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, there action mechanism responsible for the photochemical transformation of aqueous C ₆₀ clusters (nC₆₀) in sunlight has been examined. Evidence is presented that under lamps that emit light only within the solar spectrum, 1_O2 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 1_O2, stopped both reactions, indicating that 1_O2 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 1_O2 is a reaction intermediate. 1 _O2 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° 55′ W, 40° 26′ N), suspensions of 5 mg/L nC₆₀ produced 1_O2 concentrations 1 order of magnitude higher than the average value typically found in natural waters containing the same mass of natural organic carbon.