An ultra thin membrane could transform gas and water purification.
Engineers at the school have built a graphene oxide membrane less than two nanometers thick with high penetration selectivity between hydrogen and carbon dioxide gas molecules. According to engineers, the selectivity rests on molecular size. Hydrogen and helium move somewhat easily through the membrane, but carbon dioxide, oxygen, nitrogen, carbon monoxide and methane penetrate much more leisurely.
“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 team leader Miao Yu, a chemical engineer in University of South Carolina’s College of Engineering and Computing. “The membrane behaves like a sieve. Bigger molecules cannot go through, but smaller molecules can.”
The membrane is built on the surface of a permeable aluminum oxide support. Flakes of graphene oxide, with widths of 500 nm but only one carbon atom thick, were placed on the support to develop a circular membrane approximately two square centimeters in area.
The membrane is like an overlapping collage of graphene oxide flakes. Gas molecules are searching for holes anywhere they can be located, and in a membrane constructed of graphene oxide flakes, there could be holes within the flakes or holes between the flakes.