Defect-Rich SnO₂–x Polydisperse Spheres Toward the Detection of Vehicle-Emitted Category NO₂ Gas

Detection of vehicle-emitted type NO2 by metal oxides-based sensors remains challenging due to their unsatisfactory selectivity and high detection limit. In this work, we report using SnO2 polydisperse spheres (PSs) with enriched defects for the detailed sensing study of vehicle-emitted type gases. The XPS study of the SnO2 PSs reveals defects in the form of oxygen vacancy (OV) and unreacted Sn atoms (Sn0). Sensing results suggest that these defects played a crucial role in getting a very high response to NO2 (i.e., 22–1 ppm NO2) as well as a fast response time (68 s), which is further shortened to 9 s when exposed to 20 ppm NO2. Our sensor’s detection limit is 200 ppb, well covered for monitoring vehicle-emitted NO2 gas concentration (500 ppb to a few ppm). Furthermore, the selectivity study revealed that the sensor does not respond or respond negligibly to other vehicle-emitted gases like CO2 and CO, which shows the sensor’s exceptional selectivity to NO2. Finally, a comparative study shows that our sensor’s performance surpasses most previous reports on NO2 sensors, especially for detecting vehicle-emitted category NO2 gas.