Efficient electrochemical degradation of multiwall carbon nanotubes.

As the production mass of multiwall carbon nanotubes (MWCNT) increases, the potential for human and environmental exposure to MWCNTs may also increase. We have shown that exposing an aqueous suspension of pristine MWCNTs to an intense oxidative treatment in an electrochemical reactor, equipped with an efficient hydroxyl radical generating Boron Doped Diamond (BDD) anode, leads to their almost complete mineralization. Thermal optical transmittance analysis showed a total carbon mass loss of over two orders of magnitude due to the electrochemical treatment, a result consistent with measurements of the degraded MWCNT suspensions using UV-vis absorbance. Liquid chromatography data excludes substantial accumulation of the low molecular weight reaction products. Therefore, up to 99% of the initially suspended MWCNT mass is completely mineralized into gaseous products such as CO and volatile organic carbon. Scanning electron microscopy (SEM) images show sporadic opaque carbon clusters suggesting the remaining nanotubes are transformed into structure-less carbon during their electrochemical mineralization. Environmental toxicity of pristine and degraded MWCNTs was assessed using Caenorhabditis elegans nematodes and revealed a major reduction in the MWCNT toxicity after treatment in the electrochemical flow-by reactor.