Study of competitive transport of metal cations through bulk liquid membrane using 4′-nitrobenzo-18-crown-6 and diaza-18-crown-6

Abstract

The competitive metal ion transport experiments of cupper(II), cobalt(II), zinc(II), cadmium(II), silver(I), chromium(III) and lead(II) were carried out by 4′-nitrobenzo-18-crown-6 (NB18C6) and diaza-18-crown-6 (DA18C6) as carrier in organic membrane phase. The source phase contained equimolar concentrations of metal ions at pH 5 and the receiving phase being buffered at pH 3. Fluxes and selectivities for competitive metal cations transport across bulk liquid membranes by the lipophilic crown ethers have been determined in a variety of chlorinated hydrocarbon and aromatic hydrocarbon solvents. The membrane solvents include: dichloromethane (DCM), chloroform (CHCl3), 1,2-dichloroethane (1,2-DCE), nitrobenzene (NB), chloroform–nitrobenzene (CHCl3–NB) and chloroform–dichloromethane (CHCl3–DCM). The obtained results show that the selectivity and efficiency of transport for these heavy metal cations change with the nature of the ligand and also the organic solvents, which were used as liquid membrane in these experiments. Although a good selectivity was observed for lead(II) cation by 4′-nitrobenzo-18-crown-6 in all membrane systems, but the highest transport rate for this cation was obtained in DCM. Also, no transport was observed for these metal cations by diaza-18-crown-6 in all membrane systems. A linear relationship was observed between the transport rate of lead(II) cation by 4′-nitrobenzo-18-crown-6 and the composition of CHCl3–DCM binary solution, but a non-linear behavior was found in the case of CHCl3–NB binary solution. The influence of the stearic, palmitic and oleic acids as surfactant in the membrane phase on the transport of metal cations was also investigated.