Direct Air Capture of CO<sub>2</sub> by Amino Acid-Functionalized Ionic Liquid-Based Deep Eutectic Solvents
Nanigopal Bera, Puspendu Sardar, Ritwik Hazra, Amar Nath Samanta, Nilmoni Sarkar
Abstract
Direct air capture of carbon dioxide (CO 2 ) is crucial for lowering the concentration of atmospheric CO 2 and preventing global climate change. Nonetheless, a significant obstacle remains in advancing effective CO 2 capture and separation techniques. The tunable chemical structures, high thermal stability, and nominal vapor pressure of ionic liquids (ILs) make them attractive solvents for CO 2 absorption. Deep eutectic solvents (DESs) are broadly recognized as a new class of IL analogs because of their numerous similarities and features to ILs. In this work, at first, we have synthesized alanine- and lysine-based ILs, tetraethylammonium alaninate ([N 2222 ][Ala]) and tetraethylammonium lysinate ([N 2222 ][Lys]), and utilized them to prepare DESs by mixing the ILs as hydrogen-bond acceptor (HBA) and ethylene glycol (EG) as hydrogen-bond donor (HBD). Those DESs are less viscous and have a higher CO 2 absorption efficiency than their constituent ILs. The vapor–liquid equilibrium (VLE) experiment shows that the pure CO 2 absorption capacity of [N 2222 ][Lys]-based DES is considerably higher than [N 2222 ][Ala] containing DES. We have employed those amino acid-functionalized IL-based DESs to capture CO 2 from the open air for the very first time, to the best of our knowledge. The direct air CO 2 capture experiment shows that the DESs are highly efficient in capturing CO 2 from the open air. The open air saturated CO 2 uptake in [N 2222 ][Lys]-based DES is 1.06 mol/mol, whereas the uptake value in [N 2222 ][Ala] containing DES is 0.47 mol/mol. Those DESs are reversible toward the absorption and desorption of CO 2 up to several cycles. We believe that those systems will be superior for eliminating CO 2 from the highly polluted air.