【作者】 刘艳丽；

【导师】 俞汝勤； 沈国励；

【作者基本信息】 湖南大学 ， 分析化学， 2005， 博士

【摘要】 工业化发展为人类创造财富的同时,对环境也造成了很大的污染。工业生产中使用的气体原料和生产过程中产生气体的种类和数量越来越多,这些气体中,有毒、有害气体不仅污染环境,而且有产生爆炸、火灾和使人中毒的危险。因此,有必要对环境中的大气进行实时检测。基于半导体金属氧化物的电阻型气体传感器,具有灵敏度高、选择性好、稳定性高、易于微型化和自动化等优点,在工业控制和环境监测等领域具有广泛的应用前景。纳米材料,因其具有大的比表面积、高的表面活性,能使半导体金属氧化物的气敏性能显著提高,因此利用纳米合成技术改进气敏材料的性能已成为今后气敏材料发展的主导方向之一; 另外,选择适当的添加剂对气敏材料进行掺杂是提高材料气敏性能的有效方法之一。本论文一方面采用室温固相化学反应法、溶剂热法、有机溶液氧化-还原法等方法合成了一系列纳米半导体金属氧化物,并构建成旁热式气体传感器用于气体的检测; 另一方面,对部分所得纳米颗粒进行贵金属掺杂,利用贵金属良好的催化特性,实现对材料性能的增敏作用。主要完成了以下研究工作: 1、利用室温固相化学反应法制备了一系列的半导体纳米复合氧化物。室温固相化学反应是指在室温或近室温条件下的固-固相化学反应,该法制备无机纳米材料是一个全新的课题,它不需要溶剂,从根本上消除了溶剂化作用,使反应在一个全新的环境下进行,整个反应过程经历扩散、反应、成核以及核的生长四个步骤,在实验体系中加入适量的无机盐来控制材料的定向生长而得到粒径细小且分布均匀的纳米材料。本论文中,采用价格相对低廉的无机盐作为前驱体,并在体系中加入适量的NaCl以控制所得材料的粒径而得到Mg₂Fe₂O₄、CdSnO₃、NiFe₂O₄等复合氧化物。实验结果表明,该制备方法简化了工艺流程,具有污染小、产率高、节约能源等优点。贵金属作为活泼的催化剂,通常被用来作为掺杂剂来提高半导体材料的气敏性能。本论文中,在用室温固相化学反应法制得纳米材料的基础上,采用浸渍法对部分所得纳米材料进行不同贵金属掺杂,并对贵金属影响原材料的气敏性能及机理进行了分析与探讨。（1）第二章中,利用该法得到了球形Mg₂Fe₂O₄纳米材料,并将该材料制成旁热式气体传感器元件,检测了该元件对CH₄、H₂S、LPG和酒精气体的灵敏度情况。该元件在工作温度为160 oC时,能实现对低浓度H₂S的有效检测,而在工作温度为335 oC时,能实现对酒精气体的有效检测。相对其它被测气体,其抗干扰性很好。更多还原

【Abstract】 The development of industry has brought much more treasures to people. However, more and more poisonous gases produced in the development process are not only non-friendly to the environment but also dangerous to people. With the fast development of the society, people need higher efficient methods to detect the poisonous gases. Gas sensors based on metal oxide semiconductors have the advantages of high-sensitivity, nice-selectivity as well as easy miniaturization and automation. They can be applied to a wide range of analytical tasks, such as industrial control and environmental monitoring. On the one hand, nano-crystalline particles, exhibiting a large surface area with diameter less than 100 nm, might be favorable for improving the sensitivity of gas-sensing material. Carrying out researches on the preparation methods of nano-materials is one of the new research directions of current gas sensing materials. On the other hand, surface modification by proper choice of additives or dopants is often used to improve the response of the gas sensing materials for particular applications. According to the above-mentioned directions, a series of investigations including preparation of nano-materials, structural analysis and actual application in gas sensing field have been performed in this dissertation. In part one, a series of nano-sized mixed oxides has been obtained by solid-solid chemical reaction at room temperature which is a new direction in preparing inorganic nano-materials. This method doesn’t use solvent and avoids the effect of solvent. There are four steps in a typical proceeding of solid-state reaction: diffusion, reaction, nucleation and growth. The growth of the final particles is inhibited by the inorganic salts added in the reaction system. We have obtained Mg2Fe2O4, CdSnO3 and NiFe2O4 using cheap inorganic salts as precursors. The process used here is a high-yielding, low-cost procedure and environment friendly for the synthesis of the nano-materials above-mentioned. Furthermore, the noble metals, well known as active catalysts, have been confirmed to possess the promoting effects on many semiconductor gas sensors. So Pt, Pd and Au are used to better the gas sensing properties of the final materials obtained in this thesis by the impregnation technique. In chapter 2, n-type semi-conductive nanometer material MgFe2O4 was synthesized by solid state reaction of inorganic reagents MgSO4, Fe(NO3)3?9H2O, and NaOH. Conductance responses of the nanocrystalline MgFe2O4 thick film were measured by exposing the film to reducing gases like methane (CH4), hydrogen sulfide (H2S), liquefied petroleum gas (LPG) and ethanol gas (C2H5OH). It was found that the sensor exhibited various sensing responses to these gases at different operating temperature and the gas sensor can realize the detection of low concentration of H2S and ethanol at 160 oC and 335 oC, respectively. Furthermore, the sensor exhibited a fast response and a good recovery. Successive on and off responses could be repeated without observing major changes in the response signal. In chapter 3, CdSnO3, a semiconducting oxide with perovskite structure, was prepared by solid state reaction of inorganic reagents 3CdSO4?8H2O, SnCl4?5H2O and NaOH. Noble metal additive Pt of different concentrations from 0.1 at.% to 2 at.% was incorporated into CdSnO3 by impregnation technique and the effect of Pt on the gas sensing properties of nano-crystalline CdSnO3 was studied. Conductance responses of the nano-crystalline CdSnO3 thick films were measured by exposing the films to C2H5OH, CO, CH4, C4H10, gasoline and LPG at different operating temperatures. It was found that sensors doped with Pt exhibited good sensitivity and selectivity to the vapor of C2H5OH and the optimum sensitivity is 68.2 obtained with the sensor doped with 1.5 at.% Pt. In chapter 4, ultrafine NiFe2O4 powders were prepared by solid state reaction of inorganic reagents, Ni(Ac)2, Fe(NO3)3, and NaOH. Noble metals such as Au, Pd and Pt with different concentration were incorporated into NiFe2O4 by impregnation technique. The gas sensing characteristic of NiFe2O4 nanopowder with and without different noble metal dopants were investigated. The electrical resistance response to H2S gas of the sensors based on the materials was investigated at different operating temperature and different gas concentrations. The results show that NiFe2O4 is a p-type semiconductor and the gas-sensing response of the doped NiFe2O4 sensors was superior to that of the undoped ones. The sensor response increased linearly with the H2S gas concentration up to 100 ppm. The sensor with the 1.5 at.% Au doped NiFe2O4 showed excellent electrical resistance response towards 5ppm H2S gas and the sensor response was up to 35.8 at 300 oC. The 1.5 at.% Pt doped one was less sensitive to H2S but worked at lower temperature, 240 oC. The gas-sensing behavior of these materials with respect to various reducing gases like LPG, CH4, CO, C4H10 and H2 shows that the H2S gas sensor developed possesses an excellent selectivity. The interaction mechanism and correlations between the electricalresistance response and noble metal dopants were discussed. One-dimensional materials such as nanorods and nanowires have attracted much attention due to their specific physical properties and interesting application in nano-devices. The study of one dimensional (1D) materials has become a potential frontier in nanoscience and nanotechnology in the last few years. In part two, nano-sized flower-like ZnO and ZnO nano-rods were synthesized by a simple hydrothermal method and a solvothermal route, respectively (Chapter 5). The two methods are convenient, environment friendly, inexpensive and efficient process. The gas sensors based on the ZnO obtained by these two methods showed excellent responses and selectivity to ethanol gas and the responses and recoveries were both fast. In part three, ZnO nanorods were synthesized by a modified polyol process using inorganic reagents as the precursors (Chapter 6). The synthesis process without requirement of delicate equipments was a convenient, environment friendly, inexpensive and efficient method for preparing ZnO nanorods. Conductance responses of the ZnO nanorod thick film were measured by exposing the film to reducing gases like CH4, LPG, C4H10, H2 and C2H5OH. The results indicate that the device showed nice responses and selectivity to ethanol gas. Furthermore, the sensor exhibited a fast response and a good recovery property. In part four, a compound material of MWNTs coated with SnO2 was synthesized at ambient conditions, and the gas sensing properties of the material were studied (Chapter 7). Conductance responses of the compound materials were measured by exposing to reducing gases like CH4, CO, C4H10, LPG and ethanol gas. It was found that the device exhibited nearly non-sensing responses to CH4, CO and C4H10. While it showed good sensing responses to LPG and C2H5OH. Furthermore, the sensor exhibited a fast response and recovery within seconds and the gas-sensing responses increased linearly with the increment of the gas concentrations of LPG and ethanol. Many preparation methods described and nano-materials obtained in this dissertation aimed on the gas sensing materials. Their potential application area is not, however, limited to this kind of materials. In part five, nano-sized flower-like ZnO synthesized by a simple hydrothermal method was dispersed in the chitosan solution to form a ZnO/chitosan composite matrix for the fabrication of H2O2 biosensor in the complementary part of the thesis (Chapter 8). This composite combined the advantages of inorganic species (ZnO) and organic polymer (chitosan). The parameters affecting the fabrication and experimental conditions of biosensorswere optimized. Using hydroquinone as the mediator, the biosensor showed a fast response of less than 5 s with the linear range of 1.0×10-5 to 1.8×10-3 mol L-1H2O2 with a correlation coefficient of 0.995 (n =20). The detection limit of the sensor was found to be 2.0 μmol L-1, based on a signal-to-noise ratio of 3. The biosensor exhibited satisfactory reproducibility and stability and retained about 78% of its original response after 40 day storage in a phosphate buffer at 4 °C.更多还原