Simulation Study on Diffusion and Local Structure\nof CH<sub>4</sub>, CO<sub>2</sub>, SO<sub>2</sub>, and H<sub>2</sub>O Mixtures into Double-Layers Graphene

Graphene\nhas been widely studied as an ideal material for the adsorption\nand separation. In this work, we used molecular dynamics simulations\nto investigate the evolution of diffusion and local structure of CH<sub>4</sub>, CO<sub>2</sub>, SO<sub>2</sub>, and H<sub>2</sub>O mixtures\ninto double-layers graphene under seven different interlayer spacings\nand four different CO<sub>2</sub> concentrations. The results showed\nthat the adsorption of CH<sub>4</sub> and CO<sub>2</sub> molecules\non the graphene surface weakened with increased interlayer spacing.\nThe diffusion capacities of CH<sub>4</sub> and CO<sub>2</sub> in the\nmixed system were significantly improved by increasing the interlayer\nspacing. In interlayer spacings ranging from 5 to 10 nm, the diffusion\ncapacities of each component varied significantly in the order CH<sub>4</sub> > CO<sub>2</sub> ≫ H<sub>2</sub>O > SO<sub>2</sub>. Compared with CH<sub>4</sub> and CO<sub>2</sub>, the local structures\nof SO<sub>2</sub> and H<sub>2</sub>O were more affected by the interlayer\nspacing. Larger interlayer spacings or higher CO<sub>2</sub> concentrations\nwere advantageous for the formation of stronger hydrogen bond structures\nbetween H<sub>2</sub>O molecules. When the CO<sub>2</sub> concentrations\nwere between 10% and 20% and the interlayer spacing of graphene was\n8 nm, the graphene structure exhibited the best adsorption and separation\neffects on CH<sub>4</sub> and other components.