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UNC research helps explain the properties of water at very small scales in very small objects.

Recent work by the Lawrence Livermore National Laboratory brought yet another possible use for carbon nanotubes to our attention in the form of filtration systems. Immediate applications could be desalinization and other forms of water filtration. The intricate properties of the interactions between carbon nanotubes and water molecules make the filters very efficient.

Carbon itself, in forms such as nanotubes or graphene (sheets of carbon just one layer of atoms thick), is actually hydrophobic. That is to say that it actually repels water, giving it no surface to cling to. So why do these nanotube filters outperform conventional filtration systems?

Researchers at the University of North Carolina at Chapel Hill have been looking into these interactions using rolled graphene nanotubes. More specifically, they have been examining how water flows through these tubes which should be hydrophobic.

What they found was that at room temperature, water only stubbornly moved through the 1.4 nanometer diameter tubes. However, when they reduced the temperature of the nanotubes to eight degrees centigrade, water moved easily through. Yue Wu, Ph.D., leader of the study, explains that the results show that it is possible for water to assume different properties and structures based on temperature and the size and shape of the confining structure at the nanoscale.

Far from simply showing these changes, the research may have several immediate real world applications. As well as making desalinization filters like LLNL's more efficient, it could apply to simple activated charcoal filters like the ones found in homes. Gas masks and other permeable membranes could benefit from the study as understanding how temperature affects permeability would allow better systems to be designed, as well as brings the potential of temperature controlled flow control in these situations.



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I'm a dork
By PedroDaGr8 on 10/9/2008 9:56:09 AM , Rating: 4
I love how the article talks about water and the picture shows what appears to be methane (CH4) or some other tetrahedral compound.




RE: I'm a dork
By spuddyt on 10/9/2008 11:22:46 AM , Rating: 2
errrr... how could CH4 be in ANY giant structure? running out of valency?


RE: I'm a dork
By PedroDaGr8 on 10/9/2008 12:33:00 PM , Rating: 2
It wasn't in the structure. They changed the picture. The one that now shows a MWNT (Multiwalled nanotube) originally had a SWNT (Single walled nanotube) with what appeared to be CH4 molecules flying through the tube. Though you do see stuff such as CH5+ as transient species in high energy reactions. For example the superacid FSO3H–SbF5 will react with Methane to produce CH5+ as a transient species before decomposing to H3 + CH3+ (still bloody reactive, Carbon does not like an incomplete octet) which then goes on through a series of steps to react with 3CH4 molecules to form (CH3)3C+ (t-butyl ion) and 3H2. The t-Butyl is a moderately stable cation, usually created on reaction with tertbutanol.


RE: I'm a dork
By PedroDaGr8 on 10/9/2008 12:37:51 PM , Rating: 2
Doh, I can't type

FSO3HSbF5 + CH4 --> CH5+ + FSO3SBF5- <Simple H+ transfer>
CH5+ --> H 2 + CH3+ (I wrote H3)
CH3+ + 3CH4 --> (CH3)3C+ + 3H2 nice "normal" species.


RE: I'm a dork
By fic2 on 10/9/2008 2:11:22 PM , Rating: 5
Yeah, we were all laughing at you behind your back for that basic mistake.


RE: I'm a dork
By PedroDaGr8 on 10/9/2008 5:27:13 PM , Rating: 2
Haha DIAF, and I mean that in the most neighborly way possible :)


Exciting stuff
By pwndcake on 10/9/2008 9:55:37 AM , Rating: 2
I wonder if this technology could be used for improving dialysis machines. Maybe even helping to create an artificial kidney?




RE: Exciting stuff
By Spivonious on 10/9/2008 10:17:43 AM , Rating: 2
It seems that carbon nanotubes can do anything. I'm just waiting for the lawsuits to start once some weird side effect of carbon nanotubes surfaces.


RE: Exciting stuff
By austinag on 10/9/2008 10:28:00 AM , Rating: 2
Here is an article on this site already talking about possible dangers:
http://www.dailytech.com/Nanoparticles+Can+Slip+Th...


RE: Exciting stuff
By MrBlastman on 10/9/2008 11:04:36 AM , Rating: 2
Nobody has considered the dangers of carbon nanotube equipped super mosquitos!

The people demand to know more...


RE: Exciting stuff
By steven975 on 10/9/2008 4:42:27 PM , Rating: 2
Maybe for the purpose of filtering out excess water.

I don't know how it would go about removing potassium, sodium, or phosporus, though. These generally exist in compounds such as phosphates, too.

Then you have large molecules like beta-2 microglobulin which must be removed or certain bone disorders will develop. This requires large pore sizes in the membranes.

Nanotechnology has been used to make pore sizes more uniform to get rid of large molecules yet keep certain much larger molecules like albumin, which tends to seep out of current large-pore-size artificial kidneys. Carbon nanotubes probably aren't the answer unless they can be optimized for the pores to allow for seepage of molecules under ~12K daltons in size. I have a feeling the application in this story is for ultra-small pore sizes, though.

An implantable artifical kidney would be a godsend, but the issue of a way to manage water/sodium/potassium balances that is the large hurdle. Current external artifical kidneys can only be used for a few hours before your immune response makes the filters unusable and that has to be solved, too. I was on dialysis for many years, and I've done a lot of my own research into this. I have a "real" kidney now, so that's slowed a bit.


Cart before the horse?
By menace on 10/9/2008 1:40:47 PM , Rating: 2
Have they made any headway about how to efficiently mass produce CNTs? These applications are all hype until we solve that problem. Nobody's gonna pay like $50,000 for a tap water filter. Sure there may be a few limited uses like filtration sytems in space but I'd rather see more reporting on any progress in the area of production research for CNT and Fullerene structures.




RE: Cart before the horse?
By Diesel Donkey on 10/9/2008 2:45:35 PM , Rating: 2
Making them isn't hard. It's making them in something other than a jumbled mess that's difficult. Well, that and separating out the multi-walled from the single-walled CNTs.


RE: Cart before the horse?
By menace on 10/10/2008 11:33:36 AM , Rating: 2
I thought they do something like they take like 100g of carbon, blast it in a plasma arc, then sort through whats remains to recover maybe like micrograms of stuff that reformed into perfect tubes and balls. Not a very efficient process.


RE: Cart before the horse?
By Diesel Donkey on 10/10/2008 12:34:03 PM , Rating: 2
I believe that there are still three main methods of CNT creation: arc discharge evaporation (as you mentioned), laser ablation, and chemical vapor deposition. When I last checked (when writing my undergrad physics thesis two years ago), CVD had become the most popular method for its high yield to cost ratio, the ability to grow CNTs directly on a desired substrate in specific positions, and the ability to synthesize vertically aligned CNTs. I haven't been following the development of CNT creation methods very closely since then, but I think there have been some promising enhancements to the CVD process in the last couple years. So you're right that the arc discharge method is highly inefficient, but I think that other methods do provide better results.


Seen this before
By Diesel Donkey on 10/9/2008 2:51:03 PM , Rating: 2
I remember seeing a local company's exhibit at my old engineering school three years ago that depicted the startup company's work for the DoD on creating CNT water filters. They may not have figured out exactly how the water moved through them, but they were able to filter out sediment and other contaminants while killing bacteria and viruses. I think the bacteria and viruses were taken care of by molecular additions to the CNT structure. So the tubes themselves did the filtering, and little molecular arms killed the nasties.




Incredible
By 7Enigma on 10/10/2008 11:28:47 AM , Rating: 2
quote:
Yue Wu, Ph.D., leader of the study, explains that the results show that it is possible for water to assume different properties and structures based on temperature and the size and shape of the confining structure at the nanoscale.


Holy crap! Like ice?...........I kid, I kid.




By blueeyesm on 10/10/2008 12:01:00 PM , Rating: 2
A winery, brewery, etc.




If they continue to be so popular...
By Oralen on 10/12/2008 11:49:36 AM , Rating: 2
Spielberg and Lucas will put nanotubes in the next Indiana Jones script.

"They raped him, Kyle! They raped him!"




"A politician stumbles over himself... Then they pick it out. They edit it. He runs the clip, and then he makes a funny face, and the whole audience has a Pavlovian response." -- Joe Scarborough on John Stewart over Jim Cramer

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