Structure and transport properties of polymer inclusion membranes for Pb(II) separation

The structure and properties of polymer inclusion membranes for Pb(II) transport from solutions containing Pb(II), Ca(II), K(I) nitrates, and Na(I) acetate as a buffer were examined. The membranes were prepared from cellulose triacetate (support), dioctyl phthalate (plasticizer) and 2-(10-carboxydecylsulfanyl)benzoic acid methyl monoester as a new, Pb(II) selective ionophore (LSI). The effect of membrane composition upon transport rates was discussed in terms of percolation theory. The membrane structure was found inhomogeneous with a gradient-type distribution of the active phase (carrier and plasticizer). The presence of the overall transport limiting skin layer was confirmed by the application of scanning electron microscopy. The percolation parameters. i.e. critical volume fraction of the active phase Phi(AP,c) and the critical exponent tau, were found as equal to 0.62 and 1.11 +/- 0.07, respectively. However, the local parameters calculated for transport limiting layer were estimated as Phi(AP,c) equal to 0.10 and tau equal to 1.6 +/- 02. The following order of membrane selectivity was observed: Pb(II)>> K(I)approximate to Ca(II)approximate to Na(I) with the overall Pb(II) separation factors reaching the values up to 48,000 and Pb(II) fluxes up to 1.725x10(-10) mol cm(-2) s(-1). The calculated percolation parameters suggest the porous structure of the attended membranes. The transport mechanism was found as limited by the diffusion processes. (C) 2010 Elsevier B.V. All rights reserved.