Influence of functional groups on the degradation of graphene oxide nanomaterials

The influence of functional groups on the degradation of grapheneoxide nanomaterialsunder direct sunlightwas investigated by systematically varying the surface chemistry. Using a solvothermal reduction process, graphene nanomaterialswith varying oxidation levels, including grapheneoxide (GO), partially reduced grapheneoxide (rGO) and fully reduced grapheneoxide were prepared. The physical and chemical properties of the nanomaterialswere extensively characterized before and after exposure to simulated sunlight. The degradation of the nanomaterialswas determined to be directly related to the functional groups present on the basal plane of the graphene nanomaterials. Specifically, the hydroxyl and epoxy functional groups are the most susceptible to photodegradation. Upon sunlightexposure, the amount of oxygen-containing functional groups on all graphene nanomaterialsdecreases over time, with fully reduced grapheneoxide showing the lowest degradation rate due to the presence of fewer reactive functional groups on the surface. Density functional theory results also showed that the required energy of breaking C-C bond in the GO structure is higher than that of rGO, showing that the degradation of GO with lower oxidation degree is more difficult. Overall, these results suggest that the oxygen-containing functional groups on the basal plane are the major initiators of the photodegradationof graphene nanomaterials.