Efficient Photocatalytic CO₂ Conversion to CO and CH₄ by a rGO-Bridged g-C₃N₄/MoS₂ Indirect Z-Scheme Heterojunction

This study investigates CO2 photocatalytic conversion using a ternary composite of graphitic carbon nitride (GCN, g-C3N4), reduced graphene oxide (rGO), and molybdenum disulfide (MoS2). GCN was synthesized via thermal polymerization of urea with GO, followed by sonication and mixing to incorporate MoS2 (0.1–20 wt %). Characterization by XRD, FTIR, BET, FESEM, TEM, PL, photocurrent, DRS, and Mott–Schottky analyses confirmed a successful synthesis with GCN and rGO-GCN-10%MoS2 bandgaps of 2.88 and 2.68 eV, respectively. DRS, PL, and photocurrent results demonstrated enhanced charge carrier separation, electrical conductivity, and visible light absorption. The optimized rGO-GCN-10%MoS2 composite exhibited a specific surface area of 125.1 m2/g. Under 60 W LED illumination for 5 h, it achieved CO and CH4 yields of 34.08 and 13.08 μmol/g, representing 18.07-fold and 7.91-fold enhancements over GCN. The improved performance was attributed to synergistic effects, efficient charge separation, and a Z-scheme heterojunction between GCN and MoS2, confirmed by band position and product analyses.