Reaction of carbon nanotubes with chemical disinfectants: Byproduct formation and implications for nanotube environmental fate and transport

Nanomaterials (materials which have at least one dimensional feature with length less than 100 nanometers), and carbon nanotubes (CNTs) specifically, have exhibited great potential in water treatment. CNTs are cylindrical structures comprising single or multiple concentric graphene sheets and have diameters from less than 1 nanometer (nm) up to 50 nm (one nm is one millionth of a millimeter). Due to their unique and tunable structural, physical, and chemical properties, CNTs are used in environmental remediation as absorbents, catalysts or catalyst supports, membranes, and electrodes. However, a poorly understood determinant of the role of CNTs in water treatment is their interaction with chemical disinfectants (e.g., chlorine, chloramine, and ozone). To address these existing gaps in the environmental fate and reactivity of CNTs, this work establishes whether CNTs represent precursors for halogen and nitrogen containing disinfection byproducts (DBPs), which are products that form during a reaction of a disinfectant with organic matter in the water. In addition, we seek to understand how reaction with disinfectants alters CNT surface chemistry, and in turn impacts their environmental mobility and cytotoxicity. Finally, we determine how NOM and other aquatic variables known to impact DBP formation (e.g., Br⁻, NOM, and pH) influence the rate and products of CNT reaction with disinfectants. Outcomes of this work contribute to the current understanding of the role of carbon-based species as DBP precursors in disinfection and provide new context as to the environmental significance and implications of CNTs in natural and engineered aquatic systems.