Studies On Gas Sensing Properties Of Metal Oxide Nanomaterials

Gas sensors are the devices which can be used to detect combustible,flammable gases,toxic gases,oxygen consumption.Gas sensors have been widely used in many fields,such as industry,environment,fire fighting and medical care.The gas sensors based on the resistive-type metal oxide semiconductor are attractive because of their high sensitivity,low cost,simplicity,and compatibility with modern electronic devices.Nanowires,nanotubes,nanoparticles and other nanomaterials are the dominant nanostructures in this field due to their larger specific surface area,which is conducive to the surface reaction between gas molecules and sensing materials.To obtain the metal oxide semiconductor gas sensor with high sensitivity and low working temperature,in this thesis two different CuO and Fe₂O₃nanomaterials were designed and studied,including their preparations,structure characterizations,and gas sensing properties.The present study provides an important strategy to purposefully design gas sensing materials with desired surface structure for high performance gas detection.1.Study on CO gas sensing properties of CuO nanostructures Metal oxide nanomaterials have been widely applied in the high-performance gas sensors.For metal oxide semiconductors,high surface-to-volume ratio and the exposed crystal facets are the two key factors for determining their gas sensing performances.In order to study the effect of surface structure on the gas sensing properties,in this work,two types of copper oxide（CuO）nanostructures,CuO nanotubes（CuO NTs）with exposed surface plane of（111）and CuO nanocubes（CuO NCs）with exposed surface plane of（110）,were obtained from Cu nanowires（Cu NWs）and Cu₂O nanocubes（Cu₂O NCs）,respectively.The morphologies,crystal and surface structures were characterized by electron spectroscopy and X-ray techniques.The gas-sensing performances of CuO NTs and CuO NCs for CO gas detection were then studied.The results demonstrated that compared to CuO NCs,the CuO NTs exhibited lower optimum working temperature and higher sensing sensitivity for CO gas detection.At the operating temperature of 175 ^℃,the prepared CuO NTs exhibited high sensitivity,good selectivity,fast response and recovery times to CO gas.The present study indicates that for the same semiconductor sensing material,the surface crystal structure has significant influence on the sensing performance.2.Study on ethanol gas sensing properties ofγ-Fe₂O₃ nanoparticles It is critical to improve the sensing sensitivity and lower the working temperature for the application of gas sensors.For a gas sensor,the sensing materials play important roles for determining the sensing properties.In the present work,γ-Fe₂O₃ nanoparticles composed with nanoparticles were successfully fabricated by a typical facile hydrothermal process and a following annealing treatment.Interestingly,the as-synthesizedγ-Fe₂O₃ nanoparticles showed excellent sensing properties for the detection of ethanol gas with high sensitivity,and especially working temperature as low as room temperature.The gas sensing results showed that at the optimum operating temperature（200 ^℃）,the intensity response of theγ-Fe₂O₃nanoparticles for 1000 ppm ethanol gas detection can reach 74.6 and the limit of detection（LOD）is about 0.026 ppm.At room temperature,theγ-Fe₂O₃ nanoparticles still demonstrated a good response to different concentrations of ethanol gas from 1 to 1000 ppm,with a very good selectivity over other gas species and a good stability.Such study indicates that theγ-Fe₂O₃ phase could be a type of promising gas sensing material for ethanol gas detection.