Antioxidant chemistry of graphene-based materials and its role in oxidation protection technology

Abstract

Two-dimensional nanomaterials have potential as a new class of antioxidants that combine physical barrier function with ultrahigh surface area for free radical scavenging. This work presents the first measurements of the chemical reactivities of graphene-based materials toward a set of model free radicals and reactive oxygen species using electron paramagnetic resonance spectroscopy (EPR) and sacrificial dye protection assays. Graphene-based materials are shown to protect a variety of molecular targets from oxidation by these species, and to be highly effective as hydroxyl-radical scavengers. When the hydroxyl radical is produced photolytically, the overall antioxidant effect is a combination of preventative antioxidant activity (UV absorption) and ˙OH radical scavenging. Few-layer graphene is more active than monolayer graphene oxide, despite its lower surface area, which indicates that the primary scavenging sites are associated with the sp²-carbon network rather than oxygen-containing functional groups. To explain this trend, we propose that GO is a weak hydrogen donor, due to the non-phenolic nature of most OH groups on GO, which reside at basal sp³-carbon sites that do not allow for radical resonance stabilization following hydrogen donation. As an example application of graphene antioxidant behavior, we show that encapsulation of TiO₂ nanoparticles in graphene nanosacks reduces undesired photo-oxidative damage to nearby organic target molecules, which suggests graphene encapsulation as a new approach to managing adverse environmental or health impacts of redox-active nanomaterials.