An assessment of novel polymeric coatings to enhance transport and in situ targeting of nanoiron for remediation of non-aqueous phase liquids (NAPLs)

The goal of this study was to evaluate the effect of surface modifiers on nanoiron mobility and NAPL targeting and obtain a fundamental understanding of the physical and geochemical processes governing the migration and distribution of nanoiron in porous media. Physicochemical characterization, emulsification and laboratory batch column studies were used to (i) identify a set of surface modifiers that can enhance the mobility of nanoiron through water saturated porous media and provide in situ targeting of the NAPL-water interface, (ii) demonstrate NAPL/water interfacial targeting (ex-situ) afforded by amphiphilic triblock copolymer modified nanoiron, (iii) evaluate the effects of surface modifiers on nanoiron mobility for varying groundwater ionic strength and composition, pH, approach velocity, grain size, and in the presence of silica fines and clay particles. Implications of these findings for field application of nanoiron are discussed.; Three surface modifiers are used to modify NZVI, including a poly(methacrylic acid)-poly(methyl methacrylate)-poly(styrene sulfonate) (PMAA-PMMA-PSS) triblock copolymer synthesized by atom transfer radical polymerization (ATRP), a commercially available surfactant sodium dodecyl benzyl sulfonate (SDBS), and a polyaspartate polymer. Microfluidic flow cell experiments indicate that straining is the dominant mechanism of filtration for bare Reactive Nano Iron Particles (RNIP), and that mobility in model water-saturated porous media is low. At low ionic strength (<10 mM Na+), surface modification by SDBS, polyaspartate, or the triblock copolymer significantly enhanced transport. Quartz Crystal Microbalance (QCM) experiments indicate that triblock copolymer-modified RNIP has no tendency to adhere to silica grain surfaces, while SDBS- and polyaspartate-modified RNIP showed slightly higher particle-collector attachment. At low ionic strength, the tendency to adhere to silica surfaces correlated with the observed mobility enhancement. At higher ionic strength (>40mM Na+), only triblock copolymer modified RNIP was mobile, suggesting that large MW polyelectrolyte coatings are needed to enhance mobility when groundwater has a high ionic strength. Long chain polyelectrolyte in the triblock copolymer likely provides a dense adsorbed layer and an electrosteric barrier to aggregation and filtration while the low molecular weight surfactant (SDBS)- or polyaspartate-modified RNIP is electrostatically stabilized an relies on electrical double layer repulsions (EDL) to enhance mobility. (Abstract shortened by UMI.)...