Fine pore engineering in a series of isoreticular metal-organic frameworks for efficient C2H2/CO2 separation

Jun Wang,Qiang Deng,Shuguang Deng,Rui-Biao Lin,Peixin Zhang,Banglin Chen,Zheling Zeng,Yan Zhang,Yun Su,Shixia Chen,Xing Liu

doi:10.1038/s41467-021-27929-7

Abstract

The separation of C2H2/CO2 is not only industrially important for acetylene purification but also scientifically challenging owing to their high similarities in physical properties and molecular sizes. Ultramicroporous metal-organic frameworks (MOFs) can exhibit a pore confinement effect to differentiate gas molecules of similar size. Herein, we report the fine-tuning of pore sizes in sub-nanometer scale on a series of isoreticular MOFs that can realize highly efficient C2H2/CO2 separation. The subtle structural differences lead to remarkable adsorption performances enhancement. Among four MOF analogs, by integrating appropriate pore size and specific binding sites, [Cu(dps)2(SiF6)] (SIFSIX-dps-Cu, SIFSIX = SiF62-, dps = 4.4’-dipyridylsulfide, also termed as NCU-100) exhibits the highest C2H2 uptake capacity and C2H2/CO2 selectivity. At room temperature, the pore space of SIFSIX-dps-Cu significantly inhibits CO2 molecules but takes up a large amount of C2H2 (4.57 mmol g−1), resulting in a high IAST selectivity of 1787 for C2H2/CO2 separation. The multiple host-guest interactions for C2H2 in both inter- and intralayer cavities are further revealed by dispersion-corrected density functional theory and grand canonical Monte Carlo simulations. Dynamic breakthrough experiments show a clean C2H2/CO2 separation with a high C2H2 working capacity of 2.48 mmol g−1.

Highlights

The separation of C2H2/CO2 is industrially important for acetylene purification and scientifically challenging owing to their high similarities in physical properties and molecular sizes
By substituting organic linkers and/or metal nodes, the pore space in metal-organic frameworks (MOFs) can integrate shape matching and specific binding toward targeted gas molecules[25,26]
Crystal structures of the as-synthesized MOFs were determined by singlecrystal X-ray diffraction studies, and the phase purities of assynthesized and activated samples were confirmed by the XRD measurements (Supplementary Figs. 2–4 and Supplementary Table 1)

Summary

Introduction

The separation of C2H2/CO2 is industrially important for acetylene purification and scientifically challenging owing to their high similarities in physical properties and molecular sizes. Flexible MOFs usually show negligible gas uptake before gate-opening, which might lead to capture leakage when applied to the breakthrough separation of gas mixture[34,35,36,37,38] In this context, flexible-robust MOFs with permanent small pores as well as specific binding sites have been employed to selective take up targeted gas molecules, whereas minimizing the co-adsorption of counterpart gases by tuning the gate-opening pressure, which has been demonstrated by [Cu(dps)2(SiF6)] (SIFSIX-dps-Cu) for size-exclusive adsorption of C2H2 from C2H439. By integrating suitable pore size and fluorinated binding sites, the exclusive C2H2 sorption behavior was retained in [Cu(dps)2(SiF6)] (SIFSIX-dps-Cu, SIFSIX = SiF62−, dps = 4.4′-dipyridylsulfide, termed as NCU-100) with a C2H2 uptake of 4.57 mmol g−1 and negligible CO2 uptake, resulting in a high IAST selectivity of 1787 for C2H2/CO2 separation. The highly efficient C2H2/CO2 separation in [Cu(dps)2(SiF6)] has been validated by molecular modeling studies and dynamic breakthrough experiments

Methods

Results

Conclusion