Coordination-Induced In-Situ Confinement of Small-Sized Ag Nanoparticles on Ultrathin C3N4 with Strong Metal-Support Interaction for Enhanced Selective CO2 Photoreduction.

The construction of strong metal-support interaction (SMSI) between ultrasmall metal nanoparticles and semiconductor supports remains a pivotal challenge in developing high-performance photocatalysts for selective CO2 conversion. Herein, we propose a coordination-induced in-situ confinement strategy that synchronously achieves high dispersion of small-sized Ag nanoparticles (Ag NPs) and SMSI with ultrathin C3N4. Through melamine-mediated Ag-N coordination bonds, this approach orchestrates three synergistic effects: (1) Coordination-induced confinement of Ag NPs (~3.3 nm) via covalent Ag-N linkages, yielding an increase in active site density and stability compared to conventional Ag/C3N4; (2) Enhanced electron transfer from C3N4 to Ag, extending carrier lifetimes and suppressing charge recombination; (3) Interfacial electronic redistribution that promotes the generation of *COOH intermediates, steering the reaction pathway toward CO with high selectivity. Furthermore, the coordination-induced thermal condensation induces nitrogen vacancies in C3N4, which act as molecular traps to enhance CO2 adsorption capacity and synergize with Ag sites for efficient CO2 activation. As a result, the optimized catalyst exhibits a remarkable CO yield of 70.63 μmol·g-1·h-1 without the use of sacrificial agents, along with high selectivity (> 98 %) and excellent stability. This work establishes a universal paradigm for engineering metal-semiconductor interfaces through coordination chemistry, offering transformative insights into solar-driven CO2-to-fuel conversion technologies.