Tin oxide-polyaniline heterostructure sensors for highly sensitive and selective detection of toxic gases at room temperature

Nanocrystalline SnO2-Polyaniline (SnO2-PANI) heterostructure sensors have been developed for sensing trace amounts of toxic gases (2 ppm SO2 and 50 ppb NO2) at room temperature with high specificity. SnO2-PANI heterostructure has been prepared and the heterostructures have been optimized by electrochemical deposition of PANI of various thicknesses on nanocrystalline SnO2 (size ∼ 15 nm) prepared by Langmuir-Blodgett technique. Two types of sensors: sensor #1 with in-plane gold contacts one each from SnO2 and PANI and sensor #2 with in-plane gold contacts from PANI film were prepared. Sensor #1 showed high specificity towards NO2 (50 ppb) gas with response and subsequent recovery at room temperature without any carrier gas flow or UV irradiation while sensor #2 showed high response and recovery towards SO2 (2 ppm). Furthermore, the sensor #1 showed a response time of about 5 min towards NO2 gas and recovery time of about 15 min at 25 °C. Space charge modulation occurring at various interfaces such as SnO2-PANI interface and boundaries between the SnO2 nanograins explains the high toxic gas sensitivity observed for the SnO2-PANI heterostructured thin film sensor.