Lego-like Water Purifier Gives Tiny Particles Big Cleaning Punch

Francie Diep, InnovationNewsDaily Staff Writer
19 January 2012 05:59 AM ET

Electron micrograph images of carbon nanotubes by themselves (on the left) and of the nanotubes with nanoparticles attached to them. Researchers are developing these nanotubes for a water purifier.
CREDIT: Sharmila Mukhopadhyay

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A big impact can come in small packages sometimes. Researchers are working on a water purifier that uses nano-size particles to remove bacteria, chlorine and other water pollutants.

Water filters that have nano-size pores or nano-size bits of antibacterial silver are available on the market now, but the research team hopes their new material's complex structure will hold several types of nanoparticles – each aimed at different water contaminants – that can be swapped out like Lego-bricks as the situation requires. The purifier itself has a nano-size structure that lets it pack more active cleaning nanoparticles per square inch, so a small piece of material should be able to clean large volumes of water.

"These are very, very small samples able to clean quite a bit of water," said Sharmila Mukhopadhyay, a nanotechnology researcher at Wright State University in Dayton, Ohio, who's leading the effort. In their latest tests, purifier samples about 2 millimeters long and 4 millimeters wide can process a few gallons of water at a time, she told InnovationNewsDaily. She hopes to have a prototype purifier machine in one to two years. It may be something people can simply drop into the water they want to clean, she said, or something that has to be circulated through the water.

She and her research team created the basic foundation for these types of materials in 2009, when they attached carbon nanotubes to a porous base. The tiny tubes create extra surface area on the base, in the way that a shag rug has more surface area than a flat rubber mat of the same size, because the shag rug's surface area includes all those long hairs, too. Greater surface area means more space for cleaning nanoparticles to latch onto. "It is always good to have more surface area," said Qilin Li, an environmental engineer who studies water treatment at Rice University in Houston. Li was not involved in Mukhopadhyay's work.

Like other nanomaterials under study for filtering drinking water, Mukhopadhyay's new purifier should be useful for removing bacteria- or molecule-size pollutants, Li said. But because the purifier uses carbon nanotubes, it should provide more surface area — and thus work more efficiently — than most materials under study, Li told InnovationNewsDaily. The nanotubes may do some purifying work on their own, too, she said. "Nanotubes may have an additional benefit because nanotubes have been found to be toxic to bacteria."

So far, Mukhopadhyay has attached several types of nanoparticles to the high-surface-area material. She's tried metals that are antibacterial and break up chlorine. In the future, she hopes that companies can customize the material with different particles, depending on the cleanup job. "Let's say you have different catalysts for attacking different kinds of pollutants," she said. "Once we've created this underlying structure, we can change what we have on the surface."

She and her colleagues are also working on making sure the added nanoparticles are firmly attached to the purifier, so they don't fall off in the water, creating their own pollution problem.

Her lab is working with MetaMateria Technologies and other companies to commercialize one of their high-surface-area water purifiers. The team received an almost-$1 million grant from the state of Ohio toward bringing the product to market. One of their biggest challenges will be the high cost of nanomaterials, Li said. Those costs haven't come down over the past decade, she said her research indicated.

Mukhopadhyay is also studying what else a compact, active material can do. As long as she can change the nanoparticles stuck on the surface, "then basically the material can be used for something completely different," she said. Some possibilities she's testing: casings for energy storage devices and a scaffold for growing bone cells.

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