Micorwave Absorption Performance Of Cobalt-based MOFs Derivatives/ Graphene Aggregates Composites And Bimetal MOFs Derivatives

Rapid development of communication technology and widespread application of electronic equipment produce increasing electromagnetic radiation pollution.Absorbing materials can effectively absorb electromagnetic radiation to improve people's living environment,thereby drawing increasing attention.Derivatives of Metal Orgnic Frameworks(MOFs),as an adjustable multi-component composite material,can combine various loss mechanisms to give full play to the advantages of various materials in electromagnetic wave loss.Graphene aggregates(GAs)enjoy little density and great conductivity,making them favorable to adjust the electromagnetic parameters of derivatives and improve the performance of absorbing materials.In this paper,three carbon-based composite materials were successfully prepared with several synthesis methods.Based on this,studies were made on the microscopic morphology and chemical compositions of these composite materials,as well as their effects of their structures and components on electromagnetic parameters and performance of wave absorbing:(1)The Co₃O₄@NC composites were prepared with the in-situ polymerization,CVD pyrolysis and mechanically mixing.Co₃O₄@NC/GAs composites combined magnetic metal oxides(Co₃O₄),amorphous carbon and GAs to improve the microwave absorption performance of materials.Besides,efforts were made to study in detail how the amount of GAs affected the absorption performance of Co₃O₄@NC/GAs composites.And the result showed that Co₃O₄@NC/GAs-30 composite enjoyed a better absorption performance than other Co₃O₄@NC/GAs composites.Its minimum reflection loss can hit-29 dB at a thickness of 1.2 mm,and it achieved an effective absorption bandwidth covering 13.9 GHz(4.1 GHz-18 GHz)by varying the thickness of absorber from 1.2 to4.0 mm.Besides,the Co₃O₄@NC/GAs-40 composite obtained an effective absorption bandwidth of 3.6 GHz at 1.2 mm.It was also found that in Co₃O₄@NC/GAs composites,electrical conductivity loss and dielectric polarization relaxation loss play a leading role,while magnetic losserves as an auxiliary.(2)CoTe@NC/GAs composites were synthesised through the CVD pyrolysis and mechanical mixing.They combined semiconductors(CoTe),amorphous carbon and GAs to improve the microwave absorption performance of materials.Besides,efforts were made to study in detail how the amount of GAs affected the absorption performance of CoTe@NC/GAs composites.And the result showed that CoTe@NC/GAs-10 composite showed a sound performance of microwave absorption.Its minimum reflection loss reached-50 dB at a thickness of 1.9 mm,while the corresponding effective absorption bandwidth covered 2.9 GHz(7.8 GHz-10.7 GHz).Such a sound performance should be attributed to electrical conductivity loss and dielectric polarization relaxation loss.(3)Taking weak dielectric loss of carbon-based composites derived from one kind of MOFs,this chapter reasonably introduced dielectric metal oxides(Cr₂O₃)to adjust the dielectric constants of carbon-based materials.In this paper,the leaf-shaped heterobimetallic Co Cr-MOF were in-situ synthesized in one step.And then,the Bimetallic MOF-derived carbons(BMDCs)composites were prepared with the CVD pyrolysis.According to the study on the microwave absorption performance of composites,the polarization relaxation loss and absorption performance of BMDCs composites were greater than those of pure cobalt-based composites.Moreover,in order to figure out the role of loss mechanisms in the microwave absorption,a detailed study was also made on the absorption performance of BMDCs composites with different filling ratios.And the result showed that the BMDCs 4-6 absorber performed best in microwave wave absorption,as its minimum reflection loss could reach-57.4 dB while the thickness was only 2.0 mm.The effective absorption bandwidth also hit 3.6 GHz,and it could even reached 4.6 GHz at 1.5 mm.Electrical conductivity loss,dielectric polarization relaxation loss and magnetic loss all facilitated the absorption performance of BMDCs composites.