Measuring physicochemical properties (e.g., water solubility, crystal energy, Kow, and Koc) of C60 is problematic for several reasons. First, the molecule is extremely hydrophobic, making direct experimental determination of many of these properties difficult. Second, at concentrations below its aqueous phase solubility, it self-aggregates to forms aqueous phase nanoparticles, similar to the way surfactants often form micelles at concentrations below their solubility. Third, its melting point is unknown. As a result, a stepwise approach was used to discover these properties. First, a classic molecular level empirical model, Wohl's equation, was used to determine the associated molecular interaction parameters from solubility data determined for organic solvent mixtures. Next, Scatchard-Hildebrand theory was used to estimate the activity coefficient of C60 in the various solvents, from which the crystal energy was calculated. This also allowed for the calculation of subcooled liquid solubilities in all the solvent mixtures, including ethanol-water. The aqueous phase solubility was calculated from solubilities measured in non-miscible (with water) organic solvents and the corresponding organic liquid - water partition coefficients. This value was evaluated by comparing measured solubilities in ethanol-water and tetrahydrofuran-water mixtures to Wohl's equation predictions. Next, soil sorption isotherms were determined in ethanol-water mixtures at ethanol mole fractions from 0.42 to 1. Regression of the measured Koc values against the calculated (by Wohl's equation) subcooled liquid solubilities of each ethanol-water mixtures resulted in a straight line, as expected. This line was extrapolated to an ethanol mole fraction of zero, providing for an estimate of Koc for soil in equilibrium with ethanol-free water.

Physicochemical properties of C<sub>60</sub> related to its environmental fate and exposure

246th National Meeting (2013)

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Physicochemical properties of C60 related to its environmental fate and exposure

Physicochemical properties of C₆₀ related to its environmental fate and exposure