Antioxidant functions play an important role in nutrition, food and pharmaceutical formulations, environmental corrosion, sun screens, cosmetics, and the stabilization of chemical and polymer products.  Two-dimensional graphene-based nanomaterials have been explored as physical barriers that restrict access of oxidants to target surfaces, but the potential for graphene materials as chemical agents in oxidation protection has not been systematically explored. Here we study the chemical reactivity of graphene-based materials toward a variety of ROS and model free radicals. Graphene materials are shown as effective ?OH scavengers and suppress ?OH oxidation of various molecular targets. When ?OH is produced photolytically the protection is due to the combination of UV absorption and free radical scavenging. Few-layer graphene is more active than graphene oxide (GO) for ?OH scavenging despite its lower surface area, suggesting the main active sites are associated with the sp2-carbon network rather than oxygen-containing groups. GO shows only weak activity in several standard assays that use stable free radicals to measure the H-donation activity of chemical antioxidants.  We believe this is consistent with GO structure in which the majority of hydroxyl groups are found on sp3-carbon sites, and do not allow radical resonance stabilization following H-donation. The ultra-high surface area and high ?OH scavenging activity of graphene materials make them interesting as dispersed-phase oxidation retarders, or as two-dimensional barrier films or encapsulation shells that combine physical and chemical oxidation protection.  As a demonstration, graphene nanosack encapsulation of TiO2  nanoparticles is shown to reduce the undesired side effect of oxidative damage when titania is used for UV protection, which may be a new approach to manage the environmental or health impacts of redox-active nanomaterials.

Antioxidant behaviors of graphene-based materials

248th National Meeting (2014)

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