The CO 2 capture efficiency of nine newly synthesized ionic liquids (ILs), both in their pure states as well as in binary and ternary systems with water and amines, was investigated. The study encompassed ILs with fluorinated and tricyanomethanide anions as well as ILs that interact chemically with CO 2 such as those with amino acid and acetate anions. Compared to amines, some of the novel ILs exhibited a majority of important advantages for CO 2 capture such as enhanced chemical and thermal stabilities and negligible vapor pressure; the previous features counterbalance the disadvantages of lower CO 2 absorption capacity and rate, making these ILs promising CO 2 absorbents that could partially or totally replace amines in industrial scale processes. In addition to their ability to capture CO 2 , important issues including corrosivity and ecotoxicity were also examined. A thorough investigation of the capture efficiency and corrosion properties of several solvent formulations proved that some of the new ILs encourage future commercial-scale applications for appropriate conditions. ILs with a tricyanomethanide anion confirmed a beneficial effect of water addition on the CO 2 absorption rate (ca. 10-fold) and capacity (ca. 4-fold) and high efficiency for corrosion inhibition, in contrast with the negative effect of water on the CO 2 absorption capacity of ILs with the acetate anion. ILs with a fluorinated anion showed high corrosivity and an almost neutral effect of water on their efficiency as CO 2 absorbents. ILs having amino acid anions presented a reduced toxicity and high potential to completely replace amines in solutions with water but, in parallel, showed thermal instability and degradation during CO 2 capture. Tricyanomethanide anion-based ILs had a beneficial effect on the capture efficiency, toxicity, and corrosiveness of the standard amine solutions. As a consolidated output, we propose solvent formulations containing the tricyanomethanide anion-based ILs and less than 10 vol % of primary or secondary amines. These solvents exhibited the same CO 2 capture performance as the 20−25 vol % standard amine solutions. The synergetic mechanisms in the capture efficiency, induced by the presence of the examined ILs, were elucidated, and the results obtained can be used as guidance for the design and development of new ILs for more efficient CO 2 capture.

Zeolitic imidazolate framework ZIF-69 membranes were grown on porous α-alumina substrates via seeded secondary growth and further functionalized by a CO 2 -selective tricyanomethanide anion/alkylmethylimidazolium cation-based ionic liquid (IL) to plug the gaps between the ZIF crystals yet leave the framework pores open for gas diffusion. In this configuration, ZIF intergrain boundaries and defects were repaired by a medium that exhibits high selectivity for CO 2 . As a result, the selectivity of the hybrid membrane was significantly higher than that of as-grown ZIF membranes and, because of the existence of the ZIF channels, the permeability was higher than that corresponding to bulk IL. Specifically, CO 2 permeated 20 times faster than N 2 through the intact ZIF pores and 65 times faster than through the bulk IL phase. The developed membranes at room temperature and under a 2 bar transmembrane pressure exhibited CO 2 permeance of 5.6 × 10 −11 and 3.7 × 10 −11 mol m −2 s −1 Pa −1 and real CO 2 /N 2 selectivities of 44 and 64 for CO 2 /N 2 mixtures consisting of 44% and 75% (v/v) CO 2 , respectively. In addition, on the basis of the experimental evidence from the hybrid membranes, predictions were made on the expected performance of an ideal, crack-free, and homogeneous ZIF-69 membrane. This work provides a promising solution to the challenges associated with defect formation experienced during growth not only of ZIFs but also of other zeolite and inorganic membranes used for CO 2 separation.