PNP-16-crown-6 derivatives as ion carriers for Zn(II), Cd(II) and Pb(II) transport across polymer inclusion membranes

Abstract

Transport rate of metal cations can be explained by the size of substituents, namely larger substituents such as 7 and 8 prefer Pb(II) cations. The bis-PNP-lariat ethers remove Zn(II), Cd(II) and Pb(II) more efficiently than simple PNP-lariat ethers. The increase of linker length in the bis-PNP-lariat ether molecules lowers the metal cations’ transport rate. In addition, the synergetic effect for lead(II) transport across polymer inclusion membrane (PIM) with PNP-lariat ether 9 and DNNS was using PNP-lariat ethers—carriers 1 and 2 in a PIM system, Zn(II) and Cd(II) were transported with low selectivity from acidic aqueous source phase solutions. The ether 3 used to transport Zn(II) and Cd(II) cations from aqueous phase at pH 5.0 into hydrochloric aqueous solution shows high selectivity of Cd/Zn, but small efficiency of process. The competitive transport of equimolar mixtures of Zn(II), Cd(II), and Pb(II) ions from aqueous source phase ( c Me = 0.0001 M) across polymer inclusion membranes with mono- and bis-PNP-lariat ethers as ion carriers has been studied. In these experiments the influence of substituents attached to the simple PNP-lariat ether molecules on the selectivity and efficiency of Zn(II), Cd(II), and Pb(II) transport through PIMs containing cellulose triacetate as the support and o-nitrophenyl pentyl ether as the plasticizer was investigated. The PIM contained 0.3 M lariat ether and 4.0 ml ONPPE per 1.0 g CTA. The transport selectivity order for the PIM with 7 and 8 was: Pb(II) > Cd(II) > Zn(II), whereas for 1 and 4 the order: Zn(II) > Cd(II) ≥ Pb(II) was found. We also found out that the transport of metal cations across PIM with bis-lariat ether 9 occurs at the same level when sodium nitrate in source phase is in the range of 10 −3 to 0.10 M.