(200g) Synthesis of Thermoresponsive Polymer/Fe3O4 Nanoparticle Composite and Its Application

For heavy metal ion recovery from wastewater, various methods such as the usage of absorbents incorporating ion exchange groups or chelating groups have been developed. However, main disadvantage of the methods is generation of secondary wastes during recycling process. To solve the problem, we focused on poly(N-isopropylacrylamide) (PNIPAM) which was known as one of the thermoresponsive polymer. Since PNIPAM has lower critical solution temperature (LCST) around 32 ºC, if functional groups to capture heavy metal ions are copolymerized into the polymer chain, repeatable adsorption/desorption of heavy metal ions will be possible by swinging temperature and using the resulting conformation change. Therefore, in this study, thermoresponsive polymer/Fe₃O₄ nanoparticle composite was developed and applied for heavy metal ion recovery with the aim of achieving (1) repeatable adsorption/desorption property of heavy metal ion by only swinging temperature, and (2) reusability due to magnetic property. In the experiment, free radical copolymerization of N-isopropylacrylamide and acrylic acid (AA) was performed for the synthesis of straight-chained thermoresponsive copolymers. Then, an amine modified Fe₃O₄ nanoparticle was synthesized by the co-precipitation method. Finally, the copolymer was immobilized onto the amine modified Fe₃O₄ nanoparticle through amide bound formation. The results of X-ray diffractometer (XRD) analysis, Fourier transform infrared spectroscopy (FT-IR) measurement and thermogravimetric analysis (TGA) indicated that poly(NIPAM-co-AA) was immobilized on Fe₃O₄ nanoparticle and the maximum of amount of the copolymer was 0.185 g/g-Fe₃O₄. Cu(II) adsorption experiments exhibited that the saturated adsorption amounts were 0.16 mmol/g-adsorbent at 10℃ (below LCST) and 0.31 mmol/g-adsorbent at 50℃ (above LCST), respectively, for the sample which had maximum immobilized copolymer amount. In addition, repeated Cu(II) adsorption/desorption by swinging temperature was also possible. These results indicated that it was successful to synthesize reusable adsorbent which can recover heavy metal ions from wastewater without producing secondary waste during its Cu(II) adsorption/desorption process.