(185f) Synthesis of Thermoresponsive Copolymer Immobilized on Silica Coated Magnetite and Its Application for Heavy Metal Ions Recovery

To prevent aggregation and oxidation of MNP, silica coating on MNP was proposed and various methods have been reported. Recently, Setyawan et al. successfully achieved simultaneous magnetite nanoparticle formation and the modification of its surface with silica layer by using the electrooxidation method. Major advantages of the method are; the process is very simple and easy since it’s a one-step process, and aggregation and oxidation of MNP could be suppressed.

The purposes of this study are following; 1) to synthesize MNP with silica coating under various conditions by electrooxidation, and to examine the effect of the synthesis conditions on the characteristics of the resulting sample, 2) to immobilize thermoresponsive copolymer, poly(NIPAM-co-AA) on the MNP with silica coating, and to evaluate their immobilized copolymer amount and Cu adsorption property.

In the experiment, MNP with silica coating was synthesized using the electrooxidation method with changing the DC current from 0.10 to 0.80 A. Next, the surface of the resulting samples were modified using a silane coupling agent, and poly(NIPAM-co-AA), which was synthesized by free radical copolymerization, was immobilized through chemical bonding.

As a result of X-ray diffractometer (XRD) analysis and Fourier transform infrared spectroscopy (FT-IR) measurement, it was confirmed that MNP with silica coating was successfully synthesized using this method. When the current value was changed during electrooxidation synthesis, it was found that the minimum particle diameter(maximum specific surface area) was obtained at the current value of 0.60 A. The results of thermogravimetric analysis (TGA) showed that the maximum immobilized amount of the copolymer of 0.255 g/g-MNP was obtained when the sample synthesized at a current value of 0.60 A was used. The immobilized amount was 3 times larger than that of the sample prepared using MNP without silica coating. This is considered to be due to less aggregation of MNP during polymer immobilization. The results of Cu (II) adsorption experiment showed that although Cu (II) recovery amount through temperature swing was similar to those of conventional thermoresponsive “gel” type heavy metal adsorbents, time required for Cu(II) recycling process could be decreased to 1/10. These results showed the effectiveness of this method.