Science News
All nanotubes are not created equal
Significant differences among different single-walled carbon nanotubes make it difficult to model their environmental risk.
Tests of single-walled carbon nanotubes made by 10 different manufacturers reveal "extreme variability in carbon nanotube composition," according to new research published in Nanotechnology in April. The results have significant implications for environmental risk assessments of nanomaterials.
The research team included Philip Gschwend of the Massachusetts Institute of Technology, Christopher Reddy of Woods Hole Oceanographic Institution, and Desiree Plata, who is affiliated with both institutions. The researchers purchased and analyzed single-walled carbon nanotubes from all U.S. manufacturers known to produce them between September 2005 and March 2006. However, because of the industry's rapid growth, the number of these nanomaterials on the market today is likely to be much larger, they say.
The authors point out that these nanotubes "are known to contain large percentages of carbonaceous and metal impurities, [which can] account for up to 70% of the bulk [nanotube] material." Ignoring the impurities prohibits scientists from fully understanding the material's electronic character, environmental transport, transformation, and ecotoxicology.
The new analysis confirms that nanotubes can retain high levels—in the percent range—of the catalytic materials used to synthesize them. The researchers also found that the tested nanotubes contained some unexpected metals, including copper, chromium, and lead. Because these impurities can affect the nanotubes' surface properties and reactivity, they will influence the nanotubes' environmental fate. For example, the metals may react with halogenated contaminants to generate radical species and toxic degradation products.
The advantage of individual nanotubes' unique metal "fingerprints" and differing carbon isotopic signatures may ultimately allow scientists to identify them when found in the environment, the researchers conclude.
Science
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Technology
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Policy
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Business & Education
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