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."
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?
graphene oxide, not graphene (Score:5, Informative)
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.
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.
Re:Fresh water? (Score:3, Informative)
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.
Re:Super desalination? (Score:2, Informative)
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]
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...
Re:Fresh water? (Score:5, Informative)
Re:Super desalination? (Score:3, Informative)
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.
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: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.