Fine pore engineering in a series of isoreticular metal-organic frameworks for efficient C 2 H 2 /CO 2 separation.

The separation of C 2 H 2 /CO 2 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 C 2 H 2 /CO 2 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 (SiF 6 )] (SIFSIX-dps-Cu, SIFSIX = SiF 6 2- , dps = 4.4'-dipyridylsulfide, also termed as NCU-100) exhibits the highest C 2 H 2 uptake capacity and C 2 H 2 /CO 2 selectivity. At room temperature, the pore space of SIFSIX-dps-Cu significantly inhibits CO 2 molecules but takes up a large amount of C 2 H 2 (4.57 mmol g -1 ), resulting in a high IAST selectivity of 1787 for C 2 H 2 /CO 2 separation. The multiple host-guest interactions for C 2 H 2 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 C 2 H 2 /CO 2 separation with a high C 2 H 2 working capacity of 2.48 mmol g -1 .