Characteristics and configurations of task-specific deep eutectic solvents with CO₂-philic functional groups

To fulfill the international commitments to net-zero carbon emissions, the interest in the development of efficient CO2-reduction technology is increasing. The wet absorption method for carbon capture, utilization, and storage (CCUS) is expected to play a significant role. However, conventional absorbents, including alkanolamines, have drawbacks like high degradability and toxicity. Therefore, highly efficient and non-toxic absorbents must be developed. To this end, deep eutectic solvents (DESs) with high tunability, and based on the combination of a hydrogen bonding acceptor (HBA) and a hydrogen bonding donor (HBD), are studied as alternatives to conventional absorbents. To exploit the high tunability for CO2 capture, HBDs with different CO2-philic functional groups, including amino (-NH2), carbonyl (R2C=O), and ether (R-O-R') groups, are selected for functionalization and their effect on CO2 absorption is verified. The physicochemical properties, formation, and CO2 absorption characteristics of the DESs are discussed in detail. Few researchers have conducted in-depth analysis of the configurations of DESs. The DES configuration is predicted based on the CO2 absorption capacity of the DES. Furthermore, the relationship between the physical absorption capacity and free volume is demonstrated using the CO2/N2O analogy and Lorentz-Lorenz relation. This study contributes to the development of alternative absorbents for the CCUS technology and the mitigation of CO2 emissions toward a broad pursuit of carbon neutrality.