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.