Gas Sensors Based On Metal Oxides Nanowires And Air Filter Based On Fibrous Webs

The rapid development of human civilization especially the advance of industry has provided people a more convenient and faster lifestyle. However, the emission of industry pollution brings along huge damage to our living environment. Thus the environmental pollution has become an inevitable issue threatening people's life quality. How to effectively detect the hazardous gas in the environment is vital to protect human's health. Recently, the scientists have focused on the research of the air detection and filtration materials. There are many kinds of materials studied for the fabrication of gas sensors or air filters. The development of nanomaterials makes great progress in this field. Compared with traditional materials, nanomaterials show unique physical, chemical and biological properties, which make them more suitable for the application of gas detection. They possess excellent adsorption efficiency and accordingly, the sensitivity, selectivity and stability are all better than the traditional onesGas sensors based on nanomaterials are applicable and promising in the development of detecting hazardous gas. In this thesis, we have successfully synthesized semiconducting metal-oxide nanomaterials for gas sensors and polymer nanowires for the filtration of polluted air, respectively. The details are briefed as follows:?1? Ethanol gas sensor based on electrospun SnO₂ fibrous nanowebs: Electrospinning is a simple method to synthesize one-dimensional nanomaterials. The polymer solution with metal salt is used as the precursor solution and then stretched by the high voltage electrical field to form the nanofibers on the substrate. After the polymer decomposed by calcination at the high temperature, the metal oxide nanofibers will be transformed. We used the SnCl₂·2H₂O as the metal precursor to obtain the SnO₂ fibrous nanowebs. The sensor based on this pure SnO₂ nanowebs showed high repeatability and stability although its sensitivity wasn't very good enough, which was applied in the further synthesis of heterojunction nanowebs in next section.?2? Electrospun nanowebs of NiO/SnO₂ p-n heterojunctions for enhanced gas sensing:The electrospinning method can be applied not only in the fabrication of pure nanofibers but also the composite nanofibers of different metal oxides. The NiO/SnO₂ p-n heterojunction was synthesized by this technique and then used for the fabrication of gas sensor. At the operating temperature of 300?, the sensor showed a high sensitivity and low detection limit with a rapid response and recovery time of 2.9 s and 4.7 s respectively. Furthermore, it showed a better selectivity towards ethanol in comparison with other reference gases such as H₂S, CO, NH₃ and acetone.?3? Formaldehyde gas sensor based on 3-D NiO nanosheets. The Ni?OH?₂ nanosheets were fabricated by a simple reaction in the precursor solution. After annealing at high temperature in the air, the 3-D NiO nanosheets with a smaller size and better morphology were obtained. The sensor based on this material didn't show good sensitivity, repeatability, selectivity or stability towards formaldehyde gas at 150?, but it still offered us another nano structure for gas sensing.?4? High efficiency air filter based on the polyacrylonitrile ?PAN? nanowebs: As mentioned before, electrospinning is a simple and cost-effective method to fabricate nanofibers. In our work, it was used to get the functionalized PAN fibrous nanowebs by mixing polyetherimide ?PEI? and PAN solution to obtain the composite products. The polarity helps the adsorption of PM2.5 particles. Moreover, the nanoweb filter also showed good filtration efficiency for the formaldehyde gas at the same time.