Preparation And Application Of ZnO And Fe₃O₄ Nanoparticles

First, the synthesis, surface modification and application of ZnO nanoparticles were investigated. Second, the preparation, surface modification and biomedical applications of Fe₃O₄ magnetic nanoparticles were investigated.1. The precursor of ZnO nanoparticles was synthesized by precipitation using zinc acetate and ammonium carbonate as the raw materials. Then ZnO nanoparticles were obtained by calcination. To reduce the aggregation among nanoparticles and to improve the compatibility between nanoparticles and organic matters, the ZnO nanoparticles were treated with the coupling agentγ-methacryloxypropyl trimethoxy silane (KH570), followed by radical grafting polymerization in non-aqueous suspension to graft the PSt chains onto the surface of nanoparticles. The obtained samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and the results indicated that polymer chains were linked onto the surface of nanoparticles by chemical bonds. In addition, other methods such as zeta potential measurement, lipophilic degree (LD) test, photocatalytic experiments, sedimentation test were used to study the effect of modification. The results showed that the composite particles were stable even after heat treatment under high temperature. The photoluminescence of PSt-grafted ZnO nanoparticles was observed by naked eyes. However, photocatalytic activity was greatly reduced after coating with PSt. The ZnO and PSt/ZnO nanoparticles were used to reinforce poly (vinylidene fluoride) (PVDF) films and the mechanical and electric properties of the films were also improved.2. Magnetite nanoparticles (MNPs) were synthesized by the co-precipitation of Fe²⁺ and Fe³⁺ using ammonium hydroxide (NH4OH) as precipitating agent. To improve the compatibility between nanoparticles and aqueous medium, the surface of nanoparticles was modified by dextran through a two-step method. Firstly, the surface of magnetic nanoparticles was activated with amino-silane through the reaction between the hydroxyl groups and the coupling agent 3-aminopropyltriethoxysilane (APTES). Secondly, the activated nanoparticles reacted with aldehyde dextran, and the so-prepared dextran-coated iron oxide nanoparticles were obtained. Characterization techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TGA), particle size analyzer based on laser scattering and vibrating sample magnetometer (VSM) were used to delineate the structure and properties of nanocomposites. Moreover, the magnetite/dextran nanocomposites were dispersed in water to form ferrofluids (FFs). The influences of surfactants, magnetic field intensity and solid content on the rheological properties of FFs were investigated using a rotating rheometer.3. Dextran/Fe₃O₄ FFs were prepared through one-step method. Compared with the conventional method, hydrazine hydrate as reducing agent and precipitator was added in the process of preparation. At the same time, the effects of the hydrazine hydrate, the weight ratio of dextran to Fe₃O₄ and molecular weight of dextran on the stabilization of FFs, particles size of modified Fe₃O₄, coating efficiency, rheological properties and magnetic properties were discussed. To investigate the distribution of FFs in rabbits'body, some FFs were injected into the body of rabbits through ear vein infusion, and then, the contents of Fe element in blood and some organs of the rabbits at different time were measured by atomic absorption spectrometer, and the biological transportation of FF in organs was examined. The magnetic resonance images (MRI) of liver, marrow and lymph revealed that the magnetic resonance signals of these organs decreased when FFs were injected into the body of rabbits, indicating a wonderful application of FFs in MRI.