Graphene membranes etched to create molecular sieves
9 October 2012
An engineering team at the University of Colorado Boulder has
produced the first experimental results showing that atomically thin
graphene membranes with tiny pores created in them can effectively and
efficiently separate gas molecules through size-selective sieving.
The findings are a significant step toward the realization of more
energy-efficient membranes for industrial uses such as natural gas
production and reducing carbon dioxide emissions from power plant
exhaust pipes. The medical world is also likely to see uses for the
Mechanical engineering professors Scott Bunch and John
Pellegrino co-authored a paper in Nature Nanotechnology with graduate
students Steven Koenig and Luda Wang detailing the experiments. The
paper was published Oct. 7 in the journal’s online edition.
research team 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.
This illustration depicts a single
molecular-sized pore in a graphene membrane. The membrane is
separating carbon dioxide from nitrogen. A carbon dioxide molecule
is passing through the pore while nitrogen molecules are too large
to pass through. Illustration by Zhangmin Huang
“These atomically thin, porous graphene membranes represent a new
class of ideal molecular sieves, where gas transport occurs through
pores which have a thickness and diameter on the atomic scale,” said
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.
The mechanical properties of this wonder material fascinate our
group the most,” Bunch said. “It is the thinnest and strongest
material in the world, as well as being impermeable to all standard
Those characteristics make graphene an ideal material for creating a
separation membrane because it is durable and yet doesn’t require a
lot of energy to push molecules through it, he said.
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.
The importance of graphene in the scientific world was illustrated
by the 2010 Nobel Prize in physics that honored two scientists at
Manchester University, Andre K Geim and Konstantin Novoselov, for
producing, isolating, identifying and characterizing graphene.
Scientists see a myriad of potential for graphene as research
progresses, from making new and better display screens and electric
circuits to producing tiny biomedical devices.