Selective Molecular Sieving Through Porous Graphene

Membranes, which act as a selective barrier, play a key role in a number of important scientific and technological processes, from cellular compartmentalization to industrial scale chemical and gas purification. The ideal membrane should be as thin as possible to maximize flux, mechanically robust to prevent fracture, and have well-defined pore sizes to increase selectivity. Due to its atomic thickness, high mechanical strength, relative inertness, and impermeability to all standard gases, graphene is the ultimate starting point for a size selective separation membrane. However, this requires the introduction of pores which can exclude larger molecules, while allowing smaller molecules to pass through. To accomplish this, we use UV-induced oxidative etching to introduce pores onto µm-sized graphene membranes and a pressurized blister test and mechanical resonance to measure the transport of a number of gases including H2, CO2, Ar, N2, CH4, and SF6 through these pores. The experimentally measured leak rate and separation factors agree well with the model of effusion through a small number of molecular sized pores. These porous atomically-thin graphene membranes represent a new class of "ideal" molecular sieves, where gas transport occurs by effusion through molecular-sized pores with atomic-sized channel lengths.