Preparation and characterization of stable aqueous higher-order fullerenes

Stable aqueous suspensions of nC(60) and individual higher fullerenes, i.e. C-70, C-76 and C-84, are prepared by a calorimetric modification of a commonly used liquid-liquid extraction technique. The energy requirement for synthesis of higher fullerenes has been guided by molecular-scale interaction energy calculations. Solubilized fullerenes show crystalline behavior by exhibiting lattice fringes in high resolution transmission electron microscopy images. The fullerene colloidal suspensions thus prepared are stable with a narrow distribution of cluster radii (42.7 +/- 0.8 nm, 46.0 +/- 14.0 nm, 60 +/- 3.2 nm and 56.3 +/- 1.1 nm for nC(60), nC(70), nC(76) and nC(84), respectively) as measured by time-resolved dynamic light scattering. The zeta-potential values for all fullerene samples showed negative surface potentials with similar magnitude (-38.6 +/- 5.8 mV, -39.1 +/- 4.2 mV, -38.9 +/- 5.8 mV and -41.7 +/- 5.1 mV for nC(60), nC(70), nC(76) and nC(84), respectively), which provide electrostatic stability to the colloidal clusters. This energy-based modified solubilization technique to produce stable aqueous fullerenes will likely aid in future studies focusing on better applicability, determination of colloidal properties, and understanding of environmental fate, transport and toxicity of higher-order fullerenes.