Exponentially selective molecular sieving through angstrom pores

Abstract

Two-dimensional crystals with angstrom-scale pores are widely considered as candidates for a next generation of molecular separation technologies aiming to provide extreme, exponentially large selectivity combined with high flow rates. No such pores have been demonstrated experimentally. Here we study gas transport through individual graphene pores created by low intensity exposure to low kV electrons. Helium and hydrogen permeate easily through these pores whereas larger species such as xenon and methane are practically blocked. Permeating gases experience activation barriers that increase quadratically with molecules’ kinetic diameter, and the effective diameter of the created pores is estimated as ∼2 angstroms, about one missing carbon ring. Our work reveals stringent conditions for achieving the long sought-after exponential selectivity using porous two-dimensional membranes and suggests limits on their possible performance.

Gas permeation through graphdiyne-based nanoporous membranes

“…2b ). The comparable Γ * between helium and hydrogen isotopes also cannot be explained by the elongated shape of the latter diatomic molecules, because d k corresponds to their smallest cross sections, or in other words, the most favorable orientation for translocation 5 , 25 .…”

“…On the other hand, gas selectivity can greatly be improved using membranes with angstrom-scale pores of d 0 ≤ d k . In this case, molecules encounter substantial activation barriers for translocation through membranes, which leads to exponentially enhanced selectivity between gases having even marginally different d k 4 , 5 . Unfortunately, the presence of activation barriers also implies an exponential suppression of flow rates 4 , 5 .…”

“…In this case, molecules encounter substantial activation barriers for translocation through membranes, which leads to exponentially enhanced selectivity between gases having even marginally different d k 4 , 5 . Unfortunately, the presence of activation barriers also implies an exponential suppression of flow rates 4 , 5 . This tradeoff between permeability and selectivity is well known 6 and motivates the search for novel nanoporous materials with optimal tradeoff characteristics.…”

Quantum Systems for Enhanced High Energy Particle Physics Detectors

“…In particular for electrons with energies below 10 eV there is no systematic investigation to date but promising results for this low-energy region, which suggest that the transmission coefficient of electrons with energy less than 10 eV can achieve as high as 99% transparency [78]. In addition to selective ion filtering, freestanding graphene membranes with transparency to primary electrons may also be used to physically separate drift and amplification regions of the detectors working as gas separator [79][80][81] and profit from additional flexibility in the choice of gas mixtures optimised for high conversion efficiency in the drift region and suitable mixtures for high electron amplification factors.…”

Gas Permeability and Selectivity of a Porous WS2 Monolayer

“…In another study, Sun et al . studied gas transport through porous graphene with one missed carbon atom ring having an effective diameter of 2 Å.…”