Transformation of Graphitic Carbon Nitride by Reactive Chlorine Species: "Weak" Oxidants Are the Main Players.

Graphitic carbon nitride (g-C 3 N 4 ) nanomaterials hold great promise in diverse applications; however, their stability in engineering systems and transformation in nature are largely underexplored. We evaluated the stability, aging, and environmental impact of g-C 3 N 4 nanosheets under the attack of free chlorine and reactive chlorine species (RCS), a widely used oxidant/disinfectant and a class of ubiquitous radical species, respectively. g-C 3 N 4 nanosheets were slowly oxidized by free chlorine even at a high concentration of 200-1200 mg L -1 , but they decomposed rapidly when ClO· and/or Cl 2 •- were the key oxidants. Though Cl 2 •- and ClO· are considered weaker oxidants in previous studies due to their lower reduction potentials and slower reaction kinetics than ·OH and Cl·, our study highlighted that their electrophilic attack efficacy on g-C 3 N 4 nanosheets was on par with ·OH and much higher than Cl·. A trace level of covalently bonded Cl (0.28-0.55 at%) was introduced to g-C 3 N 4 nanosheets after free chlorine and RCS oxidation. Our study elucidates the environmental fate and transformation of g-C 3 N 4 nanosheets, particularly under the oxidation of chlorine-containing species, and it also provides guidelines for designing reactive, robust, and safe nanomaterials for engineering applications.