Lattice-Matched CdS@Ag2S Core–Shell Structures on g-C3N4: A High-Performance Photocatalyst for Hydrogen Evolution and Pollutant Degradation under Visible Light

A CdS@Ag₂S core–shell architecture (CSAS) was fabricated via a low-temperature cation-exchange reaction between CdS and AgNO₃, followed by hydrothermal integration with graphitic carbon nitride to form a CdS@Ag₂S–g-C₃N₄ (CSAS–g) composite. The development of a lattice-matched built-in electric field at the CSAS effectively overcame key limitations of conventional heterojunctions such as random material combinations, lattice mismatches, and high interfacial resistance, thereby significantly enhancing photocatalytic efficiency. The CSAS–g composite demonstrated remarkable bifunctional performance, achieving a significant H₂ production rate (1497.2 μmol g^–1 h^–1), corresponding to a solar-to-hydrogen efficiency (1.63%) and an apparent quantum efficiency of 3.62%─which are 35.4 and 2.1 times higher than those of CdS nanoparticles (CdS-NPs) and CSAS, respectively. Additionally, CSAS–g exhibited outstanding photocatalytic decomposition of several pollutants, including bisphenol A, methylene blue, Rhodamine 6G, and Congo red. Notably, the methylene blue degradation rate of CSAS–g was 937.5% higher than that of photolysis and significantly outperformed CdS-NPs, CSAS, and g-C₃N₄. The exceptional photocatalytic efficacy and durability of CSAS–g were ascribed to the cooperative effects of the core–shell structure and g-C₃N₄ integration, which resulted in superior light absorption, efficient charge separation, accelerated interfacial charge transport, and an abundance of active centers. Furthermore, the core–shell design provided enhanced photocorrosion resistance, ensuring long-term stability. This study highlights the transformative potential of lattice-matched core–shell heterostructures in advancing next-generation photocatalysts for renewable hydrogen production and pollution control.