Ni-MOF/g-C₃N₄ S-Scheme Heterojunction for Efficient Photocatalytic CO₂ Reduction

The rapid recombination of photoinduced charge carriers in semiconductors remains a significant challenge for their practical application in photocatalysis. This study presents the design of a step-scheme (S-scheme) heterojunction composed of carbon nitride (g-C₃N₄) and nickel-based metal-organic framework (Ni-MOF) to achieve enhanced charge separation. The establishment of an S-scheme charge transfer configuration at the interface of the Ni-MOF/g-C₃N₄ heterostructure plays a pivotal role in enabling efficient charge carrier separation, and hence, high CO₂ photoreduction efficiency with a CO evolution rate of 1014.6 µmol g^-1 h^-1 and selectivity of 95% under simulated solar illumination. CO evolution represents an approximately 3.7-fold enhancement compared to pristine Ni-MOF. Density functional theory (DFT) calculations, supported by in situ irradiated X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) experimental results, confirmed the establishment of a well-defined and strongly bonded interface, which improves the charge transfer and separation following the S-scheme mechanism. This study sheds light on MOF-based S-scheme heterojunctions as fruitful and selective alternatives for practical CO₂ photoreduction.