| 题名 | 单元强化的几种金属氧化物气敏材料的制备及其性能研究 |
| 作者 | 姚明水 |
| 学位类别 | 博士 |
| 答辩日期 | 2014-04 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 袁方利 |
| 关键词 | 金属氧化物 气敏传感器 室内空气污染 介孔结构 掺杂修饰 |
| 其他题名 | Synthesis of Units Enhanced Metal Oxides Based Gas Sensing Materials and Their Properties |
| 学位专业 | 材料学 |
| 中文摘要 | 室内空气污染问题日益引起重视，气敏传感器由于具有在线、快速检测且无需专业人员操作的优势而具有极大的研究和应用价值，半导体电阻型气敏传感器正是其中一个重要分支。气敏过程分成三个单元：气体扩散与分子捕捉单元、表面反应单元和电子传输单元，研究人员围绕这三个单元进行了大量的金属氧化物气敏材料的制备和性能研究。我们一方面利用结构与形貌控制对气敏单元的增强，制备了ZnO纳米球带花、ZnO防风林型膜和单暴露晶面的八面体WO3；另一方面利用溶剂热法在保持结构和形貌同时引入掺杂元素制备了Sn掺杂ZnO层状多孔颗粒和相应的壁挂式气敏传感器样机。同时利用高频热等离子体在保持基本形貌同时引入掺杂元素制备了晶面比例可调且晶体表面改性的WO3八面体和Cr掺杂WO3多面体，主要研究内容如下： 1.利用LBZA（layered basic zinc acetate）前驱物和热解法制备ZnO纳米球带花等级结构（dp-ZnO-SFF），高度暴露的介孔纳米带和3D立体球带花等级结构相比于其他样品提供了更多的气体传输通道，增强了气体传输单元，使得更多的被检测气能够到达ZnO表面与O2-反应，提高电阻变化率进而提升响应值。对苯气体检测下限可低至0.007 ppm（R=0.1）。将自支撑ZnO纳米球带花阵列薄膜直接作为气敏膜的传感器（ZnO-SFF）能直接跳过滴加法的高温欧姆接触处理和不可避免的等级结构大量破坏而引起的性能退化，表现出更高响应值。本法前驱物LBZA的化学式为Zn5(OH)8Ac2-2x[CO3]x?zH2O，且单根LBZA纳米带是多层带面暴露晶面为（001）的薄膜有序堆叠而成，SAED表现为矩形点阵，随时间延长所得产物可简单表达为：Zn(OH)2-ZnO-LBZA-LBZC。 2.溶液法合成自支撑ZnO微型防风林薄膜（ZMW），有两个主要优点：一是单层有序的疏松纳米带花阵列；二是仅1-2层纳米晶的规则的多孔纳米带。二者共同形成了一个有效的微型防风林结构，既有利于气体在内部的扩散，也有利于对被检测气体分子的捕捉。ZMW的单层有序纳米带花阵列和超薄规则的带状分枝最利于气体分子的扩散和吸附，经过优化晶粒连接和结构上强化气体扩散，可检测痕量的苯气体（R50ppb = 0.3851 ± 4%），响应-恢复曲线良好，显示出其在精确检测方面的巨大潜力。Pt修饰ZMW对苯气体的最佳工作温度可降低至350℃，且响应值得到极大的提升。 3.水热法和溶剂控制合成了均一的Sn掺杂ZnO层状多孔颗粒（Sn-ZLPP），颗粒尺寸分布较窄，颗粒主要由介孔片层堆叠而成的多孔颗粒。该层状多孔颗粒的形成是酯化反应、Sn4+掺杂阻止ZnO晶核团聚、奥斯特熟化和卤素离子刻蚀的共同作用下形成的。Sn-ZLPP的高气敏性能原因：一是Sn掺杂引起的晶体表面修饰（更多的活性位点和晶体缺陷）和更低的活化能，这能够强化表面反应单元和电子传输单元；二是层状多孔等级结构（更多可到达晶体表面）和颗粒尺寸的减小（更高的比表面积）利于增强气体扩散和分子捕捉单元。多单元共同强化使得5.0 at.% Sn-ZLPP表现出良好的气敏性能，对苯和臭氧气体检测下限分别低于0.030 ppm和0.001 ppm（R=0.1）。同时，利用Sn-ZLPP基材料制备了壁挂式气敏传感器样机，经第三方检测，气敏传感器工作温度在0-50℃，探头工作温度在150-500℃，适应湿度范围为5%-90%，精度优于10%，检测下限臭氧可达0.0018 ppm，甲苯可达0.0030 ppm。 4. 热等离子体法制备了WO3八面体和Cr掺杂WO3多面体。WO3八面体单晶制备成气敏传感器为纯相的稳定态γ-WO3，对苯气体的最佳工作温度为400℃，其平均响应时间和恢复时间分别低至2.19 min和3.16 min，对苯气体的检测底限浓度可达到约0.15 ppm（R=0.1）。Cr元素加入WO3母体中促使WO6八面体中的钨原子更加偏离其中心位置，掺杂量越高则沿着[001]、[010]和[100]方向的晶体生长速度越慢，所以形貌表现出八面体-截角八面体和长方体的顺序变化。适量的Cr掺杂（2.5 at.%）既能降低气敏工作温度又能提升气敏响应值，但过量掺杂会降低其气敏性能。Au沉积能克服Cr掺杂引起的响应恢复较慢的缺点，并能进一步提升气敏响应值。响应和恢复时间分别加速至2.2 - 3.0 min和1.7 - 2.7 min，对苯气体的检测下限可低至0.01 ppm（R=0.1）。 |
| 英文摘要 | Nowadays, indoor air pollution is one of the most critical concerns for governments and individuals. Metal oxide (MOX) based gas sensors, owing to their portability, real-time operability and ease of use, have attracted great concentration. Under the guidance of unit enhancement theory, this work can be divided into the two aspects. Firstly, meso-porous and single crystal materials with specific exposed facets were synthesized by enhancing single gas sensing unit. Secondly, by appropriate doping while maintaining desirable porous structures or specific exposed facets, materials with enhanced multi-units were also fabricated. The main results were summarized as follows: 1. ZnO spherical nanobelt-flowers (dp-ZnO-SFF) were obtained by heating Zn5(OH)8Ac2?2H2O (LBZA, layered basic zinc acetate) precursors, and LBZA hierarchical structures with different morphologies were designed and selectively grown by controlling the growth conditions. The highly exposed surfaces of meso-porous nanobelt branches and the 3D porous hierarchical structure of dp-ZnO-SFF were favored for gas diffusion, which was responsible for its high sensing properties (detection limit for benzene: 0.007 ppm, R = 0.1). In addition, self-standing ZnO spherical nanobelt-flower film was also directly applied as the sensing film and showed high responses to benzene gas. The detailed structure investigation revealed that the LBZA nanobelt was constructed by single crystal LBZA belts with (001) plane on their top surfaces, and the corresponding SAED patterns were ordered dots arrays due to overlap of multi-belts. As the reaction proceeds, the structural evolution was confirmed as Zn(OH)2-ZnO-LBZA-LBZC. 2. The ZnO micro-windbreak film (ZMW) was synthesized based on LBZA precursor. The ZMW sensor exhibited the highest sensing response due to the enhanced gas diffusion in single layer ordered flower arrays (highly exposed surfaces) with ultra-thin porous nanobelts (high diffusion coefficient). The ZMW sensor preserved the superb response and recovery properties even at ppb-level benzene gas (R50ppb = 0.3851 ± 4%). Furthermore, the optimal operating temperature was reduced to 350°C and the responses were significantly improved by simply sputtering Pt on both faces of ZMW to enhance the surface reaction. 3. Sn doped ZnO layered porous particles (Sn-ZLPPs) were synthesized by a solvothermal method. Each Sn-ZLPP was constructed by multi-layers of ZnO nanosheet with a thickness of 10-20 nm, and each layer was constructed by nanopores and polycrystalline ZnO nanocrystals. Sn doping was found to be the key factor to control the layered porous structure, and 5.0 at.% Sn-ZLPP exhibited the best sensing response to VOCs. The key factors affected the sensing response in this work were summarized to be the activation energy, adsorption/desorption of oxygen ions, and the meso-porous hierarchical structure. As the stability of target gas increased, the optimal operating temperature shifted from 300°C to 500°C and the highest response shifted to the sample with high atomic ratio of Sn. The later shift was attributed to the alternate influence of the activation energy and adsorption/desorption of oxygen ions. The detection limit (R = 0.1) of 5.0 at.% Sn-ZLPP for benzene and ozone was 0.030 ppm and 0.001 ppm, respectively. The wall-mounted type gas sensor prototype was also fabricated based on Sn-ZLPP materials. Tested by the third-party, the gas sensor prototype showed good sensing properties (working temperature of the whole machine: 0-50°C, operating temperature of gas sensing materials: 150-500°C, humidity range: 5% - 90%, accuracy: better than 10%, detection limit: ozone 0.0018 ppm, toluene 0.0030 ppm). 4. WO3 octahedra and Cr doped WO3 polyhedra were synthesized via a simple one-step radio frequency (RF) thermal plasma technique. WO3 octahedra (pure γ-WO3) showed good sensing performances mainly due to highly exposed {111} planes (response time: 2.19 min, recovery time: 3.16 min, de |
| 语种 | 中文 |
| 公开日期 | 2015-07-08 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/15550]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 姚明水. 单元强化的几种金属氧化物气敏材料的制备及其性能研究[D]. 中国科学院研究生院. 2014. |
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