Research Of Mass-sensitive Gas Sensor And Array For Detection Of Toxic Gas

Countries around the world pay great attention to the sustainable development in the twenty-first century. Environmental pollution is one of the most important difficulties. There is a critical need for toxic and harmful gas detection such as atmospheric pollution, industrial emissions monitoring and the detection of the quality of human settlements. Therefore, the development of low-cost portable gas sensor and array is of great significance. Among gas sensors, mass-sensitive gas sensors have been widely used in the detection of toxic and harmful gases because of their compact structure, good technology, low cost, suitable for mass production and so on. However, the selectivity of the mass-sensitive gas sensors depends on the type of the surface sensitive membrane. The dissertation focused on the mass-sensitive gas sensors. Especially, a great deal investigations have been done on the sensitive materials such as poly-enes, supramoleculars and organic inorganic composites. The mass-sensitive gas sensors deposited these sensitive materials are tested for the gas sensitivity to the flammable methane gas and toxic gas volatile organic chemicals (VOC). Furthermore, the application of surface aoustive gas sensor array to qualitalive and quantitative analysis of VOC was also described. The main research contents were as follows:1. Study on the working principle of mass-sensitive gas sensor. Establish the physical and chemical model of sensitive mechanism based on the mass-effect and the adsorption characteristics of gas on the senstive membrane. The linear solvation energy relationship (LSER) has been developed to describe and quantify these various interactions. Simulate the mass-sensitive gas sensor based on COMSOL multiphysics software. The simulation significantly reduces the amount of prototype experiments, sensor development cycle and development costs.2. Poly-2, 5-dimethoxyethynylbenzene (PDMEB) was synthesized according to stelle coupling reaction, while poly-(bistriethylphosphine)-platinum-diethynylbenzene (Pt-DEB) was synthesized by dehydrohalogenation reaction (Sonogashira coupling reaction). The polymer films were deposited onto the surface of acoustic devices by spin-coating method to fabricate gas sensors. Sensitive properties of them to methane and VOC have been studied. It was found that the PDMEB based acoustic sensor has good sensitivity to methane at room temperature. The surface morphology revealed that the existence of holes on the PDMEB surface provided adsorption sites for methane gas molecules. The infrared spectra confirmed there was a certain combination of PDMEB in methane gas. Pt-DEB based acoustic sensor has better sensitivity to VOC than PDMEB based acoustic sensor such as reversibility, reproducibility, and linear sensitivity at room temperature. The low detection limits about 1.0 ppm to trichloromethane was found. The sensing mechanism is due to the swelling phenomenon.3. Supramolecular cryptophane-A was synthesised from vanillyl alcohol using a double trimerisation method and deposited on acoustic device via electrospray method to fabricated gas sensor. The sensor was exposed to various concentrations of methane gas. The influence of humidity was also examined. The sensor's response showed that it is sensitivity to methane gas. A fast response and recovery was observed at room temperature. Detection limit for methane is 0.05% (v/v). The mechanism of CH4 interactions with cryptophane-A arises from size complementarity and efficient van der Waals interactions.4. Inorganic nanoparticles SnO2 and In2O3 were dispersed in PDMEB using an in-situ synthesis technique to prepare organic-inorganic nanocomposites PDMEB/SnO2 and PDMEB/In2O3. The nanocomposites were spun-coated on acoustic devices to fabricate gas sensors. It was found that SnO2 and In2O3 nanoparticles not only changed the morphology of PDMEB and improved the film properties, but also enhanced the sensitivity to methane at room temperature. The adsorption and desorption curves were carefully analysed using kinetic theory for the resonse of methane gas on PDMEB and PDMEB/SnO2 and PDMEB/In2O3 nanocomposites coatings. The adsorption constants of PDMEB/SnO2 and PDMEB/In2O3 nanocomposites to 1000 ppm methane are equal. The value is 0.0145, which is more than the value of pure PDMEB (0.0138). The desorption constants of PDMEB/SnO2 and PDMEB/In2O3 nanocomposites are also more than of pure PDMEB. The inorganic nanoparticles changed the selectivity of the polymer to different VOC. PDMEB/In2O3 showed good sensitivity to THF, but PDMEB and PDMEB/SnO2 had good sensitivity to alcohol (methane, ethane and isopropyl alcohol). All of them had no sensitivity to acetone and chloroform. 5. Carbon nanotubes (CNTs) based organic-inorganic composite was deposited on acoustic devices through layer-by-layer self-assembly method to fabricate gas sensors. Dispersed in different solvents, the CNTs showed different response. They showed better gas-sensing properties to the VOCs whose polarity is similar to the polarity of the solvent, which was mentioned as solvent-functionalized CNTs. This has a certain significance to improve the selectivity of CNTs based sensors. The layer-by-layer assembly carbon nanotube thin film used PDDA and PSS as polycation and polyanionic, respectively. It had has good sensing properties to ammonia at room temperature. The senosr response was decreased when the temperature increased, which is in accordance with Arrhenius equation.6. Establish surface acoustic wave (SAW) based gas sensor array and commercial semiconductor-type and catalytic sensor array. The SAW array is used to discriminate and quantify VOC with data processing methods. The commercial sensor array is used to qualitative and quantitative analysis among combustible gas methane and hydrogen.