ZnO and rGO composite-based humidity tolerant room temperature NO2 gas sensor

Abstract

The gas sensor is effectively used for the detection of hazardous gases and monitors the gaseous concentration in the environment. One of the hazardous gases, specifically NO2, is the source/cause of acid rain, photochemical smog, and a significant number of respiratory diseases. In the present work, ZnO@rGO based humidity-tolerant hybrids were fabricated on a glass substrate for NO2 gas sensing at room temperature. ZnO and rGO have been synthesized via the co precipitate and modified Hummer’s method, respectively. XRD is used to examine the crystal structures of the bare ZnO and ZnO@rGO composite. The (101) plane corresponds to the most intense diffraction peaks seen in bare ZnO at 36.22°; the FESEM image reveals that flower-like morphology of ZnO was obtained; XPS analysis confirms the Zn, C, O elements present. To study the compositional effect of rGO on gas sensing of NO2, films of ZnO@rGO with different compositions of rGO had prepared, with weight percentages of 12, 15 and, 18, and percentage responses were observed 46, 60 and, 51, respectively at room temperature after exposing 10 ppm of NO2 gas on the sensing film. Gas sensing performance has been performed at different concentrations (ppm) of gas, temperature, and relative humidity. It was observed that 25 °C (RT) and moderate relative humidity levels were ideal working conditions. Additionally, the gas sensing performance has been carried out in different gaseous environments (Cl2, H2S, C3H6O, C2H5OH, NO2), and the sensor demonstrated excellent NO2 gas selectivity. p-n heterojunction formed because of interaction between p-type rGO and n-type ZnO semiconductor. Thus, the as designed ZnO@rGO-based NO2 gas sensor, operating at RT with high %response, and humidity tolerance in a wide RH range, demonstrates selective sensing with a detection limit of 0.5 ppm, is recommended to be a great NO2 gas sensing device.