In this research, ZIF-11 crystals were successfully synthesized, characterized and incorporated into Pebax ®2533 polymer in the range of 10–70 wt% to fabricate mixed matrix membranes (MMMs). SEM images as well as results of TGA and tensile testing analyses confirmed excellent adhesion between ZIF-11 and polymer matrix, especially at 30 wt% loading. The effect of filler loading on gas transport properties of the ZIF-11/Pebax ®2533 MMMs was studied for pure H 2 , N 2 , CH 4 and CO 2 gases. The ZIF-11/Pebax ®2533 MMMs were found to suffer from polymer chain rigidification and possibly blockage of the fillers by the polymer chains (more obvious at 10 wt% loading); which reduced the permeability of the MMMs. Results showed that at higher loadings, the sieving effect of ZIF-11 dominated the rigidification or pore blockage defects. At 50 and 70 wt% ZIF-11 loadings, a few voids were seen throughout the membranes, but no agglomeration occurred even at 70 wt% loading. Nevertheless, hydrogen ideal selectivities over other gases continued the increasing trend at 50 wt% and did not significantly reduce even at 70 wt% due to high compatibility between ZIF-11 and Pebax ®2533. Addition of ZIF-11 to the polymer improved the gas transport properties of the Pebax ®2533, especially towards H 2 separation. The highest H 2 /N 2 (12.86) and H 2 /CH 4 (4.81) ideal selectivities were obtained at 50 and 70 wt% loadings, respectively. The highest CO 2 permeability (402.89 Barrer) and CO 2 /CH 4 selectivity (12.49) were obtained for 70 wt% loading among all the prepared membranes.

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