Stanford researchers purifying water with silver

September 19, 2010 12:00:00 AM PDT
Researchers at Stanford have developed a new kind of filter, a cheap and fast way to purify water in poor parts of the world and on camping trips.

In her Stanford laboratory, Alia Schoen purifies water using a new method thousands of times faster than anything previous. It uses nanotechnology and silver.

In the days before milk could be pasteurized or refrigerated, people would drop a silver coin into a bottle to preserve it. Silver is lethal to bacteria. Tiny amounts of silver are already woven into antibacterial socks, underwear and band-aids. You could build water filters out of silver, but the metal is so costly, it would kill your bank account before it killed the bacteria.

Now, nanotechnology is changing that.

It turns out that if you run a minute amount of electricity through microscopic silver, it amplifies its antibacterial powers by thousands of times. The Materials Science Lab at Stanford University is already making the first fabric batteries out of cotton infused with the hottest material in research today: carbon nanotubes.

Professor Yi Chui's team has also infused cotton with microscopic silver nanowires. A member of that team, Dr. David Schoen recalls, "What we thought was a crazy idea at the time, to combine electricity with nanowires to treat water."

The crazy combination of nanosilver and nanocarbon did the trick. It enables them to filter 98 percent of the E. coli in a water sample in one pass using so little electricity, it can run on 9-volt batteries. Professor Cui, of Stanford's Materials Science department says, "We use a tiny amount. So, it is possible to scale this filter up to a very large size. There's no reason we cannot do thousands of gallons quickly."

In fact, all the water used by one average household in a year (20,000 gallons) could be treated in just one hour with a filter the size of a kitchen sink. Safety and commercialization require still more work, but there is huge potential for poor communities.

"The biggest application," Cui is certain, "will be use in remote areas in third world countries."

What's more, with a couple of batteries, you might one day take something like this on a camping trip.


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