ABSTRACT
This chapter provides an overview of the most representative cation, anion, and ion-pair receptors that have been used as extractants under liquid–liquid extraction conditions. Liquid–liquid extraction, in particular, is a time-honored practice traditionally used to separate charged species from aqueous environments. The chapter reviews progress in the development of receptors that are effective as extractants for ions and ion pairs under liquid–liquid extraction conditions. Anion transfer from an aqueous environment to an organic solvent or solvent mixture is a process that benefits from charge neutrality. The separations such functioning receptor systems could allow ions and ion pairs of societal interest to be targeted with high specificity and efficacy. Metal isolation and purification by liquid–liquid extraction is widely used in hydrometallurgy. It plays a role in the recycling of rare earth elements from strong magnets, phosphors, and electronics, and in the treatment and management of radioactive waste.
