Rational pore-window size control in three Cu-MOFs with different pore environments for efficient capture of the greenhouse gas SF6

Abstract

Effective SF6 gas storage and SF6/N2 mixture separations are extremely important in the industry. Herein, a series of isostructural metal-organic frameworks (MOFs), [Cu6(H2O)3(NTB)4(PYZ)1.5] (SNNU-202, H3NTB = nitrilotribenzoic acid, PYZ = pyrazine), [Cu12(H2O)3(NTB)8(PYZ)3(BPY)1.5] (SNNU-203, BPY = 4,4′-bipyridine) and [Cu6(NTB)4(DABCO)1.5(BPY)1.5] (SNNU-204, DABCO = 1,4-diazabicyclo[2.2.2]octane), with different pore window sizes have been explored for the adsorption and separation performance of sulfur hexafluoride. With stepwise partitioning of the pore window, the adsorption capacity for SF6 and separation of SF6/N2 mixture are gradually improved. Notably, the SF6 uptake value for SNNU-204 is 6.0 mmol g−1 and the amount of substance ratio of SF6-to-N2 uptake can be up to 29.8 at 298 K and 1 bar, surpassing most of top-performing MOFs reported. Ideal adsorbed solution theory (IAST) calculations and breakthrough curves demonstrated that SNNU-204 exhibited excelling separation performance. The stepwise pore window partition can create more micropores, and the aromatic ring of the inserted ligand also facilitates interaction with sulfur hexafluoride gas molecules, providing an important strategy for the application of MOFs in SF6 gas adsorption and separation.