Construction of S-scheme CuInS2/ZnIn2S4 heterostructures for enhanced photocatalytic activity towards Cr(VI) removal and antibiotics degradation

The efficient and ecofriendly removal of pharmaceutical antibiotics and heavy metal Cr(VI) from water sources is a crucial challenge in current environmental management. Photocatalysis presents a viable environmentally friendly solution for eliminating organic contaminants and heavy-metal ions. In this study, a novel S-scheme CuInS₂/ZnIn₂S₄ (CIS/ZIS) heterojunction was developed using a one-pot solvothermal method. The optimized CIS/ZIS heterojunction exhibited considerably improved photocatalytic activity for the removal of antibiotics and Cr(VI), achieving over 90% removal for both tetracycline hydrochloride (TC) (20 mg/L) and Cr(VI) (20 mg/L) under visible light irradiation. The study also delved into the effect of coexisting inorganic anions and assessed the cyclic stability of the composite photocatalysts. This enhancement mechanism can be delineated into three key elements. First, the incorporation of the narrow-gap semiconductor CuInS₂ effectively augmented the photoabsorption capacity. Second, the inclusion of ZnIn₂S₄ caused an increase in surface active sites. Most importantly, the internal electric field at the interface between CuInS₂ and ZnIn₂S₄ expedited the separation of photogenerated carriers. Furthermore, the results revealed that superoxide radical and photogenerated holes are the primary active substance responsible for TC removal, while photogenerated electrons play a central role in the photoreduction of Cr(VI). To gain insights into the transport pathways of photogenerated carriers, we conducted experiments with nitrotetrazolium blue chloride (NBT) and photodeposited gold. This study offers an innovative approach to enhancing the photocatalytic performance of ternary In-based materials by constructing S-scheme heterojunctions.