title: UV irradiation and humic acid mediate aggregation of aqueous fullerene (nC₆₀) nanoparticles.
abstract: The transport and fate of engineered nanomaterials is affected by multiple environmental factors, including sunlight and natural organic matter. In this study, the initial aggregation kinetics of aqueous fullerene (nC(60)) nanoparticles before and after UVA irradiation was investigated in solutions varying in ionic strength, ionic composition, and humic acid concentration. In NaCl solutions, surface oxidation induced by UV irradiation remarkably increased nC(60) stability due to the increased negative surface charge and reduced particle hydrophobicity; although humic acid greatly enhanced the stability of pristine nC(60) via the steric hindrance effect, it had little influence on the stability of UV-irradiated nC(60) in NaCl due to reduced adsorption on oxidized nC(60) surface. In contrast, UV irradiation reduced nC(60) stability in CaCl(2) due to specific interactions of Ca(2+) with the negatively charged functional groups on UV-irradiated nC(60) surface and the consequent charge neutralization. By neutralizing surface charges of both UV-irradiated nC(60) and humic acid as well as forming intermolecular bridges, Ca(2+) facilitated humic acid adsorption on UV-irradiated nC(60), resulting in enhanced stability in the presence of humic acid. These results demonstrate the critical role of nC(60) surface chemistry in its environmental transport and fate.
authors.affiliation: Department of Civil and Environmental Engineering, Rice University, Houston, Texas 77005, USA.
authors.forename: Xiaolei
authors.initials: X
authors.lastname: Qu
authors.forename: Yu Sik
authors.initials: YS
authors.lastname: Hwang
authors.forename: Pedro J J
authors.initials: PJ
authors.lastname: Alvarez
authors.forename: Dermont
authors.initials: D
authors.lastname: Bouchard
authors.forename: Qilin
authors.initials: Q
authors.lastname: Li
mesh_terms: D037741:Fullerenes / Q000737:chemistry*; D006812:Humic Substances; D053758:Nanoparticles; D014466:Ultraviolet Rays; D014867:Water
chemical_list: D037741:Fullerenes; D006812:Humic Substances; D014867:Water; C069837:fullerene C60