Highly efficient SO2 capture by phenyl-containing azole-based ionic liquids through multiple-site interactions

Ionic liquids are suitable for the absorption of acid gases such as SO2 because of their unique properties. In this work, a new method was developed for the highly efficient capture of SO2 by introducing a phenyl group into the azole-based ionic liquids. It was found that these phenyl-containing azole-based ionic liquids reacted with SO2 through multiple-site interactions between the anion and SO2, resulting in an extremely high SO2 capacity of up to ∼5.7 mole per mole ionic liquid. Spectroscopic investigations and quantum calculations show that the dramatic enhancement in the SO2 capacity originated from the enhanced π⋯S interaction between the phenyl group on the anion and SO2. Furthermore, the captured SO2 was easy to release by heating or bubbling N2 through the ionic liquid. This efficient and reversible process using these phenyl-containing azole-based ionic liquids with an enhanced π⋯S interaction provides an excellent alternative to current SO2 capture technologies.