Topology-Oriented Assembly of Iron-2,5-Furandicarboxylate Coordination Cubes for Highly Selective CO₂/SF₆/N₂ Capture

As typical greenhouse gases, selective capture of CO₂ (carbon dioxide) and SF₆ (sulfur hexafluoride) is of great importance. Herein, on the basis of a typical six-connected <i>pcu</i> topology, three isomorphic Fe-2,5-furandicarboxylate (Fe-FDC) metal-organic framework (MOF) adsorbents (SNNU-133-135) were successfully prepared via a rational assembly of {[Fe₃O]₈(FDC)₁₂} cubic building blocks. With dihedral angles in Fe-FDC cubes varying from 80° (SNNU-133), 87° (SNNU-134), to 90°(SNNU-135), three MOF isomers show step-by-step enhancement of selective CO₂ and SF₆ capture performance. For SNNU-135, at 298 K and 1 bar, the adsorption capacities for CO₂ and SF₆ are 83.6 and 66.7 cm³/g, and the CO₂/N₂ and SF₆/N₂ selectivity values are up to 29.4 and 509.1, respectively. Furthermore, the practical breakthrough interval time of SNNU-135 can reach 75 and 185 min g^-1 (298 K, 1 bar, 1 mL min^-1, CO₂/N₂ = 15:85 and SF₆/N₂ = 10:90) with the captured CO₂ and SF₆ amounts of 1.24 and 2.34 mmol/g, and the SF₆ purity greater than 99.9%. The most regular Fe-FDC cubes, all available Fe-OMSs together with multiple weak interactions, cause SNNU-135 to have the highest CO₂ and SF₆ adsorption capacity, best CO₂/N₂ and SF₆/N₂ selectivity performance, and one-step separation ability for CO₂/SF₆/N₂ ternary mixtures.