Highly Efficient and Reversible Carbon Dioxide Capture by Carbanion-Functionalized Ionic Liquids

Due to the active unstable nature of carbon anions, it is challenging to develop carbanion-functionalized ionic liquids (ILs) for efficient and reversible carbon dioxide (CO₂) capture. Here, a series of carbanion-based ILs with large conjugated structures were designed and a promising system was achieved through tuning the nucleophilicity of carbanions and screening the cation. The ideal carbanion-functionalized IL trihexyl(tetradecyl)phosphonium N,N-diethycyanoacetoamide ([P₆₆₆₁₄][DECA]) showed equimolar chemisorption of CO₂ ( up to 0.98 mol CO₂/mol IL) under ambient pressure and excellent absorption rate. What's more, the combined CO₂ can be released easily, leading to excellent reversibility due to high stability of anion conjugated structures. More importantly, the presence of water had negligible effect on the absorption capacity, which makes it potential to be applied to the CO₂ capture in industrial flue gas. The chemisorption mechanism of the carbanion and CO₂ was confirmed by spectroscopic investigations and DFT calculations, where carboxylic acid product was formed through proton transfer after the carbanions reacted with CO₂. Considering that high capacity, quick rate as well as excellent reversibility, these carbanion-functionalized ILs should certainly represent competitive candidates for further scale up and practical application in CO₂ capture.