UC Davis

AbstractThe fate of silver nanoparticles (nAg), an emerging environmental contaminant, has been widely studied particularly around wastewater and groundwater systems. The transport and deposition of nanoparticles onto the surface of environmental porous media-like soils are most commonly modeled using classical colloid filtration theory to assess the filtration efficiency and dispersal of suspended nAg in percolating groundwater. However, the variation of porous media including surface roughness and chemical heterogeneity renders findings system specific. This work sought to determine how deep the attractive potential well must be to capture silver nanoparticles (nAg) under conditions where the equilibrium interaction potential should follow classical DLVO modeling. Using a well-defined model system of 50 nm nAg particles and 50 10 μm silica collector particles under gravity-driven flow (low Reynolds number and low Peclet number), it was determined that at -2.5 kT attractive well ~ 92 % of nAg were captured in the column. The nAg particles were released by increasing electrostatic repulsion through reduction in ionic strength. Subtle changes in the ionic strength in the range 5 to 12.5 mM, which are commonly found in soil, transitioned from transport to deposition and vice versa. These findings will be useful for predicting transport or capture in more complex systems.