Design of Task-Specific Ionic Liquids for Capturing CO2: A Molecular Orbital Study

To design task-specific ionic liquids (TSILs) for capturing CO 2, the frontier molecular orbital interactions between CO 2 and −NH 2 in TSILs, such as 1,1,3,3-tetramethylguanidinium lactate and 1- n -propylamine-3-butylimidazolium tetrafluoroborate, were systematically studied by employing B3LYP/6-31G** calculations. A detailed frontier molecular orbital study showed that the inherent intramolecular hydrogen bonds in TSILs and the electron-donating groups attaching to −NH 2 could raise the frontier occupied molecular orbital energy on −NH 2 and thus enhance the interactions between −NH 2 and CO 2 . Following the underlying interaction mechanism between CO 2 and −NH 2 in TSILs, two new TSILs, [P(C 4 ) 4 ][Ala] and [P(C 4 ) 4 ][Gly], were designed and the interactions between CO 2 and −NH 2 in such ionic liquids were investigated. This work showed a good prospect to design TSILs for selectively capturing CO 2 from gas streams by applying the molecular orbital calculations.