Surface Modification And Applications Of Magnetic Fe₃O₄@SiO₂ Nanoparticles

Magnetic nanoparticles are a kind of smart reagents which combine the properties ofboth nanomaterials and magnetic materials, such as small particle size, large surface area, magnetic response, and magneto caloric effect. In addition, the magnetic nanoparticles exhibit many particular properties, e.g. Superparamagnetism and magnetofluid, which are very important for the applications of magnetic materials.Magnetic nanoparticles have been widely used in various fields like catalysis, magnetic storage, biomedical and ecological environment.However,magnetic nanoparticles prepared by traditional methods always show some drawbacks, for example, large particle size, weak magnetic response and poor stability. These drawbacks may limit their applications in biomedical and other high-end fields.Recently, with the development and breakthrough of nanotechnology, the preparation method of magnetic nanoparticlesbecomes morediverse and efficient, which significantly improve the performance of super paramagnetic nanoparticlesin biomedical field including cell separation, targeted medicine, magnetic resonance imaging, magnetic hyperthermia and so on.Herein, the preparation, properties and applications of magnetic nanoparticles are briefly reviewed. Firstly, the mechanism and conditions for magnetic nanoparticles to generate superparamagnetism are introduced. Secondly, the main preparation methods of magnetic Fe₃O₄ nanoparticles are described, including chemical co-precipitation process, hydrothermal process andcarbonyl-precursordecomposition process. The mechanism and the advantages/disadvantages of these threemethods are compared. Thirdly, the coating procedure of Fe₃O₄ nanoparticles with SiO₂ by St?ber process and reverse microemulsion method is demonstrated. Finally, the applications of magneticnanoparticles in magnetic fluid, magnetic resonance contrast agents, catalysts, drug targeting, magnetic hyperthermia etc. are introduced.In this thesis, magnetic Fe₃O₄ nanoparticles were prepared by carbonyl-precursor based thermal decompositionmethod. These Fe₃O₄ nanoparticles were coated with a layer of SiO₂ through a reverse microemulsion procedure in water/cyclohexane solution using Triton X-100/n-Butanol as the surfactants.The Fe₃O₄@SiO₂ nanoparticles weremodified with 3-aminopropyltriethoxysilane and then grafted with Rhodamine B. The structure and morphology of magnetic nanoparticles were investigated by X- ray diffraction?XRD?, transmission electron microscopy?TEM?, and dynamic light scattering?DLS?. The magnetic properties of the samples were measured by vibrating sample magnetometer?VSM?. The surface organic content of the sample were measured by thermal gravimetric analyzer?TGA? and Fourier transform infrared spectrometer?FT-IR?. The selectivity of Rhodamine B-EDA compound and Fe₃O₄@SiO₂@Rhodamine B nanoparticlesfor Fe3+ were investigated by UV-visible spectrophotometer?UV-Vis? and fluorescence spectrophotometer?FS?.The main results achieved are listed as below:1. Magnetic Fe₃O₄ nanoparticles were successfully prepared by thermal decompositionmethod. First, ferric oleate were synthesized by the reaction of Fe Cl3 and oleic acid. The sticky ferric oleate precursor was dispersed in 1-octadecene and the magnetic Fe₃O₄ nanoparticles were obtained by a decomposition reaction at 320?. The obtained Fe₃O₄ nanoparticles show cubic crystal structure with average diameter of 18 nm, and can be dispersed well in nonpolar solvent such as cyclohexane. Moreover, the Fe₃O₄ nanoparticles exhibit super paramagnetism with saturation magnetization of 20 emu/g.2. A reverse microemulsion solution was formed with water, Triton X-100 / n-butanol and cyclohexane. The effect of the size of the aqueous domains on the appearance of the micro emulsion was investigated. The results show that the appearance of the micro emulsion is different in diverse statesdue to the different refractive index of the aqueous phase and the oil phase. There are four typical states for the emulsion solution including milk white, blue white, gray translucent and clear transparent. In addition, the size of the aqueous domains are dependent on the ratio of water to surfactant. The size of the aqueous domains becomesmaller with increasing amount of surfactant.3. The silica coating of Fe₃O₄ nanoparticles were performed via the catalysis and hydrolysis of TEOS in the reverse microemulsion mentioned above. The results show that the obtained magnetic Fe₃O₄@SiO₂ nanoparticles are core-shell structure, and the thickness of the SiO₂ shell is about 10 nm.4. The Rhodamine B-EDA compoundwas synthesized from Rhodamine B and ethylenediamine, and showed excellent selectivity for Fe3+ in aqueous solution. The limit of detection for Fe3+is 0.375?M and the complex ratio of Fe3+ and the Rhodamine B-EDA compoundis 2:1.5. The Rhodamine B were successfully grafted on the surface of Fe₃O₄@SiO₂ nanoparticles by the reaction of Rhodamine B and the amination-modified silica particles. The average number of Rhodamine B molecule on the surface of nanoparticles is determined as 670. The prepared hybrid magnetic nanoparticles can be used as fluorescent probe for the detection of Fe3+ ions in aqueous solution.