FEW DISCOVERIES over the past two decades have rivaled the excitement generated by carbon nanotubes. These tiny chemical constructions — in their simplest form a one-atom thick layer of graphene rolled up to form a seamless cylinder — boast properties that seem only just short of miraculous. They are far stronger than steel but weigh much less. They have great tensile strength, but also elastic properties. They conduct both heat and electricity. And in their various forms they can act as either a metal or a semiconductor.
Already carbon nanotubes, or CNTs, are being deployed by manufacturers in dozens of areas utilized by millions of consumers: from medical technologies and electronic-device components to common household items such as fabrics, sporting goods, paints and sunblock. As the manufacturing cost of nanotubes falls, new products appear at an ever-increasing clip.
This may not be an entirely good thing, says Baolin Deng, C.W. LaPierre Professor and chair of chemical engineering at MU. At least not until companies making products with CNTs gain a better understanding of how they may affect the people and animals who will be coming into contact with them.
“The great promise of carbon nanotubes must be balanced with caution and preparation,” he says. “We don’t know enough about their effects on the environment and human health.”
Deng’s specific concerns arise from a multi-year MU study examining CNTs’ effect on aquatic animals. Working with scientists from the U.S. Geological Survey, Deng and a team of MU scientists and students focused on a variety of small creatures living in streams and their sediments — this because the mussels, worms and shrimp-like creatures called amphipods that live in these riparian habitats would be particularly vulnerable to CNT exposures.
The results, published in the journal Environmental Toxicology and Chemistry, might serve to dampen some of the breathless industrial enthusiasm for all-things nanotube. Heavy metals such as nickel and chromium used in the manufacture of carbon nanotubes, as well as the CNTs themselves, appeared implicated in reduced growth rates and deaths among the aquatic organisms tested, the researchers determined.
The news is not all bad, says Hao Li, an MU associate professor of mechanical and aerospace engineering who worked on the study. Li is confident that with cleaner manufacturing processes, and by developing a more advanced understanding of how CNT-enhanced composite materials function in the real world, the nano revolution may yet change our planet for the better.
“One of the greatest possibilities of contamination of the environment by CNTs comes during the manufacture of composite materials. Good waste management and handling procedures can minimize this risk. Also, to control long-term risks, we need to understand what happens when these composite materials break down.”