Preparation And Microwave Absorbing Properties Of Fe (Co/Ni/Zn)-doped Tin Oxide@multi-walled Carbon Nanotubes Composites

Low thickness, lightweight, broad frequency, and strong absorption are requirements for new ideal microwave absorption fields. Tin oxide (SnO2) is an n-type semiconductor with a wide band gap. When combined with multi-walled carbon nanotubes (MWCNTs), it can be obtained better microwave absorbing properties. In the matrix of the MWCNTs, with magnetic metal (Fe/Co/Ni) or non-magnetic metal Zn as dopants, we synthesized Fe/Co/Ni/Zn-doped SnO2@MWCNTs composites. Their microwave absorption performance becomes an important research direction in the new ideal microwave absorption area.This work synthesized SnO2@MWCNTs composites and Fe (Co/Ni/Zn)-doped SnO2@MWCNTs composites. The morphology and structure of the as-prepared composites were characterized by XRD, FT-IR, SEM, TEM, Raman, et al. Moreover, the microwave absorbing properties of the as-prepared composites were studied in 2-18 GHz frequency range measured by vector network analyzer. The main works and results were shown as followings:1. We used nitric acid acidification to make pretreatment of the MWCNTs. Then we use acidified MWCNTs as substrate, SnCl4·5H2O as tin sources, ammonia as precipitant, and prepared the SnO2@MWCNTs composites by one-step hydrothermal method. The acidification method of MWCNTs and the synthesize of the composites to the dispersibility were investigated. The results demonstrated that the SnO2 nanoparticles uniformly distributed on the MWCNTs with a diameter in the range of 3-5 nm. Besides, the SnO2@MWCNTs composites attained better microwave absorbing properties than SnO2 and MWCNTs, and resulted in a maximum reflection loss of -21.6 dB.2. In acidified MWCNTs as substrate, SnCl4·5H2O as tin sources, ammonia as precipitant, nickel nitrate heaxhydrate as dopants, we prepared Ni-doped SnO2@MWCNTs composites by one-step hydrothermal method, and discussed the Ni doping contents to the microwave absorbing properties of SnO2@MWCNTs composites. The results indicated that the dopants of Ni did not change the crystal structure of SnO2@MWCNTs, and the doping belongs to the substituted doping. The interaction between SnO2 and MWCNTs strengthened after the doping of Ni.Additionlly, in terms of the microwave absorbing properties of Ni-doped SnO2@MWCNTs composites, the conclusions were summarized as follows:the 28.2% (mole percent) Ni-doped SnO2@MWCNTs composites had the best microwave absorbing properties in the range of 2-18 GHz, i.e, the maximum reflection loss reached -39.2 dB and the bandwidth of reflection loss less than-10 dB was 3.6 GHz. Obviously, it can be seen that the microwave aborption performance of Ni-doped SnO2@MWCNTs composites were significantly improved than SnO2@MWCNTs.3. In acidified MWCNTs as substrate, SnCl4·5H2O as tin sources, ammonia as precipitant, nine hydrated ferric nitrate as dopants, we obtained Fe-doped SnO2@MWCNTs composites by one-step hydrothermal method, and studied the Fe doping contents to the microwave absorbing properties of SnO2@MWCNTs composites. The results indicated that the dopants of Fe did not change the structure of SnO2@MWCNTs, and the doping belongs to the substituted doping. The interaction between SnO2 and MWCNTs strengthened after the doping of Fe.In addition, the 48.8%(mole percent) Fe-doped SnO2@MWCNTs composites possessed the best microwave absorbing properties, i.e, the maximum reflection loss was -44.5 dB and the widest frequency band was 4.5 GHz when the reflection loss exceeding-10 dB.4. We used acidified MWCNTs as substrate, SnCl4·5H2O as tin sources, ammonia as precipitant, cobalt nitrate hexahydrate and zinc nitrate hexahydrate as dopants respectively, obtained Co (Zn)-doped SnO2@MWCNTs composites by one-step hydrothermal method, and explored the Co (Zn) doping contents to the microwave absorbing properties of SnO2@MWCNTs composites. The results indicated that the dopants of Co did not change the structure of SnO2@MWCNTs, and the doping belongs to the substituted doping. Furthermore, as referring to Zn-doped SnO2@MWCNTs composites, the non-magnetic metal Zn doping SnO2@MWCNTs composites did not change the structure of SnO2@MWCNTs when the doping contents was relatively lower, that is the molar ration of Sn4+ and Zn2+ was 3:1 and 2:1. However, as the Zn doping contents was higher, namely, the molar ration of Sn4+ and Zn2+ was 1:1,1:2 and 1:3, they can be sythesied ZnSnO3 and Zn2SnO4 to some extents.Besides, the microwave absorbing properties revealed that on one hand, the 38.6%(mole percent) Co-doped SnO2@MWCNTs composites exhibited the best microwave absorption performance, i.e, the maximum reflection loss was -22.8 dB and the maximum frequency band extended 4.1 GHz. On the other hand, considering the microwave absorption performance of Zn-doped SnO2@MWCNTs composites, the performance concluded as below:when the molar ration of Sn4+ and Zn2+was 1:2, the Zn-doped SnO2@MWCNTs composites attained the excellent microwave absorbing properties, i.e, the maximum reflection loss of the composites reached -43.4 dB and the broadband absorption of 3.7 GHz when the reflection loss less than-10 dB.