Graphene's love affair with water

Feb 13, 2014
Credit: University of Manchester

Graphene has proven itself as a wonder material with a vast range of unique properties. Among the least-known marvels of graphene is its strange love affair with water.

Graphene is hydrophobic – it repels water – but narrow made from graphene vigorously suck in water allowing its rapid permeation, if the is only one atom thick – that is, as thin as graphene itself.

This bizarre property has attracted intense academic and industrial interest with intent to develop new and desalination technologies.

One-atom-wide graphene capillaries can now be made easily and cheaply by piling layers of – a derivative of graphene – on top of each other. The resulting multilayer stacks (laminates) have a structure similar to nacre (mother of pearl), which makes them also mechanically strong.

Two years ago, University of Manchester researchers discovered that thin membranes made from such laminates were impermeable to all gases and vapours, except for water. This means that even helium, the hardest gas to block off, cannot pass through the membranes whereas went through with no resistance.

Now the same team led by Dr Rahul Nair and Prof Andre Geim has tested how good the graphene membranes are as filters for liquid water. The results appear in the latest issue (Feb 14, 2014) of Science.

The researchers report that, if immersed in water, the laminates become slightly swollen but still allow ultrafast flow of not one but two monolayers of water.

Small salts with a size of less than nine Angstroms can flow along but larger ions or molecules are blocked. Ten Angstroms is equivalent to a billionth of a metre.

The graphene filters have an astonishingly accurate mesh that allows them to distinguish between atomic species that are only a few percent different in size.

On top of this ultraprecise separation, it is also ultrafast. Those ions that can go through do so with such a speed as if the graphene membranes were an ordinary coffee filter.

The latter effect is due to a property that the Manchester scientists call "ion sponging". Their graphene capillaries suck up small ions as powerful hoovers leading to internal concentrations that can be hundreds of times higher than in external salty solutions.

Dr Nair said: "The water filtration is as fast and as precise as one could possibly hope for such narrow capillaries. Now we want to control the 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."

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

Explore further: Graphene balloon yields unprecedented images of hydrated protein molecules

More information: Precise and Ultrafast Molecular Sieving through Graphene Oxide Membranes, by R. K. Joshi, P. Carbone, F. C. Wang, V. G. Kravets, Y. Su, I. V. Grigorieva, H. A. Wu, A. K. Geim and R. R. Nair, Science, 2014.

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User comments : 14

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Caliban
5 / 5 (3) Feb 13, 2014
This would resolve a huge number of issues surrounding our most critically endangered resource --fresh, clean water.

We can only hope that this research quickly yields the hoped-for results.
The Shootist
1 / 5 (6) Feb 13, 2014
This would resolve a huge number of issues surrounding our most critically endangered resource --fresh, clean water.

We can only hope that this research quickly yields the hoped-for results.


oh claptrap. There is no shortage of water, only the will to pump it where it needs to be.
TheGhostofOtto1923
4.5 / 5 (8) Feb 13, 2014
This would resolve a huge number of issues surrounding our most critically endangered resource --fresh, clean water.

We can only hope that this research quickly yields the hoped-for results.


oh claptrap. There is no shortage of water, only the will to pump it where it needs to be.
You mean like for 2000 miles from the great lakes over the rocky mountains to los angeles?

"Pollution, low water levels plague Great Lakes: Climate change to worsen the woes
by Elizabeth McCarthy Dec 05, 2013"

-Ever wonder how much energy it takes to pump water that far and over mountains like that? Might be easier to desalinate.

Heres a scary article
"These 11 Cities May Completely Run Out Of Water Sooner Than You Think"
http://www.huffin...418.html
ab3a
4.2 / 5 (6) Feb 13, 2014
We depend upon climate and terrain to give us the fresh water we need. This could be a major game changer. Water quality is an issue of energy use. This has the potential of significant reductions in energy required to filter the water.

The issue of "running out of water" is really not what most people think. There is plenty of water. Instead, it is an issue of infrastructure that depends upon high quality water from a limited resource. However, if we can filter water at a low cost to molecular purity with reasonably low energy costs, then the equation changes significantly.

I await some indication on the durability and lifetime of such filter materials...
Shakescene21
3.7 / 5 (3) Feb 13, 2014
Amazing. Desalination is an expensive and energy-intensive process that needs a game changer. I hope this will work for commercial-scale plants.

The small-scale device that can make a glass of drinkable water from seawater (and presumably river water) is a great idea too. I want one now.
sirchick
5 / 5 (1) Feb 13, 2014
This would help for filtering sea water to drinking water right ?

Would help alot of places in poverty as well if they can make cheap manufacturing for it.
StarGazer2011
1 / 5 (1) Feb 13, 2014
this is awesome; if it can purify dirty water in the 3rd world cheaply then the ecoloons will need to find a new excuse for genocide.
hughreid
not rated yet Feb 14, 2014
if it can hold hydrogen without losing it, and in a vessel of incredible strength, then usable storage for hydrogen suddenly becomes a real possibility
antialias_physorg
3.7 / 5 (3) Feb 14, 2014
This would help for filtering sea water to drinking water right ?

I'm not sure. The lattice constant for sodium chloride is given in the literature as 4-7 angstrom. If I read the above article right then this classifies as a 'small salt' (less than 9 Angstrom), which would mean: no desalination via this method.

The filtration this can be used for is more in the line of complex, hazardous chemicals (which is pretty cool in itself). But the last part seems to indicate that the mesh size can be tweaked somewhat. So maybe they can get it down to the size where salt filtration becomes feasible.
alfie_null
not rated yet Feb 14, 2014
Do these filters get fouled? Can they be cleaned? How long can they be expected to last before servicing, say, when filtering sea water?
antialias_physorg
3.7 / 5 (3) Feb 14, 2014
Do these filters get fouled? Can they be cleaned? How long can they be expected to last before servicing, say, when filtering sea water?

Slow down there, pardner.
This is a test of a sample in the lab - not a finished product where you can do all these additional tests. Those will come in time and then we'll see if this will be useful for industrial scales or 'just' for labwork, medical applications, etc.

Right now they are only focussing on tweaking the filtration properties.
Osteta
Feb 14, 2014
This comment has been removed by a moderator.
SiBorg
not rated yet Feb 14, 2014
Exciting stuff from the Manchester Uni. When they get the mesh size down to what's required for sea water it would be interesting to see what the energy requirements for desalination are in comparison with reverse osmosis. Also, at a filter size of 10 angstrom it seems like it could act like a barrier to bacteria (>5000 angstrom). Handy.
russell_russell
not rated yet Feb 14, 2014
"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." - Dr Nair.

Relax the lattice constants constraints to the elements targeted as well:
http://books.goog...8Q6AEwAw

edward_ponderer
5 / 5 (1) Feb 17, 2014
There are other issues as well. Ultimately, does it pay off in thermodynamic terms. The durability of the filters versus the usable energy in their manufacture.

Also, is there a danger of nano-fragment release into the water? [Buckminsterfullerene (C60), for example, kills water fleas, and produce organ damage in fish--particular brain damage--in relatively low concentrations. Nano particles tend to diffuse readily through cell membranes, and significant concentrations can develop in exposed cells.]

The wisdom of Einstein's observation of yesteryear that the individual human mind is capable of developing technologies whose unforeseen consequences are well beyond the capacity of that mind to solve, remains as potent a warning today as ever. The ever increasing failure of fail safe systems, from the scientific to the social, is wreaking havoc in our world today.

Progress should continue, but only with a mutually responsible, integrated humanity--effectively of a single mind.