nZVI Particles Research Articles

Assessment of different iron species as activators of S2O82- and HSO5- for inactivation of wild bacteria strains

This work assesses the potential activation of peroxymonosulfate (PMS, HSO5−) and persulfate (PS, S2O82−) by different homogeneous iron species, FeSO4 and Fe(III)-citrate and heterogeneous Fe2O3 and nano zero valent iron particles (nZVI), to generate sulfate radicals for inactivation of wild bacteria strains (Escherichia coli and Enterococcus sp.) spiked in simulated wastewater effluents. The effectiveness of each iron source as activator was studied in combination with UV-A radiation at natural pH of water (≈ 7.2) using millimolar doses of oxidants (0.5 mM) at different oxidant:iron molar ratio (1:1 and 1:2). In all cases, the addition of iron enhanced the efficiency of the treatments compared to those carried out without it (PMS/UV-A and PS/UV-A); however, significant differences were evidenced depending on the type of bacteria, oxidant and iron specie. For instance, Escherichia coli was reduced (5-log) below the limit of detection (1 CFU/mL) within 2–15 min by activation of PMS and PS with all the iron species evaluated By contrast, under analogous operating conditions the efficiency was notably lower for Enterococcus sp. In this case, it is worth mentioning the notable efficiency through the use of Fe(III)-citrate, which allowed to attained a 3.50-log removal of Enterococcus sp. after 90 min, in contrast to the low reduction (1.8-log) attained with FeSO4. On the other hand, heterogeneous iron species showed an efficiency for bacteria inactivation comparable in most cases to that of homogeneous iron sources. Taking into consideration the potential advantages of heterogeneous catalysts, as for example the recovery and reuse of the catalyst thus reducing the operating costs, the obtained results are encouraging. For instance, E.coli population was removed below the detection limit (5-log) in less than 5 min with both Fe2O3 and ZVI, whereas a 2-log decrease of Enterococcus sp. was attained after 90 min of treatment, even without PMS. Finally, it was assessed the recovery and re-use of ZVI particles. According to X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) analysis, the reaction conditions induced a progressive fading of the core-shell structure of nZVI particles, with a decrease of the efficiency for bacteria inactivation in subsequent uses. As an example, E.coli is reduced in 5-log in 15 min in the first use, and 4.70-log in 90 min with the third use of ZVI.

Effect of Hydrogen Nutrition Denitrifying Bacteria on Nanoscale Zero-Valent Iron Settlement

Nanoscale zero-valent iron (nZVI) particles has an extremely small size and can be suspended in groundwater for long periods of time to remove contaminants. However, more and more experimental results show that the migration performance of nZVI particles in groundwater is far lower than expected, and it is difficult to meet the actual needs of in-situ remediation. In order to study the effect of hydrogenotrophic denitrifying bacteria on Nano-iron, the sedimentation test was used as the main research method to discuss the demonstration. The experimental results showed that within the pure water system and in the culture solution system, the sedimentation rate of Nano-iron was decreased after adding bacteria. As the amount of bacteria in the system increases, the sedimentation rate of Nano-iron tends to decrease. When the amount of bacteria reaches a certain amount, it will have a saturating effect on the sedimentation effect of Nano-iron. XRD spectra showed that Fe3O4 and Fe2O3 were the main iron oxides in the initial oxidation, while Fe2O3, Fe3O4 and Fe2O3 were obtained in the final time of sedimentation. Amorphous 5-FeOOH (corrosion product of zero-valent iron in pure water) replaces Fe2O3 and Fe3O4 as major corrosion products after the addition of bacterial reaction.

Effective removal of Cr(VI) by attapulgite-supported nanoscale zero-valent iron from aqueous solution: Enhanced adsorption and crystallization

The attapulgite supported nanoscale zero-valent iron composite (AT-nZVI) was synthesized and used for Cr(VI) removal. X-ray diffraction (XRD) and transmission electron microscope (TEM) indicated that nZVI particles were well distributed and immobilized on the attapulgite surface. Batch experiments of Cr(VI) removal were conducted at varying mass ratios, initial Cr(VI) concentrations and kinetics. The results indicated that the removal efficiency of Cr(VI) by AT-nZVI approaches 90.6%, being greater than that by non-supported nZVI (62.9%). The removal kinetics could be more accurately explained using pseudo second order kinetics model. The composite exhibited a synergistic interaction instead of simple mixture of AT and nZVI. Reduction was the dominant mechanism at low concentrations as opposed to adsorption at high concentrations. FeCr2O4 was the main reduction product by AT-nZVI, which was attributed to the reduction of Cr(VI) by nZVI and co-precipitation of CrFe oxides on the surface of AT. In the meantime, Fe(II) ion contributed to 64% for the Cr(VI) removal, which resulted from the dissolution of nZVI during the removal process. From the analysis of XRD and XPS results, the crystallization of FeCr2O4 is believed to be formed easily after the reaction of the AT-nZVI composite with Cr(VI) which is more stable and greatly reduce the risk of secondary pollution compared with nZVI. The introduction of AT enhanced adsorption of Cr(VI) and crystallization of the products. The above results suggested that AT-nZVI could be a promising remediation material for Cr(VI)-contaminated groundwater.

Modification of the Thomas model for predicting unsymmetrical breakthrough curves using an adaptive neural-based fuzzy inference system.

The Thomas equation is a popular model that has been widely used to predict breakthrough curves (BTCs) when describing the dynamic adsorption of different pollutants in a fixed-bed column system. However, BTCs commonly exhibit unsymmetrical patterns that cannot be predicted using empirical equations such as the Thomas model. Fortunately, adaptive neural-based fuzzy inference systems (ANFISs) can be used to model complex patterns found in adsorption processes in a fixed-bed column system. Consequently, a new hybrid model merging Thomas and an ANFIS was introduced to estimate the performance of BTCs, which were obtained for Cd(II) ion adsorption on ostrich bone ash-supported nanoscale zero-valent iron (nZVI). The results obtained showed that the fair performance of the Thomas model (NRMSE = 27.6% and Ef = 64.6%) improved to excellent (NRMSE = 3.8% and Ef = 93.8%) due to the unique strength of ANFISs in nonlinear modeling. The sensitivity analysis indicated that the initial solution pH was a more significant input variable influencing the hybrid model than the other operational factors. This approach proves the potential of this hybrid method to predict BTCs for the dynamic adsorption of Cd(II) ions by ostrich bone ash-supported nZVI particles.

Characterization of nZVI nanoparticles functionalized by EDTA and dipicolinic acid: a comparative study of metal ion removal from aqueous solutions.

The simultaneous adsorption of metal ions on bare and functionalized zero-valent iron nanoparticles (nZVI) from aqueous solution was tested using inductively coupled plasma optical emission spectrometry (ICP-OES). The nanomaterials were synthetized using borohydride reduction of iron salt followed by addition of EDTA and pyridine-2,6-dicarboxylic acid (dipicolinic acid, PDCA) in different molar ratios. Functionalized materials were characterized by FT-IR, XRD and SEM-EDS methods. The ligand attachment on the particles was confirmed by FT-IR spectroscopy. The formation of a magnetite and feroxyhyte shell on the core of functionalized nanoparticles was confirmed by the XRD study. Transformation of chain-like structures into clusters of nanospheres with smaller diameter size was observed from SEM study of EDTA-nVZI particles. The average diameter of bare nZVI particles comprised 115 nm, while EDTA functionalization resulted in an average diameter of 22 and 35 nm. The PDCA-nZVI particles obtained with the molar ratio of Fe : PDCA = 1 : 1 retain the chain-like structure with enlargement of the average particle diameter to 267 nm. SEM study of PDCA-nZVI particles that were produced using the ratio Fe : PDCA = 2 : 1 have demonstrated the unique property of elongation into ellipsoidal forms of reduced dimensions (a = 61 nm; b = 28 nm). The simultaneous metal ion removal from aqueous solution was the most efficient in the case of bare nZVI particles (91–97%). EDTA functionalization was found to be highly selective for Cu and Cr removal (95%), while PDCA functionalization shows selective adsorption of Cu, Cr and V in an aqueous medium (93%). Iron nanoparticles functionalized with PDCA in both of the used ratios showed more efficient metal ion adsorption in the case when smaller ellipsoidal particles were formed.

Effects of geochemical conditions, surface modification, and arsenic (As) loadings on As release from As-loaded nano zero-valent iron in simulated groundwater

This manuscript makes a significant research impact regarding the fate of As-loaded nZVI particles under different geochemical conditions of groundwater downstream.

A novel biochar supported CMC stabilized nano zero-valent iron composite for hexavalent chromium removal from water

In this study, novel biochar supported nano-scale zero-valent iron (biochar-CMC-nZVI) stabilized by carboxymethyl cellulose (CMC) was developed and used for the removal of hexavalent chromium (Cr(VI) from aqueous solution. With the stabilization of CMC, nZVI particles (about 80 nm) were effectively dispersed onto the surface of biochar, which inhibited the aggregation of nZVI and resulted in the smaller particle size of nZVI on the surface of biochar. The results showed that the specific surface area of the composite was 11.1 m2/g, lower than that of pristine biochar. The basic element composition was C, O, and Fe with a large number of oxygen-containing functional groups (−COOH, OH, and OCO) observed on the surface. Cr(VI) was reduced to Cr(III) by the composite material, mainly due to the reduction of nZVI on the biochar surface. Upon reaction with Cr(VI), CrxFe1-x(OH)3 and FexCryO4 were deposited on the surface of biochar-CMC-nZVI composite. Electrostatic attraction, reduction, and surface complexation were the dominant removal mechanisms. The results showed that the 100 mg/L Cr(VI) could be removed completely by biochar-CMC-nZVI within 18 h, at a dosage of 1.25 g/L and an initial pH of 5.6. Cr(VI) removal by biochar-CMC-nZVI was favored by lower pH. The pseudo-second-order kinetic model and the Langmuir isothermal adsorption model fitted well with the sorption kinetic and isotherm data, indicated Cr(VI) adsorption mechanism was a chemisorption based multi-layer adsorption. The present study demonstrated the promise of biochar-CMC-nZVI composite as a low-cost, “green”, and effective sorbent for removal of Cr(VI) in the environment.

Transport of the arsenic (As)-loaded nano zero-valent iron in groundwater-saturated sand columns: Roles of surface modification and As loading

In this study, the effects of surface modification of nZVI and arsenic (As) loading on the mobility of the three types of As-loaded nZVI (As-loaded pristine, chitosan-modified and polyaniline-modified nZVI) in quartz sand-packed columns were investigated. Breakthrough curves and retention profiles for the three types of As-loaded nZVI were analyzed by the Tufenkji-Elimelech equations and the HYDRUS-1D model. The mobility of both types of As-loaded modified nZVI was higher than the As-loaded pristine nZVI at both low and high As loadings. Compared to low As loading, the mobility of the three types of As-loaded nZVI was higher at high As loading. The values of the calculated and the fitted retention parameters of the three As-loaded nZVI were lower when As loading was higher or nZVI was modified, which were in line with the experimental column findings. The mechanisms of As-loaded nZVI transport were probably due to ripening and sedimentation. The As in the effluent was mainly from the As-loaded nZVI particles when nZVI was detected and was from the As release when no nZVI was detectable. It was evident that the mobility of the three types of As-loaded nZVI particles were severely limited (the maximum transport distance was less than 60 cm), regardless of surface modification and As loading. Therefore, the As release from the As-loaded nZVI could cause potentially wide pollution and should be paid more attention regarding to the application of nZVI in As remediation.

Activated carbon supported nanoscale zero-valent iron composite: Aspects of surface structure and composition

Abstract Investigations relevant to the influences of AC support and conditions on the surface structure and composition were not reported previously. The present work synthesized a series of NZVI/AC composites using a liquid phase reduction method at a BH4− to Fe2+ molar ratio of 2:1, 4:1, 6:1, and 8:1 (designated as NZVI/AC-1, NZVI/AC-2, NZVI/AC-3, and NZVI/AC-4, respectively), which were subsequently characterized by various techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS) analysis. It was demonstrated that the amorphous NZVI partially doping with Fe3O4 was immobilized in NZVI/AC-1 sample. The surface structure of the NZVI/AC samples was divided into three types: needle-like shape, interconnected nanoparticles (∼30 nm) in or close to the pores of the AC support (self-assembling growth), and uniformly dispersed nanoparticles (20–30 nm) on the AC surface plane (individual NZVI nanospheres growth). Based on TEM images, NZVI particles found in or close to the pores of AC support were transformed from a needle-like shape to chain-like nanospheres as the molar ratio of BH4− to Fe2+ was increased from 2:1 to 8:1. Furthermore, the amount of Fe(OH)3 in the surface oxides increased along with decline of γ-FeOOH and other iron oxides as the molar ratio of BH4− to Fe2+ was increased. Meanwhile, Pb(II) removal tests indicated that NZVI/AC-4 sample afforded the highest Pb(II) removal efficiency. In summary, the small particle size and low extent of surface oxidation of AC-supported NZVI particles facilitate the intrinsic reactivity in decontaminations.

Ligand-mediated contaminant degradation by bare and carboxymethyl cellulose-coated bimetallic palladium-zero valent iron nanoparticles in high salinity environments

The application of nanoscale zero-valent iron (nZVI) for the degradation of contaminants has been extensively investigated, however, few studies have focused on degradation in high salinity environments. In this study, the ability of bare and carboxymethyl cellulose (CMC)-coated bimetallic Pd-nZVI particles to degrade 33′44′-tetrachlorobiphenyl in high saline water (SW) is examined with particular attention given to the effects of ethylenediaminetetraacetic acid (EDTA) on the rate of degradation. EDTA enhances the reactivity of Pd-nZVI in SW, with evidence provided to link this to the removal of the passivating layer. Additionally, a conceptual model is proposed which provides a quantitative description of the removal of these iron oxide layers in the presence of EDTA. An optimum EDTA to bare Pd-nZVI molar ratio of 0.1 exists, with insufficient EDTA unable to remove the passivating layer whilst excess EDTA results in Fe loss and enhanced agglomeration due to magnetic attraction of the bare Fe(0) particles. In contrast, CMC-coating of Pd-nZVI assemblages actually impedes degradation, despite the coated particles displaying a smaller average size compared to uncoated particles, with even the presence of EDTA in this case not significantly improving degradation. The reduced reactivity in the presence of CMC is primarily attributed to the effect of CMC on the association of Pd with nZVI particles. In particular, the presence of CMC reduced the total amount of Pd incorporated with the stabilized particles compared to the non-stabilized particles. Additionally, the presence of CMC results in less Pd present in its reactive zero-valent oxidation state.

Reduced expression of iron transport and homeostasis genes in Pseudomonas fluorescens during iron uptake from nanoscale iron

Plant growth-promoting rhizobacteria (PGPR) have beneficial effects on the host plant that include acquisition of nutrients such as iron (Fe). In this study, the impact of varying concentrations of nanoscale zero-valent iron (NZVI, 1, 2 and 5 g L−1) on a PGPR, Pseudomonas fluorescens' viability, growth and production of siderophores was investigated. Microscale zero-valent iron (MZVI) particles were also included in this study to determine and compare the effects of particle size on Fe acquisition and use by Pseudomonas fluorescens. Siderophores chelate insoluble forms of Fe that are then rendered bioavailable to P. fluorescens as well as some plants. This research indicates that the Fe species derived from lower concentrations of NZVI additions (1 g L−1) are bioavailable and can be utilized as a nutrient by P. fluorescens without the bacteria producing siderophores, an energy intensive process. Also, NZVI application as a fertilizer has promise for better utilization of Fe by plants. P. fluorescens colony forming units (log10 CFU mL−1) growth in cultures containing 1 g L−1 NZVI were significantly higher exceeded (14 units) than those grown without NZVI additions (13 units). The majority of P. fluorescens cells treated with 2 and 5 g L−1 were nonviable and produced limited colony forming units (4 units). The effects of NZVI on siderophore production by P. fluorescens were assessed using chrome azurol S (CAS) plates and real time quantitative reverse transcription PCR (qRT-PCR). Further, expression of genes involved in Fe utilization [putative pvdS (PFL 4190) and a bacterioferritin-associated ferredoxin gene (PFL 4858)] were targeted using real time quantitative reverse transcription PCR (qRT-PCR). Expression of both genes was below detection limits in cultures exposed to NZVI but measurable in MZVI and control treatments, again indicating potential ease in uptake of Fe by P. fluorescens from NZVI. Transmission electron microscopy (TEM) revealed the presence of NZVI particles on the exterior and interior of cells; energy dispersive X-ray spectroscopy (EDS) verified that the material was derived from NZVI and that Fe concentrations were higher in the interior of cells exposed to 1 g L−1 NZVI compared to the control. The research findings from this study indicate that NZVI has the potential to accumulate in plant growth-promoting rhizobacteria and affect the growth of organisms in environments like the rhizobiome which may affect plant growth positively. This research opens up opportunities for future studies to determine the effects of Fe and other nutrients and micronutrients derived from nanomaterials, particularly in oligotrophic systems.

Optimization of azo printing dye removal with oak leaves-nZVI/H2O2 system using statistically designed experiment

The paper investigates the potential use of nano zero-valent iron (nZVI) particles as a cheap, natural and effective catalyst in the Fenton-like system for the removal of water-based Magenta flexographic dye from aqueous solution. The functional nZVI was successfully synthesized within an environmentally friendly method, by using the natural product extract, oak leaves (OAK-nZVI). The process of Magenta removal was optimized using statistically designed experiment. The influence of four quantitative parameters on decolorization efficiency was investigated: initial dye concentration (20–180 mgL-1), OAK- nZVI dosage (0.75–60 mgL-1), H2O2 concentration (1–11 mM) and pH value (2–10). The results of statistical analysis show that OAK-nZVI dosage and pH significantly contribute to the decolorization efficiency, while the concentration of H2O2 has a significant influence on their impact. The optimization yielded highest removal efficiency of 91.95% under following conditions: initial dye concentration of 180 mgL−1, OAK-nZVI dosage of 60 mgL−1, H2O2 concentration of 11 mM and pH value 2. Optimization results were experimentally verified. Treatment of real effluent under optimized experimental conditions resulted within 84.06% Magenta removal after a reaction time of 60 min. The absorption spectra of Magenta dye clearly indicate the changes in the molecular structure in the form of the destruction of azo bond in the chromophore, leading to the decolorization of dye solution. Based on the GC–MS analysis, the mechanism for Fenton-like oxidation of Magenta was proposed.

Activated carbon impregnated by zero-valent iron nanoparticles (AC/nZVI) optimized for simultaneous adsorption and reduction of aqueous hexavalent chromium: Material characterizations and kinetic studies

Nano-scale zero valent iron (nZVI) particles are one of the efficient materials for water treatment. However, their tendency for agglomeration is one of the major reported drawbacks. In this study, nZVI particles were immobilized onto activated carbon (AC/nZVI) using a two-step synthesis procedure and were applied for simultaneous adsorption and reduction of hexavalent chromium (Cr(VI)) from aqueous solutions. Synthesized AC/nZVI was characterized by SEM, EDS, XRD, XPS, and the Tafel corrosion test. The effects of varying annealing temperatures and times in the first synthesis step were investigated by examining crystal structure changes in the final AC/nZVI samples using XRD, and by running Cr(VI) removal batch experiments. Consequently, the best annealing conditions that provided the AC/nZVI composite with the greatest amount of Cr(VI) removal was determined. The Cr(VI) removal experiments showed that the optimized AC/nZVI was significantly superior than virgin AC applied under the same conditions. A pseudo-second-order model was found to be a good fit for both the AC and AC/nZVI data, showing that Cr(VI) removal rate was 2.2 times faster when using AC/nZVI compared to AC (k′2AC/nZVI = 0.363 g mg−1 h−1 vs. k′2AC = 0.164 g mg−1 h−1). Weber and Boyd kinetics models were used to study adsorbate diffusion in AC and AC/nZVI. Isotherm studies revealed that both Freundlich and Langmuir isotherms could describe the AC data, while the Freundlich model was well suited for AC/nZVI. Comparing the constants of the Freundlich models, AC/nZVI showed 33-times higher adsorption capacity and a greater affinity for Cr(VI) than did AC. Reusability of AC/nZVI for Cr(VI) treatment was assessed by regenerating the adsorbent and indicated that the material maintained a 68% removal efficiency after five cycles.

Remediation of Contaminated Soil and Groundwater Using Nanoscale Zero-Valent Iron (nZVI) Coupled with Anaerobic Bioremediation: A Review

Background: Nanoscale zero valent iron (nZVI) is one of the most commonly used nanomaterials for soil and groundwater remediation because of its high reactivity and effective contaminant removal rate. Objective: This paper reviews the methods of nZVI syntheses and effect of nZVI application on contaminants removal, environmental conditions, and microbial growth when anaerobic bioremediation is used for polluted site restoration. Application: Dispersants have been applied to minimize the aggregation of nZVI particles and enhance its migration and influence zone. nZVI has also been applied to enhance the in situ site remediation process. Although there are advantages to combine the nZVI with bioremediation systems, the possible influences caused by the nZVI application contain changes of environmental conditions including the adverse effects on microbial species and diversity. The patents related to the designs of combining nZVI and different types of organic substrates for bioremediation enhancement are summarized in this paper. Future Study: Toxicity evaluation and risk assessment are necessities to minimize the impact of nZVI application on environments and ecosystems. Keywords: Nanoscale zero-valent iron (nZVI), reductive dechlorination, anaerobic bioremediation, toxicity, contaminated soil, hydrophobic modifiers.

Remediation of Polychlorinated Biphenyls (PCBs) in Contaminated Soils and Sediment: State of Knowledge and Perspectives

Polychlorinated biphenyls (PCBs) are one of the persistent organic pollutants (POPs) used worldwide between the 1930s and 1980s. Many PCBs can still be found in the environment such as in soils and sediments, even though their use has been heavily restricted. This review summarizes the most frequent remediation solutions including, phytoremediation, microbial degradation, dehalogenation by chemical reagent, and PCBs removal by activated carbon. New insights that emerged from recent studies of PCBs remediation including supercritical water oxidation, ultrasonic radiation, bimetallic systems, nanoscale zero-valent iron based reductive dehalogenation and biofilm covered activated carbon, electrokinetic remediation, and nZVI particles in combination with a second metal are overviewed. Some of these methods are still in the initial development stage thereby requiring further research attention. In addition, the advantages and disadvantages of each general treatment strategy and promising technology for PCBs remediation are discussed and compared. There is no well-developed single technology, although various possible technologies have been suggested. Therefore, the possibility of using combined technologies for PCB remediation is also here investigated. It is hoped that this present paper can provide a basic framework and a more profound prospect to select successful PCB remediation strategies or combined technologies.

The elucidation of surrounding alginate gels on the pollutants degradation by entrapped nanoscale zero-valent iron.

The adsorption capacity of calcium alginate (Ca-alginate) beads was evaluated by measuring the removal of three organic compounds with different charges (malachite green, p-chlophenol and methyl orange). The diffusion was investigated in Ca-alginate hydrogel as a function of solute charge. It was found that an increased electrostatic attraction between the hydrogel and solute would improve the mobility of solute and hence enhance its adsorption efficiency. The degradation kinetics of charged pollutants by Ca-alginate with NZVI entrapped (NZVI-alginate) beads was compared to that of bare NZVI and the data followed a pseudo-first-order kinetic model. Negatively charged Ca-alginate hydrogel strongly adsorbed positively charged pollutant, which led to an enhancement in degradation rate. However, the degradation efficiency of neutral and negatively charged pollutants by NZVI-alginate was comparable with that by bare NZVI. Thus, the degradation ability of NZVI-alginate was related with the diffusion and adsorption behavior of solutes in Ca-alginate hydrogel. The experimental results showed that the free calcium ions containing in Ca-alginate had a significant impact on the adsorption and degradation behaviors of positively charged pollutant, but those of neutral and negatively charged pollutants were only moderately affected. With the dispersity of NZVI particles in beads (1:1-1:4, w/w) increasing, the degradation efficiency of malachite green was improved, whereas further increase of NZVI dispersity (1:6, w/w) brought about a depressed degradation.

Zero-valent iron nanoparticles for methylene blue removal from aqueous solutions and textile wastewater treatment, with cost estimation.

Nanoscale zero-valent iron (nZVI) particles were investigated for the removal of methylene blue (MB) from aqueous solutions and the treatment of textile industry effluents. The nZVI material was characterized by XRD, TEM, EDS, FTIR, and SEM. It was demonstrated that several functional groups such as C-H, C = C, C-C, and C-O contributed to MB reduction. At initial MB concentration of 70 mg/L, the optimum pH was 6, achieving a removal efficiency of 72.1% using an nZVI dosage of 10 g/L, stirring rate of 150 rpm, and temperature of 30 °C within 30 min. The adsorption isotherm was described by the Langmuir model with monolayer coverage of 5.53 mg/g, and the Freundlich equation with multilayer adsorption capacity of 1.59 (mg/g)·(L/mg)1/n. The removal mechanisms of MB included reduction into colorless leuco-MB, precipitation as Fe(II)-MB, adsorption as ZVI-MB or FeOOH-MB, and/or degradation using •OH radicals. The synthesized nZVI particles were applied to reduce various organic and inorganic compounds, as well as heavy metal ions from real textile wastewater samples. The removal efficiencies of COD, BOD, TN, TP, Cu2+, Zn2+, and Pb2+ reached up to 91.9%, 87.5%, 65.2%, 78.1%, 100.0%, 29.6%, and 99.0%, respectively. The treatment cost of 1 m3 of textile wastewater was estimated as 1.66 $USD.

Enhanced degradation of trichloroethylene in oxidative environment by nZVI/PDA functionalized rGO catalyst

Nano zero-valent iron (nZVI) particles with higher reactivity have been recognized as more efficient catalysts than Fe(II) for the groundwater remediation. The rapid emergence of novel catalyst supports efficiently prevent the rapid aggregation of nZVI and further improve catalytic reactivity. However, the lack of ability to avoid the potential oxidation of bare nZVI-support structure in air environment hinders its wider application in the actual contaminated sites. In this study, nZVI on reduced graphene oxide (rGO) functionalized by polydopamine (PDA) (nZVI-PDA@rGO) was synthesized successfully and applied into sodium persulfate (SPS), potassium monopersulfate (PMS) and H2O2 oxidative environments to remove trichloroethylene (TCE). For comparison, nZVI supported on solely rGO was prepared. The XRD test displayed the stronger stability of α-Fe(0) in nZVI-PDA@rGO catalyst against oxidation exposed to air. Compared with nZVI-rGO, a core shell structure of nZVI-PDA@rGO was observed in TEM image obviously. The dosage tests showed nZVI-PDA@rGO had a better catalytic reactivity than nZVI-rGO for TCE removal at lower catalyst and oxidant dosages, i.e. PMS dosage: 0.3 mM, catalyst dosage: 50 mg L−1, TCE removal: 45.0% (nZVI-rGO) up to 99.6% (nZVI-PDA@rGO). TCE removal mechanisms were revealed through radical scavenger tests, demonstrating sulfate radicals played more important role in nZVI-PDA@rGO catalyzed-oxidant systems.

Improvement of the chemical synthesis efficiency of nano-scale zero-valent iron particles

This study investigates the synthesis conditions of nano-scale zero-valent iron (nZVI) formed by the chemical reduction method via an optimization process in order to enhance the nZVI’s reactivity. The properties of nZVI particles were characterized by transmission electron microscopy, laser diffraction particle size analyzer and X-ray diffraction. The performance of nZVI was evaluated using the nitrate and phosphorus solutions. The optimization results for the effective variables, namely concentration, delivery rate and liquid volume of sodium borohydride (NaBH4), precursor concentration (FeCl3), reaction temperature, mixing speed, pH and aging time were demonstrated the improvement in nZVI reactivity. The results confirm that nZVI proved high removal efficiency along with the lower particle size at NaBH4 concentration 16 g/L. The feeding rate of NaBH4 at 40 mL/min can effectively reduce the particle size and increase the nZVI reactivity. Increasing the NaBH4 liquid volume greatly improved the reactivity. Reduction of reaction aging time to 5 min and employing the acidic reaction medium of 6 pH greatly improved the nZVI reactivity. The highest mixing speed of 1000 rpm enhanced the phosphorus adsorption efficiency. However, high nitrate reduction was observed at 500 rpm. Increasing the reaction temperature resulted in decreasing the average particle size and the highest reactivity was achieved at 90 °C. nZVI reactivity significantly was improved in the direction of low precursor concentration, and the highest efficiency was gained at 20 mg/L. In conclusion, the optimized parameters enhanced the overall efficiency of nZVI of nitrate reduction and phosphorus adsorption by 27% and 9.5% respectively.

Immobilization, enrichment and recycling of Cr(VI) from wastewater using a red mud/carbon material to produce the valuable chromite (FeCr2O4)

It is a long-term goal to develop an inexpensive, eco-friendly, and effective approach for the purification of wastewater containing heavy metal elements such as Cr(VI). In this study, a red mud (RM)/carbon material with dispersed nano zero-valent iron (nZVI) is fabricated to collect, immobilize, enrich, and recycle Cr(VI) from wastewater by repeatedly using the spent sample after carbothermal regeneration. The regenerated RM/carbon sample maintains an excellent removal efficiency of Cr(VI), and the collected Cr species can be firmly immobilized and gradually accumulated through forming highly stable chromite (FeCr2O4) with the assistance of carbothermal treatment. A detailed study of structure–function relationships reveals that Cr(VI) in wastewater is first reduced to Cr(III) by nZVI, and is then collected on RM/carbon in the form of Cr-Fe hydroxide species, which is converted to a stable FeCr2O4 phase immobilized on the regenerated RM/carbon by carbothermal treatment. Moreover, the repeated use/regeneration process facilitates the gradual growth, separation, and exposure of nZVI particles on the external surface of the RM/carbon, which improves its reaction activity with H+ and Cr(VI). The elevated activity of nZVI as well as the high stability of the accumulated FeCr2O4 account for the excellent cycle efficiency of Cr(VI) removal. Nearly all of the nZVI (97.8%) in RM/carbon can be utilized to produce FeCr2O4 with more than 45 wt% Cr2O3 content in the final calcined ash, which can be recycled as a valuable substitute for natural chromite ore in the steel industry with no secondary pollution. The demonstrated superiority of the material and process offer promising technological, economic and environmental benefits for the simultaneous utilization of chromium wastewater and RM solid wastes.