The Preparation And Electromagnetic Performance Of Magnetic Porous Carbon Nanocomposite Material With Cellulose As The Carbon Source

Based on the microwave absorbing mechanism, the magnetic porous carbon nanocomposite is a potential light absorbing material. On the one hand, the combine of magnetic metal material and carbon material could not only provide the composite materials more electromagnetic wave dissipation mechanism, but also expand the effective absorption wave frequency. On the other hand, the porous structure of the composite can not only reduce the bulk density of the material, but also improve the impedance matching behavior of the material, which is helpful for the electromagnetic wave to enter the interior of the material. However, up to now, the preparation of magnetic porous carbon nanocomposites from cellulose and the investigation of their electromagnetic properties have not been attracted enough attention.In our previous work, the cellulose/nickel nanocomposite had been prepared by in situ reduction method, and the results showed that the composites exhibit ideal electrical conductivity and could be used as microwave absorption materials. Considering that the cellulose is a kind of electromagnetic inactive material, and carbon material is a typical electromagnetic wave absorbing material, in this work, the cellulose/nickel nitrate precursor was prepared by direct mixing, and then the carbon/nickel magnetic nanocomposites could be obtained by carbonization of cellulose and reduction of nickel nitrate simultaneously. Moreover, with the help of the organic composition of natural cellulose and the decomposition of nitrate, the magnetic porous carbon nanocomposites could be obtained.In this work, the electromagnetic wave dissipation capacity and the impedance matching performance of the material could be controlled by means of composition and structure regulation, and the obtained magnetic porous carbon materials could be used as high efficiency and light electromagnetic wave absorbing materials. The research contents are as follows:1. Ni/C composites were prepared by calcinations the mixture of nickel nitrate/cotton fiber in H2/Ar at high temperature. The results showed that the porous structure of the obtained samples was obvious with the increase of the concentration of nickel nitrate, which indicated that the content of nitrate was the main influence factor for the formation of porous structure. Based on the electromagnetic performance results, it could be found that nickel nitrate concentration is 0.3M and 0.5M respectively, the obtained paraffin Ni/C composite(Ni/C filler content is 50wt%) has excellent microwave absorption properties.2. In order to prepare light absorbing materials, graphene/Ni/C composites were prepared further. The results showed that within certain range, with the filler content increased, the electromagnetic wave absorption performance of the paraffin based composite is gradually enhanced, meanwhile, the effective frequency bandwidth range gradually widened. When the filler content is 40wt%, the optimized electromagnetic wave absorption performance could be obtained. For example, the value of the minimum reflectivity could be up to-22 dB at the frequency of 9.6GHz, and in the frequency range of 2.5-18 GHz, the reflectivity value is less than-5dB. This shows that the introduction of graphene could provide the composite more electromagnetic wave dissipation mechanism, and the composites could be used as a light absorbing material.3. The pore structure in the magnetic porous carbon materials could not only reduce the density of the material, but also improve the material impedance matching performance. Thus, the electromagnetic wave could penetrate into the interior of the material and the multiple reflections of electromagnetic wave in the pore structure could be expected. Here, the preparation of the magnetic porous carbon/paraffin composites was prepared by the improved sample preparation process. When the sample is uniformly dispersed in the matrix, the porous structure could be maintained. The results showed that with the help of the improved sample preparation process, ideal absorbing performance could be obtained when the filler content is only 10wt%. For example, the minimum reflectance value could reach- 37 B at 15 GHz.4. In order to further control the impedance matching performance of the material, in this work, the electromagnetic inactive materials---SiO2 were introduced into the Ni/C composite system. The influence of SiO2 content on the morphology and electromagnetic properties of Ni/C composites was studied. The results showed that the amount of SiO2 have evident effect on the electromagnetic wave absorbing performance of the composite. When the absorbing filler content is only 10wt%, the reflectance values could be as high as-45dB(8 GHz).In this work, the cellulose and nickel nitrate were used as precursor, and magnetic porous carbon nanocomposite were prepared by an in situ process. The influences of the structure, composition and morphology of the magnetic porous carbon nanocomposite on their electromagnetic properties were investigated systematically. Combined the electromagnetic wave dissipation mechanism and impedance matching performance, the optimization of electromagnetic properties of materials were achieved. When the filler content is as low as 10wt%, the electromagnetic wave absorption properties of the composite is excellent. In a word, this work provides not only a new clue on the preparation and performance regulation of light electromagnetic wave absorbing materials, but also a new idea for the utilization of cellulose materials.