Rational regulation of the torsion angle of covalent organic frameworks for enhanced CO2 photoreduction to ethane

Abstract

Light-driven CO₂ reduction to hydrocarbon fuels is a green and sustainable technology to alleviate global warming while producing high value-added chemicals. However, highly efficient production of ethane (C₂H₆) remains a great challenge due to insufficient electron deliverability and sluggish C–C coupling kinetics. Herein, a series of β-ketoenamine linked Tp-COFs-Mo with different torsion angles were designed and synthesized for the photocatalytic CO₂ reduction reaction to C₂H₆. It was disclosed that these Tp-COFs-Mo had identical structural active sites of Mo–N₃O, while different torsion angles significantly affected their photocatalytic performance. Significantly, TpPa-COF-Mo exhibited a remarkable C₂H₆ production rate of 262.6 µmol g⁻¹ h⁻¹ and a high C₂H₆ electron selectivity of 91.8%, which exceeds that of the most COF-, POP-, and MOF-based photocatalysts reported previously. Mechanism studies revealed that the smaller torsion angle of TpPa-COF-Mo led to electron accumulation within the layers and stronger electron capturing capacity of Mo sites, which improved separation and transfer of photogenerated electrons along the intralayer, enhanced *H adsorption, and reduced the energy barrier for the formation of *CHOCO intermediate species, thus promoting the efficient conversion of CO₂ to C₂H₆. This work opens a new pathway to design efficient COF catalysts by optimizing the torsion angle of COFs.