Hydrothermal Synthesis And Surface Modification Of Magnetic Iron Oxide Nanoparticles

With the development of nano-technology, magnetic ferric oxide nanoparticles arewidely studied for their application in biomedical field such as cell separation,enzyme immobilization, immunoassay, drug delivery, DNA separation and so on. Inaddition, magnetic ferric oxide nanoparticles are also widely used as magneticmaterials for information storage, catalyst, magnetic fluids, microwave absorbent et al.Their application is due to the magnetic ferric oxide nanoparticles possessing someexcellent characteristics, such as small size, great specific surface area, high surfaceactivity and magnetically responsive, and the morphology, size and crystal are theimportant factors to the magnetization of magnetic nanoparticles. So far, sphericalmagnetic ferric oxide nanoparticles have been widely synthesized and surfacemodified, while little work on synthesis or surface modification of ferric oxidenanorods or nanoplates has been done. In this thesis, the magnetic ferric oxidenanoparticles with different morphologies and sizes were synthesized and surfacemodified. The main content of the thesis is as follows:In this thesis, magnetic ferric oxide (Fe₃O₄,γ-Fe₂O₃) nanoparticles with welldispersion and regular morphology have been successfully synthesized by usingsurfactants, peptone, starch as an additive respectively under hydrothermal condition.The X-ray diffraction (XRD), transmission electron microscopy (TEM), Fouriertransform infrared spectrometer (FT-IR), thermogravimetric analysis (TGA) andvibrating sample magnetometer (VSM) techniques were used to characterize theas-synthesized magnetic nanoparticles for their structure, shape and magneticproperties. In the experiments, the influences of the reaction temperature, reactiontime and mass of the additive on the products were intensively studied and theappropriate reaction conditions were determined. The results of our experimentsindicated that the additive played a critical role in the formation of magnetic ferricoxide (Fe₃O₄,γ-Fe₂O₃) nanoparticles with different morphologies. The possiblemechanisms for the formation of maghemite (γ-Fe₂O₃) nanoplates, magnetite (Fe₃O₄)nanorods were also discussed. The magnetic properties of the synthesized samples were characterized by VSM.The results reveal that the samples show ferromagnetic behavior at room temperatureand the magnetization has been much effected by the morphology, size of the samples.The values of saturated magnetization at 300 K of the as-synthesized magnetite(Fe₃O₄) nanoparticles, maghemite (γ-Fe₂O₃) nanoplates, magnetite (Fe₃O₄) nanorodsare lower than that of the corresponding bulk materials. Also the saturatedmagnetization of magnetite (Fe₃O₄) nanorods is lower than that of magnetite (Fe₃O₄)nanoparticles. This is mainly because of the small size effect and shape anisotropy.In order to improve the stability, dispersivity and biocompatibility of magneticferric oxide nanoparticles, maghemite (γ-Fe₂O₃) nanoplates and magnetite (Fe₃O₄)nanorods were surface modified by biocompatible polymer, such as chitosan, bovineserum albumin(BSA) and inorganic molecules, such as TEOS, Na₂SiO₃, KH-560. TheTEM, FT-IR, XRD, TGA and VSM were used to characterize the surface-modifiedsamples, and the results show that magnetic chitosan nanoparticles were successfullyprepared by the suspension cross-linking technique; BSA enwrapped magneticnanoparticles were prepared by the glutaraldehyde cross-linking technique; SiO₂ weresuccessfully coated on magnetic ferric oxide nanoparticles after surface modificationby TEOS, Na₂SiO₃ and KH-560. The values of saturated magnetization of magneticiron oxide nanoparticles after surface modification decreased apparently because ofthe "dilute effect". The magnetization of the samples decreased, while they are stillmagnetically responsive.In this thesis, different morphologies of the ferric oxide nanoparticles weresynthesized under hydrothermal condition, and the as-synthesized maghemite(γ-Fe₂O₃) nanoplates and magnetite (Fe₃O₄) nanorods were surface modified. Ourwork enriches the preparations of magnetic ferric oxide nanoparticles, and providesbasic research for the application of magnetic ferric oxide in biomedical field.