Preparation And Characterization Of Iron And Cobalt Oxides (Chalcogenides) By Hydrothermal/Solvothermal Techniques

The present thesis is aimed at exploring novel low-temperature hydrothermal/solvothermal methods to synthesize iron and cobalt oxides or chalcogenides, and studing the formation mechanism of the iron and cobalt chalcogenides under the hydrothermal/solvothermal conditions. The main works achieved are summed up as following:1. Hydrothermal synthesis ofα-Fe₂O₃ nanoparticlesα-Fe₂O₃ nanoparticles were prepared by a facial hydrothermal method in the presence of polyethylene glycol-6000 (PEG-6000) at different reaction conditions. The morphology and composition of products were investigated by TEM, SEM and XRD, and the effects of the reaction conditions, reagents concentration, anions and surfactants on the nanoparticle morphology were discussed. Magnetic properties of as-obtained nanoparticles were characterized by VSM. Furthermore, the relation between the product morphologies and magnetic properties was preliminarily presented.2. Solvothermal synthesis of Co₃O₄ nanoparticles and fcc-Co microparticlesCo₃O₄ nanoparticles with diameter of ca. 70 nm and face-centered cubic cobalt (fcc-Co) microparticles with diameter of ca. 1μm were successfully synthesized from a single precursor via a facile solvothermal process. The morphology, structure and properties of the precursor CoCO₃ and as-prepared products were characterized by TEM, SEM, XRD, IR, TGA and hysteresis loops. SDBS surfactant plays an important role in the formation of Co₃O₄ and Co crystals. It acts as not only a surfactant but also a reagent. A possible formation mechanism was elaborately discussed. Preliminary magnetic measurements reveal that as-prepared Co₃O₄ nanoparticles exhibit weakly ferromagnetic properties and Co microparticles display ferromagnetic properties.3. Solvothermal synthesis of metal sulfidesA thiourea-mediated solvothermal route was used to the synthesis FeS/PVP 3D flowers in DMF solution. The morphology, structure and properties of FeS/PVP 3D flowers were characterized by TEM, SEM, XRD and IR. It is found that PVP coordinated with iron ion may serve as soft templates. The influences of reaction time and the molar ratio of FeCl₃ and PVP on the morphologies of FeS ordered architectures have been investigated, and the evolution process from nanoparticles to nanosheets to crosslike 3D flowers to particles were elaborately discussed. The decomposition of thiourea and the rearrangement of PVP chain segments both are play important roles in our experiment. This works was also used to prepare other metal sulfides/PVP composites, such as Cu₂S/PVP.