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Aqueous Solution Tested to Reduce Carbon Nanotube Toxicity

Carbon nanotube illustration (National Science Foundation)

Carbon nanotube illustration (National Science Foundation)

Engineers at University of Florida in Gainesville are investigating ways of reducing the toxicity of carbon nanotubes, a promising technology with applications in semiconductors, energy storage, and displays. The latest findings of environmental engineer Jean-Claude Bonzongo, chemical engineer Kirk Ziegler, and their Florida colleagues appear in the March 2012 issue of the journal Nanotoxicology (paid subscription required).

Bonzongo and Ziegler focus on the aqueous (water-based) solvents for use in manufacturing processes associated with carbon nanotubes. Manufacturers want to take advantage of their high conductivity, but developers of devices find carbon nanotubes tend to clump together, which means developers need to find ways to untangle and disperse them.

One way to untangle the nanotubes is to mix them with an aqueous solution that acts as a detergent and separates the tangled bundles. Bonzongo and Ziegler discovered, however, that some of the surfactants that lower the surface tension of the solvents to loosen the bundles are toxic on their own, while others become toxic in the presence of carbon nanotubes. “Depending on how the nanotubes are used, they can be toxic,” says Bonzongo, “exhibiting properties similar to asbestos in laboratory mice.”

Bonzongo and Ziegler tested carbon nanotubes suspended in a gum Arabic solution for short- and long-term effects on algae, as an indicator of toxicity. Gum Arabic is a natural, abundant, and inexpensive emulsifier. They found that controlling the ratio of gum Arabic particulate to liquid in the suspension — in this case, at or below 0.046 percent — can reduce the toxicity to virtually zero. However, the performance of carbon nanotubes untangled and dispersed with this approach still needs to be tested.

Reducing the toxicity of carbon nanotubes with a controlled aqueous solution, say the authors, has the additional benefit to manufacturers of being much less expensive than other options tried with prototypes, such as mechanical homogenization or centrifugal sifting.

Read more: Toxicity to Human Cells of Nanotubes, Nanowires Investigated

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