Toxic gas removal using deep eutectic solvents: A review of fundamentals and applications

• DESs capture SO 2 , NO x , NH 3 , and H 2 S via dual physical/chemical mechanisms. • Active sites (N, O, S, halides) enable selective gas absorption. • Supporting DESs on porous carbon materials significantly improves mass transfer. Sulfur dioxide (SO 2 ), nitrogen oxides (NO x ), ammonia (NH 3 ) and hydrogen sulfide (H 2 S) present in industrial exhaust streams pose significant environmental and health risks through the formation of acid rain and air pollution. Effective removal technologies must therefore achieve high efficiency and selectivity while maintaining economic viability and environmental sustainability. This review examines the evolving applications of deep eutectic solvents (DESs) for the capture of SO 2 , NO x , NH 3 , and H 2 S, tracing a logical progression from liquid-phase systems to advanced supported and structured architectures. The narrative is structured along three key stages: the fundamental absorption mechanisms in liquid DESs, the transition to supported DES systems to overcome mass transfer barriers, and the further enhancement into three-phase interfaces for integrated capture. DESs exhibit both physical absorption via hydrogen-bonding networks and chemical absorption through specific functional group interactions, with performance determined by active site distribution and viscosity effects. To address the inherent limitations of viscous liquid DESs, supporting them on hierarchical porous carbon materials emerges as a strategic advance. Building on this supported framework, the conversion to three-phase interfaces further enhances absorption capacity through multiple contact surfaces and interconnected diffusion pathways. Current challenges include production costs and regeneration efficiency. Strategic selection of hydrogen bond donors and acceptors, combined with optimized support structures, presents opportunities for the simultaneous capture of multiple gas species. Throughout, the review emphasizes the thematic evolution from homogeneous liquids to engineered solid–liquid composites, ensuring that each section logically introduces and foreshadows the next developmental stage.