Ground State Reactions of nC60 with Free Chlorine in Water

Facile, photoenhanced transformations of water-stable C-60 aggregates (nC(60)) to oxidized, soluble fullerene derivatives, have been described as key processes in understanding the ultimate environmental fate of fullerene based materials. In contrast, fewer studies have evaluated the aqueous reactivity of nC(60) during ground-state conditions (i.e., dark conditions). Herein, this study identifies and characterizes the physicochemical transformations of C-60 (as nC(60) suspensions) in the presence of free chlorine, a globally used chemical oxidant, in the absence of light under environmentally relevant conditions. Results show that nC(60) undergoes significant oxidation in the presence of free chlorine and the oxidation reaction rates increase with free chlorine concentration while being inversely related to solution pH. Product characterization by FTIR, XPS, Raman Spectroscopy, TEM, XRD, TOC, collectively demonstrates that oxidized C-60 derivatives are readily formed in the presence of free chlorine with extensive covalent oxygen and even chlorine additions, and behave as soft (or loose) clusters in solution. Aggregation kinetics, as a function of pH and ionic strength/type, show a significant increase in product stabilities for all cases evaluated, even at pH values approaching 1. As expected with increased (surface) oxidation, classic Kow partitioning studies indicate that product clusters are relatively more hydrophilic than parent (reactant) nC(60). Taken together, this work highlights the importance of understanding nanomaterial reactivity and the identification of corresponding stable daughter products, which are likely to differ significantly from parent material properties and behaviors.