Structure, Morphology Controlling And Surface Functionalization Of Spinel Ferrite

As typical spinel ferrites, AB₂O₄nanoparticles（NPs） are receiving increasing interestin recent years for many of their magnetic properties, such as special saturationmagnetization and coercivity, can be greatly effected by their particle size and theirgood biocompatibility. And they have been widely used in many importanttechnological applications, such as high-density magnetic data storage, biological sensor,bioseparation, antiradar coatings, magnetic fluid and magnetic resonance image （MRI）etc. In this thesis, ferric oleate are proposed to systhesize spinel ferrite magneticnanoparticles, and the main efforts are devoted to the research on effects of structureand morphology control on the magnetic performance, distribute stability of the spinelferrites after surface functionalization and their application in magnetic fluids. Magneticperformance changing of their reduction alloy nanomaterial is also carried out. And byloading graphene with magnetic spinel ferrites, the changes of electromagnetic waveabsorbing properties corresponding to the effect of the graphene are discussed.1. The Fe₃O₄NPs with average particle size of11nm are prepared by chemicalco-precipitation method, and they are coated with oleic acid as the primary layersurfactant in aqueous phase. Then the oleic acid coated Fe₃O₄NPs are transferred toheptane to be re-coated with succinimide to synthesize bilayer coated Fe₃O₄magneticNPs, and the reason for the stability of the bilayer coated Fe₃O₄magnetic NPs isdiscussed. Stable magnetic fluids of bilayer coated Fe₃O₄magnetic NPs are obtained bydispersing them in PAO_-2carrier. The viscosity, specific saturation magnetization anddensity dependence of the magnetic fluids on the content of the bilayer coated Fe₃O₄NPs is analyzed. Result shows that these properties can be obviously improved as thecontent of the bilayer coated Fe₃O₄NPs increasing. The magnetic fluids have goodmagnetic stability for no phase separation happens after360days, which may havepotential application in machinery. 2.The low-cost homemade Fe_oleate3, oil soluble polymer surfactant polyisobutenesuccimide （PIBA） and paraffin oil, are separately used as iron precursor, surfactantandand solvent. Via thermal decomposition method, the micro-sized（less than15nm） Fe₃O₄NCs with cubic, cuboctahedral and octahedral morphology are successfully prepared.And the effects of surfactant, reaction temperature, heating rate on the morphology andparticle size of the Fe₃O₄NCs are respectively discussed. Result shows that morphologycontrolling of the Fe₃O₄NCs can be realized through changing heating rate of thereaction. In the thermal decomposition reaction, the surfactant PIBA realizes thepurpose of being as stabilizer and surface modifier at the same time, which can improvethe dispersibility of Fe₃O₄NCs. The PIBA coated Fe₃O₄NCs can be easily dispersed ineither low or high boiling point solution to obtain magnetic fluid. And the obtainedmagnetic fluid shows good stability even in strong magnetic field. All the raw materialsin the reaction are cheap and nontoxic which make it easy to industrialize.3. The homemade oleic acid metal （Co, Mn, Zn, Ni） salts are used in replacing theidentity of the divalent M2+cation（A place） of the AB₂O₄structure Fe₃O₄NCs to obtainspinel CoFe₂O₄, MnFe₂O₄, ZnFe₂O₄, NiFe₂O₄magnetic NCs with average particle sizeof nearly5nm. And through changing reaction conditions, magnetic NCs with differentparticle sizes can be successfully prepared. Result presents the magnetic properties ofthe magnetic NCs can be controlled by their structure adjusting. And by reducing thesemagnetic NCs with H2, CoFe, MnFe, ZnFe, NiFe alloy nanomaterials are separatelysysthesized, their structure and magnetic properties are compared with the magneticNCs. It can be drown through the comparation that both the particle size and magneticproperties changed greatly after reduction. Spinel MFe_2-xLaxO₄（x=0.05,0.1,0.15）magnetic NCs are prepared by replacing part of the trivalent Fe₃+cations （B place） ofthe AB₂O₄structure Fe₃O₄NCs with La³⁺., We can draw through experiments that bothLa2O₃content and remanence and coercivity of the magnetic NCs increase with thegrowth of La addition amount in the spinel MFe₂-xLaxO₄systems. Afterwards the oleic acid coated MnFe₂O₄NCs are re-functionalized with secondary ligands such ascetyltrimethylammonium bromide （CTAB）, sodium dodecyl benzene sulfonate （SDBS）and sodium dodecylsulfate （SDS） to obtain well-dispersed water-soluble NCs. Theaqueous solutions of bilayer functionalized NCs are used in adsorbing Pb²⁺out ofwastewater. Test result shows CTAB coated NCs have the highest efficiency of Pb（II）associativity （nearly90%）.4. The graphene/NiFe₂O₄nanocomposite with graphene loading amount of10%,20%and30%are respectively prepared via hydrothermal reaction of Fe_oleate3, Ni（oleate）2and graphene at160℃for12h. And graphene loading amount are controlled byadjusting the additive amount of graphene. Compared with pure NiFe₂O₄NCs, theparticle size of NiFe₂O₄in the nanocomposites increases as their graphene loadingamount increasing, while their particle distribution uniformity decreaes. Absorbingproperty measurement of pure NiFe₂O₄and the three amounts of graphene/NiFe₂O₄nanocomposite reveals the doping of graphene can increase the dielectric loss of thenanocomposites, which is good for their absorbtion of electromagnetic waves. But whengraphene loading amount is over20%, electromagnetic waves absorbing property of thenanocomposites decreases. The possible reason for it is the complex permittivity of theamount accordingly matches with its complex permeability when graphene loadingamount is20%.