Simulation Study on Diffusion and Local Structure of CH₄, CO₂, SO₂, and H₂O Mixtures into Double-Layers Graphene

Graphene has been widely studied as an ideal material for the adsorption and separation. In this work, we used molecular dynamics simulations to investigate the evolution of diffusion and local structure of CH₄, CO₂, SO₂, and H₂O mixtures into double-layers graphene under seven different interlayer spacings and four different CO₂ concentrations. The results showed that the adsorption of CH₄ and CO₂ molecules on the graphene surface weakened with increased interlayer spacing. The diffusion capacities of CH₄ and CO₂ in the mixed system were significantly improved by increasing the interlayer spacing. In interlayer spacings ranging from 5 to 10 nm, the diffusion capacities of each component varied significantly in the order CH₄ > CO₂ ≫ H₂O > SO₂. Compared with CH₄ and CO₂, the local structures of SO₂ and H₂O were more affected by the interlayer spacing. Larger interlayer spacings or higher CO₂ concentrations were advantageous for the formation of stronger hydrogen bond structures between H₂O molecules. When the CO₂ concentrations were between 10% and 20% and the interlayer spacing of graphene was 8 nm, the graphene structure exhibited the best adsorption and separation effects on CH₄ and other components.