|Place of Conferral||北京|
|Keyword||爆炸物检测 氧化锌 掺杂 异质结 传感器阵列|
开发可便携、实时检测痕量爆炸物气氛的气敏传感器，对于反恐防暴和维护国家安全具有重要意义。然而，目前报道的爆炸物气敏传感器的响应时间较长，难以实现对爆炸物的快速检测，而且对响应机理缺乏系统的研究。本论文以可控制备富含表面缺陷的ZnO纳米颗粒为基础，通过过渡金属掺杂以及异质结构建两种方式，提升ZnO纳米颗粒对痕量爆炸物气氛的检测性能。系统探讨了影响响应大小、响应速度的内在因素，并在此基础上，通过构建传感器阵列，实现了对爆炸物气氛的定性识别。取得的创新性研究成果如下：一、通过调节退火温度调控ZnO纳米颗粒的表面缺陷，实现了对其气敏性能的调控。采用溶胶-凝胶法和退火处理手段制备了表面富含缺陷的ZnO纳米颗粒，电子顺磁共振谱（EPR）研究表明：与200、600 ℃的退火条件相比，经400 ℃退火处理的ZnO纳米颗粒含有的单电子氧空位表面缺陷数目最多。通过气敏测试表明，400 ℃退火处理的ZnO纳米颗粒对TNT饱和蒸气的响应最大，证明单电子氧空位表面缺陷数量与气敏响应大小密切相关。二、通过过渡金属（Fe、Co、Ni）掺杂ZnO纳米颗粒，提升其对爆炸物蒸气的响应速度，并明确其快速响应机理。一方面，Fe掺杂ZnO纳米颗粒表面富含单电子氧空位，保证了其较高的响应大小；另一方面，与纯相ZnO纳米颗粒相比，Fe掺杂可显著缩短其对硝基爆炸物气氛的响应时间和回复时间，掺杂后响应时间由28-43 s缩减到3-7 s，回复时间由32-40 s缩减到4-8 s。过渡金属掺杂改变了表面壳层的电子结构，在ZnO纳米颗粒的内部形成了一个局域电荷聚集层，导致内部电荷转移到表面缺陷的距离减小，缩短了电信号的变化时间，从而显著缩短了对爆炸物气氛的响应时间和回复时间。通过对Co、Ni掺杂的ZnO纳米颗粒的爆炸物检测性能，以及三种掺杂颗粒对高浓度苯、甲苯和硝基苯蒸气的响应性能，验证了该机理的普适性。以Fe、Co、Ni掺杂的ZnO纳米颗粒为敏感材料构建的传感器阵列，对室温下硝基爆炸物饱和蒸气和两种非制式爆炸物原料（硝酸铵和尿素）的蒸气均表现出良好的响应与区分能力。主成分分析（PCA）表明，传感器阵列可以在13秒内将9.1 ppb的三硝基甲苯（TNT）和4.9 ppt的黑索金（RDX）从高浓度的结构类似物，如12.5%的苯，3.85%的甲苯和394.7 ppm的硝基苯中很好的分辨出来。该研究首次建立了气敏响应速度与材料结构的内在联系，为传感器的实用化提供有力保障。三、通过ZnO/ZnS异质结纳米颗粒构建以及人为制造不同类型的表面缺陷，进一步明确影响气敏性能的决定因素。在ZnO纳米颗粒水热制备过程中加入硫源以及调节S/Zn比，成功实现了ZnO纳米颗粒向ZnO/ZnS异质结及ZnS纳米颗粒的转变，并探讨了硫化程度对硝基爆炸物（TNT、DNT）及非制式爆炸物原料（硫粉、黑火药、氯酸钾、高锰酸钾、硝酸铵和尿素）检测的影响。随着硫化程度的增加，样品的响应大小、响应时间和回复时间总体呈现先增加后降低的趋势。其中，当ZnO/ZnS=0.8：0.2时，整体检测性能最佳，其对TNT、DNT、黑火药、氯酸钾、高锰酸钾、硝酸铵和尿素的响应最大，达到30-50%，整体响应时间和回复时间较小，分别为10、12.6、13.3、14、10.7和9.6 s；14、13.6、14、11.3、15和12 s。通过对样品表面缺陷的测试，发现ZnO/ZnS异质结纳米颗粒的表面缺陷会随着退火气氛和温度的不同而改变，出现单电子氧空位（1.96）和另外一种表面缺陷（g=2.0）。单电子氧空位的数量决定了异质结材料的检测性能，另外的表面缺陷对检测性能基本无影响。该研究通过异质结构建的方式，进一步确定了单电子氧空位在提高ZnO纳米材料响应性能方面的决定性作用。
The development of portable real-time gas sensors for the detection of trace explosive vapors is of great significance for anti-terrorism and homeland security. However, most of the current chemiresistor sensors for explosives detection are suffering from long response time, which hinders the quick detection of explosives. Moreover, there is no systematical investigation on response mechanism of explosive vapor sensing.In this thesis, based on the controllable preparation of ZnO nanoparticles with enriched surface defect, the detection performance of ZnO nanoparticles has been enhanced by transition metal doping and by the construction of heterogeneous junction structure. A systematic study has been carried out on the underlying mechanisms for response value and response speed. And on this basis, the discriminative identification of explosive vapors has been achieved by constructing sensor array using these sensing marterials. The innovative achievements are summarized as following:(1) The surface defect of ZnO nanoparticles are regulated by adjusting the annealing temperature, realizing the control of the gas sensing properties of ZnO nanoparticles. A sol-gel and post-annealing process was adopted to prepare surface defect enriched ZnO nanoparticles. It is clearly shown in the EPR result that the ZnO nanoparticles annealed at 400 oC has the maximum number of single electron oxygen vacancy surface defect compared with ZnO nanoparticles annealed at 200 and 600 oC. In the gas sensing test, the ZnO nanoparticles annealed at 400 oC shows the largest response toward saturated TNT vapor, indicating that the amount of single electron oxygen vacancy surface defect is closely related to the gas sensing response of the materials.(2) The response speed of ZnO nanoparticles towards explosive vapors has been enhanced by transition metal doping, including Fe, Co and Ni. And the mechanism for the rapid response by transition metal doping has been discussed. On one hand, the significant amount of single electron oxygen vacancy defect on the surface of Fe-doped ZnO nanoparticles ensured its high response; on the other hand, compared with those of pure ZnO nanoparticles, both the response and recovery time of Fe-doped ZnO nanoparticle-based sensor decreased dramatically from 28-43 s and 32-40 s to 3-7 s and 4-8 s, respectively. The introduction of transition metal in ZnO nanoparticles changed the electron structure of the surface shell and created a local charge reservoir layer in the ZnO nanoparticles, which could reduce the charge transfer distance from the interior charge to the surface defect, and therefore result in a short change time of electron signal and hence a significant reduction of response and recovery time towards explosive vapors. The universality of this mechanism has been confirmed by the detection performance test of Co- and Ni-doped ZnO nanoparticles towards explosives, along with the gas sensing response of the three doped ZnO nanoparticles towards benzene, toluene and nitrobenzene vapors with high concentrations. The gas sensor array based on Fe-ZnO, Co-ZnO and Ni-ZnO exhibited well response and discriminative capability towards nitro aromatic explosive vapors and two types of improvised explosive vapors, namely ammonium nitrate and urea. The PCA analysis indicates that the sensor array can differentiate 9.1 ppb TNT and 4.9 ppt RDX from structurally similar interfering aromatic gases with high concentrations (12.5% benzene, 3.85% toluene and 394.7 ppm nitrobenzene) in less than 13 s. This study established the inherent relationship between the response speed and the structure of the sensing materials, providing a powerful guarantee for the practical application of explosive sensors.(3) In order to clarify the determining factor of the gas sensing performance, different types of surface defects have been created by constructing ZnO/ZnS heterogeneous structure. By adding sulfur source and adjusting the S/Zn ratio during the hydrothermal preparation of ZnO nanoparticles, the transformation from ZnO nanoparticle to ZnO/ZnS heterogeneous structure and further ZnS nanoparticles has been successfully accomplished. Besides, the influence of the degree of vulcanization on the sensing performance to nitro explosives, such as TNT and DNT, and improvised explosives, including sulfur, black powder, potassium chloride, potassium permanganate, ammonium nitrate and urea, was discussed. Generally, as the degree of vulcanization increases, the response, response time and recovery time of the samples increase first and then decrease. Among all of them, the ZnO/ZnS heterojunction structure (S/Zn=0.25) exhibits the best overall sensing performance, with the largest response of 30-50% towards TNT, DNT, surfur, black powder, potassium chloride, potassium permanganate, the short response time and recovery time of 10, 12.6, 13.3, 14, 10.7 and 9.6 s and 14, 13.6, 14, 11.3, 15 and 12 s, respectively. As shown in the surface defect tests, the type of surface defect in the ZnO/ZnS heterogeneous structure changes with the annealing temperature and the atmosphere, owning single electron oxygen vacancy surface defect (g=1.96) and the other type of surface defect (g=2.0). The sensing performance of the ZnO/ZnS heterogeneous structure was determined by the amount of single electron oxygen vacancy surface defect, while the influence of the other surface defect on the sensing performance is ignorable. This study further demonstrated that the single electron oxygen vacancy surface defect has a determining effect on the enhancement of the sensing performance of ZnO nanomaterials by constructing the heterojunction structure.
|屈江. ZnO纳米颗粒的结构改进方法及其对爆炸物气氛的增强检测性能研究[D]. 北京. 中国科学院大学,2016.|
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