Engineering faculty and students at the University of Colorado Boulder have produced the first experimental results showing that atomically thin graphene membranes with tiny pores can effectively and efficiently separate gas molecules through size-selective sieving.

• Graphene  can be used for more energy-efficient membranes for natural gas production and for reducing carbon dioxide emissions from power plant exhaust pipes.

The findings are a significant step toward the realization of more energy-efficient membranes for natural gas production and for reducing carbon dioxide emissions from power plant exhaust pipes.

The research team at the University of Colorado introduced nanoscale pores into graphene sheets through ultraviolet light-induced oxidative “etching,” and then measured the permeability of various gases across the porous graphene membranes.  Experiments were done with a range of gases including hydrogen, carbon dioxide, argon, nitrogen, methane and sulphur hexaflouride -- which range in size from 0.29 to 0.49 nanometers -- to demonstrate the potential for separation based on molecular size. One nanometer is one billionth of a meter.

Graphene, a single layer of graphite, represents the first truly two-dimensional atomic crystal. It consists of a single layer of carbon atoms chemically bonded in a hexagonal “chicken wire” lattice -- a unique atomic structure that gives it remarkable electrical, mechanical and thermal properties.

Other technical challenges will need to be overcome before the technology can be fully realized. For example, creating large enough sheets of graphene to perform separations on an industrial scale, and developing a process for producing precisely defined nanopores of the required sizes are areas that need further development. The CU-Boulder experiments were done on a relatively small scale.