Fragmentation characteristics of undoped and nitrogen-doped multiwalled carbon nanotubes in aqueous dispersion in dependence on the ultrasonication parameters

Abstract

Sonication techniques are commonly used to disagglomerate carbon nanotube bundles into more or less uniformly distributed individual tubes. The present study discusses the statistical length distribution of multiwalled carbon nanotubes (MWCNTs) as affected by varied sonication time, sonication amplitude and overall energy input applied. Undoped and nitrogen-doped multiwall carbon nanotubes (N-MWCNTs) were investigated, and the influence of nitrogen in the carbon structure on the length-reduction behavior during sonication was assessed. Both kinds of MWCNTs were synthesized using the same process, an Aerosol Assisted Chemical Vapor Deposition (AACVD), utilizing cyclohexane and acetonitrile as precursors. X-ray photoelectron spectroscopy (XPS) clarified the chemical bonding in the CNTs and proved the incorporation of nitrogen in the carbon lattice. A drastically shortening of the initial length, i.e. the carpet length, after short times was shown. It was also found that such incorporation of nitrogen results in distinctly modified length reduction behavior during ultrasonication. The N-MWCNTs showed a much more pronounced length-reduction with higher ultrasonication amplitude than the undoped MWCNTs. This can be explained by the weaker chemical bond between C and N in a CNT-lattice, as compared to that among the carbon atoms only. On the other hand, sonication time has no particular effect on the fracture of N-MWCNTs when compared to the undoped MWCNTs.