Graphene Membranes Superpermeable to Water 292
Dr Max writes "Not only is graphene the strongest, thinnest and best conducting material known to man, it is now shown to have superpermeability with respect to water as well. This allows a membrane made with graphene to pass water right through it (PDF), while another atom or molecule (even helium) gets blocked. 'The properties are so unusual that it is hard to imagine that they cannot find some use in the design of filtration, separation or barrier membranes and for selective removal of water,' said one of the researchers."
Does this mean... (Score:2, Insightful)
...you don't need a pressure source like you do for reverse osmosis?
Re:Does this mean... (Score:5, Insightful)
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After reading the second article, I'm not sure. I didn't read in detail, but they did some experiments with a pump. I'm not sure if it's required, but that is how they did it to research it.
Even sub um thick membranes were strong enough to withstand a differential pressure P up to 100 mbar.
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It'd actually be awful -- it might filter the oil out but it'd take all of the gases/salt/etc out of the water too.
The XPrize winning oil cleaner is probably way faster anyways since it doesn't rely on filtration (which is inherently slow)
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That's a narrow view of what is in water. Distilled / deionised water is incredibly bad for you. We can't just mix H2O and NaCl, it won't support life. Water needs a long list of nutrients and other molecules like dissolved oxygen before it can support life.
I know its not relevant at the scale we're talking, but I'm just pointing it out, there's no point in adding the salt back by itself.
Re:Does this mean... (Score:5, Informative)
...you don't need a pressure source like you do for reverse osmosis?
Even if it does not, I would think it would be much more resilient toward chlorine and iron. Perhaps it won't need as much pretreatment done to the water as a conventional film membrane requires. Currently most decent RO systems have a 10 micron sediment filter, followed by 5 and 1 micron carbon filters. If you have high iron content in the feed water, then you need a softener or some other way to reduce it prior to the sediment filter too. Since the three RO pre-filters typically need to be replaced every 6-12 months, they are the most frequent replacement item. A typical RO membrane last 2-5 years. Perhaps this would be lengthened too.
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There has also been studies showing you can make a selective filter by making nanotubes with the right diameter to let water through but not larger molecules. In addition because the walls are so "smooth" there is much less pressure to flow the water through then expected.
Re:Does this mean... (Score:5, Insightful)
Yes, but here they're showing that the membrane allows WATER through but will stop HELIUM. If I'm not mistaken, helium molecules are smallerthan water molecules. That's the freakish quality.
Might have to do with atomic forces? (Score:2)
I don't really know, but I'd suspect that it has something to do with like,electrical charge or something, not size - e.g. they're both small enough to fit through, but the helium experiences some sort of repulsive force which the water does not as it passes through the field created by the graphene.
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If only they had an article you cold read that tells you how it works.
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This is what they said:
"In conclusion, unimpeded evaporation of water through Heleaktight membranes sounds next to impossible. The closest analogy is probably the permeation of protons (atomic hydrogen) through thin films of transition metals, the phenomenon known as superpermeability. To explain our experiments, we propose the model that can be summarized as follows. GO laminates contain 2D capillaries that, under ambient conditions, are filled with an ordered monolayer of water. A capillarylike pressure p
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Hydrogen (Score:3)
One of the problems with a "hydrogen economy" is storage as hydrogen leaks out of pretty much everything.
Wonder how well this blocks it.
Re:Hydrogen (Score:4, Informative)
According to TFA (well, the BBC article on the same subject, anyway) it blocks helium molecules with what appears to be 100% efficiency. Helium molecules are smaller than the molecules in a standing mass of hydrogen, since hydrogen atoms bond together to form H2.
Helium (Score:4, Informative)
Gaseous helium difuses through pretty much everything. These graphene membranes should have truly amazing properties.
Armies of physicists will work years to explain such remarkable phenomenons. Neutrinos light than faster like just.
Re:Does this mean... (Score:5, Insightful)
Oxygen being in the center of a water molecule pretty much makes it larger than helium in ALL directions.
Re:Does this mean... (Score:4, Informative)
There has also been studies showing you can make a selective filter by making nanotubes with the right diameter to let water through but not larger molecules. In addition because the walls are so "smooth" there is much less pressure to flow the water through then expected.
Although I doubt this orientation will allow for filtering out "helium" as the original posting.
The mechanims that the original posting paper is speculating, it that the way they made the graphene oxide (not pure graphene) membrane, it is has embedded capilaries which when wet (filled with water) allow for nearly unimpeded transport of water, but when these capilaries dry out, their diameter constricts so that nothing gets through (even helium).
So to contrast, the "tubes" are not rigid and the walls are not so "smooth" in this case, the "tubes" are sort of like chinese finger puzzles. When filled with water, allow water to pass easily, but when you try to pull the last bit of water out of them, the diameter constricts and nothing can get past.. Well maybe the chinese finger puzzle analogy was a bad one, but I couldn't think of anything else...
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So, if it rained on the blimp, would the water fall all the way through? When it flies through a cloud -- is the cloud really flying through the blimp?
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Could you not use gravity? I have a filter on my counter that does just that.
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You're using energy to get that water higher than it's final location, just like a pump.
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Yeah but you could use tidal action... Sure, it limits the rate of clean water, but it's free.
Hell, if you had a cistern below sea-level then gravity would do the work for you - you'd only expend energy to pump up the water. Humans are used to that, so it's really like having free groundwater.
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You do, of course. Otherwise you'll be able to create a perpetum mobile by using this membrane to filter out pure water and then using pure water to dilute brine (it produces energy) on the other side of the membrane.
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I wonder if that's one of those things that really would work, but not because it's perpetual motion, but instead because it's taking energy out of the system that's already there. For instance, look at wind power: just stick up a windmill in a windy place and you get free energy. Except that's not quite free: there's energy in the atmosphere, which is causing this wind, so your windmill is removing (a very small amount of) energy from the atmosphere and converting it to electricity. It works ok because
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That's not a forbidden class of perpetual motion machine. It ultimately gets it's energy from the sun. And you are quite limited in the amount of energy that you can extract that way. I've never designed one, but there are a few analogous systems that are (or were, before solar power got cheaper) operating on remote islands. They were all test systems and none of them was cost effective, but that's more a design and materials problem than anything basic.
IIRC there was one system that cost several thousa
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Used to collect gifts from Shai-Hulud (Score:5, Insightful)
Now we know what the water receptacles in Dune were made of.
Super desalination? (Score:5, Interesting)
Press and squeeze a hydraulic press of water through a few layers of graphene = no more salty water?
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Better yet, no more polluted water!
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Plus we can sell the harvested toxic waste to Hormel, or Hollywood, or Congress, or somebody.
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Water so completely pure you'd have to introduce contaminants just to make it safe to drink.
http://en.wikipedia.org/wiki/Water_intoxication [wikipedia.org]
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You won't get water intoxication merely by drinking pure water. Regular drinking water contains such low proportions of minerals that, from a physiological perspective, drinking water is effectively pure water. The main problem with pure water is that it doesn't taste "right". If you've ever tried drinking distilled water... yuck.
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At the very least, it could be used for agriculture. Plants don't exactly care how water tastes. It could probably be used in soft drinks as well. Plus making cooling water that doesn't corrode stuff or build up residue - I can imagine this being used in nuclear reactors.
If it really is as simple as "run water through graphene sheets, get 100% pure hydrogen oxide", there's no limit to how many places it could be used.
water intoxication, by tap or ultrapure (Score:3)
You're right, but details are needed.
Water intoxication can happen with either tap water or ultrapure water.
If you add hydration you need to add electrolytes or your system goes out of balance. Your body can handle only so much imbalance. As it goes too far out of whack, that's effectively water intoxication.
Drinking a glass of ultrapure probably won't hurt you, nor a glass of tap. But have a bunch of either in a short period and you will have a problem. Read the Wikipedia water intoxication article's "
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Please, stop spreading the FUD. Regular tap water can just as well cause water intoxication if you drink too much of it, and ultra-pure water is by no means unsafe to drink.
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I understand that one of the current problems with desalination filtering is that the salt left behind clogs up the filter fairly quickly. Hopefully researchers will test to know for sure, but this may well suffer from the same problem. The other problem is that the water wants to be with the salt - ie. it's an energetically stable state. You have to put in some energy (usually via pressure) to get it through a filter and away from the salt. Compare that to simply filtering out fine particulates that might
Fresh water? (Score:5, Insightful)
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Or you could mine salt by dragging a net of graphene behind a boat.
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Re:Fresh water? (Score:4, Funny)
And mermaids. You ever had sex with a mermaid? Blows your mind, man. I can't even begin to imagine what it would be like to do a live one.
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Re:Fresh water? (Score:4, Insightful)
Spend a little time thinking about it, and you will realize that distilled water urban legend is silly. In your mouth, it is mixed with saliva and mucous and whatever else is stuck to your teeth, gums, and tongue. The instant it hits your stomach, it is mixed with stomach acids and whatever you ate recently. I.e. it is no longer pure distilled water. From there, the molecules wander through your body like any other water molecule. Distilling water does not give its component molecules magic properties.
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Last I checked, drinking distilled pure water is probably as bad as drinking salt water.
Where did you 'check' that? Maybe you need better sources.
There's loads of people out there who drink nothing but distilled water believing it's healthier - Google "home water distiller" for proof.
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I'm a Ph.D. Chemist who has done some water purification studies. One difficulty is the build-up of particulate matter on/in the filter which slows down (eventually stops) flow through the filter.
This problem can be addressed with the use of two filters in parallel, one of which is being back-flushed while the other operates. With the current types of filters, the system eventually plugs due to micro particulates. Perhaps this Graphine filter is immune to plugging, and merely flushing the surface will cl
Re:Fresh water? (Score:4)
nonsense, that (water intoxication) only happens if you drink too much water (whether 100% pure or not)
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Nope. There's a whole load of new-agers out there who drink nothing but distilled water. Google "water distiller" and you'll see.
The secret is that almost all foods have a lot of water in them - with some diets you might not even need to drink extra water!
The water in the food isn't distilled. Some foods even have their own minerals, too...
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I imagine the water doesn't stay super-pure for long either, after it follows a Big Ma^H^H vegan soy burger that tastes like dust into your stomach where all the other food you ate in the last couple hours is.
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Regular drinking water has such a small amount of dissolved minerals in it that, from a physiological perspective, it's effectively pure. If 10 gallons of tap water would give you water intoxication, then 9.99 gallons of pure distilled water would have the same effect. That's probably well within the error range of measuring the effect of the intoxication in the first place.
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Nonsense. I mean, lack of minerals might kill you if you NEVER ATE FOOD which contains far more minerals than any drinking water.
Re:Fresh water? (Score:5, Informative)
What you need is to make sure you obtain the electrolytes and minerals from some other source to avoid insufficiency. Other than that, pure water is safe to drink.
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Brawndo! It's got what plants crave! It's got ELECTROLYTES!
http://video.google.com/videoplay?docid=-4056644458485033927 [google.com]
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Isn't that simple diffusion rather than osmosis?
Re:Fresh water? (Score:5, Informative)
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Ah, making stuff up on Slashdot. Pure water might pull a little bit of salt from surrounding tissue. It's no big deal. It quickly becomes not-so-pure water. Any drinkable water is considerably purer than your bodily fluids and so there will be osmotic pressure.
I've drunk multi-distilled water and it's fine. I grew up drinking ordinary distilled water because our town water was so hard, and it's fine. Except for tasting slightly different, there's no noticeable effect.
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You can't drink pure H2O
Stop spreading the FUD.
it disrupts ionic balance
If you're eating properly you will get plenty of electrolytes from your food.
you could probably die from drinking too much pure water
And you could probably die from drinking too much pure Gatorade. Your point?
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And you could probably die from drinking too much pure Gatorade. Your point?
That sounds like something that Brawndo can use in a future advertising campaign.
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He's not spreading FUD. Pure H2O is possibly the most corrosive chemical in the universe and IS certainly the most corrosive chemical in the known universe. The second the stuff hits your mouth it'll leech all the minerals from your teeth. God only know what it would do to the soft tissues, but you can be certain the sodium will be gone and the cell membranes will collapse due to the saline imbalance. Nerves would certainly be rendered useless in the vicinity of the water contact as well. It would lite
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Related I would assume.
http://en.wikipedia.org/wiki/Self-ionization_of_water [wikipedia.org]
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I call BS. I challenge you to experimentally show anything you've claimed.
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He's not spreading FUD.
Yes, it most definitely is FUD, and he was spreading it, though not nearly as thickly as you.
Pure H2O is possibly the most corrosive chemical in the universe and IS certainly the most corrosive chemical in the known universe.
I think the phrase you're looking for is "universal solvent". Oxygen is the most corrosive chemical in the universe, AFAIK. Solvent != corrosive.
The second the stuff hits your mouth it'll leech all the minerals from your teeth.
Utter bullshit. The leaching process would be so slow that you'd have to leave a tooth in a glass of DI water for a long time before any substantial amount of minerals were leached out of it.
God only know what it would do to the soft tissues, but you can be certain the sodium will be gone and the cell membranes will collapse due to the saline imbalance.
Water passes through a cell membrane much more easily than those ions, so no. Osmat
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if you only drink pure water, and you only use pure water for cooking (with otherwise normal ingredients for a reasonably healthy diet), you will be perfectly fine.
if you're talking about a specific scenario (i.e. running a marathon or something similar), I would have to ask a doctor, but you should also mention this in your post.
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People don't get any significant amount of electrolytes from drinking water. So it doesn't matter the situation. Any potable water, fresh, distilled or ultra distilled, it's all the same as far as your body is concerned.
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All water is recycled. Every water molecule on the planet is at least 4.5 billion years old. All the dinosaur turds and spuge have been filtered out.
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The atoms might be at least 4.5 billion years old, but not *every* molecule of water is of that age.
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Not literally every water mollecule. There's A LOT of chemical reactions that produce water as a product or byproduct. If I remember my chemistry classes correctly, these water molecules were possibly created.
Re:Fresh water? (Score:5, Insightful)
Water is formed from hydrogen and oxygen. It is not inert, it decomposes and reforms constantly. So, no, water molecules are not at least 4.5 billion years old.
The hydrogen and oxygen atoms that make up water, or at least most of them, may well be much older than that. Particularly the hydrogen, which may be over 13 billion years old.
same atom, really? (Score:3)
Hm... When hydrogens separate from oxygens, do they always take their original electron back? Or are we getting a random one out of the, say, two valence electrons the molecule was using previously? If we're possibly getting a different electron, isn't there a constant swap going on in the universe, for perhaps all covalent molecular configuration changes?
That is, atoms reform constantly?
So, the hydrogen and oxygen atoms that make up water could themselves be relatively fresh.
wonder substance (Score:3)
But can it be used as a dessert topping?
Re:wonder substance (Score:5, Funny)
Important detail (Score:5, Informative)
It's not mentioned in the opener, but the article says it lets water "evaporate" through it.
So it's not like you can just pour water on it, and let it drip through.
I wonder if this just means steam can pass through it, or if it has to evaporate on the graphene for it to get through?
If it was the former, then why are they wording it so complicated?
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It's not mentioned in the opener, but the article says it lets water "evaporate" through it.
So it's not like you can just pour water on it, and let it drip through.
It says they sealed some water containers with graphene and the water evaporated as if the graphene wasn't there. They didn't heat/boil the tubes, they just let them stand for several days.
It doesn't say what happens if you pour water on it. It might drip...maybe they're waiting for more funding so they can perform such a complex experiment.
graphene oxide, not graphene (Score:5, Informative)
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The material they used was NOT graphene. It was graphene oxide.
Graphene monoxide or graphene dioxide?
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The material they used was NOT graphene. It was graphene oxide.
Graphene monoxide or graphene dioxide?
Graphene trioxide. Turbo. Power.
For the closest chave a man can get.
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That's okay, the substance it filtered was dihydrogen monoxide.
that shit is DEADLY.
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Breathing just one lungful will kill you.
Journalist != scientist (Score:4, Interesting)
graphene-based membranes are impermeable to all gases and liquids (vacuum-tight). However, water evaporates through them as quickly as if the membranes were not there at all.
Thanks for clarifying that. Anyway, this is a very amazing material.
Welcome to the Diamond Age (Score:2)
that is all
Graphene Condom? (Score:5, Funny)
Lets all the delicious moisture through, blocks the stuff you want blocked???
Does it erase the Water Memory? (Score:2, Funny)
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What about the Water Memory [wikipedia.org]? Does this membrane erase all this information or is a there a mechanism to determine which information to be deleted? Would be an invaluable Material for all that homeopathy stuff...
Are you clinically retarded?
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I believe the Whooosh failed to permeate the membrane.
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Water has no memory. You are being lied to so people can make money off you.
If you want cheap homeopathic results just drink tap water and believe it is fixing you.
With the proper belief you will get the benefit of the placebo effect without paying extra and as a bonus you can believe that the water is doing a whole host of killer things for you.
If it blocks Helium (Score:5, Insightful)
Helium molecules are very small. It is difficult to contain Helium gas in cylinders.
There are even far more important applications for the global economy. It may finally be possible to make Helium balloons that don't leak the tiny molecules so quickly.
More amazing uses for the miracle substance (Score:2)
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Same reason for both: money.
Meh. (Score:2)
My kids' diapers.
Negative pressure at atomistic scale ? (Score:2)
Last pdf page:
The fact that the water fills the 2D channel even under a negative pressure in the left reservoir indicates [...]
I understand that sometime negative pressure means lower pressure than global/ambiant pressure.
But here in this 2D atomistic simulation I don't know what they mean.
application to bootlegging (Score:2)
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Would be quite expensive, but letting water go thru and nothing else would save millons in remediation.
The membrane replacement cost is one of the main costs in making RO water. Energy costs are high too, but about the same order of magnitude.
So to save money the graphene membrane has to be cheaper or it has to use less energy to filter water.
I'm wondering if there are other things it lets through and not just water. Ammonia? Acetone?
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No, it would strip out -everything- except the water. Including the salts, I expect.
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Wouldn't it be less harmful to put non-salt water back in than leave oil in the water? Depending on the size of the spill, it might just dilute salt concentration a little (amongst other things).
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Graphene is one of the stiffest known materials.
Unrolling a graphene condom might be a problem but once it's on there you won't need Viagara.
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You are missing that the remaining liquid in the bottle evaporates, replacing the gas that left the bottle.