This team began in 2001 evaluating nanoparticles in water, and quickly found that the environmental chemistry of even simple nanoparticles could be extraordinarily complicated. Fullerenes, in particular C60, became a model system for CBEN work. Even in pure water we found these systems aggregated into well defined clusters, and we reported on the physical and chemical properties of these stable fullerene water suspensions (nC60) in 2004 and 2005.(Sayes, Fortner et al. 2004; Fortner, Lyon et al. 2005) Since then, this group has continued to refine the analytical tools and improve our chemical understanding of this model system.
The specific objective of this project is to understand the physical and chemical processes affecting the properties of carbon based nanomaterials in natural aqueous environment. The results from this project provide information for predicting nanoparticle properties in the aqueous phase, and are the basis for studies in fate and transport and biological interactions. To date, this group has successfully characterized aqueous C60 nanoparticles, nC60, formed through different pathways under a wide range of solution conditions representing various water qualities found in the environment. It was also found in our study that aquatic natural organic matter (NOM) plays a critical role in the rate at which C60 can enter the aqueous phase as well as the physical and chemical properties of nC60 particles formed.(Xie, Xu et al. 2008) In the presence of NOM, nC60 of significantly smaller sizes (< 10 nm) can form at much higher concentrations (up to 20 mg/L) in the aqueous phase within a shorter time of mixing than that reported by previous studies. Dissolution of nC60 by NOM is suspected. A paper based on this study was recently accepted by Environmental Science and Technology. The nC60 formed by ultrasonication in water was found to have similar structure as that formed from the solvent exchange process, both differing in crystalline structure from the bulk C60. These particles are extremely stable in water and partition linearly onto Luna soil.
This year the team expands its efforts in analytical chemistry to better determine the purity and surface chemical properties of aggregated fullerenes and to track chemical fate of fullerene in typical aqueous and soil environment. Colvin evaluates the purity of nC60 produced via solvent extraction, sonication and dissolution using mass spectroscopy, solid state NMR and total carbon analysis. Of particular focus is the quantification of any bound molecules in the interior of the aggregates; how the formation process itself influences their loading is examined. Li investigates the photochemistry of aqueous fullerenes suspensions, focusing on the the impact of photochemical transformation in the presence of NOM on dispersitivity and relevant transport properties. Masiello applies new analytical tools drawn from geochemistry to the analytical challenges of fullerenes in the environment; she optimizes existing organic geochemical techniques for improved performance in the detection of nanocarbon in environmentally complex matrices. Li and Masiello apply the developed analytical tools to identify reaction products or derivative of fullerene in simulated natural waters. Such efforts will make studies of the fate and transport of nanocarbons in soil and water more feasible.
Participating Researchers: