Selective Adsorption of CO2 / CH4 in a Graphene Pocket

Abstract: The goal of this work is to predict the selective adsorption of CO2 from a 1:1 mixture with CH4 into the pocket region between a slotted layer of graphene fixed above a graphite surface. Molecular dynamics in a canonical ensemble was used to simulate this adsorption. In the system, methane is modeled as a single, spherical Lennard-Jones (LJ) fluid. Carbon dioxide is modeled by a three site, quadrupole, rigid body LJ fluid. The slits in graphene are made by cutting and deleting carbon atoms from the lattice within a region of specified width, and the reactivity of the edges are not taken into account. Graphite is modeled in the walls perpendicular to the z-direction by a 10-4-3 LJ potential. Trials at 273K are performed with cutting regions varying from 3Å-15Å. Simulations were also conducted for a cutting region held at 4Å, and the temperature varied. Results show that there is not significant selectivity in the pocket region, though both gases are highly attracted to the region. Edge effects, such as narrow slits, and low temperature tend to increase initial selectivity, but once equilibrium is reached, little selectivity is observed.