Role of graphene quantum dots with discrete band gaps on SnO(2) nanodomes for NO(2) gas sensors with an ultralow detection limit

NO(2) is a major air pollutant that should be monitored due to its harmful effects on the environment and human health. Semiconducting metal oxide-based gas sensors have been widely explored owing to their superior sensitivity towards NO(2), but their high operating temperature (>200 °C) and low selectivity still limit their practical use in sensor devices. In this study, we decorated graphene quantum dots (GQDs) with discrete band gaps onto tin oxide nanodomes (GQD@SnO(2) nanodomes), enabling room temperature (RT) sensing towards 5 ppm NO(2) gas with a noticeable response ((R(a)/R(g)) − 1 = 4.8), which cannot be matched using pristine SnO(2) nanodomes. In addition, the GQD@SnO(2) nanodome based gas sensor shows an extremely low detection limit of 1.1 ppb and high selectivity compared to other pollutant gases (H(2)S, CO, C(7)H(8), NH(3), and CH(3)COCH(3)). The oxygen functional groups in GQDs specifically enhance NO(2) accessibility by increasing the adsorption energy. Strong electron transfer from SnO(2) to GQDs widens the electron depletion layer at SnO(2), thereby improving the gas response over a broad temperature range (RT–150 °C). This result provides a basic perspective for utilizing zero-dimensional GQDs in high-performance gas sensors operating over a wide range of temperatures.