Graphene-based sieve turns seawater into drinking water

Daydream believer said:
Extract from the article:-
Previous work had shown that graphene oxide membranes became slightly swollen when immersed in water, allowing smaller salts to flow through the pores along with water molecules.

Sorry you are correct. The water causes the product to swell as i said, but I incorrectly stated that this caused the holes to clog. I was sure that the person describing the process said that the swelling closed the holes not opened them, which if you think about it would seem correct. However, your quote would seem the correct one, although one might debate the theory behind that
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The report I saw, was via one of their 'expert' reporters, so take your pick.:D
 
I read and listened and my understanding is, the holes are just the right size for pure water molecules to pass through and in the process they pull identical pure molecules through the hole like a train making the flow through very efficient.
Salt can't get through as to move they are coated with hijacked water molecules or their own, together these are too big to go through the membrane.
These collect and as they are coated with water molecules they are easily siphoned off the membrane.

It was likened to a system a bit like gortex which will allow water vapor through your expensive water proofs but not water droplets.

Either way its awesome news and I truly hope this actually makes it to the market place with a British company.
 
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alant said:
What has that got to do with common sense?
The bigger the hole, the less pressure needed to force water through, than if the hole is smaller.
What changes just by reading something?
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It's always helpful to read what you are commenting on, in the case in point it's also the thickness of the membrane i.e. the length of the hole / tunnel that the water molecules have to travel through the thicker it is the more resistance and therefore more energy required. This will be one of the great advantages of molecular thick membranes.
 
Daydream believer said:
The water causes the product to swell as i said, but I incorrectly stated that this caused the holes to clog. I was sure that the person describing the process said that the swelling closed the holes not opened them, which if you think about it would seem correct. However, your quote would seem the correct one, although one might debate the theory behind that
Click to expand...

Perhaps it depends upon the swelling mechanism? If you took a thin sheet of metal which was pierced with holes and then heated the metal sheet so that it expands, the holes all get slightly bigger.

Richard
 
RichardS said:
Perhaps it depends upon the swelling mechanism? If you took a thin sheet of metal which was pierced with holes and then heated the metal sheet so that it expands, the holes all get slightly bigger.

Richard
Click to expand...

Well would it?
(One accepts that we are substituting expansion due to heat in lieu of swelling due to water )
If one imagines a simple flour sieve the heat would expand the wires of the sieve & the holes would get smaller. The overall size of the sieve would not necessarily get much bigger
Now taking that one stage further we have a membrane where the walls of the holes are rigidly connected, unlike the wires of the sieve. When the heat is applied the whole membrane will want to expand but each interconnecting thread around each hole will want to expand in diameter as well. Would this not effectively reduce the hole size?
One has to remember that this is a very thin material with very thin threads around the holes.
The example that you use in your metal sheet probably has more metal around the hole as a percentage of material per hole & that would be pushing the sheet outwards. If you considered the effect of heat on an individual ring then you would be correct ; but I believe that in the case of the membrane you may be wrong
 
Daydream believer said:
Well would it?
(One accepts that we are substituting expansion due to heat in lieu of swelling due to water )
If one imagines a simple flour sieve the heat would expand the wires of the sieve & the holes would get smaller. The overall size of the sieve would not necessarily get much bigger
Click to expand...

yes it would else it would buckle (in which chase the holes still get bigger)

I think the problem with visualising this is that absorbent materials (that are common knowledge) are also squishy, steel on the other hand isnt really. So, a sponge can easily be kept the same size whilst its material expands (filling the gaps) whilst to do the same with steel just isnt going to happen. (making the gaps bigger)

Quote Originally Posted by alant

What has that got to do with common sense?
The bigger the hole, the less pressure needed to force water through, than if the hole is smaller.
What changes just by reading something?
Click to expand...

Me thinks you are forgetting capillary action. Something that I guess is quite significant to 1 molecule dia holes, and was never mentioned in the oh so bright press (no surprise there then)
edit add... also with teeny weeny holes, you can get a bucket load more of them in the space... keeping the total hole cross-sectional area up.
 
Dougal Tolan said:
yes it would else it would buckle (in which chase the holes still get bigger)

I think the problem with visualising this is that absorbent materials (that are common knowledge) are also squishy, steel on the other hand isnt really. So, a sponge can easily be kept the same size whilst its material expands (filling the gaps) whilst to do the same with steel just isnt going to happen. (making the gaps bigger)



Me thinks you are forgetting capillary action. Something that I guess is quite significant to 1 molecule dia holes, and was never mentioned in the oh so bright press (no surprise there then)
edit add... also with teeny weeny holes, you can get a bucket load more of them in the space... keeping the total hole cross-sectional area up.
Click to expand...

What, has "capillary action" got to do with a liquid being forced through a hole?
 
alant said:
What, has "capillary action" got to do with a liquid being forced through a hole?
Click to expand...

When the hole is 1 molecule dia it has more to do with it than anything else. Capillary action will suck water right through the hole without any help from any pressure at all. The only snagette is getting it out the other end.
 
What surprises me is that Graphene is 0.345Nm thick but as strong as steel, so why aren't planes, ships and everything built of metal that uses power using it, the reduction in weight would make massive fuel savings.
 
KellysEye said:
What surprises me is that Graphene is 0.345Nm thick but as strong as steel, so why aren't planes, ships and everything built of metal that uses power using it, the reduction in weight would make massive fuel savings.
Click to expand...
Maybe just a bit too flexible
 
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