Development Of Environmental Gas Monitoring Sensor And Its Application In Internet Of Things

Gas sensors,as important electronic components to obtain gas types and concentrations,play an important role in environmental monitoring systems.With the development of Internet of Things technology,it is possible to monitor toxic and harmful gases in the environment remotely and in real time.Gas sensors with high sensitivity,good selectivity and stability can effectively improve the efficiency and accuracy of gas monitoring.With its advantages of simple operation,wide monitoring range,low cost and easy integration,metal oxide semiconductor gas sensors have been widely used in the detection of various volatile toxic and harmful gases.Sn₃O₄,as a typical mixed valence N-type metal oxide semiconductor,has been used as a sensitive material in the preparation of gas sensors.However,gas sensors based on pure Sn₃O₄ materials face the disadvantages of low response value,high operating temperature and poor selectivity,which limits the application of Sn₃O₄ gas sensors.In order to solve the above issues,this paper adopts the method of constructing heterostructures and metal doping to improve the sensing performance of Sn₃O₄ gas sensor,and designs a gas monitoring system to realize the practical application of the prepared formaldehyde sensor.The main work content is as follows:（1）ZnO/Sn₃O₄ composite sensing material was synthesized by hydrothermal method,and a formaldehyde gas sensor based on the gas-sensitive material was prepared.The NN heterogeneous structure of the sensing material was constructed by modifying Sn₃O₄ with ZnO nanoparticles,which improved the performance of the gas sensor.Through the gas-sensitivity performance test,it is found that compared with pure Sn₃O₄ gas sensor,ZnO/Sn₃O₄ gas sensor shows higher sensitivity to formaldehyde.At an operating temperature of 180°C,the response of the Zn O/Sn₃O₄ sensor to 100 ppm formaldehyde is 44 with a response time of 5 s,and the gas sensor has a detection limit as low as 1 ppm.The semiconductor energy band theory is used to explain the electron transfer in the conduction band of the ZnO/Sn₃O₄ composite during the sensor test,and the effect of NN heterojunction on enhancing sensing performance is analyzed.（2）Sn₃O₄ hierarchical nanoflowers with different Cu doping contents were synthesized by hydrothermal method,and a formaldehyde gas sensor based on the sensitive materials was prepared.The study found that Cu doping changed the morphology and structure of Sn₃O₄materials.As the amount of Cu doping increases,the size of Sn₃O₄ nanoflowers gradually decreases.The gas sensitivity test found that the sensor based on 4 wt%Cu-doped Sn₃O₄ has a higher response to formaldehyde.At the optimal working temperature of 160°C,the response of the 4 wt%Cu-doped Sn₃O₄ gas sensor to 100 ppm formaldehyde reached 53,and it’s about 2times higher than the response of pure Sn₃O₄ sensor.The response and recovery time to 100ppm formaldehyde are 5 s and 120 s,respectively.At the same time,the prepared gas sensor shows good formaldehyde selectivity,excellent repeatability and long-term stability.The electron depletion theory is used to explain the sensitivity mechanism of the sensor,and the reason why Cu doping improves the sensitivity of Sn₃O₄ sensor is discussed.（3）A gas monitoring system using the prepared Sn₃O₄ formaldehyde sensor as the gas signal acquisition component was designed.By connecting the OneNET cloud platform,remote real-time monitoring of the test area was realized.Using the Arduino MEGA2560development board as the processing unit,the sensor signal acquisition circuit is designed using the voltage divider circuit principle,and the gas monitoring system is connected to the Internet of Things cloud platform through the WiFi module.The transparent transmission mode is used to upload the formaldehyde concentration data to the OneNET platform to realize the storage,management and forwarding of the formaldehyde concentration data.Through the editing of the cloud platform application interface,24-hour remote real-time monitoring of the formaldehyde gas information in the test area is realized.After the actual test and analysis of the gas monitoring system,the feasibility of the gas monitoring system and the practicality of the prepared Sn₃O₄ formaldehyde gas sensor are proved.