Mechanistic Understanding of CO2 Capture in Primary-, Secondary-, and Tertiary-Amine-Functionalized Ionic Liquids and Its Implications for Direct Air Capture.

Direct air CO2 capture is essential for combating global warming because it helps to reduce the concentration of CO2 in the atmosphere, preventing global climate change. In this work, we have synthesized primary-, secondary-, and tertiary-amine-based task-specific ionic liquids (ILs): tetraethylammonium 4-aminobutanoate ([N2222][GABA]), tetraethylammonium piperidine-4-carboxylate ([N2222][4PCA]), and tetraethylammonium 1-methylpiperidine-4-carboxylate ([N2222][1MP4CA]). Investigating the CO2 capture mechanisms of primary-, secondary-, and tertiary-amine-functionalized ionic liquids (AFILs) is essential for developing more efficient, stable, and energy-efficient alternatives to conventional aqueous amine scrubbing systems. We can optimize absorption capacity and reduce viscosity by understanding how these particular amine species interact through chemical reaction processes, thereby reducing global climate change. These ILs have a few limitations, such as high viscosity, low mass transfer, and slow chemisorption kinetics. To overcome these limitations, ILs were blended with polar aprotic (dimethyl sulfoxide (DMSO)) and protic (H2O) solvents, and a vapor-liquid equilibrium (VLE) experiment was conducted for pure CO2 absorption. ILs in aqueous solution have shown higher CO2 absorption values than in DMSO for the respective amine-based ILs. [N2222][GABA], [N2222][4PCA], and [N2222][1MP4CA] in aqueous media show saturated CO2 uptake values of 1.61, 1.52, and 1.44 molCO2/molIL, respectively, whereas in DMSO, saturated CO2 uptake values are 0.94, 0.73, and 0.39 molCO2/molIL for [N2222][GABA], [N2222][4PCA], and [N2222][1MP4CA], respectively. ILs in DMSO medium are more reversible than ILs in aqueous medium with respect to the absorption and desorption of CO2. Additionally, we performed an open-air CO2 absorption study using these ILs in aqueous media. These systems, in our opinion, are likely to be better for removing CO2 from an extremely polluted environment.