| With the rapid development of electronic technology,enormous material civilization has been created by human beings,whereas a living environment full of electromagnetic radiation was also brought at the same time.Regarding the significant application value of microwave absorbing material in reducing the electromagnetic radiation pollution as well as evading radar detection,developing new absorbing materials known as "thin,light,wide and strong" has become a focus of research in current society.In the thesis,cobalt sulfide and its composites applied to microwave absorption are thus prepared,and a simple but effective method of the as-prepared materials is achieved.Moreover,the relation between structural characteristics,electromagnetic parameters and electromagnetic absorbing properties are well studied.In this paper,novel flower-like cobalt sulfide was firstly prepared via a solvothermal method by using ethylene glycol as the solvent,and various technical means including XRD,Raman,XPS,SEM,TEM and EDS were employed to characterize the structure and morphology of the resulting materials.Furthermore,the influence of surfactant,filler loading amount and absorbing layer thickness on the material structure,the electromagnetic parameters and the related microwave absorbing ability was investigated.The study reveals that,after introducing CTAB,the morphology for cobalt sulfide changes from nanospheres into hollow flower-like microspheres,and the permittivity of CHSs is significantly higher than that of CoS NPs,advantageous to reinforce the capability of dielectric loss of the materials.Therefore,the microwave absorption performance of CHSs is substantially enhanced.For CHSs microwave absorbing materials,with a 20 wt%filler loading,the effective absorption bandwidth can cover 13.2 GHz(4.8 to 18.0 GHz)by adjusting the layer thickness from 2.0 to 5.0 mm.Especially when the matching thickness is mere 2.0 mm,the minimum absorption peak can reach-43.6 dB at 15.6 GHz with an effective absorption bandwidth of 4.6 GHz(13.2-17.8 GHz).To further improve the microwave absorbing performance,cobalt sulfide/graphene(CoS/RGO)were synthesized through a solvothermal method by using the mixed solvent of water and 1,2-Propanediol,and the structure and morphology of the as-prepared material were characterized.Moreover,the influence of different adding amounts of GO on the electromagnetic parameters and corresponding microwave absorption properties of the materials was also studied.As the results indicate,the introduction of GO alters the impedance matching features of composites,and the optimal microwave absorption peak tends to shift to lower frequency with increasing addition amounts of GO.With a 20 wt%filler loading,the range of effective absorption bandwidth for CoS/RGO is 13.6 GHz(4.4 to 18.0 GHz)via adjusting the layer thickness from 1.5 to 5.0 mm.With a slight thickness of 2.0 mm,the effective absorption bandwidth is up to 4.0 GHz(12.1-16.1 GHz).And the minimum absorption peak can reach-54.2 dB at 6.8 GHz at the thickness of 4.0 mm.Finally,cobalt sulfide nanoplates/multi-walled carbon nanotubes(MWCNTs/CoS)nanocomposites have been fabricated to optimize the microwave absorption performance,and the structure and morphology of the resulting material were characterized.In addition,the influence of different combination form for the composites on the microwave absorbing ability was intensively investigated.In contrast to simple mixture of MWCNTs and CoS microspheres(MWCNTs+CoS),the strongly interacting heterostructures between CoS nanoplates and MWCNTs are found to exhibit dramatically enhanced microwave absorption performance.As an absorber,the 30 wt%MWCNTs/CoS are endowed with an effective absorption bandwidth of 13.9 GHz(4.1 to 18.0 GHz)with a variation of thicknesses from 1.5 to 5.0 mm.In addition,the bandwidth below-10 dB is up to 4.2 GHz(11.0-15.2 GHz),particularly when the matching thickness is mere 2.0 mm.And the optimum absorption peak reaches-56.1 dB at 6.6 GHz at the thickness of 3.6 mm. |
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