Gas Sensing Properties Of Metallic Oxide/Graphene Aerogelat Room Temperature

With the rapid development of global economy and the continuous improvement of industry,the global environmental pollution is a growing problem.Gas pollution effects human life all the time which has become the focus of the researchers concerned.At present,among the most kinds of air pollutants,sulfide,NO₂ is known as the great environmental pollution and threat to human health.So its effective detection has important practical value in gas sensors.Metallic oxide based gas sensor has always been used in civilian,industry,and air pollution monitoring fields.However,the application of metallic oxide based gas sensor has been limited due to its low electrical conductivity,energy consumption and weak gas discrimination.Graphene as a new type of gas sensitive materials,due to its good conductivity,large specific surface area and well gas discrimination,could effectively make up the problems the metallic oxide sensing materials faced and has been widely applied in gas sensing field.In this thesis,the gas sensing properties at room temperature of the metal oxide/graphene composites have been investgated.The preparation and gas sensing properties of copper/copper?I?oxide nanoparticles-reduced graphene oxide composites?CuGCs?have been studied.Copper nitrate as a source of copper,DMF not only as reducing agent but also as a dispersant of graphene oxide?GO?,the CuGCs were successfully synthesized.The gas sensing performance of the CuGCs was also studied systematically.Cu₂ O nanoparticles with diameter ³ nm are uniformly anchored on the surface of reduced graphene oxide?RGO?.The typical one-pot and in situ method ensures the close contact between RGO and Cu₂ O nanoparticles.Through adjusting the quantity of copper nitrate,the CuGC2 sample exhibited the best gas sensing performance for NO₂ gas at room temperature among the CuGCs and also exhibited better performance compared to RGO.The sensitivity to 50 ppm NO₂ is 15.2% and the response time is 391 s,respectively.The effective combination between Cu₂ O,copper and the RGO not only could increase the conductivity but also form multiplication effect in the composites because of being both p-type semiconductor materials.These advantages are beneficial to improving the sensing performance.Ferroferric oxide?Fe₃O₄?/RGO aerogel which shows interconnect macroporous networks has been designed and used as room temperature gas sensor for NO₂ detection.The effect of P-type Fe₃O₄ and porous structure on the gas-sensing properties has also been studied.Fe₃O₄ nanoparticles with diameter 3¹0 nm are uniformly dispersed in graphene layers.The Fe₃O₄/RGO aerogel composite has better gas response and perfect recovery performance to NO₂ at room temperature compared to RGO,whose sensitivity to 50 ppm NO₂ is 5.6% and the response time?recovery time?is 274 s?1495 s?and alsoshows excellent stability.The three dimensional porous conductive structure is beneficial for electron transfer,providing fast and versatile transport pathways in the gas sensing process.The constructing of SnO₂ nanoclusters/RGO aerogel heterostructure and its NO₂ sensing performance at room temperature has been studied.And the sensing mechanism has also been deeply dicussed by energy band model.The RGO aerogel exhibits a porous conductive network.SnO₂ nanoparticles is as small as 5¹0 nm with uniform distribution on the RGO surface.The growth of SnO₂ nanoclusters is limited by RGO;meanwhile the SnO₂ nanoclusters could effectively inhibit the stack of RGO layers.The pore structure and the formation of P-N junction could not only ensure the full contact between gas molecules and sensitive materials but also promote the flow of electronic which makes the SnO₂/RGO aerogel composite show excellent response and recovery characteristics and stability at room temperature.The sensitivity to 50 ppm NO₂ is 6%,the response and recovery time is 190 s and 224 s,respectively.By comparison with other test,we assume that the interconnected macroporous networks and large specific surface area of the graphene aerogel is very important to the improvement of the sensing performance.The graphene aerogel composite based gas sensor solves the slow recovery problem which general RGO based gas sensors exsited.The ZnO microspheres/RGO aerogel composite based gas sensor has been investgated systemically.The ZnO spheres featured a size of 0.5¹ um are anchored homogeneously on the surface of graphene layers.The three-dimensional graphene exhibits interconnected macroporous networks.ZnO spheres and RGO exhibit close contact.The ZnO/RGO aerogel based gas sensor exhibits high sensitivity and fast respond and recovery speed to NO₂ at room termperature.The sensitivity to 50 ppm NO₂ at room temperature is 9%,the response and recovery time is 203 s and 126 s,respectively.It also shows good stability and selectivity.By comparison with other test,we assume such excellent performance is inseparable with the structure.The novel structure is beneficial for electron transfer,providing fast and versatile transport pathways for gas diffusion.The enhancement of the sensing response is mainly attributed to the improved conductivity,the 3D porous structure of graphene and the heterostructure construction between p-type graphene and n-type zinc oxide.