A dispersion-corrected DFT investigation of CH4 adsorption by silver-decorated monolayer graphene in the presence of ambient oxygen molecules

The main purpose of the present article is an investigation of electronic properties of Ag-decorated graphene (Ag-G), in the presence of ambient O-2 molecules, when methane gas is adsorbed. To pursue this aim, we employ the dispersion-corrected density functional theory (DFT-D2) in which the Van der Waals interactions, as well as spinpolarization-mode, are explicitly activated. Our calculations, thereby, demonstrate the stable geometrical configuration, the corresponding parameters and the adsorption energy of CH4/(O-2-Ag-G). For a comparison, moreover, we also report the geometrical properties and adsorption energies for CH4/(O-2-G), CH4/(Ag-G) and O-2/(Ag-G). We then proceed by calculating the charge transfer and charge redistribution, as a result of adsorption, for the aforementioned combinations. The manner of charge transfer and redistribution serves to justify the electronic spin-polarized band structures and densities of states, which we also report. Our results then demonstrate that the adsorption energy of CH4 onto Ag-decorated graphene, even in the presence of ambient O-2, is by far larger than the undecorated one. In addition, considerations of the band structures, reveal an increase in the response of O-2-Ag-G to the presence of CH4 in comparison with that of O-2-G. The last point, in combination with the enhancement of adsorption energy, provide strong motivation for the use of Ag-decorated graphene as a low-cost and highly sensitive methane gas detector.