Preparation Of Graphene Based Functional Composites And Their Electrical And Microwave Absorption Properties

As the thinnest two-dimensional material, graphene has many unique properties, such as high mobility, large specific surface area, high Young’s modulus and thermal conductivity. However, graphene’s high mobility has only been observed on graphene sheets prepared by mechanical exfoliation. When graphene was synthesized by other methods, the mobility decreased due to residual defects. So examining the difference in electrical performance of graphene synthesized by various methods is the first step to study graphene electrode.Generally, desirable microwave absorption layer needs to be thin and light with strong wave-absorbing capacity within a broad-band frequency range. Graphene itself can partly meet the above demands due to its unique and superior properties, but it alone cannot meet the requirements of higher absorption capacity and broader absorption frequency due to its weak magnetism. One of the strategies to develop new microwave absorption materials is to synthesize the composites of graphene and other materials to improve impedance matching, increase magnetic loss, broaden absorption bandwidth, and enhance absorption.Incorporating graphene with other materials can prevent graphene from aggregation, keep intrinsic characteristics of graphene and other materials, and cause new cooperative effect, and then generate new physical, chemical, and mechanical properties. So graphene based composites have widespread application value and prospect.First, in this study, silane coupling agent and acrylic resin were employed to enhance the adherence between graphene sheets and the substrates. Experimental results demonstrated that different synthesis processes resulted in graphene sheets with different physical and chemical properties, such as morphology and size. With the same graphene concentration and other fabrication parameters, the thicknesses of graphene-A-, graphene-B-, and graphene-C-based thin films were 2.0,23.0, and 38.5 μm, respectively; and their minimum sheet resistances were 35.7,1591,7294 Ω/sq, respectively. High aspect ratio silver nanowires (AgNWs) were synthesized by solvothermal method, and then AgNWs-graphene composites were prepared. The results show sheet resistance of composite films was lower than those of graphene films.Second, graphene/Ni composites were successfully synthesized through a simple in-situ solution reduction process. Experimental results on microwave absorption measurements indicated that graphene/Ni composites had remarkable electromagnetic performance and could be developed for applications in microwave absorption. With a thickness of 2 mm, RGO-Ni (Ni:13.7 wt%) and RGO-Ni (Ni:63.2 wt%) had a minimum reflection loss (RL) value of -11.5 dB at 14.6 GHz and-15.2 dB at 12.5 GHz. For pure graphene and Ni nanoparticles, the minimum RL values of with a thickness of 2 mm were-6.11 dB at 6.1 GHz and-8.99 dB at 7.1 GH. The enhanced microwave absorption originated from the efficient complementarity between complex permittivity and permeability, and interfacial polarization. MnO2-graphene, SnO2-graphene, and Co3O4-graphene composites were successfully synthesized by different methods. Metal oxide nanoparticles were well dispersed on graphene sheets. In comparison to pure graphene, all three composites demonstrated enhanced absorption characteristics. The minimum RL values of MnO2-, SnO2-, and Co304-graphene composite were-20.9 dB at the frequency of 14.8 GHz,-15.28 dB at 15.94 GHz, and-7.3 dB at 9.6 GHz, respectively.Third, Cu-Ni hybrid nanostructures with various morphologies including different sizes of nanowires and nanospheres were successfully prepared by adjusting experimental parameters, and the composite of graphene decorated with Cu-Ni nanoparticles were also fabricated using the same method in order to compare their microwave absorption properties. The results show Cu-Ni nanowires and nanospheres had different RL values though with the same composition; Cu-Ni nanowires or nanospheres with different atomic ratio of Cu and Ni had different RL values though with the same morphology; composite with Cu-Ni and graphene had enhanced microwave absorption compared with pure graphene.