Delivery vehicles for zerovalent metal nanoparticles in soil and groundwater

Anionic, hydrophilic carbon (Fe/C) and poly(acrylic acid)-supported (Fe/PAA) zerovalent iron nanoparticles were studied as a reactive material for the dehalogenation of chlorinated hydrocarbons in groundwater and soils. The transport of Fe/C nanoparticles was studied by elution through columns packed with model soils from different regions of the USDA soil textural triangle, and was compared to that of unsupported Fe nanoparticles. The Fe/C and Fe/PAA particles form colloidal suspensions that settle very slowly (hours to days) in water. Their anionic surface charge facilitates transport through soil- and sand-packed columns. Elution lengths from column breakthrough studies were compared with calculations based on the Tufenkji-Elimelech model (Environ Sci. Technol. 2004, 38, 529). It can be concluded from this comparison that nanoparticle diffusion is the dominant filtration mechanism, and that Fe/PAA and Fe/C particles have sticking coefficients on the order of 0.36 and ≤0.07, respectively, in sand and 0.05 and ≤0.01, respectively, in clay-rich Chagrin soil. In contrast, unsupported Fe nanoparticles rapidly agglomerate in water and are efficiently filtered by all of the soils tested, except for the clay-rich soil in which clay platelets may also act as an anionic support material. Trichloroethylene reduction by Pd-catalyzed Fe/C is rapid, and the reaction is unchanged by elution of a suspension of the material through a sand column.