Transformation of Nanomaterials in Environment: Surface Activation of SWCNTs during Disinfection of Water with Chlorine

Carbon nanotubes are new class of active environmental pollutants. The authors report interactions between chlorine used as disinfectant/oxidant during typical water treatment and single-wall carbon nanotubes (SWCNTs). Alterations in SWCNT morphology were determined by TEM, while FT-IR spectra helped to determine chemical changes before, during and after chlorination. The analysis of original FT-IR spectra, and their second order derivatives revealed the formation of new, oxygen-bearing groups, namely quinones, ethers, and additional carboxyl groups on the surface of SWCNTs. The two-step reaction mechanism: (1) initial adsorption of mixture of hypochlorous acid and hypochlorite anions on the surface of carbon nanotubes, and (2) oxidation of surface and formation of new functional groups, was suggested. It was found that standard disinfection has activated previously inert carbon nanotubes and turn them into active species able to participate in further cross-contamination reactions. Interestingly, the oxygen-bearing groups were formed as a product of reaction with chlorine.