Tuning the Electronic and Optical Properties of Graphene via Doping to Realize Nitrogen Dioxide Sensing: A Computational Study

Recently, doped graphene has emerged as a promising material for gas sensing applications. In this study, we performed first-principles calculations to investigate the adsorption of nitrogen dioxide (NO₂) on pristine, nitrogen (N)-doped, ruthenium (Ru)-doped, and N-Ru-co-doped graphene surfaces. The adsorption energies, Mulliken charge distributions, differential charge densities, electronic density of states, and optical properties of NO₂ on the graphene surfaces were evaluated. The adsorption energies follow the order N-Ru-co-doped > Ru-doped > N-doped > pristine graphene, suggesting that doped graphene has higher sensitivity to NO₂ gas molecules than pristine graphene. Analysis of the charge transfer and differential charge densities indicated weak physisorption of NO₂ on pristine and N-doped graphene, whereas stronger chemisorption of NO₂ occurred on Ru-doped and N-Ru-co-doped graphene because of the formation of chemical bonds between NO₂ and the doped surfaces. The peak absorption and reflection coefficients of NO₂ adsorbed on N-Ru-co-doped graphene are approximately 2.88 and 7.75 times higher, respectively, than those of NO₂ adsorbed on pristine graphene. The substantial changes of the electronic and optical properties of N-Ru-co-doped graphene upon interaction with NO₂ can be exploited for the development of highly sensitive and selective NO₂ gas sensors.