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Study on Hydrothermal Synthesis of WO3Nanostructures and Their Gas-sensing Properties

Author: ZhangHeJing
Tutor: LiuTianMo
School: Chongqing University
Course: Materials Science and Engineering
Keywords: WO3 hydrothermal method size and morphology growth mechanism gas-sensing properties
CLC: O614.613
Type: Master's thesis
Year: 2013
Downloads: 239
Quote: 0
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Abstract


Tungsten trioxide （WO3） is a typical n-type semiconductor functional materials, itis also one of the common metal oxide semiconductor （MOS）. In the past few decades,WO3has attracted the affection of many researchers due to its numerous potentialapplications in gas sensors, electrochromism, chemical catalysis and electrochemistry,etc. The design and rational synthesis of metal oxide semiconductors with tailoredcharacteristics （morphology, crystal phase, components, crystallinity, etc） have attractedincreasing attention because they largely determine the various properties of thematerials. The introduction of modern nanometer material science and technology eithercan enhance some performance of materials to a certain extent or makes it show someunexpected properties.The hydrothermal solution method and water bath method, which are belong tosolution method, have the advantages of simple economy, low energy consumption, andmaking the nano material high crystallinity and purity, etc. However, the changing PHvalue, hydrothermal temperature and time, kinds and concentrations of auxiliary agentin the solution have important influence on the size, shape, structure and crystallinestructure of WO3. At the same time, for the same kind of crystal phase, the influence ofdifferent size and morphology of WO3on properties of its gas sensitivity remains to befurther improved. Therefore, hydrothermal preparation of nanometer WO3, growthmechanism and gas sensitive properties researches have extremely importantsignificance on theory and practice. Main content of this article is as follows:Firstly, we studied the influence of different size and morphology of WO3on theperformance of gas-sensing properties. We prepared cubic-like particle monoclinicphase nanometer WO3, plate-like and layered flower-like WO3·H2O by hydrothermalmethod and water bath method, respectively, where sodium tungstate was using as rawmaterials, CTAB and oxalate as auxiliary additives. The WO3·H2O transformed tomonoclinic WO3and keep the original plates and flower-like structures after sinteringprocessing. The best working temperature of the different size and morphology of WO3is300℃and flower-like structure showed the highest sensitivity. The results showedthat the morphology and size monoclinic phase of WO3have great influence ongas-sensing properties. We explained gas-sensing mechanism of the three samples byband depletion theory model. Then, we studied the influence of different measurement of auxiliary additives onthe morphology and crystal phase of WO3in the hydrothermal process. We found thatmalic acid played a significant role in governing morphologies of precursors duringhydrothermal process. A possible formation mechanism was also proposed in detail.Experimental results showed that the optimized hydrothermal precursor could bedehydrated to mixed composition of hexagonal and monoclinic WO3with the uniquesphere-like porous architecture after being annealed. Besides, gas-sensing measurementindicated that the well-defined3D assembled sphere-like architectures exhibited thehighest sensor response to ethanol gas at the optimal temperature of250℃among thesamples.Finally, we studied the influence of different kinds of auxiliary additives on themorphology and crystal phase of WO3in the hydrothermal process. We prepared1D（nanorods and nanowires） hexagonal phase WO3with three different auxiliary additives（Na2C2O4、Na2SO4and H2C2O4） by hydrothermal method under the180℃and24hcondition. Combined with the experimental results and related references, we focus onthe influence of common ions Na+, SO42-, C2O42-and H2C2O4-on the nucleation andgrowth role of WO3in the process of preparation. Results showed that the threedifferent types of auxiliary additives have no effect on the crystal phase of the product.Subsequent gas-sensing measurement indicated that Na2C2O4assisted synthesis of WO3nanorods showed the highest sensitivity, which was mainly attributed to its highdispersion degree and crystallinity.

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CLC: > Mathematical sciences and chemical > Chemistry > Inorganic Chemistry > Metal elements and their compounds > Part Ⅵ group metal elements and their compounds > The chromium Vice family ( Ⅵ B group metal elements) > Tungsten W
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