Effects of Solution Chemistry on Quantum Dot Transport and Retention in Porous Media
Abstract
Engineered nanomaterials with tunable surface chemistries, such as quantum dots, are becoming increasingly prevalent in commercial and medical applications. This increase in usage corresponds to an elevated risk of environmental exposures, and limited data are available on the fate and transport of quantum dots in the environment. The objective of this study was to quantify quantum dot transport and retention behavior under a variety of solution chemistries and in the presence of a non-aqueous phase liquid (NAPL) phase. The quantum dots were prepared with a CdSe/CdZnS core/shell that was coated with an amphiphilic copolymer. The primary quantum dot coating used in this study was octylamine modified polyacrylic acid, which yields a negative surface charge (zeta potential) ranging from -30 to -40 mV in water. The mean diameter of the quantum dots in deionized water ranged from 20-30 nm based on dynamic light scattering (DLS) analysis. Higher salt concentrations, ranging from 3 to 1000 mM NaCl, resulted in increased diameters of the quantum dots (28 to 190 nm, respectively). Transport and retention behavior of the quantum dots was evaluated using borosilicate glass columns (2.5 cm i.d. x 10 cm length) packed with 40-50 mesh (d50 = 355 µm) Ottawa sand that had been completely saturated with water. A pulse (ca. 60mL) of quantum dot suspension was introduced to the column at a flow rate of 1mL/min (pore-water velocity of 8m/d), followed by three pore volumes of particle-free solution. To evaluate effects of the presence of a NAPL phase, a uniform distribution of residual NAPL (Soltrol 220) was established prior to the quantum dot pulse injection. Concentrations of quantum dots in the column effluent and extracted from solid samples, quantified using an Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES), were used to construct an effluent breakthrough curve and retention profile for each experiment. The presence of a residual NAPL phase had negligible impact on quantum dot transport and retention in porous media, while the increasing NaCl concentrations (1 to 1000mM) drastically increased quantum dot retention within the columns.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H51F0978E
- Keywords:
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- 1832 HYDROLOGY / Groundwater transport