Enhanced visible-light-driven heterogeneous photocatalytic CO₂ methanation using a Cu₂O@Cu-MOF-74 thin film

Cuprous oxide is a potential photocatalyst for the reduction of CO₂. However, its high rate of charge recombination and low ability to adsorb CO₂ limit its activity, particularly when gaseous CO₂ was used. Herein, a Cu-based metal-organic framework (Cu-MOF-74) with high CO₂ adsorption is coated onto Cu₂O nanowires by a topotactic transformation method. The optimized Cu₂O@Cu-MOF-74 composite thin film showed a CH₄ evolution rate 4.5 times higher than that of bare Cu₂O under visible light illumination (>420 nm), with water vapor as the electron donor. Analysis results of electrochemical impedance spectroscopy, transient photocurrent measurements, and fluorescence spectroscopy collectively suggest that the decoration of Cu₂O with Cu-MOF-74 facilitates electron extraction from excited Cu₂O, thereby inducing long-lived photocharges for the reduction of CO₂. This study provides insights into the modification of transition metal oxides for application in photocatalysis by coating the surface with metal-organic frameworks.