Impact of Sunlight and Humic Acid on the Deposition Kinetics of Aqueous Fullerene Nanoparticles (nC60)

TLDR: The results highlight the importance of environment-induced changes in nC₆₀ surface chemistry in its fate and transport in aquatic environments.

Abstract: Nanoparticle transport in natural settings is complex due to interactions with the surrounding environment. In this study, the impact of UVA irradiation and humic acid (HA) on deposition of aqueous fullerene nanoparticles (nC60) on a silica surface as a surrogate for natural sediments was studied using packed column experiments and quartz crystal microbalance with dissipation monitoring under various solution conditions. Surface oxidation of nC60 induced by UVA irradiation greatly retarded its deposition due to the increased negative surface charge and hydrophilicity. Dissolved HA, once adsorbed onto the nC60 surface, also hindered its deposition mainly through steric hindrance forces. The extent of this effect depended on the properties and the amount of HA adsorbed, which is a function of ionic strength and HA concentration. HA has limited adsorption on UVA-irradiated nC60 and is expected to play a less important role in its stability. HA immobilized onto the silica surface had a variable effect on nC60 deposition, depending on the complex interplay of Derjaguin−Landau−Verwey−Overbeek (DLVO) and non-DLVO interactions such as electrostatic interaction, steric hindrance, and hydrogen bonding as well as HA molecular conformation. These results highlight the importance of environment-induced changes in nC60 surface chemistry in its fate and transport in aquatic environments.