(169g) Aggregation Kinetics Of Fullerene (C60) Nanoparticles In The Presence Of Humic Acid

Buckminsterfullerene C₆₀ is a nanomaterial with potential applications in the fields of optics, electronics, and biomedical engineering. With the impending widespread utilization of fullerene in industrial and consumer products, fullerene pollution of natural waters is inevitable. Under aqueous conditions, hydrophobic fullerene molecules bind strongly together to form negatively charged fullerene nanoparticles. To better understand the fate and transport of these nanoparticles in natural aquatic systems, we employ time-resolved dynamic light scattering to investigate their aggregation kinetics in the presence of Suwannee River humic acid and common monovalent and divalent electrolytes. In the absence of humic acid, the aggregation behavior of the fullerene nanoparticles in the presence of sodium, magnesium, and calcium ions was consistent with the classic DLVO theory. In the presence of humic acid and sodium or magnesium ions, humic acid adsorbed onto the fullerene nanoparticles resulting in steric repulsion, which stabilized the nanoparticle suspension. This increase in the nanoparticle stability was similarly observed in the presence of humic acid at low calcium ion concentrations. However, enhanced aggregation occurred at higher calcium concentrations. Light scattering measurements and TEM imaging of the fullerene aggregate structures indicated that bridging of the fullerene nanoparticles and aggregates by the humic acid aggregates was the likely mechanism for the enhanced aggregation.