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Can carbon nanotubes solve the world's drinking water woes?

Researchers at the Bhabha Atomic Research Centre (BARC) in Mumbai, India, are studying the potential use of carbon nanotubes—hollow carbon fibers—to filter viruses, bacteria, toxic metal ions, and large noxious organic molecules out of water. According to Physorg.com, "the smooth and water repellant interior of carbon nanotubes means that a filter based on this technology would be very efficient, allowing a high flow rate of water through the filter without fouling. Importantly, the power needed to drive water through such a system will be low compared to conventional membrane technology."

As CleanTechnica.com points out, solutions to the problem of contaminated water are desperately needed. But carbon nanotubes are not likely to be that solution, at least not any time soon.

Among the reasons:

  • Nanotubes would be extremely difficult to arrange into a filter. The caveat that Physorg.com mentions touches on a very important point that could pose the greatest stumbling block to carbon nanotube-based water filters: "To be useful as a nanotech filtration system for contaminated water, these nanoscale structures need to be engineered to form well-defined arrangements to allow the efficient decontamination of water." As I learned this week at a nanotech workshop at the University of Wisconsin-Madison, nanotubes don't exist in individual forms. Instead, they cluster in clumps and are very difficult to separate. In fact, it was only two years ago that researchers at Trinity College Dublin discovered that carbon nanotubes could be unbundled without damaging or weaking them, according to Philip Streich, the 17-year old co-founder of Graphene Solutions, LLC in Platteville, Wis. Trying to filter water through a clump of nanotubes pointing in different directions (with some tubes possibly being blocked by other tubes) is not likely to be efficient.
  • The nanotubes would have to be extremely tiny (even by nano standards) to filter out contaminants. Although bacteria are about 1,100 nanometers in diameter, viruses can be between 70 and three nanometers in diameter. You would need a carbon nanotube with roughly the dimensions of a strand of DNA in order to block out the smallest contaminants.
  • The carbon nanotubes  may pose health risks There is no conclusive evidence that ingesting carbon nanotubes is dangerous, but there also are no studies proving that it's safe. Until scientists have a better handle on this, it's probably wise to avoid drinking or inhaling them. The former would be hard to do if any of the nanotubes were to shake loose from the filter and end up in the water supply.
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