The Preparation Of Carbon Dioxide Thin Film Sensors And Gas Sensitive Properties Research

Carbon dioxide （CO₂） is the main part of the greenhouse gases. Due to a largenumber of emissions of carbon dioxide, the greenhouse effect has caused great damageto the environment of human life. Detecting CO₂is necessary and important in manyfields such as: clean energy technologies, agricultural production, demand controlventilation, emissions, food industry, chemical industry, storage, geological research andtransportation. In particular, CO₂sensor has been successfully used in renewable energyapplications. Since CO₂generally is an unreactive molecule, the design of CO₂sensoroperated at room temperature with new sensitive materials had many difficult issues. Inthis paper, the Hard Soft Acid Base （HSAB） theory was introduced as a new tool toselect or design sensitive materials for CO₂detection. Carbon dioxide gas sensoraccording to HSAB based on QCM and SAW for the detection of CO₂provided a newway.The main research contents were as follows:（1） In this paper, sensitive layer were deposited on the SAW by spin-coating method.At room temperature and atmospheric pressure, sensors’s sensitive effect of the inert gasCO₂, acid gases NO₂, and alkaline gas NH₃were tested. In addition, the influence ofstarch and temperature had also been studied. The responses of the sensors towardsdifferent concentrations of CO₂were investigated. It was found that the responsibility ofPEI/Starch towards CO₂, NO₂, and NH₃is larger than that of other layer sensors, whilethe response speed and the recovery speed of THEED to CO₂, and NO₂is better thanother two layers sensors, but THEED layer sensor has a weak response.to NH₃.（2） Sensitive layer were deposited on the QCM by spin-coating method. The studyfound that the responsibility of PEI/Starch towards CO₂, NO₂, and NH₃is larger than thatof other layer sensors, while the frequency shift of THEED to CO₂is better than othertwo layers sensors, but THEED layer sensor has a weak response.to NO₂and NH₃. Theresponse speed of PEI to NO₂and NH₃is better than PEI/Starch layer sensor. Responsetime: the response speed of three QCM sensors are samilar the recovory speed of its.The study found that the response time of THEED towards CO₂is faster than that of other layer sensors, while the response time of THEED towards NO₂and NH₃has weakresponse. In addition, the response speed of PEI sensor to NO₂and NH₃is shorter thanPEI/Starch layer sensor. Repeatability: the repeatability of PEI/Starch and THEED layersensors are better than PEI layer sensor. Temperature characteristics: The resultsindicate that PEI and PEI/Starch sensors at different temperatures show a similartemperature profile. The only difference was that the sensitivity of PEI/Starch sensorhas been found to be larger than that of single PEI layer coated sensors. In addition,THEED sensor has different temperature characteristics. With the temperature rise, itsfrequency shift decreases.