## 3 Results and Discussion
### Adsorption of Single Molecule, Double Molecules on Pt-Graphene
#### 3.2.1 Analysis of Adsorption Structures and Electronic Properties  
After optimizing the adsorption structures, the gas molecules were relaxed to various positions on the Pt-graphene surface. The adsorption of single and multiple gas molecules were both studied. In order to obtain the most stable adsorption structure of each gas molecule, we simulated the adsorption structure at different adsorption angles and distances. The most stable structures are shown in Figures 3-5. In order to analyze the adsorption properties, as shown in Table 1, the binding energies \(E_{ads}\), charge transfer \(Q_{T}\) and adsorption distance \(D\) for different gas adsorption structures are shown. \(D\) represents the closest distance between the gas molecules and the surface of the Pt-graphene, where \(D_{1}\) and \(D_{2}\) represent the distances of the different gas molecules from the Pt nanoparticles, respectively. Similarly, \(Q_{T1}\) and \(Q_{T2}\) represent charge transfer between two different gas molecules and the surface, respectively. \(E_{ads}\) is the adsorption energy, and negative values indicate that the adsorption is exothermic and the reaction can occur spontaneously. The adsorption parameters and structures of single SO\({}_{2}\), SOF\({}_{2}\) and SO\({}_{2}\)F\({}_{2}\) molecules adsorbed on graphene are shown in Table 1 and Table S3 and Figure 3a-c. The O atom of SO\({}_{2}\) is the closest to the Pt atom. Since the electronegativity of O atom is strong, the adsorption distance is 2.261 A. The S atom is far from the surface of Pt doped graphene because it establishes a stable covalent bond with O atom and it is difficult to interact with Pt atoms. The structure of SO\({}_{2}\) remains almost unchanged during  
Figure 3: The adsorption structures for single SO\({}_{2}\), SOF\({}_{2}\) and SO\({}_{2}\)F\({}_{2}\) adsorption on Pt-graphene. (**a**) SO\({}_{2}\); (**b**) SOF\({}_{2}\); (**c**) SO\({}_{2}\)F\({}_{2}\). Figure 2: Geometric structures after optimization: (**a**) Int-graphene; (**b**) Top view of Pt-graphene; (**c**) Side view of Pt-graphene. (Grey = Carbon; Dark blue = Platinum, the labels are also applied to the following figures.). the adsorption process, and the S-O bond length of SO\({}_{2}\) itself is gradually extended from 1.480 A to 1.581 A, indicating that a new Pt-O bond may be formed during the interaction between SO\({}_{2}\) and Pt-doped graphene, resulting in the stretching of S-O bond of SO\({}_{2}\) itself. When a SO\({}_{2}\) gas molecule or a SO\({}_{2}\)F\({}_{2}\) molecule is close to Pt-graphene, the length of the S-F\({}_{1}\) bond of the adsorbed SOF\({}_{2}\) molecule is extended to 2.966 A, and the length of the S-F\({}_{2}\) bond of the SO\({}_{2}\)F\({}_{2}\) molecule is extended to 3.434 A, indicating that the S-F bond may have been broken. According to Figure 3b,c, the broken F atom tends to form a new bond with the Pt atom. The distance between the two atoms is 2.012 A and 2.029 A. At the same time, the S atom tends to form a Pt-S bond with the Pt atom. In order to explore the strength of adsorption, the adsorption energies under various conditions were discussed. It can be seen from Table 1 that the adsorption of SO\({}_{2}\)F\({}_{2}\) gas molecules is the strongest, because the adsorption energy is \(-\)2.429 eV. The adsorption of SO\({}_{2}\) on the Pt-doped graphene surface is lower than that of the SO\({}_{2}\)F\({}_{2}\). The adsorption of SOF\({}_{2}\) and Pt doped graphene is the weakest because the adsorption energy is \(-\)1.254 eV. The charge transfer quantities of SO\({}_{2}\), SOF\({}_{2}\) and SO\({}_{2}\)F\({}_{2}\) molecules with Pt-doped graphene surface as shown in Table 1 are \(-\)0.412 \(e\), \(-\)0.679 \(e\) and \(-\)0.981 \(e\). The charge transfer quantities \(Q\) in all three cases are negative. It is shown that electrons transfer from Pt doped graphene surface to gas molecule during the adsorption process. The gas molecules SO\({}_{2}\)F\({}_{2}\), SO\({}_{2}\) and SOF\({}_{2}\) all show the characteristics of electron acceptor.