One-Pot Method Synthesis of Bimetallic MgCu-MOF-74 and Its CO2 Adsorption under Visible Light

A magnesium-based metal–organic framework (Mg-MOF-74) exhibits excellent CO2 adsorption under ambient conditions. However, the photostability of Mg-MOF-74 for CO2 adsorption is poor. In this study, MgxCu1–x-MOF-74 was synthesized by using a facile “one-pot” method. Furthermore, the effects of synthesis conditions on the CO2 adsorption capacity were investigated comprehensively. X-ray diffraction, Fourier transform infrared, scanning electron microscopy, thermo gravimetric analysis, inductively coupled plasma atomic emission spectroscopy, ultraviolet–visible spectroscopy and photoluminescence spectroscopy, and CO2 static adsorption–desorption techniques were used to characterize the structures, morphology, and physicochemical properties of MgxCu1–x-MOF-74. CO2 uptake of MgxCu1–x-MOF-74 under visible light illumination was measured by the CO2 static adsorption test combined with the Xe lamp. The results revealed that MgxCu1–x-MOF-74 exhibited excellent photocatalytic activity. Furthermore, the CO2 adsorption capacity of MgxCu1–x-MOF-74 was excellent at a synthesis temperature and time of 398 K and 24 h in dimethylformamide (DMF)-EtOH-MeOH mixing solvents, respectively. MgxCu1–x-MOF-74 retained a crystal structure similar to that of the corresponding monometallic MOF-74, and its CO2 uptake under visible light was superior to that of the corresponding monometallic MOF-74. Particularly, the CO2 uptake of Mg0.4Cu0.6-MOF-74 under Xe lamp illumination for 24 h was the highest, up to 3.52 mmol·g–1, which was 1.18 and 2.09 times higher than that of Mg- and Cu-MOF-74, respectively. The yield of the photocatalytic reduction of CO2 to CO was 49.44 μmol·gcat–1 over Mg0.4Cu0.6-MOF-74 under visible light for 8 h. Mg2+ and Cu2+ functioned as open alkali metal that could adsorb and activate CO2. The synergistic effect between Mg and Cu metal strengthened MgxCu1–x-MOF-74 photostability for CO2 adsorption and broadened the scope of its photocatalytic application. The “bimetallic” strategy exhibits considerable potential for use in MOF-based semiconductor composites and provides a feasible method for catalyst design with remarkable CO2 adsorption capacity and photocatalytic activity.