Insights into the H(2)/CH(4) Separation Through Two-Dimensional Graphene Channels: Influence of Edge Functionalization

A molecular simulation technique is employed to investigate the transport of H(2)/CH(4) mixture through the two-dimensional (2D) channel between adjacent graphene layers. Pristine graphene membrane (GM) with pore width of 0.515~0.6 nm is found to only allow H(2) molecules to enter rather than CH(4), forming a molecular sieve. At pore widths of 0.64~1.366 nm, both H(2) and CH(4) molecules could fill into the GM channel, where the permeability of methane is more preferential than that of hydrogen with the largest CH(4)/H(2) selectivity (1.89) at 0.728 nm. The edge functionalization by –H, –F, –OH, –NH(2), and –COOH groups could significantly alter gas permeability by modifying the active surface area of the pore and tuning attractive and/or repulsive interaction with molecules at the entrance of channel. At the pore width of 0.6 nm, the H(2) permeability of molecular sieve is enhanced by –H, –F, and –OH groups but restrained by –NH(2), especially –COOH with a passing rate of zero. At pore widths of 0.64 and 0.728 nm, both –H and –F edge-functionalized GMs show a preferential selectivity of methane over hydrogen, while the favorable transport for GM–OH is changed from H(2) molecules at 0.64 nm to CH(4) molecules at 0.728 nm. For GM–NH(2), it exhibits an excellent hydrogen molecular sieve at 0.64 nm and then turns into a significant H(2)/CH(4) selectivity at 0.728 nm. Meanwhile, small H(2) molecules start to enter the channel of GM–COOH at the pore width up to 0.728 nm. For the largest pore width of 1.336 nm, the influence of edge functionalization becomes small, and a comparable CH(4)/H(2) selectivity is observed for all the considered membranes. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s11671-015-1199-2) contains supplementary material, which is available to authorized users.