Lewis basic site (LBS)-functionalized zeolite-like supramolecular assemblies (ZSAs) with high CO2 uptake performance and highly selective CO2/CH4 separation

Abstract

Herein, three functional isoreticular zeolite-like supramolecular assemblies (ZSAs), [Co₄(NH₂-ImDC)₄(1,2-PDA)₄]·8H₂O (ZSA-7), [Co₄(CH₂OH-ImDC)₄(1,2-PDA)₄]·8H₂O (ZSA-8), and [Co₄(Pr-ImDC)₄(1,2-PDA)₄]·9H₂O (ZSA-9), NH₂-ImDC = 2-amino-4,5-imidazoledicarboxylic acid, CH₂OH-ImDC = 2-hydroxymethyl-4,5-imidazoledicarboxylic acid, Pr-ImDC = 2-propyl-4,5-imidazoledicarboxylic acid, 1,2-PDA = 1,2-propanediamine, were hydrothermally synthesized and structurally characterized. All three compounds are isoreticular to ZSA-1, with the modification of different functional groups of –NH₂, –CH₂OH, and –Pr in imidazole dicarboxylate ligands. ZSA-7 and ZSA-8 display high CO₂ adsorption abilities (109.8 and 114.0 cm³ g⁻¹ at 273 K, respectively, under 1 bar) and outstanding natural gas selectivity separation, especially for CO₂ over CH₄ (39.8 and 35.7 for CO₂/CH₄ = 0.5/0.5 and 76.0 and 51.6 for CO₂/CH₄ = 0.05/0.95, respectively, under 1 bar at 298 K). In contrast, ZSA-9 is used for comparison to illustrate the effect of the introduction of Lewis basic sites (LBSs). Thus, all three ZSAs are promising materials for gas adsorption and purification applications.