Targeted removal of bioavailable metal as a detoxification strategy for carbon nanotubes

Xinyuan Liu, Lin Guo, Daniel Morris, Agnes B. Kane, Robert H. Hurt

Research output: Contribution to journalArticlepeer-review

126 Scopus citations


There is substantial evidence for toxicity and/or carcinogenicity upon inhalation of pure transition metals in fine particulate form. Carbon nanotube catalyst residues may trigger similar metal-mediated toxicity, but only if the metal is bioavailable and not fully encapsulated within fluid-protective carbon shells. Recent studies have documented the presence of bioavailable iron and nickel in a variety of commercial as-produced and vendor "purified" nanotubes, and the present article examines techniques to avoid or remove this bioavailable metal. First, data are presented on the mechanisms potentially responsible for free metal in "purified" samples, including kinetic limitations during metal dissolution, the re-deposition or adsorption of metal on nanotube outer surfaces, and carbon shell damage during last-step oxidation or one-pot purification. Optimized acid treatment protocols are presented for targeting the free metal, considering the effects of acid strength, composition, time, and conditions for post-treatment water washing. Finally, after optimized acid treatment, it is shown that the remaining, non-bioavailable (encapsulated) metal persists in a stable and biologically unavailable form up to two months in an in vitro biopersistence assay, suggesting that simple removal of bioavailable (free) metal is a promising strategy for reducing nanotube health risks.

Original languageEnglish (US)
Pages (from-to)489-500
Number of pages12
Issue number3
StatePublished - Mar 2008
Externally publishedYes

ASJC Scopus subject areas

  • General Chemistry
  • General Materials Science


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