Boosting CO2 selectivity by mono- and dicarboxylate-based ionic liquids impregnation into ZIF-8 for post-combustion separation

• Monocarboxylate- and dicarboxylate-based ILs were used to produce IL@MOF materials. • Composite [C2MIM]2[Glu]@ZIF-8 showed the highest CO2 sorption at 0.15 bar. • The anionic carbon chain size can tailor the selectivity of composites at 1 bar. • Composite [C2MIM][Cap]@ZIF-8 was nearly 5-times more selective than pristine ZIF-8. Post-combustion carbon dioxide (CO 2 ) capture/separation is considered one of the main ways to minimize the impact of global warming caused by this greenhouse gas. This work used eight mono- and dicarboxylate-based ionic liquids (ILs) to impregnate metal-organic framework (MOF) ZIF-8. This anionic effect was studied for these mostly unreported IL@MOF composites to determine its impact on gas sorption and selectivity performance. Characterization results confirmed IL impregnation into the structure of ZIF-8, along with the conservation of microporosity and crystallinity in composites. Sorption-desorption equilibrium measurements were performed, and CO 2 and nitrogen (N 2 ) isotherms were obtained at 303 K for ZIF-8 and IL@ZIF-8 composites. At 0.15 bar, the dicarboxylate-based composite [C 2 MIM] 2 [Glu]@ZIF-8 showed the highest CO 2 gas sorption, showing 50 % more sorption capacity than the best monocarboxylate-base composites at this pressure. Dicarboxylate-based composites also showed remarkable N 2 sorption in the low-pressure range. The ideal CO 2 /N 2 selectivity for a typical post-combustion composition was calculated, and a trend regarding the anionic carbon chain size was observed. The composite [C 2 MIM][Cap]@ZIF-8 showed nearly five times more selectivity than the pristine ZIF-8 at 1 bar of total pressure. Dicarboxylate-based composites, given their low-pressure high N 2 sorption capacity, were not as selective as their respective monocarboxylate-based IL@ZIF-8 materials with the same carbon chain size.