New ultra-thin membrane could have applications in water purification

One of the thinnest membranes ever made is also highly discriminating when it comes to the molecules going through it. Engineers at the University of South Carolina have constructed a graphene oxide membrane less than 2 nanometers thick with high permeation selectivity between hydrogen and carbon dioxide gas molecules.

The selectivity is based on molecular size, the team reported in the journal Science. Hydrogen and helium pass relatively easily through the membrane, but carbon dioxide, oxygen, nitrogen, carbon monoxide and methane permeate much more slowly.

"The hydrogen kinetic diameter is 0.289 nm, and carbon dioxide is 0.33 nm. The difference in size is very small, only 0.04 nm, but the difference in permeation is quite large" said Miao Yu, a chemical engineer in USC's College of Engineering and Computing who led the research team. "The membrane behaves like a sieve. Bigger molecules cannot go through, but smaller molecules can."

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