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

Recently, doped graphene\nhas emerged as a promising material for\ngas sensing applications. In this study, we performed first-principles\ncalculations to investigate the adsorption of nitrogen dioxide (NO<sub>2</sub>) on pristine, nitrogen (N)-doped, ruthenium (Ru)-doped, and\nN–Ru-<i>co</i>-doped graphene surfaces. The adsorption\nenergies, Mulliken charge distributions, differential charge densities,\nelectronic density of states, and optical properties of NO<sub>2</sub> on the graphene surfaces were evaluated. The adsorption energies\nfollow the order N–Ru-<i>co</i>-doped > Ru-doped\n> N-doped > pristine graphene, suggesting that doped graphene\nhas\nhigher sensitivity to NO<sub>2</sub> gas molecules than pristine graphene.\nAnalysis of the charge transfer and differential charge densities\nindicated weak physisorption of NO<sub>2</sub> on pristine and N-doped\ngraphene, whereas stronger chemisorption of NO<sub>2</sub> occurred\non Ru-doped and N–Ru-<i>co</i>-doped graphene because\nof the formation of chemical bonds between NO<sub>2</sub> and the\ndoped surfaces. The peak absorption and reflection coefficients of\nNO<sub>2</sub> adsorbed on N–Ru-<i>co</i>-doped graphene\nare approximately 2.88 and 7.75 times higher, respectively, than those\nof NO<sub>2</sub> adsorbed on pristine graphene. The substantial changes\nof the electronic and optical properties of N–Ru-<i>co</i>-doped graphene upon interaction with NO<sub>2</sub> can be exploited\nfor the development of highly sensitive and selective NO<sub>2</sub> gas sensors.