Polyimide/ZIFs mixed matrix membranes with tunable interfacial interaction for efficient gas separation

Manipulating favorable interfacial microstructure is crucial to rationally design a high-performance mixed matrix membrane with defect-free interface. We describe herein an efficient pathway to finely tune the interfacial adhesion through balancing the metal organic frameworks and polymer functionality. The varied number of hydrogen bonds are established involving the CHO groups in hybrid ZIF-8-90(x) fillers with varied carboxaldehyde-2-imidazole linker contents and 6FDA-DAM:DABA copolyimides having adjustable COOH groups concentrations, thereby precisely controlling the membrane interfacial bonding behavior. As expected, the gas selectivity of the resulting membranes is gradually enhanced with increasing carboxaldehyde-2-imidazole linker substitution ratio in ZIF-8-90(x), mainly contributed by significant improvements in hydrogen bonding strength. The enhanced interaction is confirmed by good adhesion visualized in SEM images and the CO vibration band shift in FTIR spectra. Meanwhile, adjusting the proportion of DABA moiety in polymers is an auxiliary path to regulate the interfacial bonding strength. The optimized membrane of 6FDA-DAM:DABA (1:1)/10 wt.% ZIF-8-90(30) has enhanced H2/CH4 and CO2/CH4 ideal selectivities of 75.4 and 43.6, respectively, with H2 and CO2 permeabilities of 222 Barrer and 128 Barrer. These findings imply that progressively regulating filler and polyimide functionality is a feasible route to finely tailor interfacial hydrogen bonding strength to achieve a membrane with tunable separation performance.