MOF-derived carbon and dicarboxylate ionic liquid in mixed matrix membranes: Exploring single and combined filler effects for CO2 separation

Mixed-matrix membranes (MMMs) based on the polymer PEBAX® 1657, incorporating a metal-organic framework (MOF) ZIF-8-derived carbon (C_ZIF-8), a dicarboxylate ionic liquid ([C 2 MIM] 2 [Glu]), or both, were produced to investigate the individual and combined effects of CO 2 -philic fillers on membrane morphology, surface wettability, thermal and mechanical behavior, and gas permeation performance. Characterization showed that C_ZIF-8 formed distinct carbon-rich regions that influenced surface wettability and gas transport, while the IL was homogeneously dispersed and exhibited interactions with both polyamide and polyethylene oxide segments of PEBAX® 1657, thus affecting thermal and mechanical properties. Pure-gas permeation measurements revealed that C_ZIF-8-MMMs exhibited a pronounced enhancement in CO 2 permeability, exceeding a sixfold increase at high carbons loadings (30 wt.% C_ZIF-8) , while ideal selectivity was maintained or slightly improved. These gains were attributed to fast CO 2 diffusion pathways and preserved size-sieving effects inherited from the ZIF-8 precursor. In contrast, IL-MMMs presented only moderate changes in CO 2 permeability. For two-filler MMMs, CO 2 permeability was primarily determined by C_ZIF-8 content, with the IL exerting a secondary, composition-dependent influence. The gas mixture and humidity effects on the gas permeation performance of selected MMMs were also investigated. For C_ZIF-8-MMMs, the CO 2 /CH 4 mixture reduced CO 2 permeability and decreased selectivity at high carbon loadings due to flux-dominated competitive transport. In contrast, the CO 2 /N 2 mixture enhanced CO 2 both permeability and selectivity relative to pure-gas predictions, reflecting favorable competitive sorption effects. In two-filler MMMs, the presence of the IL reduced CO 2 permeability and selectivity under mixture conditions, indicating therefore a hindering effect. Moderate humidity (25% RH) consistently increased CO 2 permeability in CO 2 /N 2 mixtures for all membranes without significantly affecting N 2 transport, highlighting the relevance of these membranes for realistic flue gas separation.