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

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