Development of rGO/ZIF-67-integrated poly-ether-block-amid membranes for high-performance CO2 separation

The trade-off between carbon dioxide (CO 2 ) permeability and selectivity remains a major challenge in the development of polymeric mixed matrix membranes (MMMs) for gas separation. In this study, poly(ether-block-amide) (Pebax 2533) was employed as the polymer matrix, while reduced graphene oxide/zeolitic imidazolate framework-67 (rGO/ZIF-67) was incorporated as a hybrid nanofiller at loadings ranging from 0 to 20 wt% to investigate its influence on membrane morphology and CO 2 separation performance. The hybrid filler was selected based on previous studies demonstrating that incorporating reduced graphene oxide (rGO) into metal–organic framework (MOF)-based fillers can enhance membrane performance in other polymer systems, whereas its effect in Pebax 2533-based MMMs has not been systematically investigated. Structural characterization confirmed the successful synthesis of the rGO/ZIF-67 hybrid nanofiller and its effective incorporation into the Pebax 2533 matrix. Field emission scanning electron microscopy (FESEM) revealed relatively uniform filler dispersion at moderate loadings, whereas partial agglomeration was observed at 20 wt%, consistent with the corresponding changes in membrane performance. Gas permeation measurements demonstrated that the membrane containing 15 wt% rGO/ZIF-67 exhibited the optimum separation performance. At 30 °C and 10 bar, the CO 2 permeability increased from 392.1 Barrer for the pristine Pebax 2533 membrane to 718.2 Barrer, while the CO 2 /CH 4 and CO 2 /N 2 selectivities increased from 10.0 to 38.06 to 17.2 and 61.9, respectively. Furthermore, increasing the feed pressure enhanced CO 2 transport performance. Compared with the pristine membrane, the membrane containing 15 wt% rGO/ZIF-67 exhibited 25.2% and 47.6% higher CO 2 permeability at 6 and 10 bar, respectively. Under the same conditions, the CO 2 /CH 4 and CO 2 /N 2 selectivities increased by approximately 25% and 16% at 6 bar, reaching approximately 40% and 25%, respectively, at 10 bar. The enhanced gas separation performance is attributed to the synergistic effects of the porous ZIF-67 framework, which provides preferential CO 2 adsorption sites, and rGO, which improves polymer–filler interfacial compatibility and promotes more efficient gas transport pathways. These findings demonstrate that incorporating an appropriate amount of hybrid rGO/ZIF-67 nanofiller is an effective strategy for simultaneously improving the permeability and selectivity of Pebax 2533 MMMs for CO 2 separation.