Effect of Different Functional Groups on the Free Radical Scavenging Capability of Single-Walled Carbon Nanotubes

The effect of different functional groups on the free radical scavenging capability of single-walled carbon nanotubes (SWCNT) is investigated using density functional theory calculations. The reaction mechanism that is considered in this study is the radical adduct formation. The reactions of a (OH)-O-center dot radical with eight different functionalized SWCNTs (armchair and zigzag) were studied. All of them were found to be exothermic and exergonic. Different sites of reaction were considered, and the increase on reactivity with respect to pristine tubes was found to be site-dependent. The presence of functional groups on the sidewalls of SWCNTs is predicted to increase their OH radicals scavenging activity. To enhance this property, the best functional groups are -CH2-OH for the armchair (3,3) SWCNT and -CONH-CH3 for the zigzag (5,0) fragment. The major conclusion from this work is that functionalized SWCNTs, in addition to be soluble in different media, are also very good free radical scavengers, being the armchair tubes better than the zigzag ones, when they are ultrashort fragments.