Two task-specific ionic liquids (TSILs) were encapsulated into the framework of a Zeolite imidazolate framework-8 (ZIF-8) to enhance its CO₂ capture capacity and CO₂/N₂ selectivity at post-combustion conditions. 1-Ethyl-3-methylimidazolium amino-acetate {[EMIM][glycine (Gly)]} and 1-Ethyl-3-methylimidazolium (S)-2-aminopropionate {[EMIM][alanine (Ala)]} were selected as TSILs. TSIL@ZIF-8 composite sorbents were prepared by varying the loading of TSIL, and properties such as sorbent thermal stability, porous structure and crystal nature of the composite were investigated. The incorporation of TSIL into ZIF-8 led to a dramatic rise in CO₂ uptake particularly at pressures lower than 1.0 bar. At this low-pressure range, CO₂ uptake was greater than in pristine ZIF-8 for all TSIL loadings and TSIL@ZIF-8 composites with 30 wt.% [Emim][Gly] reached a CO₂ uptake capacity of 0.76 mmol·g^-1 solid at 0.1 bar, and 0.88 mmol/g-solid at 0.2 bar at 303 K. These values were 13 and 7 times higher that CO₂ uptake in pristine ZIF-8 at identical conditions. TSIL functionalized composites also exhibited much higher selectivity than pristine ZIF-8 at all pressures. For instance, at 30 wt.% [EMIM][Gly] loading, CO₂/N₂ ideal selectivities at 313 K were 28 and 19 at 0.1 and 0.2 bar, respectively. This synthesized composite sorbent, with significantly high CO₂ uptake, better CO₂/N₂ selectivity at the low-pressure region (<1.0 bar), and low isosteric heat of adsorption (Q_st), confirms that TSIL@ZIF-8 composites can be potential candidates for post-combustion CO₂ capture processes and opens the door for the further development of suitable TSIL@MOF composite sorbent to be deployed in the CO₂ capture process.

This work presents the encapsulation of two amino acid-based ionic liquids (AAILs), 1-Ethyl-3-methylimidazolium glycine [Emim][Gly], and 1-Ethyl-3-methylimidazolium alanine [Emim][Ala], into an highly porous metal organic framework, MOF-177, to create a state-of-the-art composite for post-combustion CO₂ capture. The AAILs@MOF-177 composite sorbents were synthesized at varying loadings of AAILs. These composite sorbents were then evaluated and examined for their thermal and structural integrity, CO₂ capture capability, CO₂/N₂ selectivity, and heat of adsorption. Thermogravimetric analysis of the composites demonstrated that the encapsulation was successful, and the slow degradation of the composites suggested that AAILs and MOF-177 interacted with each other to some extent. Both the surface area and the pore volume of the composites experienced a dramatic decrease as a direct result of the encapsulation of the AAILs. The findings of the XRD analysis also showed that an increase in the loading of AAILs greater than a particular limit produced a degradation in the structural integrity of the parent support. At pressures below 1 bar (post-combustion conditions), the AAILs encapsulated composites outperformed the pure MOF177 in terms of CO₂ uptake and selectivity. The maximum CO₂ uptake was found to be at 20 wt.% loading for both [Emim][Gly]@MOF-177 and [Emim][Ala]@MOF-177 at 0.2 bar, 303 K, and the uptake values were about three times higher than MOF-177. In addition, the CO₂/N₂ selectivity of 20-[Emim][Gly]@MOF-177 and 20-[Emim][Ala]@MOF-177 increased from 5 (pristine MOF-177) to 13 and 11, respectively. However, it was discovered that the ideal amount of AAILs was 20 wt.%, and after that, increasing the loading any further, even to 30%, did not increase the CO₂ uptake. The results of this study shed light on the stability of AAILs@MOF-177 composites, as well as their overall performance in capturing CO₂ and CO₂/N₂ selectivity under post-combustion CO₂ capture conditions.