A Study On Methanol/ethanol Sensing Properties Of Metal Oxide Nanofibers

Metal oxide thin film gas sensors have been widely used in today's industrial production in the gas detection, environmental protection, the atmospheric monitoring, the detection of alcohol in traffic safety, the public safety of the toxic gas detection, combustible gas as well as fires warning. However, they usually suffer from several critical limitations such as relative low sensitivity, long response and recovery time and poor selectivity. Along with industrial development and technological advances, it is difficult to meet the requirements of modern industry. Therefore, it requires developing new gas-sensing materials, designing the new structure of the sensor to solve these problems. The rapid development of nanotechnology and nano-materials with nano-effects makes great success in the improvement of gas sensors. With larger surface area, smaller size than the bulk material, sensitive material in a nano-scale can significantly enhance the sensitivity of the sensor performance.One-dimensional (1D) material with excellent physical and chemical properties has a wide range of applications in the optoelectronic devices, bio-medicine, catalysis and sensor. Recent studies have shown that 1D metal oxide-based gas sensor has more excellent gas-sensing properties. Thus development of a new 1D material is an effective way to improve gas-sensing properties. In all the methods and technology to prepare 1D nanomaterials, electrospinning technique is most simple and inexpensive. It is to be recognized as a fast 1D nanostructures of production technology. Unfortunately, there are few reports on the gas sensor based on electrospun nanofibers. In this thesis, the sensors based on electrospun metal oxide nanofibers have been investigated systematically. The thesis is divided into the following four parts:(1)α-Fe₂O₃ ceramic nanofibers were prepared by electrospinning and followed by calcination. The experimental results exhibit that our product shows good characteristics to ethanol vapor. In particular, the sensor's response and recovery time is excellent, response time and recovery is 3 s and 5 s, respectively. However, the sensitivity needs to be improved.(2) In₂O₃ nanofibers have been fabricated by electrospinning, followed by calcination in air at 700 ?C. The sensor based on the as-prepared In₂O₃ nanofibers showed high response, fast response and recovery time towards ethanol gas. The weakness and low sensitivity to ethanol of the sensor based onα-Fe₂O₃ nanofiber has been initially solved. Noble metals are widely used in catalysis and gas sensing performance could be enhanced by doping the appropriate noble metals. In order to improve the properties of the sensor, we presented a simple and effective solution route to deposit Pt nanoparticles on electrospun In₂O₃ nanofibers for H2S gas detection and exhibited excellent gas sensing properties. In the previous studies, too little attention has paid to methanol which is a toxic substance and important industrial raw materials. Therefore, the study of methanol sensor has enormous and commercial value. In order to develop a methanol sensor, nanofibers in the In₂O₃-doped SnO2 appropriate to improve the response for methanol have been fabricated. Experiments show that when the content of In₂O₃ 25% in the composite (In₂O₃/SnO2), which shows the best response for methanol, 600 ppm, the sensitivity is up to 130, response and recovery time is 8 s and 15 s, respectively.(3) Rare earth oxides are important industrial raw material which has a good catalytic performance. Therefore, three representative oxides, La₂O₃, Eu₂O₃, CeO2 were used as additive-doped indium oxide In₂O₃ nanofibers to enhance the response of methanol. Experiments show that the 2% Eu₂O₃/In₂O₃ composite nanofiber had the best performance for methanol gas. The sensor sensitivity is 5.3 when methanol concentration is 3 ppm. With the methanol concentration increased to 400 ppm, the sensitivity is actually up 834.(4) Perovskite-type (ABO3) metal oxide nanofibers were prepared to study the LaFeO3, LaCoO3, LaInO3 gas-sensing properties for methanol. Experimental results show that LaFeO3 composite nanofibers have the best responses on the methanol among the three perovskite-type nanofibers. When the concentration of methanol is 500 ppm, the sensitivity is 163, the response and recovery time is 12 s, 21 s (average). The selectivity can be improved not only by changing the types of atoms in the B but also by changing the operating temperature.