Solid-phase extraction of indium(III) ions onto thermosensitive poly(N-isopropylacrylamide)

The feasibility of a metal separation technique using thermosensitive N-isopropylacrylamide (NIPA) polymer was examined. A solid-phase extraction (SPE) technique was proposed, which involved the complexation of a target heavy metal ion and an extractant in an aqueous solution and the subsequent adsorption of the metal–extractant complexes onto the NIPA polymer precipitates through a hydrophobic interaction above the lower critical solution temperature. In a model system consisting of In(III) ions, n-octyl phosphate as an organophosphorus extractant, and NIPA polymer, the proposed SPE technique was successfully implemented. Approximately 90% of the In(III) ions were extracted from the aqueous solution at pH ca. 2, and In(III) and Zn(II) ions were mutually separated. The extractant effectively played the dual role of a separator and a mediator to adsorb a target metal selectively onto the NIPA polymer. The SPE technique is simple, environmentally friendly, and potentially applicable to a variety of metal separation processes in industries.