Detection of Ultralow Concentration NO₂ in Complex Environment Using Epitaxial Graphene Sensors

We demonstrate proof-of-concept graphene sensors for environmental monitoring of ultralow concentration NO₂ in complex environments. Robust detection in a wide range of NO₂ concentrations, 10-154 ppb, was achieved, highlighting the great potential for graphene-based NO₂ sensors, with applications in environmental pollution monitoring, portable monitors, automotive and mobile sensors for a global real-time monitoring network. The measurements were performed in a complex environment, combining NO₂/synthetic air/water vapor, traces of other contaminants, and variable temperature in an attempt to fully replicate the environmental conditions of a working sensor. It is shown that the performance of the graphene-based sensor can be affected by coadsorption of NO₂ and water on the surface at low temperatures (≤70 °C). However, the sensitivity to NO₂ increases significantly when the sensor operates at 150 °C and the cross-selectivity to water, sulfur dioxide, and carbon monoxide is minimized. Additionally, it is demonstrated that single-layer graphene exhibits two times higher carrier concentration response upon exposure to NO₂ than bilayer graphene.