Molten-Salt-Engineered Graphitic C₃N₄/ZnIn₂S₄ Composites for Accelerated Charge Separation in Photocatalytic Hydrogen Production

The practical application of graphitic carbon nitride (g-C3N4) in photocatalysis is severely hindered by its rapid charge recombination and limited visible-light absorption. To address this, we developed a synergistic strategy combining molten salt treatment and heterojunction engineering. g-C3N4 nanoparticles (NPCN) were synthesized via molten salt treatment and subsequently integrated with ZnIn2S4 nanoflowers (ZIS) to construct a hierarchical nanoheterostructure through a hydrothermal approach. These modifications not only adjusted the conduction band positions of g-C3N4 and increased its electron density but also broadened its light absorption range, accelerating the carrier transfer and separation in g-C3N4. The results show that all prepared NPCN-ZIS heterostructures exhibit excellent photocatalytic activity. Among them, the optimized sample NPCN-ZIS-0.4 achieves a hydrogen production rate of 17,511 μmol g–1 h–1 under visible light (λ > 420 nm) irradiation, which is 239.72 and 2.41 times higher than that of NPCN and ZnIn2S4, respectively. This significantly improved hydrogen production performance demonstrates the synergistic effect of molten salt treatment and heterojunction engineering in enhancing the photocatalytic efficiency of g-C3N4-based materials. In addition, the reaction mechanism of photocatalytic hydrogen production was deeply investigated by density functional theory calculations in this paper, which is crucial for understanding the photocatalytic process and further optimizing the catalyst design. This work not only provides a high-performance photocatalyst for solar hydrogen production but also offers a generalized molten salt-assisted heterojunction design strategy for developing efficient and stable photocatalytic systems.