An overview about the extraction of heavy metals and other critical pollutants from contaminated water via hydrophobic deep eutectic solvents

Water pollution is a critical and problematic issue that threatens the sustainability of human civilization. Wastewater streams include a variety of major contaminants that must be eliminated prior to being discharged into the environment. A class of neoteric solvents called hydrophobic deep eutectic solvents (HDESs) has recently attracted much interest in the academic and industrial communities. Because of their remarkable characteristics, which include their low vapor pressure, a broad liquid range, minimal water miscibility, low flammability, and high solvation ability; HDESs are prospective substitutes for organic solvents currently used in industry. In this review, recent results on the removal of toxic/heavy metals, phenolic pollutants and polycyclic aromatic hydrocarbons from an aqueous environment using HDESs are presented. The effects of various parameters on extraction performance, such as the nature of hydrogen bond donor or acceptor, the molar ratio of HDES constituents, the mass ratio of HDES to water, and the initial concentration of contaminants are discussed. Various obstacles and possible improvements in the treatment processes are also addressed. These findings can serve as a basis for future research to develop effective HDES-based processes to treat contaminated water and thereby address a growing global environmental challenge.