(619d) Aggregation of Fullerene (C60) Nanoparticles in Monovalent and Divalent Electrolytes: Implications for Fate, Transport, and Bioavailability

Buckminsterfullerene C₆₀ has been attracting attention in recent years both for its potential as a nanomaterial as well as its toxicity towards certain microorganisms and human cells. In aquatic environments, fullerene C₆₀ molecules self-assemble to form negatively charged nanoparticles. The objective of this study is to investigate the aggregation behavior of fullerene nanoparticles in the presence of monovalent (NaCl and KCl) and divalent (CaCl₂) electrolytes prevalent in natural aquatic systems. A comprehensive knowledge of the aggregation behavior of the nanoparticles will facilitate the prediction of their fate, transport, and bioavailability in natural aquatic systems. Furthermore, the aggregation state of these nanoparticles is expected to play a critical role in determining the degree of fullerene toxicity. In this study, the electrophoretic mobilities of fullerene nanoparticles synthesized through two methods are shown to become less negative when electrolyte concentrations are increased, indicative of charge screening effects. By conducting time-resolved dynamic light scattering measurements, the aggregation kinetics of both fullerene nanoparticles are found to increase with increasing salt concentrations. At high enough salt concentrations, the charges of the nanoparticles are completely screened and the nanoparticles undergo diffusion-limited aggregation. Even though the stabilities of both fullerene nanoparticles are very different, their Hamaker constants are experimentally derived and demonstrated to be similar, indicating their bulk material to be the same despite different synthesis methods. The influence of particle size and solution pH on the stability of fullerene nanoparticles will also be discussed.