Graphene membrane may have frac water application
Engineers at the University of South Carolina have constructed a graphene oxide (GO) membrane less than 2 nm thick with high permeation selectivity between hydrogen and carbon dioxide gas molecules.The team, led by Miao Yu, an assistant professor in USC's department of chemical engineering, believes that one possibility for the technology could be purifying polluted water produced by hydraulic fracturing.
Ultrathin, Molecular-Sieving Graphene Oxide Membranes for Selective Hydrogen Separation was published in Science 4 October 2013: 95-98.
The paper reports the production of ultrathin GO membranes, with thickness approaching 1.8 nm, prepared by a facile filtration process. These membranes showed mixture separation selectivities as high as 3,400 and 900 for H2 /CO2 and H2 /N2 mixtures, respectively, through selective structural defects on GO.
The membrane is constructed on the surface of a porous aluminum oxide support. Flakes of graphene oxide, with widths on the order of 500 nm but just one carbon atom thick, were deposited on the support to create a circular membrane about 2 cm² in area.
The team found by atomic force microscopy that a single graphene oxide flake had a thickness of approximately 0.7 nm. Thus, the 1.8‑nm‑thick membrane on aluminum oxide is only a few molecular layers thick, with molecular defects within the graphene oxide that are essentially uniform and just a little too small to let carbon dioxide through easily.
The advance has a range of potential applications. With widespread concerns about carbon dioxide as a greenhouse gas, the efficient separation of carbon dioxide from other gases is a high research priority. Moreover, hydrogen represents an integral commodity in energy systems involving, for example, fuel cells, so purifying it from gas mixtures is also an active area of interest.
Yu also notes that the dimensions of the molecular sieve are on the order of the size of water, so, for example, purifying the copious amounts of tainted water produced by hydraulic fracturing (fracking) is another possibility.