Research On Gas Sensing Properties Of Based On Metal-Organic Framework And Graphene Composites For Detection Of SF₆ Decomposed Species

SF6 gas is an arc extinguishing medium widely used in gas insulated switchgear(GIS).However,the insulation defects inside GIS can lead to partial discharge(PD)and other faults.SF6 decomposes in the overheated environment of long-term malfunction,and its products generate H2S,SO2,SO2F2,SOF2,CF4,CS2 and other major decomposition components in the presence of micro-water and micro-oxygen,which reduces the insulation of the equipment and endangers the stable operation of the power system.The type and concentration of these decomposition products are closely related to the fault types.Therefore,using the gas sensor method centered with nano gas sensitive materials to detect the decomposition components of SF6 in GIS equipment is an effective and fast method to diagnose discharge faults and guarantee the safe operation of electrical insulation equipment.Metal-organic frameworks are a new class of inorganic-organic hybrid materials.Due to their flexibility in design and synthesis,structural diversity and plasticity.adjustable pore size and high specific surface area and pore volume.they have unique structures and properties and become an ideal platform for various advanced functional materials and applications.In this paper,Mg-MOF-74 and Zr-MOF-808 are selected as the basic materials to composite with graphene oxide in different ways to construct different types of MOFs and GO composites as new gas sensing materials for detectingSF6 and its characteristic decomposition components,so as to realize the sensitive identification of these gases.The research is carried out from three aspects:theoretical calculation,material synthesis and gas sensing experiment.In the aspect of theoretical calculation,the gas molecular model is constructed in GaussView software,and the structure of MOFs material is simplified by extracting clusters and replacing ligands to construct the adsorption substrate model.After structure optimization,the Gaussian 16 software based on the principle of quantum chemistry is used to simulate the binding energy,charge transfer amount,adsorption distance,gas molecular bond length and bond angle changing,and orbital occupancy changes of Mg-MOF-74 and Zr-MOF-808 intrinsic materials and Mg-MOF@GO and Zr-MOF@GO composites for SF6 and its main decomposition components,comprehensively describes the adsorption mechanism of various materials on gas.The calculation results show that:the above four materials have strong adsorption capacity for H2S,SO2,SO2F2 and SOF2 gases,the adsorption capacity for CS2 is weak;it has weak adsorption for SF6 and CF4 gases.In addition,the simulation calculations show that the Mg-MOF-74 and GO composite systems and the Zr-MOF-808 and GO composite systems have strong substrate binding energies,it indicates that the oxygen-containing groups of GO in the two systems coordinate with Mg or Zr in MOFs to form stable composite materials.In terms of material synthesis,the two intrinsic materials Mg-MOF-74 and Zr-MOF-808 have low conductivity,and the response is too intense when detectingSF6 and its main decomposition component gases,in this study,MOFs are introduced into the sheets of graphene oxide to design MOFs-graphene oxide composites for modification.On the premise of retaining the gas adsorption of the intrinsic MOFs material,the conductivity of the material is improved and the adsorption response value is reduced by graphene oxide to meet the detection requirements.In this research,we use(1)physical composite method to prepare MOFs/GO-n series materials by combining intrinsic MOFs with GO;(2)MOFs@GO-n series materials are synthesized by combining MOFs with GO by vacuum impregnation method;(3)MOFs-derived metal oxide/rGO composites are synthesized by annealing/etching method with MOFs/GO-n as template.Another new type of carbon material-MOFs derived PC/rGO composite is prepared by etching the latter with dilute acid.The 20 composites prepared by the above three methods are characterized by SEM.TEM,XRD,XPS and Raman spectroscopy to study their structure,composition and microstructure.In terms of gas sensing experiments,two intrinsic MOFs materials and 20 composite materials are studied in this paper.The resistance changes of the sensor under different gas distribution types and concentrations are measured at room temperature.The adsorption and desorption response rules and repeatability of the above materials toSF6.H2S,SO2,SO2F2,SOF2,CF4 and CS2 are analyzed,and the sensing performance of each material is measured.The experimental results show that(1)In the same type of material,the ratio of MOF and GO is different,and the composite material shows a large difference in conductivity and gas sensitivity.(2)The conductivity and gas sensitivity of MOFs and GO composites are greatly different due to the different composite methods.(3)Four kinds of composite materials are:Mg-MOF@GO-1 and Zr-MOF@GO-1 in the MOFs@GO-n series and Mg-MOF/GO-1 and Zr-MOF/GO-1 in the MOFs/GO-n series.At room temperature,their comprehensive performance of conductivity,adsorption and repeatability are the most excellent,which are suitable for the detection of SF6 and its main decomposition components at room temperature,and has great value and significance in further research.In this paper,a composite material based on metal-organic framework and graphene is constructed for the detection of SF6 and its main decomposition components at room temperature,which realizes the leap from inorganic materials to metal-organic framework materials of this kind of gas-sensing material.It lays the foundation for on-line monitoring of SF6 decomposition gases at room temperature,and also provides a new idea for exploiting new gas sensitive materials.