Surface Modification Of Fe₃O₄Megnetic Nanomaterial And Research Of Related Properties

Due to their unique phisical and chemical properties, magnetic nanoparticles are applied in a wide range of disciplines, including magnetic fluids, catalysis, biotechnology, magnetic resonance imaging and data storage. While as a common magnetic iron oxide, successful applications of Fe3O4in the areas listed above require the magnetite nanoparticles to be monodispersed and superparamagnetic with a size smaller than20nm and good response to applied magnetic fields. Among the methods of sythesizing magnetic nanoparticles, thermal decomposition of organic complexes seems to exhibit advantages in preparing high-quality monodispersed magnetite nanoparticles. Here, we use a modified thermal decomposition method to prepare monodispersed Fe3O4nanoparticles with uniform size and controllable surface properties and modify the surface with different molecules, then combine them with conducting polymer to explore the application in the field of microwave absorption. The specific studies are as follows:Firstly, we obtain well monodispersed and oil-soluble Fe3O4nanoparticles through modification with oleic acid, and study the adsorption of oleic acid molecules on the surface of iron oxide nanoparticles from the aspects of concertration and temperature by TGA and FT-IR.Secondly, We disperse the oleic acid coated Fe3O4nanoparticles in the organic phase of microemulsion by taking advantage of their good oil-solubility, then synthesize monodispersed polyaniline coated iron oxide nanoparticles composite with core-shell structure by microemulsion polymerization and characterize the morphology, structure,conductivity and magnetism of the composite through TEM, XRD, etc. At the same time, we also explore the application of the composite in the field of microwave absorption. The results indicate that the frequency of the maximum reflection loss moves to low frequency and the effective bandwidth decreases with the thickness of the absorbent increases. There is a maximum of reflection loss,which is-26.98dB at10.52GHz when the thickness of the absorbent is 3mm and the effective bandwidth was3.74GHz, from8.65to13.39GHz.On the other hand, water-based magnetic fluids have attracted a lot of attention because of their potential applications in the field of bio medicine and other. We use sodium citrate molecules as ligands and obtain well monodispersed and water-soluble Fe3O4nanoparticles and characterize them by laser particle sizer and FT-IR. The results indicate that after modification by sodium citrate, iron oxide nanoparticles show good resistance to acid, alkali and salt and maintain stability in the range of pH4-9and salt concertration0-0.2M. Additionally, the sodium citrate coated Fe3O4nanoparticles can provide wide applications in the fields of bio medicine and magnetic separation because the carboxyl groups on their surface can react with other functional groups.We also try to use the intrinsic peroxidase-like activity of iron oxide nanoparticles to catalyze the polymerization of anilie without the presence of polyanion template to synthesize polyaniline coated Fe3O4nanoparticles composite and optimize the reaction conditions from the aspects of pH, concentration of surfactant and H2O2. After obtain the optimal reaction conditions, we use sodium citrate coated Fe3O4nanoparticles mentioned above to ensure their dispersibility in the composite. Through the characterization by TEM, FT-IR and XRD,etc, we confirm that polyaniline coat on the iron oxide nanoparticles by catalyzed polymerization. Moreover, we explore the application of the composite in the field of microwave absorption. The results show that the the maximum reflection loss in the range of8-12GHz increases and moves to low frequency and the effective bandwidth increases with the thickness of the absorbent increases. While the maximum reflection loss in the range of13-16GHz first increases and then decreases. There is a maximum of reflection loss when the thickness of the absorbent is3mm. Although the microwave absorption property of the composite still needs to be enhanced, it is a little improved compared with the results reported in the literature.