Metal ion separations in aqueous biphasic systems and room-temperature ionic liquids.

摘要

Aqueous biphasic systems (ABS) and ionic liquids (ILs) have been previously developed for biomaterial separations and as battery electrolytes, respectively, although both systems are now receiving attention as alternative systems for separations. Both systems are capable of sustaining liquid/liquid separations from aqueous media, but neither rely on traditional organic solvents to provide the extracting phase. In this manner, both ABS and ILs are being examined from a new perspective that includes the partitioning of metal ions and associated applications. However, an in-depth understanding of what types of extractants will facilitate metal ion separations and how the system conditions affect the partitioning is largely unknown for the IL systems.; Initial results highlight the partitioning of metal ions in a polyethylene glycol/salt ABS where, in order to increase the affinity of the metal ions for the PEG-rich phase, a series of azo dyes were used as extractants. These results contribute to the number of extractants that have been examined in ABS and present pH-dependent partitioning as a stripping mechanism.; The partitioning of a number of different metal ions in hydrophobic ILs containing the 1-alkyl-3-methylimidazolium ([C_nmim]+) cation and either the hexafluorophosphate (PF₆−) or bis(trifluoromethylsulfonyl)imide (N(SO₂CF₃) ₂−) anions has been investigated. In the absence of an extractant, the metal ions remain in the aqueous phase and both molecular and anionic extractants are shown to increase the affinity of the metal ions for IL phase. The combination of well-known extractants and slight changes to the properties of the IL through [C_nmim]+ substitution has been examined to determine how the change influences the metal ion partitioning results. An in-depth analysis of the solution chemistry of UO₂ 2+ also reveals differences in the coordination environment for the extracted species.; Two new types of ILs are also introduced: Task Specific Ionic Liquids for metal ion separations and a series of ILs incorporating the alkyl-isoquinolinium cation.; The investigation of a variety of metal ion separations in IL/aqueous systems has helped to establish a fundamental understanding of the principles associated with extraction in these systems. These initial metal ion extraction results suggest success in other IL systems could also be attainable.