CO2 adsorption in natural deep eutectic solvents: insights from quantum mechanics and molecular dynamics

CO2 capture is an important process for mitigating CO2 emissions in the atmosphere. Recently, ionic liquids have been identified as possible systems for CO2 capture processes. Major drawbacks of such systems are mostly in the high cost of synthesis of such liquids and poor biodegradability. Natural deep eutectic solvents, a class of eutectic solvents using materials of natural origin, have been developed, which compared to ionic liquids are low-cost and more environmentally benign. However, very little is known on the details at a molecular level that govern the CO2 adsorption in these systems and what the limits are of the adsorption features. Elucidating such aspects would represent a step forward in the design and implementation of such promising systems in mitigating CO2 emissions. Herein, we report a computational study on the mechanisms and characteristics of CO2 adsorption in natural deep eutectic solvents containing arginine/ glycerol mixtures. We establish details of the hydrogen bonding effects that drive the carbon dioxide capture in systems composed of L-arginine and glycerol using molecular dynamics and quantum mechanics simulations. Our findings indicate that, although both arginine and glycerol contain multiple atoms capable of acting as hydrogen bond donors and hydrogen bond acceptors, L-arginine primarily functions as the hydrogen bond acceptor while glycerol serves as the hydrogen bond donor in most interactions. Furthermore, both compounds contribute hydrogen bond donors that participate in CO2 binding. This study provides valuable insights into the behaviour of CO2 adsorption in natural deep eutectic solvents and enhances our understanding from the perspective of hydrogen bonding interactions.