Fluorine-Modified Porous Graphene as Membrane for CO2/N2 Separation: Molecular Dynamic and First-Principles Simulations

It is demonstrated that the fluorine-modified porous graphene membrane has excellent selectivity for CO2/N-2 separation by using molecular dynamic (MD) simulations. We also investigated in detail the mechanism of the fluorine-modified porous graphene membrane for CO2/N-2 separation by using first-principles simulations. We find that the diffusion barriers for CO2 and N-2 to pass through the pore-22 (with 22 carbon atoms drilled out) graphene membrane are relatively small, which indicates that the pore-22 has a low selectivity for CO2/N-2 separation. After fluorine modification, the diffusion barrier for CO2 to pass through decreases to 0.029 eV, while the diffusion barrier for N-2 greatly increases to 0.116 eV. Therefore, N-2 gets more difficult, while CO2 gets easier to penetrate through the fluorine-modified pore-22. The fluorine-modified pore-22 porous graphene shows a great enhancement of selectivity for CO2/N-2 separation, which is consistent with the MD results. Our studies show that first-principles simulations can be well used to understand the MD results and propose an economical and efficient means of separating CO2 from N-2,N- which may be useful for designing new concept membranes for gas separation, like CO/N-2 and SO2/N-2 separations.