Reversible adsorption of calcium ions by imprinted temperature sensitive gels

摘要

With the aim of developing polymeric gels sensitive to external stimuli and able to reversibly adsorb and release divalent ions, copolymer gels ofN-isopropylacrylamide (NIPA) andmethacrylic (MAA) monomers were prepared. We chose calcium as a target divalent ion. Two MAAs form a complex with a calcium ion, and the NIP A component allows the polymers to swell and shrink reversibly in response to temperature. The adsorbing site develops an affinity to target ions when the adsorbing molecules come into proximity, but when they are separated, the affinity diminishes. To enhance the affinity to calcium, an imprinting techniqu~ was applied using Ca2+ and Pb2+ ions as templates in methylsulfoxide and dioxane media, respectively. The adsorption capacity of the imprinted gels was ::ompared with that of the nonimprinted gels, and the effects of the templates, the solvents, and the lillount of methacrylic monomers used in the synthesis and the medium temperature over the Ca2+ idsorption capacity of the gels from aqueous solutions were evaluated. The analysis of the idsorption revealed that (a) the adsorption can be described by the Langmuir isotherms; (b) there is ill approximately linear relationship between saturation and methacrylic monomer concentration; c) the affinity depends on the degree of gel swelling or shrinkage that can be switched on and off )y temperature; (d) in the shrunken state, the affinity depends approximately linearly on the MAA :oncentration in the imprinted gels, whereas in the nonimprinted gels it is proportional to the square If MAA concentration; (e) the imprinted gels adsorb more than the nonimprinted.gels when MAA oncentration is less than that of permanent cross linkers. The success of imprinting of CaMAA2 nd PbMAA2 complex is evidence for memory of such complex onto the weakly cross-linked gel.