Preparation of molecular imprinted thermosensitive gel adsorbents and adsorption/desorption properties of heavy metal ions by temperature swing

A gel adsorbent which adsorbs and/or desorbs specific heavy metal ions selectively by temperature swing was prepared by copolymerizing the chelating monomer, N-(4-vinyl)benzyl ethylenediamine (Vb-EDA) with N-isopropylacrylamide (NIPA) as thermosensitive component by using the molecule imprinting technique. Copper ion, Cu(II) was selected as a target ion in imprinting. The adsorption amount of Cu(II) ions on imprinted gel depended on the temperature, and the maximum amount was obtained at a specific temperature where the size of gel network corresponds to that memorized in the preparation of gel. The adsorption amount depended on the gel composition, namely, the concentrations of NIPA and cross-linker. The adsorption amount increased linearly with the increasing Vb-EDA content in the gel, and the slope was almost 1/2. This implies that one Cu(II) ion coordinates with two molecules of Vb-EDA. The adsorption amount was well described by the Langmuir isotherm formula. The adsorption and desorption could be done repeatedly by temperature swing. Furthermore, the selective adsorption of Cu(II) ions was confirmed by comparing the adsorption amounts of other metal ions, Ni(II), Zn(II) and Mn(II).