Ultralow Emissions\nof Low-Concentration SO<sub>2</sub> in Flue Gas Using Azole-Based\nIonic Liquids

In recent years, ultralow emissions (ULE) have attracted\nmore attention\ndue to the stricter environmental pollution standards. Developing\ndesulfurizers to meet the needs of ultralow emissions standards is\npressingly needed. Herein, various ionic liquids (ILs) were designed\nusing the basicity-tunable and cation-tunable strategies for the capture\nof 2000 ppm of SO<sub>2</sub> in flue gas. Furthermore, NMR spectra,\nFT-IR spectra, and DFT calculations, including noncovalent interaction\n(NCI) and reduced density gradient (RDG) analysis, were used to testify\nthe absorption mechanism. Anions of ILs were proved to play a vital\nrole in ultralow emissions, and [Bentriz] was regarded as an ideal\nanion for the ultralow emission in this work, while cations of ILs\nhad little effect on ultralow emissions performance. [P<sub>4442</sub>][Bentriz] exhibited excellent ability of ultralow emissions (5 ppm),\nsplendid removal efficiency (>99%), outstanding absorption capacity\n(1.03 mol SO<sub>2</sub>/mol IL), and good reversibility (6 cycles).