This article reports a new way to covalently bond chlorine to multiwalled carbon nanotubes (MWCNTs) by using a carbon tetrachloride cold plasma treatment. Several factors controlling the efficiency of the plasma treatment were considered. In particular, the methodology to produce the plasma and the temperature and time of treatment were taken into account. The largest chlorine surface concentration was obtained when the MWCNTs were treated with helium plasma before the CCl 4 plasma to activate the surface. Short periods of plasma treatment (5−10 min) were then sufficient to reach high degrees of chlorination (up to 19.2% by weight) much larger than those previously reported. The functionalization takes place mainly in the borders and defects of the tubes, thus preserving the conjugation existing in the graphene layers. Moreover, the treatments show no influence on the textural characteristics of the nanotubes (i.e., porosity and interlayer spacing). Therefore, the method proposed in this work is an excellent approach to introducing surface chlorine atoms, capable of acting as leaving groups, as a first step for further functionalization with more complex molecules, while preserving the morphology and mechanical properties of the nanotubes still intact.

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