Research On The Stability Of Magnetic Nanoparticles And The Synthesis And Application Of Fe₃O₄/SiO₂ Nanocomposite

Owing to the property of finite-size effects, strong coercivity, magnetic nanoparticles have a broad application on industry areas such as microwave material, magnetic record material, cell separation, targeted drug delivery. Considering the strict conditions of biomedical application, magnetic nanoparticles need to satisfy the requirement of having narrow size distribution, strong magnetic property and chemical stability. But nanoparticles have a large ratio of area to volume, which tend to aggregate in order to decrease the surface energy, so researchers have devoted to finding out the optimized synthetic conditions and surface modification is a necessity.Much works have been done on finding out the effects of the synthesis condition, such as reaction temperature, pH value, the molar ratio of Fe3+ to Fe2+ on the property of nanoparticles, but little work is done on the effect of coating occasion on the stability of nanoparticles. Moreover, the study of the influence of surfactants on the stability of water-dispersed magnetic nanoparticles is not systematically conducted.In this thesis, the effect of coating occasion on the stability and size distribution were studied. In a view of crystal growth, three routes were designed to synthesize magnetite Fe3O4 nanoparticles by adding OA at different time. The obtained nanoparticles were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), zeta potential and the surface free energy. The results show that adding OA just after the process of co-precipitation can obtain stable and narrow- dispersive particles. The effect of oleic acid was explained by the LaMer mechanism.In addition, the effect of three kinds of surfactants and their combination were systematically studied. The results show that citric acid is the best surfactant for obtaining well-dispersed nanoparticles in water. The particle size is 15nm, and the magnetic resonance is high.In order to realize the application of nanoparticles on biomedical field, magnetic nanocomposite and Fe3O4@mSiO2@nSiO2 mesoporous microsphere were synthesized. No remanence was detected for both samples and the coercivity is zero, which indicated they all had superparamagnetism.