Study On Synthesis And Performance Of Magnetic Mirco-and Nanostructures

The size, shape, and surface state of micro-nanomaterials tremendously affect theirphysical and chemical properties. In this thesis, many efforts have been made to design andsynthesize micro-and nanostructured magnetic materials with tunable sizes and morphologies.We have systematically studied the formation mechanisms and magnetic properties of thesematerials. The main contents and achievemants are presented as follows:(1) Synthesis of monodisperse iron oxide nanoparticles (NPs) with superparamagneticproperties by the thermal decomposition of iron oleate complex. The influences oftemperature and time on the size of NPs were studied, and mechanism of iron oxide growthprocess using trioctylamine was put forward. Ideal iron oleate complex precursor wasprepared by a developed method using oleic acid instead of sodium oleates, providing a lowcost route for synthesis. Preparation conditions including reaction time and temperature, theconcentration of the complex, and the ratio of TOA and ODE affected the size and sizedistribution of resulting Fe3O4NPs. Temperature and time accelerated the growth of the NPs.However, TOA makes the NPs more smaller.(2) Besides, size-and morphology-controllable Fe3O4NPs have been successfullysynthesized through the decomposition of the iron oleate complex by tuning reactiontemperature, time, the amount and kind of reagents. The effects of various organic amines,including oleylamine, trioctylamine, and hexadecylamine, on the formation of Fe3O4NPswith spherical, truncated octahedral, cubic, and tetrahedral shapes have been also discussed.Truncated octahedral shape was gradually changed into quasi-cubic shape if adding TOA inthe reaction system for a long time. In contrast, spherical, cubic, and tetrahedral Fe3O4NPswere fabricated in the case of OAm used. HDA resulted in spherical Fe3O4NPs a large size.It is confirmed that organic amine molecules were bound on the surface of the NPs bymeasursing the Fourier transformation infrared spectroscopy of samples.(3) Moreover, micro-and nano-structures of iron oxide with tunable morphologies andsizes were fabricated by a solvothermal process. Sodium bicarbonate, ethylenediamine,ethylene glycol was systematially studied on the influence of iron oxide morphology andcomposition. In this route, the ethylene glycol (EG) solution of ferric chloride hexahydrate (FeCl3·6H2O), sodium bicarbonate (NaHCO3), and ethylenediamine (EDA) was heat-treatedto create the micro-and nano-structures of Fe3O4, where EG acted as both solvent andreducing agent. NaHCO3and EDA were crucial for the morphology and size of these micro-and nano-structures. The micro-and nano-structures with solid, porous and hollowmorphologies were obtained by changing the reaction parameters such as reaction time, thekinds of solvents, the amount of NaCO3and ethylenediamine. As the reaction progressed,nanoparticles aggregated together to form solid Fe3O4spheres, and then inner nanoparticlesdissolved and recrystallized onto the outer shell of Fe3O4spheres. These Fe3O4micro-andnano-structures revealed excellent magnetic properties. Hematite (α-Fe2O3) was synthesizedusing ethyl alcohol instead of EG. These magnetic micro-and nano-structures revealedexcellent magnetic properties.(4) In addition, α-Fe2O3, Fe3O4micro-and nanostructures with different morphologies weresynthetized through the decomposition of iron precursors. The iron alkoxide precursorconstructed by the self-assembly of nanoflakes was prepared using ferric chloride hexahydrate,urea, cetyltrimethyl ammonium bromide (CTAB), ethylene glycol (EG). Fe3O4nanostructureswith blocks with a structure of the truncated octahedron were obtained by calcination of theprecursors under N2protection. α-Fe2O3nanostructures were prepared when precursors werecalcined in an air atmosphere. The values of maximum adsorption capacity of flower-likeα-Fe2O3micro-and nanostructures for Cr6+ions were much higher than that of commercialbulk α-Fe2O3. Furthermore, precursors were heat-treated using a solvothermal synthesis invarious solvents to investigate the growth kinetics of Fe2O3and Fe3O4. Fe3O4NPs with theaverage size of10nm were obtained when ethanol acted as a solvent. In the case of waterinstead of ethanol, α-Fe2O3NPs with the average size of28nm were prepared.UsingL-cysteine as a linker, Fe2O3/Ag hybrid composites with different morphologies weresynthetized via different methods (an aqueous synthesis and light irradiation).(5) Furthermore, hematite nanoplates were fabricated through a solvothermal process usingFeCl3and CH3COONa in an ethanol solution. Time-dependent experiments indicated that thenanoplates were fabricated for2to20h. The exposed facets of the nanoplates are (001) facets.This is ascribed to CH3COO-groups favour to adsorb on the (001) facets of Fe2O3. Theamount of CH3COONa plays an important role for the morphologies of samples. Hexagonal-like nanoplates, octahedron, and nanoplates were created through adjusting theamount of CH3COONa. Solvents were also crucial for the preparation of the nanoplates oncethe mixture of water and ethanol or isoproponal instead of ethanol. In addition, the nanoplateswere assembled into micro spheres and a face-to-face situation. In contrast, the assembly wasnot observed in the case of the nanoplates prepared using polyvinylpyrrolidone (PVP).