nZVI Particles Research Articles

Removal of Zinc by Nano-Scale Zero Valent Iron in Groundwater

Groundwater has long been identified as potential alternative of clean water supply due to its reliable quantity. However, pollution of groundwater due to anthropogenic factor still remains a challenging issue. To date, nanoscale zero valent iron (nZVI) has received great attention for its capability to treat various contaminants including chlorinated organics and metals. This study investigate Zinc (Zn) removal in aqueous solution by nanoscale zerovalent iron (nZVI). The characteristics study of the synthesized nZVI particles were investigated by its particle size and surface morphology using Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). SEM and TEM analyses verified that the particles size of synthesized nZVI were 71nm (< 100 nm). Structure of nZVI congragate to each other and a thin layer of oxide layer formed on the outer part of the nZVI particle. In the batch study, removal kinetic of Zn increased from 0.14 to 0.18 mins-1 as the concentration of Zn increased from 0.1 to 0.5 ppm. However, the removal kinetic decreased from 0.162 to 0.148 mins-1 as the amount of nZVI was increased from 0.25 mg/L to 2.50 mg/L. At pH 7, removal kinetic reached 0.157 mins-1. However as the pH suspension decreases to pH 6.5, the removal kinetics decreased significantly to 0.144 mins-1. The same behaviour was observed at pH 9 where the removal kinetics was decreased to 0.117 mins-1. Removal kinetic of Zn significantly decreased at basic condition due to the formation of passivation layer which decreased the density of reactive surface area (e.g., Fe0 and Fe2+) on the surface of nZVI. Experimental results from this study can provide basic knowledge of effectiveness of Zn removal mechanisms by nZVI at different environment conditions and provide potential remediation technology for the treatment of toxic heavy metals in groundwater.

Enhanced ultrasound-assisted degradation of methyl orange and metronidazole by rectorite-supported nanoscale zero-valent iron

In this study, the rectorite-supported nanoscale zero-valent iron (nZVI/R) was synthesized through a reduction method. X-ray diffraction analysis showed the existence of the nZVI in the nZVI/R composite and X-ray photoelectron spectroscopy analysis indicated that the nZVI particles were partly oxidized into iron oxide. Scanning electron microscopy analysis revealed that the nZVI particles were highly dispersed on the surface of the rectorite. The specific surface area of the nZVI/R composite is 21.43m2/g, which was higher than that of rectorite (4.30m2/g) and nZVI (17.97m2/g). In the presence of ultrasound (US), the degradation of methyl orange and metronidazole by the nZVI/R composite was over 93% and 97% within 20min, respectively, which is much higher than that by the rectorite and the nZVI. The degradation ratio of methyl orange and metronidazole by the nZVI/R composite under US was 1.7 and 1.8 times as high as that by the nZVI/R composite without US, respectively. The mechanism of the enhanced degradation of methyl orange and metronidazole under US irradiation was studied. These results indicate that the US/nZVI/R process has great potential application value for treatment of dye wastewater and medicine wastewater.

Evaluation of highly active nanoscale zero-valent iron coupled with ultrasound for chromium(VI) removal

An integrated technology consisting of highly active nanoscale zero-valent iron (nZVI) and ultrasound (US) was proposed for chromium(VI) removal. The parameters affecting Cr(VI) removal, such as the ultrasonic frequency, power, reaction temperature, initial pH and Cr(VI) concentration, were investigated. Based on the investigation and the characterization of the nZVI particles, the removal mechanism of Cr(VI) in US-nZVI system is proposed. Ultrasound not only contributed to an increase on available surface area, but also activated the surface of nZVI particles to induce many new reactive sites for the chemical reaction, which greatly enhanced the rate and efficiency of Cr(VI) reduction. Moreover, ultrasound could also remove the products that covered the surface of the nZVI particles, thus helping them to retain adequate reactive sites for Cr(VI) removal. The apparent kinetics for Cr(VI) removal by this new system could be well expressed by two-parameter pseudo-first-order model, and the observed rate constant (kobs) under ultrasound was much higher than that under shaking. The activation energy (Ea) of the process was calculated to be 21.53kJmol−1. The results indicated that the value of Ea was effectively reduced by introducing ultrasound into the nZVI/Cr(VI) reaction system, which was a benefit for Cr(VI) removal.

Oxidative degradation of clindamycin in aqueous solution using nanoscale zero-valent iron/H2O2/US

In this study, we investigated clindamycin (CLM) removal efficiency by using nanoscale zero-valent iron (nZVI) particles in the presence of hydrogen peroxide and sonolysis process. Laboratory experiments were performed at 21 ± 2°C. Also, the effects of initial CLM concentration (45, 80, and 100 mg/L), the molar ratio of H2O2 (0.1, 0.5, and 1 mM), nZVI (0.06, 0.1, and 0.2 g/L), pH (3, 7, and 10), in the presence of ultrasonic waves (35 and 130 kHz with 500W power) were studied. The results demonstrated that the sonolysis process combined with nZVI and H2O2 in nZVI/H2O2/US system improved the degradation efficiency. Results indicate that the CLM degradation rate increased with decreasing pH and increasing contact time, temperature, nZVI concentration (0.2 g/L), H2O2 concentration (to 180 mM), and ultrasound frequency (130 kHz/500 W). The optimal concentration of the H2O2, according to the extent of the ⋅OH scavenging reaction with these reagents, was demonstrated for CLM removal.

Removal of decabromodiphenyl ether (BDE-209) by sepiolite-supported nanoscale zerovalent iron

Nanoscale zerovalent iron (nZVI) synthesized using sepiolite as a supporter was used to investigate the removal kinetics and mechanisms of decabromodiphenyl ether (BDE-209). BDE-209 was rapidly removed by the prepared sepiolite-supported nZVI with a reaction rate that was 5 times greater than that of the conventionally prepared nZVI because of its high surface area and reactivity. The degradation of BDE-209 occurred in a stepwise debromination manner, which followed pseudo-first-order kinetics. The removal efficiency of BDE-209 increased with increasing dosage of sepiolite-supported nZVI particles and decreasing pH, and the efficiency decreased with increasing initial BDE-209 concentrations. The presence of tetrahydrofuran (THF) as a cosolvent at certain volume fractions in water influenced the degradation rate of sepiolite-supported nZVI. Debromination pathways of BDE-209 with sepiolite-supported nZVI were proposed based on the identified reaction intermediates, which ranged from nona- to mono-brominated diphenylethers (BDEs) under acidic conditions and nonato penta-BDEs under alkaline conditions. Adsorption on sepiolite-supported nZVI particles also played a role in the removal of BDE-209. Our findings indicate that the particles have potential applications in removing environmental pollutants, such as halogenated organic contaminants.

Iron nanoparticles decoration onto three-dimensional graphene for rapid and efficient degradation of azo dye

Porous three-dimensional graphene (3DG) prepared by chemical vapor deposition, was utilized as a matrix to support nanoscale zero-valent iron (nZVI) particles. The strategies to manipulate the morphology, distribution and size of nZVI particles on the 3DG support were demonstrated. The immobilized nZVI particles with a size of 100nm and dense deposition were achieved. A 94.5% of orange IV azo dye was removed in 60min using nZVI particles immobilized 3DG (3DG-Fe), whereas only 70.9% was removed by free Fe nanoparticles in aqueous solution. Meanwhile, a reaction rate with orange IV of 3DG-Fe was approximately 5-fold faster than that of free Fe nanoparticles. The effects of 3DG-Fe dosage, dye concentration, reaction pH and temperature on dye degradation were also addressed. Those results imply that both lowering pH and increasing temperature led to higher reaction efficiency and rate. The kinetic data reveal that the degradation process of orange IV dye, modeled by the pseudo-first-order kinetics, might involve adsorption and redox reaction with an activation energy of 39.2kJ/mol.

Electron efficiency of nZVI does not change with variation of environmental parameters

Nanoscale zero-valent iron particles (nZVI) are already applied for in-situ dechlorination of halogenated organic contaminants in the field. We performed batch experiments whereby trichloroethene (TCE) was dehalogenated by nZVI under different environmental conditions that are relevant in practice. The tested conditions include different ionic strengths, addition of polyelectrolytes (carboxymethylcellulose and ligninsulphonate), lowered temperature, dissolved oxygen and different particle contents. Particle properties were determined by Mössbauer spectroscopy, XRD, TEM, SEM, AAS and laser obscuration time measurements.TCE dehalogenation and H2 evolution were decelerated by reduced ionic strength, addition of polyelectrolytes, temperature reduction, the presence of dissolved oxygen and reduced particle content. The partitioning of released electrons between reactions with the contaminant vs. with water (selectivity) was low, independent of the tested conditions. Basically out of hundred electrons that were released via nZVI oxidation only 3.1±1.4 were used for TCE dehalogenation. Even lower selectivities were observed at TCE concentrations below 3.5mgl−1, hence particle modifications and/or combination of nZVI with other remediation technologies seem to be necessary to reach target concentrations for remediation.Our results suggest that selectivity is particle intrinsic and not as much condition dependent, hence particle synthesis and potential particle modifications of nZVI particles may be more important for optimization of the pollutant degradation rate, than tested environmental conditions.

Nanoscale zero-valent iron particles supported on reduced graphene oxides by using a plasma technique and their application for removal of heavy-metal ions.

Nanoscale zero-valent iron particles supported on reduced graphene oxides (NZVI/rGOs) from spent graphene oxide (GO)-bound iron ions were developed by using a hydrogen/argon plasma reduction method to improve the reactivity and stability of NZVI. The NZVI/rGOs exhibited excellent water treatment performance with excellent removal capacities of 187.16 and 396.37 mg g(-1) for chromium and lead, respectively. Moreover, the NZVI/rGOs could be regenerated by plasma treatment and maintained high removal ability after four cycles. X-ray photoelectron spectroscopy analysis results implied that the removal mechanisms could be attributed to adsorption/precipitation, reduction, or both. Such multiple removal mechanisms by the NZVI/rGOs were attributed to the reduction ability of the NZVI particles and the role of dispersing and stabilizing abilities of the rGOs. The results indicated that the NZVI/rGOs prepared by a hydrogen/argon plasma reduction method might be an effective composite for heavy-metal-ion removal.

Intensify Removal of Nitrobenzene from Aqueous Solution Using Nano-Zero Valent Iron/Granular Activated Carbon Composite as Fenton-Like Catalyst

To obtain a good catalytic effect of removing refractory organics from water by Fenton process, granular activated carbon (GAC) supported nano-zero valent iron (nZVI) composite (nZVI/GAC) was prepared by adsorption–reduction method, and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS). The catalytic degradation activity of the composite was evaluated to remove nitrobenzene (NB) pollutant via a heterogeneous Fenton-like system, and the initial pH value, nZVI/GAC dosage, and H2O2 concentration influencing on NB removal were also investigated at room temperature. Experimental results showed that nZVI particle was uniformly dispersed over GAC matrix, and average particle size was 40–100 nm without agglomeration. The nZVI/GAC composite was very efficient in removing NB with average percentage of more than 85 %. However, the removal rate of Fenton-like reaction was highly affected by pH value, H2O2 concentration, and nZVI/GAC dosage. The optimal reaction conditions were pH 4.0, 40 mg/L NB, 5.0 mmol/L H2O2, and 0.4 g/L nZVI/GAC in this study. Stability and repeatability tests as well as mechanism analysis illustrated that GAC improved catalytic action via enhancing nZVI dispersion and accelerating Fe(III)/Fe(II) cycle attributing to internal iron–carbon microelectrolysis in nZVI/GAC composite. Iron utilization efficiency, which played an important role in NB degradation by Fenton-like greatly increased resulting in dissolved iron <0.6 mg/L. This phenomenon strongly implied that the nZVI/GAC Fenton-like process was not only a practical combination of adsorption and Fenton oxidation but also some synergetic effects existing in such an nZVI/GAC composite.

Preparation of wrapped nZVI particles and their application for the degradation of trichloroethylene (TCE) in aqueous solution

Three types of wrappped nanoscale zero-valent iron (W-nZVI) with different coatings including agar, starch, and carboxyl methyl cellulose, were synthesized using a rheological phase reaction method. The structure and morphology of W-nZVI particles were characterized by scanning electron microscopy and transmission electron microscopy. Batch degradation experiments exhibited that W-nZVI dosage, initial trichloroethylene (TCE) concentration and solution pH had significant effects on TCE dechlorination. Experimental results proved that the highest dechlorination efficiency was obtained within 320 minutes for 10 mg/L of TCE at the optimal pH of 5.0 and W-nZVI dosage of 0.5 g/L. Kinetic study revealed that TCE dechlorination by W-nZVI in aqueous solution obeyed the quasi-first-order reaction kinetics. The product after the reaction could be easily separated by the permanent magnet for re-use.

Synthesis and Characterization of Marine Clay-Supported Nano Zero Valent Iron

This study reports the preparation and characterization of marine clay nano zero valent iron (MC+nZVI) where marine clay acts as the composite material. Marine clay was air dried and pulverized before used. Basically, MC+nZVI was synthesized by chemical reduction method. The materials synthesized were left oven dried overnight at 50i‚°C. The obtained materials were characterized by Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR). FESEM images show that the nZVI particles dispersed well on the surface of marine clay thus reducing aggregation of nZVI. TEM images show that the particles have the shell-core structure and the particles sizes were around 29.92-57.11 nm for MC+nZVI. XPS spectrums indicate the existence of Fe0 on the synthesized MC+nZVI. Other than that, XRD and FTIR results also show that there exists the formation of iron oxides on the surface of MC+nZVI. The adsorption capability of MC+nZVI is increased by 15% compared to marine clay. Therefore, increment of MC+nZVI adsorption capacity might be due to the well-dispersed nZVI thus enhancing the performance of MC+nZVI.

Kinetics of Solvent Blue and Reactive Yellow removal using microwave radiation in combination with nanoscale zero-valent iron

We investigated the efficiency and kinetics of the degradation of soluble dyes over the pH range 5.0–9.0 using a method employing microwave radiation in combination with nanoscale zero-valent iron (MW–nZVI). The nZVI particles (40–70nm in diameter) were prepared by a liquid-phase chemical reduction method employing starch as a dispersant. Compared to the removal of Solvent Blue 36 and Reactive Yellow K-RN using only nZVI, more rapid and efficient dye removal and total organic carbon removal were achieved using MW–nZVI. The dye removal efficiency increased significantly with decreasing pH, but was negligibly affected by variation in the microwave power. The kinetics of dye removal by MW–nZVI followed both an empirical equation and the pseudo first-order model, while the kinetics of dye removal using nZVI could only be described by an empirical equation. It was also concluded that microwave heating of the dye solutions as well as acceleration of corrosion of nZVI and consumption of Fe(II) were possible reasons behind the enhanced dye degradation.

In-situ Pb(2+) remediation using nano iron particles.

Originally, application of nano zero valent iron (nZVI) particles for the removal of lead (Pb2+) in porous media was studied. At first, stabilized nZVI (S-nZVI) was prepared and characterized, then used in batch and continuous systems. Based on the batch experiments, corresponding reaction kinetics well fitted with the pseudo-first-order adsorption model, and reaction rate ranged from 0.01 to 0.04 g/mg/min depend on solution pH and the molar ratio between Fe and Pb. In batch tests, optimal condition with more than 90% removal efficiency at 60 min was observed at a pH range of 4 to 6 and Fe/Pb ratio more than 2.5. Continuous experiments exposed that Pb2+ remediation was as well influenced by seepage velocity, grain size, and type of porous media. The maximum Pb2+ removal efficiency in batch and bench-scale systems were 97% and 81%, correspondingly. The results have shown the ability of S-nZVI to use in permeable reactive barriers, as an efficient adsorbent for Pb2+, because of its excellent stability, high reducing power, and a large surface area.Electronic supplementary materialThe online version of this article (doi:10.1186/s40201-015-0157-3) contains supplementary material, which is available to authorized users.

Removal of selenium from water with nanoscale zero-valent iron: Mechanisms of intraparticle reduction of Se(IV)

Increasing evidences suggest that nanoscale zero-valent iron (nZVI) is an effective agent for treatment and removal of selenium from water. For example, 1.3 mM selenite was quickly removed from water within 3 min with 5 g/L nZVI. In this work, reaction mechanisms of selenite [Se(IV)] in a single core–shell structured nanoscale zero-valent iron (nZVI) particle were studied with the method of spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) integrated with X-ray energy dispersive spectroscopy (XEDS). This method was utilized to visualize solid phase translocation and transformation of Se(IV) such as diffusion, reduction, deposition and the effect of surface defects in a single nanoparticle. Se(IV) was reduced to Se(-II) and Se(0), which then formed a 0.5 nm layer of selenium at the iron oxide-Fe(0) interface at a depth of 6 nm from the surface. The results provided near atomic-resolution proof on the intraparticle diffusion-reduction of Se(IV) induced by nZVI. The STEM mapping also discovered that defects on the surface layer accelerate the diffusion of selenium and increase the capacity of nZVI for selenium sequestration.

Can zero-valent iron nanoparticles remove waterborne estrogens?

Steroidal estrogens are one of the most challenging classes of hazardous contaminants as they can cause adverse effects to biota in extremely low concentrations. They emerge in both waste waters and surface waters serving as a source of drinking water. Environmental Quality Standards for 17β-estradiol (E2) and 17α-ethinylestradiol (EE2), promulgated within the EU Water Framework Directive, are 0.4 and 0.035 ng L−1, respectively. Because nanoscale zero-valent iron (nZVI) particles have been previously used in numerous remediation technologies and have the advantage of possible magnetic separation, interaction of nZVI with E2 and EE2 in water was investigated to assess the potential role of nZVI in removing steroidal estrogens. A mixture of E2 and EE2 dissolved in water was shaken with varying doses of nZVI for 1–5 h. Concentration-dependent removal of the estrogens was observed but removal did not increase significantly with time. Concentrations of the estrogens were determined by HPLC/MS/MS and a biodetection reporter gene assay. Sorption and nonspecific oxygen-mediated oxidation of estrogens were identified as the most probable removal mechanisms. Two independent experiments confirmed that significant decrease of estrogens concentration is achieved when at least 2 g L−1 of nZVI is applied. The presented study provides insights into the mechanisms of nZVI interaction with steroidal estrogens under aerobic conditions prevailing in currently applied water treatment technologies.

Zero-Valent Iron Nanoparticles (NZVI) Supported by Kaolinite for CuII and NiII Ion Removal by Adsorption: Kinetics, Thermodynamics, and Mechanism

This research concerns the adsorption of CuII and NiII using zero-valent iron nanoparticles supported by kaolinite (nZVI-Kaolinite). The characterization studies indicated that the surface of kaolinite or the kaolinite fragments were filled with nZVI particles. The kinetics of CuII and NiII adsorption were evaluated for various contact times. The adsorption of CuII and NiII at different initial concentrations was examined by injecting 0.5 g of adsorbent to achieve equilibrium. The adsorption of CuII and NiII was a chemisorption process, which fitted well with the Freundlich and the Temkin isotherm models. The low value of activation energy suggests the occurrence of a redox process and both physical and chemical processes for CuII and NiII adsorption respectively. The negative values for the Gibbs free energy (ΔG0) and enthalpy of adsorption (ΔH0) revealed that the adsorption process was spontaneous and exothermic. Both surface diffusion and pore diffusion were involved in the rate-limiting step. The possible removal mechanisms involved redox, adsorption, precipitation, and co-precipitation, depending on the adsorption process studied (CuII or NiII adsorption).

Potential environmental implications of nanoscale zero-valent iron particles for environmental remediation.

ObjectivesNanoscale zero-valent iron (nZVI) particles are widely used in the field of various environmental contaminant remediation. Although the potential benefits of nZVI are considerable, there is a distinct need to identify any potential risks after environmental exposure. In this respect, we review recent studies on the environmental applications and implications of nZVI, highlighting research gaps and suggesting future research directions.MethodsEnvironmental application of nZVI is briefly summarized, focusing on its unique properties. Ecotoxicity of nZVI is reviewed according to type of organism, including bacteria, terrestrial organisms, and aquatic organisms. The environmental fate and transport of nZVI are also summarized with regards to exposure scenarios. Finally, the current limitations of risk determination are thoroughly provided.ResultsThe ecotoxicity of nZVI depends on the composition, concentration, size and surface properties of the nanoparticles and the experimental method used, including the species investigated. In addition, the environmental fate and transport of nZVI appear to be complex and depend on the exposure duration and the exposure conditions. To date, field-scale data are limited and only short-term studies using simple exposure methods have been conducted.ConclusionsIn this regard, the primary focus of future study should be on 1) the development of an appropriate and valid testing method of the environmental fate and ecotoxicity of reactive nanoparticles used in environmental applications and 2) assessing their potential environmental risks using in situ field scale applications.

Trace concentrations of iron nanoparticles cause overproduction of biomass and lipids during cultivation of cyanobacteria and microalgae

Cultivation in Zehnder medium containing 5.1 mg L−1 zero-valent iron nanoparticles (nZVI) boosted the growth of the green algae Desmodesmus subspicatus, Dunaliella salina, Parachlorella kessleri and Raphidocelis subcapitata and the eustigmatophycean algae Nannochloropsis limnetica and Trachydiscus minutus. In the cyanobacterium Arthrospira maxima, growth stimulation occurred at 1.7–5.1 mg L−1 nZVI. In all studied microorganisms, 5.1 mg L−1 nZVI strongly enhanced lipid accumulation, decreased the content of saturated and monounsaturated fatty acids with the exception of palmitoleic acid and increased the content of polyunsaturated fatty acids in cells. The nZVI particles may provide a suitable source of iron causing increased cell growth and induce metabolic changes resulting in higher lipid production and changes in fatty acid (FA) composition. Altered lipid synthesis may reflect the oxidative action of nZVI. Further research may contribute to optimizing the economical production of oils from oleaginous microorganisms and help clarify the mechanism of nZVI action.

Effect of humic acid and transition metal ions on the debromination of decabromodiphenyl by nano zero-valent iron: kinetics and mechanisms

E-waste sites are one of the main sources of the pollutant decabromodiphenyl ether (BDE209); contaminated farmland and water bodies urgently need to be remediated. As a potential in situ remediation technology, nano zero-valent iron (nZVI) technology effectively removes PBDEs. However, the humic acid (HA) and heavy metals in the contaminated sites affect the remediation effects. In this study, we explored the influence of HA and transition metals on the removal of PBDEs by nZVI. The specific surface area and average size of the nZVI particles we prepared were 35 m2/g and 50–80 nm, respectively. The results showed that HA inhibited the removal of PBDEs; as the concentration of HA increased, its inhibitory effect intensified and the kobs decreased. However, the three metal ions (Cu2+, Co2+, and Ni2+) enhanced the removal of PBDEs. The enhancement effect was followed the order Ni2+ > Cu2+ > Co2+. As the concentration of metal ions increased, the promotion effect improved. The synergistic effect of HA and the metal ions was manifested in the combination of the inhibitory effect and the enhancement effect. The values of the first-order kinetic constants (kobs) under the combined effect were between the values of the rate constants under the individual components. The inhibitory mechanism was the chemisorption of HA, i.e., the benzene carboxylic and phenolic hydroxyl groups in HA occupied the surfactant reactive sites of nZVI, thus inhibiting the removal of BDE209. The promotion mechanism of Cu2+, Co2+, and Ni2+ can be explained by their reduction to zero valence on the nZVI surface; furthermore, Ni2+ strongly affects the debromination and dehydrogenation of BDE209, leading to a stronger promotability than Cu2+or Co2+.

Numerical prediction of diffusion and electric field-induced iron nanoparticle transport

Zero valent iron nanoparticles (nZVI) are considered very promising for the remediation of contaminated soils and groundwaters. However, an important issue related to their limited mobility remains unsolved. Direct current can be used to enhance the nanoparticles transport, based on the same principles of electrokinetic remediation. In this work, a generalized physicochemical model was developed and solved numerically to describe the nZVI transport through porous media under electric field, and with different electrolytes (with different ionic strengths). The model consists of the Nernst–Planck coupled system of equations, which accounts for the mass balance of ionic species in a fluid medium, when both the diffusion and electromigration of the ions are considered. The diffusion and electrophoretic transport of the negatively charged nZVI particles were also considered in the system. The contribution of electroosmotic flow to the overall mass transport was included in the model for all cases. The nZVI effective mobility values in the porous medium are very low (10−7–10−4cm2V−1s−1), due to the counterbalance between the positive electroosmotic flow and the electrophoretic transport of the negatively charged nanoparticles. The higher the nZVI concentration is in the matrix, the higher the aggregation; therefore, low concentration of nZVI suspensions must be used for successful field application.