Facilitated transport of Zn(II), Cd(II) and Pb(II) across polymer inclusion membranes doped with imidazole azocrown ethers

Cellulose triacetate membranes doped with imidazole azocrown derivatives as fixed carriers have been prepared and applied for investigation of facilitated transport of Zn(II), Cd(II), and Pb(II) ions from aqueous nitrate source phase (cMe = 0.001 M, pH = 5.0). The transport selectivity of the Polymer Inclusion Membranes (PIMs) with 1–5 were: Pb(II) > Zn(II) > Cd(II). The influence of HCl concentration in receiving phase on metal ions transport across PIM doped with azocrown was studied. The initial fluxes of Zn(II), Cd(II), and Pb(II) ions increase with HCl concentration in receiving phase whereas the selectivity coefficients Pb(II)/Zn(II) and Pb(II)/Cd(II) are the best for pure water. The influence of azocrown ether concentration on metal ions transport across PIM was studied. The initial fluxes of transported metal ions depend on the hydrophile-lipophile balance (HLB) and molecular volumes (Vx) of azocrown ethers. The initial fluxes of Zn(II), Cd(II), and Pb(II) ions decrease with increase of hydrophile-lipophile balance value for azocrown, i.e. 3 > 4 > 5 > 1 > 2. The best selectivity Pb(II)/Cd(II) coefficient (46.0) was found for compound 3, whereas the best selectivity Pb(II)/Zn(II) coefficient (17.4) for compound 4. The influence of the plasticizer, i.e. o-nitrophenyl pentyl ether (o-NPPE), o-nitrophenyl octyl ether (o-NPOE), or bis(2-ethylhexyl)adipate (DOA) on the metal ions transport through PIM with azocrown ethers was also presented. The initial fluxes of Pb(II), Zn(II), and Cd(II) ions slightly increase with decrease of plasticizers viscosity, in the following order: DOA < o-NPOE < o-NPPE. The highest initial Pb(II) ions flux (1.7859 μmol/m2·s) was found for o-NPPE, while the lowest value was observed for DOA (1.5369 μmol/m2·s). Moreover, the influence of Cu(II), Co(II), and Ni(II) ions on the initial fluxes and on percentage removal of Zn(II), Cd(II), and Pb(II) ions in PIMs was studied.