Synthesis and Characterization of Molecularly Imprinted Uranyl Ion Exchange Resins

Abstract

Ion exchange resins with enhanced capacity and selectivity for UO₂ ²⁺ have been prepared using the molecular imprinting method. The imprinted structure was introduced by copolymerization of styrene with uranyl vinylbenzoate in the presence of divinylbenzene as the cross‐linking agent. The polymerization was carried out in bulk with free‐radical initiation using 2‐methoxyethanol as a solvent and porogen. Upon removal of the template, specific sites for UO₂ ²⁺ rebinding remained. In equilibrium binding experiments with a variety of metal ions, the polymers preferentially bound UO₂ ²⁺. Control experiments were performed with reference polymers prepared without the template (unimprinted) and Ni²⁺ imprinted polymers. Selectivity data show that the imprinted polymers have a higher affinity for UO₂ ²⁺ than any of the competing metal ions tested. Several variables, that are crucial in improving the capacity and selectivity of imprinted polymers, were investigated in detail. The variables included (1) the effects of template monomer content, (2) the degree of covalent cross‐linking, and (3) the particle size. The effects of the variables on capacity and selectivity were examined and are discussed.

Keywords:

• Molecularly imprinted polymer
• ion exchange
• uranyl

Acknowledgments

This work was supported in part by funding from the U.S. Department of Energy (DOE) grant number DE‐FG07‐97ER14823. We wish to thank Dunja Schauki and Sharon Costigan of Johns Hopkins University Applied Physics Laboratory for their initial assistance with ICP‐MS analyses.