After the effectively creation of single layer graphene sheets by Novoselov et al. [1], several studies on the basic properties of graphene-based structures have been started. Graphene and its
relatives are of the new active research area towards adsorption of different gas molecules [2]. It is proven that enhancement in the charge concentration of graphene after adsorption of different gas molecules could be utilized to create high sensitive sensors [3]. The altering in the resistivity because of gases adsorbed on graphene corresponds to sensing properties which can be considered as donors or acceptors. In addition, special binding sites in graphene
can help understanding of interactions near the surface [4]. Numerous theoretical researches based on DFT calculations have been done to show the interaction energies of small molecular
with a graphene sheet [4–8]. For example Freitas et al. [6] performed first-principles DFT calculations to address the interactions of small water aggregates with a periodically extended
graphene layer. Based on their study, small interaction of adsorbates yields mild effect in the electronic structure of graphene. In another work, Lee and Kim [7] theoretically investigated the adsorption of CO2 on graphene sheets using density functional theory (DFT) and MP2 calculations. They used different levels of theory to computing the geometric parameters and adsorption energies. Ao et al. [8] investigated the adsorption property of CO on pristine as well as Al-doped graphene sheets. Based on their report Al-doped graphene has potential to be used as CO sensor.