Insights into the photocatalytic mechanism of g-CN/CsBBr (B = Pt, Sn, Ti) heterojunction photocatalysts by density functional theory calculations

Among all well-studied photocatalysts, g-C 3 N 4 has attracted significant research interest in various fields. However, the recombination rate of photogenerated electron-hole pairs in unmodified g-C 3 N 4 is high, leading to a decrease in photocatalytic efficiency. In practical applications, it is often necessary to introduce appropriate amounts and types of surface cocatalysts to amplify the photocatalytic activity of g-C 3 N 4 . The heterojunctions between g-C 3 N 4 and perovskite materials can facilitate efficient charge separation, leading to improved photocatalytic performance while maintaining the stability of the photocatalyst. In recent years, lead-free halide double perovskites, such as A 2 BX 6 , have been widely applied in the field of photocatalysis. In this study, we conducted systematic investigations on the band structures and charge transfer of g-C 3 N 4 /Cs 2 BBr 6 (B = Pt, Sn, Ti) heterojunctions using density functional theory (DFT) calculations, and explored the interaction between the Cs 2 BBr 6 (001) surface and the g-C 3 N 4 . The results show that the g-C 3 N 4 /Cs 2 PtBr 6 as well as g-C 3 N 4 /Cs 2 SnBr 6 heterojunctions exhibit staggered band alignment, which facilitates the migration of photogenerated charge carriers and enhances catalytic activity. Besides, the g-C 3 N 4 /Cs 2 TiBr 6 heterojunction exhibited a straddling gap. Furthermore, the analysis of density of states, charge density differences, and Bader charges reveals that the presence of an internal electric field promotes the partition of electron-hole pairs at the heterojunction interface, effectively suppressing the recombination of charge carriers. Therefore, depending on the specific metal ions at the B site in the g-C 3 N 4 /Cs 2 BBr 6 structure, the resulting heterojunctions will exhibit different band alignments and photocatalytic performances. This work contributes to providing theoretical insights for the design of novel high activity heterojunction photocatalysts. The interaction between g-C 3 N 4 and Cs 2 BBr 6 (B = Pt, Sn, Ti) forms heterojunctions that enhance charge separation, thereby improving photocatalytic performance.