Evidence for covalently bonded chlorine–fullerene formed by ozonation and chlorination at room temperature

Abstract

This article reports for the first time that fullerene (nC₆₀) can form chlorinated disinfection by-products in aqueous systems at ambient temperature. The ability of nC₆₀ to form colloidal suspensions in aqueous media increases the chance that these particles will migrate in the environment and then in drinking water supply systems. Since nC₆₀ is not completely removed by conventional water treatment, any residual nC₆₀ is likely to be oxidized during disinfection process. While the ozonation of nC₆₀ has been studied, little is known about the reaction between nC₆₀ and chlorine. To address this issue, we subjected aqueous nC₆₀ suspensions to chlorination and sequential ozonation/chlorination at ozone dosages of 4.5, 10, 15 and 24 mg O₃/mg nC₆₀. The morphology and physicochemical properties of oxidized nC₆₀ aggregates were evaluated by scanning electron microscopy, transmission electron microscopy, UV–visible absorption spectroscopy and X-ray photoelectron spectroscopy (XPS). We found that while the particles in the as-prepared nC₆₀ were predominantly spheres, the ozonation of nC₆₀ resulted in the formation of irregularly shaped aggregates. The concentration of atomic carbon found by XPS in the nC₆₀ samples decreased from 92 % for the as-prepared nC₆₀ to 50 % for the aggregates ozonated at 24 mg O₃/mg nC₆₀ and then chlorinated at 68 mg Cl₂/L and allowed to react for 100 min. The presence of Cl atoms covalently bonded to C atoms was confirmed by XPS peaks corresponding to a binding energy (E _b) of 200.1–202.4 eV. This demonstrates the need to better assess and monitor the formation of potentially toxic chlorinated disinfection by-products from carbon nanomaterials during water treatment.