SPR-enhanced photocatalytic CO₂ reduction over CuO_x/N-vacancy-rich g-C₃N₄ heterojunction: Unraveling the synergistic roles of defect engineering and charge transfer pathways

Constructing efficient photocatalysts for CO₂ reduction is challenging due to the inefficient CO₂ activation and rapid photoinduced charge recombination. In this work, a ternary Cu/Cu₂O/N-vacancy-rich g-C₃N₄ (CuO_x/NVCN) heterostructure photocatalyst is rationally designed and synthesized via an ice-assisted photoreduction method. The introduction of nitrogen vacancies (NVs) into the g-C₃N₄ framework serves as active sites for enhanced CO₂ adsorption and activation. The construction of an S-scheme heterojunction between Cu₂O and creates a built-in electric field that drives the efficient spatial separation of photogenerated charge carriers while preserving their strong redox potentials. Furthermore, the incorporation of plasmonic Cu nanoparticles extends light absorption via the surface plasmon resonance (SPR) effect and provides an additional pathway for hot electron injection. This multi-component system establishes a synergistic electron transfer highway and accelerates the generation and transformation of key intermediates. Consequently, the optimized CuO_x/NVCN catalyst achieves a remarkably enhanced CO production rate of 6.13 μmol g−1 h−1, which is 4.6 times that of pristine g-C₃N₄. This work underscores the profound potential of coupling defect engineering, S-scheme heterojunctions, and plasmonic effects for advanced solar fuel production.