Nanoporous graphene – a two-dimensional membrane for efficient ³He/⁴He separation

Graphene nanopores of suitable size allow for a separation of fermionic Helium-3 from its bosonic counterpart helium-4 due to quantum tunneling. The transmission probabilities are crucially depending on the diameter of the pore. A necessary fine-tuning of the pore diameter is realized by a partial dotation of C-H bonds on the pore rim by nitrogen atoms. Potential barriers for several different types of pores are calculated with density-functional theory applying a long-range corrected density functional to account for weak van der Waals interactions. The results are used as input for the numerical calculation of the transmission probabilities for ³He and ⁴He. We show that slight deviations in the tunneling probability for the two isotopes can lead to a high selectivity at an industrially acceptable gas flux.