Preparation And Microwave Absorbing Properties Of Biomass-derived Hierarchical Porous Carbon-based Composite

Recently,due to the wide application of communication and electronic equipment in life and military fields,electromagnetic radiation and electromagnetic pollution have become important sources of environmental pollution.The application of high performance microwave absorbing materials(MAMs)is an effective way to control electromagnetic pollution and radiation.In the research of MAMs,designing different special structures,especially three-dimensional porous structures,can adjust the impedance matching and improve the microwave absorbing ability of materials.For carbon based composite MAMs,the particles loading characteristics and the overall microwave absorbing performance are affected by the structure of porous carbon.The preparation process of porous carbon based materials with hierarchical porous structure is complex in reports,which has become the main problem restricting the development and application of it.In this case,the biological structure in nature provides a reference scheme for researchers.The porous structure in biology is formed after long-term evolution and development,and its structure is regular and stable.The motion resistance of marine organisms is large,and the biological structure formed by its development has the characteristics of high strength and light weight.Therefore,the marine biological structure is an ideal carbon based MAMs.This research provides a reference for the development of this field.In this study,biological porous materials were selected.The micro pore structure of the selected materials was orderly,and the pore structure gradually decreased from the outside to the inside.It was suitable to be used as carbon based MAMs.Activation on the basis of carbonization made the materials have hierarchical porous structure.The biomass is also rich in iron.After“reduction activation”,it is embedded in porous carbon structure in the form of Fe nanoparticles.The degree of graphitization of carbon can be controlled during heat treatment process,and achieve hierarchical porous structure in carbon.The minimum reflection loss at 10.4 GHz is-53.6 dB at the thickness of 2.08 mm.The effective bandwidth(reflection loss?-10 dB)of the hierarchical porous carbon obtained by heat treatment and activation can reach 4.0 GHz(13.96-17.96 GHz)at the thickness of 1.43mm.Ferromagnetic particle loaded hierarchical porous carbon composites were prepared by one-step pyrolysis method.In the process of preparation,the composition,morphology and microstructure of the composites were controlled by adjusting the loading amount of magnetic particles,heat treatment temperature and the amount of pore forming agent(ZnCl₂),and then the effects of the above factors on the electromagnetic properties of the composites were discussed and analyzed.The results show that at the thickness of 4.88mm,the minimum reflection loss of-35.32 dB is obtained at 5.12 GHz,the effective bandwidth of the composite is 5.52 GHz(12.48?18 GHz)at 1.95 mm when the heat treatment temperature is 800?and the iron carbon mass ratio is 0.83:1.