Ultrasensitive NO<sub>2</sub> Gas Sensor at Room Temperature\nBased on a Glycerol-Cross-Linked PEDOT:PSS-MoS<sub>2</sub> Nanocomposite

Nitrogen dioxide (NO<sub>2</sub>)\nis a tremendously toxic environmental\npollutant that can be lethal to humans and extremely dangerous to\nthe environment. NO<sub>2</sub>, being a highly volatile gas, undergoes\nphotochemical reactions that can cause acid rain or generate ozone.\nExposure to extremely low concentrations of NO<sub>2</sub> can severely\nimpact human health, primarily damaging lung tissues. Thus, fabricating\nhighly sensitive and portable sensors for room-temperature detection\nof NO<sub>2</sub> gas with a very low response/recovery time is extremely\nimportant for environmental monitoring and human safety. To address\nthe above challenges, we have fabricated an extremely sensitive and\nhighly selective NO<sub>2</sub> gas sensor based on a glycerol-cross-linked\nPEDOT:PSS/MoS<sub>2</sub> nanocomposite using two-dimensional MoS<sub>2</sub> nanosheets. The deposition of the gas sensor over the substrate\nwas facilitated by increasing the roughness of the substrate and the\nadhesion of the conducting polymeric films. Increased roughness facilitated\nbetter gas adsorption, which in turn increased the gas sensing capacity\nof the sensor. Three different nanocomposites were prepared using\ndifferent concentrations of MoS<sub>2</sub> nanosheets, and the sensor\nwith the greatest responsivity to NO<sub>2</sub> gas was optimized.\nThe sensor material showed an N-type semiconducting behavior in the\npresence of NO<sub>2</sub> gas with swift response and recovery times\nof 10.2 and 5.5 s in the presence of 100 ppb NO<sub>2</sub> gas. The\nfabricated gas sensor gave a superior response to extremely low concentrations\nof NO<sub>2</sub> gas even at room temperature. The sensor showed\na response of 500.3% to 50 ppm of NO<sub>2</sub> and 22.1% to 100\nppb of NO<sub>2</sub> gas, and the detection limit was 40.02 ppb.\nThe highly selective sensor shows a zero or very low response toward\nother oxidizing/reducing gases. Moreover, room-temperature gas sensing\nis an additional advantage because it reduces the power consumption\nof the device. The large surface area of the polymeric nanofilms is\nproposed to help enhance the charge transfer phenomenon between the\nN-type electron-rich semiconductor and the electron-accepting oxidizing\ngas, resulting in their excellent gas-sensing performance. This study\nproposes potential semiconducting nanostructured sensor materials\nwith prospects for real-time NO<sub>2</sub> detection for human protection\nand environmental safety.