Preparation And Microwave Absorption Of Functional Molybdenum Disulfide-based Composites

With the development of our science and technology,electromagnetic（EM）pollution is becoming more and more serious,especially,in the field of national defense and security due to the abuse of EM waves in communication,satellite signal,navigation,remote control,positioning,home appliances（microwave oven,induction cooker）,medical equipment and so on.In order to solve previous problems,various electromagnetic-protected materials with wide absorption frequency range,low density,strong absorption property,good thermal stability and antioxidant capability have been widely exploited and the corresponding absorbing theory has been improved.In this study,based on the background of absorbing materials at home and abroad as well as the fundamental properties of EM waves,a series of two-dimensional（2D）materials:molybdenum disulfide（MoS₂）based materials were prepared and the microwave absorption performances were investigated.The detail investigation as following:1.A series of MoS₂-based materials with different morphology,including MoS₂nanosheets（MoS₂-NS）,hierarchical MoS₂（H-MoS₂）microspheres,hollow hierarchical MoS₂（HH-MoS₂）microspheres and hydrangea-like MoS₂/C（MoS₂/C）microspheres,were synthesized via hydrothermal reaction.More importantly,the microwave absorption mechanism and the dielectric properties as well as microwave absorption performance（MAP）were systemically studied.The results indicated that MoS₂/C exhibited eminent dielectric properties and MAP,which resulted from the unique structure and component.The minimum reflection loss（RL）value of MoS₂/C microspheres/wax with 30 wt%loading is-44.67 d B at the thickness of 1.4 mm,and the corresponding bandwidth with effective attenuation（RL<-10d B）is up to 3.3 GHz（11.7 GHz-15.0 GHz）.For MoS₂-NS,H-MoS₂ and HH-MoS₂ the optimum RL value is-34.8 d B,-39.8 d B and-41.2 d B,respectively.It was revealed that MoS₂doped by C not only improve attenuation coefficient but also enhance impedance matching.Moreover,the limiting factor of MoS₂’s microwave absorption is attenuation property rather than impedance matching property,indicating exploiting novel MoS₂-based composites with higher attenuation property is the dominate research interests in the future.2.In order to enhance the attenuation property of MoS₂,MoS₂@Fe₃O₄and MoS₂@Fe₃O₄@PANI composites were successfully synthesized by hydrothermal reaction and in-suit polymerization.The microwave absorbing performances were investigated,the optimum RL values of MoS₂-NS,MoS₂@Fe₃O₄ and MoS₂@Fe₃O₄@PANI composites were-25.4 d B,-26.8 d B and-40.97 d B,respectively.In addition,for MoS₂@Fe₃O₄@PANI composites,the bandwidth with effective attenuation is completely covered X band（8.2 GHz-12.4 GHz）.According to the contrastive analysis of impedance matching and attenuation property,which demonstrates Fe₃O₄ nanoparticles enhanced the attenuation property of MoS₂-NS,but decreased the impedance performance.Moreover,the impedance property of MoS₂@Fe₃O₄@PANI is better than MoS₂@Fe₃O₄ composites but the attenuation is lower than that.3.To further reveal the relationship between microstructure and microwave absorbing performances,a series of PANI@MoS₂@Fe₃O₄ NW（e1,e2,e3 and e4）and as-prepared MoS₂@Fe₃O₄@PANI with the same composition were prepared by complexing reaction and hydrothermal reaction.One of the absorbents’（e2）optimum RL was-49.7 d B and the corresponding effective bandwidth was 4.3 GHz（13.7 GHz-18.0 GHz）with the coating thickness 1.3 mm.while the coating thickness up to 1.7 mm,the effective attenuation bandwidth was 6.48 GHz（10.28 GHz-16.76 GHz）.Finally,the absorbing mechanism was investigated based on the contrastive analysis of impedance matching and attenuation property.It was revealed that the limiting factors to PANI@MoS₂ NW’s microwave absorbing performance is originated from insufficient attenuation and impedance mismatching.Moreover,it found that the Fe₃O₄ nanoparticles improved the impedance matching and attenuation property.However,the limiting factors to PANI@MoS₂@Fe₃O₄ NW’s microwave absorption is insufficient attenuation.More importantly,attenuation properties were greatly dependent on the content of Fe₃O₄ nanoparticles that has little effect on impedance matching.4.A series of CF@MoS₂-x（x=1,2 and 3）composites were successfully prepared by vertical coating MoS₂-NS over CF surfaces for exploiting a kind of low-density and high-performance microwave absorbent.Concerning the inferior CF microwave absorption,the limiting factors to CF’s microwave absorption was higher conductivity originated from the conductive network,leading to skin effect,due to the induce current.With respect to the investigation of CF@MoS₂-x（x=1,2 and 3）composites’microwave absorption,it was found that the the common idea that only magnetic materials can enhance or optimize the microwave absorption properties of CF was reviewed showing that CF@MoS₂-2 has potential practical applications because of its wide-bandwidth（10.85 GHz;defined by reflection loss<-10 d B from 7.15 GHz-18.0 GHz）.The enhanced MAP may be the result of a synergy between polarization loss and conductive loss.The limiting factor to the MAP of CF is impedance matching rather than attenuation,which can be optimized by coating MoS₂-NS over CF,although this simultaneously reduces the attenuation.Therefore,there is competition between these two effects.There is a new competition between magnetic loss and conductive loss after decorating Fe₃O₄ particles onto CF@MoS₂-2 composites;this plays a dominant role in the MAP.Finally,the occurrence of multi-reflection phenomena of EM waves in absorbers are critically analyzed.5.In order to verify the universilaty of as-proposed opinion and develop a kind of low-density and multi-function composite as reinforcement and microwave absorbents.According to the diazo and in situ polymerization reation,a series of CF@PANI-x（x=1,3 and 5）composites were prepared by covalent bond grafting PANI nanorods over CF surface.The MAP of as-prepared samples was investigated based on the comparative study among the length of PANI,morphology and conductivity.It was revealed that the impedance matching of CF was optimized by PANI nanorods,but the limiting factors to CF@PANI-x composites’microwave absorption is still impedance mismatching due to the higher conductive of PANI,which cannot effective decrease the conductive of CF@PANI-x composites.For CF@PANI-5 composites,the optimum RL values were-33.8 d B with the coating thickness 1.1 mm and the corresponding effective attenuation bandwidth was up to 4.5 GHz（13.5 GHz-18.0 GHz）,which can be responsible for the higher dipole polarization of PANI nanorods.Finally,Michael Green et.al.method to quantitatively analysis polarization loss and conduction loss was critically investigated.