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The need to chemically convert CO2 at the interface of aqueous amine solutions has become particularly relevant for the development and the broad distribution of cost-effective and near-future devices for direct air capture working at low (e.g., ambient) partial pressure. Here, we have determined the stability of a CO2-monoethanolamine zwitterion and its chemical conversion into carbamate at the vapor/liquid water interface by first-principles molecular dynamics simulations coupled with a recently introduced enhanced sampling technique. Contrary to the bulk water case, our results show that both the zwitterion and carbamate ions are poorly stable at the vapor/amine aqueous interface, further stating the differences between the homogeneous and heterogeneous CO2 chemical conversion. The design of novel and cost-effective capture systems, such as those offered by amine-based scrubbing solutions, working at low (e.g., ambient) CO2 partial pressure should explore the use of novel solvents, different from aqueous mixtures, to overcome the limits of the current absorbents.

Carbon dioxide scrubbing by aqueous amine solution is considered as a promising technology for post-combustion CO 2 capture, while mitigating climate change. The lack of physicochemical details for this process, especially at the interface between the gas and the condensed phase, limits our capability in designing novel and more cost-effective scrubbing systems. Here, we present classical and f irst-principles molecular dynamics results on CO 2 capture at the gas/amine solution interfaces using solvents of different polarities. Even if it is apolar, carbon dioxide is absorbed at the gas/ monoethanolamine (MEA) aqueous solution interface, forming stable and interfacial [CO 2 •MEA] complexes, which are the first reaction intermediate toward the chemical conversion of CO 2 to carbamate ions. We report that the stability of the interfacial [CO 2 • MEA] precomplex depends on the nature and polarity of the solution, as well as on the conformer population of MEA. By changing the polarity of the solvent, using chloroform, we observed a shift in the interfacial MEA population toward conformers that form more stable [CO 2 •MEA] complexes and, at the same time, a further stabilization of the complex induced by the solvent environment. Thus, while lowering the polarity of the solvent could decrease the solubility of MEA, at the same time, it favors conformers that are more prone to CO 2 capture and mineralization. The results presented here offer a theoretical framework that helps in designing novel and more cost-effective solvents for CO 2 scrubbing systems, while shedding further light on the intrinsic reaction mechanisms of interfacial environments in general.