nZVI Particles Research Articles

Impacts of nanoscale zero-valent iron on nitrite accumulation performance of nitritation granular sludges with different spatial morphologies and its biosorption behavior

To explore the potential impacts of nanoscale zero-valent iron (nZVI) particles on nitrite accumulation performance of nitritation granular sludge (NGS), two types of NGS (NGSA and NGSH) with different spatial morphologies were employed to exposure under a wide dosage of nZVI in batch tests. The biosorption behavior of nZVI was also investigated by determining adsorption isotherm. Results showed that the ecotoxic effect of nZVI was ascribed to its fast adsorption to the granules. Although NGSA and NGSH shared a similar bacterial community structure dominated by genus Nitrosomonas based on high-throughput pyrosequencing, the compact and small granules of NGSA showed a stronger tolerance for nZVI exposure than NGSH with loose spatial structure. The 50% inhibition dosage of nZVI for ammonium-oxidizing bacteria activity in NGSA and NGSH was 88.5 and 21.3 mg g−1 VSS, respectively. As a crucial self-protection mechanism of microbes, the secretion of extracellular polymeric substances was dramatically enhanced with nZVI exposure at a low dosage, and a simultaneous decrease in both extracellular polymeric substances contents and ammonium-oxidizing activity of NGS was observed with a high accumulation of total iron in sludge phase. Overall, the results suggested that ammonium-oxidizing bacteria in granules were susceptible to inhibition by nZVI exposure, and release of engineered nanoparticles into wastewater treatment system increased the risk of failure in autotrophic nitrogen removal process.

A new insight into the main mechanism of 2,4-dichlorophenol dechlorination by Fe/Ni nanoparticles

Three possible dechlorination mechanisms of chloroorganics by nanoscale zero-valent iron (n-ZVI) have been proposed and widely accepted, however, the main mechanism is still controversial and not verified by experimental results. In this study, 2,4-dichlorophenol (2,4-DCP) was selected as the target pollutant and the experiments were carried out for the screening of the main mechanism of 2,4-DCP dechlorination by n-ZVI and Fe/Ni nanoparticles (n-Fe/Ni). The results indicated that >95% of 2,4-DCP could be dechlorinated to phenol by n-Fe/Ni within 120 min, while 2,4-DCP could hardly be dechlorinated by n-ZVI particles. The active hydrogen atom (H*) that transformed from H2 under the catalysis of Ni was responsible for >90% of 2,4-DCP dechlorination by n-Fe/Ni and <10% of the dechlorination was attributed to the direct electron transfer from ZVI. Fe2+ was not able to dechlorinate 2,4-DCP. Correspondently, Ni in n-Fe/Ni mainly acted as a catalyst, while the acceleration of electron transfer from ZVI by Ni had a positive effect on 2,4-DCP dechlorination. The investigations on the relative importance of these three mechanisms are essential to iron-based remediation technology.

Preparation of Biomass Activated Carbon Supported Nanoscale Zero-Valent Iron (Nzvi) and Its Application in Decolorization of Methyl Orange from Aqueous Solution

The nanoscale zero-valent iron (nZVI) has great potential to degrade organic polluted wastewater. In this study, the nZVI particles were obtained by the pulse electrodeposition and were loaded on the biomass activated carbon (BC) for synthesizing the composite material of BC-nZVI. The composite material was characterized by SEM-EDS and XRD and was also used for the decolorization of methyl orange (MO) test. The results showed that the 97.94% removal percentage demonstrated its promise in the remediation of dye wastewater for 60 min. The rate of MO matched well with the pseudo-second-order model, and the rate-limiting step may be a chemical sorption between the MO and BC-nZVI. The removal percentage of MO can be effectively improved with higher temperature, larger BC-nZVI dosage, and lower initial concentration of MO at the pH of 7 condition.

Fe(0)-embedded thermally reduced graphene oxide as efficient nanocatalyst for reduction of nitro compounds to amines

The recent progress in metal nanoparticle-based catalytic systems has prompted the research community to focus on combining the unique physicochemical properties with their catalytic activities. In this context, magnetic nanomaterials offer significant advantage as they can be separated after the catalytic reaction and reused. Among such systems, Fe-based nanoparticles are undeniably the most popular as they can be synthesized from the earth-abundant resources. However, in view of the poor chemical stability of nanoscale zero-valent iron (nZVI) particles during the reaction process, their use in advanced catalytic systems is still challenging. Herein, we present a Fe(0) species embedded in a thermally reduced graphene oxide matrix (Fe/TRGO) as a nanocatalyst for the reduction of nitro compounds. The catalyst exhibits high substrate scope with high yield and selectivity and can be recycled up to four times without any significant loss in activity. The unique rGO (reduced graphene oxide)-entrapped doughnut-shaped structure of the Fe(0) species, accompanied by the thin oxide protection layer, is responsible for the superior catalytic activity. Due to the scalable synthesis and high catalytic efficiency the catalyst offers a real application potential in industrial transformations of nitro compounds.

Nanoscale zero-valent iron modified with carboxymethyl cellulose in an impinging stream-rotating packed bed for the removal of lead(II)

A novel impinging stream-rotating packed bed (IS-RPB) was proposed to continuous, macro and industrialized prepare nanoscale zero-valent iron (nZVI) with simultaneously modified with carboxymethyl cellulose (CMC) for the removal of Pb2+. The obtained CMC-nZVI particles were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The components on the surface of CMC-nZVI after react with Pb2+ were also analyzed by X-ray photoelectron spectroscopy (XPS). The IS-RPB makes it possible for the continuous, macro and industrialized preparing of CMC-nZVI particles, and CMC can significantly improve the dispersion and reduce aggregation of nZVI particles. The effects of solution pH, initial Pb2+ concentration and reaction time on the removal efficiency of Pb2+ by nZVI and CMC-nZVI particles were also investigated. The results show that CMC-nZVI particles outperform nZVI particles in removing Pb2+, and the removal efficacy reaches a maximum of 838.84 mg·g−1 for nZVI particles and 1237.32 mg·g−1 for CMC-nZVI particles at pH = 6.0. The adsorption of Pb2+ by nZVI and CMC-nZVI particles can be described by the Langmuir isotherm adsorption model with a R2 of 0.999, and the calculated maximum adsorption capacity is 900.90 and 1376.07 mg·g−1 for nZVI and CMC-nZVI particles. The adsorption of Pb2+ follows the pseudo second-order kinetics with a linear correlation coefficient R2 of 0.999. In addition, the effect of co-existing cations such as Na+, Cu2+, Ni2+ and Cd2+ on Pb2+ removal efficiency was also investigated. The results showed that Na+ had no effect on Pb2+ removal efficiency and Cu2+ and Ni2+ had inhibited Pb2+ removal efficiency. Cd2+ had an inhibitory effect on Pb2+ removal efficiency when the concentration was 50 mg·L−1 and 100 mg·L−1, Cd2+ enhanced Pb2+ removal efficiency while the concentration of Cd2+ was 200 mg·L−1.

Highly Efficient Utilization of Nano-Fe(0) Embedded in Mesoporous Carbon for Activation of Peroxydisulfate.

Nanoscale zerovalent iron (nZVI) particles have received much attention in environmental science and technology due to their unique electronic and chemical properties. However, the aggregation and oxidation of nZVI brings much difficulty in practical application of environmental remediation. In this study, we reported a composite nano-Fe(0)/mesoporous carbon by a chelation-assisted coassembly and carbothermal reduction strategy. Nano-Fe(0) particles with surface iron oxide (Fe2O3·FeO) were wrapped with graphitic layers which were uniformly dispersed in mesoporous carbon frameworks. The unique structure made the nano-Fe(0) particles stable in air for more than 20 days. It was used as a peroxydisulfate (PDS) activator for the oxidation treatment of 2,4,6-trichlorophenol (TCP). The TOF value of MCFe for TCP degradation is nearly 3 times higher than those of FeSO4 and Fe2O3·FeO and nearly 2 times than that of commercial nZVI. The reactive oxygen species (ROS) including •SO4-, HO•, and •O2-, 1O2 are efficiently generated by PDS activation with MCFe. The PDS activation process by nano-Fe(0) particles was intrinsically induced by the ferrous ions (Fe(II)) continuously generated at the solid/aqueous interface. Namely, the nano-Fe(0) particles were highly efficiently utilized in sulfate radical-based advanced oxidation processes (SR-AOP). The porous structure also assists the absorption and transfer of TCP during the degradation process.

Experimental and theoretical aspects of biochar-supported nanoscale zero-valent iron activating H2O2 for ciprofloxacin removal from aqueous solution

Ciprofloxacin has been frequently detected in water environment, and its removal has become a significant public concern. Biochar-supported nanoscale zero-valent iron (BC/nZVI) to activate hydrogen peroxide (H2O2) has many advantages on promoting the removal of organic contaminants. In this paper, the BC/nZVI activating H2O2 degradation of ciprofloxacin was systematically investigated by experimental and theoretical approaches. The morphologies and property analysis showed that nZVI particles distributed uniformly on the biochar surface, which mainly include -OH, >CO and COC and CO groups. Different reaction conditions were compared to define the optimal conditions for ciprofloxacin removal in BC/nZVI/H2O2 system. More than 70% of ciprofloxacin was removed in the optimal conditions: acidic condition (pH 3∼4), low doses of H2O2 (20 mM), and temperature of 298 K. The hydroxyl radical (•OH) oxidation was the primary pathway in BC/nZVI/H2O2 degradation of ciprofloxacin process. The theoretical calculation indicated that hydrogen atom abstraction (HAA) pathways were the dominant oxidation pathways contributing 92.3% in overall second‒order rate constants (k) of •OH and ciprofloxacin. The current results are valuable to evaluate the application of BC/nZVI activating H2O2 degradation of ciprofloxacin and other fluoroquinolone antibiotics in water treatment plants.

Nanoscale zero-valent iron supported on biochar for the highly efficient removal of nitrobenzene

The application of nanoscale zero-valent iron (nZVI) in the remediation of contaminated groundwater or wastewater is limited due to its lack of stability, easy aggregation and iron leaching. To address this issue, nZVI was distributed on oak sawdust-derived biochar (BC) to obtain the nZVI/BC composite for the highly efficient reduction of nitrobenzene (NB). nZVI, BC and nZVI/BC were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). For nZVI/BC, nZVI particles were uniformly dispersed on BC. nZVI/BC exhibited higher removal efficiency for NB than the simple summation of bare nZVI and BC. The removal mechanism was investigated through the analyses of UV-Visible spectra, mass balance and XPS. NB was quickly adsorbed on the surface of nZVI/BC, and then gradually reduced to aniline (AN), accompanied by the oxidation of nZVI to magnetite. The effects of several reaction parameters, e.g., NB concentration, reaction pH and nZVI/BC aging time, on the removal of NB were also studied. In addition to high reactivity, the loading of nZVI on biochar significantly alleviated Fe leaching and enhanced the durability of nZVI.

Nanoscale zero-valent iron (nZVI) immobilization onto graphene oxide (GO)-incorporated electrospun polyvinylidene fluoride (PVDF) nanofiber membrane for groundwater remediation via gravity-driven membrane filtration

Nanoscale zero-valent iron (nZVI), with its high reactivity towards a broad range of contaminants, has been a promising material for groundwater remediation. Membrane-supported nZVI can both avoid nZVI agglomeration for better reactivity and recycle nZVI to lower the risk of secondary pollution. In this study, we successfully fabricated a PVDF-GO membrane via electrospinning technology and employed the functionalized nanofiber membrane to immobilize nZVI particles. The addition of GO into PVDF nanofibers can both increase the hydrophilicity to improve membrane flux and offer –COOH as a binder to immobilize nZVI particles. PVDF-GO-nZVI membranes with different GO loadings (0%, 0.5%, 1%, 3% of PVDF) were tested with two typical nZVI-targeted contaminants (Cd(II) and trichloroethylene (TCE)) via gravity-driven membrane filtration. The results show that membrane with 1% GO had the best nZVI distribution against the aggregation and a better performance in both Cd removal (100%) and TCE removal (82%). The nZVI membrane had a high flux in gravity-driven filtration at 255 LMH for Cd(II) and 265 LMH for TCE respectively. Generally, the developed PVDF-GO-nZVI electrospun nanofiber membrane had an excellent performance in the gravity-driven membrane filtration system for groundwater remediation.

Persulfate activation by natural zeolite supported nanoscale zero-valent iron for trichloroethylene degradation in groundwater

In the advanced oxidation processes, using persulfate (PS) as a radical precursor for pollutant degradation in groundwater has received increasing attention. In this study, zeolite supported nZVI composites (Z/nZVI) were synthesized through an ion exchange and borohydride reduction method to investigate their ability to activate PS for the TCE degradation. Based on preliminary screening of the PS activation by the Z/nZVI (PS-Z/nZVI) system in terms of TCE degradation, Z/nZVI composite with a zeolite to nZVI mass ratio of 1:1 (Z/nZVI (1)) was optimized as the best composition and chosen for further characterization and examination. Especially, for this PS-Z/nZVI system, PS concentration, solution matrix effects (i.e., solution pH, coexisting anions and natural organic matter) were studied. Characterization results revealed that the aggregation of nZVI particles was alleviated and they were good dispersed on the zeolite sheet with a large SSA (159.49 m2/g) compared to the unsupported nZVI (8.77 m2/g). The synthesized Z/nZVI (1) composite exhibited excellent activated ability towards PS (1.5 mM) and effectively degraded 98.8% of TCE at pH 7 within 120 min. The PS-Z/nZVI system was observed to operate effectively over a wide range of pH (i.e., 4–7) for TCE degradation. Moreover, the presence of nitrates (1 mM) and bicarbonates (10 mM) decreased the TCE degradation efficiency to 91.5% and 59.6%, respectively. Scavenger tests demonstrated that both sulfate and hydroxyl radicals participated in the TCE degradation. The ion chromatography analysis suggested the formation of oxalic acid and formic acid as the reaction intermediates during the TCE degradation process in the PS-Z/nZVI system.

In situ fabrication of dynamic nano zero-valent iron/activated carbon nanotubes membranes for tellurium separation

Recovery of valuable elements from (industrial process) photovoltaic wastes would be beneficial for both economical and sustainability reasons. In this work, nano zero-valent iron/activated carbon nanotubes (NZVI/ACNTs) hybrid membranes were fabricated by using NZVI as dynamic layer and CNTs as substrate for deep tellurium extraction, where the NZVI particles were formed by in situ reduction. Batch experiments were conducted to investigate the adsorption properties of NZVI/ACNTs hybrid membranes under different solution conditions such as pH, temperature, sorbent dosage, and competitive ions. Energy dispersive X-ray and X-ray photoelectron spectroscopy results confirmed good adsorption capacity of tellurium by NZVI/ACNTs through redox reactions. The tellurium adsorption capacities decreased in the presence of competitive ions and as the concentration of NO3− significantly increased, the adsorption quantity dropped from 331.6 to 286.5 mg/g. Extraction of tellurium under weakly acidic conditions had a positive effect and reached a maximum adsorption capacity about 800 mg/g at pH 4.7. Kinetic models and equilibrium isotherms fitted well to the adsorption experimental data indicating that chemical adsorption dominate during the adsorption process of NZVI/ACNTs-Te. As a reusable and high-efficient adsorbent, NZVI/ACNTs membrane has tremendous potential to handle and recycle toxic tellurium containing compounds.

Recyclable nanoscale zerovalent iron (nZVI)-immobilized electrospun nanofiber composites with improved mechanical strength for groundwater remediation

Nanoscale zero-valent iron (nZVI), as a promising material, has been widely used in groundwater remediation. Membrane-supported nZVI can both avoid nZVI agglomeration for better reactivity and recycle nZVI/contaminants to lower the risk of secondary pollution. However, membrane mechanical strength is a critical property for long-term operation and the regeneration of nZVI membranes. This study tried to use a high molecular weight dual-crosslinking method to improve the mechanical strength of polymeric electrospun nanofiber membranes. Specifically, high molecular weight polyacrylic acid (PAA, Mw = 450,000) was dual-crosslinked by adding polyvinyl alcohol (PVA) as covalent cross-linker (named as M450k) and Fe(II) or Fe(III) as the ionic cross-linker (named as M450k-II and M450k-III). The results indicated that the M450k had better thermal resistance against membrane shrinkage, thus having larger surface areas and more –COOH groups to immobilize more nZVI particles. Besides, M450k-III had the highest tensile strength at 8.5 MPa, 5 times the figure for the mono-crosslinked low molecular weight membrane (M2k). In terms of nZVI immobilization and filtration performance, the Fe(II)-crosslinked membrane had better nZVI immobilization with the highest removal capacity at 463 mg/g while Fe(III)-crosslinked membrane had overwhelming mechanical strength with decent and stable removal capacity under multiple nZVI regenerations over 15 filtration cycles. Generally, the high molecular weight Fe(III)-crosslinked PAA-PVA electrospun nZVI showed better potential for long-term filtration process.

Degradation of Anionic Dye (Acid Orange II) by Bentonite Supported Nano-Zero Valent Iron

The nano-zero valent iron (nZVI) has been reported as an excellent material to decolourize the anionic dyes. Aggregation of nZVI tends to reduce its reactivity. Due to this reason, modifications of nZVI were applied by using bentonite. Bentonite supported nano-zero valent irons (B-nZVI) was synthesized by using reduction method of ferrous ions and sodium borohydride in presence of bentonite. The objective of this study was to evaluate the performance of composite nanoscale zero-valent iron (nZVI) in decolorized of acid orange II from aqueous solutions. All the three adsorbent materials (nZVI, B-nZVI and bentonite) were characterized by physical, chemical, mineralogical and morphological properties such as Brunnaer-Emmett-Teller (BET) surface area, X-ray photoelectron spectroscopy with auger electron spectroscopy (XPS-AES), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The batch adsorption tests for all adsorbent materials have been conducted to determine the effectiveness of both materials in dye removal. The five effects have been analyzed in Batch test among others concentration, dose, pH, kinetic and temperature. The study found in all effects, BnZVI (qe opt = 8.9286 mg/g) showed the higher adsorption capacity followed by nZVI (qe opt = 8.1224 mg/g) and bentonite (qe opt = 5.8469 mg/g). The effectiveness of B-nZVI was due to the dispersion of nZVI particles bentonite particles, consequently provided more sites for adsorption. This study discovered that B-nZVI has a high potential to be a low-cost adsorbent for decolorized anionic dye from synthetic dye wastewater.

Application of Stabilized Nano Zero Valent Iron Particles for Immobilization of Available Cd2+, Cu2+, Ni2+, and Pb2+ Ions in Soil

The present manuscript studies the effectiveness of commercial nano zero valent iron (nZVI) particles in decreasing the availability of Cd, Cu, Ni, and Pb in spiked soil samples and to remove the same heavy metals from aqueous solutions. The difference of nZVI efficiency between single and multi-metal contamination was evaluated. The application of nZVI in water samples showed higher effectiveness in the cases of single metal contamination. The effectiveness of single- and multi-metal (mixtures of Cu, Ni, Pb and Cd, Cu, Ni, Pb) immobilization in soil using different doses (0%, 0.85%, 1.7%, 2.55%, and 5.1%) of nZVI was determined. Immobilization efficiency was assessed using the leaching procedure and depended on a particular metal and the dose of nZVI. In all cases, it was determined that an increasing amount of nZVI resulted in decrease in the leaching of analysed metals. In cases, where higher nZVI doses were used, higher immobilization efficiency was observed for heavy metals in multi-metal contamination. The application of nZVI significantly reduced leaching of all heavy metals and this strategy can be successfully used for heavy metals stabilization in soils.

Removal of chloramphenicol in aqueous solutions by modified humic acid loaded with nanoscale zero-valent iron particles

As a natural organic carbon skeleton, humic acid (HA) was loaded with nanoscale zero-valent iron (nZVI) Particles to remove chloramphenicol (CAP) from aqueous solution. The pore morphology and structure, the type, the distribution and valence state of element, and the class of functional groups on the surface of the material were shown by SEM/EDS, XPS, BET and FTIR. When the load ratio of nZVI on HA was 1:30, the iron content in the material was minimized, the specific gravity of the economic material-HA was increased, and the removal efficiency of CAP was 80.0% or higher. In addition, the mass ratio of nZVI on HA, the dosage of nZVI/HA-30, the initial pH and CAP concentration of the solution, these four general factors, played an important role in the efficiency and equilibrium time of the CAP removal. The removal efficiency of CAP by nZVI/HA-30 was 84.2% when the dosage was 1.0 g (100 mL)−1, the initial concentration of CAP was 30 mg L−1 and the pH was 3. The reaction pathway and removal mechanism of ZVI/HA-30 were studied by the concentration of total and ferrous iron ions in the solution, UV–Vis and MS. The CAP was continuously denitrified and dechlorinated, decomposed into easily degradable substances by nZVI particles supported on HA, which was consistent with the first-order kinetic model within 5 min. This newly synthesized material was economical and efficient, easy to store, effectively prevented agglomeration and passivation of nZVI, and had a good application prospect for removing contaminants from water.

Preparation of porous semi-IPN temperature-sensitive hydrogel-supported nZVI and its application in the reduction of nitrophenol

Nanoscale zero-valent iron (nZVI) particles supported on a porous, semi-interpenetrating (semi-IPN), temperature-sensitive composite hydrogel (PNIPAm-PHEMA). nZVI@PNIPAm-PHEMA, was successfully synthesized and characterized by FT-IR, SEM, EDS, XRD and the weighing method. The loading of nZVI was 0.1548 ± 0.0015 g/g and the particle size was 30–100 nm. NZVI was uniformly dispersed on the pore walls inside the PNIPAm-PHEMA. Because of the well-dispersed nZVI, the highly porous structure, and the synergistic effect of PNIPAm-PHEMA, nZVI@PNIPAm-PHEMA showed excellent reductive activity and wide pH applicability. 95% of 4-NP in 100 mL of 400 mg/L 4-NP solution with initial pH 3.0–9.0 could be completely reduced into 4-AP by about 0.0548 g of fresh supported nZVI at 18–25 °C under stirring (110 r/min) within 45 min reaction time. A greater than 99% 4-NP degradation ratio was obtained when the initial pH was 5.0–9.0. The reduction of 4-NP by nZVI@PNIPAm-PHEMA was in agreement with the pseudo-first-order kinetics model with Kobs values of 0.0885–0.101 min−1. NZVI@PNIPAm-PHEMA was able to be recycled, and about 85% degradation ratio of 4-NP was obtained after its sixth reuse cycle. According to the temperature sensitivity of PNIPAm-PHEMA, nZVI@PNIPAm-PHEMA exhibited very good storage stability, and about 88.9% degradation ratio of 4-NP was obtained after its storage for 30 days. The hybrid reducer was highly efficient for the reduction of 2-NP, 3-NP, 2-chloro-4-nitrophenol and 2-chloro-4-nitrophenol. Our results suggest that PNIPAm-PHEMA could be a good potential carrier, with nZVI@PNIPAm-PHEMA having potential value in the application of reductive degradation of nitrophenol pollutants.

Efficient preparation of nanoscale zero‐valent iron by high gravity technology for enhanced Cr(VI) removal

AbstractOwing to its strong reducibility capacity, nanoscale zero‐valent iron (nZVI) can be widely used in the treatment of wastewater. In this study, nZVI particles with an average size of 14 nm were continuously prepared using a rotating packed bed (RPB) reactor with stainless wire mesh packing. The effects of the surfactant type and the rotating speed of the RPB reactor on the particle size of nZVI were investigated. The results indicated that the average particle size could be notably reduced with the proper addition of PVP in the preparation process. Meanwhile, the particle size could be further decreased by increasing the rotating speed of the RPB. Compared to a stirred tank reactor (STR), the RPB reactor had nZVI with a smaller particle size and a much shorter reaction time. The as‐prepared nZVI was further employed to remove Cr(VI) in the simulated sewage. The results indicated that lower pH, higher nZVI dosage, and higher temperature were beneficial to the efficient removal of Cr(VI). The removal process of Cr(VI) well conformed to a pseudo‐first‐order kinetic model. Thermodynamic studies showed that the reduction of Cr(VI) by nZVI was a spontaneous endothermic reaction process with increased entropy. In addition, nZVI prepared in the RPB displayed higher removal efficiency than the counterpart in the STR, and the removal rate was greatly increased by 17.4 times.

Electric-field enhanced reactivity and migration of iron nanoparticles with implications for groundwater treatment technologies: Proof of concept

The extensive use of nanoscale zero-valent iron (nZVI) particles for groundwater treatment has been limited, in part, because of their non-selective reactivity and low mobility in aquatic environments. Herein, we describe and explore progressive changes in the reactivity and migration of aqueous dispersed nZVI particles under an applied DC electric field. Due to the applied electric field with an intensity of about 1 V cm−1, the solution oxidation-reduction potential (ORP) remained as low as −200 mV for at least 32 days, which was in agreement with the persistence of the reduced iron species (mainly Fe(II)), and led to substantially prolonged reactivity of the original nZVI. The treatment of chlorinated ethenes (DCE > PCE > TCE) was markedly faster, individual CHC compounds were eliminated with the same kinetics and no lesser-chlorinated intermediates were accumulated, following thus the direct dechlorination scheme. When nZVI-dispersion flows towards the anode through vertical laboratory columns filled with quartz sand, significant enhancement of nZVI migration was recorded because of lower extent of nanoparticle aggregation and increased repulsion forces between the nanoparticles and the surface of silica dioxide. The results of this study have significant consequences for groundwater remediation, mainly for the treatment of slowly degradable DCE in real CHC contaminated groundwater, where it could improve the reactivity, the longevity and the migration of nZVI particles.

Polyaniline/attapulgite-supported nanoscale zero-valent iron for the rival removal of azo dyes in aqueous solution

In this paper, polyaniline/attapulgite (PANI/APT)-supported nanoscale zero-valent iron (nZVI) composites were synthesized by liquid-phase chemical reduction method and used for the removal of two kinds of dyes. The structure of as-prepared nZVI/PANI/APT was characterized by various test methods. The removal property and degradation mechanism for azo (alizarin yellow R, methyl red, chrome black T, methyl orange) and non-azo (methylene blue, rhodamine B) dyes in aqueous solution were investigated. The presence of PANI/APT can decrease the aggregation of nZVI particles with maintenance of reactivity and improving adsorption capacity for degradation azo dye. The experiment results showed that the removal property of the composite materials on azo dyes is obviously better than that on non-azo dyes. The varying removal efficiencies of dyes depend on the different degradation mechanisms. Azo dyes removal by nZVI/PANI/APT was mainly due to the reductive cleavage of the N = N of nZVI, while non-azo dyes removal mainly contributes to the adsorption of PANI/APT. The study demonstrated that nZVI/PANI/APT has potential applications for the removal of azo dyes from wastewaters.

High reactive nano zero-valent iron produced via wet milling through abrasion by alumina

The performance of new nano zero-valent iron (nZVI) particles produced by a promising new milling method in organic solvent was examined. The basic feature of the new process involves the addition of abrasive alumina particles having an average particle size of 5 μm during milling. The milled particles with alumina had a specific surface area exceeding 20 m2·g−1 as well as high percentages of Fe(0) content of 75–80%. The reactivity against Cr(VI), Trichloroethylene, and Tetrachloroethylene was determined and in all cases, the removal capacity of the milled particles was higher than that of commercial available nZVI particles. This high reactivity may be related to the absence of a thick and continuous oxide layer on the surface, the high disorder levels of the metallic structure and the large number of reaction sites. Sedimentation tests revealed very good suspension stability, while in mobility tests, the particles could be distributed throughout the column length. The results showed a low tendency to agglomerate in aqueous solution. This behaviour has been attributed to two factors related to the milling process: first, the high ζ-Potential found in the particles, which enhances electrostatic repulsion. The second factor is the significant decrease of saturation magnetization of the milled particles with alumina in comparison with the values of the commercial nZVI particles, leading to a reduction in magnetic interparticle interaction. This decrease may be related to the introduction of a significant carbon content in the iron particles (0.65–1.35%wt, depending on the sample) and the presence of a highly deformed nanostructure.