On the mechanism of gas adsorption for pristine, defective and   functionalized graphene
  Defect is no longer deemed an adverse aspect of graphene. Contrarily, it can pave ways of extending applicability of graphene. Here, we discuss the effects of three types of defects on graphene: carbon deficiency, adatom (single Fe) dopant and introduction of functional groups (carboxyl, pyran group) on NO2 gas adsorption via density functional theory method. We have observed that the unsaturated carbon in defected graphene is highly active to attract NO2 molecules. Our study suggests that introducing Fe on graphene can enhance the NO2 adsorption process. Adsorption energy calculations suggest the enhancement in NO2 adsorption is more profound for Fe-doped mono and tetra vacant graphene than Fe doped bi- and tri-vacant graphene. This study could potentially be useful in developing adsorption-based applications of graphene. 
Y. You, J. Deng, X. Tan, N. Gorjizadeh, M. Yoshimura, S. C. Smith, V.   Sahajwalla, R. K. Joshi
cond-mat.mtrl-sci