New Insights into CO2 Absorption Mechanisms with Amino-Acid Ionic Liquids

Graphical Soak it up : The electrostatic environment around amine groups in ionic liquids (ILs) has critical influence on their CO 2 absorption mechanism, which enables the achievement of higher CO 2 capacity by tuning the local structure around the amine. Moreover, this work indicates that the actual CO 2 absorption mechanism by amino-acid ILs goes beyond the apparent CO 2 /amine stoichiometry. The last decade saw an explosion of interest in using amine-functionalized materials for CO 2 capture and conversion, and it is of great importance to elucidate the relationship between the molecular structure of amine-functionalized materials and their CO 2 capacity. In this work, based on a new quantitative analysis method for the CO 2 absorption mechanism of amino-acid ionic liquids (ILs) and quantum chemical calculations, we show that the small difference in the local structure of amine groups in ILs could lead to much different CO 2 absorption mechanisms, which provides an opportunity for achieving higher CO 2 capacity by structure design. This work revealed that the actual CO 2 absorption mechanism by amino-acid ILs goes beyond the apparent CO 2 /amine stoichiometry; a rigid ring structure around the amine group in ILs creates a unique electrostatic environment that inhibits the deprotonation of carbamic acid and enables actually equimolar CO 2 /amine absorption.