Green Synthesis of MOF-801(Zr/Ce/Hf) for CO2/N2 and CO2/CH4 Separation

Thepurification of natural gas and the removal of carbon dioxidefrom flue gases are crucial to economize precious resources and effectivelyrelieve a series of environmental problems caused by global warming.Metal-organic framework (MOF) materials have demonstrated remarkableperformance and benefits in the area of gas separation; however, obtainingmaterials with high gas capacity and selectivity simultaneously remainsdifficult. In addition, harsh synthesis conditions and solvent toxicityhave been restricted in large-scale production and industrial application.Therefore, MOF-801-(Zr/Ce/Hf) was created based on the green synthesisof the MOF-801 construction unit by altering the kinds of metal salts,and the impact of three metal nodes on the performance of gas adsorptionand separation was demonstrated by contrasting the three MOFs. Theresults showed that MOF-801-(Ce) has the best CO2 adsorptioncapacity (3.3 mmol/g at 298 K), which also was demonstrated with insitu diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)results, CO2/CH4 (ideal adsorbed solution theory(IAST) = 13.28 at 298 K, 1 bar, CO2/CH4 = 1:1,v/v), and the separation performance of CO2/N-2 (IAST = 57.46 at 298 K, 1 bar, CO2/N-2 = 1:1,v/v) among the group. Green synthesis of MOF-801-(Zr/Ce/Hf) is an idealcandidate for flue gas separation and methane purification becauseof its high regeneration capacity and strong cyclic stability. MOF-801-(Zr/Ce/Hf) was successfully synthesizedby the greensynthesis method, which was developed for gas separation of CO2/N-2 and CO2/CH4. Due to theenvironments of the pores varied by the different metal nodes, itwas found that the MOF-801-(Zr/Ce/Hf) with the same topology showedgreat difference in the gas separation performance. The in situ DRIFTSwas helpful to explain this phenomenon at the mechanism adsorptionlevel.