Preparation Of Graphene-based Thin Film Sensors And Study Of Their Sensitive Mechanism In Multiple Atmospheres

Graphene,two-dimensional zero-band-gap crystal formed by the close packing of a single layer of carbon atoms.In recent years,it has attracted much attention because of its excellent physical and chemical properties.The extremely high electrical conductivity and large specific surface area make it suitable for gas sensors.Studies have shown that the detection limit of graphene materials to target gas can reach ppb level,even a single gas molecule.However,unmodified graphene has the disadvantages of limited detection ability of gas molecules and poor gas sensitivity selectivity.Graphene oxide is produced in the process of preparing graphene by redox method and is a two-dimensional material similar to graphene structure.Because it has a large number of oxygen-containing functional groups,it has gas sensing properties different from graphene.However,the process of preparing graphene oxide by the improved Hummers method uses a large amount of oxidant and high reaction heat to make the type of oxygen functional groups in its structure uncontrollable,resulting in the defect of poor selectivity of gas-sensitive materials.In order to further solve the problems in the gas-sensitivity research of graphene materials,this paper improves the preparation process of graphene oxide based on previous studies,and synthesizes hydroxy-type graphene oxide that responds to a single gas-sensitivity and has a large diameter with better stability.Graphene oxide;using graphene gas-sensing materials in combination to solve the problem of graphene oxide material selectivity;loading the graphene material gas-sensing sensing element on the development board,and designing and writing programs to obtain the graphene material gas sensing device.It has a certain significance for the application and development of graphene materials in gas-sensitive materials.It was found in the experiment that there is a functional group evolution process in the oxidation process of graphite.Reducing the activation energy of the entire reaction system can effectively control the oxidation process of graphite.Therefore,hydroxy-type graphene oxide with a carbon-to-oxygen ratio of 70.04 and a C-OH ratio of 80.60%was prepared under the conditions of ice water bath without changing the original material ratio and process,and was characterized by XRD,FT-IR,Raman,etc.The means show that the structure,types of functional groups,and defects of graphite gradually change with time.Gas-sensitivity testing showed that the hydroxy-type graphene oxide exhibited a single gas-sensitivity?selectivity?to NH3before being oxidized in an ice water bath for 12 hours,and exhibited the properties of a p-type semiconductor after absorbing NH₃.The detection limit of NH₃ at room temperature and atmospheric background is about 20 ppm.By expanding graphite first,and then performing secondary intercalation,oxidation,and exfoliation,a large-diameter graphene oxide with a sheet diameter of about 200-350?m and high sheet integrity is obtained.XRD test showed that the surface spacing of large-diameter graphite oxide was 0.04 higher than that of graphene oxide.FT-IR test showed that the functional groups in large-diameter graphene oxide and graphene oxide were basically the same.Gas-sensitive tests have shown that this large-diameter graphene oxide has the advantages of better moisture sensitivity and high stability.It was formulated into solutions with different solid contents to be filmed on the interdigitated electrode,and the gas-sensing performance was tested.As the thickness of the coating film increased,the humidity-sensing performance showed a tendency to increase sharply and then stabilize.In order to solve the problem of arraying graphene material gas sensors,gas-sensing elements made of hydroxy-type graphene oxide and graphene oxide were used for comprehensive testing of NH₃ and humidity,and the analytical curves of the sensor array for the two main atmospheres in the atmospheric environment were obtained.Through single sensitivity and two gas tests,it is known that graphene materials have defects of poor selectivity in complex environments.Such defects lead to the problem of preemption of active sites in gas-sensitive materials when the materials are in contact with gas molecules.Using a single sensitive gas sensor and poorly selected graphene material gas sensor array design idea can effectively improve the sensor recognition and detection capabilities.According to the single sensitivity curve,combined with the current single-chip technology and development board technology,the display and alarm functions are integrated on the arduino development board to make a simple single-signal graphene material gas sensing device to realize the detection of NH₃ gas in the air under atmospheric environment;Write the analytical curve of concentration response in two gas environments to the development board,integrate a single NH₃ signal identification element and graphene oxide gas sensing element,and make a simple gas sensor device for graphene material for simultaneous detection of NH₃ and humidity in atmospheric environment.