Modulation of Sulfur Vacancies in MOF-Derived 3D Hollow ZnCo ₂ S ₄ Polyhedra on 2D g-C ₃ N ₄ Nanosheets for Enhanced Photocatalytic Hydrogen Evolution

Precisely engineered semiconductor heterojunctions with tunable morphologies are emerging as efficient systems for solar energy conversion. We report a rationally designed 3D hollow ZnCo 2 S 4 polyhedron, derived from MOFs and intimately coupled with 2D g-C 3 N 4 (CN) nanosheets via a hydrothermal route. The formation of an S-scheme ZnCo 2 S 4 –CN heterojunction significantly enhances light absorption and accelerates charge carrier separation. Structural and spectroscopic characterizations confirm the strong interfacial coupling, which induces an internal built-in electric field and Coulombic interactions that promote directional charge transfer while maintaining the strong redox potentials of each component. Owing to these synergistic effects, the optimized 20 wt % ZnCo 2 S 4 –CN composite achieves an exceptional hydrogen evolution rate of 2390 μmol g –1 h –1 under visible-light irradiation, which is 57 and 13 times higher than that of pristine CN and ZnCo 2 S 4, respectively. Moreover, the composite exhibits excellent stability and recyclability over prolonged photocatalytic cycles. This work highlights that engineering sulfur-vacancy-rich, MOF-derived sulfides on CN is an effective strategy for constructing high-performance heterojunction photocatalysts for sustainable hydrogen production.