Self-assembly of snowflake-like Cu₂S with ultrathin ZnIn₂S₄ nanosheets to form S-scheme heterojunctions for photocatalytic hydrogen production

Step-scheme (S-scheme) heterojunction has attracted much attention in the design of heterostructures for photocatalysts. In this study, we successfully utilized the principle of electrostatic self-assembly to load ultrathin ZnIn₂S₄ nanosheets onto snowflake-like Cu₂S using a simple grinding method, and synthesized Cu₂S/ZnIn₂S₄ S-scheme heterojunctions according to the different work functions (Φ). At the optimal Cu₂S loading ratio (5 wt%), the hydrogen yield of the Cu₂S/ZnIn₂S₄ composites reaches 5.58 mmol·h^-1·g^-1, which is 5.12 times higher than that of pure ZnIn₂S₄ (1.09 mmol·h^-1·g^-1). The apparent quantum efficiency (AQE) of the Cu₂S/ZnIn₂S₄ composites reaches 5.8 % (λ = 370 nm), which is an improvement compared to pure ZnIn₂S₄ (2.7 %). The AQE of pure ZnIn₂S₄ is 0.4 %, while the AQE of Cu₂S/ZnIn₂S₄ composites is enhanced to 1.0 % at λ = 456 nm. The heterojunction interface of Cu₂S and ZnIn₂S₄ builds a built-in electric field (IEF), which greatly reduces the recombination rate of photogenerated electrons and holes, retains highly reduced photoelectrons in the conduction band (CB) of ZnIn₂S₄. The snowflake structure of Cu₂S effectively increases the active sites and specific surface area, and improves the light absorption. This work opens a new avenue for designing photocatalysts, synergizing energy development and protecting the environment.