Selective removal of 90Sr and 60Co from aqueous solution using N-aza-crown ether functional poly(NIPAM) hydrogels

The ability of temperature and pH responsive cross-linked poly(NIPAM-co-AAc) hydrogel beads containing covalently bound N-aza-crown ethers to selectively complex 90Sr and 60Co under competitive and non-competitive conditions is demonstrated using a combination of autoradiography and scintillation measurements. Due to the presence of copolymerised acrylic acid, which is incorporated to introduce pH responsive behaviour as well as acting as the site of covalent attachment of the N-aza-crown ether, the decrease in particle diameter as a function of increasing temperature on going through the LCST of PNIPAM is reduced in the presence of electrolyte. At pH 2 no complexation of either 90Sr or 60Co was observed. At pH 7 the incorporation of acrylic acid under non-competitive conditions results in the ability to complex ca. 90% 90Sr and 60Co which increases to between 94% and 96% on inclusion of N-aza-crown ether. Under competitive conditions the hydrogels lose the ability to selectively complex 90Sr, although the selectivity for 60Co was enhanced in the presence of N-aza-crown ether. Subsequent recovery of bound 60Co from the hydrogel on lowering to pH 2 was only partially successful, and lead to a decrease in the swelling behaviour on readjustment to pH 7.