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Synthesis and the Enhanced Gas Sensing Properties of Molybdenum Oxide Nanocomposites

Author: XiaoGang
Tutor: ChenYuJin
School: Harbin Engineering University
Course: Materials Science
Keywords: MoO3 surface modification nanocomposites gas sensing properties
CLC: TB33
Type: PhD thesis
Year: 2011
Downloads: 72
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Abstract


Gas sensors can monitor toxic gases, and thus they have very important applications inmany aears such as environmental protection, traffic safety, food safety, and even in militaryfields. Now, More in-depth study had been done in the application of nanomaterials for gassensors. However, there are some issuse need to be solved for single nanostructures, such asthe bad selectivity and the high working temperature. In the thesis, the sensing properties ofgas sensors based on molybdenum oxide were improved by the surface modification. Thoseenhanced sensing properties include the decrease in the working temperature and the increasein the sensitivity and selectivity.α-MoO3/TiO2core/shell nanorods were synthesized by a wet chemical method. XRD,SEM and TEM analyses showed that the thickness of crystalline TiO2in the nanorods couldbe controlled to be15-45nm. It was found that the core/shell nanorods exhibited enhancedsensing properties compared to the bare α-MoO3nanorods, especially for one with thiner shell.The enhanced sensing mechanism was proposed in terms of the change of heterojunctionbarrier, which was experimently proved by the gas sensitive properties of CeO2/TiO2core/shell nanorods.α-MoO3/iron based nano composites were synthesized by a simple wet chemical method.The growth mechanism about the nanocomposits was proposed according to the analyses ofthe crystalline micro-structures. The response properties of the nanocomposites to alcoholwere investigated, and it was found that the samples showed enhanced sensing properties toalcohol. The enhanced sensing mechanism was discussed and analyzed in terms of thechemical and physical characteristics of the second phase.α-MoO3/CuO PN junction nanocomposite was synthesized by a simple wet chemicalmethod. The nanocomposite showed enhanced sensing properties to H2S gas. The sensitivityof the namocomposite was one order of magnitide higher than that of the bare nanorods. Theenhanced sensing properties to H2S gas were explained in terms of the data of energy band ofCuO and α-MoO3and the change in P-N junction barrier. The mechanism was proved by theexperiment in which the CuO structure was changed when the nanocomposite contacted withH2S gas. α-MoO3/SnO2nanocomposites were synthesized by a wet chemical method. The microstructure of the sample was carefully analyzed. These nanocomposites showed enhancedsensing properties to H2S gas. The mechanism of enhanced sensing properties was analyzed.α-MoO3/ZnO cage-like composite which, consists of nanowires and nanosheets wassynthesized by a hydrothermal method. The cage-like α-MoO3/ZnO composite showed goodcorresponding properties to H2S gas. For example, it could detect500ppb H2S at270℃. Atthe same time, the cage-like composite exhibited enhanced sensing properties compared to thebare α-MoO3nanorods. The mechanism was explained in term of shape and structuralcharacters of the cage-like composite.Therefore, the sensing properties of α-MoO3can be significantly enhanced by surfacemodification mechods. This provide effective approachs and methods to fabricate gassensor with high performance.

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