Experimental and density functional theory investigations on the antioxidant mechanism of carbon nanotubes.

Carbon nanotubes (CNTs) could improve the antioxidant properties of polymers because of their radical scavenging activities, but the interaction between CNTs and radicals is ambiguous. We investigated the thermal-oxidative aging resistance of fluorosilicone rubber (FSR) with and without multi-wall carbon nanotubes (MWCNTs), and tracked the concentration of peroxy radicals using chemiluminescence measurements. The results showed that 0.1–0.5 wt% of MWCNTs could block the auto-oxidation degradation of FSR by scavenging the alkyl radicals, thereby showing an antioxidant effect. Based on the structural characterizations of nanocarbons, a set of polycyclic aromatic phenols and polycyclic aryloxy radicals (PArO ·) were constructed and optimized to mimic CNTs. The spin density distribution, spin population, and the formation and reaction of PArO · were calculated using density functional theory (DFT). The results indicated that the CNTs were an open-shell system with a spin density distribution focused on the aryloxy groups and nearby sp2-hybridized carbon atoms. Those atoms with spin populations ranging from 0 to 0.6 a.u. were inert but could react with high-reactivity radicals, including alkyl radicals. This mechanism was confirmed by electron spin resonance measurements of the nanocarbons and heat-treated pyrenols. This study contributed to the development of nanocarbons in antioxidants, catalysts, and reactive oxygen species scavengers. [Display omitted] [ABSTRACT FROM AUTHOR]