Modified Nanoscale Zero-valent Iron Research Articles

Enhanced Oxidative and Adsorptive Removal of Diclofenac in Heterogeneous Fenton-like Reaction with Sulfide Modified Nanoscale Zerovalent Iron.

Sulfidation of nanoscale zerovalent iron (nZVI) has shown some fundamental improvements on reactivity and selectivity toward pollutants in dissolved-oxygen (DO)-stimulated Fenton-like reaction systems (DO/S-nZVI system). However, the pristine microstructure of sulfide-modified nanoscale zerovalent iron (S-nZVI) remains uncovered. In addition, the relationship between pollutant removal and the oxidation of the S-nZVI is largely unknown. The present study confirms that sulfidation not only imparts sulfide and sulfate groups onto the surface of the nanoparticle (both on the oxide shell and on flake-like structures) but also introduces sulfur into the Fe(0) core region. Sulfidation greatly inhibits the four-electron transfer pathway between Fe(0) and oxygen but facilitates the electron transfer from Fe(0) to surface-bound Fe(III) and consecutive single-electron transfer for the generation of H2O2 and hydroxyl radical. In the DO/S-nZVI system, slight sulfidation (S/Fe molar ratio = 0.1) is able to nearly double the oxidative removal efficacy of diclofenac (DCF) (from 17.8 to 34.2%), whereas moderate degree of sulfidation (S/Fe molar ratio = 0.3) significantly enhances both oxidation and adsorption of DCF. Furthermore, on the basis of the oxidation model of S-nZVI, the DCF removal process can be divided into two steps, which are well modeled by parabolic and logarithmic law separately. This study bridges the knowledge gap between pollutant removal and the oxidation process of chemically modified iron-based nanomaterials.

Sensitive determination of bisphenol A, 4-nonylphenol and 4-octylphenol by magnetic solid phase extraction with Fe@MgAl-LDH magnetic nanoparticles from environmental water samples

Abstract Mg-Al-layered double hydroxide (Mg-Al-LDH) modified nanoscale zero-valent iron (NZVI) (Fe@MgAl-LDH) was firstly synthesized and characterized by several techniques. The results showed that the layered double hydroxides were coated on the surface of nanoscale zero-valent iron particles. This new material exhibited good adsorption for bisphenol A, 4-octylphenol and 4-nonylphenol from water samples. Based on these, a sensitive method was developed for the extraction and preconcentration of bisphenol A, 4-octylphenol and 4-nonylphenol using magnetic Fe@MgAl-LDH nanoparticles as the solid phase extraction adsorbents prior to high performance liquid chromatography coupled with variable wavelength detection. Under the optimal conditions, linear responses were achieved in the range of 0.5–200 μg L −1 with the correlation coefficients (r) above 0.999. The detection limits of three analytes were in the range of 0.24–0.34 μg L −1 , and precisions were all below 2.5% (n = 6). The proposed method was evaluated with real water samples and the excellent spiked recoveries in the range of 96.0–99.3% were achieved.

Electromagnetic induction of nanoscale zerovalent iron particles accelerates the degradation of chlorinated dense non-aqueous phase liquid: Proof of concept

In this study, a novel electromagnetically enhanced treatment concept is proposed for in situ remediation of a source zone of chlorinated dense non-aqueous phase liquid (DNAPL) that is slowly dissolved, causing contaminated groundwater for centuries. Here, we used polystyrene sulfonate (PSS)-modified nanoscale zerovalent iron (NZVI) particles (ferromagnetic) in combination with a low frequency (LF) (150 kHz) AC electromagnetic field (EMF) to accelerate the degradation of the DNAPLs via enhanced dissolution and reductive dechlorination. Trichloroethylene (TCE) and tetrachloroethylene (PCE) were used in a bench-scaled evaluation. The PSS-modified NZVI successfully targeted the DNAPL/water interface, as evidenced by the Pickering emulsion formation. Dechlorination of TCE- and PCE-DNAPL was measured by quantifying the by-product formation (acetylene, ethene, and ethane). Without magnetic induction heating (MIH) by LF EMF, PSS-modified NZVI transformed TCE- and PCE-DNAPL to ethene and ethane at the rate constants of 12.19 × 10−3 and 1.00 × 10−3 μmol/h/m2, respectively, following pseudo zero-order reactions. However, four MIH cycles of PSS-NZVI increased the temperature up to 87 °C and increased the rate constants of TCE-DNAPL and PCE-DNAPL up to 14.58 and 58.01 times, respectively, in comparison to the dechlorination rate without MIH. Theoretical analysis suggested that the MIH of the PSS-modified NZVI enhanced the dechlorination of TCE- and PCE-DNAPL via the combination of the enhanced thermal dissolution of DNAPL, the effect of increasing the temperature on the rate constant (the Arrhenius equation), and the accelerated NZVI corrosion. Nevertheless, the effect of the Arrhenius equation was dominant. For the first time, this proof-of-concept study reveals the potential for using polyelectrolyte-modified NZVI coupled with LF EMF as a combined remediation technique for increasing the rate and completeness of in situ chlorinated DNAPL source remediation.

Immobilization of Cd in river sediments by sodium alginate modified nanoscale zero-valent iron: Impact on enzyme activities and microbial community diversity

This paper investigated how sodium alginate (SA)-modified nanoscale zero-valent iron (NZVI), play a constructive role in the remediation of cadmium (Cd) contaminated river sediments. The changes of the fraction of Cd, enzyme activities (urease, catalase, dehydrogenase) and bacterial community structures with the treatment by SNZVI were observed. The sequential extraction experiments demonstrated that most mobile fractions of Cd were transformed into residues (the maximum residual percentage of Cd increases from 15.49% to 57.28% after 30 days of incubation at 0.1 wt% SA), with the decrease of bioavailability of Cd. Exclusive of dehydrogenase, the activities of the other two enzymes tested were enhanced with the increase of incubation time, which indicated that dehydrogenase might be inhibited by ferric ions formed from SNZVI whereas no obvious inhibition was found for other enzymes. Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analyses were used for the detection of microbial community changes, and the results showed that SNZVI and NZVI could increase bacterial taxa and improve bacterial abundance. All the experimental findings of this study provide new insights into the potential consequences of SNZVI treatments on the metal Cd immobilization in contaminated river sediments.

Enhancing the reactivity of bimetallic Bi/Fe0 by citric acid for remediation of polluted water

In this study, the environmentally benign citric acid (CA) was utilized to improve the aerobic degradation of 4-chlorophenol (4-CP) over bismuth modified nanoscale zero-valent iron (Bi/Fe0). The characterization results revealed the existence of bismuth covering on the Fe0 surface under zero-valent state. And, the Bi/Fe0-CA+O2 system performed excellent reactivity in degradation of 4-CP due to the generation of reactive oxygen species (ROS), which was confirmed by electron spin resonance (ESR) spectroscopy. After 30min of reaction, 80% of 4-CP was removed using Bi/Fe0-CA+O2 accompanying with high dechlorination rate. The oxidative degradation intermediates were analyzed by HPLC and LC-MS. We found that CA could promote the bismuth-iron system to produce much reactive oxygen species ROS under both aerobic and anaerobic conditions due to its ligand function, which could react with Fe3+ to form a ligand complex (Fe(III)Cit), accompanying with a considerable production of Fe2+ and H2O2. This study provides a new strategy for generating ROS on nZVI and suggests its application for the mineralization of many recalcitrant pollutants.

Reductive immobilization of Re(VII) by graphene modified nanoscale zero-valent iron particles using a plasma technique

Technetium-99 (99Tc), largely produced by nuclear fission of 235U or 239Pu, is a component of radioactive waste. This study focused on a remediation strategy for the reduction of pertechnetate (TcO4-) by studying its chemical analogue rhenium (Re(VII)) to avoid the complication of directly working with radioactive elements. Nanoscale zero-valent iron particles supported on graphene (NZVI/rGOs) from GOs-bound Fe ions were prepared by using a H2/Ar plasma technique and were applied in the reductive immobilization of perrhenate (ReO4-). The experimental results demonstrated that NZVI/rGOs could efficiently remove Re from the aqueous solution, with enhanced reactivity, improved kinetics (50 min to reach equilibrium) and excellent removal capacity (85.77 mg/g). The results of X-ray photoelectron spectroscopy analysis showed that the mechanisms of Re immobilization by NZVI/rGOs included adsorption and reduction, which are significant to the prediction and estimation of the effectiveness of reductive TcO4- by NZVI/rGOs in the natural environment.

Influence of chitosan on modified nanoscale zero-valent iron for arsenate removal

Chitosan-modified nanoscale zero-valent iron (CNZVI) was synthesized for arsenate removal from water. Batch experiments were carried out to examine the influence of weight percent of chitosan loading in the CNZVI, and the initial solution pH including acidic, neutral, and basic conditions. As a result, the arsenate removal rate increased with higher weight percent of chitosan loading, but decreased with higher initial pH. In addition, the efficiencies of CNZVI for arsenate removal did not change significantly for the three investigated pH conditions, when higher percentage of chitosan loading was applied. The results demonstrate that CNZVI has the potential as an effective agent for field arsenic removal.

Removal of Cu2+ ions with 2-phosphonobutane-1,2,4-tricarboxylic acid–modified nanoscale zero-valent iron

Applications of nanoscale zero-valent iron (N-Fe0) and modified Fe0 with 2-phosphonobutane-1,2,4-tricarboxylic acid (P-Fe0) prepared by borohydride reduction for removal of Cu2+ in water are investigated under a variety of experimental conditions. Characterizations with X-ray diffractometer, scanning electron microscopy and transmission electron microscopy confirm that N-Fe0 and P-Fe0 have a core shell structure similarly. The uptake experiments investigated the effects of the dosages of N-Fe0 and P-Fe0, pH and the adsorption kinetics. The results showed that the ratio of removal efficiencies is more than 90% with the condition of initial concentrations of 10.0–70.0 mg/L, pH of 7 at 25 °C and the adsorbent of 0.4 g/L N-Fe0 and P-Fe0. Within the applied conditions, the order rate of Cu2+ adsorption kinetics equation on the N-Fe0 and P-Fe0 was the pseudo-second. According to X-ray photoelectron spectroscopy results, Cu2+ ions were removed primarily via a redox mechanism that resulted in the formation of Cu0 and Cu2O. The contact of N-Fe0 and P-Fe0 with aqueous media caused extensive formation of iron oxide. The research reveals that Cu2+ can be efficiently removed by the means of N-Fe0 and P-Fe0 in solution, and the appropriate factors, involving pH value and the dosages of Fe0, were important keys in the process, and the modified Fe0 will be extensively utilized for the removal of Cu2+ from wastewater.

Degradation of Trichloroethylene Contaminated Soil by Zero-Valent Iron Nanoparticles

Trichloroethylene (TCE) contaminated soil has received extensive attention in the environmental issues. Nanoscale zero-valent iron (NZVI) is considered as an excellent reduction catalyst due to fast degradation of chlorinated solvents. Therefore, this paper aims to evaluate TCE removal from soil by surfactant modified nanoscale zero-valent iron (SNZVI). In this respect, fixed 500 g soil having a diameter range 0.5–1 mm was polluted with 10 mL TCE and put inside glass column of 2.5 cm diameter × 300 cm length. The NZVI solution was prepared from reduction of FeCL3 by NaBH4 and coating with 2.5 g nonionic surfactant (Tween 85) to produce iron nanoparticle concentration of 0.1 g/L. The prepared iron nanoparticle was poured into contaminated soil and left to stir at a constant rate for 24 days. The reductive dechlorination of TCE was measured as a function of increasing chloride ion. It was found that the TCE dechlorination in the presence of iron surfaces displayed pseudo first-order kinetics. The TCE degradation rate constant () is . Also, about 30% of TCE was removed within initial 6 days. The obtained specific rate constant () was and is lower than other studies carried into aqueous phase by about 23 orders of magnitude. Finally, the SNZVI was found to be effective and fully removed to TCE within 456 hours.

Removal of tetracycline from aqueous solutions using polyvinylpyrrolidone (PVP-K30) modified nanoscale zero valent iron

The interactions of tetracycline (TC) with nanoscale zerovalent iron (NZVI) modified by polyvinylpyrrolidone (PVP-K30) were investigated using batch experiments as a function of reactant concentration, pH, temperature, and competitive anions. Transmission electron micrographs (TEM), BET surface area and Zeta (ζ)-potential analyses indicated that the mean particle size was 10–40 nm with a surface area of 36.90 m 2/g, and a iso-electric point of PVP-NZVI was 7.2. The results of X-ray diffraction (XRD) and high-resolution X-ray photoelectron spectroscopy (HR-XPS) of modified nanoscale zerovalent iron (PVP-NZVI) revealed that the iron nanoparticles likely have a core of zero-valent iron (Fe 0), while a shell is largely made of iron oxides. Degradation of TC was strongly dependent on pH and temperature. The presence of silicate and phosphate strongly inhibited the removal of TC, whereas acetate and sulfate only caused slight inhibition. LC–MS analysis of the treated solution showed that the degradation products from TC resulted from the removal of functional groups from the TC ring. The degradation products were detected both in the treated solution (initial pH of 3.0 and 6.5) and on the surface of PVP-NZVI after 4-h interaction, indicating that PVP-NZVI can adsorb both TC and its degradation products.

Development of a Trajectory Model for Predicting Attachment of Submicrometer Particles in Porous Media: Stabilized NZVI as a Case Study

A new trajectory simulation algorithm was developed to describe the efficiency of a single collector (pore) to catch submicrometer particles moving through saturated porous media. A constricted-tube model incorporating the deterministic (interception, hydrodynamic retardation, van der Waals force and gravitational sedimentation), stochastic (Brownian diffusion), and thermodynamic (electrostatic and steric repulsion force) mechanisms was established to predict the transport and deposition of surface modified nanoscale zerovalent iron (NZVI) particles by applying Lagrangian trajectory analytical approach. The simulation results show good agreement with the results predicted by existing energy-barrier-free models except for the particle size less than 100 nm at low approach velocity. The number of realizations per start location could be decreased down to 100 with the simulations still exhibiting acceptable relative standard deviation for engineering purposes. With the consideration of energy barriers, the model successfully describes the breakthrough curve of polymer-modified NZVI in a benchtop soil column as well. The novel simulation scheme can be a useful tool for predicting the behavior of the nanoscale colloidal particles moving through filter beds or saturated soil columns under conditions with repulsion and attraction forces among surfaces.

Aqueous Ethanol modified Nanoscale Zerovalent Iron in Bromate Reduction: Synthesis, Characterization, and Reactivity

Nanoscale zerovalent iron (NZVI) was evaluated for the reduction of bromate that is a highly persistent and carcinogenic oxyhalid formed as an ozonation byproduct during oxidative disinfection in drinking water treatment Solid-phase NZVI with different surface areas was controllably synthesized using a liquid phase reduction. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and a Brunauer-Emmett-Teller (BET) surface area and porosity analyzer were utilized to characterize particle size, surface morphology, surface area, and corrosion layers formed onto NZVI before and afterthe reduction of bromate. Surface area of synthesized NZVI was found to be influenced strongly by ethanol contents during synthesis with a maximum surface area of 67.51 +/- 0.35 m2/g in a 90% aqueous ethanol; additionally, capsule structures of NZVI with amorphous phase, in which tens of particles with diameters of 2-5 nm were packed into an iron oxide/hydroxide layer, were also synthesized using 100% ethanol as a solvent. Subsequent XRD and TEM results revealed that in a 20 min bromate reduction NZVI mostly converted to Fe2O3 and Fe3O4 corrosion products mixed with iron hydroxides. Compared to bromate reduction using microsized ZVI in a pseudo-first-order kinetic model, NZVI enhanced the reduction efficiency following a second-order kinetic model, with observed second-order rate constants (kobs) of 2.57 x 10(-4) to 2.19 x 10(-3) microg(-1) min(-1) L. Humic acid was found to be the most influencing factorto decrease NZVI reactivity in bromate reduction. However, the effect of sonication pretreatment showed that the bromate reduction efficiency could be enhanced by increasing the actual reactive surface area. Our results suggest that application of NZVI is a viable process for bromate reduction in water treatment.