Photochemical reactivity of aqueous fullerene clusters: C₆₀ versus C₇₀

Highlights: • Aqueous C₆₀ and C₇₀ clusters (nC₆₀ and nC₇₀) formed through direct mixing with water adopted a face-centered cubic crystal structure. • The AQYs of nC₆₀ were greater than those of nC₇₀. • Both nC₆₀ and nC₇₀ lost considerable organic carbon contents (>80%) after ∼8 months of outdoor sunlight irradiation. • The intermediate photoproducts of nC₆₀ and nC₇₀ exhibited an increased content of oxygen-containing functionalities. - Abstract: Over the past few years, there has been a strong interest in exploring the potential impact of fullerenes in the environment. Despite that both C₆₀ and C₇₀ have been detected in environmental matrices, the research on the impact of higher fullerenes, such as C_70, has been largely missing. This study evaluated and compared the phototransformation of aqueous C₆₀ and C₇₀ clusters (nC₆₀ and nC₇₀) and their ¹O₂ production under sunlight and lamp light irradiation (315 nm, 360 nm and 420 nm). The nC₆₀ and nC₇₀ samples formed by direct mixing with water adopted a face-centered cubic (FCC) crystal structure. The apparent quantum yields (AQYs) of fullerene phototransformed were relatively constant over the examined wavelengths, while ¹O₂ production AQYs decreased with increased wavelengths. The long-term fate studies with outdoor sunlight indicated that both nC₆₀ and nC₇₀ lost considerable organic carbon contents (>80%) in water after ∼8 months of irradiation and that the intermediate photoproducts of nC₆₀ and nC₇₀ exhibited a progressively increased level of oxygen-containing functionalities. Overall, the study indicates that nC₇₀ can be photochemically removed under sunlight conditions and that the photoreactivity of nC₆₀ based on AQYs is greater than that of nC₇₀.