| The detection of toxic and harmful gases is of great significance in environmental protection and good health.As one of the main air pollutants,NO2 has a wide range of sources,huge emissions and many harms to both environment and health.WO3 in MOS materials has some advantages,such as high sensitivity,fast response,low cost,easy to make small size,etc.It is obvious that WO3 is a highly potential material sensitive to NO2.In this paper,WO3 was selected as the research object,and low concentrations(<3 ppm)of NO2 at operating temperature(<60?)was set as the research target.In this paper,the sol-gel method and the hydrothermal method were used to prepare pure WO3 with different morphologies,and then pure WO3 with relatively good performance was compounded with highly conductive polymer polyaniline(PANI).The complex of WO3/PANI formed a p-n junction to further improve the gas sensitivity of NO2.This paper also used a variety of analytical characterization methods to test and analyze the information,such as the morphology,structure,and element valence and composition.Through multivariate analysis,the gas sensing mechanism was to be explained.We hope that this paper could provide some ideas for WO3 based gas sensors sensitive to NO2.The specific work is as follows:(1)The granule WO3 was prepared by the sol-gel method and then manually coated on a ceramic tube electrode to make a traditional gas sensor.Through the initial exploration of the experiment,it can be seen that pure WO3-based gas sensor detected 0.4 ppm NO2 at a heating voltage of 1 V,which met the test limit requirements of this subject.Under the condition of heating voltage of 3 V,the recovery time of the gas sensor reached 20 s to 10 ppm NO2.At the same time,the response value of the gas sensor was as high as 460 to 50 ppm NO2,which was nearly three times more than the response value of that in the 2 V heating.(2)Flower-like WO3 was directly grown on the FTO substrate by hydrothermal method to form a new-structure gas sensor.different sizes and morphologies of WO3 was obtained by adjusting the reaction time and sintering temperature.Various characterization methods such as XRD,SEM,XPS were used to study the structure and properties of the material.The best preparing condition of flower-like WO3 were a reaction time of 6 h and a sintering temperature of 500?.The limit of NO2 concentration detected by gas sensor is 2 ppm at the operating temperature of 50?.At the same operating temperature,the response value of the device to 30 ppm NO2 reached 27.5.In the 35-day test,the response of WO3 sensitive to 10 ppm NO2 fluctuated slightly around 2.3,which indicated that the repeatability of WO3 was good.In addition,through the performance analysis of the material,the gas sensing mechanism was also discussed.(3)the hydrothermal method and chemical in situ growth method were used to successfully synthesize WO3/PANI composites with different composite ratios by controlling the deposition time.Through a series of XRD,SEM,TEM,XPS,TG tests and gas sensitivity characteristics tests.It was investigated that the compound basically returns to its original point at low concentration(<10 ppm)at the operating temperature of 50°C,which improved the recoverability of pure sample at low concentration.The response value of WO3/PANI to 30 ppm NO2 reached 60.2,which is about 3 times than that of pure WO3.The improving gas-sensing property was due to the formation of p-n junctions,bigger surface area,more oxygen vacancies,and good electron channels of PANI.Among the compounds with the best gas-sensing properties,PANI accounted for 7%of the total mass of the compound.In addition,comparing the sensitivity to 30 ppm SO2,NH3,NO2,ethanol and acetone at the operating temperature of 50°C,the composite showed higher response to NO2.In the condition of 20-60%RH,the material was hardly affected by relative humidity. |
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