Effect of magnetic field on the zero valent iron induced oxidation reaction

Weak magnetic field and coexisting ions accelerate phenol removal by ZVI/H2O2 system: Their efficiency and mechanism

Human activity and industrial production have led to phenol becoming a significant risk factor. The proper treatment of phenol in wastewater is essential. In this study, the utilization of weak magnetic field (WMF) and zero-valent iron (ZVI) was proposed to activate H2O2 to degrade phenol contaminant. The results show that the weak magnetic field has greatly enhanced the reaction rate of ZVI/H2O2 removal of phenol. The removal rates of phenol by ZVI/H2O2/WMF generally decreased with increasing initial pH and phenol concentrations, and firstly increase and then decrease with increasing Fe0 or H2O2 dosage. When the initial pH is 5.0, ZVI concentration of 0.2 g L-1, H2O2 concentration of 6 mM, and phenol concentration of 100 mg L-1 were used, complete removal of phenol can be achieved within 180 min at 25 °C. The degradation process was consistent with the pseudo-first-order kinetic model when the experimental data was fitted. The ZVI/H2O2/WMF process exhibited a 1.05-2.66-fold enhancement in the removal rate of phenol under various conditions, surpassing its counterpart lacking WMF. It was noticed that the presence of 1-5 mM of Ca2+, Mg2+, Cl-, SO42- ions can significantly enhance the kinetics of phenol removal by ZVI/H2O2 system with or without WMF to 2.22-10.40-fold, but NO3-, CO32-, PO43- inhibited the reaction significantly in the following order: PO43- > CO32- > NO3-. Moreover, pre-magnetization for 3 min could enhance the ZVI/H2O2 process which was valuable in treatment of real wastewater. The hydroxyl radical has been identified as the primary radical species responsible for phenol degradation. The presence of WMF accelerates the corrosion rate of ZVI, thereby promoting the release of Fe2+ ions, which in turn induces an increased production of hydroxyl radicals and facilitates phenol degradation. The compounds hydroquinone, benzoquinone, catechol, maleic acid, and CO2 were identified using GC-MS, and degradation pathways were proposed. Employing WMF in combination with various ions like Ca2+, Mg2+, Cl-, SO42- is a novel method, which can enhance oxidation capacity of ZVI/H2O2 and may lead to economic benefit.

Integrated influence of sulfide modification on the reactivity of nanoscale zero-valent iron towards decabromodiphenyl ether under an electromagnetic field

Individual application of sulfide modification and electromagnetic field (EMF) can enhance the reactivity of nanoscale zero-valent iron (nZVI), yet the potential of both in combination is not clear. This work found that the reactivity of nZVI towards decabromodiphenyl ether was significantly enhanced by the combined effect of sulfidation and EMF. The specific reaction rate constant of nZVI increased by 7 to 10 times. A series of characterization results revealed that the sulfidation level not only affects the inherent reactivity but also the magnetic-induced heating (MIH) and corrosion (MIC) of nZVI. These collectively influence the degradation efficiency of nZVI under EMF. Sulfidation generally diminished the MIH effect. The low degree of sulfidation (S/Fe = 0.1) slightly reduced the MIC effect by 21.4%. However, the high degree of sulfidation (S/Fe = 0.4) led to significantly enhanced MIC effect by 107.1%. For S/Fe = 0.1 and 0.4, the overall enhancement in the reactivity resulting from EMF was alternately dominated by the contributions of MIH and MIC. This work provides valuable insights into the MIH and MIC effects about the sulfidation level of nZVI, which is needed for further exploration and optimization of this combined technology.

Enhanced Degradation of Methyl Orange and Trichloroethylene with PNIPAm-PMMA-Fe/Pd-Functionalized Hollow Fiber Membranes

Trichloroethylene (TCE) is a prominent groundwater pollutant due to its stability, widespread contamination, and negative health effects upon human exposure; thus, an immense need exists for enhanced environmental remediation techniques. Temperature-responsive domains and catalyst incorporation in membrane domains bring significant advantages for toxic organic decontamination. In this study, hollow fiber membranes (HFMs) were functionalized with stimuli-responsive poly-N-isopropylacrylamide (PNIPAm), poly-methyl methacrylate (PMMA), and catalytic zero-valent iron/palladium (Fe/Pd) for heightened reductive degradation of such pollutants, utilizing methyl orange (MO) as a model compound. By utilizing PNIPAm's transition from hydrophilic to hydrophobic expression above the LCST of 32 °C, increased pollutant diffusion and adsorption to the catalyst active sites were achieved. PNIPAm-PMMA hydrogels exhibited 11.5× and 10.8× higher equilibrium adsorption values for MO and TCE, respectively, when transitioning from 23 °C to 40 °C. With dip-coated PNIPAm-PMMA-functionalized HFMs (weight gain: ~15%) containing Fe/Pd nanoparticles (d_p~34.8 nm), surface area-normalized rate constants for batch degradation were determined, resulting in a 30% and 420% increase in degradation efficiency above 32 °C for MO and TCE, respectively, due to enhanced sorption on the hydrophobic PNIPAm domain. Overall, with functionalized membranes containing superior surface area-to-volume ratios and enhanced sorption sites, efficient treatment of high-volume contaminated water can be achieved.

Advances in magnetic field-assisted electrolyte's physicochemical properties and electrokinetic parameters: A case study on the response ability of chloramphenicol on Fe3O4@carbon spheres-based electrochemical nanosensor

Despite the utilization of external magnetic field (MF) in promoting the intrinsic unique features of magnetic nanomaterials in many different applications has been reported, however the origin of MF-dependent electrochemical behaviors as well as the electrochemical response of analytes at the electrode in sensor applications is still not clear. In this report, the influence of MF on the electrolyte's physicochemical properties (polarization, mass transport, charge/electron transfer) and electrode's properties (conductivity, morphology, surface area, interaction, adsorption capability, electrocatalytic ability) was thoroughly investigated. Herein, the working electrode surface was modified with carbon spheres (CSs), magnetic nanoparticles (Fe₃O₄NPs), and their nanocomposites (Fe₃O₄@CSs), respectively. Then, they were directly used to enhance the electrochemical characteristics and response-ability of chloramphenicol (CAP). More interestingly, a series of various kinetic parameters related to the diffusion-controlled process of K₃[Fe(CN)₆]/K₄[Fe(CN)₆)] and the adsorption-controlled process of CAP were calculated at the bare electrode and the modified electrodes with and without the presence of MF. These parameters not only exhibit the crucial role of the modification of electrode surface with the proposed materials but also show positive impacts of the presence of external MF. Besides, the mechanism and hypothesis for the enhancements were proposed and discussed in detail, further demonstrating the development potential of using Fe₃O₄@CS nanocomposites with MF assistant for advanced energy, environmental, and sensor related-applications.

Enhanced dechlorination of trichloroethene by sulfidated microscale zero-valent iron under low-frequency AC electromagnetic field

In this study an electromagnetic heating strategy is proposed for remediation of trichloroethene (TCE) by ball milled, sulfidated microscale zero valent iron (S-mZVI^bm) particles. S-mZVI^bm is ferromagnetic, which generates heat under the application of a low-frequency alternating current electromagnetic field (AC EMF). We found that the temperature reached up to ~120 ℃ during 30-min electromagnetic induction heating of 10 g/L S-mZVI^bm (with S/Fe molar ratio of 0.1), compared with ~55 ℃ and ~80 ℃ for ZVI and ball milled mZVI^bm, respectively. The application of AC EMF accelerated the TCE degradation rate (k_TCE = 5.5 × 10^-1 h^-1) by up to 4-fold without compromising or even enhancing electron efficiency of S-mZVI^bm compared to no-heating. Furthermore, this process halved the generation of chlorinated intermediate, cis-DCE. In contrast, water-bath heating only increased the dechlorination rate 2-fold with unchanged cis-DCE generation and lowered electron efficiency. This is attributed to both rising temperature by induction heating and accelerated ZVI corrosion and surface Fe⁰ exposure caused by AC EMF. In real groundwater, the AC EMF maintained the same promoting effects for TCE dechlorination by S-mZVI^bm. This study shows that combination of filed-scale available AC EMF with S-mZVI^bm provides a promising approach for remediation of chlorinated hydrocarbons in contaminated groundwater.

Electron competition and electron selectivity in abiotic, biotic, and coupled systems for dechlorinating chlorinated aliphatic hydrocarbons in groundwater: A review

Chlorinated aliphatic hydrocarbons (CAHs) have been frequently detected in aquifers in recent years. Owing to the bioaccumulation and toxicity of CAHs, it is essential to explore high-efficiency technologies for their complete dechlorination in groundwater. At present, the most widely used abiotic and biotic remediation technologies are based on zero-valent iron (ZVI) and functional anaerobic bacteria (FAB), respectively. However, the main obstacles to the full potential of both technologies in the field include their lowered efficiencies and increased economic costs due to the co-existence of a variety of natural electron acceptors in the environment, such as dissolved oxygen (DO), nitrate (NO₃^-), sulfate (SO₄^2-), ferric iron (Fe (III)), bicarbonate (HCO₃^-), and even water, which compete for electrons with the target contaminants. Therefore, a clear understanding of the mechanisms governing electron competition and electron selectivity is significant for the accurate evaluation of the effectiveness of both technologies under natural hydrochemical conditions. We collected data from both abiotic and biotic CAH-remediation systems, summarized the dechlorination and undesired reactions in groundwater, discussed the characterization methods and general principles of electron competition, and described strategies to improve electron selectivity in both systems. Furthermore, we reviewed the emerging ZVI-FAB coupled system, which integrates abiotic and biotic processes to enhance dechlorination performance and electron utilization efficiency. Lastly, we propose future research needs to quantitatively understand the electron competition in abiotic, biotic, and coupled systems in more detail and to promote improved electron selectivity in groundwater remediation.

The sequestration of Cr(VI) by zero valent iron under a non-uniform magnetic field: An interfacial dynamic reaction

A non-uniform magnetic field was applied to sequester Cr(VI) with microscale zero-valent iron (ZVI). When the non-uniform magnetic field was applied, the average removal rate of Cr(VI) was increased and the lag phase was shortened with the increasing of magnetic field intensity. The instantaneous rate was fast at the beginning and about 40% of the Cr(VI) was sequestered rapidly when ZVI was added into the magnetic field system. Later, the sequestration rate of Cr(VI) was reduced and remained stable with time until Cr(VI) was removed completely. The instantaneous removal rate was positively correlated with ZVI dosage and the rate per unit mass of ZVI was 0.455 mg/(L·min·gZVI). The constant rate stage was not affected by the initial and the residual concentration of Cr(VI). In the case where no magnetic field was applied, the removal of Cr(VI) is a process in which ZVI is depassivated and its reactivity is restored continuously. The promotion of a magnetic field on the removal of Cr(VI) is mainly due to increasing the role of adsorbed reducing species of Fe²⁺ or Fe⁰ on the ZVI surface. Aging of ZVI under a magnetic field could enhance the release rate of Fe²⁺ in the initial 5 min though the remanence of this kind of ZVI had little effect on the enhancement of the sequestration of Cr(VI).

Simultaneously implement of both weak magnetic field and aeration for ciprofloxacin removal by Fenton-like reaction

This study evaluates the ability of heterogeneous Fenton-like reaction (nano zero-valent iron (NZVI)/H₂O₂) in combination with weak magnetic field (WMF) under continuous oxygen supply by air bubbling for pollutant abatement (using ciprofloxacin as a model pollutant). The considered operating variables were initial pH, catalyst dosage, reaction time and different intensities of magnetic field. Results indicated that NZVI/H₂O₂/aeration/weak magnetic field could effectively decompose ciprofloxacin at neutral condition and higher removal rates are observed at higher pH and NZVI concentrations. Superimposing a weak magnetic field leads to 20% enhancement in ciprofloxacin removal by catalytic Fenton under aeration condition. Employing simultaneously magnetic field induction and aeration exhibit excellent capability to the NZVI oxidation and significantly increased the dissolution rate of iron. Based on Fourier transform infrared spectroscopy, transformation products of NZVI are Fe₃O₄ and FeO(OH). The faster mass transport due to Lorentz and field gradient force, more oxygen diffusion to the iron surface and promoted electrochemical reactions results in more OH° production. Generation of weak magnetic field by permanent magnets and using aeration for both mixing and in situ oxygen supply significantly enhanced the Fenton reaction performance. This combination technology doesn't need any energy input and costly chemicals hence can be used easily for wastewater treatment applications.

Degradation of atrazine by catalytic ozonation in the presence of iron scraps: performance, transformation pathway, and acute toxicity

Degradation of atrazine by catalytic ozonation in the presence of iron scraps (ZVI/O₃) was carried out. The key operational parameters (i.e., initial pH, ZVI dosage, and ozone dosage) were optimized by the batch experiments, respectively. This ZVI/O₃ system exhibited much higher degradation efficiency of atrazine than the single ozonation, ZVI, and traditional ZVI/O₂ systems. The result shows that the pseudo-first-order constant (0.0927 min^-1) and TOC removal rate (86.6%) obtained by the ZVI/O₃ process were much higher than those of the three control experiments. In addition, X-ray diffraction (XRD) analysis indicates that slight of γ-FeOOH and Fe₂O₃ were formed on the surface of iron scrap after ZVI/O₃ treatment. These corrosion products exhibit high catalytic ability for ozone decomposition, which could generate more hydroxyl radical (HO^•) to degrade atrazine. Six transformation intermediates were identified by liquid chromatography-mass spectrometry (LC-MS) analysis in ZVI/O₃ system, and the degradation pathway of atrazine was proposed. Toxicity tests based on the inhibition of the luminescence emitted by Photobacterium phosphoreum and Vibrio fischeri indicate the detoxification of atrazine by ZVI/O₃ system. Finally, reused experiments indicate the approving recyclability of iron scraps. Consequently, the ZVI/O₃ system could be as an effective and promising technology for pesticide wastewater treatment.

Alternative Approach to Current EU BAT Recommendation for Coal-Fired Power Plant Flue Gas Desulfurization Wastewater Treatment

Fossil fuel combustion is a serious environmental problem. Significant quantities of flue gasses and wastewater, requiring further treatment, are produced. This article compares three wet flue gas desulfurization (FGD) wastewater treatment methods: coagulation with precipitation using iron(III) ions—recommended by the European Union as the best available technique (BAT)—and two alternative advanced oxidation processes (Fe2+/H2O2 and Fe0/H2O2). Both oxidation processes that were used met the technical FGD wastewater treatment requirements of the BAT. The best treatment effects, expressed as pollutants’ removal, were obtained for the Fe2+/H2O2 process for 150/300 mg/L reagent doses. It allows effective removal of boron up to 212 mg/L and heavy metals up to below the detection limit <0.010 mg/L for Pb and <0.005 mg/L for Cu. Therefore, the Fe2+/H2O2 process could be an option for FGD wastewater treatment as an alternative to the BAT recommended iron(III)-based coagulation with precipitation. Additionally, an analysis of variance was applied to check the significance of the two independent variables and their interactions. Statistical analysis confirmed high efficiency and applicability of treatment process.

Dynamic interactions between sulfidated zerovalent iron and dissolved oxygen: Mechanistic insights for enhanced chromate removal

Recent research on contaminant removal by zerovalent iron (ZVI) has evolved from investigating simple model systems to systems that encompass increased dimensions of complexity. Sulfidation and aerobic conditions are two of the most broadly relevant complications. Combining these two, this study investigated the dynamic interactions between sulfidated microscale ZVI and dissolved O₂, for removal of Cr(VI), a model contaminant for metals and metalloids. The results show that the coupling of sulfidation and oxygenation significantly improves Cr removal, which is attributed to enhanced Fe(II) production that resulted from accelerated corrosion of Fe(0). The Cr(VI) removal rate increased with increasing O₂ saturation from 0% to 100% but showed a bimodal dependence on the S/Fe ratio. At the optimal S/Fe ratio, the ZVI exhibits a highly porous surface morphology, which, according to prior literature on sulfur induced corrosion, promotes corrosion. In addition, a novel time series correlation was developed between aqueous Fe(II) and Cr(VI) based on data collected in the presence and absence of 1,10-phenanthroline, to probe for changes of reductants during the reaction time course. The analysis indicated that Fe(0) was responsible for the initial small amount of Cr(VI) removal, which then transitioned to a phase controlled by surface Fe(II). The slopes of the time series correlations during the latter phase of the reaction vary with experimental conditions but are mostly much higher than the theoretical stoichiometric ratio between Cr(VI) and Fe(II) (i.e., 0.33), indicating that Fe(II) regeneration contributes significantly to Cr removal.

A novel strategy for longevity prolongation of iron-based nanoparticle thin films by applied magnetic force

Products of ionised/vaporised iron and excited nitrogen gas were obtained via a sparking process in different magnetic fields.

Cosmetic wastewater treatment by the ZVI/H2O2 process

The ZVI/H₂O₂ process was applied for cosmetic wastewater treatment. Two commercial zero-valent iron (ZVI) types with different granulations were chosen: Hepure Ferrox PRB and Hepure Ferrox Target. In addition, the pH and stirring method influence on ZVI/H₂O₂ process efficiency was studied. During the ZVI and ZVI/H₂O₂ processes, linear Fe ions concentration increase was observed. The addition of H₂O₂ significantly accelerated the iron dissolution process. The highest COD removal was obtained using finer ZVI (Hepure Ferrox Target) for doses of reagents ZVI/H₂O₂ 1500/1600 mg/L, in a H₂O₂/COD weight ratio 2:1, at pH 3.0 with stirring on a magnetic stirrer. After 120 min of the process, 84.0% COD removal (from 796 to 127 mg/L) was achieved. It was found that the efficiency of the process depends, as in the case of the Fenton process, on the ratio of the reagents (ZVI/H₂O₂) and their dose in relation to the COD (H₂O₂/COD) but does not depend on the dose of the iron itself. Statistical analysis confirms that COD removal efficiency depends primarily on H₂O₂/COD ratio and ZVI granulation, but ZVI dose influence is not statistically significant. The head space, solid-phase microextraction, gas chromatography, mass spectrometry results confirm high efficiency of the ZVI/H₂O₂ process.

Magnetic Hyperthermia and Oxidative Damage to DNA of Human Hepatocarcinoma Cells

Nanotechnology is addressing major urgent needs for cancer treatment. We conducted a study to compare the frequency of 3-(2-deoxy-β-d-erythro-pentafuranosyl)pyrimido[1,2-α]purin-10(3H)-one deoxyguanosine (M₁dG) and 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG) adducts, biomarkers of oxidative stress and/or lipid peroxidation, on human hepatocarcinoma HepG2 cells exposed to increasing levels of Fe₃O₄-nanoparticles (NPs) versus untreated cells at different lengths of incubations, and in the presence of increasing exposures to an alternating magnetic field (AMF) of 186 kHz using ³²P-postlabeling. The levels of oxidative damage tended to increase significantly after ≥24 h of incubations compared to controls. The oxidative DNA damage tended to reach a steady-state after treatment with 60 μg/mL of Fe₃O₄-NPs. Significant dose–response relationships were observed. A greater adduct production was observed after magnetic hyperthermia, with the highest amounts of oxidative lesions after 40 min exposure to AMF. The effects of magnetic hyperthermia were significantly increased with exposure and incubation times. Most important, the levels of oxidative lesions in AMF exposed NP treated cells were up to 20-fold greater relative to those observed in nonexposed NP treated cells. Generation of oxidative lesions may be a mechanism by which magnetic hyperthermia induces cancer cell death.

Combined Effect of Weak Magnetic Fields and Anions on Arsenite Sequestration by Zerovalent Iron: Kinetics and Mechanisms

In this study, the effects of major anions (e.g., ClO₄^-, NO₃^-, Cl^-, and SO₄^2-) in water on the reactivity of zerovalent iron (ZVI) toward As(III) sequestration were evaluated with and without a weak magnetic field (WMF). Without WMF, ClO₄^- and NO₃^- had negligible influence on As(III) removal by ZVI, but Cl^- and SO₄^2- could improve As(III) sequestration by ZVI. Moreover, the WMF-enhancing effect on As(III) removal by ZVI was minor in ultrapure water. A synergetic effect of WMF and individual anion on improving As(III) removal by ZVI was observed for each of the investigated anion, which became more pronounced as the concentration of anion increased. Based on the extent of enhancing effects, these anions were ranked in the order of SO₄^2- > Cl^- > NO₃^- ≈ ClO₄^- (from most- to least-enhanced). Furthermore, the inhibitory effect of HSiO₃^-, HCO₃^-, and H₂PO₄^- on ZVI corrosion could be alleviated taking advantage of the combined effect of WMF and SO₄^2-. The coupled influence of anions and WMF was associated with the simultaneous movement of anions with paramagnetic Fe²⁺ to keep local electroneutrality in solution. Our findings suggest that the presence of anions is quite essential to maintaining or stimulating the WMF effect.

An insight in magnetic field enhanced zero-valent iron/H2O2 Fenton-like systems: Critical role and evolution of the pristine iron oxides layer

This study demonstrated the synergistic degradation of 4-chlorophenol (4-CP) achieved in a magnetic field (MF) enhanced zero-valent iron (ZVI)/H2O2 Fenton-like (FL) system and revealed an interesting correlative dependence relationship between MF and the pristine iron oxides layer (FexOy) on ZVI particles. First, a comparative investigation between the FL and MF-FL systems was conducted under different experimental conditions. The MF-FL system could suppress the duration of initial lag degradation phase one order of magnitude in addition of the significant enhancement in overall 4-CP degradation. Monitoring of intermediates/products indicated that MF would just accelerate the Fenton reactions to produce hydroxyl radical more rapidly. Evolutions of simultaneously released dissolved iron species suggested that MF would not only improve mass-transfer of the initial heterogeneous reactions, but also modify the pristine ZVI surface. Characterizations of the specific prepared ZVI samples evidenced that MF would induce a special evolution mechanism of the ZVI particles surface depending on the existence of FexOy layer. It comprised of an initial rapid point dissolution of FexOy and a following pitting corrosion of the exposed Fe(0) reactive sites, finally leading to appearance of a particular rugged surface topography with numerous adjacent Fe(0) pits and FexOy tubercles.

Sequestration of Antimonite by Zerovalent Iron: Using Weak Magnetic Field Effects to Enhance Performance and Characterize Reaction Mechanisms

Many oxyanion-forming metals (As, Sb, Se, Tc, etc.) can be removed from water by adsorption and/or redox reactions involving iron oxides, including the oxides associated with zerovalent iron (ZVI). The rate of antimonite (Sb(III) hydrolysis species) removal by ZVI was determined in open, well-mixed batch reactors as a function of experimental factors, including aging of the ZVI, addition of Fe(II), Sb dose, mixing rate, pH, initial concentrations of Sb(III), etc. However, the largest effect observed was the roughly 6-8 fold increase in Sb(III) removal rate due to the application of a weak magnetic field (WMF) during the experiments. The WMF effect on Sb removal arises from stimulated corrosion and delayed passivation of the ZVI, as evidenced by time series correlation analysis of "geochemical" properties (DO, Fetot, Eh, and pH) measured synchronously in each experiment. The removal of Sb under the conditions of this study was mainly due to oxidation of Sb(III) to Sb(V) and adsorption and coprecipitation onto the iron oxides formed from accelerated corrosion of ZVI, as evidenced by Sb K-edge XANES, EXAFS, and XPS. The degree of the WMF enhancement for Sb(III) was found to be similar to the WMF effect reported previously for Sb(V), As(III), As(V), and Se(VI).

Electromagnetic Induction of Zerovalent Iron (ZVI) Powder and Nanoscale Zerovalent Iron (NZVI) Particles Enhances Dechlorination of Trichloroethylene in Contaminated Groundwater and Soil: Proof of Concept

This study evaluates the concept of using zerovalent iron (ZVI) powder or nanoscale zerovalent iron (NZVI) particles in combination with a low frequency (150 kHz) AC electromagnetic field (AC EMF) to effectively remove trichloroethylene (TCE) from groundwater and saturated soils. ZVI and NZVI are ferromagnetic, which can induce heat under applied AC EMF. The heat generated by ZVI and NZVI induction can increase the rate of dechlorination, according to Arrhenius' equation, and increase the rate of TCE desorption from TCE-sorbed soil. Both dechlorination and TCE desorption enhance the overall TCE removal rate. We evaluated this novel concept in laboratory batch reactors. We found that both ZVI and NZVI can induce heat under applied AC EMF up to 120 °C in 20 min. Using ZVI and NZVI with AC EMF enhanced dechlorination of dissolved TCE (no soil) up to 4.96-fold. In addition to increasing the temperature by ZVI and NZVI induction heating, AC EMF increased intrinsic ZVI and NZVI reactivity, ostensibly due to accelerated corrosion, as demonstrated by the increased ORP. In a soil-water-TCE system, NZVI together with AC EMF thermally enhanced desorption of TCE from soil and increased the degradation of TCE up to 5.36-fold compared to the absence of AC EMF. For the first time, this study indicates the potential for ZVI and NZVI coupled with AC EMF as a combined remediation technique for increasing the rate and completeness of in situ cleanup of adsorbed phase contaminants.

The Role of ESR Spectroscopy in Advancing Catalytic Science: Some Recent Developments

Recent progress is surveyed in regard to the importance of molecular species containing unpaired electrons in catalytic systems, as revealed using ESR spectroscopy. The review begins with studies of enzymes and their role directly in biological systems, and then discusses investigations of various artificially created catalysts with potential human and environmental significance, including zeolites. Among the specific types of catalytic media considered are those for photocatalysis, water splitting, the degradation of environmental pollutants, hydrocarbon conversions, fuel cells, ionic liquids and sensor devices employing graphene. Studies of muonium-labelled radicals in zeolites are also reviewed, as a means for determining the dynamics of transient radicals in these nanoporous materials.

The limitations of applying zero-valent iron technology in contaminants sequestration and the corresponding countermeasures: the development in zero-valent iron technology in the last two decades (1994-2014)

Over the past 20 years, zero-valent iron (ZVI) has been extensively applied for the remediation/treatment of groundwater and wastewater contaminated with various organic and inorganic pollutants. Based on the intrinsic properties of ZVI and the reactions that occur in the process of contaminants sequestration by ZVI, this review summarizes the limitations of ZVI technology and the countermeasures developed in the past two decades (1994-2014). The major limitations of ZVI include low reactivity due to its intrinsic passive layer, narrow working pH, reactivity loss with time due to the precipitation of metal hydroxides and metal carbonates, low selectivity for the target contaminant especially under oxic conditions, limited efficacy for treatment of some refractory contaminants and passivity of ZVI arising from certain contaminants. The countermeasures can be divided into seven categories: pretreatment of pristine ZVI to remove passive layer, fabrication of nano-sized ZVI to increase the surface area, synthesis of ZVI-based bimetals taking advantage of the catalytic ability of the noble metal, employing physical methods to enhance the performance of ZVI, coupling ZVI with other adsorptive materials and chemically enhanced ZVI technology, as well as methods to recover the reactivity of aged ZVI. The key to improving the rate of contaminants removal by ZVI and broadening the applicable pH range is to enhance ZVI corrosion and to enhance the mass transfer of the reactants including oxygen and H(+) to the ZVI surface. The characteristics of the ideal technology are proposed and the future research needs for ZVI technology are suggested accordingly.

Weak magnetic field accelerates chromate removal by zero-valent iron

Weak magnetic field (WMF) was employed to improve the removal of Cr(VI) by zero-valent iron (ZVI) for the first time. The removal rate of Cr(VI) was elevated by a factor of 1.12-5.89 due to the application of a WMF, and the WMF-induced improvement was more remarkable at higher Cr(VI) concentration and higher pH. Fe2+ was not detected until Cr(VI) was exhausted, and there was a positive correlation between the WMF-induced promotion factor of Cr(VI) removal rate and that of Fe2+ release rate in the absence of Cr(VI) at pH4.0-5.5. These phenomena imply that ZVI corrosion with Fe2+ release was the limiting step in the process of Cr(VI) removal. The superimposed WMF had negligible influence on the apparent activation energy of Cr(VI) removal by ZVI, indicating that WMF accelerated Cr(VI) removal by ZVI but did not change the mechanism. The passive layer formed with WMF was much more porous than without WMF, thereby facilitating mass transport. Therefore, WMF could accelerate ZVI corrosion and alleviate the detrimental effects of the passive layer, resulting in more rapid removal of Cr(VI) by ZVI. Exploiting the magnetic memory of ZVI, a two-stage process consisting of a small reactor with WMF for ZVI magnetization and a large reactor for removing contaminants by magnetized ZVI can be employed as a new method of ZVI-mediated remediation.

Disinfection of wastewater effluents with the Fenton-like process induced by electromagnetic fields

This research work is focused on the application and assessment of effectiveness of the Fenton-like processes induced by radiofrequency for the inactivation of faecal bacteria (Escherichia coli and Enterococcus sp.) present in treated urban wastewater effluents. Fenton processes were carried out at near neutral pH (pH 5) with different iron sources, such as iron salts (ferric chloride, 5, 50 and 100 mg/L Fe(3+)), magnetite (1 g/L) and clay (80 g/L), hydrogen peroxide (25 mg/L) and in absence and presence of radiofrequency. Two different electromagnetic field intensities (1.57 and 3.68 kA/m) were used in Fenton processes induced by radiofrequency. Different agents used in the Fenton processes induced by electromagnetic fields (iron source, hydrogen peroxide and RF) were analyzed individually and in combination under the same experimental conditions. First assays of ferromagnetic material/H2O2/radiofrequency processes achieved promising results in terms of bacterial inactivation. For instance, Fe(3+)/H2O2/Radiofrequency achieved a maximum level of E. coli inactivation of 3.55 log after 10 min of treatment. These results are higher than those obtained in absence of radiofrequency. The thermal activation of iron atoms allows the Fenton reaction to intensify, increasing the final yield of the treatment. On the other hand, different behavior was observed in the inactivation of E. coli and Enterococcus sp. due to the structural differences between Gram-negative and Gram-positive bacteria.

Coupled effects of aging and weak magnetic fields on sequestration of selenite by zero-valent iron

The sequestration of Se(IV) by zero-valent iron (ZVI) is strongly influenced by the coupled effects of aging ZVI and the presence of a weak magnetic field (WMF). ZVI aged at pH 6.0 with MES as buffer between 6 and 60 h gave nearly constant rates of Se(IV) removal with WMF but with rate constants that are 10- to 100-fold greater than without. XANES analysis showed that applying WMF changes the mechanism of Se(IV) removal by ZVI aged for 6-60 h from adsorption followed by reduction to direct reduction. The strong correlation between Se(IV) removal and Fe2+ release suggests direct reduction of Se(IV) to Se(0) by Fe0, in agreement with the XANES analysis. The numerical simulation of ZVI magnetization revealed that the WMF influence on Se(IV) sequestration is associated mainly with the ferromagnetism of ZVI and the paramagnetism of Fe2+. In the presence of the WMF, the Lorentz force gives rise to convection in the solution, which narrows the diffusion layer, and the field gradient force, which tends to move paramagnetic ions (esp. Fe2+) along the higher field gradient at the ZVI particle surface, thereby inducing nonuniform depassivation and eventually localized corrosion of the ZVI surface.

Weak magnetic field significantly enhances selenite removal kinetics by zero valent iron

The effect of weak magnetic field (WMF) on Se(IV) removal by zero valent iron (ZVI) was investigated as functions of pH and initial Se(IV) concentrations. The presence of WMF significantly accelerated Se(IV) removal and extended the working pH range of ZVI from 4.0-6.0 to 4.0-7.2. The WMF induced greater enhancement in Se(IV) removal by ZVI at lower initial Se(IV) concentrations. The influence of WMF on Se(IV) removal by ZVI was associated with a more dramatic drop in ORP and a more rapid release of Fe(2+) compared to the case without WMF. SEM and XRD analysis revealed that WMF accelerated the corrosion of ZVI and the transformation of amorphous iron (hdyr)oxides to lepidocrocite. XANES analyses showed that WMF expedited the reduction of Se(IV) to Se(0) by ZVI at pH 6.0 when its initial concentration was ≤20.0 mg L(-1). Se(IV) dosed at 40.0 mg L(-1) was removed by ZVI via adsorption followed by reduction to Se(0) at pH 7.0 but via adsorption at 7.2 in the presence of WMF. Regardless of WMF, Se(IV) applied at 40.0 mg L(-1) was removed by reduction at pH 4.0-6.0. The WMF-induced improvement in Se(IV) removal by ZVI may be mainly attributable to the Lorentz force and magnetic field gradient force. Employing WMF to enhance Se(IV) removal by ZVI is a promising and environmental-friendly method since it does not need extra energy and costly reagents.

Unpaired electrons as probes of catalytic systems

An overview is provided of the importance of molecular species containing unpaired electrons in catalytic systems, as revealed using ESR spectroscopy. The review aims to demonstrate the considerable extent of scientific progress that has been made in this broad topic during the past few decades. Studies of catalytically active surfaces, including zeolites, are surveyed, and the detection of radical species, formed as intermediates in their reactions, using matrix isolation and spin-trapping techniques. Radical cation formation in zeolites is discussed, and the employment of muon spin rotation and relaxation techniques to study the mobility of labelled radicals in various porous and catalytic media. Among the specific types of catalytic media considered are those for photocatalysis, water splitting, degradation of environmental pollutants, hydrocarbon conversions, fuel cells and sensor devices employing graphene. The review concludes with recent developments in the study of enzymes and their reactions, using ESR-based methods.

Nano-Fe⁰ encapsulated in microcarbon spheres: synthesis, characterization, and environmental applications

Nanoscaled zerovalent iron (ZVI) encapsulated in carbon spheres (nano-Fe⁰@CS) were prepared via a hydrothermal carbonization method, using glucose and iron(III) nitrate as precursors. The properties of the nano-Fe⁰@CS were investigated by X-ray diffraction (XRD), thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption/desorption isotherms. Nano-Fe⁰@CS was demonstrated, for the first time, as an effective material in activating Oxone (peroxymonosulfate, PMS) for the oxidation of organic pollutants. It was found that the efficiency of nano-Fe⁰@CS was higher than ZVI particles, iron ions, iron oxides, and a cobalt oxide. The mechanism of the high performance was discussed. The structure of the nano-Fe⁰@CS not only leads to high efficiency in the activation of PMS, but also good stability. This study extended the application of ZVI from reductive destruction of organics to oxidative degradation of organics by providing a green material for environmental remediation.

Enhanced decomposition of dimethyl phthalate via molecular oxygen activated by Fe@Fe2O3/AC under microwave irradiation

In this study, we demonstrate that the decomposition of dimethyl phthalate under microwave irradiation could be greatly enhanced over Fe@Fe(2)O(3) nanowires supported on activated carbon (Fe@Fe(2)O(3)/AC). The great enhanced decomposition of dimethyl phthalate could be attributed to a unique microwave induced molecular oxygen activation process. Upon microwave irradiation, electrons could be transferred from activated carbon to zero-valent iron, and then react with molecular oxygen to form O(2)(-) and OH radicals for the decomposition of dimethyl phthalate. The deactivation and the regeneration of Fe@Fe(2)O(3)/AC catalyst were systematically studied. We also found that microwave heating could accelerate the electron transferring from AC to Fe@Fe(2)O(3) to generate more reactive oxygen species for the decomposition of DMP than conventional oil bath heating. This novel molecular oxygen activation approach may find applications for wastewater treatment and drinking water purification.