Graphenic Nanoparticles from Combustion Sources Scavenge Hydroxyl Radicals Depending Upon Their Structure

Graphenic nanomaterials like fullerenes, carbon nanotubes (CNT), and carbon black (CB) are known to scavenge free radicals. This antioxidant activity makes these materials promising in all applications where radical reactions need to be controlled. Therefore, CNT and fullerenes has been proposed as stabilising additives for composites and in medicine to prevent free-radicals-mediated diseases. CB has been used for more than a century as a stabilising filler in rubbers. The mechanisms responsible of the scavenging activity and the role of the nanoparticles structure in the antioxidant potency are still poorly known. In the present study, two samples of very pure soot having different structure were prepared as model of graphenic nanoparticles and tested for their capability to scavenge hydroxyl radicals by means of electron paramagnetic resonance (EPR)/spin trapping technique. The mechanism of the reactions occurring between the soot samples and the free radicals was evaluated by EPR spectroscopy of the dry powder while the possible introduction of oxygenated acidic functionalities during the reaction was evaluated by titration and confirmed by measuring the variation in ζ-potential of particles. The results indicate that soot persistently scavenge hydroxyl radicals through a reaction leading to the introduction of acidic functionalities at the surface. The scavenging activity was found to depend upon the bulk/surface structure of soot. When tested on alveolar macrophages MH-S cells, both samples did not induce cell damage (lactate dehydrogenase leakage) and oxidative stress (intracellular GSH depletion), suggesting a possible safe use of graphenic nanoparticles.