SYNTHESIS AND CHARACTERIZATION OF SITE-SELECTIVE ION-EXCHANGE RESINS TEMPLATED FOR LEAD(II) ION

Ion-exchange resins that exhibit enhanced selectivity for the Pb(II) i on have been synthesized by the copolymerization of styrene with lead( Il) vinylbenzoate. Removal of the Pb(II) ion by acid washing left cavi ties templated for the Pb(II) ion. Sorption characteristics of the tem plate resins have been studied over a large range of template loadings by varying the degrees of crosslinking, and with or without the use o f ultrasonification during copolymerization. The capacity of the lead templated resins increases logarithmically with the increase of templa te complex content for levels of lead template content below 5 mol%. T he complexation equilibrium constants of the resins reach a maximum at 3 mol% template complex content. The resins show marked preference fo r binding the Pb(II) ion. The selectivity, alpha(Pb,Cd), has been foun d to be 174 for the 1 mol% templated polymer. In comparison to untempl ated resins, the template process enhances the selectivity by roughly a factor of 3 over Cu2+ and 2 over Cd2+. The selectivity enhancement i s mainly ascribed to ''coordination-geometry selectivity.''