Synergistic Confinement and S-Scheme Charge Transfer Enhance CdS/COF Photocatalysis for Nitrate Reduction

Abstract CdS exhibits promising potential for photocatalytic nitrate reduction (PNRR). However, simultaneously achieving high activity and long-term stability remains challenging due to severe photo-corrosion induced by hole accumulation and insufficient interfacial active sites arising from its low bulk-specific surface area. Herein, we propose a synergistic strategy integrating pore confinement and S-scheme charge transfer to construct a COF-confined, highly dispersed, small-sized CdS S-scheme heterojunction photocatalytic system (CdS/COF). The ordered nanochannels of the COF serve as an in-situ growth template, enabling uniform anchoring of highly dispersed CdS nanocrystals, thereby maximizing active-site exposure and shortening charge diffusion pathways. The S-scheme interface facilitates the selective recombination of low-energy charge carriers, preserves the strong reduction potential of CdS-derived electrons, and continuously extracts photogenerated holes, thereby effectively suppressing photo-corrosion. As a result, the CdS/COF system delivers an NH4+ yield of 138.21 μmol g−1 h−1 in PNRR, markedly surpassing those of single-component and non-confined counterparts. Multi-scale in-situ characterizations elucidate the critical roles of confinement effects and S-scheme charge transfer in boosting catalytic performance and structural stability. This work establishes a general “confinement-interface” coupling strategy for structural construction and regulation, offering an effective route toward photo-corrosion resistance and efficient multi-electron conversion in CdS-based PNRR photocatalysts.