Preparation And Properties Of NO₂ Gas Sensor With Nanoporous Structure

Along with the development of society and the enhancement of human life,the environmental pollution is more and more serious.NO₂ as one of the main cause of environmentpollution,can cause acid rain and photochemical smog,which is a serious threat to the survival of the human living environment.As a result,NO₂endangers people's health.The preparation of NO₂ gas sensor with low temperature and low detection limit is around the corner.As is known to all,pore structure can increase the specific surface area of sensing materials,and provide more active sites for gas adsorption and catalysis.This topic is mainly to design pore structure on the surface of sensing materials,and assemble resistance-type,current-type,mixed electromotive force-type and balanced electromotive force-type NO₂ gas sensor.What's more,the performance of the sensor is studied.The specific contentsare as follows:?1?Electrochemical treatment of commercial ITO glass to obtain ITO film with composite nanopore structure,and assembed simple structure and low-cost resistance-type NO₂ gas sensor.The test results show that the sensor can work at a lower temperature,with an optimal operating temperature of 100^oC.The sensor has good response,selectivity and repeatability to NO₂ at 0.1-500ppm.After electrochemical treatment,the response of the sensor to ppb NO₂ was improved by nearly 200 times.The mechanism of the sensor is discussed,and the reason of improving the sensor performance is explained by Knudsen diffusion.?2?WO₃ nanoparticles,WO₃ nano-sheet and mesoporous WO₃ were prepared by different methods.WO₃ with three nanostructures was used as sensing electrode to assemble current-type NO₂ sensor with NASICON as solid electrolyte for comparison.The test results show that mesoporous WO₃ has the lowest test temperature and the highest sensitivity,as well as good repeatability and selectivity.The mechanism of current-type sensor is discussed and Knudsen diffusion is used to explain the good performance of mesoporous WO₃.?3?The simple structure mixed electromotive force-type NO₂ gas sensor was assembled with mesoporous WO₃ as the sensing electrode and tested in low concentration?0.06-10ppm?and high concentration?30-500ppm?respectively.The minimum detection limit of the sensor is 60ppb.Under the low concentration,the optimal test temperature is 500^oC,and in high concentration,the optimal test temperature is 300^oC and 500^oC.The sensor has high sensitivity,excellent stability,repeatability and selectivity.Based on the mechanism of mixed electromotive force sensor and the results of XPS and NO₂-TPD,the reasons for the two optimal test temperatures of the sensor under high concentration were analyzed.And the influence of mesoporous structure on the sensor performance was discussed by using the Knudsen diffusion model.?4?Mesoporous ZrO₂-WO₃ nanotubes were obtained by anodic oxidation,and the ordered and disordered structures were obtained by controlling experiment conditions.Mixed electromotive force-type NO₂ sensor was prepared by combining mesoporous ZrO₂-WO₃ nanotubes with YSZ.The sensor has high sensitivity under400^oC.On this basis,the well-ordered mesoporous ZrO₂ nanotubes grown in situ were used to assemble the nano ZrO₂-WO₃ membrane.Both types of sensors have good repeatability and stability.Finally,the mechanism of the two types of sensors is discussed,and the influence of mesoporous nanotube structure on the sensor performance is analyzed by Knudsen diffusion.