
Graphene: The perfect water filter - ukdm
http://www.extremetech.com/extreme/115909-graphene-the-perfect-water-filter
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aprescott
On the water filtration front, one thing I'm curious to know is what happened
to the LifeSaver bottle. Was that just the victim of TED hype?

<http://en.wikipedia.org/wiki/LifeSaver_bottle>

[http://www.ted.com/talks/michael_pritchard_invents_a_water_f...](http://www.ted.com/talks/michael_pritchard_invents_a_water_filter.html)

From the Wikipedia page: "In 2007, the LifeSaver bottle was tested by the
London School of Hygiene & Tropical Medicine and the results found it to
completely filter out all bacteria and viruses."

This may be a stupid question, but is that simply nothing remarkable?

Since graphene seems to be the best thing discovered for filtering evaporated
water, not liquid water, is the LifeSaver not as great a solution as the TED
video makes it out to be, for some reason?

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mtgentry
The LifeSaver bottle is remarkable but it seems like the filtering process
doesn't scale well. Imagine having to use this throughout the day each time
you fill up.

My company works w/ a charity in rural India that makes BioSand filters. The
filters allow people to clean large amounts of water and then save it in
containers for later. 90-95% of the impurities are removed. More info here if
curious: <http://faucetface.com/pages/1-for-100>

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swombat
Water filtration is indeed a key survival technology for humanity in the next
50-100 years, so seeing technology already providing possible solutions to the
so-called "water wars" of the future is great!

I presume such a filter will also remove all bacteria/etc from the water. So
basically, you could grab some water from the Thames, stick it through one of
those filters, and drink it. It might lack some minerals, but it won't get you
sick.

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yourapostasy
From the article, they are talking about filtering _evaporated_ water through
the membrane. It sounds like you will be waiting a long, long time for that
drink of water filtered via its gaseous phase through this material.

Regarding bacterial contamination concerns that the posters below discussed,
they are likely remedied if the filtration occurs in the gaseous phase of
water, though some bacteria can climb substrate walls against gravity so it
would be an interesting engineering design challenge.

~~~
unwind
But getting water into the gaseous state is quite easy, by adding heat, right?
I realize that takes (quite a lot of) energy, but if all of the water that is
heated past vaporization becomes 100% cleaned with no other energy input and
no moving parts, that sounds like a rather nifty machine.

I'm sure there are engineering constraints that I'm not aware of, like the
filtering clogging up and so on, of course. Still, it sounds almost magical
with such a perfect filter.

~~~
seanalltogether
You can do all of that without the filter though. There are very low tech
products that already do this.
<http://www.celsias.com/media/uploads/admin/watercone1.jpg>

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tylerritchie
The watercone is great for non-potable water that isn't contaminated with
compounds that also boil below or near 100 °C and are either in A) high
proportion or B) that bio-accumulate.

If the preliminary findings with the graphene oxide are hold true, you could
stick a cap made of the stuff on a watercone evaporating a bunch of zombie
blood and end up with ASTM Type I water to keep you hydrated after the zombie
apocalypse.

~~~
grannyg00se
In order for this statement to be relevant I think you must be of the opinion
that zombie blood contains compounds that boil below or near 100°C. Otherwise
you still wouldn't need graphene oxide cap.

So I'm wondering if zombie blood is known to have these type of compounds. But
more importantly, how common is it for typically impotable water to have these
type of compounds?

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kijin
Off the top of my head, I can think of one toxic substance that easily mixes
with water and boils below 100°C: methanol.

Some hydrocarbons might also fit the description.

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seanalltogether
You're right, which would explain why they experimented with vodka. It seems
this filter is better at filtering water _out_ of a substance, rather then
filtering _substances_ out of water.

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samirahmed
As a research who has worked with graphene. I would like to point out that
Graphene oxide and graphene are two very different materials in terms of
properties and synthesis.

The graphene oxide mentioned in this article tends to exhibit weaker
electrical and mechanical properties than graphene oxide but is much easier to
synthesize than conventional graphene, and so a future with graphene oxide
products is not as far as away as one with real monolayer graphene.

~~~
humbledrone
FTA:

> _Now, technically graphene oxide isn’t quite the same thing as graphene, but
> in a good way: graphene oxide is much easier to make._

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nutjob123
Evaporated water is already very clean. I would like to see this material
tested as a regular filtration mechanism. Normally filters are rated by the
size of molecule they allow to pass through them, flow rate and how many
liters of water they can filter before it is necessary to replace or clean. I
would also like to point out that filtration and sterilization are different
processes. Filtration is usually a mechanical process and sterilization is
normally done chemically (although not always).

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Corrado
Original story:
[http://www.sciencedaily.com/releases/2012/01/120126100639.ht...](http://www.sciencedaily.com/releases/2012/01/120126100639.htm)

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brador
How can I make graphene? How's it made? What do I need?

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draggnar
Apparently you can make it with a pencil and some sticky tape:
<http://youtu.be/LwmxSjydPEE>

edit: here they are in the lab at Manchester using a similar technique:
<http://youtu.be/ehvksWx3AJQ>

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nosse
This article only makes fun about making hard liqueur this way, but this could
really revolutionize that business. Normal distillation is very violent
procedure that unavoidably affects the taste. It would be possible to produce
large amounts of rum just by leaving sugar cane juice in glass bottles to
sunlight for a couple of months, with every bottle sealed with grapheme oxide.

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alanh
How much does it currently cost to obtain a 16cm^2 sheet of graphene oxide?

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jcfrei
I hope this works as proclaimed - the only two questions i have left are: do
traditional desalination techniques require more energy than boiling the
equivalent amount of water? if so, this might indeed be a breakthrough. and
the second question: will the membrane ever need to be replaced?

~~~
uvdiv
"do traditional desalination techniques require more energy than boiling the
equivalent amount of water?"

No, far less, because the end product is condensed liquid water (not vapor).
When* the desalination method is distillation (evaporating + re-condensing),
the heat used to evaporate water is released again when the steam is
condensed, and can be recovered and reused. E.g. [1]. The real-world figure
wikipedia cites is about 90 MJ/m^3, compared to about 2,250 MJ/m^3 for boiling
water at STP [2]. The theoretical limit from thermodynamics -- the minimum
energy needed to separate salt and water -- is about 3 MJ/m^3 for seawater [3]
(or [4-5]).

*(as opposed to methods like reverse osmosis [6], which is forcing water through a filter with atom-sized holes -- no boiling involved)

[1] <http://en.wikipedia.org/wiki/Multi-stage_flash_distillation>

[2]
[http://en.wikipedia.org/wiki/Enthalpy_of_vaporization#Other_...](http://en.wikipedia.org/wiki/Enthalpy_of_vaporization#Other_common_substances)

[3]
[http://http://www.sandia.gov/water/docs/MillerSAND2003_0800....](http://http://www.sandia.gov/water/docs/MillerSAND2003_0800.pdf)

[4] <http://en.wikipedia.org/wiki/Enthalpy_change_of_solution>

[5] <http://en.wikipedia.org/wiki/Seawater>

[6] <http://en.wikipedia.org/wiki/Reverse_osmosis>

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yock
Would this include other areas of water purification such as softening and
desalanization?

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prolepunk
I don't think graphine oxide would be as applicable in the near future since
these experiments use water vapour and pass it through the membrane, meaning
that you already need to expand energy to heat up all that water, and there
already exist more efficient methods of desalinization.

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api
Four words: water recycling in spacecraft.

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kahawe
Now we just need SOMETHING to identify those Cylon sleepers that are going to
blow up the water tanks...

On a more serious note, there certainly are regions on EARTH that could dearly
use such a filter before we jump on building spacecrafts.

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adrianwaj
"finds that graphene capillaries either shrink in low humidity or get clogged
with water molecules"

How useful will the filter be if it gets clogged? Reverse Osmosis needs high
pressure and produces much less water than it takes in, then it needs
remineralization. Same situation?

Maybe it will be better for filtering steam or air.

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LargeWu
Exactly. I can see this being useful in, say, coal power plants which release
a lot of water vapor, but also a lot of toxic chemicals. If one could develop
a useful filter from this, could the burning of coal actually become a clean
source of energy?

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DarkShikari
Coal can't be "clean" unless you can find a place to put the vast amount of
carbon dioxide.

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ricopags
Use it to make more graphene oxide, obviously.

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eridius
I keep seeing articles about all the wonders of Graphene (and its derivatives,
like Graphene Oxide). When will I actually see any of these wonders affecting
my life?

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chillyconker
Yes. Previously this role was played by carbon nanotubes.

Even supposing we work out a way to manufacture graphene cheaply, it seems to
me that there are lots of technical solutions to problems out there which
remain undeveloped for lack of a viable financial model (or simply bad luck I
suppose).

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racketeer
This is what I've always used <http://www.steripen.com/>

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