Investigation Of Carbon Dioxide Gas Sensor Based On QCM

Large amounts of carbon dioxide emission have gradually affected people’s normal life, so the research on a kind of low cost, high sensitivity of carbon dioxide gas sensor becomes extremely necessary. Gas sensors with thin film materials have many characteristic such as: particular physical, chemical properties, flexible membrane structure and excellent surface characters, which make the thin films technology become the key factor of the gas sensor development. This dissertation carried out a series of analysis and research on the sensing mechanism of carbon dioxide(CO2) based on Quartz Crystal Microbalance(QCM), it can been seen that polyethyleneimine(PEI) with rich primary amino group is the ideal material of carbon dioxide thin film sensor. What’s more, PEI has the advantages of simple preparation, good film forming process and high sensitivity. In this paper, an insight into the relevant sensing mechanisms was under investigation combined with some analytical methods. The main content includes the following points:(1) Firstly, the different concentration of PEI aqueous solution(5mg/ml, 7.5mg/ml and 10mg/ml) was deposited onto QCMs with different spin coating proceeding to study the effect of film thickness on sensing response of the QCM devices. Secondly, PEI/ MWCNTs, PEI/Cu Cl and PEI/Starch composite films were spin-deposited on QCM, and the effect of the different quantity(2mg, 6mg and 10mg) of starch on the property of devices were studied to get the appropriate starch proportion of PEI/Starch composite film. Finally, PEI-MWCNTs, PEI-Starch and PEI-Sn O2 bilayer films were prepared to analyze the influence of bilayer film to CO2.According to the test results, PEI film with the concentration of 7.5mg/m L has outstanding response performance to CO2. As the starch has strong hygroscopicity and water molecules can promote chemical reaction between the amino and CO2, so PEI composite film which doped with starch exhibits better response performance than PEI film. Compared the sensitive performance with PEI bilayer film and PEI film, it has been found that PEI-Sn O2 not only promote the responsibility but also reduce the recovery time of the sensor.The study indicated that the responsibility of PEI composite film doped with starch towards CO2 was better than the PEI film and other composite films. Following, PEI bilayer films were prepared with different substrate materials, and then test the sensitivity of these PEI bilayer films. According to the results, it can be seen that PEI/Sn O2 bilayer film has better performance. Finally, the stability of PEI、PEI/Starch and PEI/Sn O2 gas sensor were tested and the results show that all of these gas sensors have huge attenuation on the response to CO2 at 15 days later. Therefore, the package technology of gas sensor is particularly important.(2) In order to solve the problems caused by environmental factors on the thin film sensors, this paper analyzes the influence of humidity on PEI sensor and PEI/Starch sensor. It has been found that the existence of water molecules affect the performance of QCM sensors, and this effect promote the response between the sensors and CO2. According to the test results, the response to carbon dioxide of PEI/Starch sensor increased almost 90 percents. Furthermore, the temperature characteristic of PEI sensor,PEI/Starch sensor, PEI-Starch sensor and PEI-Sn O2 sensor were detected to analysis the influence of the temperature fator. The experimental results show that all of these four sensors perform well at 60℃ and their desorption rate both have a great ascension. The results also show that the PEI-Sn O2 sensor has a broad range of temperature stability due to the stable resistance at high temperature.