This would sure open new opportunities all over the coastal areas of Baja!!
A new approach to water desalination
Graphene sheets with precisely controlled pores have potential to purify water more efficiently than existing methods.
David L. Chandler, MIT News Office
July 2, 2012
The availability of fresh water is dwindling in many parts of the world, a problem that is expected to grow with populations. One promising source of
potable water is the world’s virtually limitless supply of seawater, but so far desalination technology has been too expensive for widespread use.
Now, MIT researchers have come up with a new approach using a different kind of filtration material: sheets of graphene, a one-atom-thick form of the
element carbon, which they say can be far more efficient and possibly less expensive than existing desalination systems.
When water molecules (red and white) and sodium and chlorine ions (green and purple) in saltwater, on the right, encounter a sheet of graphene (pale
blue, center) perforated by holes of the right size, the water passes through (left side), but the sodium and chlorine of the salt are blocked.
Graphic: David Cohen-Tanugi
“There are not that many people working on desalination from a materials point of view,” says Jeffrey Grossman, the Carl Richard Soderberg Associate
Professor of Power Engineering in MIT’s Department of Materials Science and Engineering, who is the senior author of a paper describing the new
process in the journal Nano Letters.
Grossman and graduate student David Cohen-Tanugi, who is the lead author of the paper, aimed to “control the properties of the material down to the
atomic level,” producing a graphene sheet perforated with precisely sized holes. They also added other elements to the material, causing the edges of
these minuscule openings to interact chemically with water molecules — either repelling or attracting them.
“We were very pleasantly surprised” by how well graphene performed compared to existing systems in computer simulations, Grossman says.
One common method of desalination, called reverse osmosis, uses membranes to filter the salt from the water. But these systems require extremely high
pressure — and hence, energy use — to force water through the thick membranes, which are about a thousand times thicker than graphene. The new
graphene system operates at much lower pressure, and thus could purify water at far lower cost, the researchers say.
While reverse osmosis has been used for decades, “really basic mechanisms of separating salt from water are not well understood, and they are very
complex,” Cohen-Tanugi says, adding that it’s very difficult to do experiments at the scale of individual molecules and ions. But the new
graphene-based system, he says, works “hundreds of times faster than current techniques, with the same pressure” — or, alternatively, the system could
run at similar rates to present systems, but with lower pressure.
The key to the new process is very precise control over the size of the holes in the graphene sheet. “There’s a sweet spot, but it’s very small,”
Grossman says — between pores so large that salt could pass through and ones so small that water molecules would be blocked. The ideal size is just
about one nanometer, or one billionth of a meter, he says. If the holes are just a bit smaller — 0.7 nanometers — the water won’t flow through at all.
Other research groups have worked to create pores in graphene, Cohen-Tanugi says, but at very different sizes and for very different purposes — for
example, making much bigger holes to filter large molecules such as DNA, or to separate different kinds of gases. The methods used for those processes
were not precise enough to make the tiny holes needed for desalination, he says, but more advanced techniques — such as helium-ion bombardment to make
precise holes in graphene, chemical etching and self-assembling systems — might be suitable.
For now, Grossman and Cohen-Tanugi have been doing computer simulations of the process to determine its optimal characteristics. “We will begin
working on prototypes this summer,” Grossman says.
Because graphene is the subject of research into many different applications, there has been a great deal of work on finding ways of making it
inexpensively and in large quantities. And for desalination, because graphene is such a strong material — pound for pound, it’s the strongest material
known — the membranes should be more durable than those presently used for reverse osmosis, Grossman says.
In addition, the material needed for desalination does not need to be nearly as pure as for electronic or optical uses, he says: “A few defects don’t
matter, as long as they don’t open it up” so that salt could pass through.
Joshua Schrier, an assistant professor of chemistry at Haverford College, says, “Previous simulations had studied the flow of water through very small
holes in graphene, and the design of pores that selectively allow ion passage, but — despite the social and engineering relevance to desalination —
nobody had thought to examine the intersection of these two fields.” The work by the MIT team could open a whole new approach to desalination, he
says.
Schrier adds, “Manufacturing the very precise pore structures that are found in this paper will be difficult to do on a large scale with existing
methods.” However, he says, “the predictions are exciting enough that they should motivate chemical engineers to perform more detailed economic
analyses of … water desalination with these types of materials.”
The work was funded by the MIT Energy Initiative and a John S. Hennessy Fellowship, and used computer resources from the National Energy Research
Scientific Computing Center.
Printwoody with a view - 7-10-2012 at 01:53 PM
it's all there^^^^. the highest purity flake graphite deposit in the world. this is one of my early retirement long shots.....Mulegena - 7-10-2012 at 02:01 PM
Graphene, sheets of carbon one-atom thick in hexagonal bonds.
Wow! We might even find our dear little Higgs boson lurking about.
This would change the world! The implications for Baja alone are tremendous.
Living in a desert land, water is a prime concern.
Thanks for this, Runner.
Woodz, are you saying one can add this to an investment portfolio?
woody with a view - 7-10-2012 at 02:14 PM
Quote:
Originally posted by Mulegena
Woodz, are you saying one can add this to an investment portfolio?
i own a grip of FCSMF which is down, as is the rest of the market. i' won't be READY to retire for another 10 years so i got time.....Mulegena - 7-10-2012 at 02:17 PM
Forward thinking, Woodman.
How'd you find it?
Most folks have no idea what's in their portfolio.bajaguy - 7-10-2012 at 02:27 PM
What do they do with the sodium and chlorine by product, and how much water do they process to get one gallon of "pure" water????woody with a view - 7-10-2012 at 02:38 PM
Quote:
Originally posted by Mulegena
Forward thinking, Woodman.
How'd you find it?
Most folks have no idea what's in their portfolio.
i've been into GWMGF for quite awhile and while looking for more info came across Focus Graphite. instead of owning microsoft or facebook, i'm looking
for a small company that is leading the charge towards the next big thing that will change our lives.
either fully funded or sitting on the largest, purest source of a mineral gives me confidence.
another good shot at easy retirement $ is UURAF.
[Edited on 7-10-2012 by woody with a view]woody with a view - 7-11-2012 at 02:03 PM
11 July 2012 Last updated at 07:15 ET
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Graphene holes 'heal themselves'
By Jason Palmer Science and technology reporter, BBC News
Illustration of graphene lattice Graphene forms in a neat sheet of interlocked six-sided figures just one atom thick, but is easily damaged
Continue reading the main story
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Graphene - the "wonder material" made of sheets of carbon just one atom thick - undergoes a self-reparing process to correct holes, researchers
report.
Graphene's outstanding mechanical strength and electronic properties make it a promising material for a wide range of future applications.
But its almost ethereal thinness makes it easily damaged when working with it.
The study, published in Nano Letters, suggests it can be repaired by simply exposing it to loose carbon atoms.
It was carried out by researchers at the University of Manchester, UK - including Konstantin Novoselov, who shared a Nobel prize as graphene's
co-discoverer - and at the SuperStem Laboratory of the Engineering and Physical Sciences Research Council in Daresbury, UK.
The team was initially interested in the effects of adding metal contacts to strips of graphene, the only way to exploit its phenomenal electronic
properties.
The process routinely creates holes in the atom-thick sheets, so the researchers were trying to understand how those holes form, firing electron beams
through graphene sheets and then studying the results with an electron microscope.
But to their surprise, they found that when carbon atoms were also near the samples, the atoms snapped into place, repairing the two-dimensional
sheet.
"It just happened that we noticed it," said co-author of the study Quentin Ramasse of the SuperStem laboratory.
"We repeated it a few times and then tried to understand how that came about," he told BBC News.
The team found that when metal atoms were around, they too would snap into the edges of the holes, and when carbon was around as part of molecules
called hydrocarbons, the carbon atoms from them could form irregular shapes in the sheets.
But pure carbon atoms would bump metal atoms out of the way, perfectly repairing the holes and forming a fresh and uninterrupted lattice of hexagons -
textbook graphene - as they report in an online preprint of the article.
"If you can drill a hole and control that 'carbon reservoir', and let them in in small amounts, you could think about tailoring edges of graphene or
repairing holes that have been created inadvertently," Dr Ramasse said.
"We know how to connect small strips of graphene, to drill it, to tailor it, to sculpt it, and it now seems we might be able to grow it back in a
reasonably controlled way."
