A long-lasting TIF-4 MOF glass membrane for selective CO2 separation

Membrane technology with environmentally friendly and cost-efficient features has been well acknowledged as a promising solution for effective CO2 separation. Metal organic framework (MOF) glasses are one of the most attractive membrane materials currently, because of their easy processability, absence of grain-boundary defects, and permanent porosity. In this study, a mixed linker tetrahedral imidazolate framework-4 (TIF-4) MOF with ultrahigh glass forming ability was selected for fabricating highly CO2 selective membranes. Through adjusting the molar ratio of the imidazole (Im) and 5-methylbenzimidazolate (5-mbIm) linkers in the TIF-4 framework, the melting temperatures as well as the CO2 adsorption property could be controlled systematically. After vitrification, TIF-4 glasses (agTIF-4) with varying 5-mbIm content were prepared, and all of them exhibit higher isosteric heat of CO2 adsorption than the corresponding TIF-4 crystals. Both CO2/CH4 and CO2/N2 uptake ratio (298 K, 1 bar) of agTIF-4 samples are more than twice as that of TIF-4 crystals, suggesting the great potential of agTIF-4 for CO2 separation. Further, agTIF-4 membranes were successfully prepared by the melt-quenching process from the polycrystalline membranes. agTIF-4 membranes are highly CO2 selective with CO2/N2 and CO2/CH4 separation factors of 27 and 30. More importantly, agTIF-4 membrane displays long-term stability up to 10 months, which is highly conductive to its industrial application for CO2 separation.