Generation of disinfection byproducts by graphene quantum dot: Graphene nanostructures and water chemistry

Graphene quantum dot (GQD), as one of the smallest graphene nanomaterials (GNMs), has the potential to be widely used due to its excellent fluorescence properties, hydrophilicity, and good biocompatibility. GQD remaining in water will generate DBPs when entering the disinfection process, and whether the generation mechanism and influencing factors are similar to those of other GNMs has not been proven and thoroughly investigated. In this study, the total amount, effect, and mechanism of DBPs formation from GQD chlorination were investigated and compared with graphene oxide (GO) and graphene. The results show that GQD produced a total trichloromethane (TCM) amount of 1019.6 μg/L, which is significantly higher than that produced by GO (99.2 μg/L) and graphene (7.0 μg/L) at a concentration of 500 mg/L. The key factors are abundant functional groups and strong hydrophilicity of GQD after the characterization and comparison of physicochemical properties. Different water chemistry conditions influence DBPs formation, such as Br^- increased the formation of brominated DBPs, and high pH led to a decrease in TCM generated by GQD, which is different from other GNMs. However, NaCl concentration can be negligible. Moreover, residual GQD in natural water can participate in the DBPs formation and increase the content of DBPs, which may be influenced by the diversity of chemical composition in surface water. This study highlights the unique impact of GQD on DBPs formation.