Ionic liquids and deep eutectic solvents: A brief prologue and their applications in sustainable extraction and separation processes

Abstract

Sustainable extraction and separation methods are vital for reducing environmental impact and ensuring economic efficiency. Such techniques can minimise resource depletion and pollution while promoting circular economy principles and advancing green technological solutions. Researchers are actively seeking sustainable solvents for extraction and purification processes. Ionic liquids (ILs) and deep eutectic solvents (DESs) have recently been introduced as designer solvents to overcome the environmental issues associated with conventional extraction and separation techniques. ILs are synthesized from organic cations and organic or inorganic anions, whereas DESs are low-melting mixtures formed from two or more components via hydrogen bonding interactions. Both of these benign solvents have similar physicochemical characteristics, and due to their unique properties, they are suitable for a wide range of applications. This review offers a brief summary of the development of IL and DES chemistry, focusing on their origin, classifications, similarities and differences, and unique properties of these solvents. Later, the review discusses the growing impact of ILs and DESs across various fields, including wastewater treatment, biomolecule extraction, e-waste management, spent nuclear fuel reprocessing, biomass dissolution, CO₂ capture, desulfurization of fuels, and other relevant extraction/separation processes. Overall, the review highlights the versatility and efficiency of ILs and DESs in addressing various challenges across multiple domains.