Separation of Carbon Dioxide from Mixed Vapors by Blockage of Methane in Graphene Nanoribbons*

We study numerically the adsorption of a mixture of CO2 and CH4 on a graphite substrate covered by graphene nanoribbons (NRs). The NRs are flat and parallel to the graphite surface, at a variable distance ranging from 0.6 nm to 1.4 nm. We show that the NRs- graphite substrate acts as an effective filter for CO2. Our study is based on Molecular Dynamics (MD) simulations. Methane is considered a spherical molecule and carbon dioxide is represented as a linear rigid body. Graphite is modeled as a continuous material, while the NRs are approached atomistically. We observe that when the NRs are placed 0.6 nm above the graphite sur- face, methane is blocked out, while CO2 molecules can diffuse and be collected in between the NRs and the graphite surface. Consequently, the selectivity of CO2 is extremely high. We also observe that the initial rate of adsorption of CO2 is much higher than CH4. Overall we show that the filter can be optimized by controlling the gap between NRs and the NRs-graphite separation.