Fate and Transport of Nanoscale Buckminsterfullerene Aggregates (nC60) in Heterogenous Porous Media.
Wolfand, Jordyn Michelle.
- Buckminsterfullerene (C60), an allotrope of carbon, has unique physical and chemical properties that have led to its use in a variety of commercial applications, ranging from organic photovoltaics to biopharmaceuticals. It is inevitable that C60 will be released into the environment during manufacture, transportation, application, and disposal. C60 is nearly insoluble in water, though several ... read moremethods have been developed to disperse C60 aggregates in water without the aid of stabilizing agents. These C60 aggregates have diameters of 5â��200 nm, are negatively charged, and are referred to as nC60. It has been suggested that nC60 is the most environmentally relevant form of C60, but understanding of the retention and transport of these particles in heterogeneous is limited. This research sought to characterize the transport and retention behavior of nC60 in a two-dimensional (2-d) aquifer cell packed with heterogeneous porous media. It was hypothesized that nC60 would accumulate at the interfaces between high and low permeability sands. Initially, two sets of one-dimensional (1-d) column experiments were completed to prepare for injection into the 2-d aquifer cell, and to determine parameters needed to simulate transport of nC60 with modified filtration theory. The first series of column studies was conducted to determine a background electrolyte that would result in 75% breakthrough of nC60 after a pulse injection into the 40/50 mesh sand matrix. A second series of 1-d column experiments was completed at the optimal electrolyte concentration to determine two parameters needed for simulation by modified filtration theory â�� maximum retention capacity (Smax), and the particle attachment rate (Katt) of the porous medium. After determination of the relevant transport parameters in the 1-d column studies, nC60 was injected into the 2-d aquifer cell. nC60 breakthrough was found to increase with an increase in ionic strength of the background electrolyte, in accordance with previous literature. 6 mM NaCl and 0.05 mM NaHCO3 was chosen as the background electrolyte for the 2-d cell. Smax was determined to be 0.57, 3.17, and 0.54, 3.2, and 4.7 ?g/g, and katt was found to be 0.25, 1.1, and 1.4 h-1 for 40/50, 80/100, and 100/140 mesh natural Ottawa sand, respectively. nC60 was injected separately into three of the ports of the 2-d aquifer cell (upstream of a 80/100 mesh low-permeability lens, upstream of a 100/140 mesh low-permeability lens, and in the background matrix of 40/50 mesh sand. A significant amount of nC60 mass was retained near the port of injection. Enhanced accumulation of sorbed-phase nC60 at the textural interface did not occur as expected. Though sorbed-phase concentration of nC60 decreased after the interface, accumulation did not occur on the horizontal boundaries of the lens. Results indicate that nC60 transport at textural interfaces is controlled by changes in local flow velocities through heterogeneous media.read less