Transformation of Diffusion and Local Structure of CH4, CO2, SO2 and H2O Mixtures in Graphene Under Wide Temperature and Pressure Range: A Molecular Dynamics Simulation Study

As a material with high specific surface area and excellent chemical stability, graphene exhibited remarkable adsorption and separation performance as well as a wide range of potential applications. The graphene layer played a significant role in influencing gas transmission. In this study, we employed molecular dynamics simulation to investigate the diffusion characteristics and local structures of a mixed system consisting of CH4, CO2, SO2 and H2O. Additionally, we further examined the transformation of the behavior of these mixtures within graphene layers. The order of diffusion coefficients of the four molecules without graphene was H2O>SO2>CO2 >> CH4. However, in the double-layer graphene, the order changed to CH4>CO2 >> H2O>SO2. Higher temperatures and lower pressures were found to facilitate gas diffusion. Temperature and pressure had great effects on the local structures of CH4, CO2 and SO2, while their impact on H2O was limited due to the extensive network of hydrogen bonds formed by H2O molecules. The statistical results of average coordination number revealed that CH4 tended to aggregate with itself, whereas CO2 and SO2 exhibited a tendency to aggregate with H2O. The graphene structure enhanced the separation and transportation of CH4 from mixed systems.