Yang Tingqiang, Liu Yueli, Jin Wei, Han Yiyang, Yang Shuang, Chen Wen
State Key Laboratory of Silicate Materials for Architectures, School of Materials Science and Engineering, Wuhan University of Technology , Wuhan 430070, P. R. China.
State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology , Wuhan 430070, P. R. China.
ACS Sens. 2017 Jul 28;2(7):1051-1059. doi: 10.1021/acssensors.7b00363. Epub 2017 Jul 19.
Absorbed oxygen plays a key role in gas sensing process of ZnO nanomaterials. In this work, the transformation of absorbed oxygen on ZnO (101̅0) and its effects on gas sensing properties to ethanol are studied by a novel thermal pulse method and density functional theory (DFT) simulation. Thermal pulse results reveal that the absorbed O molecule dissociates into two individual oxygen adatoms by extracting electrons from ZnO surface layers when temperature is above 443 K. The temperature at which absorbed O molecule begins to dissociate is the lowest working temperature for gas sensing. DFT simulation demonstrates the dissociation process of O at ZnO (101̅0) surface, and the activation energy (E) of dissociation is calculated to be 351.71 kJ/mol, which suggests that the absorbed O molecule is not likely to dissociate at room temperature. The reactions between ethanol and absorbed O molecule, as well as reactions between ethanol and O adatom, are also simulated. The results indicate that ethanol cannot react with absorbed O molecule, while it can be oxidized by O adatom to acetaldehyde and then to acetic acid spontaneously. Mulliken charge analysis suggests electrons extracted by O adatom return to ZnO after the oxidation of ethanol.
吸附氧在ZnO纳米材料的气敏过程中起着关键作用。在本工作中，采用一种新型热脉冲方法和密度泛函理论（DFT）模拟研究了ZnO(101̅0)上吸附氧的转变及其对乙醇气敏性能的影响。热脉冲结果表明，当温度高于443 K时，吸附的O分子通过从ZnO表面层提取电子而分解为两个单独的氧吸附原子。吸附的O分子开始分解的温度是气敏的最低工作温度。DFT模拟展示了O在ZnO(101̅0)表面的分解过程，计算得出分解的活化能（E）为351.71 kJ/mol，这表明吸附的O分子在室温下不太可能分解。还模拟了乙醇与吸附的O分子之间的反应以及乙醇与氧吸附原子之间的反应。结果表明，乙醇不能与吸附的O分子反应，而它可以被氧吸附原子自发氧化为乙醛，然后再氧化为乙酸。Mulliken电荷分析表明，乙醇氧化后，氧吸附原子提取的电子返回ZnO。
