Graphyne-3: a highly efficient candidate for separation of small gas molecules from gaseous mixtures

Abstract

Two-dimensional nanosheets, such as the general family of graphenes have attracted considerable attention over the past decade, due to their excellent thermal, mechanical, and electrical properties. We report on the result of a study of separation of gaseous mixtures by a model graphyne-3 membrane, using extensive molecular dynamics simulations and density functional theory. Four binary and one ternary mixtures of H${}_2$, CO${}_2$, CH${}_4$ and C${}_2$H${}_6$ were studied. The results indicate the excellence of graphyne-3 for separation of small gas molecules from the mixtures. In particular, the H${}_2$ permeance through the membrane is on the order of ${10}^7$ gas permeation unit, by far much larger than those in other membranes, and in particular in graphene. To gain deeper insights into the phenomenon, we also computed the density profiles and the residence times of the gases near the graphyne-3 surface, as well as their interaction energies with the membrane. The results indicate clearly the tendency of H${}_2$ to pass through the membrane at high rates, leaving behind C${}_2$H${}_6$ and larger molecules on the surface. In addition, the possibility of chemisorption is clearly ruled out. These results, together with the very good mechanical properties of graphyne-3, confirm that it is an excellent candidate for separating small gas molecules from gaseous mixtures, hence opening the way for its industrial use.