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 C-60 clusters (nC(60)) in sunlight has been examined. Evidence is presented that under lamps that emit light only within the solar spectrum, O-1(2) is produced via aqueous nC(60) suspensions, using furfuryl alcohol (FFA) as all indicator. In air-equilibrated suspensions, the losses of 0.2 mM FFA and 0.8 mg/L C-60 were >90% and 70% after 15 h, while removing oxygen, the precursor of O-1(2), stopped both reactions, indicating that O-1(2) was produced and mediated nC(60) phototransformation. Similar reactions performed in deuterium oxide and with added azide ion resulted in accelerated and slowed loss of FFA, respectively, as expected if O-1(2) is a reaction intermediate. O-1(2) 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 nC(60) produced O-1(2) concentrations 1 order of magnitude higher than the average value typically found in natural waters containing the same mass of natural organic carbon.