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Abstract:
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Silver nanoparticles (AgNPs) have been increasingly applied in various nanotechnology areas due to their unique optical and antimicrobial properties that are absent in bulk form. With elevated release of AgNPs into the environment, their interaction with groundwater and soil needs to be examined. The goal of this study is to model the transport of colloidal AgNPs through water saturated porous media at low flow rates (1 mL/min), fixed pH (~8) and ionic strength (0.01 mM KCl), and for AgNP of diameters within the 1-100 nm range. The colloidal AgNPs were synthesized using a Creighton method and were size-selected using a tangential flow ultrafiltration approach. The physical and chemical properties of AgNPs (purity, shelf life time, average size, size distribution, aggregation state, surface plasmon resonance, concentration, and surface charge) were then determined via Raman spectroscopy, ultraviolet-visible absorption spectroscopy, transmission electron microscopy, flame atomic absorption spectroscopy, and Zeta potential measurements. AgNPs (15 ppm of silver) and a conservative tracer (Cl- ions) were injected in upward direction through a one-dimensional column (2.5 cm diameter, 5.0 cm length) that was pre-packed with saturated glass beads. A 2 mL volume of effluent was collected every two minutes. The samples were chemically digested and diluted quantitatively with nitric acid. The concentration of silver in the colloids was determined using flame atomic absorption spectroscopy, and inductively coupled plasma optical emission spectroscopy. Breakthrough graphs were created by plotting the normalized concentration of total Ag versus the pore volume. The transport of AgNPs of 1-100 nm diameter size range showed no retardation with respect to the tracer, while a mass loss within the media pores was observed. More experiments will be performed in the future to verify the effect of colloidal AgNPs in heterogeneous porous media (sand and real soil). |
