May 18 - Knight Ridder/Tribune Business News - Betsy Mason Contra Costa Times, Walnut Creek, Calif.

Microscopic tubes made of carbon could provide a cheaper way to remove salt from sea water and to separate carbon dioxide from power plant emissions, one step toward curbing global warming.

Scientists from Lawrence Livermore and Lawrence Berkeley laboratories have created a filtration membrane smaller than a quarter riddled with a billion tiny tubes that are 50,000 times thinner than a human hair. These "nanotubes" are special molecules made up of carbon atoms in the shape of a hollow tube. Water and other liquids can flow through them while larger molecules like salt are blocked.

To make a useful membrane, a team of researchers at the Livermore lab grew the carbon nanotubes on a silicon chip and then filled the spaces between the tubes with an impermeable ceramic matrix. Because the tubes assemble themselves into hollow cylinders with capped ends, the team sliced the top and bottom off of the membrane to open the tubes.

The result is a filter with over a trillion microscopic pores per square inch that allow gases and liquids to flow quickly and freely through them.

"Ordinarily you would expect the flow through such small channels to be orders of magnitude smaller than we observed," said Livermore materials scientist Jason Holt a lead author of the research along with mechanical engineer Hyung Gyu Park of UC Berkeley. Their work was published Friday in the journal Science.

It's not clear yet why the flow through the tubes is so fast, but the team suspects it is because the surface of the tubes is extremely slippery. The carbon atoms that make up the tubes fit together perfectly.

"We're trying to get closer to understanding the mechanism," said physicist Olgica Bakajin.

Regardless of why it works, the membrane has many potential applications.

Desalinization is usually done by forcing water through less porous membranes with high pressure, an expensive process. The nanotube membranes could bring the cost down by 75 percent, an advance that would be critical in places where fresh water is becoming more and more scarce.

The technology would also be an improvement over current gas separation techniques. Even though the nanotubes are smaller than the pores in conventional separators, faster flow through the tubes makes the membranes more efficient.

This would be particularly useful for removing carbon dioxide directly from power plant emissions. Keeping the greenhouse gas out of the atmosphere would help curb global warming.

The team plans to work on designing membranes for specific applications and Bakajin estimates the technology could be put to practical industrial use within five to ten years.

 

Betsy Mason covers science and the national laboratories. Reach her at 925-847-2158 or bmason@cctimes.com.