Preparation of IPN-type stimuli responsive heavy-metal-ion adsorbent gel

We apply the interpenetration network (IPN) gel of poly(N-isopropylacrylamide) (PNIPAm) and poly(sodium acrylate) (PNaAAc) to the stimuli-responsive heavy-metal-ion adsorbent system. In the IPN gel system, PNIPAm and PNaAAc units are expected to behave independently. Therefore, the IPN gel of PNIPAm exhibits a thermosensitive volume-phase transition behavior in spite of the presence of polyelectrolytes like PNaAAc that are well known to prevent PNIPAm from shrinking when above their lower critical solution temperature (LCST). NIPAm-co-NaAAc copolymer gel (copoly gel) absorbed water and adsorbed Cu(II) ions sufficiently but did not exhibit the volume-phase transition behavior at all in the Cu(II) ion adsorption-condition. On the other hand, the IPN gel consisting of PNIPAm and PNaAAc exhibited the volume-phase transition behavior in the adsorbtion-condition. That is, the IPN gel adsorbed Cu(II) ion sufficiently below its LCST but not above the LCST. We could thermally control the adsorption abilities for heavy-metal ions by using the IPN gel system. The swelling IPN gel, which adsorbed Cu(II) ions, suddenly shrank when the temperature rose above the LCST. The IPN gel released water but did not release heavy-metal ions when shrinking. We are planning to construct an easy-recovery system for heavy-metal ions from wastewater by using this stimuli-responsive IPN gel. That is, we quickly adsorb the heavy metal ions from wastewater by using our swelling IPN gel below the LCST, and then squeeze the swelling IPN gel, which has bound the heavy metal ions, by raising the temperature above the LCST in order to facilitate ion handling. Finally, we can remove the heavy metal ions by means of acidic-treatment of the IPN gel and recycle the IPN gel-adsorbent. Copyright (C) 2003 John Wiley Sons, Ltd.