Ionic liquids (ILs) are organic salts that exist in the liquid phase at temperatures < 100 °C and there are up to 1018 possible candidates for this group of compounds. By using different ions arrangements it is possible to design ILs to fit the requirements of a certain application which is the most important feature of ILs. Also, ILs can be designed to be non-toxic (the third generation of ILs) or with significantly reduced toxicity compared to conventional organic solvents. ILs as highly potent, designed solvents with tunable physical and chemical properties can be successfully applied in extraction processes as solvents and task-specific extractants at the same time. Since the replacement and reduction of organic solvents belong to the main postulates of green chemistry, the design and synthesis of new ILs are in a line with green chemical principles. Additionally, the extraction procedure can be optimized so that more than 95% of the extraction mixture content is water. Aqueous biphasic systems (ABSs) are one of the green extraction approaches.
ABSs based on designed ILs have been investigated and applied as an effective substitute for classical liquid-liquid extraction for (1) extraction of pesticides and textile dyes as an alternative method for their removal from waste manufacture waters; (2) sample preparation before analytical quantification (selective extraction and enrichment of Cu(II) from wastewater and biological samples with task-specific ILs); (3) recover and reuse of bioactive value-added compounds from food waste as a circular economy perspective; (4) recycling of technology critical elements; (5) isolation of active pharmaceutical ingredients from biomass.