Effects of sunlight on the fate of graphene oxide and reduced graphene oxide nanomaterials in the natural surface water

Graphene nanomaterials have been commercialized for use in the electronic and biomedical industries, increasing their dissemination into surface waters and subsequent transformation in natural aquatic environment. While the photodegradation of graphene oxide nanomaterials has been investigated in the past, previous research did not consider actual natural aquatic environment and also focused on primarily graphene oxide nanomaterials. In this study, photodegradation of graphene nanomaterials with varying oxidation levels, including graphene oxide (GO) and partially reduced graphene oxide (rGO-2 h) are evaluated in Columbia River Water and compared with each other. Our results indicate that both direct and indirect photolysis of graphene-based nanomaterials will occur simultaneously in natural surface water. However, environmentally relevant concentrations of photosensitizers in surface water are not capable of producing sufficient ·OH to initiate degradation of GO via indirect photolysis. For all conditions tested, GO showed more rapid photodegradation compared to rGO. Overall, direct and indirect photodegradation of graphene oxide nanomaterials in natural surface water is minimal and slow indicating that phototransformation of graphene-based nanomaterials will be insignificant in natural surface water.