| As people pay more attention to air pollution,real-time monitoring of air composition can effectively help people deal with the change of air quality in time.Therefore,research and development of high-performance gas sensors for air quality monitoring is an important task to be solved urgently.In this paper,the gas sensing properties of Mo S2 have been studied scientifically.Meanwhile,in view of the deficiency of Mo S2 in gas detection,constructing heterostructure is selected to optimize and modify Mo S2.In addition,a gas sensor data acquisition and wireless data transmission system based on FPGA has been designed for the Mo S2/Pb S gas sensor.The main work of this paper is divided into the following three parts:1. Mo S2 nanosheet with transverse dimensions over 20?m is successfully synthesized by mechanical exfoliation,and Raman spectroscopy,Field emission scanning electron microscope?FE-SEM?,and surface profilometer are used to characterize the as-prepared Mo S2.The gas sensing properties of the gas sensor based on the Mo S2 nanosheet are studied,and it is found that the Mo S2 gas sensor could realize the detection of NO2 at room temperature,showing N-type response behavior and exhibiting good sensitivity and selectivity.The sensitive behavior of the Mo S2 gas sensor is attributed to the electron exchange between the Mo S2 nanosheet and the NO2 gas molecule.However,because Mo S2 is easy to be oxidized by oxygen in the air,the Mo S2 gas sensor has shortcomings such as low response value,poor stability and slow response/recovery speed,which need to be improved urgently.2. Mo S2/Pb S composites are successfully synthesized via combining the mechanical exfoliation method with the facile wet-chemical precipitation.X-ray diffraction?XRD?,Raman spectroscopy,FE-SEM,and X-ray photoelectron spectroscopy?XPS?are used to characterize the as-prepared Mo S2/Pb S composites.The characterization results show that Pb S particles are evenly dispersed on the surface of Mo S2 nanosheet,and the modification of Pb S could effectively suppress the oxidation of Mo S2.The results of the gas sensing performance test at room temperature show that the response value of the Mo S2/Pb S gas sensor against NO2 is significantly improved compared with the pure Mo S2 gas sensor.At the same time,the modification with Pb S also accelerates the response speed of Mo S2,and the response time is almost reduced by two orders of magnitude.In addition,the Mo S2/Pb S sensor performs good reliability and large detection range?the limit of NO2 detection is 200 ppb?,which can be expected to meet the needs of early warning about acute health problems caused by NO2.The excellent gas sensing properties of Mo S2/Pb S sensor could be attributed to the synergistic effects between n-type Mo S2 nanosheets and p-type Pb S particles,including the effective modulation of the conductive channel,the increased active sites,and the approximate defect-free surface of mechanically exfoliated Mo S2.Experiments show that Constructing the heterostructure is an effective way to improve the sensor performance,which provides useful guidance for the design of high-performance gas sensors.3. The data acquisition and wireless data transmission system based on FPGA is designed for the Mo S2/Pb S gas sensor.According to the functional requirements of the system,the system is divided into a gas-sensitive data conversion system,a data processing system,and a data transmission system.The related modules are designed by Verilog HDL and downloaded to the FPGA development board.The data acquisition and wireless data transmission system based on FPGA is built by combining Mo S2/Pb S gas sensor and related components.Through the calibration experiment of the gas sensing system,it is found that the overall error of the actual NO2 detection is within 10%,and the detection of low concentration of NO2 exhibits high precision,which is expected to be used for the early warning of respiratory diseases caused by NO2 in real life. |
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