Precisely engineered Cd–S bonds in CdS-QDs@ZrMOF-SH toward enhanced photocatalytic CO₂ reduction

Although covalent heterojunctions have been extensively demonstrated to enhance quantum dot dispersibility and charge transfer efficiency, the regulatory mechanism of covalent bond strength and density on catalytic performance remains uncharted territory. The strength of covalent bonds governs interfacial electronic coupling efficiency critical for charge transport, while excessive bond density inevitably influences the size of QDs (vital for rapid mass/charge transfer) and dispersion uniformity (essential for accessible active site density). In this study, a series of CdS QDs@UiO-66-X composites (X = OH, NH₂, SH, (SH)₂) were synthesized by modulating the interfacial covalent interactions, where CdS QDs@UiO-66-(SH)₂(ligand 2,5-dimercaptoterephthalic acid) was used to investigate the density of SH and catalytic capacity. Comprehensive characterization and analysis reveal that a monothiol (-SH)-functionalized ZrMOF interacts with CdS QDs through strong directional Cd-S bonds, resulting in uniform dispersion of QDs within the MOF pores and excellent structural stability. Leveraging the superior dispersibility and stability conferred by the -SH group, the optimized CdS loading amount (31.24 wt%) in the ZrMOF achieves a high CO₂ reduction rate of 365.61 μmol g^-1 h^-1 and 95.6% CO selectivity. This demonstrates remarkable cycling durability, retaining 86.3% of initial activity after thirty reaction cycles. This work highlights the critical role of regulated covalent bonding in promoting efficient charge separation and transfer, thereby significantly enhancing photocatalytic performance.