Successive preconcentration and mechanistic investigation of Au(iii), Pd(ii), Pt(iv) and Rh(iii) via cloud point extraction using a functionalised ionic liquid

Abstract

This study proposes the efficient separation of Au(III)/Pd(II)/Pt(IV)/Rh(III) through the 2-mercaptobenzothiazole-functionalised ionic liquid ([C₆mim][2MBT]) using a cloud point extraction system. Direct cloud point extraction of Au(III) (about 99.9%) was realised without involving any functionalised ionic liquids. A significant enhancement of the Pd(II) extraction performance was found by adding rationally constructed [C₆mim][2MBT]. Consequently, a fairly high extraction percentage of about 99.4% was obtained. However, further advancement of the proposed cloud point extraction showed that it could not be applied for the preconcentration of Pt(IV) and Rh(III) without adding stannous chloride, which plays a critical role in the segregation and could be adjusted by changing the hydrochloric acid concentration. Under the optimised conditions, the Rh(III) extraction process shows a high yield percentage (ca. 83.0%), where the majority of Pt(IV) was enriched in the aqueous phase. In addition, the underlying possible extraction mechanism was investigated using UV-vis, FT-IR and TEM measurements, which indicated that TX-114 acted as a solvent for the extracted metals. The developed procedure reveals efficient direct Au(III)/Pd(II)/Pt(IV)/Rh(III) separation using [C₆mim][2MBT] via cloud point extraction.