Synthesis And Characterization Of Ultrafine Well-dispersed Magnetite Nanoparticles

Due to their small size(1-100nm), nanoparticles exhibit novel materials properties that differ conciderably from those of the bulk solid state. Especcially in recent years, Magnetic nanoparticles are widely studied for their application in biology and medicine such as enzyme and protein immobilization, genes, radiopharmaceuticals, magnetic resonance imaging MRI, diagnostics, immunoassays, RNA and DNA purification,magnetically controlled transport of anti-cancer drugs as well as hyperthermia generation. The method for preparing magnetic nanomaterials is a improtant topic for people to study.Compared to other synthesize ways for Fe3O4,co-precipitation is superior in its convenient operation, lower-cost and high-productivity. But one of its disadvantages is that the so-prepared nanoparticles are always bigger than 8nm and have wide size distributions, which will limit the effect of magnetic particles in their applications. Our work mainly deals with the preparation of ultrafine well-dispersed magnetic nanoparticles. In our experiments, the citrate irons were introduced in the coprecipitation method and well-dispersed Fe3O4 nanoparticles were directly prepared with average size small than 5nm. The effects of relevant conditions on size, crystallization, magnetism and surface adsorption of particles were investigated. The results showed that the size of particles decrease with the increasing amount of the citrate ions and a lower saturation magnetization is found as a consequence of smaller particle size. In addition, some conclusions were obtained as follow: the reaction must proceed under the protection of N2 to avoid the unwanted oxidation; the final pH value of system has obvious effect on the size distribution and stability of the particles.In this thesis, we investigated the dispersibility of Fe3O4 particles in aqueous media. The results show that the citrate ions are chemically adsorbed on the surface of Fe3O4 particles, which could bring negative electric charges on particle surface to prevent their aggregation. The so-prepared particles are stable in a wide pH range (4