Anion extractants constructed by macrocycle-based anion recognition

Water pollution is a global challenge. One general class of pollutants is anions, which collectively can have adverse effects on both human health and the environment. These impacts necessitate the development of new water purification technologies capable of addressing anionic pollutants. This review summarizes macrocycle-based approaches to anion extraction with a focus on systems reported by our group in recent years. These extractants remove targeted anions from aqueous source phases via three complementary modes: (1) liquid–liquid extraction involving two phase organic solvent/water systems, wherein the anions are ideally extracted from the aqueous phase into the organic phase; (2) solvent swollen polymer networks (gels) that adsorb anions from water; (3) solids that adsorb anions directly. The present treatment is organized according to the nature of the receptors used as the putative extractants, specifically calix[4]pyrrole-based systems, Schiff-base macrocycles, and approaches that rely on so-called “Texas-sized” molecular boxes.