Synthesis, Self-assembly And Characterization Of Ferromagnetic Materials

As important ferromagnetic materials, Co, Ni and Fe3O4has drawn remarkable interestbecause of their unique attributes and potential applications in high-density magneticrecording, magnetic separation, sensors and especially catalysis. As is known, magnetic andelectronic properties of these materials are related to their structure and morphology.Therefore, it is of great significance to synthesize these magnetic micro/nano materials withthe novel and ordered structure via a facile, simple approach. The thesis focuses on thehigh-yield solvothermal synthesis of magnetic Co chains, Fe3O4vesicular nanospheres andflower-like Ni microspheres. The main results are as follows:①Novel magnetic1D Co chains with lengths of up to10–100μm, composed ofcross-linked hexagonal Co microflakes with an average diameter of2–10μm and a thicknessof about130nm, have been successfully synthesized in high yield using a solvothermal routein the presence of surfactants of both polyvinyl pyrrolidone (PVP) and dodecanethiol. Thesynthetic parameters such as reaction time, reaction temperature, the volume ratio of Veg/Ven,NaOH concentration, and dosages of both PVP and dodecanethiol during the solvothermaltreatment were found to play important roles in the formation of chain-like Co assemblies.Theresults show that the cross-linked Co microflakes exhibit well-crystalline hexagonalclose-packed(hcp) phase and are self-assembled to1D chain-like structure. Besides, theformation mechanisms of Co chains in solvothermal systems are conjectured based on theexperimental observations.②Monodispersed Fe3O4nanospheres with a diameter of about160nm have beensynthesized by a simple solvothermal procedure in an ethylene glycol/ethylenediamine mixedsolution with PVP used as surfactant. The microstructure and magnetic properties of theproducts were characterized by XRD, Raman, SEM, TEM/HRTEM, N2adsorption-desorptionand SQUID techniques. It is found that spherical Fe3O4nanoparticles contain numerousvesicles, and besides, are structurally uniform with a distinct lattice spacing of about0.26nm,which corresponds to the separation of the (311) planes of magnetite. The as-synthesizedFe3O4vesicular nanospheres exhibit a ferromagnetic characteristic with a high saturationmagnetization of86.9emu/g as high as the counterpart bulk, showing potential applications inadvanced magnetic materials and biomedical fields. ③Ni microspheres with the diameter of2-3μm, assemblied by Ni nanoplates with50-100nm in thickness were fabricated via one-pot solvothermal process.