Development of Separation Process of Heavy Metals by Adsorption with Molecular Imprinted Thermosensitive Microgel Particles

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In this work, a novel gel adsorbent, which adsorbs and/or desorbs specific heavy metal ions selectively by temperature swing, were examined. The chelating groups, which interact with heavy metal ions, were introduced into the thermosensitive N-isopropylacrylamide (NIPAM) gel using the molecular imprinting technique. Copper (Cu) was selected as a target metal, and N-(4-vinylbenzyl)ethylenediamine (Vb-EDA) was used as a chelating monomer. The maximum adsorption amount of Cu ions was obtained at a specific temperature, at which the swelling degree of gel was the same as that in the preparation of gel, and the adsorption/desorption by temperature swing was possible. It means that the adsorption sites memorized in the preparation were reproduced at a specific temperature. It was confirmed that one Cu ion coordinates with two molecules of Vb-EDA, and that the gel has the selectivity for Cu ion. Furthermore, it was found that the equilibrium adsorption amount was well described by the Langmui … More r isotherm formula. However, it took more than 100 hours to reach the equilibrium adsorption amount, though the ground gel particles of about 100 μm were used. It was considered due to the fact that the thermosensitive gel particles aggregate by the hydrophobic interaction because the peak temperature of adsorption was above the transition temperature of poly(NIPAM), about 32℃. To alleviate this problem the thermosensitive microgel particles involving Vb-EDA were prepared with an anionic polymerizable surfactant. Such microgel particles dispersed stably above the transition temperature of poly(NIPAM). Although the temperature dependence of the adsorption amount and the selectivity for Cu ion were almost the same as those of the ground gel particles mentioned above, the adsorption rate was improved extremely. The adsorption amount reached the equilibrium within 100 minutes. Although it needs further investigations because such microgel particles have a problem for handling, the -possibility for the development of a novel thermosensitive gel adsorbent could be shown Less