In this study, systematic examination of the effect of different polymer types (functional groups) on the one-step synthesis of polymer immobilized magnetite nanoparticle via the modified coprecipitation method was carried out. By using five different polymers with different functional groups of polyacrylic acid (PAA), polyacrylamide (PAM), polyethylene glycol (PEG), polyethylene imine (PEI), and polyvinyl alcohol (PVA), the effect of the polymer difference on magnetite nanoparticle formation, polymer immobilization, composite particle size, zeta potential and magnetic properties of the resulting composite were measured in detail. The results show that the immobilized polymer yield varied significantly depending on the type of polymer used and their order was as follows; PEG < PEI < PAM < PAA < PVA. Despite the simple method, PVA/MNP achieved high immobilized polymer amount of 0.2 g/(g-Fe 3 O 4 ), which was about 1.8 times larger than that prepared by a conventional method. Furthermore, the different zeta potentials and hydrodynamic diameter corresponding to each functional group of the immobilized polymer were observed. The results of the vibrating sample magnetometer (VSM) measurement confirmed that all the polymer/MNP composites showed a superparamagnetic behavior. These results showed that the proposed method is very simple, facile, and applicable to various polymers to synthesize polymer immobilized on magnetite nanoparticle.

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To enhance chemical stability and suppress of aggregation of magnetite nanoparticles (MNPs), which are used as a support for thermoresponsive copolymer immobilization, silica coating of the MNPs is applied via the electrooxidation method. Although the resulting silica coated-MNPs also formed aggregates, the size distribution of the aggregate shifted to smaller size range. Because of that, the surface area available for copolymer immobilization increased approximately 6.7 times at maximum as compared with that of the uncoated MNPs. It contributed to the increase of the amount of the immobilized copolymer on the silica-coated MNPs, which is approximately four times larger than that on the uncoated MNPs. Fe 3 O 4 dissolution test confirmed enhancement of chemical stability of MNPs. The thermoresponsive copolymer immobilized on the silica-coated MNPs shows the ability to recycle Cu(II) ion from Cu(II) containing solution by changing temperature with significantly shorter time than those in other thermoresponsive adsorbents in gel form.

The objectives of this study are 1) to investigate the effect of silica source concentration on the properties of the silica-coated magnetite nanoparticle (MNP) prepared using the electrooxidation method, and (2) to apply the resulting silica-coated MNP for the immobilization of thermoresponsive copolymer, (poly(NIPAM-co-AA)), which we developed for heavy metal ion recovery. The results of laser diffraction analysis show that the particle size distributions of the silica-coated MNP are smaller than that of the uncoated MNP, which indicates that the aggregation of MNP is suppressed by silica coating. Thermogravimetric analysis (TGA) results show that the immobilized copolymer amount on the silica-coated MNP is approximately 5 times larger than that on the uncoated MNP. These results indicate that the successful suppression of MNP aggregation through silica coating using the electrooxidation method contributes to the increase of the available surface area for the copolymer immobilization.