Cationic effect study in acetate-based ionic liquids/ZIF-8 composites for CO2 sorption

Several strategies can be considered for the mitigation of carbon dioxide (CO 2 ) emissions to the atmosphere, and among them is its post-combustion capture/separation from flue gas emitted from coal-fired power plants. In this work, six imidazolium, ammonium- and DABCO-based ionic liquids (ILs) containing the acetate anion were used to impregnate the metal-organic framework (MOF) ZIF-8. The cationic effect was studied to determine how the different cationic families and side alkyl chain size influence the gas sorption performance of the produced IL@MOF composites. The combination of different characterization techniques confirmed IL impregnation, and that the composite materials were microporous and crystalline. Single-component CO 2 and nitrogen (N 2 ) sorption-desorption equilibrium measurements were performed at 303 K for ZIF-8 and the IL@ZIF-8 materials. At the low-pressure regime (0–1 bar), synergy was observed for the imidazolium-based composites, especially for the one with the long-side alkyl chain. The ideal CO 2 /N 2 selectivity was calculated for post-combustion composition, and, at 1 bar, [C 10 MIM][Ac]@ZIF-8 was over four times more selective than ZIF-8, while the selectivity of [C 2 MIM][Ac]@ZIF-8 at this pressure almost tripled when compared to the MOF. A chemical reaction between CO 2 and the imidazolium ILs explained the results. • Acetate-based ILs with different cations were used to produce IL@ZIF-8 materials. • Imidazolium-based composites showed the highest CO 2 sorption between 0 and 1 bar. • Cation nature and side alkyl chains size can tune the selectivity at low pressures. • [C 10 MIM][Ac]@ZIF-8 was over four-times more selective than pristine ZIF-8 at 1 bar.