| As a frontier technology of contemporary society,nanotechnology has gained more and more attention,and got rapid development.Spinel ferrite has attracted great attention of many researchers due to its unusual electric and magnetic properties.Spinel ferrite nanomaterials combine the electromagnetic properties of ferrite and the unique advantages of nanomaterials,resulting in a more optimized performance.The chemical composition,size and morphologies of materials have a great influence on their physical and chemical properties.It is of great significance to design and synthesize nanoferrite and its composites,and to further discuss the relationship between microstructure and properties.In this thesis,two kinds of ferrites,ZnFe2O4 and NiFe2O4,have been fabricated by solvothermal method.In addition,their applications in the field of electrochemistry and microwave absorption are investigated in detail,respectively.1.Preparation of porous ZnFe2O4 nanospheres and the evaluation as an anode for Li-ion battery.Porous ZnFe2O4 nanospheres with diameter around 200 nm were successfully synthesized via solvothermal treatment followed by calcination.Crystallographic phases and chemical composition are investigated by powder XRD and XPS.The morphologic and detailed structure information can be confirmed by SEM and TEM.The characteristics of mesoporous,surface area and total pore volume can be analyzed by the N2 adsorption-desorption isotherm and BET model.The composite is then evaluated as an anode for Li-ion battery,which shows excellent electrochemical properties.The correlations between morphology and structure on the performance are discussed.The porous characteristics greatly increase the surface area of nanospheres and provide sufficient space to accommodate the large volume variation of anodes during charging and discharging process,thus relieving the structure collapse problem and enchancing the cycling performance.The small particles size can efficiently shorten the reaction pathway of lithium ions,promote ion transport,thereby increasing the rate performance.2.Synthesis and microwave absorption properties of NiFe2O4 microrods and NiFe2O4 @PPy composites.NiFe2O4 microrods were prepared by solvothermal process followed by calcination.Moreover,NiFe2O4 @PPy composites were obtained by in-situ chemical oxidative polymerization.The composition of materials is investigated by powder XRD.The existence of PPy is proved by Raman spectroscopy.The morphologic and detailed structure information can be confirmed by SEM and TEM.The trait of porous can be investigated by N2 adsorption-desorption isotherm.The magnetic characterization is analyzed by VSM.The composite of NiFe2O4 and NiFe2O4@PPy are evaluated as microwave absorbing materials.The maximum reflection loss（RL）value of NiFe2O4@PPy composite reaches-28.06 dB at the coating thickness of 2.5 mm.It is higher than bare NiFe2O4 whose maximum reflection loss（RL）value reaches-7.82 dB at the thickness of 3 mm.The existence of dielectric material PPy gives rise to the better impedance matching,thus enhancing microwave absorption properties.The interfaces between NiFe2O4 nanoparicles and PPy shell have a dominant role in enhancing dielectric performance and also cause multiple reflections,further consuming the EM energy. |
