SELECTIVE CAPTURE AND ENCAPSULATION OF METALLIC CATIONS BY HYDROGELS CONSISTING OF COPOLY(N-ISOPROPYLACRYLAMIDE/FUNCTIONAL MONOMER) NETWORKS

Abstract

Under the U.S. Department of Energy Waste Treatment Baseline and Integrated Waste Management Strategy the recycling of spent nuclear fuel to minimize waste, to assure maximum energy recovery, and to pursue science-based R&D to possibly eliminate the need for geologic waste repositories, are programmatic goals. We have developed both polymer gel and porous materials for the separation and adsorption of targeted contaminants. Here, we have investigated capture and encapsulation capabilities of hydrogels consisting of thermally-sensitive copoly[N-isopropylacrylamide(1-x) / functional monomer(x)] networks, where functional denotes carboxylic, hydroxyl, or cyanide group (mol fraction x); the captured and encapsulated species were: Cr3+, Co2+, Cu2+, Ni2+, Eu3+, Ho3+ and Tb3+ present in aqueous medium. Natural diffusions of cations into gel phase and the physico-chemical affinity of functional groups for cations played a major role in capturing cations. Encapsulation of cations trapped in hydrogels was achieved by loss of water and conformational transformation of networks through a volumetric phase transition. Experimental determinations of cation amounts (mass) and copolymer composition were carried out by atomic absorption and elemental analyses of carbon, nitrogen and hydrogen, respectively. We developed two approaches for determination of efficiency and selectivity metrics describing capture and encapsulation of cations by functional groups using two theories: 1) mean field theory and 2) first-order thermodynamic perturbation theory. The integrated results thus obtained show that: Cu2+ and Co2+ were selectively encapsulated by carboxylic and cyanide groups, respectively. Carboxylic and hydroxyl groups were superior extractants for Cr3+, Eu3+ and Ho3+. Further the cyanide group was also efiective for Eu3+ and Ho3+. However, all functional groups examined here were ineffective in capture and encapsulation ofNi2+.