Highly sensitive and flexible NO₂ gas sensor based on nitro-functionalized graphene film

We report a flexible nitrogen dioxide (NO₂) gas sensor based on nitro-functionalized graphene operated at a moderate temperature of 150 °C. Nitro-containing functional groups were introduced onto CVD-grown graphene films through diazonium chemistry, and the resulting chemical modification was supported by Raman spectroscopy and X-ray photoelectron spectroscopy. The nitro-functionalized graphene sensor exhibited an enhanced response to low-concentration NO₂ compared to pristine graphene under the tested conditions. This improvement is attributed to the electron-withdrawing nature of the nitro-functionalized surface, which promotes p-type behavior and facilitates charge-transfer interactions with NO₂ molecules. The sensor also showed stable operation under repeated gas exposure and mechanical bending, indicating its potential for flexible NO₂ sensing platforms. These results suggest that chemical functionalization of graphene is an effective strategy for improving the sensing performance of flexible graphene-based NO₂ sensors.