Microwave-Assisted Rapid Synthesis of Well-Shaped MOF-74 (Ni) for CO2 Efficient Capture

In the present work, a series of MOF-74 (Ni) materials with narrow micropore channels and abundant unsaturated metal sites was respectively prepared via hydro thermal (HT), condensation reflux (CE), and microwave assisted (MW) methods. The physicochemical properties of synthesized materials were characterized by powder X-ray diffraction, N-2-sorption, field-emission scanning electron microscopy, Fourier-transform infrared (FTIR), thermogravimetric (TG)/TG-FTIR, X-ray photoelectron spectroscopy, UV-vis-near infrared, NH3/CO2-temperature programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy. Their CO2/N-2 adsorption performances were evaluated by isotherm adsorption and dynamic adsorption experiments. We found that the MW is a rapid and facile protocol for the synthesis of MOF-74 (Ni) materials with highly efficient CO2 capture capacity. The well-shaped MW-140 adsorbent with superior CO2 adsorption capacity of 5.22 mmol/g at 25 degrees C can be obtained within 60 min by the MW process, almost 6 times higher than that of the commercial activated carbon (0.89 mmol/g). Results of dynamic adsorption experiments showed that the MW-140 material possesses the highest CO2 adsorption capacity of 3.37 mmol/g under humid conditions (RH = 90%). Importantly, MW-140 has excellent adsorption stability and recyclability, superior CO2 capture selectivity (CO2/N-2 = 31), and appropriate isosteric heat in CO2 adsorption (21-38 kJ/mol), making it a promising and potential material for industrial CO2 capture. Characterization results demonstrated that the high capture capability of MOF-74 (Ni) materials can be attributed to the synergistic effect of abundant narrow micropore channels and rich five-coordinated Ni2+ open metal sites which are beneficial for the trapping of CO2 molecules.