Water Permeation Through Periodically Porous Graphene

Polyphenylene superhoneycomb network (PSN) is an experimentally realized periodically porous graphene with subnanometer-sized pores, which is a type of covalently linked hydrocarbon superhoneycomb network. Here, we report a computational study of permeation of a water molecule through monolayer PSN as well as N-substituted PSN, where a fraction of the H-terminated C atoms are substituted with N atoms. For the investigation, we performed first-principles calculations within van der Waals density functional theory. The lowest energy barrier was calculated to be 1.5 eV for permeation of vertically oriented water molecules through the pores of regular PSN. The pore expanded on the order of 0.1 Å to allow water permeation, with vertical displacements by ~0.8 Å owing to H-bonding with the water molecule. Upon N-substitution, the pore size increased slightly and the barrier was lowered to 0.5 eV, a more feasible value for permeation. Interestingly, we found horizontally oriented water molecules to pass through the pores more easily. Therefore, our results demonstrate that the introduction of N atoms can be a good strategy to enhance the applicability of PSN as a water purification membrane.