Study On The Graphene-based NO₂ Gas Sensor At Room Temperature

It is well known that nitrogen dioxide(NO2) is a common toxic and harmful gas, and NO2 primarily comes from burning fuel at high temperature and exhaust of motor vehicle. The increase levels of NO2 in cities cause dramatic environmental pollution as well as severe damages on human respiratory tract. Therefore, the detection of NO2 is thus of great importance in both environmental protection and human health. Recently, NO2 sensors based on metal oxide semiconductor-type materials usually exhibit some obvious disadvantages including high operating temperature, high power consumption and difficulty in integration. The development of NO2 sensors operating at room temperature has important practical significance. The sensing materials play an important role in enhancing NO2 sensing performances. Since discovered in 2004, graphene has been used to fabricate NO2 sensors operating at room temperature due to its high specific surface area, high carrier mobility at room temperature, special surface functional groups and p-type semiconductor properties. In this paper, we focus on the fabrication graphene-based materials and their application for detection of NO2 at room temperature.For the first part of this dissertation, Ag NPs/Sn O2/RGO hybrids were prepared by a two-step wet-chemical method. Firstly, Sn O2/RGO hybrids were synthesized by hydrothermal treatment. Then, Ag NPs/Sn O2/RGO hybrids were obtained by in situ reduction of Ag NO3 on the surface of Sn O2/RGO hybrids. The sensor based on Ag NPs/Sn O2/RGO hybrids exhibits good sensing performance for NO2 sensing operating at room temperature. For example, the response time and recovery time of the sensor based on Ag NPs/Sn O2/RGO hybrids for 5 ppm NO2 are 49 s and 339 s, which are better sensing performances than that of Sn O2/RGO hybrids, indicating that the sensing performances for NO2 sensing at room temperature have been tremendously enhanced by introduction of Ag NPs into Sn O2/RGO hybrids.For the second part of this dissertation, Sn O2 nanoparticles/nitrogen-doped reduced graphene oxide hybrids were fabricated by one-step hydrothermal strategy to enhance the sensing performances of graphene-based materials. The Sn O2/N-RGO hybrids show higher NO2 sensing performance with high sensitivity of 1.38, short response time and recovery time of 45 s and 168 s towards 5 ppm NO2 at room temperature, which are much shorter than that of Sn O2/RGO hybrids(415 s and 740 s), indicating that the excellent gas sensing performances for NO2 sensing were attributed to incorporation of N atoms into the Sn O2/RGO hybrids.In this dissertation, we focus on the application of graphene-based materials in NO2 sensor. The graphene-based materials were evidenced to exhibit better gas sensing properties for NO2 sensor. Furthermore, they provide new directions for the application of NO2 sensors at room temperature.