• Journal of Soil and Groundwater Environment
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• v.13 no.6
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• pp.93-102
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• 2008

Experimental studies were conducted to characterize the synthesized nanoscale zero-valent iron (NZVI) which is resistant to oxidation in the atmospheric environment. XRD, XPS, and TEM analyses revealed that the oxidation-resistant NZVI particles formed under various controlled air contact conditions (4, 8 and 12 mL/min) have shells with ${\sim}$5 nm thickness. The shells consist of magnetite (${Fe_3}{O_4}$) and maghemite (${\gamma}-{Fe_2}{O_3}$), predominantly. No substantial differences were found in the shell components and thickness among NZVI particles formed under the various air flow rates. On the other hand, shell was not detected in the TEM image of rapidly oxidized NZVI particles. NZVI particles synthesized under the various air flow rates showed similar TCE degradation performances ($k_{obs}$= 0.111, 0.102, and 0.086 $hr^{-1}$), which are equivalent to approximately 80% of those obtained by the fresh NZVI particles. TCE degradation efficiencies of the NZVI particles(fresh, controlled air contact and rapidly oxidized) were improved after equilibrating with water for one day, indicating that depassivation of the shells occurred. The performances of NZVI particles decreased to 90% and 50% of those of the fresh NZVI particles, when they were equilibrated with the atmosphere for a week and two months, respectively. The NZVI particles synthesized under the controlled air contact would have advantages over traditional NZVI particles in terms of practical application into the site, because of their inertness toward atmospheric oxygen.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.4
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• pp.471-479
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• 2009

A Nanoscale Zero-Valent Iron(NZVI) was modified to build a reactor system to treat nitrate. Shell layer of the NZVI was modified by slow exposure of the iron surface to air flow, which produced NZVI particles that are resistant to aerial oxidation. A XANES (X-ray Absorption Near-Edge Structure) analysis revealed that the shell consists of magnetite ($Fe_3O_4$) dominantly. The shell-modified NZVI(0.5 g NZVI/ 120 mL) was able to degrade more than 95% of 30 mg/L of nitrate within $30 hr^{-1}$ ( pseudo first-order rate constant($k_{SA}$) normalzed to NZVI surface area ($17.96m^2/g$) : $0.0050L{\cdot}m^{-2}{\cdot}hr^{-1}$). Ammonia occupied about 90% of degradation products of nitrate. Nitrate degradation efficiencies increased with the increase of NZVI dose generally. Initial pH values of the reactor systems at 4, 7, and 10 did not affect nitrate removal rate and final pH values of all experiments were near 12. Nitrate removal experiments by using the shell-modified NZVI immobilized on a cellulose acetate (CA) membrane were also conducted. The nitrate removal efficiency of the CA membrane supported NZVI ($k_{SA}=0.0036L{\cdot}m^{-2}{\cdot}hr^{-1}$) was less than that of the NZVI slurries($k_{SA}=0.0050L{\cdot}m^{-2}{\cdot}hr^{-1}$), which is probably due to less surface area available for reduction and to kinetic retardation by nitrate transport through the CA membrane. The detachment of the NZVI from the CA membrane was minimal and impregnation of up to 1 g of NZVI onto 1 g of the CA membrane was found feasible.