Synthesis and characterization of Zn2GeO4/Mg-MOF-74 composites with enhanced photocatalytic activity for CO2 reduction

Abstract

Strategies for effectively enhancing the photoreduction of CO₂ have been studied for several decades. In this work, Zn₂GeO₄/Mg-MOF-74 composites were prepared via a hydrothermal method. The X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM) images and transmission electron microscopy (TEM) images demonstrate the successful synthesis of Zn₂GeO₄/Mg-MOF-74 composites. The infrared spectra and TEM images indicate a close interaction between Zn₂GeO₄ and Mg-MOF-74, which is attributed to tetramethylammonium hydroxide (TMAOH) adsorbed on Zn₂GeO₄ and interacts with 2,5-dioxide-1,4-benzenedicarboxylate (H₄DOBDC) from Mg-MOF-74. The CO₂ adsorption isotherms illustrate that the incorporation of Mg-MOF-74 into Zn₂GeO₄ nanorods improved the adsorption of CO₂. Only with water as the sacrificial agent, the hydrothermally prepared Zn₂GeO₄/Mg-MOF-74 catalyst exhibited a superior performance for the conversion of CO₂ into carbon monoxide compared to that of single Zn₂GeO₄ or a physical mixture of Zn₂GeO₄/Mg-MOF-74, which is attributed to its higher adsorption capacity for CO₂ and reduced recombination of photogenerated electron–hole pairs. In situ photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) further demonstrated that the Zn₂GeO₄/Mg-MOF-74 catalyst exhibits superior charge-transfer properties. This work may provide a useful strategy to design novel and efficient photocatalysts to reduce the atmospheric concentration of CO₂.