatalyst for Water Splitting Reaction: A DFT+U Study

In this study, we present a novel approach by employing boron and fluorine as modulators to induce a transition in the band alignment of a g-C3N4/CoN4 heterostructure, shifting it from a type I to a z scheme. The initial investigation of the photocatalytic mechanism involved the utilization of density functional calculations on a heterostructure consisting of g-C3N4 and CoN4. The formation energy, total density of states (TDOS), partial density of states (PDOS) and optical absorbance of the g-C3N4/CoN4 heterojunction were comprehensively examined. The findings indicate that the formation of heterojunctions between g-C3N4 and CoN4 is facilitated, and the incorporation of CoN4 leads to a notable enhancement in the light absorption properties of g-C3N4. Nevertheless, the initial formation of a type-I heterojunction between g-C3N4 and CoN4 is not conducive to the separation of photo-induced electron-hole pairs. In order to handle this, a model is developed for B,F co-doped g-C3N4, which is subsequently joined with CoN4 to form the B,F co-doped g-C3N4/CoN4 heterojunction. A more comprehensive examination of the work function, charge density difference and electric field direction reveals that the combination of B,F co-doped g-C3N4 and CoN4 exhibits the ability to establish a z scheme heterojunction. This approach has the potential to efficiently segregate photogenerated charge carriers while maintaining their activity, hence enhancing the overall photocatalytic efficiency. Modulating the band alignment of the photocatalytic heterostructure through rational interface engineering can offer valuable insights into the generation of the z scheme mechanism and contribute to the advancement of highly efficient photocatalytic systems and beyond.