The percentage of electronic waste occupying our landfills has grown at an alarming rate over the last decade, giving rise to concerns about the toxicity2 of components3 used in consumer electronics. Researchers at the University of Florida are looking for ways to minimize environmental hazards associated with a material likely to play an increasingly important role in the manufacture of these goods in the future. The results of their most recent studies are published in the March 2012 issue of Nanotoxicology.
Carbon nanotubes are already being used in touch screens and to make smaller, more efficient transistors4. And if current research to develop them for use in lithium ion batteries is successful, carbon nanotubes could become important technology for powering everything from smartphones to hybrid5 vehicles. But for all of the promise developers see in this emerging technology, there is also some concern.
"Depending on how the nanotubes are used, they can be toxic1 -- exhibiting properties similar to asbestos(石棉) in laboratory mice," said Jean-Claude Bonzongo, associate professor of environmental engineering at UF's College of Engineering. He is involved in a research collaboration6 with Kirk Ziegler, a UF associate professor of chemical engineering, to minimize this important material's potential for harm.
In particular, the UF team is investigating toxicity associated with aqueous(水的) solutions of carbon nanotubes that would be used in certain manufacturing processes.
"At the nano-scale, electron interactions between atoms are restricted, and that creates some of the desirable traits like the high conductivity that manufacturers want to take advantage of with carbon nanotubes," Ziegler said. "But exploiting those properties is difficult because the nanotubes tend to clump7 together."
For that reason, carbon nanotubes have to be treated in some way to keep them dispersed8 and available for electron interactions that make them good conductors. One way to do it is to mix them with an aqueous solution that acts as a detergent9(清洁剂) and separates the tangled10 bundles.
"Some of the surfactants(表面活性剂) , or solutions, are toxic on their own," Bonzongo said. "And others become toxic in the presence of carbon nanotubes."
He and Zeigler are focusing their investigations11 on solutions that become hazardous12 when mixed with the carbon nanotubes. Their most recent results indicate that toxicity can be reduced by controlling the ratio of liquid to particulate13.
A cost-effective means of unbundling nanotubes remains14 one of the last hurdles15 for manufacturers to clear before they can employ the technology in mass-produced electronics. Current processes used for laboratory prototypes, including mechanical homogenization or centrifugal sifting16, would be too expensive for manufacturing consumer electronics. For that reason, liquid suspension agents may be the way forward if we are to have nano-tech products for the masses.
"It's an emerging technology," Bonzongo said. "We want to get ahead of it and make sure that the progress is sustainable -- in terms of the environment and human health."