Highly Efficient SO2 Sensing by Light-Assisted Ag/PANI/SnO2 at Room Temperature and the Sensing Mechanism

Sulfur dioxide (SO2) is one of the most hazardous and common environmental pollutants. However, the development of room-temperature SO2 sensors is seriously lagging behind that of other toxic gas sensors due to their poor recovery properties. In this study, a light-assisted SO2 gas sensor based on polyaniline (PANI) and Ag nanoparticle-comodified tin dioxide nanostructures (Ag/PANI/SnO2) was developed and exhibited remarkable SO2 sensitivity and excellent recovery properties. The response of the Ag/PANI/SnO2 sensor (20.1) to 50 ppm SO2 under 365 nm ultraviolet (UV) light illumination at 20 °C was almost 10 times higher than that of the pure SnO2 sensor. Significantly, the UV-assisted Ag/PANI/SnO2 sensor had a rapid response time (110 s) and recovery time (100 s) to 50 ppm SO2, but in the absence of light, the sensors exhibited poor recovery performance or were even severely and irreversibly deactivated by SO2. The UV-assisted Ag/PANI/SnO2 sensor also exhibited excellent selectivity, superior reproducibility, and satisfactory long-term stability at room temperature. The increased charge carrier density, improved charge-transfer capability, and the higher active surface of the Ag/PANI/SnO2 sensor were revealed by electrochemical measurements and endowed with high SO2 sensitivity. Moreover, the light-induced formation of hot electrons in a high-energy state in Ag/PANI/SnO2 significantly facilitated the recovery of SO2 by the gas sensor.