Interaction of Fullerene (C60) Nanoparticles with Humic Acid and Alginate Coated Silica Surfaces: Implications for Fate and Transport
Kai Loon Chen, Department of Geography and Environmental Engineering, Johns Hopkins University, Baltimore, MD 21218 and Menachem Elimelech, Department of Chemical Engineering, Yale University, Mason Lab, 313A, 9 Hillhouse Avenue, New Haven, CT 06520.
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. In aqueous solutions, 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 the quartz crystal microbalance (QCM) to derive the deposition kinetics of fullerene (C60) nanoparticles onto bare silica surfaces and surfaces pre-coated with humic acid and alginate. The deposition behavior of these nanoparticles is investigated over a range of monovalent (NaCl) and divalent (CaCl2) concentrations. The deposition kinetics of fullerene nanoparticles onto bare silica surface are shown to be controlled by electrostatic interactions, consistent with the classical DLVO theory. The presence of dissolved humic acid and alginate in the solution leads to the adsorption of the macromolecules onto fullerene nanoparticles, resulting in significantly slower deposition rate due to steric repulsion. Pre-coating the silica surfaces with humic acid and alginate exerts similar steric influences in the presence of NaCl. At lower NaCl concentration, the increase in surface roughness, specifically for the alginate-coated surface, may result in faster initial deposition kinetics followed by slower deposition in the later stages. In the presence of CaCl2, the deposition kinetics of fullerene nanoparticles onto both humic acid- and alginate-coated surfaces are relatively high due to the macromolecules undergoing complex formation with Ca2+ which reduces the surface charge and steric influences of the layers.