Ionic liquids for sustainable SO2 capture: Mechanisms, critical factors and prospects

Ionic liquids (ILs) are a new type of SO2 absorbent, featuring low volatility and high capture efficiency. Their functionalization can be controlled by regulating anion and cation types. This article reviews the capture mechanisms of various ionic liquids for SO2, including physical adsorption, chemical absorption, multi-point capture, and synergistic adsorption with other substances. Among them, composite adsorbents generated by ionic liquids with metal-organic frameworks or activated carbon matrices are a pioneering approach to achieve synergistic SO2 capture. This is accomplished through optimization of pore structure, creation of high-density active adsorption sites, and enhancement of the kinetics of host-guest interactions. Under room temperature and normal pressure conditions, the capture amounts of SO2 by different ionic liquids range from approximately 0.005 mol SO2/mol IL to 6.30 mol SO2/mol IL. The various influencing factors during the capture process of SO2 by ionic liquids include temperature, pressure, the concentration of SO2, and its solubility. Additionally, during the capture process, interference from CO2 and NO gases will also occur. Future research is developing new ionic liquids that can efficiently capture SO2 under extreme conditions. Designing advanced dual-functional materials that simultaneously capture SO2 and competing gases with superior efficiency and long-term stability is also proposed. This review may provide references for the latest SO2 capture by ionic liquids developments.