Stabilized Nanoscale Zero-valent Iron Research Articles

Overlooked encounter process that affects physical behaviors of stabilized nanoscale zero-valent iron during in situ groundwater remediation

Dynamic encountering between groundwater matrices and nanoscale zero-valent iron (NZVI) injected for in situ subsurface remediation affects NZVI’s mobility and has not been well recognized. Polyacrylic acid (PAA)-stabilized NZVI (NZVI–PAA) and Mg(OH)2-coated NZVI (NZVI@Mg(OH)2) were investigated as representative NZVIs stabilized by enhanced electrostatic repulsion and reduced magnetic attraction, respectively. Encounters with divalent cations and humic acid (HA) induced the drastic aggregation and sedimentation (presedimentation) of NZVI–PAA owing to Lewis acid–base interactions and heteroaggregation. In addition, encountered groundwater electrolytes could not effectively provide electrostatic repulsion for NZVI–PAA, resulting in breakthrough ripening dynamics. The presedimentation and ripening behaviors of NZVI–PAA were eliminated and unheeded after mixing the NZVI slurry with groundwater by sonication. In comparison, the encountering process barely impacted NZVI@Mg(OH)2, for which settling was hindered. Although the particle–collector attraction promoted NZVI@Mg(OH)2 adsorption on pristine and hybrid-coated sands, the Langmuirian blocking dynamics of the NZVI@Mg(OH)2 breakthrough demonstrated its high mobility after adsorption sites of sand surface were exhausted. Extended Derjaguin−Landau−Verwey−Overbeek analysis and transport modeling provided insights into overlooked effects of encountering on physical behaviors of different stabilized NZVIs, which should be considered during practical applications under diverse subsurface conditions.

Nanoscale Zerovalent Iron Immobilized on Functionalized Nonwoven Cotton Fabric for As(V) Adsorption

A functionalized nonwoven cotton fabric-Fe(0) (denoted as FNCF-ZVI) as a novel adsorbent material was synthesized in two main steps for water treatment of arsenate ions. Firstly, the Fe(III)-immobilized chelating fabric with iminodiacetic acid (IDA) functional groups was synthesized through an epoxy group–containing glycidyl methacrylate (GMA) grafted to the nonwoven cotton fabric (NCF) via plasma-initiated emulsion graft polymerization. Subsequently, the obtained Fe(III)-immobilized FCNF was followed by a reduction of Fe(III) into Fe(0) to obtain stabilized nanoscale zerovalent iron (ZVI) on the surface of FNCF. FNCF-ZVI was applied for arsenic(V) removal in batch experiments at different pH values (2.00–9.00) and concentrations ranging between 1 and 500 mg/L As(V). The FNCF-ZVI had a positive impact on the absorption of As(V) species under acidic conditions, and the highest adsorption was seen at a pH value of 3.00. The adsorption equilibrium of adsorbent was reached in 420 min with initial solution concentrations at 1 mg/L, 10 mg/L, and 50 mg/L, and the process better fitted to the nonlinear pseudo-second-order model than to the nonlinear pseudo-first-order model. The resulting FNCF-ZVI showed a high maximum adsorption capacity of 158.73 mg/g at 35 °C for As(V) adsorption, and the adsorption data fitted the Freundlich isotherm model. Regeneration studies displayed that after 3 times usage, the adsorption capacity can remain up to 86%. It has been observed that ZVI nanoparticles have superior adsorption capacity compared to Fe(III) under their optimum conditions.

Synthesis of Guar Gum Stabilized Nanoscale Zero-valent Iron for Cr (VI) Removal in Water

Guar gum was used in the preparation of a new stabilized nanoscale zero-valent iron (nZVI), as a biodegradation stabilizer. The TEM results showed that the nanoparticles were coated by guar gum, and average particle size was 87.4 nm; XRD results showed that guar gum stabilized nZVI was α-nanoFe0. The batch test results showed that the degradation rate of guar gum stabilized nZVI was 12 times than 200 mesh reduced iron powder. Guar gum could hinder the formation of Fe(III)-Cr(III) precipitate by chelating Fe(III), consequently enhanced the reduction of Cr(VI) to Cr(III).

Nanoscale zerovalent iron, carbon nanotubes and biochar facilitated the phytoremediation of cadmium contaminated sediments by changing cadmium fractions, sediments properties and bacterial community structure

Environment functional materials have been widely used, but whether their effects on the contaminated environment could facilitate phytoremediation is not yet well understood. In this study, starch stabilized nanoscale zerovalent iron (SN), multiwall carbon nanotubes (MW) and tea waste derived biochar (TB) were used to facilitate the phytoremediation of cadmium (Cd) contaminated sediments by Boehmeria nivea (L.) Gaudich. Results showed that 100 mg/kg SN, 500 mg/kg MW and 500 mg/kg TB facilitated phytoremediation, as evidenced by increasing Cd accumulation and/or promoting plant growth. These concentrations of materials increased the reducible fraction of Cd by 9–10% and decreased the oxidizable proportion of Cd by 48–52%, indicating the improvement of Cd bioavailability through converting the oxidizable Cd into reducible form. The activities of urease, phosphatase and catalase, which related to nutrient utilization and oxidative stress alleviation, increased by 20–24%, 25–26%, and 8–9% in the sediments treated with 500 mg/kg MW and 500 mg/kg TB, respectively. In addition, the 16S rRNA gene sequence results showed that these concentrations of materials changed the bacterial diversity. The abundance of Acidobacteria, Actinobacteria, Nitrospirae and Firmicutes were increased by some of the applied materials, which could promote plant growth, change Cd bioavailability and reduce Cd toxicity. These findings indicated that the applied environment functional materials could facilitate the phytoremediation of Cd contaminated environment by changing Cd fractions, sediments properties and bacterial community structure.

Removal of hexabromocyclododecane by carboxymethyl cellulose stabilized Fe and Ni/Fe bimetallic nanoparticles: The particle stability and reactivity in water

Aggregation of nanoparticles (NPs) can hinder the degradative reactivity of particles towards organic pollutants as it reduces available surface area for reaction. This limitation may be circumvented by applying dispersant to improve colloidal stability of nanoparticle suspension. This study examined the removal of hexabromocyclododecane (HBCD), a recently listed persistent organic pollutant, by carboxymethylcellulose (CMC) stabilized nanoscale zerovalent iron (CMC-NZVI) and bimetallic Ni/Fe nanoparticles (CMC-Ni/Fe) under the influence of suspension chemistry. The mass-normalized removal rate constants of HBCD by CMC−Ni/Fe NPs increased with lower particle aggregation. However, the coating could introduce diffusion resistance as HBCD diffused through the CMC layer to the Fe surface. The activation energy was estimated to be 26.8 kJ mol−1, indicating the overall reaction process was neither surface-limited nor diffusion-controlled. The reactivity of CMC−Ni/Fe NPs toward HBCD was not affected by aqueous initial pH substantially. Common monoanions (Cl−, NO3−, and HCO3−) generally enhanced HBCD adsorption but diminished its debromination. The removal rate did not differ significantly among the studied monoanions over a concentration of 2.5–10 mM except HCO3−. Overall, CMC coating can stabilize Ni/Fe NPs, increase their adsorption of HBCD, provide buffer pH capacity, and overcome common inhibition effects of anions in water. These findings suggested the high potential of using CMC–Ni/Fe NPs for in–situ remediation.

Solvent-free synthesis of a 2D biochar stabilized nanoscale zerovalent iron composite for the oxidative degradation of organic pollutants

A facile solvent-free approach to prepare 2D nZVI/biochar with a shearing/carbonization method using lignocellulosic waste and FeCl3·6H2O as precursors.

Nanoremediation of cadmium contaminated river sediments: Microbial response and organic carbon changes

The application of nanomaterials to contaminated river sediments could induce important changes in the speciation of heavy metals with potential impacts on ecosystem. Here, rhamnolipid (RL)-stabilized nanoscale zero-valent iron (RNZVI) was conducted to test its potential performance in changing the mobility and speciation of cadmium (Cd) in river sediments, with consideration of the influences of microbial community and organic carbon (OC). Compared to NZVI, RNZVI was more effective in transforming labile Cd to stable fraction with a maximum residual concentration increasing by 11.37 mg/kg after 42 days of incubation. Bacterial community structure was tracked using high-throughput sequencing of 16S rRNA genes. Results indicated that the application of RNZVI changed the bacterial community structure and increased the relative abundance of Fe(III)-reducing bacteria, which could redistribute Fe combined Cd into a more stable Fe mineral phase. The contents of OC were gradually decreased and became stable, might resulting from OC bioavailability’s being stimulated by RNZVI through changing the bacterial community composition. This study indicates that abiotic process (i.e., from reaction with NZVI) and biotic process fueled by RNZVI lead to the immobilization of Cd in river sediments.

In situ remediation of hexavalent chromium contaminated soil by CMC-stabilized nanoscale zero-valent iron composited with biochar.

In this study, the remediation experiments were performed outdoors in natural conditions. Carboxymethyl cellulose (CMC)-stabilized nanoscale zero-valent iron (CMC-nZVI), biochar (BC) and CMC-stabilized nanoscale zero-valent iron composited with biochar (CMC-nZVI/BC) were synthesized and investigated for their effect on the in situ remediation of hexavalent chromium [Cr(VI)] contaminated soil and the concentration of available iron was tested after the remediation, compared with the untreated soil. The results of toxicity characteristic leaching procedure (TCLP) test showed that CMC-nZVI and CMC-nZVI/BC used as remediation materials could obviously improve the remediation rate of Cr contaminated soil and when the ratio of CMC-nZVI to Fe0 was 2.5 g/Kg, the leachability of Cr(VI) and Crtotal can be reduced by 100% and 95.8% simultaneously. Moreover, sequential extraction procedure (SEP) showed that most exchangeable Cr converted to carbonate-bound and Fe-Mn oxides-bound, reducing the availability and leachability of Cr in the soil.

Cadmium immobilization in river sediment using stabilized nanoscale zero-valent iron with enhanced transport by polysaccharide coating

Proper management of metal-contaminated sediment plays a key role in sediment recovery and reuse. This study synthesized two kinds of stabilized nanoscale zero-valent iron (nZVI) with starch (S-nZVI) and carboxymethyl cellulose (C-nZVI) for the in situ immobilization of Cd(II) in river sediment and investigated their transport in porous media. Experimental data showed that when the sediment sample was treated with C-nZVI for 56 days at a dosage ranging from 5 to 10 mg/g-sediment as Fe0, the TCLP (toxicity characteristic leaching procedure) leachability of Cd(II) in the sediment decreased by 93.75–96.43%, and the PBET (physiologically-based extraction test) bioaccessibility of Cd(II) decreased by 22.79–71.32%. Additionally, the acid soluble fraction of Cd(II) was partially transformed to a residual fraction, resulting in a 32.4–33.1% decrease of acid soluble Cd(II) and a 125.4–205.6% increase of the residual-Cd(II) fraction. Surface complexation with iron oxyhydroxide minerals might be the main mechanism of Cd(II) immobilization in sediment. Column experiments indicate that starch or carboxymethyl cellulose (CMC) could extend the travel distance of nZVI, but inherent site physical and chemical heterogeneities still posed challenges for nanoparticle transport. Over all, this study verifies the effectiveness of stabilized nZVI for Cd(II) immobilization in sediment and discusses the potential immobilization mechanism.

Stabilized Nanoscale Zerovalent Iron Mediated Cadmium Accumulation and Oxidative Damage of Boehmeria nivea (L.) Gaudich Cultivated in Cadmium Contaminated Sediments.

Nanoparticles can be absorbed by plants, but their impacts on phytoremediation are not yet well understood. This study was carried out to determine the impacts of starch stabilized nanoscale zerovalent iron (S-nZVI) on the cadmium (Cd) accumulation and the oxidative stress in Boehmeria nivea (L.) Gaudich (ramie). Plants were cultivated in Cd-contaminated sediments amended with S-nZVI at 100, 500, and 1000 mg/kg, respectively. Results showed that S-nZVI promoted Cd accumulation in ramie seedlings. The subcellular distribution result showed that Cd content in cell wall of plants reduced, and its concentration in cell organelle and soluble fractions increased at S-nZVI treatments, indicating the promotion of Cd entering plant cells by S-nZVI. In addition, the 100 mg/kg S-nZVI alleviated the oxidative damage to ramie under Cd-stress, while 500 and 1000 mg/kg S-nZVI inhibited plant growth and aggravated the oxidative damage to plants. These findings demonstrate that nanoparticles at low concentration can improve the efficiency of phytoremediation. This study herein develops a promising novel technique by the combined use of nanotechnology and phytoremediation in the remediation of heavy metal contaminated sites.

Reductive dechlorination of trichloroethylene by polyvinylpyrrolidone stabilized nanoscale zerovalent iron particles with Ni

We developed a novel stabilized nanoscale zerovalent iron (NZVI) particles with Ni using an electron conducting polymer, polyvinylpyrrolidone (PVP), to selectively dechlorinate trichloroethylene (TCE) to non-toxic intermediates. The size of the PVP stabilized NZVI-Ni ((PVP-NZVI-Ni), average diameter: ∼20nm) is smaller than that of bare NZVI (50–80nm) due to the prevention of agglomeration of the resultant iron particles by PVP. PVP-NZVI-Ni showed a complete removal of TCE in 1h with superior dechlorination kinetics (kobs=5.702h−1) and ethane selectivity (98%), while NZVI-Ni showed 5 times slower dechlorination kinetics (1.218h−1). Other PVP-NZVI-metals (i.e., Cu, Sn, Co, and Mn) also enhanced the TCE dechlorination, but they were much slower (kobs=0.024−0.411h−1) than that of PVP-NZVI-Ni. In column test, PVP-NZVI-Ni exhibited better mobility (95% of PVP-NZVI-Ni recovery in the eluent) than NZVI-Ni (1%). In addition, PVP-NZVI-Ni reductively transform TCE to ethane even under 10 cycles of repeated TCE dechlorination treatment.

Contributions of Abiotic and Biotic Dechlorination Following Carboxymethyl Cellulose Stabilized Nanoscale Zero Valent Iron Injection

A pilot scale injection of nanoscale zerovalent iron (nZVI) stabilized with carboxymethyl cellulose (CMC) was performed at an active field site contaminated with a range of chlorinated volatile organic compounds (cVOC). The cVOC concentrations and microbial populations were monitored at the site before and after nZVI injection. The remedial injection successfully reduced parent compound concentrations on site. A period of abiotic degradation was followed by a period of enhanced biotic degradation. Results suggest that the nZVI/CMC injection created conditions that stimulated the native populations of organohalide-respiring microorganisms. The abundance of Dehalococcoides spp. immediately following the nZVI/CMC injection increased by 1 order of magnitude throughout the nZVI/CMC affected area relative to preinjection abundance. Distinctly higher cVOC degradation occurred as a result of the nZVI/CMC injection over a 3 week evaluation period when compared to control wells. This suggests that both abiotic and biotic degradation occurred following injection.

Remediation of hexavalent chromium contaminated soil by stabilized nanoscale zero-valent iron prepared from steel pickling waste liquor

Abstract The removal of Cr(VI) from contaminated soil using sodium carboxymethyl cellulose (CMC)-stabilized nanoscale zero-valent iron prepared from steel pickling waste liquor was systematically investigated. Laboratory batch experiments indicated that 0.09 g L −1 of Fe 0 nanoparticles at a soil to solution ratio of 1 g: 10 mL completely reduced the aqueous-bound Cr(VI), which contributed about 46% of the pre-sorbed Cr(VI) in the soil (Cr(VI) = 102 mg kg −1 ). Furthermore, the addition of Fe 0 nanoparticles only removed a portion of the soil-bound Cr(VI). When the soil was treated with 0.3 g L −1 of Fe 0 nanoparticles for 72 h, 80% of the loaded Cr(VI) was reduced to Cr(III), which resulted in a residual Cr(VI) concentration of 20 mg kg −1 . Based on the studies of elemental distributions and XPS analysis, it is proposed that reduction and immobilization may be equally important removal mechanisms for Cr(VI) by CMC-nZVI. Following the treatment by CMC-nZVI, the TCLP leachability of the Cr(VI) and Cr total was significantly reduced by 100% and 82%, respectively. This study sheds new light on the remediation of Cr(VI)-contaminated soil by CMC-nZVI.

Emergency remediation of simulated chromium (VI)-polluted river by nanoscale zero-valent iron: Laboratory study and numerical simulation

The remediation effectiveness and negative effect on ecotoxicity are needed to be considered in a suitable emergency remedial action for polluted river. In this work, the stabilized nanoscale zero-valent iron (nZVI) was applied in the remediation of a simulated Cr(VI)-polluted river, and a mathematical model was developed based on a reaction network to describe the process. The results showed that the remediation effectiveness was improved with the increasing nZVI dose, decreasing initial concentration of pollution source and water flow rate. Water analysis was conducted to investigate the effects of the nZVI to the process. Toxicity evaluation indicated that almost no toxicity was detected in 36days’ exposure of reaction products in the water. Model parameters including mass-loss coefficient (K1) and reaction coefficient (K2) were obtained in laboratorial experiment, and a statistical comparison method was employed to assess the simulated results. Thus, the obtained mathematical modeling and physical modeling could be exploratory researches for practical remediation of polluted river.

Air-stable nZVI formation mediated by glutamic acid: solid-state storable material exhibiting 2D chain morphology and high reactivity in aqueous environment

We report a new chemical approach toward air-stable nanoscale zero-valent iron (nZVI). The uniformly sized (approx. 80 nm) particles, formed by the reduction of Fe(II) salt by borohydride in the presence of glutamic acid, are coated by a thin inner shell of amorphous ferric oxide/hydroxide and a secondary shell consisting of glutamic acid. The as-prepared nanoparticles stabilized by the inorganic–organic double shell create 2D chain morphologies. They are storable for several months under ambient atmosphere without the loss of Fe(0) relative content. They show one order of magnitude higher rate constant for trichlorethene decomposition compared with the pristine particles possessing only the inorganic shell as a protective layer. This is the first example of the inorganic–organic (consisting of low-molecular weight species) double-shell stabilized nanoscale zero-valent iron material being safely transportable in solid-state, storable on long-term basis under ambient conditions, environmentally acceptable for in situ applications, and extraordinarily reactive if contacted with reducible pollutants, all in one.

Use of Electrophoresis for Transporting Nano-Iron in Porous Media

Research has been conducted to evaluate if electrophoresis could transport surface stabilized nanoscale zero-valent iron (nZVI) through fine grained sand with the intent of remediating a contaminant in situ. The experimental procedure involved determining the transport rates of polymer modified nZVI and hematite in fine grained sands under an applied electrical gradient under different physical and chemical conditions. Results indicated transport of polymer modified nZVI and hematite can be accomplished by electrophoresis, with rates found to be much higher than diffusion alone and comparable to those predicted by electrokinetic theory. This study indicates there is potential for this method to deliver polymer modified nZVI into contaminated zones within fine grained sands for the purpose of remediation.

Toxicity assessments of nanoscale zerovalent iron and its oxidation products in medaka (Oryzias latipes) fish

Iron-based nanotechnologies are increasingly used for environmental remediation; however, toxicologic impacts of iron nanoparticles on the aquatic ecosystem remain poorly understood. We treated larvae of medaka fish (Oryzias latipes) with thoroughly characterized solutions containing carboxymethyl cellulose (CMC)-stabilized nanoscale zerovalent iron (nZVI), aged nanoscale iron oxides (nFe-oxides) or ferrous ion (Fe[II]) for 12–14days’ aqueous exposure to assess the causal toxic effect(s) of iron NPs on the fish. With the CMC-nZVI solution, the dissolved oxygen level decreased, and a burst of reactive oxygen species (ROS) was generated as Fe(II) oxidized to ferric ion (Fe[III]); with the other two iron solutions, these parameters did not significantly change. CMC-nZVI and Fe(II) solutions caused acute lethally and sublethally toxic effects in medaka larvae, with nFe-oxide-containing solutions causing the least toxic effects. We discuss modes of toxic action of iron NPs and chronic toxic effects in terms of hypoxia, Fe(II) toxicity and ROS-mediated oxidative damage.

Immobilization of arsenic in soils by stabilized nanoscale zero-valent iron, iron sulfide (FeS), and magnetite (Fe3O4) particles

Arsenic is a widespread contaminant in soils and groundwater. While various iron-based materials have been studied for immobilizing arsenic in contaminated soils, the feasibility of stabilized iron-based nanoparticles has not been reported. This study investigates the effectiveness of using three types of starch-stabilized iron-based nanoparticles, including zero-valent iron (ZVI), iron sulfide (FeS), and magnetite (Fe3O4), for immobilization of arsenic in two representative As-contaminated soils (an orchard soil and a fire range soil). To test the effect of the nanoparticles on the arsenic leachability, As-contaminated soils were amended with the nanoparticles at various Fe/As molar ratios (5:1–100:1) and contact time (3 and 7 d). After three days’ treatments of a field-contaminated sandy soil, the PBET-based bioaccessibility of As decreased from an initial (71.3±3.1)% (mean±SD) to (30.9±3.2)% with ZVI, (37.6±1.2)% with FeS, and (29.8± 3.1)% with Fe3O4 at an Fe/As molar ratio of 100:1. The TCLP-based leachability of arsenic in a spiked fire range soil decreased from an initial (0.51±0.11)% to (0.24±0.03)%, (0.27±0.04)% and (0.17±0.04)% by ZVI, FeS, and Fe3O4 nanoparticles, respectively. The Fe3O4 nanoparticles appeared to be more effective (5% or more) than other nanoparticles for immobilizing arsenic. When the two soils were compared, the treatment is more effective on the orchard soil that has a lower iron content and higher initial leachability than on the range soil that already has a high iron content. These results suggest that these innocuous iron-based nanoparticles may serve as effective media for immobilization of As in iron-deficient soils, sediments or solid wastes.