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Surface Modification and Gas Sensing Properties of Vanadium Oxide Nanotubes

Author: JinWei
Tutor: ChenWen
School: Wuhan University of Technology
Course: Materials Physics and Chemistry
Keywords: Vanadium oxide nanotubes Surface modification Core-shell structure Sensitivity Selective
CLC: TB383.1
Type: PhD thesis
Year: 2010
Downloads: 160
Quote: 0
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Abstract


In recent years, nanomaterials, due to its special structure and excellent performance, attract the attention of the majority of scholars. Vanadium oxide nano-materials exist a large number of the active sites of the gas-selective effect, can be used to fabricate a high-sensitivity gas sensors. In many of the vanadium oxide nano materials, vanadium oxide nanotubes (VONTs) having a larger specific surface area, is more conducive to the adsorption of the gas, for the gas-sensitive material to improve the sensitivity, stability, selectivity, and other properties have a great potential . This article select vanadium oxide nanotubes as the research object, its surface modification study two aspects starting from the material structure control and sensing mechanism, system study of vanadium oxide nanotubes structure, composition and gas sensing performance, made a number of innovations The study results. As follows: 1. Vanadium oxide nanotubes produced next to the thermal gas sensor test its gas sensing performance by static gas distribution. The study found that vanadium oxide nanotubes gas sensor ethanol gas recovery with high sensitivity and short response time, and the best working temperature of 270 ° C. 330 ℃ 1000 ppm ethanol gas sensitivity of up to 2.3, and the detection limit as low as 50 ppm. By correlation analysis of the structure and properties of the nanotubes, it is pointed out that the one-dimensional vanadium oxide nanotubes unique layered shape of a large number of gas passages and has a higher specific surface area itself prone to oxidation-reduction reaction may be the reason of its high sensitivity. 2. Secondary hydrothermal synthesis of vanadium oxide nanotubes surface load Fe203 nanoparticles. By studying the solvent, the reaction temperature, the coupling agent factors on the surface load of the structure and properties of Fe203 nano-particles of vanadium oxide nanotubes, discovered by Fe203 nanoparticle surface modification of vanadium oxide nanotubes gas sensing performance have been greatly improved. Fe203 nanoparticles surface load at 190 ℃, vanadium oxide nanotubes detection limit of 10 ppm of ethanol gas. 330 ℃, 1000 ppm ethanol gas sensitivity of up to 7.4. - Temperature curve, sensitivity - temperature curve, Fe203 particle size of the nanotubes sensitivity results infer its gas sensing mechanism in accordance with the resistance of the composite structure for surface adsorbed oxygen control model Fe203 particles exist is equivalent to an increase of the active site, nano, tube - dimensional morphology for electron transfer provides a fast-track, a result of both the role of sensitivity has been greatly improved. Using microwave irradiation method to load the shape of the uniform surface of vanadium oxide nanotubes dispersed the uniform Ag and Pd nanoparticles, the particle size of about 10 nm. Compared with pure vanadium oxide nanotubes, the modified noble metal surface of the vanadium oxide nanotubes gas sensor having a better stability and lower operating temperatures. Ag nanoparticles surface modification can significantly improve the selectivity of vanadium oxide nanotubes ethanol gas. The Pd nanoparticles surface modified vanadium oxide nanotubes can improve the sensitivity of the ammonia. The main reason for the component gas sensing performance improvement is a precious metals \Polymer monomer in situ chemical polymerization of the cladding thickness 5-20 nm vanadium oxide nanotubes / polyaniline core - shell structure and the thickness of the coating layer 40 nm vanadium oxide nanotubes / poly pyrrole core - shell structure. Through the polymer-coated, vanadium oxide nanotubes gas room temperature detected by the gas sensors to greatly broaden the range of applications of the gas-sensitive material of vanadium oxide nanotubes. Vanadium oxide nanotubes / polyaniline-core - shell structure gas sensor sensitivity to 1000 ppm ammonia at room temperature up to 6.2. Vanadium oxide nanotubes / polypyrrole core - shell structure at room temperature to 1000 ppm ethanol gas sensitivity of 2.4. Through a series of structure and characterization of polymer vanadium oxide nanotubes is not a simple mixing, there are synergies between the two. The synergy between the two causes the pn junction formed between the P-type polymers and N-type vanadium oxide nanotubes, to reduce the depletion layer barrier height, and its sensitivity is improved.

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