The Preparation And Performance Of SnO₂-NiO Heterojunction Gas Sensor

Gas sensors are widely used in environmental monitoring,disease detection,artificial intelligence,petrochemical and other fields.Semiconductor gas sensors have been one of the research hotspots in the field of sensors due to their high sensitivity,good stability and fast response.The sensitive characteristics of sensing materials directly affect the properties of gas sensors.At present,the heterojunction is also an important sensitization method except doping and modification,and the fabrication of heterojunction has become one of the hot spots in the industry.However,the current research is generally focused on the construction of nanometer heterojunction,and less researcher has focus on the construction and sensing properties of large-area macroscopic heterojunction.The dip-coating method can grow the material on any substrate,so it is suitable for the fabrication of large-area heterojunction devices.In this paper,the macro SnO₂-NiO heterojunction was constructed innovatively by dip-coating method on the ceramic tube and nickel foam respectively.The preparation methods have been optimized,the relevant gas sensitive properties have been researched and the sensitive mechanism have been discussed.This paper lays a foundation for the application of macroscopic heterojunction in gas sensor.The main research contents are as follows:First,we used dip-coating method to grow a tin dioxide gas sensitive material on the ceramic tube.And the surface morphology and crystal structure were characterized.It is proved that the dip-coating method can achieve the growth of tin dioxide and uniform film formation on ceramic tubes.We studied the influence of the preparation conditions of monolayer tin dioxide on its gas-sensitive property,and the results showed that the components also had certain gas-sensitive characteristics,which laid a foundation for the construction of macroscopic heterostructure structure.On the basis of growing tin dioxide film,the heterostructure of SnO2-NiO was constructed by growing nickel oxide layer by dip-coating.The morphology and structure of the material were characterized,and the characterization results showed that the nickel oxide layer could grow on the tin oxide layer,and it was attached to the tin oxide film in the form of an agglomerated block,forming a layered heterogeneous structure.Research on the gas-sensitive characteristics of heterojunction devices shows that the construction of heterojunction greatly improves the gas-sensitive characteristics of devices,and the sensitivity to 10ppm methanol at 225^oC reaches 15,the response time is 18s,and the recovery time is 7s.Compared with the literature,the sensitivity and response,recovery speed of the prepared components are better.Finally,in order to further enhance the gas-sensitive performance of the device by increasing the heterojunction area,we attempted to construct SnO₂-NiO heterojunction on nickel foam with high specific surface area.The nickel foam surface was oxidized to NiO by direct heat method,and the growth of SnO₂-NiO heterojunction was achieved by dip-coating.The layered distribution of heterojunction was confirmed by SEM,TEM and XRD.The sensitivity of foam based SnO₂-NiO heterojunction devices is greatly improved by optimizing the reaction conditions.At 205^oC,the sensitivity of the device to 10ppm toluene reached 19.By comparing with the literature,it is found that the Ni foam based SnO₂-NiO heterojunction device in this work has higher sensitivity,faster response,recovery speed and is in the leading level in performance.