수열합성법에 의해 제조된 다양한 형태의 나노 산화철

Abstract

The aim of this thesis is to discuss about synthesis and processing of iron based nanocrystals with tailored properties, such as chemical (composition of the bulk and surface functionalized groups) and structural (size and morphology) characteristics, which are the main features for the design of nano-objects in specific applications. Three kinds of synthesized approaches are utilized to form iron oxide nanocrystals on a nano-scale, namely “co-precipitation of Fe3+ and Fe2+ synthesis”, “thermal decomposition” and “hydrothermal synthesis”. In particular, the focus of the thesis is various nano-structured iron oxide nanocrystals generated by hydrothermal method. Modified co-precipitation of Fe2+ and Fe3+ can readily prepare magnetite nanoparticles coated with the polymer for the enhancement of both water-solubility and biocompatibility. There are two synthetic procedures that have been introduced to create these particles. One operates on the principle of the physical interaction between the polymer and the magnetite core in a one-step reaction. Alternatively, hydrochloric acid is used routinely for erosion of the nanoparticles’ surface, thus giving rise to the stronger affinity. However, it is becoming apparent that the particles are not uniform. Thermal decomposition is recently one of the most commonly employed techniques to exploit uniform and mono-dispersed metal or metal oxide nanocrystals, which occurs when iron carboxylate salts are effectively pyrolyzed under the protection of oleic acid in this dissertation. On the level of its application, attempts have been made to alter the surface property of the newly synthesized samples, from hydrophobic property to hydrophilic property, using various polymers and silica for forming shells around the magnetite seeds. The disadvantage of the system is the poor scale-up. Therefore, to efficiently scale up high-quality nanocrystals, a fully synthetic system is needed. The idea of synthesizing nano-materials in the hydrothermal environment is not new, but this initial experiment opens the door for the fabrication of various nanostructured iron oxide nanocrystals. The sophisticated structure is a highly attractive and desirable feature owing to their unique physical properties and potential applications in sensors, magnetic, and even as building blocks for nanoscale devices. Magnetite, hematite and goethite nanocrystals with controllable shape are formed in terms of a polymer/water system, an organic acid/water system and ion solutions, respectively. As a consequence, nanoparticles, nanocubes, nanorods, nanoplates and nanorings are prepared for fundamental study. Progress in this regard has been limited, as some crystals are not magnetic in nature. To overcome this defect, the strategy of heat treatment for phase transferring has been developed in a reduce-and-oxidate fashion.