Transport of Engineered Silver Nano Particles through Saturated Porous Media

Abstract

Silver nanomaterials are released into environmental receptors due to their increased application in consumer products and research. However, the interaction of silver nanoparticles (AgNPs) with soil and groundwater is not well understood. This study simulates bench-scale transport of Creighton colloidal AgNPs through a one-dimensional column packed with saturated porous media. The AgNPs were synthesized by reduction of silver nitrate with sodium borohydride, and characterized using ultraviolet- visible absorption spectroscopy (shape, size distribution, aggregation state, and surface plasmon resonance), Raman spectroscopy (purity), transmission electron microscopy (average size and size distribution), flame atomic absorption spectroscopy (concentration), dynamic light scattering (hydrodynamic size), and Zeta potential (surface charge). A glass column (5.0 cm length, 2.5 cm diameter) was packed with glass beads. AgNPs and a conservative tracer (chloride ion) were injected as a pulse into the column in an upward direction at fixed pH (~8) and ionic strength (0.01 mM of KCl). Aliquot samples were collected throughout the adsorption and desorption phases using a fraction collector. Breakthrough curves were constructed for the effluent to influent concentration ratio (C/C0) as a function of pore volume (PV). The breakthrough curve showed a mass loss in the effluent for the transport of AgNPs of 1-100 nm in diameter and no retardation compared to the tracer. This behavior may be attributed to the irreversible capture of the AgNPs by the glass beads. Our future experiments will target the transport of surface modified AgNPs in the presence of organic matter.