Transformation of Aggregated C₆₀ in the Aqueous Phase by UV Irradiation

Abstract

This study demonstrates that water-stable C60 cluster (nC60) undergoes a photochemical transformation(s) when irradiated with monochromatic UV light at 254 nm. Upon UV exposure, characteristic absorption of nC60 in the visible (ca. 450-550 nm, indicative of a cluster structure) and UV regions (indicative of underivatized molecular C60) gradually disappeared. Concurrently, a new product with absorption centered at 210 nm formed. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses confirmed a complete reduction in aggregation and formation of a soluble product. Negligible loss of total organic carbon (TOC) and drastic retardation in degradation kinetics in the absence of oxygen collectively implied that photochemical transformation was accomplished via oxidative pathway without carbon mineralization. MS (LDI), FTIR, and XPS analyses indicated a 60 carbon cage product, containing various oxygen functional groups such as epoxides and ethers. In addition, this product demonstrated significantly less antibacterial effects on Escherichia coli when compared to the parent nC60. The results of this study suggest that accurate assessment of C60 in environmental life cycles and impact should consider the light-mediated transformation of C60 in the aqueous phase and resulting water-soluble products.

Production and consumption of reactive oxygen species by fullerenes

“…Previous studies have demonstrated the formation of watersoluble photoproducts with oxygen-containing functional groups during the phototransformation of aqu/nC 60 [23,32]. The present study found new evidence to support this mechanism by first extracting the irradiated aqu/nC 60 with toluene, then measuring the fluorescence EEM of the water layer after the extraction.…”

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).…”

Carbon nanomaterials in clean and contaminated soils: environmental implications and applications

“…Degradation of C 60 in aqueous solutions through photochemical processes have been identified by numerous investigations (Sect. 3.3) (Hou and Jafvert, 2008;Lee et al, 2009;Li et al, 2009), which may be an important step in both its breakdown and the activation of pre-…”