Electrified Cotton Filter Soaked in Nanotech Cheaply and Quickly Purifies Large Volumes of Water

By Clay Dillow Posted 08.31.2010 at 1:00 pm 11 Comments

Silver Nanowires A microscope image shows the silver nanowires in which the cotton cloth is dipped. Courtesy of Yi Cui, Stanford University

Water, water everywhere, but in the developing world or in areas ravaged by natural disasters – like the ongoing flooding in Pakistan, for instance – there’s often not a clean, purified drop to be found. Water is usually made potable in such places via filters that physically trap bacteria as water flows through, but researchers at Stanford have shown devised a high-speed filter composed of nothing but plain cotton cloth and nanotubes that can quickly filter nearly all bacteria from dirty water using less power than slower conventional water purifiers.

Most water filters simply trap living bacteria as it passes through a series of tiny pores, a method that is effective but prone to a variety of problems. For one, they are painfully slow, and in disaster situations that can lead to critical shortages as thirsty populations wait for the water to trickle through.

Further, the water must be driven through the filters with pumps, which themselves require a decent amount of electricity – a resource that can be in short supply in remote regions or at disaster sites. Such filters are also susceptible to biofouling, in which trapped bacteria form a film that clogs the pores of the filter.

The Stanford team’s filter circumvents most of these problems by simply letting the bacteria pass freely through, zapping them with fatal doses of voltage as they go. By dipping plain cotton cloth procured at Wal-Mart into a solution of carbon nanotubes and silver nanowires, the team created a filter that can kill 98 percent of Escherichia coli bacteria in water with a mere 20 volts of electricity, less than is required to operate the pumps on conventional filters.

Addressing the problems with conventional filters noted above, the team knew that carbon nanotubes are efficient conductors of electricity and that silver has bacteria-killing chemical properties. So they went about figuring out how to get all these ingredients into a single, inexpensive filter (the amount of silver used is so small that it’s negligible). The cotton simply serves as an inexpensive platform on which to lay their nanotube/nanowire structure.

Plugged into a couple of 12-volt batteries or a hand cranked generator, the filter can run until the energy runs out, its larger pores letting vast volumes of water pass quickly, and cleanly, through. No pump is needed because the pores are large enough that gravity does the trick.

The next step is trying the filter on various other bacteria to see how universal the silver-carbon combo really is. One filter can kill 98 percent of the Escherichia coli in water, but a compound filter with layers of different materials might be able to push that number even closer to 100 percent for a variety of bacteria known to cause water-borne illnesses.

[Eurekalert]

Previous Article: NIH Research Chief: Shut Down Human Embryonic Stem Cell Experiments Immediately

Next Article: What Created This Smooth, 200-Mile-Long Trench On Mars?

11 Comments

Link to this comment

nhan1st

08/31/10 at 2:24 pm

Great idea, but how do you run an electrical current through a piece of silver cloth?
You could do it from one end to another, but then electricity goes through the least resisting path doesn't it? Not through the whole cloth.
Can anyone explain this to me?

Link to this comment

edisonkenevil

08/31/10 at 2:58 pm

My guess is that they positively charge the silver/nanotube substrate and it is released through the water which is grounded.

This system does not appear to do anything for toxins in the water such as heavy metals or such. If they add a combination filter for toxins would'nt that slow it down drasticaly?

The article says it can be run on 20VDC but at what aperage? I work on 24VDC pumps running at 30A and I wouldn't exacly call them "efficent" and I sure wouldn't want to power them via a hand crank.

Link to this comment

samcallis

08/31/10 at 4:08 pm

What about the health effects of the carbon nanotubes. I don't think drinking those would be very good and I can't imagine the cotton fiber holding 100% of them.

Link to this comment

Solace

08/31/10 at 6:06 pm

Yeah, according to another article on here, free carbon nanotubes are about as bad as free asbestos fibers. You can still make them into structural elements, but not really for anything medical. Although, if it's in a filter anyway, they might just be planning to filter out the nanotubes somewhere at the end of the filter.

Link to this comment

Moon born

08/31/10 at 10:04 pm

@Dillow Why do you never use pertinent units. Telling us the voltage tells us pretty much nothing. What we need to know is the mW per liter. Louis Bergeron posted his email in the publication you'r regurgitating here, could you not have taken a few minutes to contact him for this piece of information.

@Solace obsolete news is obsolete they found that we all have the ability to quickly break down carbon nano tubes.
In the little go box type "Break Down Carbon Nanotubes" to read something Clay disgorged about the subject.

I would have posted a link to the article but the spam filter is so intelligent that it thinks tings linked to popsci (dot) com are spam. I really wish you would whitelist yourself youtube, and wikipedia.

Link to this comment

sqush-u-like-bug

09/01/10 at 12:03 am

why dont they put a mechanical weele so that when the water runs over the weele turning it, it creats a electronic current zapping the bacteria with its own power?

Link to this comment

nhan1st

09/01/10 at 2:58 pm

That's too inefficient, because the electricity generated from that tiny wheel spinning is worthless to power up the device.

Link to this comment

tcolguin

09/02/10 at 5:09 am

One thing I find interesting is that they think 98% is a good number when you are dealing with a deadly bacteria. Put that in perspective. Say you have a very small set of colonies of bacteria say on your hand. On a normal hand not in dirty conditions, this can easily be a 1,000,000 bacteria so kill 98% and you get 20,000 left. Apply this to large volumes of water.

Link to this comment

nhan1st

09/02/10 at 2:57 pm

Actually, I think the 20,000 bacteria will just kill you instead of that one million, lol.

Link to this comment

vivioo7

12/01/10 at 1:52 pm

favorite

Link to this comment

Daedelus

11/06/12 at 10:29 pm

I think its a pretty good idea.
Just insert some graphene sheets at the end to filter out any leftover debris, bacteria, or nanotubes.
Apart from that, this would actually roll.

Popular Tags

Science

All Tags All Photos All Videos

Science

+ More Photo Galleries

June 2013: American Energy Independence

Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.