Covalent bromination of multi-walled carbon nanotubes by iodine bromide and cold plasma treatments

The covalent bromination of multi-walled carbon nanotubes by the reaction with a solution of IBr in CCl4 at mild temperatures and by CH3Br cold plasma is reported. The samples have been analyzed by X-ray photoelectron spectroscopy, thermal programmed desorption, thermogravimetry, Raman spectroscopy, X-ray diffraction and nitrogen adsorption. Both treatments preserve the structure of the nanotubes. The degree of bromination reached by the simple reaction of the first method rises up to 3.5 at.%. An important advantage of this procedure is that the oxygen content of the nanotubes does not increase with respect to the raw material (an unresolved problem of previously reported methods), and that 96% of the bromine is covalently bound. The bromination reached by the second procedure is even larger so that 4.9 at.% is achieved in only 10 min. Moreover, 99% of this bromine is covalently bound to the nanotubes. It is shown that, without a doubt, the bromine is covalently bound, that it appears in three chemical environments and that the thermal stability of bromine containing groups depends on the treatment. An important consequence of the bromination is that the brominated nanotubes have a valence band distinctive of semiconductors.