摘要
近年来，随着工业化进程的加快，人们所使用和接触的气体越来越多，工业生产和室内装修所使用的有机挥发性气体（VOCs，如丙酮、甲醛、苯和甲苯等）；煤矿瓦斯和家庭燃气等易燃易爆气体（如H_2、CH_4、CO）；固定燃烧装置和汽车尾气排放的有毒有害气体（如NO_x、NH_3、H_2S、SO_2、Cl_2）等不仅污染环境、影响生态平衡，而且严重危害人类的健康。因此，要求对这些气体成分进行检测、报警的领域也日益扩大。水蒸气作为一种特殊的气体，可谓无处不在，从航空航天、气象预报、温室种植到日常家庭生产和生活活动都与水蒸气（湿度）密切相关。因此，开发出具有高灵敏、高选择、快速响应、小型化的气体和湿度传感器是人类迫切需要解决的问题。半导体型化学传感器兼具以上优点，而受到学术界和产业界的广泛关注。半导体型化学传感器是以氧化物半导体为敏感材料，基于待测气体与敏感元件之间的相互作用，引起电特性变化来测量气体浓度的。现阶段研究表明，开发和设计具有多孔结构、大比表面积的氧化物半导体，是改善化学传感特性的有效方案之一。
介孔材料具有管状、蠕虫状、球形等孔道结构，增加了材料的比表面积，而且还具有孔道大小均匀可调、表面易于功能化修饰、极强的吸附能力等显著的优点。因此，介孔材料作为一种新型高科技材料，广泛应用于化学传感器、催化剂、吸附剂、光电器件等重要的领域。
面向高性能化学传感器的构建，考虑到介孔材料所具有的优点，如果能把氧化物半导体这一类典型敏感材料介孔化，将会对传感器的化学敏感特性有所提高。本文采用硬模板法合成有序的介孔氧化物半导体以及对其进行修饰，进而探讨它们对几种典型气体（挥发性有机气体CH_3COCH_3、易燃易爆气体H_2、大气污染物NO_2）和湿度（H_2O）的敏感特性，并对反应机理进一步阐释。
第二章，以二维六方介孔二氧化硅SBA-15为硬模板，通过纳米浇铸的方法合成具有介孔结构的SnO_2。通过对材料表征，可以得知采用硬模板法合成的介孔SnO_2具有有序的介孔孔道结构、高的热稳定性，而且比采用沉淀法合成的纳米颗粒SnO_2表现出更高的比表面积和孔体积。以两种类型SnO_2为敏感材料制作传感器，对挥发性有机气体丙酮进行气敏性能测试，发现具有介孔结构的SnO_2比普通的纳米颗粒SnO_2具有更高的灵敏度。其主要原因是介孔SnO_2敏感材料具有的有序孔道结构有利于目标气体在敏感材料内部进行扩散；高的比表面积能在敏感体表面提供更多的活性位点，从而导致目标气体更容易在其表面进行反应。
在成功合成介孔SnO_2的基础上，第三章将结合贵金属掺杂的方法提高其对典型的可燃性气体氢气的敏感性能。以介孔SBA-15为硬模板，通过纳米浇铸法成功合成了有序的介孔SnO_2和Pd/SnO_2。分别采用直接原位法和间接浸渍法对介孔SnO_2进行贵金属Pd掺杂，探讨掺杂方法对敏感材料结构以及对H_2敏感特性的影响。结果表明，通过直接原位掺杂法比通过间接浸渍掺杂法制得的敏感材料对氢气的灵敏度更高。直接掺钯法合成的介孔Pd/SnO_2传感器具有高灵敏、低检测下限、快速响应等良好的气敏特性，这与敏感材料的多孔性、高比表面积以及掺杂剂Pd的状态密切相关。
一般来说，气体分子在三维结构材料比在二维结构材料中的扩散效果更好。在上两章研究的基础上，第四章进一步利用三维立方的介孔二氧化硅KIT-6作为硬模板，通过纳米浇铸的方法合成介孔铁掺杂的三氧化二铟（Fe-doped In2O_3）。它具有高比表面积、周期性排列的有序介孔孔道结构以及结晶良好的孔壁。基于介孔Fe-doped In2O_3传感器对具有强烈刺激性和腐蚀性的大气污染物NO_2气体具有良好的敏感特性。介孔Fe-doped In2O_3敏感材料优异的气体敏感特性除了源于其较高的比表面积和孔体积之外，与铁掺杂能提高对NO_2的吸附能力密切相关。
以上几章的研究已经表明，采用纳米浇铸法合成的结晶性良好的介孔氧化物半导体是一种极具潜力的气体敏感材料。由于介孔材料具有优异的物理和化学性质，同样也可以作为湿度传感材料。第五章，以SBA-15为硬模板，通过纳米浇铸法合成了介孔钙钛矿型LaFeO_3。以介孔LaFeO_3为敏感材料制作了陶瓷湿度传感器，并对其湿敏特性进行测试。结果表明，测试频率在10Hz条件下，当相对湿度从11％变化到98％时阻抗变化超过5个数量级，在整个湿度区域内显示了高的灵敏度、快的响应时间、低的湿滞和良好的长期稳定性。介孔LaFeO_3比普通的体相材料LaFeO_3具有更优异的湿度敏感特性。通过复阻抗谱图（能斯特谱图）对湿度传感器的敏感机制进行了研究。
本论文系统地研究了硬模板法制备介孔氧化物半导体以及对其化学传感特性研究。确立一些典型介孔氧化物半导体的制备方法，对其化学传感特性进行测试。结果表明，介孔氧化物半导体比普通纳米颗粒材料具有更优异的气敏和湿敏特性，为构筑高性能的化学传感器提供了途径。
In recent years, the rapid development of industrialization, various types of gasare frequently used. Volatile organic gases (VOCs, such as C2H5OH, CH_3COCH_3,HCHO), flammable or explosive gases (such as H_2, CH_4, CO); toxic and harmfulemissions (such NO_x、NH_3、H_2S、SO_2、Cl_2) not only pollute the environment, but alsohave seriously harm to human health. Requirements detection of these gascomponents are also increasing. Water vapor as a special kind of gas, play a vital rolein numerous fields, such as environmental monitoring, food processing industries,medicine, meteorology and research labs. All nature processes are closely related towater vapor (humidity). Therefore, the development of high sensitivity, fast response,low detection limit, high selectivity, portable gas and humidity sensors are urgentissue to be solved.
Mesoporous materials with tubular, worm-like and spherical pore structure, havehigh surface area, large pore volume, uniform pore diameter, easy surfacefunctionalization and strong adsorption capacity, rendering the unique materials usefulin wide spectrum of fields. They are widely used in catalysts, adsorbents,optoelectronic devices, and other important areas.
Mesoporous metal oxides are also considered promising candidates in thedevelopment of chemical sensors. In this paper, several mesoporous metal oxideshave been successfully synthesized by hard template method to detect several typical gas (CH_3COCH_3, H_2, NO_2) and humidity (H_2O), and the sensing mechanism is furtherto be discussed.
The ordered mesoporous SnO_2have been successfully synthesized viananocasting method using the hexagonal mesoporous SBA-15as template. A study ontheir gas sensing properties for CH_3COCH_3reveals that the sensor utilizingmesoporous SnO_2displays swift response and recovery rate, and much highersensitivity to CH_3COCH_3compared to those based on nanoparticle SnO_2viaprecipitation technique. It is supposed that the outstanding gas sensing properties ofmesoprous SnO_2sensor synthesized by hard template is arisen from the large surfacearea and high porosity, which lead to highly effective surface reaction between thetarget gas molecules and the surface active sites in mesoporous SnO_2sensor.
The ordered mesoporous SnO_2and Pd/SnO_2have been successfully synthesizedvia nanocasting method using the hexagonal mesoporous SBA-15as template. Astudy on their gas sensingproperties for H_2reveals that the sensor utilizing Pd/SnO_2via direct synthesis method displays swift response and recovery rate and much highersensitivity to H_2compared to those based on mesoporous SnO_2and Pd/SnO_2viaimpregnation technique. It is supposed that the outstanding gas sensing properties ofPd/SnO_2sensor synthesized by direct synthesis method is arisen from the largesurface area, high activity and well dispersion for Pd additive, as well as high porosity,which lead to highly effective surface reaction between the target gas molecules andthe surface active sites in Pd/SnO_2.
The utilization of mesoporous KIT-6silica as a hard template has turned out to bea versatile tool for the synthesis of mesoporous Fe-doped In2O_3in the nanocastingprocess. It exhibits high specific surface area, oredered periodically arrangedmesopores structure with well crystalline walls and high thermal stability. The productis a promising material for application as gas sensor, since its excellent physical andchemical properties. The Gas sensing measurements reveal significantly increasedsensitivity response to NO_2gas in comparison with the mesoporous pure In2O_3. It issupposed that the outstanding gas sensing properties of the mesoporous Fe-dopedIn2O_3sensor is attributed to higher specific surface area and the pore volume. Besides, Fe species loaded on the sensor is effective to adsorb NO_2gas on the surface, which isalso beneficial to the sensitive response of the sensor.
Mesoporous LaFeO_3was successfully synthesized via the nanocasting methodby using SBA-15as a replica matrix. A ceramic humidity sensor based on themesoporous LaFeO_3was fabricated and evaluated. Humidity sensing measurementsreveal that impedance greatly changes by more than five orders magnitude when therelative humidity varies from11%to98%at10Hz, and it also displays high response,fast response time, low hysteresis and long-time stability in the entire humidity region.The sensing mechanism of humidity sensors was interpreted by the compleximpedance spectra (Nyquist plot). Furthermore, the sensor based on the mesoporousLaFeO_3displays the higher response compared with that of bulk LaFeO_3prepared bythe sol–gel method. It can be concluded that thus-obtained mesoporous LaFeO_3is anexcellent material for application as humidity sensor because of their high surfacearea and pore volume with mesoporous structure.
In the paper, we have fabricated of mesoporous oxide semiconductor and studiedof chemical sensing properties. The results show that the mesoporous oxidesemiconductor sensing materials display more excellent gas and humidity sensingperformence than that of nanoparticles sensing materials. It provides a new strategy tobuild excellent chemical sensors.
引文
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