Preparation And Microwave Absorption Properties Of ZIF-67 Derived Metal Oxides And Graphene Composites

In recent years,with the rapid developments of science and technology,personal intelligent electronic devices such as mobile phones,personal computers and wireless networks have become more and more necessary for people's lives.A large amount of electromagnetic waves are generated for the high-frequency using of electronic equipment.Meanwhile,the radiation of electromagnetic waves bring tremendous bad influence on life and technology,and become a new source of pollution.Besides,a large number of electromagnetic waves in life can also cause health problems,such as heart rate increasing and immunity declining.Therefore,high-performance electromagnetic wave absorption material has become a research hot spots.The ideal electromagnetic wave absorption material not only has stong absorption properties,but also a wide range of absorption frequency,thin thickness,light weight and so on.Based on the characteristics of ideal electromagnetic waves,carbon-based materials are often used in the field of electromagnetic wave absorption because of their high dielectric constant and light weight.Metal organic frameworks(MOFs)material derived compounds have a porous structure and chemical diversity,which have been reported as electromagnetic wave absorbing materials.This paper focuses on the research of carbon-based materials(graphene,RGO),the preparation of Co-based MOF(ZIF-67)complexes and the properties of electromagnetic wave absorption.In this paper,the different molar ratio of graphene oxide was added to investigate the effect of graphene on the microwave absorbing properties of the composite.At the same time,the best molar ratio would be found,and the samples with the best molar ratio were calcined at different temperatures,and analyzing the influence of temperature on the microwave absorbing properties of the composites.The whole thesis consists of four chapters.The main research contents are as follows:(1)Using graphite powder as raw material,concentrated sulfuric acid,potassium permanganate and hydrogen peroxide as a strong oxidant.Graphene oxide was prepared by Hummers method,and the prepared graphene oxide was obtained by high temperature reduction graphene.And RGO was analyzed using scanning electron microscopy(SEM)and thermogravimetric analysis(TG).RGO was found to be very thin and of high quality.The electromagnetic parameters of RGO were measured by a network vector analyzer(VNA).The calculated reflection loss of RGO was-6.6 dB.This is because graphene has a high dielectric constant and poor impedance matching characteristics,resulting in weaker absorption of electromagnetic waves.In this paper,the GO and ZIF-67 prepared above were used as precursors.Herein,the molar ratio of GO was adjusted to prepare different molar ratios of ZIF-67/GO complex and calcined at 500 ? under the protection of argon.The as-prepared three products were labeled as Sample 500-1,500-2 and 500-3.The prepared Co3O4/RGO complex was analyzed by XRD,SEM,TEM and VNA.By simulating the value of the reflection loss(RL),the values of the reflection loss of the three samples of 500-1,500-2 and 500-3 were-10.5 dB,-18.25 dB and-39.8 dB,respectively.It is found that with the increase of the molar ratio of GO,the reflection loss of composites increases.The mechanism of the effect of GO on electromagnetic wave performance was analyzed and the best molar ratio of GO was found out.For the 500-3 sample,its RL value is greater than pure RGO(-6.5 dB)and pure ZIF-67(-35.3 dB).The final conclusion is that high electromagnetic wave absorption performance may be related to dielectric loss,dipole polarization,interface polarization and porous structure.(2)XRD and Raman analysis of three samples calcined at sample 3 with the best GO molar ratio above(500 ?,600 ? and 700 ?)showed that the composite obtained with the temperature change.In contrast,the 500-3 sample is Co3O4/RGO,the 600-3 sample is Co3O4/Co/RGO,and the 700-3 sample is Co/RGO.The same sample calcined at different temperatures get different materials,resulting in a difference in performance,600 ? sample is Co3O4/Co/RGO,which has best absorbing properties.The RL of the composite reaches-52.8 dB at a frequency of 13.12 GHz.Through the analysis of their performance,it is found that in addition to the mechanism of absorbing waves above mentioned,it is concluded that the synergistic effect of Co3O4 and Co and the improvement of material impedance matching can enhance the absorption performance of electromagnetic waves.