CO2 Permeation through Nanoporous graphene: a theoretical study

One of the most promising fields for application of Nanoporous graphene is that of membranes for gas separation [1-10]. For instance, Wu et. al., [7] reported that the fluorine-modified porous graphene membrane can be used for the separation of CO2 from N2 molecules, since CO2 moves easier through such a membrane, contrary to N2. Sun et. al., [8] identified a nanopore graphene membrane that is permeable to H2 and He, significantly permeable to N2 and impermeable to CH4. They also showed that pore functionalization may significantly affect the molecular permeation [8]. Similar results have been found by Jiang et. al., [9], who reported high selectivity for the separation between H2 and CH4 for graphene membranes with nitrogen functionalized pores. The effect of nitrogen functionalization was also reported by Wei et. al., [10] and Zhu et. al., [11], who showed that porous graphene membranes with pyridinic pores are very efficient in separating He and H2 over Ne, Ar, N2, CO and CH4. In the present work, we investigate theoretically the permeation of CO2 through pyridinic pores in graphene, as part of a systematic study of gas permeation through graphene membranes. Our study focuses on seven membrane systems which are shown schematically in Fig. 1. Apart from pristine graphene (Fig. 1(a)), these membranes, are constructed by removing some neighbouring carbon atoms of the graphene layer, while the pore boundary atoms are replaced by nitrogen (pyridinic pores). Using the method described below, we try to reach the transition state for the minimum energy path that transfers the CO2 molecule from the one side of the membrane to the other through the pore and estimate the energy barrier which corresponds to that transition state. Using the energy barriers, we then estimate the CO2 permeabilities of the membranes utilizing the kinetic theory of gasses.