Selective Bulk Liquid Membrane Transport of Metal Ions Using Dibenzopyridinio-18-Crown-6 as Ionophore

Abstract

The transport experiments standardized concentric cells in which the aqueous source and receiving phases were separated by an organic phase viz., chloroform (CHCl₃), 1,2-dichloroethane (1,2-DCE), dichloromethane (DCM), nitrobenzene (NB) and chloroform-nitrobenzene binary mixed solvents. The aqueous source phase consisted of a buffer solution (CH₃COOH/CH₃COONa) at pH = 4.9 and containing an equimolar mixture of Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Ag⁺ and Pb²⁺ metal cations. The organic phase contained the macrocyclic ligand, dibenzopyridinio-18-crown-6 (DBPY18C6) as an ionophore and the aqueous receiving phase consisted of a buffer solution (HCOOH/HCOONa) at pH = 3. The obtained results show that dibenzopyridinio-18-crown-6 is a highly selective ionophore for silver ion and under the employed experimental conditions, it transport only this metal cation among the seven studied metal cations. The influence of the stearic acid, palmitic acid and oleic acid in the membrane phase on the silver ion transport was also investigated. The results show that the transport efficiency of the Ag⁺ ion increases in the presence of stearic and palmetic acids. The sequence of transport efficiency for Ag⁺ ion in organic solvents is: NB > DCM > 1,2-DCE > CHCl₃. The non-linear behaviour was observed for variations of the transport rate of silver ion vs. the composition of chloroform-nitrobenzene binary mixtures was discussed in terms of changing the chemical and physical properties of the constituents solvents when they mixed with one another.