Unraveling the CO2 reaction mechanism in bio-based amino-acid ionic liquids by operando ATR-IR spectroscopy

Tackling global warming through the reduction of greenhouse gases is a key challenge mankind is called to face in the close future. Carbon dioxide is one of the main causes of such temperature increase, thus avoiding its release in the atmosphere through capture and/or utilization strategies is a valuable tool to limit greenhouse effect. Presently, the applied technology for sequestrating CO2 relies on its reaction with amines in aqueous solutions, giving rise to the formation of carbamates and carbonates. However, due to the energy intensive release step, toxicity and corrosiveness, amine scrubbing could not represent a long-term solution in CO2 capture. Ionic liquids (ILs), organic salts in the liquid state near room temperature, are a class of emerging materials with a great potential towards CO2 capture. Recently the combination of the choline cation with amino acids based anions gave rise to a wide set of bio-inspired ILs with low toxicity, that, due to the presence of amino groups in the amino acid moiety, are optimal candidates for CO2 capture. In the present work, two choline-amino acids ILs were synthesized, containing glycine and proline, according to an innovative procedure, overcoming some drawbacks proper of the classical methods. A throughout IR operando study of the CO2 absorption process in these amino acids based ILs was performed. Even though elementary reactions are the same for all the investigated systems, different absorption pathways were recognized depending on the amino acid based anion. The reversibility of the absorption process differs between the two systems as well, further remarking the role played by the selected amino acid in the overall absorption performances. Such fundamental information, still missing in the literature, will contribute to rationally develop choline-amino acids ILs with optimal CO2 absorption/activation properties.