Proteinate-Capped Silver Nanoparticle Transport in Water-Saturated Sand

The transport of proteinate-capped silver nanoparticles (AgNPs) was evaluated in well-defined water-saturated Ottawa sand over a range of water chemistry conditions and sand particle sizes. AgNP retention in the columns increased with solution ionic strength and reductions in mean sand particle diameter, with the influence from ionic strength having the more significant effect on AgNP retention. Increased retention of AgNPs in the porous media with increasing ionic strength appears to be caused by increased nanoparticle–sand interaction rather than increased aggregation of nanoparticles with a resulting increase in physical filtration. Effluent AgNP concentrations over time were effectively simulated using the transient, one-dimensional advection–dispersion equation with maximum attachment capacity (Smax) and attachment/detachment coefficients (katt and kdet). In almost all cases, significant amounts of AgNPs exited the columns, suggesting that AgNPs are relatively mobile in sand. At ionic strengths typical of natural groundwater (e.g., 10 mM), only 30–50% of the AgNPs were retained.