FATE OF C₆₀ NANOPARTICLES AND ADSORBED HYDROCARBONS - COMPARISON WITH ACTIVATED CARBON AND SOIL ORGANIC CARBON

Xuekun Cheng*
Mason B. Tomson
Amy T. Kan
Rice University
MS-519, Dept. of Civil & Envir. Engr.
6100 Main St.
Houston, TX 77005
Voice: 713-348-2026
Fax: 713-348-5203
E-mail: xkcheng@rice.edu

The interaction of common environmental contaminants with C₆₀ fullerene has been studied to evaluate the environmental impact of carbon nanomaterials. The adsorption and desorption interactions of hydrophobic contaminants, e.g., naphthalene and dichlorobenzene, and C₆₀ fullerene was characterized. Natural processes that may affect the wetting and deaggregation of C₆₀ fullerene nanoparticles may affect the extent of organic contaminant adsorption to C₆₀ aggregates by over three orders of magnitude. Desorption of these contaminants from dispersed C₆₀ aggregates exhibit hysteresis. The experimentally observed adsorption/desorption hysteresis was explained by a two-compartment desorption model: adsorption to the external surface of C₆₀ aggregates in contact with the solvent or water, and second, adsorption to the internal surfaces within the aggregates. Adsorption to the external surfaces appears to be "normal" and characterized by predictable interaction energies, whereas intra-nanoparticulate adsorption is very strong and essentially irreversible, entrapping organic molecules inside the aggregates. As a result, desorption of the compounds from the first region is easy and rapid, while that from the second region is extremely slow. All carbon forms tested in this study (fullerene, activated carbon, and soil organic carbon) showed a similar two-compartment hysteretic sorption pattern. The similarity of desorption of organic compounds from C₆₀ colloidal particles, activated carbon colloidal particles, and soil carbon phase most likely indicates a common mechanistic origin of desorption hysteresis observed in natural systems.