Defect engineering of CVD graphene and real-time Raman study of NO2 adsorption toward enhanced sensing sensitivity

[Display omitted] •Real-time Raman was employed to study adsorption mechanism of NO2 on monolayer graphene (MG).•The edge sites of the MG were found to be more favorable for adsorbing gas molecules.•The defect engineering utilizing hydrothermal treatment was applied to enrich number of edge sites on MG.•The porous MG exhibited higher sensitivity upon NO2 exposure compared to pristine MG. In this study, an adsorption mechanism of NO2 gas on monolayer graphene (MG) was investigated by using real-time Raman mapping to record data during the NO2 sensing process. The Raman mapping was able to monitor the electronic states on several regions of MG fakes and revealed the electronic transformation by displaying intensities of the characteristic peaks. Importantly, it was found that edge sites of the graphene are more favorable for absorbing the gas molecules. Porous MG (P-MG) prepared by steamed hydrothermal method was employed, which showed higher sensitivity upon exposure to NO2 concentration of 50 ppm, approximately 1.5 times higher than that of the MG-based sensor. The result is attributed to high number of active edge sites induced from defects on the basal plane of the MG. Also, the mechanism by which the adsorbed molecules affect the intensity of characteristic peaks was greatly explained by experimental results and literatures.