Boosting Photocatalytic H₂O₂ Self-Supply and Surface Antibacterial Activity via Interfacial Electric Field-Regulated S-Scheme Mn_0.2Cd_0.8S/ZnIn₂S₄ Heterojunction

Surface biofouling is a pervasive and intractable challenge that accelerates the corrosion of cement-based marine infrastructures, drastically impairs their structural durability and shortens their service life. Herein, to address these critical issues, an interfacial electric field-driven S-scheme Mn_0.2Cd_0.8S/ZnIn₂S₄ (MCS/ZIS) heterojunction was rationally designed and fabricated as a high-performance photocatalytic coating for sustainable surface antibacterial protection. Owing to the Fermi level difference between MCS and ZIS, a robust internal electric field is constructed at the heterojunction interface, which not only boosts the directional charge transfer across the interface but also effectively suppresses the recombination of photogenerated electron-hole pairs. More importantly, the unique S-scheme charge transfer pathway enables the selective retention of highly reductive electrons in the conduction band of MCS and strongly oxidative holes in the valence band of ZIS, which synergistically facilitates the efficient two-electron oxygen reduction reaction for in situ hydrogen peroxide (H₂O₂) generation. The optimized MCS/ZIS composite achieves a remarkable H₂O₂ production rate of 899.7 μmol·g^-1·h^-1 under simulated sunlight irradiation, which is 2.1 times higher than that of pristine MCS. When integrated onto the surface of cement-based materials, the as-prepared MCS/ZIS photocatalytic coating continuously generates H₂O₂ under light illumination, exhibiting excellent antibacterial activity against Staphylococcus aureus with a minimum inhibitory concentration of 20.33 μg·mL^-1. This work not only provides a novel photocatalytic antifouling strategy for enhancing the durability of cement-based materials but also offers a feasible design idea for the construction of high-efficiency S-scheme heterojunction photocatalysts for environmental remediation applications.