Exponentially selective molecular sieving through angstrom pores

TL;DR

This study demonstrates that graphene pores created by electron exposure can achieve exponential molecular selectivity based on size, allowing small gases like helium and hydrogen to permeate while blocking larger molecules.

Contribution

First experimental demonstration of angstrom-scale pores in graphene enabling size-dependent gas separation with exponential selectivity.

Findings

Helium and hydrogen permeate easily through the pores.

Larger gases like xenon and methane are effectively blocked.

Permeation activation barriers increase quadratically with molecular size.

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.