Synergistic Visible-Light-Driven CO ₂ Reduction and H ₂ O Oxidation over Ti ₃ C ₂ Quantum Dot-Modified Cu/g-C ₃ N ₄ Photocatalysts

Photocatalytic CO 2 reduction into value-added fuels using water as the electron donor represents a sustainable route for artificial photosynthesis, yet it is often hindered by rapid charge recombination and insufficient thermodynamic driving force. Herein, we report a ternary heterojunction photocatalyst composed of zero-dimensional Ti 3 C 2 quantum dots (QDs) and metallic Cu comodified on two-dimensional g-C 3 N 4 (denoted as CCNT). The Cu nanoparticles broaden the visible-light absorption and negatively shift the conduction band of g-C 3 N 4, providing a strong driving force for CO 2 reduction. Meanwhile, the highly conductive Ti 3 C 2 QDs act as efficient electron reservoirs, rapidly extracting photogenerated electrons from Cu/g-C 3 N 4 and redistribute photogenerated electrons. This prevents charge accumulation at Cu sites, stabilizes the reduction centers, and maintains electron–hole balance. The optimized CCNT-5 composite achieves CO and CH 4 production rates of 24.59 and 20.24 μmol g –1 h –1 under visible light, resulting an electron selectivity toward CO 2 reduction as high as 94.90%. Moreover, the catalyst enables simultaneous water oxidation with a nearly 1:1 electron-to-hole consumption ratio and excellent long-term stability. This work demonstrates a rational 0D/metal/two-dimensional (2D) architecture for efficient and stable solar-driven CO 2 reduction.