Knowledge Management System Of Institute of process engineering,CAS
随着我国社会经济的快速发展，气敏传感器在检测环境空气质量、工业废气监测、易燃易爆与有毒害气体检测、人体呼出气体检测等领域的作用愈加重要。但是目前电阻型气敏传感器存在对低浓度的气体（小于5 ppm）灵敏度不高，选择性差等问题，因此开发高灵敏与高选择性的气敏传感器显得尤为重要。本论文从材料结构设计出发，尝试构建贵金属-氧化锌异质界面，探索这种异质界面在气敏传感中的作用，制备高灵敏的氧化锌基气敏材料。本论文选取苯、丙酮与二氧化氮作为目标气体，通过一系列表征与测试手段探究了贵金属-氧化锌异质界面对氧化锌基材料的气敏传感性能的作用与规律，并在此研究的基础之上，研制出一系列的高灵敏度与高选择性的贵金属-氧化锌核壳纳米颗粒气敏传感材料。本论文的主要研究内容和结果如下：（1）Au-ZnO异质界面的调控以及其对气敏传感性能的影响。采用两步法合成金-氧化锌核壳材料：首先采用水热法合成金-氧化锌核壳结构前驱体，利用CTAB调控ZnO在Au表面的生长速度；然后在高温下煅烧得到Au@ZnO颗粒。制备所得到的核壳Au@ZnO颗粒对低浓度苯（小于5 ppm）气敏性能较纯氧化锌有所提升，主要是因为Au与ZnO之间存在功函数差异引起了ZnO外壳电子状态改变。为了进一步地提高气敏性能，进行了尝试调控金的功函数的实验，对Au纳米颗粒进行Pd和Pt修饰。经过表面修饰之后，煅烧后的Au@ZnO核壳纳米颗粒ZnO外壳晶粒变大，气敏性能得到提高。（2）探索贵金属-氧化锌异质界面对氧化锌基材料气敏传感性能的作用机制。采用水热与煅烧两步法合成了三种Au@ZnO、Pd@ZnO与Pt@ZnO核壳纳米颗粒。利用多种表征手段分析这几种颗粒结构与物性上的差别，并比较它们的气敏性能。发现了贵金属-氧化锌异质界面对于ZnO基材料性质的影响规律性：贵金属与氧化锌之间功函数差异越大（功函数差异比较Pt@ZnO> Pd@ZnO≈Au@ZnO），表面氧比例越高，气敏性能越好。其中Pt@ZnO核壳纳米颗粒对低浓度苯有很高的灵敏度（对1 ppm苯响应为2.7），低检测下限（10 ppb），选择性和优秀的长期稳定性，以上表明Pt@ZnO是一种非常优秀的苯系物气敏材料。（3）发现元素掺杂与贵金属-氧化锌异质界面的协同作用。实验结果表明，元素掺杂的方法可以进一步提高贵金属-氧化锌核壳纳米颗粒的气敏性能。合适的元素选择与掺杂量，既可以保留原本的核壳结构，又可以对外壳进行改性。掺杂与贵金属-氧化锌异质界面的协同作用，使得气敏传感性能得到进一步增强。适量Al元素掺杂与Pt-ZnO异质界面的协同作用促使ZnO外壳表面吸附氧比例被大大提高，从而提高了材料的气敏传感灵敏度。其中4%-Al-Pt@ZnO核壳纳米颗粒低浓度丙酮有高的灵敏度（对1 ppm与100 ppm丙酮响应分别为9.26与128），低的检测下限（20 ppb），良好的选择性和稳定性，有作为人体呼出气体检测气敏传感材料的潜质。（4）1%-Ga-Pt@ZnO核壳纳米颗粒是一种具有多种功能应用的气敏材料。首先，其对低浓度丙酮有很高的灵敏度（对1 ppm与50 ppm丙酮响应分别为13.6与296），很低的检测下限（10 ppb），良好的选择性和稳定性，有作为人体呼出气体检测气敏传感材料的潜质。1%-Ga-Pt@ZnO核壳纳米颗粒还对NO2气体有可逆p-n型半导体传导率转变现象，我们画出了其p-n型半导体传导率转变区域相图。借助这相图，可以相对准确地判断在某工作温度（T）与NO2气体浓度（C）下1%-Ga-Pt@ZnO核壳纳米颗粒对于NO2气体的p-n型半导体传感类型，因此这种材料有识别低浓度NO2气体的应用前景。借助经典兰纳-琼斯势（Lennard-Jones potential function）数学模型解释了工作温度（T）与NO2气体浓度（C）调控1%-Ga-Pt@ZnO核壳纳米颗粒的可逆p-n型半导体传导率转变的机制。;With the increasing demand for health and safty，gas sensitive sensors gradually play an increasingly important role in the detection of environmental air, industrial exhaust gas monitoring, flammable and toxic gas detection, exhalation gas detection and other areas. At present, the gas sensor has some problems, such as unsatisfactory sensitivity and poor selectivity. Therefore, it is particularly important to develop highly sensitive and selective gas sensor. This research is aiming on designing and synthesizing highly sensitive and selective gas sensor materials. Through a series of characterization and performance test, we found out the role of metal-ZnO hetero-interfaces in enhancing sensing performance. Based on the finding, we synthesized a series of highly sensitive and selective Metal@ZnO core-shell nanoparticles. The detail content and results were listed below.(1) The adjustment of Au-ZnO heterogenous interface and its role in gas sensing. Au@ZnO nanoparticles were firstly synthesized through a facile hydrothermal reaction and subsequently sintering treatment. During the hydrothermal reaction, CTAB was added to the mix solution, in order to control the growth rate of ZnO. The gas sensing performances of the as-synthesized core-shell nanoparticles were evaluated comparatively in detecting low-concentration benzene (less than 5 ppm). Due to the unique structure, the effects of Au-ZnO hetero-interfaces were analyzed and discussed. The work function differences between Au and ZnO which adjusted the electronic state of the ZnO shell is the main reason of enhanced sensing performance. After doping with Pd and Pt, the Au-Pd@ZnO and Au-Pt@ZnO nanoparticles showed further improvement of sensing performances.(2) The role of metal-ZnO heterogenous interface in gas sensing. The core-shell Metal@ZnO nanoparticles (Metal=Au, Pd, Pt) were synthesized via hydrothermal reaction and thermal decomposing. The formation, morphological, and compositional properties of the typical core@shell structure were confirmed by using various techniques. The obtained core-shell Metal@ZnO nanoparticles (M=Au, Pd, Pt) were applied to sensor devices and their gas sensing properties towards ppb-ppm level benzene in comparison to the pure singular ZnO nanoparticles were examined. The core-shell Metal@ZnO based sensor performed better sensing performance than pure ZnO based sensor towards low concentration benzene. In addition, Pt@ZnO based sensors displayed significantly high sensitivity, ultralow detection limit (10 ppb), high selectivity and long-term stability. The sensitivity sequence of various core-shell nanoparticles and pure ZnO towards benzene is Pt@ZnO >> Pd@ZnO > Au@ZnO > ZnO, and is well consistent with the work function differences (Pt@ZnO >> Pd@ZnO ≈ Au@ZnO > ZnO). It is implied that the bigger difference of work function between metal and ZnO exists, the higher sensitive performance performs.(3) Synergistic effect between doping and metal-ZnO heterogenous interface. Doping seems to be an efficient way to further improve the sensing performance of Metal@ZnO core-shell nanoparticles. Appropriate element selection and doping amount can keep original core-shell structure unchanged and change the morphology and performance of ZnO shell. Core-shell 3 mol% Al doped Pt@ZnO, 4 mol% Al doped Pt@ZnO and 5 mol% Al doped Pt@ZnO nanoparticles were synthesized via hydrothermal reaction and thermal decomposing. Various techniques were conducted to characterize the compositional properties and analyze the sensing properties of all nanoparticles. Among those nanoparticles, 4 mol% Al doped Pt@ZnO based sensor presents excellent acetone sensitive. The response of the sensor to 1 and 100 ppm acetone is as high as 9.26 and 128, and the detect limit towards acetone is as low as 20 ppb. Moreover, the 4%-Al-Pt@ZnO based sensor presents excellent selectivity and stability toward acetone at low and high concentration range. Al doping induces structure adjustment of ZnO shells and ZnO shells could provide more active sites for gas molecules. The synergistic effect between doping and metal-ZnO heterogenous interface enhanced sensing property of metal@ZnO core-shell nanoparticles. The doping of Al was proved as a feasible method for fabricating acetone sensor, with high sensitivity and selectivity. (4) 1 mol% Ga doped Pt@ZnO based sensor presents excellent acetone sensitive and interesting reversible switching from P- to N-type NO2 sensing. The response of the 1 mol% Ga doped Pt@ZnO based sensor to 1 ppm and 50 ppm acetone is as high as 13.6 and 296, and the detecting concentration limit to acetone and NO2 is as low as 10 ppb and 20 ppb. The analogical binary p-n transition phase diagram was established to understand the NO2-sensing reversible switching as a function of operating temperature (T) and NO2 gas concentration (C). The role of Ga doping in enhancing the sensing property and the mechanism of NO2 p–n sensing transition is elaborated. With the help of classical Lennard-Jones (LJ) potential function, there is a possible T-C transition mechanism which was established to understand the NO2-sensing reversible switching as a function of operating temperature (T) and NO2 gas concentration (C).
|龚龑. 贵金属-氧化锌核壳颗粒的气敏传感机制探究与掺杂改性研究[D]. 中国科学院大学,2019.|
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