Nitrogen-doped graphene quantum dot decorated ultra-thin ZnO nanosheets for NO2 sensing at low temperatures

Nitrogen dioxide (NO2), as a toxic gas, seriously harms the environment and human health. Semiconductor metal oxide (MOS) nanocomposites modified by N-doped graphene quantum dots (N-GQDs) have attracted extensive attention as sensing materials for NO2. Here, the N-GQDs modified ZnO composite material was successfully prepared by the hydrothermal method. Compared with pure ZnO, G-Z-2 (N-GQDS doping amount of 2 mL) exhibits excellent sensing performance for NO2. The G-Z-2 based sensor reduces the working temperature from 160 degrees C to 100 degrees C. The G-Z-2 is shown to be sensitive to 5 ppm NO2 and has a massively enhanced response of about 11.6 times. The detection limit was as low as 0.1 ppm. Moreover, it shows excellent reproducibility, selectivity and stability for the detection of NO2. The highly active N atom doping enhances the electron transfer of ZnO to N-GQDS and the adsorption of NO2 molecules. The heterojunction between ZnO and N-GQDS interface expands the resistance modulation, which improves the sensor sensitivity. This work can provide a promising strategy for improving the NO2 gas sensing performance based on semiconductor metal oxide.