UV Irradiation and Humic Acid Mediate Aggregation of Aqueous Fullerene (nC60) Nanoparticles

• Published in: Environmental science & technology 2010-10, Vol.44 (20), p.7821-7826
• Main Authors: Qu, Xiaolei, Hwang, Yu Sik, Alvarez, Pedro J. J, Bouchard, Dermont, Li, Qilin
• Format: Article
• Language: English
• Subjects: Acids; Applied sciences; Aqueous solutions; Environmental Processes; Exact sciences and technology; Fullerenes; Fullerenes - chemistry; Humic Substances; Ions; Nanoparticles; Pollution; Studies; Ultraviolet radiation; Ultraviolet Rays; Water
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es101947f

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 (nC60) 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 nC60 stability due to the increased negative surface charge and reduced particle hydrophobicity; although humic acid greatly enhanced the stability of pristine nC60 via the steric hindrance effect, it had little influence on the stability of UV-irradiated nC60 in NaCl due to reduced adsorption on oxidized nC60 surface. In contrast, UV irradiation reduced nC60 stability in CaCl2 due to specific interactions of Ca2+ with the negatively charged functional groups on UV-irradiated nC60 surface and the consequent charge neutralization. By neutralizing surface charges of both UV-irradiated nC60 and humic acid as well as forming intermolecular bridges, Ca2+ facilitated humic acid adsorption on UV-irradiated nC60, resulting in enhanced stability in the presence of humic acid. These results demonstrate the critical role of nC60 surface chemistry in its environmental transport and fate.