Phase Transfer of Palladized Nanoscale Zerovalent Iron for Environmental Remediation of Trichloroethene

Palladium-doped nanoscale zerovalent iron (Pd-NZVI) has been shown to degrade environmental contaminants such as trichloroethene (TCE) to benign end-products through aqueous phase reactions. In this study we show that rhamnolipid (biosurfactant)-coated Pd-NZVI (RL-Pd-NZVI) when reacted with TCE in a 1-butanol organic phase with limited amounts of water results in 50% more TCE mass degradation per unit mass of Pd-NZVI, with a 4-fold faster degradation rate (k(obs) of 0.413 day(-1) in butanol organic phase versus 0.099 day(-1) in aqueous phase). RL-Pd-NZVI is preferentially suspended in water in biphasic organic liquid-water systems because of its hydrophilic nature. We demonstrate herein for the first time that their rapid phase transfer to a butanol/TCE organic phase can be achieved by adding NaCl and creating water-in-oil emulsions in the organic phase. The significant enhancement in reactivity is caused by a higher electron release (3e(-) per mole of Fe-0) from Pd-NZVI in the butanol organic phase compared to the same reaction with TCE in the aqueous phase (2e(-) per mole of Fe-0). XPS characterization studies of Pd-NZVI show Fe-0 oxidation to Fe(III) oxides for Pd-NZVI reacted with TCE in the butanol organic phase compared to Fe(II) oxides in the aqueous phase, which accounted for differences in the TCE reactivity extents and rates observed in the two phases.