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

Abstract

Several strategies can be considered for the mitigation of carbon dioxide (CO₂) 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 CO₂ and nitrogen (N₂) 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 CO₂/N₂ selectivity was calculated for post-combustion composition, and, at 1 bar, [C₁₀MIM][Ac]@ZIF-8 was over four times more selective than ZIF-8, while the selectivity of [C₂MIM][Ac]@ZIF-8 at this pressure almost tripled when compared to the MOF. A chemical reaction between CO₂ and the imidazolium ILs explained the results.