Preparation Of Phosphorus/Nitrogen-Doped Graphene-Based Composites And Their Microwave Absorption Properties

Microwave absorption materials are a kind of functional materials which can absorb the electromagnetic waves and convert them into thermal energy or eliminate them through interferences.Microwave absorption materials have been widely used to reduce electromagnetic radiation pollution and improve the operational ability of electronic equipment in complex electromagnetic environments,which have greatly important values in fields of electronic equipment and military stealth technology.Nowadays,the research topic has been focused on developing novel microwave absorption materials with thin thickness,lightweight,low density,highly efficient,broad absorption bandwidth and good environmental applicability characteristics.By tuning the magnetic loss and dielectric loss,designing novel composite materials which can satisfy impedance matching condition is an effective approach to improve their microwave absorption performance.Graphene processes several advantages of high electrical conductivity,large specific surface area and light weight.Besides,its electrical loss performance can be affected by the structure.The common magnetic loss materials include iron,nickel and their oxides.They have many advantages,such as abundant,low cost,various types,anti-oxidation and so on.Therefore,exploring high-efficiency microwave absorption composite materials by combining graphene?or graphene derivatives?and traditional magnetic loss materials have good potential applications.We mainly investigate the influence of nanostructure,loading amounts and interfacial effects of doped graphene/nanoparticles on their microwave absorption performance.The complex permeability and permittivity of nanocomposites were tuned by controlling the types and morphologies of nanoparticles on doped graphene.The synergistic effect between nanoparticles and doped graphene were studied to enhance the electromagnetic wave absorption characteristics.In this thesis,P-GN,P-GN/Fe₂O₃,P-GN/Fe₃O₄ and N-GN/Ni nanocomposites were fabricated and their microwave absorption properties were greatly investigated.Moreover,the electronic conductivity of P-GN is also theoretically studied,which can guide the design of P doped.1.Synthesis and microwave absorption properties of P-GNBased on the excellent conductivity of P-GN,transparent P-GN was prepared by a one-step solvothermal method.The structures,morphologies,surface electronic states and bond bonding modes of P-GN were characterized by XRD,TEM,SEM,FTIR and XPS.Microwave absorption results show that the microwave absorption efficiency of P-GN is significantly improved compared with graphene oxide?GO?.P-GN/paraffin hybrids with 50wt%of P-GN had a minimum reflection loss of-14.1 dB at 15.3 GHz when the thickness is only 1.5 mm.2.Synthesis and microwave absorption properties of P-GN/Fe₂O₃ nanocompositesTo further improve the microwave absorption properties,P-GN/Fe₂O₃ nanocomposites were synthesized by a one-step hydrothermal method.TEM investigations show that hexagonal Fe₂O₃ nanoflakes were uniformly anchored on P-GN.The P-GN/Fe₂O₃nanocomposites exhibit strongest microwave absorption performance compared to the pure P-GN and Fe₂O₃ nanoflakes.The P-GN/Fe₂O₃ nanocomposites with P-GN of 50 mg show minimum RL value of-28.2 dB at 5.5 GHz when the absorber thickness is 5.0 mm and the effective absorption bandwidth can reach 2.8 GHz?4.3-7.1 GHz?.3.Synthesis and microwave absorption properties of P-GN/Fe₃O₄ nanocompositesTo optimize the impedance matching condition of materials and enhance the microwave absorption performance,P-GN/Fe₃O₄ nanocomposites were fabricated by annealing-reduction method.TEM characterization shows that Fe₃O₄ was uniformly loaded on P-GN and maintained the hexagonal nanoflake structures.The microwave absorption performance of P-GN/Fe₃O₄ nanocomposites was tested.The results show that P-GN/Fe₃O₄nanocomposites show stronger microwave absorption properties in comparison with P-GN/Fe₂O₃ nanocomposites and bare Fe₃O₄ nanoflakes.The P-GN/Fe₃O₄ show a minimum RL value of-58.5 dB with thickness of only 1.7 mm.4.Synthesis and microwave absorption properties of N-GN/Ni nanocompositesFor study of absorbing properties of graphene doped,we researched the experiment of N-GN.N-GN/Ni nanocomposites were synthesized by solvothermal method.TEM shows that spinous Ni particles are regularly decorated on N-GN.The N-GN/Ni nanocomposites show minimum RL value of-47.1 dB at 13.6 GHz when absorber thickness is only 1.6 mm.This thesis reveals that P or N dopants in graphene lattice can adjust the complex permittivity of graphene and improve the defects in graphene,which can effectively attenuate the entered microwaves.Furthermore,the interfacial effect and synergistic effect between magnetic nanoparticles and doped graphene can greatly improve the absorbing properties of nanocomposites.