Structure Design,Preparation And Performances Of Novel Functional Hybrid Materials Based On Ferrite

With the rapid development of modern science and technology,human life has become increasingly convenient.However,issues such as energy shortages,environmental pollution,electromagnetic radiation and information security have also emerged.The design of functional composite materials,especially electromagnetic wave absorption and energy storage composite materials has become current research highlights,and the preparation of these functional composite materials by green synthetic methods has also attracted many attentions.At the same time,ferrit has been widely applied in the synthesis of these functional composite materials.In these research background,the thesis adopted different methods to synthesize several new ferrite composite materials,and applied as electromagnetic wave absorbing or energy storage composite hybrid materials.By systematically characterizing the synthesized composite hybrid materials,their micro-morphology and structure,chemical composition,crystal structure,surface functional group distribution,thermal stability,magnetic properties,electromagnetic wave absorption performances and energy storagecapacity were carefully measured.On the basis of characterization,the mechanism of electromagnetic wave absorptionand energy storagecapacity of the synthesized products were also explored and analyzed.(1)Synthesis and excellent electromagnetic wave absorption performance of carbon@nickel-cobalt ferritenanospheres with core-shell structureThe application of cobalt ferrite and nickel ferrite inelectromagnetic wave absorbing composite materialsare the current research hotspot.In recent years,it has been reported frequently,but there was no report to compare them systematically.Thus,the electromagnetic wave absorbing performances of these two kinds of ferrite@carbon composites were researched comprehensively.In this work,five kinds ofmagnetic nanospheres include NiFe₂O₄,cobalt-doped nickel ferrite(Ni_0.75Co_0.25Fe₂O₄),nickel-cobalt ferrite(Ni_0.5Co_0.5Fe₂O₄),nickel-doped cobalt ferrite(Ni_0.25Co_0.75Fe₂O₄)and Co Fe₂O₄ were fabricated via solvothermal method firstly.Then,they were uniformly coated by carbon,respectively,and the corresponding five kinds of C@Ni_xCo_1-xFe₂O₄composite nanospheres with perfect core-shell structure were obatined.The mechanism of the synthesis reaction,and the magnetic performances,electromagnetic wave absorbing performance,also include the electromagnetic wave absorbingmechanism of the composites nanospheres were thoroughly explored and analyzed.The hysteresis loop of the obtained samplesindicated that the five composite microspheres all exhibit typical paramagnetic and soft magnetic characteristics,and the magnetic saturation strength are all around 40 emu.g^-1,which is very conducive to enhancing the magnetic loss mechanism of material.The results of the absorbing performances showed that when x is 0.75,the obtained composite microspheres exhibittheoptimum absorbing capacity forelectromagnetic wave.When the sample thickness is just 1.9 mm,the minimum reflection loss value can reach-51 dB,and the effective absorption band width is 3.3GHz.The excellent electromagnetic wave absorbing performance of C@Ni_0.75Co_0.25Fe₂O₄ composite nanospheres can mainly be attributed to its fair electromagnetic matching and impedance matching.For the two kinds ofcommonly used ferrites of Co Fe₂O₄ and NiFe₂O₄,when combined with intrinsic dielectric carbon,C@NiFe₂O₄ is more suitable aselectromagnetic wave absorber,and a small amount of cobalt atoms doped in NiFe₂O₄ crystal can further improve its absorbing efficiency.Theresearch can provide a reference for future researchers to choose these two most commonly used ferrites to prepare new high-performance microwave absorbing composites.(2)Green synthesis and EM wave absorption performance of MoS₂@nitrogen doped carbon hybrid decorated with ultrasmall cobalt ferrite nanoparticlesDue to the increasingly serious problem of environmental pollution,the concept of green synthesis is more and more advocated by researchers,and play an important rolein solving the problem of environmental pollution.In this work,the MoS₂@n-C@Co Fe₂O₄ hybridswere skillfullysynthesized via one pot method,and the whole preparation procedure is green and environmental friendly.The careful structural characterization testified the microstructure,crystal form,chemical elemental composition,surface functional groups of the designed composite materials.The optimized MoS₂@n-C@Co Fe₂O₄-600 sample obtained by adjusting the calcination temperatureexhibited good thermal stability and excellent EM wave absorbing efficiency,with a R_Lminvalue of-46.7 dB at a specimen thickness of 2.4mm.The hybrid can be regarded as an ideal competitive EM wave absorber,and the synthesis concept involved in the method used in this work is helpful to promote the development of green synthesis.(3)Capacitive behavior of MoS₂ decorated with Fe S₂@carbon nanospheresThe development of modern science and technology has an urgent demand for new energy storage materials.In the current reports,composite metal sulfide energy storage materials have gradually replaced the traditional metal oxides and become a research hotspot.In this work,a new composite hybrid with novel hierarchical structure constructed by three dimensional1T/2HMoS₂nanoflower decorated withwatermelon-like Fe S₂@carbonnanospheres was facilly synthesizedfrom thetransition product Fe₃O₄@C.Due to the synergistic effect ofappropriate ratio of MoS₂ framework,carbon layer and Fe S₂as well as the mesoporous structure in composite hybrid materials,the sample Fe S₂@C@MoS₂-200 performed high specific capacitance(1321.4 F·g^-1at 2 A·g^-1)and good cyclical stability at a high current density(specific capacitance retention rate of 81.2%at 6 A·g^-1 after 1000 cycles),revealing its performance advantages and application potential as an ideal capacitor electrode material.