The demand for cost-efficient separations requires membranes with high gas flux and high selectivity which opens the path for further improvements. Mixed matrix membranes (MMMs) made from 33.3 wt % ZIF-8 in 6FDA-durene were tested at 35 °C and 3.5 atm. At 33.3 wt % loading of ZIF-8, H 2 , N 2 , O 2 , and CH 4 gas permeabilities increased approximately 400%. Cross-linking the surface of this MMM, by reacting with ethylenediamine vapor, yielded a 10-fold increase in H 2 /CO 2 , H 2 /N 2 , and H 2 /CH 4 selectivities with respect to 6FDA-durene, preserving 55% of the H 2 permeability of 6FDA-durene. The permselective properties of the cross-linked skin of the MMM fall above the most recent permeability−selectivity trade-off lines (2008 Robeson upper bounds) for H 2 /CO 2 , H 2 /N 2 , and H 2 /CH 4 separations. To the best of our knowledge, this is the first example of a cross-linked ZIF/polymer MMM for gas separation.

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An immiscible polymer blend comprised of high-performance copolyimide 6FDA-DAM:DABA(3:2) (6FDD) and polybenzimidazole (PBI) was compatibilized using 2-methylimidazole (2-MI), a commercially available small molecule. Membranes were fabricated from blends of 6FDD:PBI (50:50) with and without 2-MI for H2/CO2 separations. The membranes demonstrated a matrix-droplet type microstructure as evident with scanning electron microscopy (SEM) imaging where 6FDD is the dispersed phase and PBI is the continuous phase. In addition, membranes with 2-MI demonstrated a uniform microstructure as observed by smaller and more uniformly dispersed 6FDD domains in contrast to 6FDD:PBI (50:50) blend membranes without 2-MI. This compatibilization effect of 2-MI was attributed to interfacial localization of 2-MI that lowers the interfacial energy similar to a surfactant. Upon the incorporation of 2-MI, the H2/CO2 selectivity improved remarkably, compared to the pure blend, and surpassed the Robeson's upper bound. To our knowledge, this is the first report of the use of a small molecule to compatibilize a high-performance immiscible polymer blend. This approach could afford a novel class of membranes in which immiscible polymer blends can be compatibilized in an economical and convenient fashion.

Herein we report a series of porous organic polymers (POPs) synthesized through a Sonogashira cross-coupling reaction containing hexaphenylbenzene (HEX) and hexabenzocoronene (HBC) with varying peripheral substitution. We observed vastly different gas sorption properties depending on substituent size and the extent of conjugation in the monomer core structure with BET surface areas ranging from 320 m2/g for HBC-POP-4 to 1140 m2/g for HEX-POP-3. In order to more clearly understand the effects of functional group substitution on the properties of these materials, we have characterized these POPs using N2, CO2, and H2 sorption measurements, powder X-ray diffraction, FT-IR spectroscopy, TGA, and EDX.

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