Transformation of Diffusion and Local Structure of CH ₄ , CO ₂ , NO, and H ₂ O Mixtures into Bilayers Graphene: A Molecular Dynamics and Density Functional Theory Study

Graphene has emerged as a promising candidate for adsorption and separation applications due to its exceptional properties. In this study, the diffusion properties and local structure of the CO₂-NO flue gas, CH₄, and H₂O mixtures in the free state and those confined within graphene layers were investigated via molecular dynamics simulation. Additionally, density functional theory calculation was performed to determine the adsorption energies of these four components at different adsorption sites on graphene. The results showed that the graphene structure significantly altered the diffusion coefficients of the four substances, with the order becoming CH₄ > NO > CO₂ ≫ H₂O. By contrast, in the absence of graphene at low temperatures, the diffusion coefficient order was H₂O > CO₂ > NO > CH₄. Simultaneously, the temperature and pressure exerted pronounced regulatory effects on CH₄, CO₂, and NO. Analysis of the relative diffusion coefficients of CH₄ and NO revealed that the optimal conditions for the adsorption and separation of this mixture with bilayer graphene structures were 1-10 MPa and 275 K.