Photochemical Transformation of Aqueous C₆₀ Clusters in Sunlight

Abstract

C60 is emerging in a variety of potential applications; however, its environmental fate remains largely unknown. Photochemical transformation may be an important fate process of C60 in the aquatic environment due to its strong light absorption within the solar spectrum. In this study, the photochemical transformation of aqueous C60 clusters (nC60) in sunlight (West Lafayette, IN, 86 degrees 55' W, 40 degrees 26' N) and in lamp light (300-400 nm wavelengths) was investigated. When exposed to light, the brown to yellow color of nC60 was lost gradually, and the cluster size decreased as the irradiation time increased. TOC analysis on the water phase of centrifuged samples indicated that water soluble products formed and that with continued light exposure, these intermediates eventually mineralized, volatilized, or were converted to other products not quantified by TOC after centrifugation and filtration. In sunlight at approximately 1 mg/L C60, the decay rate of C60 in small clusters (diameter = 150 nm) was greater than for C60 in larger (500 nm) clusters, with half-lives of 19 and 41 h, respectively. The presence of fulvic acid, changes in pH, and the preparation method of the clusters had minimal effects on the phototransformation rate. Deoxygenated samples resulted in negligible loss after 17 h of lamp exposure, indicating O2 played a role in the phototransformation mechanism. These findings suggested that release of nC60 into surface waters will result in photochemical production of currently unknown products.

Methodological considerations for testing the ecotoxicity of carbon nanotubes and fullerenes: Review

“…Along these lines, it was recently shown that germanium NP attachment directly to DNA during the alkaline Comet assay procedure probably resulted in arbitrary DNA fragmentation, a determination made by observing apparent DNA damage to cells harvested immediately after the NP addition [115]. In addition, fullerene NPs have recently been shown to oxidize in the presence of sunlight, forming a currently not-well-defined set of byproducts [116,117]. Thus, researchers should be cautious of potential artifacts that may occur for fullerenes that are exposed unintentionally to sunlight or room light.…”

A Review of the Properties and Processes Determining the Fate of Engineered Nanomaterials in the Aquatic Environment

“…Adsorption of NOM induces an increase of the degree of repulsion within the aggregate matrix and results in aggregate rupture. Additionally, UV and sunlight radiation have been shown to induce disaggregation of fullerenes (C 60 ) and the formation of soluble product (60 carbon cages containing various oxygen functional groups; Hou and Jafvert, 2008;Lee et al, 2009).…”

“…For instance, sunlight can catalyze some redox reactions (photooxidation and photoreduction) of photoactive NMs (e.g., TiO 2 , CNTs, fullerenes) and produces reactive oxygen species when exposed to sunlight (Chen and Jafvert, 2011). Others may be oxidized or reduced by sunlight, changing their redox state, charge, and therefore aggregation state and toxicity (Hou and Jafvert, 2008;Lee et al, 2009). Sunlight has been shown to cause the degradation of gum arabic coating on AgNMs and result in enhanced aggregation and removal (sedimentation) of NMs from solution (Cheng et al, 2011).…”

Current status and future direction for examining engineered nanoparticles in natural systems

“…Carbonaceous nanomaterials such as CNTs and fullerenes are prone to producing carboxy and hydroxyl groups on its surface as well as generating reactive oxygen species (ROS) in the presence of sunlight. [65] The chemical alteration of the ENP, possibly accompanied by size changes, require characterisation techniques that can capture these changes and detection methods that remain sensitive to the ENPs.…”