Graphene: The perfect water filter | Hacker News Reader

Graphene: The perfect water filter

extremetech.com

204 pointsukdm40 comments

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...

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?

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

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.

Well, that presumes a perfect seal on the filter, because otherwise the bacteria can just take the long way around the filter and into your filtered water.

That's not a show-stopper, though, is it? I mean, you could get near-perfect just by making the filter the right shape and having several layers of filtering, thus reducing the chance of a bacteria getting through down to some infinitesimal probability...

Graphene filters combined with SODIS methods would be the ticket.

http://www.sodis.ch

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.

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.

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

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.

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?

Ignoring the zombie blood for a second (because you're absolutely correct) I'll approach your last question.

> how common is it for typically impotable water to have these type of compounds?

My gut feeling is, "not very... right now." The "right now" is pretty much the problem with the speculated water wars (though a bunch of the water in the Gulf of Mexico does contain those compounds).

With landfill's "impermeable" barriers becoming permeated and cholesterol medications, caffeine, birth control, and various other drugs remaining in the treated effluent from waste water facilities coupled with humanity's generally reckless disregard for consequences to its actions there's a significantly non-zero chance that fresh, clean potable water will become scarce in multiple developed locations worldwide.

On the other hand, it could very well be that as our understanding of bio-remediation increases and our utilization of passive and active purification techniques and/or technologies increases we'll keep from having that be a problem. Potentially, we'll even stop actively polluting our water supplies with industrial, agricultural and residential wastes to "save a buck."

Anyway, the watercone is great. They've tackled usability issues present in other solar distillation devices and for areas with access to water with high salinity, or biologically contaminated water (though, there is risk of cross-contamination when harvesting your purified water). It's just that solar stills aren't always a replacement for filters.

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.

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.

I guess we'll have to worry less about global warming as well (or at least the concerns about increase in sea level) :)

Reverse osmosis filters can already remove salt from water, and far more efficiently as well I believe.

You can do that now with camping water filters from companies like First Need or PUR.

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.

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.

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).

Original story: http://www.sciencedaily.com/releases/2012/01/120126100639.ht...

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

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

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.

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

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?

No, because boiling the equivalent amount of water is the key energy required in distillation, which will also desalinate the water. It's unclear if this is actually in fact, much of a win.

"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_...

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

[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

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

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.

Four words: water recycling in spacecraft.

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.

"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.

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?

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

Use it to make more graphene oxide, obviously.

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?

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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This website loads the full desktop page before redirecting to the mobile version.

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