Co-modulation of graphene by N hetero-doping &vacancy defects and the effect on NO2 adsorption and sensing: First-principles study

Modulation by hetero-doping or vacancy defect has been proved effective on gas-sensing response enhancement of intrinsic graphene. To explore the synergistic effect of hetero-doping and vacancy defects, in this work, the adsorption of NO2 molecule on the defective graphene co-modulated with N-doping and C-vacancy was studied using first-principles calculations. The doping&vacancy models of defective graphene were constructed by creating single/double C-vacancies with partial or total marginal C atoms around the defect substituted by N atoms. The calculations about band structure, DOS and atomic Mulliken population reveal that the sub-fully doped configurations achieve significant enhancement for NO2 adsorption and interaction with the defective surface in corresponding vacancy systems. Further analysis on geometry and charge density difference demonstrates that the sub-full doping of N atoms causes strong asymmetry in charge distribution around the vacancy, which is further correlative to the improved adsorption characteristic of the co-modulated graphene from the perspective of a local built-in electric field. In addition, the effect of pyrrolic and pyridinic nitrogen-doping on NO2 adsorption is also discussed. The present work provides theoretical understanding for the NO2 adsorption characteristic and mechanism of N-doping&vacancy co-modulated graphene. It is clearly demonstrated that the defective graphene with appropriate hetem-doping&vacancy co-modulation is attractive and promising for enhanced NO2 adsorption and NO2 -sensing.