Computational Design of Porous Graphenes for Alkane Isomer Separation

Using first-principles calculations, we systematically evaluated a series of single-layer porous graphene membranes with different sized pores passivated by hydrogen atoms for separating short alkane isomers (C = 5–7). We found that graphene membranes with appropriate pore size (e.g., the pore19 model whose pore size is 8.0 × 5.8 Å) could efficiently separate dibranched isomers from their monobranched and linear counterparts. When alkane molecules diffused through a membrane, the porous graphene might exhibit significant distortion. At the same time, the passing molecule would be forced to change its own geometry as well. More importantly, we found that the geometric deformations of both the penetrating molecule and the membrane concertedly lowered the diffusion barrier by similar magnitudes. Therefore, when designing two-dimensional (2D) separation materials, it is necessary to consider the geometric flexibility of both the separation material and the molecules to be separated. Our results theoretically verified the feasibility of utilizing porous graphene and possibly other 2D materials for screening alkane isomers, which could lead to a wide range of energy and environment related applications.