Photochemistry of Aqueous C₆₀ Clusters: Evidence of ¹O₂ Formation and its Role in Mediating C₆₀ Phototransformation

The expected rapid expansion of nanotechnology industries has raised concern over the environmental fate and effects of materials created by these industries, including carbon-based fullerenes. In this study, the reaction mechanism responsible for the photochemical transformation of aqueous C60 clusters (nC60) in sunlight has been examined. Evidence is presented that under lamps that emit light only within the solar spectrum, 1O2 is produced via aqueous nC60 suspensions, using furfuryl alcohol (FFA) as an indicator. In air-equilibrated suspensions, the losses of 0.2 mM FFA and 0.8 mg/L C60 were >90% and 70% after 15 h, while removing oxygen, the precursor of 1O2, stopped both reactions, indicating that 1O2 was produced and mediated nC60 phototransformation. Similar reactions performed in deuterium oxide and with added azide ion resulted in accelerated and slowed loss of FFA, respectively, as expected if 1O2 is a reaction intermediate. 1O2 production (as measured by FFA loss) increased with time as more water-soluble intermediate products accumulated in solution. In summer sunlight (West Lafayette, IN, 86 degrees 55' W, 40 degrees 26' N), suspensions of 5 mg/L nC60 produced 1O2 concentrations 1 order of magnitude higher thanthe average value typically found in natural waters containing the same mass of natural organic carbon.