Facilitated co-transport of Ag(I), Cu(II), and Zn(II) ions by using a crown ether as carrier: influence of the SLM preparation method on ions flux

Abstract

This article reports and discusses the study of facilitated co-transport of silver(I), copper(II), and zinc(II) ions through a supported liquid membrane (SLM) containing a specific extractant of metals: dibenzo-18-crown-6 (DB18C6) in chloroform as solvent. Mode and duration of immersion of the macroporous support in the organic phase, physical characteristics of the support (porosity, pore size, and thickness) as well as wettability of the SLM that influence the transport have been examined. Three preparation modes of the SLM (vacuum impregnation, impregnation by immersion in a high-vacuum chamber, simple impregnation by immersion (SI)) were compared and the best result was obtained with SI. In the last case, the obtained results showed that full impregnation of the support in the organic phase can take a long time (26 days) for obtaining high fluxes, if DB18C6 concentration is above 5×10−3 M because of the difficulty in impregnation due to carrier aggregation and precipitation. After 26 days, the support degrades under the action of the solvent. In fact, Fourier transformed-infrared spectroscopy showed support degradation while scanning electron microscopy observations showed that porosity and pore size were reduced with increasing impregnation time. On the other hand, at DB18C6 concentration below 5×10−3 M, impregnation took less time (30–60 min) because of the reduced ability of the carrier to form aggregates. Transport experiments showed an order of permeability, Ag(I)>Cu(II)>Zn(II). The Cu(II) flux, using 1 hr impregnation time, reached the highest value when the organic solution was made by dissolving 10−3 M DB18C6 in CHCl3. The flux for the above-mentioned ions increased with the increasing pore size and porosity of the polymeric support and decreasing thickness.