Synthesis,Characterization And Electromagnetic Properties Of Graphene/Manganese Oxide Composite Structures

Manganese dioxide?MnO₂?is widely applied in microwave absorbing materials due to its simple preparation process,controllable morphological structures and excellent electromagnetic properties.However,manganese dioxide is a kind of dielectric loss medium with low conductivity and poor magnetic loss,which leads to the narrower effective absorption band and poor overall loss performance.At present,the electrical conductivity of the material can be improved by compounding high conductive substrate,and thus to improve the electromagnetic wave absorbing property of MnO₂ material.In the present thesis,rGO/MnO₂ nanocomposites were successfully prepared by different methods,their electromagnetic parameters are calculated and their microwave absorbing properties and examined.The main work and conclusions are as follows:?1?rGO/MnO₂ nanocomposites were synthesized by hydrothermal and water-bathing method.By changing the ratio of reactants,different rGO/MnO_x composites with different rGO contents were made.After the combination of rGO,the microwave absorbing properties of MnO₂ nanomaterials were improved obviously and microwave absorbing property is manily dominated by dielectric loss.When GO addition is low in the reactants,there is MnOOH forming in the products,thus leading a poor absorbing performance.When the addition of GO is high,the products are pure rGO/MnCO₃ composites,and displaying great absorbing performances.For example,when KMnO₄:GO=1:1,the SY1:1 product obtained from water-bathing method has an absorbing peak value of-32.43 dB with a thickness of 8 mm.Moreover,its effective absorption bandwidth reaches 2.32 GHz?12.24-14.56 GHz?.?2?The morphological structures and thus the absorbing properties can be changed through the introduction of surface active agents of sodium dodecyl benzene sulfonate?SDBS?or polyvinylpyrrolidone?PVP?in the reaction process of hydrothermal method or water-bathing method.When GO is added in low concentration,there is MnOOH in the products and thus leads to a poor absortion.When the GO concentration is high,in the case of two different surface active agents,the composites show great absortion properties with a large thickness.When SDBS is added,the SD1:2 composite with a thickness of 8 mm shows a good microwave absorption performance at the high frequency section.The maximum absorbing peak reaches-23.56 dB,and the effective absorption bandwidth is 3.12 GHz?13.36-16.48 GHz?.When PVP is added,the PV1:2 composite gets an absorbing peak of-32.85 dB with a thickness of 8 mm.The effective absorption bandwidth also reaches 3.12 GHz?from 13.12 GHz to 16.24 GHz?.?3?When manganese sulfate was added in the PVP composites as a further manganese source,the products are pure rGO/?-MnO₂ nanocomposites.Due to its great dielectric loss properties of?-MnO₂,the nanocomposites show excellent microwave absorption performances with absorbing peak values larger than-10 dB.When KMnO₄:GO=10:1,the absorbing peak values are all superior to-20 dB.