Preparation And Microwave Absorption Properties Of Graphene-conducting Polymers-magnetic Nanoparticles Composites

With continuing growth of electronic technique, the harm of electromagnetic wave radiation becomes more obvious. Electromagnetic wave irradiation has influenced the operation of electronic devices, not only inenvironmental pollution, but also being harmful to the health of human beings. Microwave absorption materials can absorb electromagnetic waves effectively and convert electromagnetic energy into thermal energy, so it has been widely used. Graphene can be used as microwave absorption materials due to its excellent physical and chemical properties, such as large specific surface area, low density, good conductivity, high temperature resistance and oxidation resistance. However, the single graphene is not an ideal microwave absorption material due to the high dielectric loss and the low magnetic property. The combination of graphene with magnetic absorbents can effectively improve the impedance matching and enhance the microwave absorption properties. At present, the research about microwave absorption materials is mainly focused on the binary graphene-based composites, and few reports on the ternary composites. For the preparation of materials with excellent microwave absorption performance, the novel ternary composites consisting of graphene, conducting polymers and magnetic nanoparticles are synthesized, and their microwave absorption properties were studied. The researches are as follows:（1） The ternary composites, such as RGO-PANI-Co3O4, RGO-PPy-Co3O4 and RGO-PEDOT-Co3O4, were prepared by the three-step method. Firstly, the conducting polymers were coated on the surface of graphene oxide by the in situ polymerization. Secondly, Co3O4 nanoparticles were prepared by the hydrothermal method. Thirdly, graphene oxide has been reduced by hydrazine hydrate. The results indicated that the microwave absorption properties of graphene-polyaniline, graphene polypyrrole and graphene-poly（3, 4-ethylenedioxythiophene） can be greatly enhanced by adding Co3O4 nanoparticles, in the terms of absorption intensity and frequency bandwidth. The maximum reflection losses of RGO-PANI-Co3O4, RGO-PPy-Co3O4 and RGO-PEDOT-Co3O4 are up to-44.5 dB,-43.5 dB and-46.5 dB, the absorption bandwidths exceeding-10 dB are 4.3 GHz, 6.4 GHz and 2.1 GHz, respectively. Therefore, the ternary composites can be used as novel microwave absorption materials.（2） Various ternary composites, such as RGO-PANI-Fe₃O₄, RGO-PPy-Fe₃O₄ and RGO-PEDOT-Fe₃O₄, were synthesized by the two-step method, including in situ polymerization and coprecipitation method. The electromagnetic data demonstrates that the impedance matching between dielectric loss and magnetic loss can be improve by adding Fe₃O₄ nanoparticles, the interfacial polarization produced by multi-layer interface and the dipole polarization and electron polarization produced by Fe₃O₄ nanoparticles affect the microwave absorption performance. It can be found that the maximum reflection losses of RGO-PANI-Fe₃O₄, RGO-PPy-Fe₃O₄ and RGO-PEDOT-Fe₃O₄ are-43.9 dB,-56.9 dB and-56.3 dB, the absorption bandwidth exceeding-10 dB are 3.4 GHz, 2.7 GHz and 2.9 GHz, with absorber thicknesses of 2.5 mm, 5.3 mm and 2.9 mm, respectively.（3） Three kinds of ternary composites, RGO-PANI-NiFe₂O₄, RGO-PPy-NiFe₂O₄ and RGO-PEDOT-NiFe₂O₄, were prepared by the two-step method, including in situ polymerization and hydrothermal method. In hydrothermal method, alkaline solution is selected to accomplish two functions. In the first place, it plays an important role in the formation of NiFe₂O₄ nanoparticles. In the second place, it can be used as a reducing agent, promoting the reduction reaction of graphene oxide in the solvothermal system, without using reducing agent. These NiFe₂O₄ nanoparticles with diameter in the range of 5-20 nm appear some reunion phenomenon, and the ternary composites have superparamagnetic character due to the presence of NiFe₂O₄ nanoparticles. The electromagnetic data demonstrates that the combination of graphene with conducting polymers and NiFe₂O₄ nanoparticles can improve the impedance matching, and the interfacial polarization and dipole polarization enhance the dielectric loss. The maximum reflection losses of RGO-PANI-NiFe₂O₄, RGO-PPy-NiFe₂O₄ and RGO-PEDOT-NiFe₂O₄ are-50.6 dB,-44.8 dB and-45.4 dB, the absorption bandwidths exceeding-10 dB are 5.5 GHz, 4.5 GHz and 4.8 GHz, respectively.（4） The in situ polymerization and hydrothermal method have been used to synthesize the RGO-PANI-Co Fe₂O₄, RGO-PPy-Co Fe₂O₄ and RGO-PEDOT-Co Fe₂O₄ composites. The ternary composites have ferromagnetic character due to the presence of Co Fe₂O₄ nanoparticles. The electromagnetic data demonstrates that the maximum reflection losses of RGO-PANI-Co Fe₂O₄, RGO-PPy-Co Fe₂O₄ and RGO-PEDOT-Co Fe₂O₄ are-39.7,-50.8 dB and-43.1 dB, the absorption bandwidths exceeding-10 dB are 4.8 GHz, 4.3 GHz and 2.7 GHz, respectively. The enhanced microwave absorption performance of the ternary composites are related with the improved impedance matching, enhanced interfacial polarization and the charge transfer between graphene sheets and conducting polymers.（5） A series of RGO-NiFe₂O₄-CuS nanoplates composites have been synthesized by the two-step method using CTAB as the surfactant. The RGO-NiFe₂O₄-CuS composites have superparamagnetic character due to the presence of NiFe₂O₄ nanoparticles, and the content of CTAB has an effect on the morphology of CuS nanoplates. The results indicate that the microwave absorption performance of RGO-NiFe₂O₄-CuS composites is better than that of single graphene and graphene-NiFe₂O₄. When the thickness of the absorber is 2.5 mm, the maximum reflection loss is up to-50.4 dB at 11.4 GHz and the absorption bandwidths corresponding to the RL values below-10 dB are 4 GHz（from 9.6 GHz to 13.6 GHz）. The excellent microwave absorption properties can be explained by the special three-dimensional porous structure, the larger specific surface area and high pore volume, enhanced interfacial polarization, and improved impedance matching.