• Journal of Soil and Groundwater Environment
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• v.20 no.6
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• pp.117-126
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• 2015

Reductive degradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by nanoscale zero-valent iron (nZVI) was investigated to evaluate the feasibility of using it for in-situ groundwater remediation. Batch experiments were conducted to quantify the kinetics and efficiency of RDX removal by nZVI, and to determine the effects of pH, dissolved oxygen (DO), and ionic strength on this process. Experimental results showed that the reduction of RDX by nZVI followed pseudo-first order kinetics with the observed rate constant (k_obs) in the range of 0.0056-0.0192 min⁻¹. Column tests were conducted to quantify the removal of RDX by nZVI under real groundwater conditions and evaluate the potential efficacy of nZVI for this purpose in real conditions. In column experiment, RDX removal capacity of nZVI was determined to be 82,500 mg/kg nZVI. pH, oxidation-reduction potential (ORP), and DO concentration varied significantly during the column experiments; the occurrence of these changes suggests that monitoring these quantities may be useful in evaluation of the reactivity of nZVI, because the most critical mechanisms for RDX removal are based on the chemical reduction reactions. These results revealed that nZVI can significantly degrade RDX and that use of nZVI could be an effective method for in-situ remediation of RDX-contaminated groundwater.

• Journal of Soil and Groundwater Environment
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• v.17 no.1
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• pp.33-41
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• 2012

Nanoscale zero-valent iron (nZVI) has recently received much attention for remediation of soil and groundwater contaminated with trichloroethylene (TCE). But there have been many debates on the toxic or inhibitory effects of nZVI on the environment. The objective of this study was to investigate the effects of nZVI on the activity of Geobacter lovleyi and to determine the potent effect of combination of abiotic and biotic treatment of TCE dechlorination. TCE degradation efficiencies of Geobacter lovleyi along with nZVI were more increased than those when nZVI was solely used. The amount of total microbial protein was increased in the presence of nZVI and hydrogen evolved from nZVI was consumed as electron donor by Geobacter lovleyi. In addition, dechlorination of TCE to cis-DCE by Geobacter lovleyi along with nZVI in respiking of exogenous of TCE shows that the reactivity of Geobacter lovleyi was also maintained. These results suggest that the application of Geobacter lovleyi along with nZVI for the dehalorination is beneficial for the enhancement of TCE degradation rate and reactivity of Geobacter lovleyi.

• Environmental Engineering Research
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• v.25 no.2
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• pp.197-204
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• 2020

A number of different nanoscale zero-valent iron (nZVI) materials have been prepared and compared depending on the desired properties for the particular application, but different physicochemical properties of this prepared nZVI make it difficult to universally compare and standardize them to the same scale. In this study, we aimed to demonstrate a simple microplate-based colorimetric assay using 4-chlorophenol as an indicator with respect to the remediation of real treatment targets, such as trichloroethylene (TCE), 1,1,1-trichloroethane (TCA), and atrazine. Effect of nickel contents on 4-chlorophenol reduction was successfully investigated by the miniaturized colorimetric assay. In the same manner, the effect of nickel contents on dehalogenation of TCE, TCA, and atrazine was investigated and the pseudo-first-order kinetic constants were compared with the results for 4-chlorophenol. The similar pattern could be observed between 4-chlorophenol reduction obtained by colorimetric assay and TCE, TCA, atrazine reduction obtained by a traditional chromatographic method. The reaction kinetics does not match perfectly, but the degree of reaction can be estimated. Therefore, the colorimetric assay can be a useful and simple screening tool to determine nZVI reactivity toward halogenated organics before it is applied to a particular remediation site.

• Environmental Engineering Research
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• v.24 no.3
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• pp.463-473
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• 2019

Nanoscale zero-valent iron (nZVI) has proved to be an effective tool in applied environmental nanotechnology, where the decreased particle diameter provides a drastic change in the properties and efficiency of nanomaterials used in water purification. However, the agglomeration and colloidal instability represent a problematic and a remarkable reduction in nZVI reactivity. In view of that, this study reports a simple and cost-effective new strategy for ultra-small (< 7.5%) distributed functionalized nZVI-EG (1-9 nm), with high colloidal stability and reduction capacity. These were obtained without inert conditions, using a simple, economical synthesis methodology employing two stabilization mechanisms based on the use of non-aqueous solvent (methanol) and ethylene glycol (EG) as a stabilizer. The information from UV-Vis absorption spectroscopy and Fourier transform infrared spectroscopy suggests iron ion coordination by interaction with methanol molecules. Subsequently, after nZVI formation, particle-surface modification occurs by the addition of the EG. Size distribution analysis shows an average diameter of 4.23 nm and the predominance (> 90%) of particles with sizes < 6.10 nm. Evaluation of the stability of functionalized nZVI by sedimentation test and a dynamic light-scattering technique, demonstrated very high colloidal stability. The ultra-small particles displayed a rapid and high nitrate removal capacity from water.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.6
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• pp.679-687
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• 2007

Nanoscale zero valent ion (nZVI) technology is emerging as an innovative method to treat contaminated groundwater. The activity of nZVI is very high due to their high specific surface area, and supporting this material can help to preserve its chemical nature by inhibiting oxidation. In this study, nZVI particles were attached to granular ion-exchange resin through borohydride reduction of ferrous ions, and chemical reduction of nitrate by this material was investigated as a potential technology to remove nitrate from groundwater. The pore structure and physical characteristics were measured and the change by the adsorption of nZVI was discussed. Batch tests were conducted to characterize the activity of the supported nZVI and the results indicated that the degradation of nitrate appeared to be a pseudo first-order reaction with the observed reaction rate constant of $0.425h^{-1}$ without pH control. The reduction process continued but at a much lower rate with a rate constant of $0.044h^{-1}$, which is likely limited by mass transfer. To assess the effects of other ions commonly found in groundwater, the same experiments were conducted in simulated groundwater with the same level of nitrate. In simulated groundwater, the rate constant was $0.078h^{-1}$ and it also reduced to $0.0021h^{-1}$ in later phase. The major limitation in application of ZVI for nitrate reduction is ammonium production. By using a support material with ion exchange capacity, the problem of ammonium release can be solved. The ammonium was not detected in the batch test, even when other competitive ions such as calcium and potassium existed.

• Advances in environmental research
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• v.3 no.2
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• pp.107-116
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• 2014

This study aimed to synthesize dispersed and reactive nanoscale zero-valent iron (nZVI) with poly(1-vinylpyrrolidone-co-vinyl acetate) (PVP/VA), nontoxic and biodegradable stabilizer. The nZVI used for the experiments was prepared by reduction of ferric solution in the presence of PVP/VA with specific weight ratios to iron contents. Colloidal stability was investigated based on the rate of sedimentation, hydrodynamic radius and zeta potential measurement. The characteristic time, which demonstrated dispersivity of particles resisting aggregation, increased from 21.2 min (bare nZVI) to 97.8 min with increasing amount of PVP/VA (the ratios of 2). For the most stable nZVI coated by PVP/VA, its reactivity was examined by nitrate reduction in a closed batch system. The pseudo-first-order kinetic rate constants for the nitrate reduction by the nanoparticles with PVP/VA ratios of 0 and 2 were 0.1633 and $0.1395min^{-1}$ respectively. A nitrogen mass balance, established by quantitative analysis of aqueous nitrogen species, showed that the addition of PVP/VA to nZVI can change the reduction capacity of the nanoparticles.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.12
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• pp.667-675
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• 2016

Nanoscale zero-valent iron (nZVI) has been effectively applied for environmental remediation due to its ability to reduce various toxic compounds. However, quantification of nZVI reactivity has not yet been standardized. Here, we adapted colorimetric assays for determining reductive activity of nZVIs. A modified indophenol method was suggested to determine reducing activity of nZVI. The method was originally developed to determine aqueous ammonia concentration, but it was further modified to quantify phenol and aniline. The assay focused on analysis of reduction products rather than its mother compounds, which gave more accurate quantification of reductive activity. The suggested color assay showed superior selectivity toward reduction products, phenol or aniline, in the presence of mother compounds, 4-chlorophenol or nitrobenzene. Reaction conditions, such as reagent concentration and reaction time, were optimized to maximize sensitivity. Additionally, pretreatment step using $Na_2CO_3$ was suggested to eliminate the interference of residual iron ions. Monometallic nZVI and bimetallic Ni/Fe were investigated with the reaction. The substrates showed graduated reactivity, and thus, reduction potency and kinetics of different materials and reaction mechanism was distinguished. The colorimetric assay based on modified indophenol reaction can be promises to be a useful and simple tool in various nZVI related research topics.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.9
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• pp.521-527
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• 2016

Nanoscale zero valent iron (nZVI) has been intensively studied for the treatment of a plethora of pollutants through reductive reaction, however, the nano size should be of concern when nZVI is considered for water treatment, due to difficulties in recovery. The loss of nZVI causes not only economical loss, but also potential risk to human health and environment. Thus, the immobilization onto coarse or structured support is essential. In this study, two representative processes for nZVI immobilization on granular activated carbon (GAC) were evaluated, and optimized conditions for synthesizing Fe/GAC composite were suggested. Both total iron content and $Fe_0$ content can be significantly affected by preparation processes, therefore, it was important to avoid oxidation during preparation to achieve higher reduction capacity. Synthesis conditions such as reduction time and existence of intermediate drying step were investigated to improve $Fe_0$ content of Fe/GAC composites. The optimal condition was two hours of $NaBH_4$ reduction without intermediate drying process. The prepared Fe/GAC composite showed synergistic effect of the adsorption capability of the GAC and the degradation capability of the nZVI, which make this composite a very effective material for environmental remediation.

• Journal of Environmental Science International
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• v.23 no.5
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• pp.903-910
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• 2014

This study examined the treatment characteristics of hard-to-degrade pollutants such as TCE which are found in organic solvent and cleaning wastewater by nZVI that have excellent oxidation and reduction characteristics. In addition, this study tried to find out the degradation characteristics of TCE by Fenton-like process, in which $H_2O_2$ is dosed additionally. In this study, different ratios of nZVI and $H_2O_2$, such as 1.0 mM : 0.5 mM, 1.0 mM : 1.0 mM, and 1.0 mM : 2.0 mM were used. When 1.0 mM of nZVI was dosed with 1.0 mM of $H_2O_2$, the removal efficiency of TOC was the highest and the first order rate constant was also the highest. When 1mM of nZVI was dosed with 0.5 mM of $H_2O_2$, the first order rate constant and removal efficiency were the lowest. The size of first order rate constant and removal efficiency was in the order of nZVI 1.0 mM : $H_2O_2$ 1.0 mM > nZVI 1.0 mM : $H_2O_2$ 2.0 mM > nZVI 1.0 mM : $H_2O_2$ 0.5 mM > $H_2O_2$ 1.0 mM > nZVI 1.0 mM. It is estimated that when 1.0 mM of nZVI is dosed with 1.0 mM of $H_2O_2$, $Fe^{2+}$ ion generated by nZVI and $H_2O_2$ react in the stoichiometric molar ratio of 1:1, thus the first order rate constant and removal efficiency are the highest. And when 1.0 mM of nZVI is dosed with 2.0 mM of $H_2O_2$, excessive $H_2O_2$ work as a scavenger of OH radicals and excessive $H_2O_2$ reduce $Fe^{3+}$ into $Fe^{2+}$. As for the removal efficiency of TOC in TCE by simultaneous dose and sequential dose of nZVI and $H_2O_2$, sequential dose showed higher first order reaction rate and removal efficiency than simultaneous dose. It is estimated that when nZVI is dosed 30 minutes in advance, pre-treatment occurs and nanoscale $Fe^0$ is oxidized to $Fe^{2+}$ and TCE is pre-reduced and becomes easier to degrade. When $H_2O_2$ is dosed at this time, OH radicals are generated and degrade TCE actively.

• Analytical Science and Technology
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• v.23 no.6
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• pp.560-565
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• 2010

Perchlorate ion ($ClO_4^-$) has been widely used as oxidizing agent in military weapon system such as rocket and missile fuel propellant. So it has been challenging to remove the pollutant of perchlorate ion. nanoscale zero valence iron (nZVI) particles are widely employing reduction catalyst for decomposition of perchlorate ion. nZVI particles has increasingly been utilized in groundwater purification and waste water treatment. But it have strong tendency of aggregation, rapid sedimentation and limited mobility. In this study, we focused on reduction of perchlorate ion using nZVI particles immobilized in alginate polymer bead for stabilization. The stabilized nZVI particles displayed much greater surface area, and much faster reaction rates of reduction of perchlorate ion. In this study, an efficient way to immobilize nZVI particles in a support material, alginate bead, was developed by using $Ca^{2+}$ as the cross-linking cations. The efficiency and reusability of the immobilized Fe-alginate beads on the reduction of perchlorate was tested at various temperature conditions.