Ligand-defective Ni-MOF-74/g-C₃N₄ heterojunction via in situ growth for boosted photocatalytic CO₂ reduction

Solar-driven photocatalytic reduction of CO₂ into value-added fuels offers a promising route to address greenhouse gas emissions and energy shortages. Herein, we report the in situ growth of ligand-defective Ni-MOF-74 (Ni-DMOF) on graphitic carbon nitride (g-C₃N₄) to construct a series of heterojunction photocatalysts (denoted as XCNN, X = 100, 200, 300 mg of g-C₃N₄). Ligand defects in Ni-DMOF expose abundant unsaturated Ni active sites and optimize charge transfer behavior, while the in situ heterojunction with g-C₃N₄ promotes interfacial contact and efficient spatial separation of photogenerated electron-hole pairs. The optimized 300CNN catalyst exhibits a remarkable CO production rate of 3.52 mmol g^-1 h^-1 with a high CO selectivity of 96.77%, which is 2.66 times higher than that of pure Ni-DMOF. Moreover, 300CNN exhibits good stability over six consecutive catalytic cycles. Comprehensive characterization studies reveal that the enhanced performance originates from the synergistic effects of defect engineering in Ni-DMOF and the charge transfer pathway in the Ni-DMOF/g-C₃N₄ heterojunction, which accelerates charge separation, suppresses carrier recombination, and retains strong redox capability. This work provides a feasible strategy for designing high-efficiency MOF/semiconductor heterojunction photocatalysts for CO₂ conversion.