nZVI Particles Research Articles

The decreasing aggregation of nanoscale zero-valent iron induced by trivalent chromium

Environmental contextNanoscale zero-valent iron is a promising material for environmental engineering and groundwater remediation. However, the environmental behaviour and fate of nanoscale iron that is essential for applications and risk assessment is still uncertain. We report a study on the aggregation behaviour and mobility of nanoscale iron in the aquatic environment using colloidal chemical methods. AbstractDespite high magnetisation, nanoscale zero-valent iron (nZVI) exhibits weak aggregation when treating hexavalent chromium (CrVI) (0.02mmol L–1) under anaerobic circumstances, which leads to the enhancement of its mobility in the aquatic environment. To elucidate such an unexpected phenomenon, the influences of different valences of chromium on the aggregation behaviour of nZVI were examined. Results indicate that trivalent chromium (CrIII) greatly decreases the aggregation of nZVI in acidic conditions (pH 5), while little influence is observed at a higher pH (pH 7). We suggest that such influences are mainly a result of precipitation on the surface of nZVI particles, which prevents the formation of chain-like aggregates. Accordingly, although the particles are highly magnetic (magnetite content >70%, saturation magnetisation=363 kA m–1), the magnetic attraction between aggregates and particles is not strong enough to promote further aggregation. Furthermore, the Cr(OH)3 shell blocks collisions between particles and greatly enhances their zeta-potential, which also assists in preventing aggregation. Our results suggest that heavy metals can significantly affect the environmental behaviours of nanoparticles.

Study of the presence of PCDDs/PCDFs on zero-valent iron nanoparticles

Studies show that nanoscale zero-valent iron (nZVI) particles enhance the formation of chlorinated compounds such as polychlorinated dioxins and furans (PCDD/Fs) during thermal processes. However, it is unclear whether nZVI acts as a catalyst for the formation of these compounds or contains impurities, such as PCDD/Fs, within its structure. We analyzed the presence of PCDD/Fs in nZVI particles synthesized through various production methods to elucidate this uncertainty. None of the 2,3,7,8-substituted congeners were found in the commercially-produced nZVI, but they were present in the laboratory-synthesized nZVI produced through the borohydride method, particularly in particles synthesized from iron (III) chloride rather than from iron sulfate. Total PCDD/F WHO-TEQ concentrations of up to 35 pg/g were observed in nZVI particles, with hepta- and octa-chlorinated congeners being the most abundant. The reagents used in the borohydride method were also analyzed, and our findings suggest that FeCl3 effectively contains PCDD/Fs at concentrations that could explain the concentrations observed in the nZVI product. Both FeCl3 and nZVI showed a similar PCDD/F patterns with slight differences. These results suggest that PCDD/Fs might transfer from FeCl3 to nZVI during the production method, and thus, care should be taken when employing certain nZVI for environmental remediation.

New insights into the role of Ni loading on the surface structure and the reactivity of nZVI toward tetrabromo- and tetrachlorobisphenol A

Nanoscale zero-valent iron (nZVI) and nickel/nanoscale zero-valent iron (Ni/nZVI) bimetallic particles were explored for tetrabromobisphenol A (TBBPA) and tetrachlorobisphenol A (TCBPA) dehalogenation under ambient condition. The characteristics of the fresh and aged nanoparticles were analyzed by SEM, BET, XRD, XPS and FTIR, and found out that bimetal nanoparticles accelerated the corrosion of Fe0 in the synthesized particles during the reaction. The results shows that the addition of Ni to nZVI particles with low Ni loading (⩽0.5wt%) significantly enhanced dehalogenation of TBBPA and TCBPA compared to the pure nZVI, while high Ni loading (>0.5wt%) did less favor. The observed pseudo first-order rate constant (kobs) of 0.5%Ni/nZVI for TBBPA and TCBPA were 3.74 (±0.29)×10−2 and 0.95 (±0.04)×10−2min−1, which were about 27 and 20 times higher than that of nZVI, respectively, probably due to the formation of highly activated hydrogen atom (H*) and galvanic cells. Ni/nZVI with lower Ni loading (<0.5wt%) resulted in partial dehalogenation of TBBPA and TCBPA, while with higher Ni loading (⩾0.5wt%) curtailed the accumulation of intermediates and completely transformed them to bisphenol A (BPA). A dramatic decrease in oxidation–reduction potential (ORP) values from about +300 to −750mV after Ni/nZVI addition indicates that Ni/nZVI is an effective material to achieve highly reducing conditions. Both ORP and pH shows a correlative tendency with TBBPA and TCBPA removal efficiency. This suggests that ORP and pH can serve as indicators for the reductant reactivity.

A novel green synthesis of zero valent iron nanoparticles (NZVI) using three plant extracts and their efficient application for removal of Cr(VI) from aqueous solutions

In the present study, NZVI particles were synthesized from the plant extracts including Rosa damascene (RD), Thymus vulgaris (TV), and Urtica dioica (UD). The FTIR arspectshowed that polyphenols, proteins and organic acids which serve as reducing and stabilizing agents play a significant role in the synthesis of NPs and reduce the possibility of aggregation of NPs compared to chemical techniques of NPs synthesis. The amount and type of compounds in plant extracts affect the structure and also agglomeration of NPs after adsorption process. Based on the results, the highest removal efficiency occurred at pH 2. With increase in contact time and amount of dose, the percentage removal increases. Inversely, increase of initial concentration of Cr(VI) decreases the removal efficiency of the contaminant. These nanoparticles have a high adsorption capacity. Accordingly, by applying a dose of 0.2g/l and contact time of 10min,the three NPs yielded >90% removal efficiency. Also, for 1mincontact time, the percentage removal was 94.87%, 83.48% and86.8% for RD-Fe, UD-Fe and TV-Fe, respectively. By an increase to 25min, the removal percentage reached to 100% for TV-Fe and UD-Fe. Moreover, 30min was required to remove Cr(VI) completely by RD-F.

Optimized nano-scale zero-valent iron supported on treated activated carbon for enhanced nitrate and phosphate removal from water

Supported nano-scale zero-valent (nZVI) iron is a suitable material for groundwater and wastewater treatment applications. It can prevent the agglomeration of nanoparticles and increase their hydraulic conductivity. However, these supported nZVI particles suffer corrosion and greater pore diffusion resistance. Synthesis in ethanol medium, thermal treatment, acid treatment and acid thermal treatment were applied to deal with these problems and produce several treated composites of different nZVI to activated carbon (AC) mass ratios. Produced composites were characterized and applied in batch experiments to remove nitrate (200mg NO3−/L), phosphate (50mg PO43−-P/L) and a mixture of nitrate and phosphate from their aqueous solutions. Among 25 composites, AC-supported nZVI (F12AT2950) was selected at optimum nZVI/AC mass ratio of 2:1 and treatment conditions of 950°C for 2h. This study introduced thermal treatment of AC before supporting nZVI, which modified its textural and surface chemistry properties to attract contaminant anions with a higher affinity towards nZVI. F12AT2950 composite succeeded to increase removal efficiency of nitrate by 50% and of phosphate by 100% from their aqueous solutions and of nitrate by 170% along with a complete removal of phosphate from their solution. Interference studies were executed for actual field applications. The novel composite was tested in the presence of hardness, humic acid, phosphorus, sulfate ions, domestic wastewater and cuprous and cupric ions. The latter interference enhanced the removal efficiencies by about 10–50% according to concentrations and the type of copper compounds. The novel composite can be implemented as a promising reagent in environmental wastewater and groundwater technologies.

Nanoscale zerovalent iron (nZVI) supported by natural and acid-activated sepiolites: the effect of the nZVI/support ratio on the composite properties and Cd2+ adsorption.

Natural (SEP) and partially acid-activated (AAS) sepiolites were used to prepare composites with nanoscale zerovalent iron (nZVI) at different (SEP or AAS)/nZVI ratios in order to achieve the best nZVI dispersibility and the highest adsorption capacity for Cd2+. Despite the higher surface area and pore volume of AAS, better nZVI dispersibility was achieved by using SEP as the support. On the other hand, a lower oxidation degree was achieved during the synthesis using AAS. X-ray photoelectron spectroscopy (XPS) analysis of the composite with the best nZVI dispersibility, before and after Cd2+ adsorption, confirmed that the surface of the nZVI was composed of oxidized iron species. Metallic iron was not present on the surface, but it was detected in the subsurface region after sputtering. The content of zerovalent iron decreased after Cd2+ adsorption as a result of iron oxidation during Cd2+ adsorption. The XPS depth profile showed that cadmium was present not only at the surface of the composite but also in the subsurface region. The adsorption isotherms for Cd2+ confirmed that the presence of SEP and AAS decreased the agglomeration of the nZVI particles in comparison to the pure nZVI, which provided a higher adsorption capacity. The results showed that the prevention of both aggregation and oxidation during the synthesis was necessary for obtaining an SEP/AAS-nZVI composite with a high adsorption capacity, but oxidation during adsorption was beneficial for Cd2+ removal. The formation of strong bonds between Cd2+ and the adsorbents sites of different energy until monolayer formation was proposed according to modeling of the adsorption isotherms.

Zero-valent iron particles embedded on the mesoporous silica–carbon for chromium (VI) removal from aqueous solution

Nanoscale zero-valent iron (nZVI) particles were embedded on the walls of mesoporous silica–carbon (MSC) under the conditions of high-temperature carbonization and reduction and used to remove chromium (VI) from aqueous solution. The structure and textural properties of nZVI–MSC were characterized by the powder X-ray diffraction, transmission electron microscopy and N2 adsorption and desorption. The results show that nZVI–MSC has highly ordered mesoporous structure and large surface area, indistinguishable with that of MSC. Compared with the support MSC and iron particles supported on the activated carbon (nZVI/AC), nZVI–MSC exhibited much higher Cr(VI) removal efficiency with about 98 %. The removal process obeys a pseudo first-order model. Such excellent performance of nZVI–MSC could be ascribed to the large surface and iron particles embedded on the walls of the MSC, forming an intimate contact with the MSC. It is proposed that this feature might create certain micro-electrode on the interface of iron particles and MSC, which prevented the formation of metal oxide on the surface and provided fresh Fe surface for Cr(VI) removal.

Enhanced reductive debromination and subsequent oxidative ring-opening of decabromodiphenyl ether by integrated catalyst of nZVI supported on magnetic Fe3O4 nanoparticles

The magnetic Fe0@Fe3O4 nanocomposite was prepared and used to achieve the reductive/subsequent oxidative ring-opening of decabromodiphenyl ether (BDE209) in this work. The characterization results indicated that the structure of the composite consisted of small nanoscale zero-valent iron (nZVI) particles surrounding the surface of Fe3O4 nanoparticle (NP). A 100% removal efficiency and 80% degradation efficiency of BDE209 was reached by the composite accompanied with ultrasound(called NP/US system) for 36h, which is higher than that obtained with conventional nZVI particles. Furthermore, the enhanced debromination and ring-opening of BDE209 was realized by a Fenton-like degradation process lasting for 12h after the addition of H2O2 to the NP/US reaction at 36h. Based on the degradation products identified, a two-stage reduction/oxidation degradation mechanism was proposed. During the first stage, which was reductive debromination, the major reductive activity of nZVI was efficiently enhanced in the presence of nano Fe3O4, which served as a catalyst to improve the stability of the nZVI nanoparticles and accelerate electron transfer, enhancing the degradation efficiency of BDE209. During the second stage, the oxidative ring-opening, the debromination products of BDE209 were proved to be attacked by abundant hydroxyl radicals generated both in the solution and on the surface of the Fe0@Fe3O4 nanoparticles. Thus, this work provides an efficient method to achieve the complete ring-opening of PBDEs using iron-based nanomaterials.

Synthesis, characterization and performance of high energy ball milled meso-scale zero valent iron in Fenton reaction

Understanding contaminant degradation by different sized zero valent iron (ZVI) particles is one important aspect in addressing the long-term stability of these particles in field studies. In this study, meso zero valent iron (mZVI) particles were synthesised in a milling time of 10 h using ball milling technique. The efficacy of mZVI particles for removal of phenol was quantitatively evaluated in comparison with coarse zero valent iron (cZVI) and nano zero valent iron (nZVI) particles. Phenol degradation experiments were carried out in sacrificial batch mode at room temperature independently with cZVI, nZVI and mZVI under varied pH conditions of 3, 4, 6, 7, 8 and 10. Batch experiments substantiating the reactivity of mZVI under unbuffered pH system were also carried out and compared with buffered and poorly buffered pH systems. mZVI particles showed consistent phenol degradation at circum-neutral pH with efficiency of 44%, 67%, and 89% in a span of 5, 10 and 20 min respectively. The dissolved iron species and residual iron formation were also measured as a function of pH. Unbuffered systems at circum-neutral pH produced less residual iron when compared to buffered and poorly buffered systems. At this pH, oxidation of Fe2+ produced a different oxidant Ferryl ion, which was found to effectively participate in phenol degradation.

Evaluating the mobility of polymer-stabilised zero-valent iron nanoparticles and their potential to co-transport contaminants in intact soil cores

The use of zero-valent iron nanoparticles (nZVI) has been advocated for the remediation of both soils and groundwater. A key parameter affecting nZVI remediation efficacy is the mobility of the particles as this influences the reaction zone where remediation can occur. However, by engineering nZVI particles with increased stability and mobility we may also inadvertently facilitate nZVI-mediated contaminant transport away from the zone of treatment. Previous nZVI mobility studies have often been limited to model systems as the presence of background Fe makes detection and tracking of nZVI in real systems difficult. We overcame this problem by synthesising Fe-59 radiolabelled nZVI. This enabled us to detect and quantify the leaching of nZVI-derived Fe-59 in intact soil cores, including a soil contaminated by Chromated-Copper-Arsenate. Mobility of a commercially available nZVI was also tested. The results showed limited mobility of both nanomaterials; <1% of the injected mass was eluted from the columns and most of the radiolabelled nZVI remained in the surface soil layers (the primary treatment zone in this contaminated soil). Nevertheless, the observed breakthrough of contaminants and nZVI occurred simultaneously, indicating that although the quantity transported was low in this case, nZVI does have the potential to co-transport contaminants. These results show that direct injection of nZVI into the surface layers of contaminated soils may be a viable remediation option for soils such as this one, in which the mobility of nZVI below the injection/remediation zone was very limited. This Fe-59 experimental approach can be further extended to test nZVI transport in a wider range of contaminated soil types and textures and using different application methods and rates. The resulting database could then be used to develop and validate modelling of nZVI-facilitated contaminant transport on an individual soil basis suitable for site specific risk assessment prior to nZVI remediation.

Metal(loid)s behaviour in soils amended with nano zero-valent iron as a function of pH and time

Nano zero-valent iron (nZVI) is currently investigated as a stabilising amendment for contaminated soils. The effect of pH (4–8) and time (48 and 192 h) on the behaviour of nZVI-treated Pb-Zn and As-contaminated soil samples was assessed. Additionally, soil leachates were subsequently used to study the direct interaction between soil solution components and nZVI particles in terms of mineralogical changes and contaminant retention. A typical U-shaped leaching trend as a function of pH was observed for Cd, Pb and Zn, while As was released predominantly under alkaline conditions. Oxidising conditions prevailed, so pH was the key controlling parameter rather than redox conditions. Generally, longer contact time resulted in increased soluble concentrations of metal(loid)s. However, the stabilisation effect of nZVI was only observed after the direct soil leachate-nZVI interactions, showing enhanced redox and sorption processes for the studied metals. A significant decrease of dissolved As concentrations was observed for both experimental soils, but with different efficiencies depending on neutralisation capacity, organic matter content or solid fractionation of As related to the origin of the soils. Scorodite (FeAsO4·2H2O) was predicted as a potential solubility-controlling mineral phase for As. Sorption of metal(loid)s onto secondary Fe- and Al-(oxyhydr)oxides (predicted to precipitate at pH > 5) represents an important scavenger mechanism. Moreover, transmission electron microscopy confirmed the retention of Zn and Pb under near-neutral and alkaline conditions by newly formed Fe oxides or aluminosilicates. This study shows that the efficiency of nZVI application strongly depends not only on soil pH-Eh conditions and contaminant type, but also on the presence of organic matter and other compounds such as Al/Fe/Mn oxyhydroxides and clay minerals.

Chemically stable and reusable nano zero-valent iron/graphite-like carbon nitride nanohybrid for efficient photocatalytic treatment of Cr(VI) and rhodamine B under visible light

Graphite-like carbon nitride (g-C3N4) displays strong potential applications in visible-light photocatalytic for water treatment, but its applications are greatly restricted by high recombination probability of photo-generated electron-hole pairs, as well as a weak reduction ability toward the heavy metals. In this work, we reported the synthesis of nZVI-g-C3N4 nano-hybrid with highly efficiency toward the photodegradation of RhB and Cr(VI) under the visible light irradiation. The nZVI nanoparticles can well be immobilized and dispersed on the surface of g-C3N4 nanosheets by a facile borohydride-reduction method. As-synthesized nZVI-g-C3N4 has an improved photocatalytic activity much better than that of the pure g-C3N4, wherein over 92.9% of Cr(VI) and 99.9% of RhB can be removed by using nZVI-g-C3N4. The nZVI particles not only contributes to the reduction and immobilization of Cr(VI), but also accelerates the photocatalytic degradation efficiency of RhB due to a lower recombination rate of photoexcited holes and electrons. Moreover, nZVI-g-C3N4 preserves superior photodegradation efficiency after five experimental cycles. It can be attributed that nZVI-g-C3N4 photocatalyst is chemically stable, and part of nZVI can be recovered by g-C3N4. We believe that, the composite of nZVI-g-C3N4 reported here could provide guidance for the design of efficient and reusable materials to remove both the organic compounds and heavy metal ions from waste waters.

The influence of polyelectrolyte modification on nanoscale zero-valent iron (nZVI): Aggregation, sedimentation, and reactivity with Ni(II) in water

Polyelectrolyte modification on the surface of nanoscale zero-valent iron (nZVI) particles could affect colloidal stability, aggregation, mobility, oxidation as well as reactivity. In this article, two anionic polyelectrolytes with different molecular weight (MW), anionic polyacrylamide (APAM, MW=3million) and carboxymethylcellulose sodium (CMC, MW=300–800) were modified on the surface of nZVI. Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and X-ray diffraction (XRD) were used to characterize the polyelectrolyte-modified nZVI. Results from UV–vis spectrophotometer (UV) and sedimentation tests showed that APAM modification led to the aggregation of nZVI in suspension, CMC modification made nZVI disperse well. XRD results indicated that polyelectrolyte modification made the slow oxidation of nZVI under ambient conditions. APAM-modified nZVI had much lower Ni2+ removal efficiency than that of bare nZVI while CMC-modified nZVI had higher Ni2+ removal efficiency after 1.5hours (h). The study provided the information on the modification effect of nZVI on the colloidal stability and aggregation, sedimentation, reduction and sorption of heavy metal ions in the environment.

Ageing decreases the phytotoxicity of zero-valent iron nanoparticles in soil cultivated with Oryza sativa.

This paper was aimed to study the impact of "ageing" (aged in non-saturated soil for 2 and 4weeks prior to exposure) nanoscale zero-valent iron (nZVI) on the terrestrial plant. The effects of nZVI on Oryza Sativa germination, seedlings growth, chlorophyll biosynthesis, oxidative stress and the activities of antioxidant enzymes at low (250mg/kg) and high (1000mg/kg) concentrations were investigated in this study. The results showed that neither the freshly added nor the "ageing" nZVI to the soil had a significant effect on germination, regardless of concentration. At the low concentration, the freshly added nZVI had no visible toxic effects on the rice seedlings growth, but the rice seedlings exhibited obvious toxic symptoms at the high concentration. At the high concentration, toxicity effects of nZVI were reduced after aging with 2 and 4weeks in soils compared to fresh nZVI, but the "ageing" nZVI continued to significantly inhibit the rice seedlings growth compared with the control, and the inhibition rates of 2 and 4-week-old nZVI were not significantly different. The mechanism of ageing decreased the phytotoxicity of nZVI was due to nZVI particles incomplete oxidation, and some of which had remained in the soil after 4weeks aged.

In situ sequentially generation of acid and ferrous ions for environmental remediation

Novel heterogeneous Fenton composite materials were developed by grafting acid precursors and nano zero-valent iron particles on an acid leached diatomite, which can sequentially generate acid and ferrous ions in situ. The results show that the composite materials can potentially solve two of the biggest obstacles, which prevent the conventional Fenton reaction from being widely and practically adopted, namely: the continuous feed of ferrous ions and the maintenance of the optimum acidic pH condition during the reaction. In this study, samples were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Thermogravimetric analysis and micro organic analysis. The novel materials’ degradation capacities for bisphenol A (BPA) were evaluated and optimized. This material can be easily applied to treat wastewater via Fenton-like reaction without changing pH or adding ferrous ions. The relationships between BPA removal efficiency, the amount of grafted organosilane acid precursor and doped nZVI particles on the composite materials were investigated. It is evident from the results that the novel composite materials afford highly effective removal of BPA from water at 250mg/g. The work thus demonstrates that the novel materials could potentially be utilized for efficient remediation of recalcitrant organic compounds from the environment.

The role of nanoscale zerovalent iron particles in the biosorption and biodegradation of BDE-47 by Pseudomonas stutzeri under aerobic conditions

This study investigated the effects of nanoscale zerovalent iron (nZVI) particles on the biosorption and biodegradation of 2, 2, 4, 4-tetrabromodiphenyl ether (BDE-47) by Pseudomonas stutzier KS0013 (Ps) under aerobic conditions. nZVI (>0.5 g l−1) had an inhibitory effect on Ps growth, whereas less than 0.5 g l−1 nZVI produced a negligible influence on bacteria growth, especially with a prolonged incubation time. In the initial stage (<12 h), the total removal of BDE-47 was mainly attributed to adsorption and the Fenton-like reaction with nZVI, and nZVI impeded the accessibility of Ps to BDE-47 and weakened the total removal and biosorption of BDE-47 by Ps. However, with increasing incubation time, Ps adapted to the nZVI and played a predominant role in the total removal of BDE-47, with the result that the final total removal efficiency increased from 91 percent (without nZVI) to 95 percent. This result implied that nZVI could promote the total removal efficiency of BDE-47, but the enhancement in BDE-47 removal was limited. In addition, TEM and XPS analyses confirmed that nZVI particles had been integrated with Ps to achieve the total removal of BDE-47 via a Fenton-like reaction under aerobic conditions.

Decolorization of Methyl Orange by a new clay-supported nanoscale zero-valent iron: Synergetic effect, efficiency optimization and mechanism

In this study, a novel nanoscale zero-valent iron (nZVI) composite material was successfully synthesized using a low-cost natural clay, “Hangjin 2# clay” (HJ clay) as the support and tested for the decolorization of the azo dye Methyl Orange (MO) in aqueous solution by nZVI particles. According to the characterization and MO decolorization experiments, the sample with 5:1 HJ clay-supported nZVI (HJ/nZVI) mass ratio (HJ-nZVI5) showed the best dispersion and reactivity and the highest MO decolorization efficiency. With the same equivalent Fe0 dosage, the HJ-nZVI1 and HJ-nZVI5 samples demonstrated a synergetic effect for the decolorization of MO: their decolorization efficiencies were much higher than that achieved by physical mixing of HJ clay and nZVIs, or the sum of HJ clay and nZVIs alone. The synergetic effect was primarily due to the improved dispersion and more effective utilization of the nZVI particles on/in the composite materials. Higher decolorization efficiency of MO was obtained at larger HJ-nZVI dosage, higher temperature and under N2 atmosphere, while the MO initial concentration and pH were negatively correlated to the efficiency. HJ clay not only works as a carrier for nZVI nanoparticles, but also contributes to the decolorization through an “adsorption-enhanced reduction” mechanism. The high efficiency of HJ-nZVI for decontamination gives it great potential for use in a variety of remediation applications.

Incorporation of zero valent iron nanoparticles in the matrix of cationic resin beads for the remediation of Cr(VI) contaminated waters

The objective of present study was to obtain the fixation of nano zero valent iron (nZVI) particles on a permeable matrix and evaluate the performance of this composite material for the removal of Cr(VI) from contaminated waters. The experiments were carried out using the cationic resin Dowex 50WX2 as porous support of the iron nanoparticles. The work was carried out in two phases. The first phase involved the fixation of nZVI on the resin matrix. The resin granules were initially mixed with a FeCl3 solution to obtain the adsorption of Fe(III). Then the Fe(III) loaded resin (RFe) was treated with polyphenol solutions to obtain the reduction of Fe(III) to the elemental state. Two polyphenol solutions were tested as reductants, i.e. green tea extract and gallic acid. Green tea was found to be inefficient, probably due to the relatively big size of the contained polyphenol molecules, but gallic acid molecules were able to reach adsorbed Fe(III) and reduce the cations to the elemental state. The second phase was focused on the investigation of Cr(VI) reduction kinetics using the nanoiron loaded resins (R-nFe). It was found that the reduction follows a kinetic law of first order with respect to Cr(VI) and to the embedded nanoiron. Compared to other similar products, this composite material was found to have comparable performance regarding reaction rates and higher degree of iron utilization. Namely the rate constant for the reduction of Cr(VI), in the presence of 1 mM nZVI, was equivalent to 1.4 h of half-life time at pH 3.2 and increased to 24 h at pH 8.5. The degree of iron utilization was as high as 0.8 mol of reduced Cr(VI) per mole of iron. It was also found that this composite material can be easily regenerated and reused for Cr(VI) reduction without significant loss of efficiency.

Removal of Pb, Cd, Cu and Ni from aqueous solution using nano scale zero valent iron particles

Nanoparticles offer the potential to improve environmental treatment technologies due to their unique properties. Adsorption of metal ions Pb(II), Cd(II), Cu(II), Ni(II) to nano zero valent iron (nZVI) particles of surface iron oxide was examined. nZVI particles were synthesized by reduction of ferric chloride with sodium borohydride. In this work, transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy are applied to study the compositional and structural of nZVI. Batch equilibrium experiments were performed to study the removal efficiency of heavy metal ions. The effect of different parameters such as contact time, initial concentration, pH and nZVI dose on the adsorption process were investigated. The adsorption kinetics well fitted using a pseudo-second order kinetic model. SEM and TEM images showed that of particles were mostly spherical shape in chains with an average size 43.1±11.9nm. The initial sorption rate for all the metals is in order Pb2+>Cu2+>Cd2+>Ni2+. Short adsorption equilibrium contact time favors the application of the adsorption process. The formation of FeOOH on the surface of nZVI could be the main factor of cations removal due to its high adsorption affinity for aqueous solutes. Therefore, with the strong adsorption at pH<6.5 which is representative of several natural groundwater and the ability to adsorb multiple metal ions simultaneously, nZVI may offer a potential remediation method for the removal of metals from water and environment.

Effect of Structural Transformation of Nanoparticulate Zero-Valent Iron on Generation of Reactive Oxygen Species.

While it has been recognized for some time that addition of nanoparticlate zerovalent iron (nZVI) to oxygen-containing water results in both corrosion of Fe(0) and oxidation of contaminants, there is limited understanding of either the relationship between transformation of nZVI and oxidant formation or the factors controlling the lifetime and extent of oxidant production. Using Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, we show that while nZVI particles are transformed to ferrihydrite then lepidocrocite in less than 2 h, oxidant generation continues for up to 10 h. The major products (Fe(II) and H2O2) of the reaction of nZVI with oxygenated water are associated, for the most part, with the surface of particles present with these surface-associated Fenton reagents inducing oxidation of a target compound (in this study, (14)C-labeled formate). Effective oxidation of formate only occurred after formation of iron oxides on the nZVI surface with the initial formation of high surface area ferrihydrite facilitating rapid and extensive adsorption of formate with colocation of this target compound and surface-associated Fe(II) and H2O2 apparently critical to formate oxidation. Ongoing formate oxidation long after nZVI is consumed combined with the relatively slow consumption of Fe(II) and H2O2 suggest that these reactants are regenerated during the nZVI-initiated heterogeneous Fenton process.