Visible-Light-Driven Photocatalytic CO ₂ Reduction to CO Using g-C ₃ N ₄ Nanostructures Coupled with a Molecular Re(I) Catalyst for Solar Fuel Generation

Visible - light-driven photocatalysts for carbon dioxide (CO 2 ) reduction offer a promising strategy for generating chemical fuels and addressing energy and environmental challenges. Herein, a heterogeneous photocatalyst Re(py)/g-C 3 N 4 comprising graphitic carbon nitride (g-C 3 N 4 ) nanostructures as a photosensitizer and [Re(CO) 3 (3-(2-pyridyl)-1,2,4-triazole)Cl] (Re(py)) as a CO 2 reduction catalyst) was constructed for the efficient reduction of CO 2 to carbon monoxide (CO) under visible-light irradiation. The improved photocatalytic performance of Re(py)/g-C 3 N 4 is attributed to strong interfacial interactions between Re(py) and g-C 3 N 4, evidenced by increased Brunauer–Emmett–Teller surface area, suppressed electron–hole recombination, improved charge separation, and efficient interfacial charge transfer. Linkage between Re(py) and g-C 3 N 4 through −OH groups on treated-g-C 3 N 4 and −NH groups on the triazole ring was confirmed using XRD, FTIR, XPS, TEM, and SEM. Photocatalytic CO 2 reduction using Re(py)/g-C 3 N 4 exhibited high selectivity for CO over H 2, with turnover numbers of 36.86 for CO and 1.59 for H 2 after 300 min of irradiation, corresponding to a CO selectivity of 98% (compared to 93% for Re(py). The CO formation by Re(py)/g-C 3 N 4 was 24.23 times higher than that of Re(py), confirming the synergistic effect of the hybrid photocatalyst. Mechanistic studies indicate that photoexcited electrons from the conduction band of g-C 3 N 4 are thermodynamically transferred to Re(py), which catalyzes the CO 2 -to-CO reduction. This study demonstrates a heterogeneous photocatalytic system with potential for solar fuel production and carbon recycling through selective CO 2 -to-CO reduction.