Tuning Ag Loading and Particle Size in Ag@g-C3N4 Photocatalysts for Selective CO2 Conversion to CO and CH4

Elucidating the mechanisms of CO2photocatalytic conversion systems is crucial for tackling the challenges of carbon neutrality. In this study, a series of Ag@g-C3N4photocatalysts were constructed with metal particle size modulation as the core strategy to systematically reveal the modulation mechanism of Ag nanoparticles (Ag NPs) size variation on the selectivity of CO2photoreduction products. Systematic characterizations revealed that increasing Ag size enhanced visible light absorption, promoted charge separation, and improved CH4selectivity. Photocatalytic tests showed Ag3.0%@CN achieved optimal activity and electron utilization. Energy band analyses indicated that Ag modification preserved favorable conduction band positions while increasing donor capacity. Further density-functional theory (DFT) calculations reveal that Ag NPs size variations significantly affect the adsorption stability and conversion energy barriers of intermediates such as *COOH, CO and CHO, with small-sized Ag7NPs favoring the CO pathway, while large-sized Ag NPs stabilize the key intermediates and drive the reaction towards the CH4pathway evolution. The experimental and theoretical results corroborate each other and clarify the dominant role of Ag NPs size in regulating the reaction path between CO and CH4. This study provides mechanistic guidance for the selective regulation of the multi-electron reduction pathway, which is of great significance for the construction of efficient and highly selective CO2photocatalytic systems.