Silver nanoparticles as electron mediators in a Z-scheme g-C₃N₄/rhenium complex photocatalyst for CO₂-to-CO reduction

A hybrid photocatalyst g-C₃N₄/Ag/Re, comprising silver nanoparticle (AgNP) modified graphitic carbon nitride (g-C₃N₄/Ag) nanosheets and [Re(CO)₃(2,2'-bipyridine-4,4'-dicarbonyl acid)Cl], was successfully constructed. Compared with g-C₃N₄/Re, g-C₃N₄/Ag/Re exhibits enhanced photocatalytic CO₂-to-CO conversion under visible-light irradiation, demonstrating that AgNPs improve the interfacial interaction between g-C₃N₄ and the Re complex. The turnover number (TON) for CO of g-C₃N₄/Ag/Re reaches 70.60 at 150 min, representing 7.60- and 1.31-fold increases compared with the Re complex and g-C₃N₄/Re, respectively. The CO selectivity of g-C₃N₄/Ag/Re and g-C₃N₄/Re is determined to be 94.5% and 94.8%, respectively. These results indicate that AgNP modification enhances the visible-light absorption of g-C₃N₄, promotes charge separation, and facilitates interfacial electron transfer from g-C₃N₄ to the Re complex. The photocatalytic mechanism of g-C₃N₄/Ag/Re is proposed to follow a Z-scheme-like charge-transfer pathway, in which g-C₃N₄ acts as the light-harvesting component, the Re complex serves as a CO₂ reduction site, and AgNPs function as electron mediators. This study provides a promising strategy for developing highly efficient photocatalysts for CO₂ reduction.