Preparation And Electromagnetic Shielding Propertie Of GO@Fe₃O₄@Silicate/PVDF Composites

How to optimize the design of microstructures and components is one of the hot topics in the field of electromagnetic shielding materials research.Graphene is a promising carbon-group electromagnetic shielding material,but it is difficult to achieve the effects of multi-band,wide frequency band and strong absorption by graphene alone.Hierarchical nanostructures can not only have the superior performance of a single assembly unit due to their micro-nano structure and special morphology,but also can produce synergistic effects and coupling effects through the arrangement and assembly of the building units.In this dissertation,graphene,nano-iron tetroxide and silicate were first used to construct a three-dimensional nano-composite electromagnetic shielding material with multi-component and multi-layer structure.On the one hand,it was hoped that by combining the components,the electromagnetic parameters could be adjusted to broaden the absorption band;on the other hand,the construction of the micro/nano structure could be used to increase the specific surface area of the graphene-based absorbing material,so it could enhance the interface polarization,increase the multiple reflection and scattering to improve absorption efficiency.,the graphene graded heterogeneous nanomaterials?GO@Fe₃O₄@silicate?were used to adsorb CO₂and explore the possibility of acting as a heterogeneous nucleating agent for supercritical CO₂ foaming materials.On this basis,the prepared GO@Fe₃O₄@silicate was combined with PVDF to study the influence of the distribution of GO@Fe₃O₄@silicate in PVDF on the microstructure,dielectric properties and electromagnetic shielding properties of the material.The specific research content and research results are as follows:1.Two nanocomposites with different composition order?GO@Cusilicate@Fe₃O₄ and GO@Fe₃O₄@Cusilicate?were prepared by hydrothermal method and sacrificial template method,and their microstructure and electromagnetic shielding performance were studied and compared.The effect of different Fe₃O₄ content on the electromagnetic shielding performance of the product was studied,and the electromagnetic shielding mechanism of GO@Fe₃O₄@Cusilicate was explored.On this basis,the micropowder and PDVF were compounded to make a composite material,and the microstructure and electromagnetic shielding properties of GO@silicate micropowder and GO@silicate/PVDF were studied.The results showed that:GO@Cusilicate@Fe₃O₄and GO@Fe₃O₄@Cusilicate both have a three-dimensional structure and a large specific surface area.However,the internal and external order of Fe₃O₄ in the hierarchical structure had a greater impact on their electromagnetic shielding efficiency.When Fe₃O₄ was in the middle?attached to graphene?,due to the superposition of various loss effects,GO@Fe₃O₄@Cusilicate maintained a high shielding efficiency?over 40 d B?in a wide frequency range?8.2-12.4 GHz?.By combining the prepared GO@Fe₃O₄@Cusilicate with PVDF,a material with better electromagnetic shielding performance could be prepared.The electromagnetic shielding performance of PVDF composites prepared by laminated pressing was better than that of PVDF composites prepared by chaotic pressing.With the increase of GO@Fe₃O₄@Cusilicate content,the intensity of the?-phase characteristic peak of PVDF would be stronger and the electromagnetic wave shielding performance of GO@Fe₃O₄@Cu Silicate/PVDFmaterialwouldbehigher.GO@Cu Silicate@Fe₃O₄/PVDF composite material?25 wt%filler content?could achieve a maximum shielding effectiveness of 22.3 d B at a frequency of 11.5 GHz.2.Using the GO core and Fe₃O₄ as the intermediate layer,a shell formed by Mg Silicate and Ni Silicate nanosheets was constructed on the surface of GO@Fe₃O₄ by hydrothermal method.The surface morphology,mesoporous performance and CO₂adsorption performance of GO@Fe₃O₄@Silicate were studied.We constructed and preparedGO@Fe₃O₄@silicate/PVDFcompositematerial(?GO@Fe₃O₄@silicate/PVDF?surfacelayer?/PVDF?core layer?/GO@Fe₃O₄@silicate/PVDF?bottom layer??,and characterized the structure and performance of this composite material.On the basis of the above research,the prepared sandwich composite material was subjected to supercritical CO₂ foaming.The results indicated that three GO@Fe₃O₄@silicates have good CO₂ adsorption properties.The CO₂ adsorption properties of GO@Fe₃O₄@Ni Silicate,GO@Fe₃O₄@Cu Silicate and GO@Fe₃O₄@Mg Silicate were 180.73 mg/g,90.49 mg/g and 78.69 mg/g,respectively.All of them have the possibility of acting as heterogeneous nucleating agents for CO₂.The introduction of GO@Fe₃O₄@silicate could decrease the?crystal form of PVDF and increase the?crystal form.Among them,GO@Fe₃O₄@Cu Silicate could convert most of the?crystal form in PVDF to?crystal form.Compared with non-sandwiched PVDF composites,the sandwiched GO@Fe₃O₄@silicate/PVDF composites have better electromagnetic shielding properties.Compared with the respective non-sandwich composite materials,the the maximum shielding effectiveness of GO@Fe₃O₄@Mg Silicate/PVDF,GO@Fe₃O₄@Ni Silicate/PVDFand GO@Fe₃O₄@Cu Silicate/PVDF with a sandwich structure had been improved 36.80%,62.68%and 82.80%.