Silver(I) ion-selective transport across polymer inclusion membranes containing new pyridino- and bipyridino-podands

A novel technique was developed for Ag+ ion separation from complex mixtures including transition metal ions. Ag+ ion-selective transport is observed across polymer inclusion membranes (PIMs) containing several tridentate podands. These podands have three pyridine nitrogen atoms at tridentate coordinating positions and exhibit Ag+ ion selective binding. Using PIM systems, Ag+ ion could be selectively removed from a complex mixture containing high concentrations of Cd2+, Zn2+, Co2+, Ni2+, Pb2+ and Cu2+ ions. The present study revealed remarkable effects of stereochemically controlled substitution of the podand on Ag+ ion permeability. Thus, design of podand-type carriers based on guest-targeted ligand geometry and stereochemically controlled substitution provide a new, effective methodology in developing cation-specific membranes. The present type of PIMs was stable for long period experiments and showed high flux and selectivity for Ag+ ion at practical levels (j>2x10(-5) mol/m(2) s). (C) 1998 Elsevier Science B.V. All rights reserved.