1.Department of Basic Science, Air Force Engineering University, Xi’an 710051, China 2.Tsinghua National Laboratory for Information Science and Technology, Institute of Microelectronics, Tsinghua University, Beijing 100084, China 3.The First Aeronautic Institute, Air Force Engineering University, Xinyang 464000, China 4.Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 51672154, 51774191, 11405270), the National Key Research and Development Plan, China (Grant No. 2016YFA0200200), and the Natural Science for Basic Research Program of Shaanxi Province, China (Grant No. 2017JM6072).
Received Date:20 December 2018
Accepted Date:27 March 2019
Available Online:01 June 2019
Published Online:05 June 2019
Abstract:Reduced graphene oxide, as a candidate for gas detection due to its unique atomic structure, is arousing the wide interest of researchers. In this paper, hydrazine hydrate is used to reduce graphene oxide prepared by the modified Hummers method. A chemical resistance gas sensor is fabricated. The prepared reduced graphene oxide is used as a gas sensitive layer of Au planar interdigital electrode. The gas sensing characteristics such as responsivity, recovery and repeatability of NO2 gas are studied. The results show that the graphene oxide reduced by hydrazine hydrate can detect the NO2 gas at a concentration of 1?40 ppm under room temperature. It has good responsivity and repeatability. The recovery rate can reach more than 71%. However, the sensitivity is only 0.00201 ppm–1, and there is much room for improvement. In addition, the response time and recovery time for NO2 at 5 ppm concentration are 319 s and 776 s, respectively. The sensing mechanism of the hydrazine hydrate-reduced graphene oxide gas sensor can be attributed to charge transfer between the NO2 molecule and the sensing material. The outstanding electrical properties of the reduced graphene oxide promote the electron transfer process. This allows the sensor to exhibit excellent gas sensing performance at room temperature. The reduced graphene oxide appears as a typical p-type semiconductor and the oxidizing gas NO2 acts as an electron acceptor. Therefore, the adsorption of NO2 gas leads to the enhancement of the hole density and conductivity of the reduced graphene oxide. Another reason is the presence of defects and oxygen-containing functional groups on graphene sheets. Some oxygen-containing groups remain on the graphene surface after an incomplete reduction reaction. Compared with pure graphene, the reduced graphene oxide has hydroxyl groups and epoxy groups remaining on the surface. These functional groups will functionalize the material and promote the adsorption of gases. At the same time, the reduction reaction will further produce vacancies and structural defects. This will provide more reaction sites and thus conduce to the material further adsorbing the gas. In summary, the experimental research in this paper is of significance for studying the mechanism and characteristics of the reduced graphene oxide by using hydrazine hydrate as a reducing agent, and it can provide reference and lay a foundation for the applications of future graphene sensors. Keywords:reduced graphene oxide/ hydrazine hydrate/ nitrogen dioxide/ gas sensing
传感器的重复性可以通过记录连续暴露于10 ppm NO2后的三次循环实时响应曲线来得到, 如图4所示. 传感器在每个循环中保持几乎相同的响应和完全恢复, 在室温下表现出优异的可重复特性. 图 4 传感器对10 ppm二氧化氮气体响应的重复性测试 Figure4. Repeatability of the sensor after exposure to 10 ppm NO2.
23.3.对NO2气体的响应和恢复时间测试 -->
3.3.对NO2气体的响应和恢复时间测试
传感器的响应时间定义为: 从通入待测气体开始, 到传感器的电阻变化达到最大电阻变化的90%所用的时间. 而传感器的恢复时间是从解吸附开始, 到传感器电阻变化达到最大电阻变化的90%所需要的时间. 图5是室温下传感器对5 ppm浓度的NO2的响应变化曲线, 可以看出其响应和恢复时间分别是319 s和776 s. 图 5 传感器对5 ppm NO2气体的响应和恢复时间 Figure5. Response and recovery times of the sensor to 5 ppm NO2.