Post-Synthesis Separation and Storage of Zero-Valent Iron Nanoparticles.

Zero-valent iron (ZVI) nanoparticles are susceptible to oxidation and are therefore sensitive to postsynthesis processing, including both separation and storage techniques. Two separation methods, centrifugation and magnetic separation, were evaluated in this study. Nanoparticle stability during storage in ethanol-water solutions was also studied, and the influence of both water and aeration on nanoparticle oxidation was determined. Nanoparticle morphology and extent of oxidation were analyzed with electron microscopy, elemental analysis, zeta potential, and X-ray photoelectron spectroscopy. Microscopy results suggest that the separation method used affects the extent of stabilizer that remains adsorbed to the nanoparticles, but both separation methods result in minimal oxidation of the nanoparticles. However, the addition of aerated water to nanoparticle-ethanol storage solutions caused nanoparticle oxidation; an increase in the volume fraction of water added caused a linear increase in oxygen content based on elemental analysis of nanoparticle samples. X-ray photoelectron spectroscopy results suggest that organic stabilizer is incorporated into the nanoparticle structure as oxidation occurs.