Tuning the Interplay between Selectivity and Permeability of ZIF-7 Mixed Matrix Membranes

Nanoparticles of zeolitic imidazolate framework-7 (nZIF-7) were blended with poly(ether imide) (PEI) to fabricate a new mixed-matrix membrane (nZIF-7/PEI). nZIF-7 was chosen in order to demonstrate the power of postsynthetic modification (PSM) by linker exchange of benzimidazolate to benzotriazolate for tuning the permeability and selectivity properties of a resulting membrane (PSM-nZIF-7/PEI). These two new membranes were subjected to constant volume, variable pressure gas permeation measurements (H2, N2, O2, CH4, CO2, C2H6, and C3H8), in which unique gas separation behavior was observed when compared to the pure PEI membrane. Specifically, the nZIF-7/PEI membrane exhibited the highest selectivities for CO2/CH4, CO2/C2H6, and CO2/C3H8 gas pairs. Furthermore, PSM-nZIF-7/PEI membrane displayed the highest permeabilities, which resulted in H2/CH4, N2/CH4, and H2/CO2 permselectivities that are remarkably well-positioned on the Robeson upper bound curves, thus, indicating its potential applicability for use in practical gas purifications.