Transformation of graphene oxide by chlorination and chloramination: Implications for environmental transport and fate

The rapidly increasing and widespread use of graphene oxide (GO) calls for immediate attention on the environmental fate of this material. To date, very little is known about the environmental transformation of GO. This study explored the changes of physicochemical properties of GO from chlorination and chloramination, which simulated the reactions occurring in water and wastewater treatment systems. Significant changes of GO surface O-functionalities occurred and scrolling of graphene sheets (those of very large sizes) were observed upon the treatments. Chloroform, a byproduct from chlorination was also detected, indicating the ring-opening on the edge of GO nanosheets. The changes of GO surface O-functionalities were attributable to the oxidation of quinone groups of GO by chlorine or chloramine. The scrolling of large-sized GO sheets may be attributable to the destruction of benzene rings at the edge of the GO. The results of membrane filtration experiments and column transport experiments indicated that chlorination and chloramination enhanced the mobility and transport of GO, likely by increasing the colloidal stability and inhibiting the agglomeration of GO nanosheets. The findings of this study further underline the significant implications of GO transformation on the fate and transport of this new nanomaterial.