| In modern materials, properties and applications of magnetic materials receivedtremendous attention of the researchers. The properties of materials depend not only on itschemical composition, but also related to its morphology, size and structure. The applicationperformance of vast majority of materials is directly determined by their morphology, sizeand structure. Therefore, the control of materials with different morphologies, sizes andstructures has become one of the forefront of materials science research.The study emphasis of the present thesis is morphological control and propertiesinvestigation of Ni microspheres and octahedral Fe3O4. In this study, the morphology andconfiguration of surface of Ni and Fe3O4are conducted by etching reaction, and the etchingmechanism is preliminarily discussed. The direction of etched nickel microsphere in theapplications of sewage treatment and the electrochemical catalytic oxidation of methanol isviewed. The main research contents and results are as follows:1. Nickel microspheres withdiameter in the range of1to4μm were synthesized throughasimple solvothermal method, particularly, presenting rough surfaces and mixed phasesof fcc and hcp in structure. Subsequently, the dried nickel microspheres suffered anoptimal etching process, where a20mL solution of Glycerol containing0.9mmolFeCl3·6H2O used as the etching liquor, and the etching process was maintained at90oC in a water bath under mechanical stirring for90min. The etched nickel microspheresstill remain mixed phases of fcc and hcp in structure, but the content of hcp phasedecreases, due to the oxidation of nickel in hcp phase by Fe3+ions. After that, theperformance in the application of adsorption and electrocatalytic oxidation of methanolof nickel microspheres before and after etching is studied, the experimental results showthat: the etched nickel microspheres show higher adsorption capacity (157.5mg/g) andoxidation current density (177.83A/cm2) than the unetched ones. That is the etchednickel microspheres have better adsorption property and catalytic ability of methanol.Thereby, the high reaction activity of etched nickel microspheres may be caused by theirnanostructured surface, as well as the large amount existence of dislocations and defects.2. The morphology and microstructure of the etched nickel microspheres were detected byTEM and HRTEM micrographs. Surprisingly, some extraordinary coalescencephenomena, where four etched nickel microspheres were aggregated into onepeaked-cap-like particle in47s, were observed. Records the process of solid crystalswith coalescence. The quick coalescence phenomenon, which happens at several nickelmicrospheres, is rare reported. Joule heat induced by high electrical field under HRTEMprocess results in most superficial nanostructured nickel in hcp phase of nickelmicrospheres melting, which makes the surrounding molecules or atoms adsorbed on thesurface to reduce the surface energy and rearrange, this may be the major reason for thecoalescence.3. The octahedral Fe3O4nanoparticles with good dispersion were synthesized through asimple solvothermal method, where hydrazine hydrate was used as reducing agent. Then, the dried Fe3O4nanoparticles were etched by acetic acid to change their surfacemorphology. During the etching process, we observed the effect of etching temperature,time and the amount of acid (alkali) on the evolution of surface morphology and size ofoctahedral Fe3O4. The magnetic property of the products obtained in different etchingconditions were studied by comparing the hysteresis loops. It can be seen that thesample obtained in the etching conditions of5mg Fe3O4+10mL CH3COOH+30mLGly+mechanical stirring for120min at room temperature possesses the highestsaturation magnetization. In addition, a probable etching mechanism of Fe3O4nanoparticles were concluded: in the etching process, Ostwald ripening processhappened to the octahedral Fe3O4nanoparticles. |
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