(536g) Synthesis of Thermoresponsive Composite and Application for Water Treatment

Poly (N-isopropylacrylamide) (PNIPAM) is known as representative thermoresponsive polymer that exhibits lower critical solution temperature (LCST) around 32 ºC. In our laboratory, we have been synthesizing thermoresponsive composite in which PNIPAM polymer or gel and inorganic nanoparticles were combined, and also have been tried to apply them for heavy metal ion recovery or organic compound decomposition in the solution. For heavy metal ion recovery, poly(PNIPAM-co-AA)/Fe₃O₄ composite adsorbents were synthesized under various conditions. The result of Cu(II) adsorption experiment showed that the adsorption capacity at above LCST (60 °C) was larger than that at below LCST (10 °C). Then, repeated Cu(II) adsorption/desorption operation was performed by swinging temperature. The result showed that the adsorption/desorption behavior was reversible and recovery of Cu(II) ion could be achieved by only swinging temperature. This would eliminate the production of secondary waste such as acid waste during recovering process of heavy meal ions. For organic compound decomposition, highly functionalized thermoresponsive composites gel beads in which two kinds of functional inorganic particles and thermoresponsive polymer work concertedly were prepared. In this study, poly(N-isopropylacrylamide) and calcium alginate were used as the thermoresponsive polymer and structure support polymer, respectively. TiO₂ and Fe₃O₄ were used as functional inorganic nanoparticles. The resulting composites exhibited thermoresponsive volume change and photocatalytic activity to decompose methyl orange. Localized heating of the thermoresponsive bead containing Fe₃O₄ was also achieved by applying an alternating current (AC) magnetic field on the bead. Due to the localized heating property, repeated shrinking-swelling movement (i.e., pumping movement) of the composite was achieved by applying an AC magnetic field intermittently. Finally, based on the experimental results, the effect of the promoted mass transfer of the substrate and product due to thermoresponsive pumping on the enhancement of the apparent photocatalytic activity was simulated. The results showed the effectiveness of thermoresponsive pumping in improving the apparent photocatalytic activity of TiO₂ nanoparticles embedded in the composite gel.