Graphene May Be Used To Make Super-Efficient Water Filters

By Shweta Iyer on February 13, 2014 5:18 PM EST

water
Researchers say that while removing salt from sea water may seem complicated right now, graphene may hold the answer to perfecting the process. (Photo: Photo courtesy of <a href=&)

Imagine if you could drink sea water. Wouldn't that be a great solution to the world's water shortage problem? But is desalination (removing salt from sea water) a simple process? Researchers at the University of Manchester say that while desalination may seem too complicated right now, Graphene may hold the answer to perfecting the process, according to a press release Thursday.

Graphene is often considered to be a miracle material because of its myriad uses in medicine, distillation processes, integrated circuits, conductors, and filteration. It is a 2-dimensional crystalline allotrope of carbon and can be described as a one atom thick layer of graphite. Graphene sheets are highly effective filters because, tiny capillaries in these sheets rapidly absorb water and allow it to permeate through but at the same time hold back other impurities. This unique property of graphene is being harnessed to make water filtration and desalination systems.

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These filters, which are one-atom-wide graphene capillaries, are made of graphene oxide, a derivative of graphene. Layers of graphene oxide are piled on top of each other and the resultant multilayer stacks, also called laminates, have a structure as mechanically strong as nacre (mother of pearl).

"The water filtration is as fast and as precise as one could possibly hope for in such narrow capillaries. Now we want to control the graphene mesh size and reduce it below nine Angstroms to filter out even the smallest salts like in seawater. Our work shows that it is possible", said Dr. Rahul Nair, one of the main collaborators of the research.

Researchers at the University of Manchester have been conducting several experiments on graphene and have concluded that these laminates block all gases and vapors while selectively allowing water to pass through. Even helium, which is an inert and light gas, and difficult to block, cannot pass through the membranes of a graphene filter.

The researchers are also studying graphene's potential as an ultrafast water purifier. They report that when the filters are immersed in water, they absorb water and appear swollen but water can still pass through very fast. Ions or molecules greater than nine Angstroms are blocked while the smaller salts are allowed to pass through astonishingly fast. This is due to an effect called ion sponging. The graphene capillaries absorb large quantities of small ions. This large intake implies highly concentrated solutions inside the capillaries, hundreds of times higher than the external salty solutions, thus facilitating their quick permeability through the filter.

 "Our ultimate goal is to make a filter device that allows a glass of drinkable water made from seawater after a few minutes of hand pumping. We are not there yet but this is no longer science fiction", added Dr Irina Grigorieva, a co-researcher.

Source: Nair, R. Grigorieva, I. et al. Precise and Ultrafast Molecular Sieving Through Graphene Oxide Membranes. Science. 2014.

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