Gas Sensing Properties of High-Purity Semiconducting Single-Walled Carbon Nanotubes for NH3, H2, and NO

Gas sensors are advantageous as they can be applied in various fields. The metal-oxide semiconductor gas sensor is the most widely used gas sensor. In this study, the gas-sensing properties of high-purity semiconducting single-walled carbon nanotubes (SWCNTs), which behave as p-type semiconductors, are analyzed at temperatures of 50, 100, and 200 °C for NH3, H2, and NO at various O2 concentrations. The SWCNTs are separated from a mixture of metallic and semiconducting SWCNTs based on the agarose gel column chromatography. The SWCNT gas sensor responds to all the gases in 20% O2, and the gas selectivity to NH3 and H2 is controlled by the operating temperature. NO transforms to NO2 in the presence of O2 and decreases the resistance of the sensor as an oxidizing gas. The sensor can detect NH3, H2, and NO without O2. Along with the good conductivity of the SWCNTs, the good conductive paths between the SWCNTs through the semiconducting polymer dispersant reduce the noise of the sensor resistance and enable the detection of small changes in the resistance to minimal gas concentration.