【作者】 郭正；

【导师】 刘锦淮；

【作者基本信息】 中国科学技术大学 ， 无机化学， 2008， 博士

【摘要】 半导体氧化物气体传感器发展至今已有很长历史,提高敏感性能一直是其研究所追求的目标。特别是灵敏度和选择性,它们是制约传感器实际应用的两个重要因素。如何从根本上改善气体传感器的灵敏度以及提高选择性,实现对待测物的低检测限和定性识别依然是目前传感器研究的热点之一。纳米材料的出现以及纳米科技的发展为传感器敏感性能的改善提供了新的契机。近年来,半导体氧化物纳米材料的气敏性研究越来越受到人们重视,其中多孔结构的纳米材料因具有更大的活性表面积而倍受关注。合成具有多孔结构的半导体氧化物纳米材料来制作气敏元件,对提高传感器敏感性能具有非常重要的意义。本论文主要是在合成多孔氧化物纳米材料的基础上,进一步考察了它们的气敏特性及其它相关性质。此外,以多孔氧化物为气敏材料设计制作了一种结构新颖的传感器件,通过与气相色谱分离柱联用,探索并提出了弥补气体传感器在实际检测中存在选择性不足的新方法。主要内容如下:一、水热法合成了类碱式碳酸镉化合物纳米线;以其为前驱体,在空气中高温煅烧首次制备了多孔氧化镉纳米线。详细研究了前驱体形貌及组分随煅烧温度的变化,提出了氧化镉纳米线多孔结构的形成机制。此外,气敏性研究表明:由多孔氧化镉纳米线制作的传感器对低浓度的氮氧化物（NO_x）表现出良好的气敏性能。检测限低,对1 ppm的NO_x仍然有明显的敏感响应;拥有高的信噪比;同时具有良好的选择性,对有机体还原性气体几乎没有明显的响应;且功耗低,工作温度仅约为100℃。光学性质研究发现:多孔氧化镉纳米线的PL谱呈现出发射波长随激发波长的增加而红移;对于UV-vis吸收光谱,在505nm处有一个较宽的吸收峰。二、合成了单分散、粒径大小可控的碳质纳米粒子。以碳质纳米粒子为模板,成功地制备了多孔结构的氧化铟纳米空心球。表征结果显示:In₂O₃纳米球大小约为200 nm;壳层厚约30 nm,由粒径大小约为6-13 nm的In₂O₃纳米晶和纳米孔组成。与实心纳米球相比,独特的空心和多孔结构的In₂O₃纳米球有利气体分子的扩散,同时应具有较大的活性表面积。气敏性研究表明:它们对乙醇、甲醇、丙酮和乙醚等有机挥发性气体表现出良好的气敏响应特性,如高灵敏度、低检测限和可逆性,充分体现了多孔纳米材料在提高传感器气敏性能中的作用。此外,为了理解多孔In₂O₃纳米空心球的良好气敏性能,提出了其气敏响应模型。光学性质研究发现:在309 nm处多孔In₂O₃纳米空心球有一个强的紫外吸收峰;同时,与已报道的In₂O₃纳米材料类似,在室温下也表现出荧光性质。三、为间接实现气体传感器在混合样品检测中的选择性（即对待测物定性识别）,提出了气相色谱柱和气体传感器联用技术。以多孔气敏性氧化物为敏感材料,设计制作了一种结构新颖的传感器件应用为气相色谱检测器。通过对甲醇、乙醇、异丙醇以及它们混合样品的测试,成功地证实了气相色谱柱和气体传感器联用技术的可行性以及独特优点。基于不同浓度甲醇、乙醇、异丙醇以及它们混合样品的测试,初步探讨气体传感器对各组分响应的灵敏度与浓度关系。结果表明气体传感器用作气相色谱检测器对样品的定量分析也具有一定的参考价值。通过研究柱前压和柱温等因素对气相色谱分离以及传感器检测的影响,发现整个检测过程遵循气相色谱仪的工作原理。此外,该联用技术的实现同时也为发展便携式气相色谱仪提供了新的思路。更多还原

【Abstract】 Improving gas-sensing properties has been being a pursuing goal, in spite of the development of gas sensors based on semiconductor oxides with a long history. Especially for sensitivity and selectivity, they are two important factors, which could affect the application of gas sensors. In order to realize low detection limit and the qualitative identification, the topic about how to improve the sensitivity and selectivity is still a critical issue about the research of gas sensors. Recently nanomaterials and nanotechnology provide new opportunities for improving the performance of gas sensors. In the past several decades, the sensing properties of semiconductor metal oxide nanomaterials have been widely investigated. Owing to the existence of the large activated surface areas, it could cause the detected gas samples to easily diffuse and interact with sensing materials, especially for porous nanomaterials. Therefore, the syntheses of porous nanomaterials would be of importance for improving gas sensing properties.In this dissertation, many porous semiconductor oxide nanomaterials have been prepared. Their sensing and other properties have also been investigated. Furthermore, based on as-prepared hollow and porous In₂O₃ nanospheres, a novel structure sensor device has been fabricated. In order to improve the selectivity of gas sensors, the gas chromatography was employed to separate the mixture sample, combining with gas sensors used to as a detector. The main conclusions are summarized as follows:1. Highly porous （CdO） nanowires have been prepared by calcining the hydroxy and carbonate-containing cadmium compound precursor nanowires in air, which have been synthesized through hydrothermal method. In order to illustrate the formation mechanism of porous structures, the morphology and composition evolvements of precursor nanowires were further investigated under different stages of the calcining process. Gas sensing properties have been explored for the sensor device fabricated with highly porous CdO nanowires. The results demonstrate that it has good response （even for 1 ppm concentration） owing to its special structure, great selectivity to NO_x （no response to reducing organic gases）, high signal-to-noise ratio, and low power. Furthermore, the UV-visible absorption spectrum of the porous CdO nanowires presents a broad absorption peak at 505 nm; and the photoluminescence band shifts as excitation wavelength changes. 2. Monodisperse and diameter controllable carbonaceous nanoparticles have been synthesized. Hollow and porous In₂O₃ nanospheres have been prepared by the hydrolysis of InCl₃ using carbonaceous spheres as templates in combination with calcination. Based on the observation of scanning electronic microscopy （SEM） and transmission electron microscopy （TEM）, it has been revealed that the as-prepared In₂O₃ nanospheres have a uniform diameter of around 200 nm and hollow structures with thin shells of about 30 nm consisted of numerous 6-13 nm nanocrystal and nanopores. Owing to the hollow and porous structures, In₂O₃ nanospheres possessing more active surface area exhibit a good response, low detection limit and reversibility to some organic gases such as methanol, alcohol, acetone and ethyl ether. In addition, the response mechanism of hollow and porous In₂O₃ nanospheres to organic gases has been proposed. Furthermore, these prepared In₂O₃ spheres showed a UV-visible absorption peak centered at around 309 nm; and their photoluminescence spectra have also been investigated.3. In order to improve the selectivity of gas sensors, the idea of semiconductor sensors combined with the gas chromatography was offered and investigated. Based on as-prepared hollow and porous In₂O₃ nanospheres, a novel structure sensor device has been fabricated, which was used to be a new chromatography detector offering another approach for preparing a portable gas chromatograph. The experimental results show that the above idea is feasible. It could also be helpful for quantitative analysis. Furthermore, the effecting factors, such as the pressure and temperature of column, were also explored.更多还原