Ultramicroporous Metal-Organic Frameworks Functionalized With Acyclic Ether Oxygen Bonds for Efficient C2H2/CO2 and C2H2/C2H4 Separation.

Abstract

Designing and tailoring porous materials to realize the precise separation of C₂H₂, C₂H₄ and CO₂ with nearly identical kinetic diameters is an extremely challenging research task. In this study, a novel microporous metal-organic framework (MOF) designated UPC-523 (Zn₃(H₄edda)₂·DMF) has been synthesized by employing 5,5'-(ethane-1,2-diylbis(oxy))diisophthalic acid (H₄edda), which is constructed with ethylene ether linkages (-O-CH₂-CH₂-O-). This rational design strategy employs ethylene ether moieties to construct a highly electronegative pore microenvironment within the framework. UPC-523 is endowed with abundant electronegative sites, the uncoordinated oxygen atoms in the confined pores selectively capture C₂H₂ from CO₂ and C₂H₄ through hydrogen-bonding interactions, enabling it to achieve selective adsorption of C₂H₂. At 298 K and 100 kPa, this MOF exhibits a C₂H₂ adsorption capacity of 44.9 cm³/g, coupled with a moderate isosteric heat of C₂H₂ adsorption (Q_st) of 33.7 kJ/mol, a property conducive to the direct desorption and regeneration of UPC-523. The IAST selectivities of C₂H₂/C₂H₄ (v/v = 50/50) and C₂H₂/CO₂ (v/v = 50/50) are 2.1 and 3.4, respectively, comparable to the majority of reported MOFs under identical conditions. Dynamic breakthrough experiments reveal that UPC-523 can efficiently separate C₂H₂ from C₂H₂/CO₂ or C₂H₂/C₂H₄ mixtures.