Block copolymer micellization induced microphase mass transfer: Partition of Pd(II), Pt(IV) and Rh(III) in three-liquid-phase systems of S201–EOPO–Na2SO4–H2O

Abstract

Three-liquid-phase partitioning of Pd(II), Pt(IV) and Rh(III) in systems of S201(diisoamyl sulfide)/nonane–EOPO(polyethylene oxide–polypropylene oxide random block copolymer)–Na2SO4–H2O was investigated. Experimental results indicated that the selective enrichment of Pd(II), Pt(IV) and Rh(III) respectively into the S201 organic top phase, EOPO-based middle phase and Na2SO4 bottom phase was achieved by control over the phase behavior of the three-liquid-phase systems (TLPS). The microphase mass transfer behavior of Pt(IV), Pd(II) and Rh(III) was closely related to the micellization of EOPO molecules. A suggested micro-mechanism model and a mass transfer model describe the micellization of EOPO molecules and the effect on mass transfer of platinum ions across the microphase interfaces. The salting-out induced continuous dehydration and ordered arrangement of the hydrophilic PEO segments in amphiphilic EOPO micelle, and these are the main driving forces for mass transfer of platinum metal ions onto the exposed activity sites of the dehydrated PEO segments. The differences in microphase interfacial structure of EOPO micelles are crucial for the efficient separation between Pt(IV), Pd(II) and Rh(III).