Metal-ion recognition-competitive bulk liquid membrane transport of transition and post-transition metal cations using a thioether donor acyclic ionophore

Abstract

The competitive bulk liquid membrane transport of Cr3+, Co2+, Cu2+, Zn2+, Cd2+, Ag+ and Pb2+ metal cations with a new synthetic sulfur donor acyclic ligand (pseudo-cyclic ionophore), i.e. 1-(2-[(2-hydroxy-3-phenoxypropyl)sulfanyl]ethylsulfanyl)-3-phenoxy-2-propanol; (C20H26O4S2), was examined using some organic solvents as membranes. The membrane solvents include: chloroform (CHCl3), 1,2-dichloroethane (1,2-DCE), dichloromethane (DCM), nitrobenzene (NB), chloroform-nitrobenzene (CHCl3-NB) and chloroform-dichloromethane (CHCl3-DCM) binary mixtures. The transport process was driven by a back flux of protons, maintained by the buffering the source and receiving phases with pH 5 and 3, respectively. The aqueous source phase consisted of a buffer solution (CH3COOH/CH3COONa) at pH = 5 and containing an equimolar mixture of these seven metal cations. The organic phase contained the acyclic ligand, as an ionophore and the receiving phase consisted of a buffer solution (HCOOH/HCOONa) at pH = 3. For these systems that displayed transport behaviour, sole selectivity for Ag+ cation was observed under the employed experimental conditions in this investigation. The amount of Ag+ transported follows the trend: 1,2-DCE > CHCl3 > DCM > NB in the bulk liquid membrane studies. The transport of the metal cations in CHCl3-NB and CHCl3-DCM binary solvents is sensitive to the solvent composition. The influence of the stearic acid, palmitic acid and oleic acid in the membrane phase on the ion transport was also investigated.