钒氧化物纳米管的表面修饰与气敏特性研究
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摘要
近年来,纳米材料由于其特殊的结构和优越的性能,吸引了广大学者的关注。钒氧化物纳米材料存在大量与气体选择性作用的活性位点,可用于制作高灵敏度气体传感器。在众多的钒氧化物纳米材料中,钒氧化物纳米管(VONTs)具有更大的比表面积,更利于气体的吸附,对于提高气敏材料的灵敏度、稳定性、选择性等性能有很大潜能。本文选择钒氧化物纳米管为研究对象,对其进行表面修饰,从材料结构控制和气敏机理研究两方面出发,系统研究钒氧化物纳米管结构、组成与气敏性能的关系,取得了一些创新性研究结果。具体如下：
1.将钒氧化物纳米管材料制作成旁热式气敏元件,通过静态配气法测试其气敏性能。研究发现钒氧化物纳米管气敏元件对乙醇气体具有较高的灵敏度和较短的响应恢复时间,且最佳工作温度为270℃。330℃时对1000 ppm乙醇气体的灵敏度高达2.3,探测极限低至50ppm。通过纳米管结构与性能相关性的分析,指出一维钒氧化纳米管独特的层状形状形成大量气体通道,具有较高的比表面积、自身易发生氧化还原反应可能是其灵敏度较高的原因。
2.利用二次水热法合成了表面负载Fe203纳米颗粒的钒氧化物纳米管。通过研究溶剂、反应温度、耦合剂等因素对表面负载Fe203纳米颗粒钒氧化物纳米管的结构与性能的影响,发现经Fe203纳米颗粒表面修饰的钒氧化物纳米管气敏性能得到大幅度提高。在190℃,表面负载Fe203纳米颗粒的钒氧化物纳米管对乙醇气体的探测极限为10 ppm。在330℃,对1000 ppm乙醇气体的灵敏度高达7.4。根据复合结构的电阻-温度曲线、灵敏度-温度曲线,Fe203颗粒尺寸对纳米管灵敏度的影响等结果推断其气敏机理为表面吸附氧控制模型,Fe203颗粒的存在相当于增加了活性位点,纳米管的-维形貌为电子的转移提供了快速通道,两者共同作用的结果导致灵敏度得到大幅度改善。
3.采用微波辐照法分别在钒氧化物纳米管表面负载了形状均一、分散均匀的Ag和Pd纳米颗粒,粒径约10 nm。与纯钒氧化物纳米管相比,贵金属表面修饰的钒氧化物纳米管气敏元件具有更好的稳定性和更低的工作温度。Ag纳米粒子表面修饰可以明显提高钒氧化物纳米管对乙醇的气体选择性。Pd纳米粒子表面修饰可以提高钒氧化物纳米管对氨气的灵敏度。元件气敏性能得到改善的主要原因是贵金属的“电子增敏作用”。
4.采用聚合物单体的原位化学聚合制备了包覆厚度5-20 nm的钒氧化物纳米管/聚苯胺核-壳结构和包覆层厚度为40 nm的钒氧化物纳米管/聚吡咯核-壳结构。通过聚合物的包覆,实现了钒氧化物纳米管气敏元件对气体的室温检测,极大拓宽了钒氧化物纳米管气敏材料的应用范围。其中钒氧化物纳米管/聚苯胺核-壳结构气敏元件在室温下对1000 ppm氨气的灵敏度高达6.2。钒氧化物纳米管/聚吡咯核-壳结构在室温下对1000 ppm乙醇气体的灵敏度为2.4。通过一系列结构与性能表征,发现聚合物与钒氧化物纳米管并不是简单的混合,两者之间存在协同作用。两者之间的协同作用导致P型聚合物与N型钒氧化物纳米管之间形成p-n结,降低耗尽层势垒高度,使其灵敏度得到提高。
In recent years, great attention has been focused on the nanostructured materials due to their special structures and excellent properties. Vanadium oxide nano-materials have a large number of selective effects with gas sites that can be used in the production of high-sensitivity gas sensor. Among various kinds of them, vanadium oxide nanotubes has great potential for improving gas materials sensitivity, stability selectivity, and other properties because of the larger surface area and more suitable for gas absorption. Thus, we selected vanadium oxide nanotubes (VONTs) as our research objects, and modified the surface morphology, systemically studied the synthesis, the relations of materials structure, morphology and gas sensing properties. Some progresses were gained. The details of our research works are presented as follows:
1. The gas sensing properties of VONTs were measured by mixing detected gas and air in static state. The test results showed that VONTs have good gas sensitivity to ethanol and shorter response and recovery time. The best working temperature for VONTs is 270℃. The sensitivity can reach 2.4 for 1000 ppm ethanol at 300℃and the threshold value is 50 ppm. It can be known that one dimensional nanomaterials can formed a large number of gas channel by crossing each other, more big surface volume ratio is the reason caused a higher gas sensitivity of VONTs.
2. Fe2O3 nanoparticles surface modified VONTs was synthesized by means of hydrothermal methods. The effects of the factors such as solvent, reactive temperature, reactive time on the structure and gas sensing properties of the samples were studied. The results of gas sensing properties showed that Fe2O3 modified VONTs gas sensor has higher sensitivity than VONTs gas sensor. The threshold value is as low as 10 ppm, and the sensitivity can reach 7.4 for 1000 ppm ethanol at 300℃. It can be guessed that Fe2O3 modified VONTs belongs to surface-controlled sensing mechanism according to the curves of resistance vs temperature and sensitivity vs temperature as well as Fe2O3 size effect of VONTs gas sensitivity. The appearance of Fe2O3 supply more active sites, and VONTs can provide a channel for charge transfer, lead to an improvement of sensitivity.
3. Ag or Pd surface modified VONTs was synthesized by microwave heating method. The gas sensing properties showed that have the best stability and lower working temperature among the tested VONTs. Modified VONTs with Ag can improve the selectivity to ethanol, and modified with Pd can improve the sensitivity to NH3. This is to take advantage of the spillover effects afforded by the metal nanoparticles as a result of the "electronic sensitization" mechanism.
4. VONTs/polyaniline (VONTs/PANI) and VONTs/polypyrrole (VONTs/PPY) core-shell structure with have been synthesized through an in situ polymerization of poly monomers in the presence of prepared VONTs. The thickness of PANI and PPY coatings are 20 and 40 nm, respectivly. The hybrids were characterized by TEMS SEM、XRD、IR、TG. Experimental data showed certain synergetic interaction existed in the hybrids, probably resulting in the enhanced thermal stability of polymer coatings. Gas sensing tests showed that the core-shell structure possessed very fast response and high sensitivity at room temperature, implying its potential application for gas sensor. Especially, the sensitivity of VONTs/PANI to 1000 ppm NH3 is as high as 6.4, and the sensitivity of VONTs/PPY to 1000 ppm ethanol is 2.4. The very fact that the synergic interaction between intimately contacted p-type Polymer and n-type VONTs form p-n junctions. The p-n junctions formed in the donor-acceptor system could increase the depletion barrier height, thus leading to an improved response of the sensor.
1.将钒氧化物纳米管材料制作成旁热式气敏元件,通过静态配气法测试其气敏性能。研究发现钒氧化物纳米管气敏元件对乙醇气体具有较高的灵敏度和较短的响应恢复时间,且最佳工作温度为270℃。330℃时对1000 ppm乙醇气体的灵敏度高达2.3,探测极限低至50ppm。通过纳米管结构与性能相关性的分析,指出一维钒氧化纳米管独特的层状形状形成大量气体通道,具有较高的比表面积、自身易发生氧化还原反应可能是其灵敏度较高的原因。
2.利用二次水热法合成了表面负载Fe203纳米颗粒的钒氧化物纳米管。通过研究溶剂、反应温度、耦合剂等因素对表面负载Fe203纳米颗粒钒氧化物纳米管的结构与性能的影响,发现经Fe203纳米颗粒表面修饰的钒氧化物纳米管气敏性能得到大幅度提高。在190℃,表面负载Fe203纳米颗粒的钒氧化物纳米管对乙醇气体的探测极限为10 ppm。在330℃,对1000 ppm乙醇气体的灵敏度高达7.4。根据复合结构的电阻-温度曲线、灵敏度-温度曲线,Fe203颗粒尺寸对纳米管灵敏度的影响等结果推断其气敏机理为表面吸附氧控制模型,Fe203颗粒的存在相当于增加了活性位点,纳米管的-维形貌为电子的转移提供了快速通道,两者共同作用的结果导致灵敏度得到大幅度改善。
3.采用微波辐照法分别在钒氧化物纳米管表面负载了形状均一、分散均匀的Ag和Pd纳米颗粒,粒径约10 nm。与纯钒氧化物纳米管相比,贵金属表面修饰的钒氧化物纳米管气敏元件具有更好的稳定性和更低的工作温度。Ag纳米粒子表面修饰可以明显提高钒氧化物纳米管对乙醇的气体选择性。Pd纳米粒子表面修饰可以提高钒氧化物纳米管对氨气的灵敏度。元件气敏性能得到改善的主要原因是贵金属的“电子增敏作用”。
4.采用聚合物单体的原位化学聚合制备了包覆厚度5-20 nm的钒氧化物纳米管/聚苯胺核-壳结构和包覆层厚度为40 nm的钒氧化物纳米管/聚吡咯核-壳结构。通过聚合物的包覆,实现了钒氧化物纳米管气敏元件对气体的室温检测,极大拓宽了钒氧化物纳米管气敏材料的应用范围。其中钒氧化物纳米管/聚苯胺核-壳结构气敏元件在室温下对1000 ppm氨气的灵敏度高达6.2。钒氧化物纳米管/聚吡咯核-壳结构在室温下对1000 ppm乙醇气体的灵敏度为2.4。通过一系列结构与性能表征,发现聚合物与钒氧化物纳米管并不是简单的混合,两者之间存在协同作用。两者之间的协同作用导致P型聚合物与N型钒氧化物纳米管之间形成p-n结,降低耗尽层势垒高度,使其灵敏度得到提高。
In recent years, great attention has been focused on the nanostructured materials due to their special structures and excellent properties. Vanadium oxide nano-materials have a large number of selective effects with gas sites that can be used in the production of high-sensitivity gas sensor. Among various kinds of them, vanadium oxide nanotubes has great potential for improving gas materials sensitivity, stability selectivity, and other properties because of the larger surface area and more suitable for gas absorption. Thus, we selected vanadium oxide nanotubes (VONTs) as our research objects, and modified the surface morphology, systemically studied the synthesis, the relations of materials structure, morphology and gas sensing properties. Some progresses were gained. The details of our research works are presented as follows:
1. The gas sensing properties of VONTs were measured by mixing detected gas and air in static state. The test results showed that VONTs have good gas sensitivity to ethanol and shorter response and recovery time. The best working temperature for VONTs is 270℃. The sensitivity can reach 2.4 for 1000 ppm ethanol at 300℃and the threshold value is 50 ppm. It can be known that one dimensional nanomaterials can formed a large number of gas channel by crossing each other, more big surface volume ratio is the reason caused a higher gas sensitivity of VONTs.
2. Fe2O3 nanoparticles surface modified VONTs was synthesized by means of hydrothermal methods. The effects of the factors such as solvent, reactive temperature, reactive time on the structure and gas sensing properties of the samples were studied. The results of gas sensing properties showed that Fe2O3 modified VONTs gas sensor has higher sensitivity than VONTs gas sensor. The threshold value is as low as 10 ppm, and the sensitivity can reach 7.4 for 1000 ppm ethanol at 300℃. It can be guessed that Fe2O3 modified VONTs belongs to surface-controlled sensing mechanism according to the curves of resistance vs temperature and sensitivity vs temperature as well as Fe2O3 size effect of VONTs gas sensitivity. The appearance of Fe2O3 supply more active sites, and VONTs can provide a channel for charge transfer, lead to an improvement of sensitivity.
3. Ag or Pd surface modified VONTs was synthesized by microwave heating method. The gas sensing properties showed that have the best stability and lower working temperature among the tested VONTs. Modified VONTs with Ag can improve the selectivity to ethanol, and modified with Pd can improve the sensitivity to NH3. This is to take advantage of the spillover effects afforded by the metal nanoparticles as a result of the "electronic sensitization" mechanism.
4. VONTs/polyaniline (VONTs/PANI) and VONTs/polypyrrole (VONTs/PPY) core-shell structure with have been synthesized through an in situ polymerization of poly monomers in the presence of prepared VONTs. The thickness of PANI and PPY coatings are 20 and 40 nm, respectivly. The hybrids were characterized by TEMS SEM、XRD、IR、TG. Experimental data showed certain synergetic interaction existed in the hybrids, probably resulting in the enhanced thermal stability of polymer coatings. Gas sensing tests showed that the core-shell structure possessed very fast response and high sensitivity at room temperature, implying its potential application for gas sensor. Especially, the sensitivity of VONTs/PANI to 1000 ppm NH3 is as high as 6.4, and the sensitivity of VONTs/PPY to 1000 ppm ethanol is 2.4. The very fact that the synergic interaction between intimately contacted p-type Polymer and n-type VONTs form p-n junctions. The p-n junctions formed in the donor-acceptor system could increase the depletion barrier height, thus leading to an improved response of the sensor.
引文
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