## 3 Results and Discussion
### Adsorption of Single Molecule, Double Molecules on Pt-Graphene
#### 3.2.2 Analysis of Electronic Density of States  
In this section, we analyze the electronic density of states (DOS) of individual gas molecules SO\({}_{2}\), SOF\({}_{2}\) and SO\({}_{2}\)F\({}_{2}\). The DOS diagrams of Pt-graphene are shown in Figures 6-8, which confirms that the system modified by Pt atom has good conductivity. Comparing with Figure 6a, b the DOS at Fermi level increased significantly after SO\({}_{2}\) adsorption, which is attributed to the increase of the carrier number after SO\({}_{2}\) adsorption. As shown in Figure 6c, the DOS of the system adsorbed SOF\({}_{2}\) increases slightly below the Fermi level, but the DOS above the Fermi level is unchanged. The DOS at the Fermi level also increase. For a single SO\({}_{2}\)F\({}_{2}\) adsorption (Figure 6d), DOS on the left side of Fermi level increases, but DOS on the right-side decreases, and there is no significant change at Fermi level. In fact, the decomposition products present in the SF\({}_{6}\) insulating device is a mixed gas. Therefore, the adsorption of multiple gas molecules was considered in this study. Due to the limited adsorption capacity of a single Pt-doped graphene, the adsorption of two gas molecules is sufficient to analyze the adsorption of multiple gas molecules. Figure 6: The change of density of states (DOS) (**a**) before and after (**b**) single SO\({}_{2}\), (**c**) single SOF\({}_{2}\) and (**d**) single SO\({}_{2}\)F\({}_{2}\) adsorption on Pt-graphene. Figure 7: The change of DOS (**a**) before and after (**b**) double SO\({}_{2}\), (**c**) double SOF\({}_{2}\) and (**d**) double SO\({}_{2}\)F\({}_{2}\) adsorption on Pt-graphene. Firstly, the adsorption characteristics of adsorbed double gas molecules are discussed. The comparison of DOS before and after adsorbing gas molecules is shown in Figure 7. Two SO\({}_{2}\) adsorbed on Pt-graphene active sites at the same time enhances the molecular movement between Pt-graphene and adsorbing gas. Comparing with Figure 7a, b DOS has been improved in all energy distribution regions. Although the DOS curve lower than Fermi level changes little, the DOS higher than Fermi level increases. When two identical SO\({}_{2}\) and SO\({}_{2}\)F\({}_{2}\) molecules interact with Pt-graphene, the DOS near the Fermi level increases. As can be seen in Figure 7c, the DOS after adsorption of SO\({}_{2}\) is significantly increased at the Fermi level, and as shown in Figure 7d, the DOS at the Fermi level is increased after the adsorption of SO\({}_{2}\)F\({}_{2}\). In the case of a mixed gas decomposed in the SF\({}_{6}\) insulation equipment, in addition to the above-mentioned double gas adsorption, the Pt-graphene surface also adsorbs different gas molecules. According to the DOS shown in Figure 8, compared with the adsorption of single and double gas molecules, the change of DOS is significantly different, and all DOS diagrams close to the Fermi level are increased, and the overall DOS obviously moves to the right which is attributed to the change of Fermi-level compared to the bare Pt-graphene. It means that the conductivity decreases significantly. When SO\({}_{2}\) and SOF\({}_{2}\) interact with Pt-graphene, the SOF\({}_{2}\) molecule leaves the Pt-graphene surface according to the structure discussed above. Comparing SO\({}_{2}\) and SOF\({}_{2}\) adsorbed DOS (Figure 8b) compared with DOS single SO\({}_{2}\) adsorption, we found that DOS changes showed the same growth trend due to the key role of SO\({}_{2}\) adsorption. For the adsorption of SO\({}_{2}\) and SO\({}_{2}\)F\({}_{2}\) as the structure shown in Figure 8d, only the fractured fluorine atom and one SOF\({}_{2}\) contribute to the change of conductivity. In the process of adsorption, SO\({}_{2}\)F\({}_{2}\) molecules are away from the surface of graphene, and only one F atom forms a chemical bond with Pt atoms. The increase of DOS below the Fermi level mainly comes from the contribution of F atoms adsorption.