Controlling NO2 adsorption on defective graphene through strain: A DFT study

Graphene is a promising material for detecting the hazardous gas NO 2 at parts per billion (ppb) levels. Mechanical strain has been proposed to tune its sensing performance, but intrinsic defects such as Stone-Wales and single vacancies also affect its gas sensing behavior. To understand the underlying mechanisms and improve the reliability of strain-controlled gas sensors, the effect of strain on NO 2 adsorption on these defective graphene surfaces was investigated using density functional theory (DFT). It was found that Stone-Wales graphene (SWG) favors physisorption, while single vacancy graphene (SVG) promotes dissociative chemisorption due to dangling bonds. Moreover, it was found that strain weakens NO 2 adsorption on both surfaces. For SWG, the adsorption strength decreases to weaker physisorption, while for SVG, the effect of strain is more pronounced, with adsorption transitioning from dissociative to weaker physisorption, changing from –2.653 eV (0% strain) to –0.293 eV (10% strain). These trends are further supported by charge transfer and band structure analysis. Finally, a strain-induced adsorption modulation model based on the strain-dependent energy differences in graphene (e.g., Fermi level, localized defect states) and molecular orbitals (e.g., lowest unoccupied molecular orbital (LUMO)) was proposed. These findings provide valuable insights for enhancing graphene-based gas sensors using strain engineering.