Study On The Synthesis,Characterization And Gas-sensing Properties Of SnO₂ And ZnO Composite Nanomaterials

The increasing concerns with air pollution on health and safety require the development of effective gas sensors to monitor all aspects of the environment in real time.Gas sensors based on metal oxide semiconductors,which are attractive because of their high sensitivity,low cost,simplicity and compatibility with modern electronic devices.However,those gas sensors have some disadvantages such as poor selectivity and anti-interference performance,long response-recovery time,high power loss,very sensitive to environmental temperature and humidity and the mechanism of gas sensors is not very comprehensive.Nanomaterials is fabricated mainly through experiences or a trial and error,thus limiting their wide applications and developments.In view of gas sensors based on semiconductors in the exiting problems,this dissertation has been synthesized heterojunction structure to enhance gas sensing performance by various methods and systematically investigated the synthesis of composite nanomaterials,characterization,gas-sensing test and the formation of sensing mechanisms.The results are summarized as follows:?1?Pure SnO₂,pure ZnO and SnO₂-ZnO composite nanofibers were fabricated by the electrospinning method,and studied on ethanol gas sensing properties of SnO₂doping on ZnO nanofiber and the formation process of heterostructure.The results show that the doping of SnO₂ leads to the formation of ZnO nanofibers N-N heterojunction and increases the specific surface area of the nanofibers,which greatly enhances the SnO₂-ZnO composite nanofibers on ethanol gas adsorption ability,thus significantly improve the gas sensing properties of ethanol.The gas sensor of SnO₂-ZnO shows the higher response value,short response-recovery time and good stability by comparing pure SnO₂ and ZnO.The responses of pure SnO₂,pure ZnO and SnO₂-ZnO gas sensors to 100 ppm ethanol are 6.7,10 and 78 at 300?,respectively.The response and recovery time of the SnO₂-ZnO composite nanofibers are 25 s and 9 s,respectively,and exhibiting good selectivity and stability toward ethanol.?2?Biomorphic pure ZnO,CeO₂-ZnO hollow tubular fibers were prepared using cotton fiber as the bio-template.The samples are characterized and tested by XRD,SEM,TEM and gas sensing test instrument for the composition of synthetic materials,crystalline state,morphology,dimensions and gas sensing properties.The results show that the surface of CeO₂-ZnO hollow fibers is relatively loose and porous,the tube wall has many small holes,the dimension of the outer diameter is about 8-14?m with 2?m in thickness.Due to the porous and hollow structure,the BET surface areas of the CeO₂-ZnO hollow fibers is larger than pure ZnO,thus improving the gas sensing properties.The response of CeO₂-ZnO gas sensor to 200 ppm ethanol is 46 at260?.In addition,the gas sensor has good linear in the range of 5-500 ppm and excellent selectivity to ethanol.?3?Pure SnO₂ nanoparticles and CeO₂-SnO₂ composite nanosheets were synthesized by a simple hydrothermal method.The morphology and structure of two samples and their gas sensing properties are studied.The results show that the size of CeO₂-SnO₂ nanosheets is about 800-1000 nm and the thickness is about 15-30 nm.These have a lot of square nanoporous on nanosheets,and the length and the width are about 20-30 nm.After doping CeO₂,the CeO₂-SnO₂ composite materials have been greatly reduced the aggregation of nanoparticles,and the porous structure improves the gas sensing properties.The response of CeO₂-SnO₂ composite nanosheets to 100ppm ethanol is 44 at 340?.The response and recovery time is 25 s and 6 s,respectively,which is faster than the pure SnO₂ nanoparticles with good selectivity to ethanol.?4?Finally,this dissertation simple introduces the main applications of gas sensors,namely the method of electronic nose measurement.Though the research of odour measurement method and system constitution,it makes a clear research direction for the development and application of gas sensors in the future.