Study of C 60 transport in porous media and the effect of sorbed C 60 on naphthalene transport
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In this study, the transport of water-stable “nano-C60 particles” (a term used to refer to underivatized C60 crystalline nanoparticles, stable in water for months) through a soil column (packed with Lula soil, 0.27% organic carbon) was investigated for the first time. Nano-C60 particle breakthrough experiments were conducted at different flow rates, while other column operating parameters remained fixed through all the experiments. Nano-C60 particles were observed to be more mobile at higher flow velocity: at the flow velocity of 0.38 m/d, the maximum percent of nano-C60 breakthrough (C/C0) was 47%; at the flow velocity of 3.8 m/d, the plateau value of nano-C60 breakthrough was 60%; and at the flow velocity of 11.4 m/d, the plateau value of nano-C60 breakthrough was almost 80%. At the low flow velocity (0.38 m/d), which is typical of groundwater flow, nano-C60 particles showed very limited mobility: after about 57 pore volumes, they deposited to the soil column so rapidly that virtually no nano-C60 was detected in the effluent. This observed “favorable deposition” (attachment efficiency ␣ ⳱ 1) was probably due to “filter ripening.” Also the release of nano-C60 particles after flow interruption was observed. The transport of naphthalene through the same soil column containing 0.18% nano-C60 particles deposited was measured. A retardation factor of about 13 was observed, possibly suggesting that sorbed nano-C60 particles in the soil column sorbed naphthalene similar to soil organic carbon. An asymmetric naphthalene breakthrough curve was observed, which is possibly due to “sorption nonequilibrium.”
I. INTRODUCTION
Since fullerenes are expected to be produced by the ton,1 it is of no doubt that those nanomaterials will ultimately be found in the environment at measurable concentrations. It is likely that the aquatic environment will be one of the most important sink for fullerene materials, although it is still unknown at what quantities they are present in the environment. Since C60 is virtually insoluble in water,2 one might expect that this hydrophobic nanomaterial would not enter groundwater in great quantities. However, several methods have produced waterstable nano-C60 particles,3–5 indicating that C60 might be mobile in groundwater. Recent studies have shown that this underivatized form of C60 (nano-C60) causes oxidative damage to both fish brain cells and cultured human cells.6,7 If this nano-C60 is indeed mobile in groundwater, people should be more concerned about the potential exposure to those materials through groundwater transport. It has been reported that the existence of dissolved
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0402 3244
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 12, Dec 2005 Downloaded: 16 Jul 2014
organic matter in groundwater could enhance the partition of neutral organic contaminants into water and thus enhance the transport of those compounds.8 Significant enhancement for naphthalene transport through groundwater
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