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

Abstract

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.

Proteomics-based safety evaluation of multi-walled carbon nanotubes

“…Iron and PAHs have been reported to contribute to the oxidation reaction (Baulig et al, 2003;Kagan et al, 2006;Guo et al, 2007;Byrne and Baugh, 2008;Liu et al, 2008). Thus, we thought that the impurities (iron and PAHs) in MWCNTs cause the inhibition of cell proliferation.…”

Exploring the diameter and surface dependent conformational changes in carbon nanotube-protein corona and the related cytotoxicity

“…S3). Previous study has shown that toxicity of CNTs may be attributed from metal catalyst impurities [14]. However, Energy Dispersive Spectrometer (EDS) data ( Fig.…”

Stability, metal leaching, photoactivity and toxicity in freshwater systems of commercial single wall carbon nanotubes

“…To date little work has been done to quantify the release of metal residues from CNT matrices in natural waters, or the toxicological implications of the bioavailable metals (Schwab et al, 2011;Hull et al, 2009;Blaise et al, 2008). It was previously thought that CNT purification removed almost all metals that could leach in solution, but there may be some residual metals since metal dissolution is kinetically limited and most purification processes are too short in duration (Liu et al, 2008). In addition, acid purification degrades the protective CNT encapsulation of the metals (Liu et al, 2008;Shen et al, 2005), and also exposes defects in the CNT structure.…”