Carbon nanotubes as free-radical scavengers

Density functional theory calculations have been used to model the potential ability of single-walled carbon nanotubes (SWCNT) to act as free-radical scavengers. The reactions of a (5,5) SWCNT fragment with six different radicals have been studied, and for hydroxyl radical, which is the most reactive and dangerous from all of the studied set, up to four additions were modeled. Energetic considerations show that, once a first radical is attached to the nanotube, further additions are increasingly feasible, suggesting that SWCNTs can act as free-radical sponges. For reactions with OH radicals, subsequent additions are expected to lead to products where the OHs are distributed in groups rather than regularly spread on the nanotube. Because nanotubes with none or an even number of OH groups attached are stable (nonradical) species that can be used for other purposes, their properties were analyzed in terms of global reactivity indexes and density of states (DOS). The results from these analyses suggest that, by controlling the proportion of OH on the nanotubes, their properties can be manipulated.