Aggregation and Deposition Kinetics of Fullerene Nanoparticles Onto Quartz Surface
Kai Loon Chen, Department of Geography and Environmental Engineering, Johns Hopkins University, Baltimore, MD 21218 and Menachem Elimelech, Department of Chemical Engineering, Environmental Engineering Program, Yale University, New Haven, CT 06520-8286.
The 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 aquatic systems may become a major concern. This is especially so as some studies have indicated fullerene to be toxic to bacteria and fish. Under aqueous conditions, hydrophobic fullerene molecules bind strongly together to form fullerene nanoparticles. In order to better understand the fate and transport of these nanoparticles when fullerene is released into natural aquatic systems, we investigate the aggregation and deposition kinetics in the presence of common monovalent and divalent electrolytes. The fullerene nanoparticles synthesized in our laboratory are generally spherical, having diameters mostly ranging from 30–70 nm. Aggregation kinetics of the negatively-charged nanoparticles in the presence of sodium and calcium chlorides are derived through dynamic light scattering. We observe diffusion- and reaction-limited regimes in both electrolytes, indicating aggregation behavior consistent with DLVO theory. Deposition kinetics of the nanoparticles onto quartz surface are also studied with the quartz crystal microbalance (QCM). We find increase in deposition kinetics with increases in concentration of both electrolytes. However, once we approach the critical coagulation concentration, the deposition rate decreases drastically, due to concurrent aggregation of the particles. This fast formation of aggregates greatly reduces the convective-diffusive transport of the fullerene towards the quartz surface. The release of deposited nanoparticles from the quartz surface is also looked into under different chemical conditions.