Biocarbon-based Microwave Absorbents Modified By Magnetic Waste And Magnetic Field Alignment

From a wide range of materials,biocarbon has got a lot of attention from the last few years because of its easy accessibility,eco-friendly and abundance.It has been used in many applications such as adsorbents,soil remediation,carbon sequestration,wastewater treatment,supercapacitors,gas storage and microwave absorption.Tree leaves or agricultural garbage are thrown away or burned to ashes,which is dangerous for the environment.But this biowaste can be used in different applications for the betterment of humankind.It is cheap and offers different dimensionality and natural templating.In this dissertation,different biocarbon waste,industrial ferrites waste and their composite are studied.The fabrication techniques were carefully done and structural and morphological characterizations are thoroughly examined.The magnetic properties,dielectric properties and microwave absorption performance have conversed in-depth.Following are the main parts of my dissertation.(1)The utilization of biomass waste and solid industrial waste,one of the basic solutions of the green economy,has become an important topic in chemical and materials science.Individual bio-carbon,magnetic oxides,and their composites have been used in making microwave absorbers.Here,by utilizing coffee waste bio-carbon and industrial waste MnFe2O4 particles,an efficient microwave absorber has been realized based on their composites.The microwave absorption performance,as well as the magnetization of as-synthesized composites,can be tuned by adjusting the particle size of MnFe2O4.The minimum reflection loss(RLmini)can be enhanced around 5 times from-7.7 dB to-38.80 dB at 9.8 GHz when the mean particle size of MnFe2O4 in the composites is reduced from 9.7 down to 0.9 ?m.Meanwhile,a wide effective absorption bandwidth(7.8-1 1.4 GHz)is achieved in this bio-industrial-waste composite.Such enhancement is explained from the viewpoint of appropriate impedance matching as well as the synergetic effect between the bio-carbon and the MnFe2O4.Our work provides a route for the utilization of bio-carbon waste and industrial magnetic waste in the field of microwave absorption.(2)The magnetic field is one of the most potent ways to acquire the material's alignment in micro and nanodevices.Still,the magnetic field's applied direction also dramatically influences the properties of the material.Here,biocarbon flakes/epoxy resin composites were fabricated and a magnetic field was applied in the parallel(? MF)and perpendicular(? MF)direction of the sample using a permanent magnet.The control sample(0 MF)was also prepared in the absence of magnetic field.Results reveal that the magnetic field aligns the biocarbon flakes in the epoxy resin in the magnetic field direction.This work provides a simple and contactless route to align the biocarbon flakes by applying the magnetic field in the desired order.(3)The performance of the materials critically depends on the alignment of the particles in a specific direction.Here,the magnetic field is applied in the parallel and perpendicular directions of the sample surface to align the biocarbon flakes in two different directions.Control sample is also fabricated without a magnetic field.Microwave absorption properties of the samples were studied;which reveal that the magnetic field applied in the parallel direction of the sample has a RLmini of-44.5 dB with 3 mm thickness.Moreover,effective absorption bandwidth covers the whole ku band.While the sample with the magnetic field applied in a perpendicular direction shows poor reflection loss(-13 dB).These results indicate that the alignment of the biocarbon flakes in different direction influences the permittivity as well as microwave absorption performance.This work provides a simple route for promising microwave absorption materials by the effect of the magnetic field in different directions.