Carbon nanotube networks as gas sensors for NO2 detection

Networks of different carbon nanotube (CNT) materials were investigated as resistive gas sensors for NO2 detection. Sensor films were fabricated by airbrushing dispersions of double-walled and multi-walled CNTs (DWNTs and MWNTs, respectively) on alumina substrates. Sensors were characterized by resistance measurements from 25 to 250 °C in air atmosphere in order to find the optimum detection temperature. Our results indicate that CNT networks were sensitive to NO2 concentrations as low as 0.1 ppm. All tested sensors provided significantly lower response to interfering gases such as H2, NH3, toluene and octane. We demonstrate that the measured sensitivity upon exposure to NO2 strongly depends on the employed CNT material. The highest sensitivity values were obtained at temperatures ranging between 100 and 200 °C. The best sensor performance, in terms of recovery time, was however achieved at 250 °C. Issues related to the gas detection mechanisms, as well as to CNT network thermal stability in detection experiments performed in air at high operation temperatures are also discussed.