Functional ionic liquids for SO2 capture and conversion

Abstract

Owing to their many unique properties, ionic liquids (ILs) have emerged as novel solvents and catalysts for gas capture and utilization compared with conventional organic solvents. SO₂, an acidic gas, is usually emitted during the combustion of fossil fuels and leads to the formation of acid rain and haze. In the last few decades, many types of ILs, especially functional ILs, have been developed and their corresponding absorption mechanisms were investigated. Besides, SO₂ can be used to produce various value-added chemicals, including sulfur (S₈), cyclic sulfites, and benzenesulfinic acids, from green chemistry and engineering viewpoints. In this critical review, we focus on the design of task-specific ILs for SO₂ capture and conversion. Initially, we present a brief introduction on ILs and then systematically summarize the different active sites and active groups in task-specific ILs. In contrast to other reviews, we discuss the absorption models, mechanisms, influencing factors, and several strategies for the design of active sorbents. For SO₂ conversion to value-added products, this review, for the first time, highlights IL-based catalysts that are also absorbents. Finally, the future directions and prospects for SO₂ capture and conversion using ILs are outlined. This work will open the door to the development of novel task-specific IL-based materials for gas capture, separation, and conversion.