Presence Of Fe0 Research Articles

The activation of PMS for PFOA degradation by adjustable metal stripping Fe/Co/N@BC catalysts: Degradation performance with single-line oxygen and high-valent metal oxides as the main active substances

In this study, a modified biochar (P-Fe/Co/N@BC) catalyst was prepared with wood chips as raw material by hydrothermal method for the activation of peroxymonosulfate (PMS) and degradation of perfluorooctanoic acid (PFOA). Scanning electron microscopy (SEM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) characterization methods were used to demonstrate the presence of FeNx, CoNx, Fe-Co and CO active sites, which contribute to the improvement of the PMS activation capacity for single-line oxygen (1O2). Electron paramagnetic resonance spectroscopy (EPR), reactive oxygen species (ROS) scavenging experiments and methyl phenyl sulfoxide (PMSO) conversion experiments were performed to clarify the main mechanisms of PFOA degradation by reactive species. Further, 1O2, sulfate radical (SO4−), hydroxyl radical (OH), high-valent metal oxides (Fe(IV) and Co(IV)) were jointly involved in the degradation of PFOA, and nonradical were the main activation pathway of PMS. In particular, Fe3+ decomposed from Fe(IV) in the presence of Fe0 and Co2+ decomposed from Co(IV) are able to enhance iron cycling and cobalt cycling, respectively. Meanwhile, Co0 accelerates the conversion of Co3+ to Co2+. The findings suggested that the removal rate of the P-Fe/Co/N@BC-PMS system (99 %) was much higher than that of the P-Fe-N-C/PMS (68.9 %) over 180 min. It emphasized that the incorporation of PTFE (polytetrafluoroethylene) can regulate metal leaching significantly and improve the cycling stability of the catalysts. This study aimed to prepare efficient and stable modified biochar catalysts to activate PMS, which provided an effective solution to the problem of metal ion leaching from metal-modified biochar materials.

Influence of Water Salinity on the Efficiency of Fe0-Based Systems for Water Treatment

Metallic iron (Fe0) is a reactive material for treating polluted water. The effect of water salinity on the efficiency of Fe0-based remediation systems is not yet established. This work aims to clarify the reasons why Cl− ions are often reported to improve the efficiency of Fe0/H2O remediation systems. Quiescent batch experiments were carried out to characterize the effect of chloride (Cl−) ions on the efficiency of methylene blue (MB) discoloration in the presence of Fe0. Cl− was used in the form of NaCl at concentrations ranging from 0 to 40 g L−1. The MB concentration was 10 mg L−1, the Fe0 loading was 5 g L−1, and the duration of the experiment varied from 2 to 46 days. Four different Fe0 materials were tested in parallel experiments. Tests with different NaCl levels were performed in parallel with three other organic dyes: Methyl orange (MO), orange II (OII), and reactive red 120 (RR 120). The results clearly show that the presence of Cl− reduces the extent of dye discoloration in all systems investigated. The efficiency of the dyes increased in the order MB < MO < RR 120 < OII. In systems with varying NaCl concentrations, dye discoloration initially decreases with increasing NaCl and slightly increases for [NaCl] > 30 g L−1. However, the extent of dye discoloration for [NaCl] = 40 g L−1 remains much lower than for the system with [NaCl] = 0 g L−1. The results clearly demonstrate that the presence of Cl− fundamentally delays the process of contaminant removal in Fe0/H2O systems, thus improving the understanding of the contaminant interactions in Fe0-based remediation systems. These results also suggest that the effects of other inorganic anions on the efficiency of Fe0/H2O systems should be revisited for the design of field applications.

Boosted carbon resistance of ceria-hexaaluminate by in-situ formed CeFexAl1−xO3 as oxygen pool for chemical looping dry reforming of methane

High potential to carbon deposition over metallic Fe0 greatly limits the improvement of methane-to-syngas selectivity via chemical looping technology. Herein, we found that the in-situ formed CeFexAl1−xO3 over ceria-hexaaluminate as “oxygen pool” could greatly improve carbon resistance even with presence of Fe0. Formation of CeFexAl1−xO3 only proceeds in ceria-hexaaluminate composite while not occurs in CeO2-Fe2O3-Al2O3, which was probably originated from the strong interaction between CeO2 and the adjacent Fe and Al ions in BaFe3Al9O19 hexaaluminate structure. CeFexAl1−xO3 with outstanding oxygen ion conduction capacity was in close contact with metallic Fe0 exsoluted from Fe-hexaaluminate in a unique CeFexAl1−xO3/Fe0/hexaaluminate sandwich-like structure, which provided a convenient pathway for CeFexAl1−xO3 as “oxygen pool” to supply sufficient oxygen for in-time oxidation of carbon over adjacent Fe0. Consequently, the recycled ceria-hexaaluminate displayed both outstanding carbon resistance and high CH4 conversion (∼90%) with enhanced syngas yield that 105% and 72% higher than CeO2-Fe2O3-Al2O3 oxide and Fe-hexaaluminate, respectively.

Degradation of formaldehyde by photo-Fenton process over n-ZVI/TiO2 catalyst.

The degradation of formaldehyde in a photo-Fenton reaction was studied using n-ZVI/TiO2 as the catalyst. The effects of %n-ZVI loading, catalyst dosage, H2O2, and pH on formaldehyde degradation were studied. The n-ZVI/TiO2 catalysts were prepared by impregnation with chemical reduction, and their catalytic activity was evaluated in a batch reactor under UVC light. Transmission electron microscopy (TEM) was used to determine that the n-ZVI nanoparticle size was 39.41nm. X-ray photoelectron spectroscopy (XPS) was used to study the oxidation states of 2%n‑ZVI/TiO2, and the Fe 2p spectrum of 2%n-ZVI/TiO2 indicated the presence of Fe0. The optimal conditions for the complete removal of formaldehyde within 30min were an n-ZVI loading of 2 wt.%, a catalyst dosage of 0.5g/L, 30mM H2O2, and an initial pH of 3. After the reaction, the C-H functional group of formaldehyde was not observed due to the •OH radicals generated by Fe0 and H2O2 attacking the formaldehyde molecule. Moreover, no Fe leaching was observed, presenting an advantage compared with homogeneous Fe catalysts. Therefore, 2%n‑ZVI/TiO2 shows excellent potential as a photo-Fenton catalyst for the environmentally friendly degradation of formaldehyde.

Cost-effective degradation of pollutants by in-situ electrocatalytic process on Fe@BN-C bifunctional cathode: Formation of 1O2 with high selectivity under nanoconfinement

Electrochemical advanced oxidation processes (EAOPs) capable of in-situ producing highly active species are regarded as promising technologies for organic pollutants removal without chemicals addition, however their efficiency is not cost-effective especially under neutral and alkaline condition. Herein, an in-situ electrocatalytic process using bifunctional cathode of N, B-codoped carbon nanotubes with embedded nano-iron particles (Fe@BN-C) was developed, which simultaneously achieved the efficient generation of H2O2 and selective formation of 1O2. The Fe@BN-C cathode exhibited higher activity for sulfamethazine (SMT) degradation (5.6-folds faster) and H2O2 generation (3.6-folds higher) than OH-mediated non-confined analog. Also it exhibited promising application prospect for treatment of various pollutants and real wastewaters over wide pH ranges to 9 with the electrical energy consumption (EEC, 0.064 kWh log−1 m−3 for SMT degradation) only one tenth of the conventional electro-Fenton. Density functional theory calculations and in-situ Fourier transformed infrared spectroscopy verified that the presence of hexagonal boron nitride (h-BN) enhanced the H2O2 selectivity (close to 100 %), and H2O2 as intermediate in the presence of Fe0 could be electrochemically converted into OOH/O2− and further activated by the generated surface OH to form 1O2. This work will provide new insight into the design and understanding of efficient in-situ electrocatalytic process by bifunctional cathode with nanoconfinement for water purification.

In situ induced cation-vacancies in metal sulfides as dynamic electrocatalyst accelerating polysulfides conversion for Li-S battery

Cation vacancy engineering is considered to be one of the effective methods to solve the issues of shuttling and sluggish redox kinetics of LiPSs owing to the intrinsic tunability of electronic structure. However, cation vacancies are few studied in the Li-S realm due to their complex and rigid preparation methods. In this work, one-step pyrolysis is reported to in situ introduce Fe-vacancies into iron sulfide (Fe0.96S) as a sulfur host. For this host structure, Fe0.96S is first employed as an adsorbent and catalyst in Li-S system. During the carbonization process, a tight contact structure of Fe0.96S crystal and carbon network (Fe0.96S@C) is in situ constructed, and the carbon layer as a conductor provides smooth electrons transfer pathways for redox reactions. Meanwhile, due to the introduction of Fe-vacancies in FeS crystal, the adsorption capability and catalytic effect for LiPSs have been substantially enhanced. Moreover, the presence of Fe0.96S crystal favors the mobility of electron and diffusion of Li+, which is revealed by the experiments and theoretical calculations. Through synergy respective advantages effect of Fe0.96S and carbon, the Fe0.96S@C-S cathode delivers high-rate capability at 5.0 C and stable long-life performance. Even under a high sulfur loading of 3.5 mg/cm2, the durable cyclic stability is still exhibited with the capacity retention of 93% over 400 cycles at 1.0 C, and the coulombic efficiency is ≥98%. Noting that this strategy greatly simplifies the synthetic process of currently known cation-vacancy materials and furnishes a universal mentality for designing both divinable and astonishing new cation-vacancy materials.

Nitrite as a causal factor for nitrate-dependent anaerobic corrosion of metallic iron induced by Prolixibacter strains.

Microbially influenced corrosion (MIC) may contribute significantly to overall corrosion risks, especially in the gas and petroleum industries. In this study, we isolated four Prolixibacter strains, which belong to the phylum Bacteroidetes, and examined their nitrate respiration‐ and Fe0‐corroding activities, together with two previously isolated Prolixibacter strains. Four of the six Prolixibacter strains reduced nitrate under anaerobic conditions, while the other two strains did not. The anaerobic growth of the four nitrate‐reducing strains was enhanced by nitrate, which was not observed in the two strains unable to reduce nitrate. When the nitrate‐reducing strains were grown anaerobically in the presence of Fe0 or carbon steel, the corrosion of the materials was enhanced by more than 20‐fold compared to that in aseptic controls. This enhancement was not observed in cultures of the strains unable to reduce nitrate. The oxidation of Fe0 in the anaerobic cultures of nitrate‐reducing strains occurred concomitantly with the formation of nitrite. Since nitrite chemically oxidized Fe0 under anaerobic and aseptic conditions, the corrosion of Fe0‐ and carbon steel by the nitrate‐reducing Prolixibacter strains was deduced to be mainly enhanced via the biological reduction of nitrate to nitrite, followed by the chemical oxidation of Fe0 to Fe2+ and Fe3+ coupled to the reduction of nitrite.

Metal immobilization and nitrate reduction in a contaminated soil amended with zero-valent iron (Fe0)

Technologies based on zero-valent iron (Fe0) are increasingly being used to immobilize metals in soils and remove metals and nitrate from waters. However, the impact of nitrate reduction on metal immobilization in metal contaminated soils has been poorly investigated so far. Here, different concentrations of Fe0 filings (1%, 2% and 5%; wt%) were applied to a metal contaminated soil. The resulting nitrate reduction and metal (Cd and Zn) immobilization was investigated using a column leaching experiment for 12 weeks. Corrosion of Fe0 filings and precipitation of Fe oxyhydroxydes (FeOOH) on the surfaces of the filings were observed using SEM-EDS and EMPA-WDS at the end of the experiment. Compared to the untreated soil, total nitrate amounts released were lowered by 47%, 59% and 87% in the presence of 1%, 2% and 5% of Fe0, respectively. Concomitantly with nitrate reduction, Cd and Zn concentrations in leachates were strongly alleviated in the presence of Fe0, which was partly attributed to the rise of soil pH subsequent to nitrate reduction. More importantly, biotests with Lupinus albus L. revealed that the mechanisms involved in metal immobilization are stable to root-induced acidification. However, Fe0 was not efficient to reduce Cd concentration in Lolium multiflorum Lam., indicating that root processes other than acidification may re-mobilize metals.

EVALUACIÓN DE LA CAPACIDAD ADSORBENTE DE GEL DE SÍLICE DOPADO CON NANOPARTICULAS DE HIERRO, EN AZUL DE METILENO Y PARAQUAT DERIVADO DEL SECTOR TEXTIL Y AGRÍCOLA

The objective of this work was to evaluate the capacity as nano-adsorbent of NFe, synthesized by green synthesis, supported on silica (SGNFe) and without supporting, for the elimination of dye (methylene blue) in water and the toxic herbicide Paraquat, in contaminated water. The NFe by green synthesis from eucalyptus extract, did not result in an absolute reducing effect as expected, which would allow obtaining the NFe only in zero valence. Only a partial reduction of Fe2+ was obtained, which was denoted by the presence of Fe0 in the XRD and a partial oxidation of Fe2+ to Fe3+ observed by the presence of the magnetite phase. If the presence of almost spherical NFe was corroborated by the analysis and distribution of particle size and corroborated by scanning electron microscopy (SEM). The NFe obtained and the doped silica gel (SGNFe), as well as the silica (SG) used as a precursor, showed negative charges in semi-colloidal suspensions, checked by zeta potential (pZ) and electrophoretic mobility. The SG, NFe and SGNFe in this study report cationic dye adsorption efficiencies AM between 98-99% as well as adsorption capacities (qt) between 24.5-24.8 mg/g. However, the percentages of efficiency in the adsorption of the cationic herbicide Paraquat in water, oscillated with efficiencies between 81-98% and presented a very low adsorption capacity (qt) very low, between 0.53-0.89 mg/g. It is important to continue this line of research, seeking to improve and/or optimize the synthesis conditions to increase the values of qt Keywords: Nanoparticles, adsorption capacity, paraquat, eucalyptus, efficiency.

Aqueous Cr(VI) removal by a novel ball milled Fe0-biochar composite: Role of biochar electron transfer capacity under high pyrolysis temperature.

A novel ball milled Fe0-biochar composite was synthesized by ball milling the mixture of biochar (pyrolyzed at 300 °C, 500 °C, and 700 °C) and micron grade iron powder. FTIR, SEM, TEM-EDS, XRD, and XPS were applied to characterize this composite. XRD results showed that iron carbide phase was formed during the ball milling process. The ability of this synthesized composited to remove aqueous Cr(VI) was tested. Removal rates of Cr(VI) (49.6%, 65.8%, and 97.8%, respectively) by ball milled Fe0-biochar composite consisting of biochar pyrolyzed at 300 °C (300BMFe0-BC), 500 °C (500BMFe0-BC), and 700 °C (700BMFe0-BC) were much higher than those (19%, 11%, and 4%, respectively) by pristine biochar pyrolyzed at 300 °C (300BC), 500 °C (500BC), and 700 °C (700BC). Cr(VI) removal rate by 700BMFe0-BC increased from 15.4% to 97.8% when prolonging ball milling time from 6 h to 48 h. Ball milling promoted the combination of Fe0 and biochar as well as reduced the hydrodynamic diameter of the composite. Acidic conditions favored Cr(VI) removal. Ball milling exposed the functional groups of biochar and improved its Cr(VI) removal rate. Raman spectra showed that the degree of graphitization in 700 °C ball milled biochar (700BMBC) was the highest. Electrochemical analysis demonstrated that 700BMBC had the highest electron transfer capacity. In the presence of Fe0, graphitized structure in 700BMBC acted as an electron conductor, facilitating electron transfer from Fe0 to Cr(VI). Ball milling also destroyed the surface iron oxide layer to regenerate the composite.

Enhanced oxidative activity of zero-valent iron by citric acid complexation

In this study, we systematically investigated the oxidative degradation of 4-chlorophenol (4-CP) using nano zero valent iron (nZVI, Fe0) cooperated with citric acid (CA), and the role of CA as well as the mechanism of oxidation were deeply evaluated. 56.2% of 4-CP was removed after 60 min under dark condition without any ventilation of oxygen in the presence of Fe0 and CA. The addition of CA accelerated the release of ferrous ions and promoted the Fenton reaction to generate much more reactive oxygen species (ROS), which was confirmed by EPR. The MINEQL+ 4.6 soft was utilized to calculated the existent species in Fe0-CA system, and Fe(II)[Cit]− was found to be the key species playing an important role on the degradation of 4-CP. Fe(II)[Cit]− adsorbed on iron surface accelerated the transportation of electron from Fe0 to O2 to produce more OH. This study puts forward the possible mechanism of generating ROS on Fe0 enhanced by CA and provides an application for the oxidation of pollutants.

Simultaneous adsorption and degradation of 2,4-dichlorophenol on sepiolite-supported bimetallic Fe/Ni nanoparticles

A functional sepiolite-supported Fe/Ni (Sep-Fe/Ni) nanocomposite material synthesised through borohydride reduction method was used to degrade 2,4-dichlorophenol (2,4-DCP) from an aqueous solution. 2,4-DCP was completely removed using Sep-Fe/Ni within 120 min, whereas Fe/Ni or sepiolite in isolation yielded removal efficiencies of 90.8% and 8.4%, respectively. As confirmed by scanning electron microscopy and transmission electron microscopy, sepiolite played a role as the supporting material, which distributed Fe/Ni nanoparticles and significantly diminished their aggregation and correspondingly increased reactivity in adsorption and degradation of 2,4-DCP. The presence of Fe0 and Ni0 nanoparticles onto Sep-Fe/Ni was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The optimized contents of Fe and Ni were 5.19 and 0.51 wt%, respectively which resulted in the higher performance of Sep-Fe/Ni catalyst. The key parameters controlling the degradation of 2,4-DCP such as the initial pH of the solution, catalyst amount and reaction time were systematically explored. Furthermore, Sep-Fe/Ni was shown to exhibit promising capability toward removal of total organic carbon. Kinetic analysis revealed that depletion of 2,4-DCP was consistent with a pseudo first-order kinetic model. The possible adsorption and catalytic degradation mechanism were proposed while the degraded products were identified by chromatographic techniques with ultraviolet and mass spectrometry detection. This study showed the promise of Sep-Fe/Ni as a new environmental pollution management candidate for the remediation of water sources contaminated by chlorophenols.

Progress in Understanding the Mechanism of CrVI Removal in Fe0-Based Filtration Systems

Hexavalent chromium (CrVI) compounds are used in a variety of industrial applications and, as a result, large quantities of CrVI have been released into the environment due to inadequate precautionary measures or accidental releases. CrVI is highly toxic to most living organisms and a known human carcinogen by inhalation route of exposure. Another major issue of concern about CrVI compounds is their high mobility, which easily leads to contamination of surface waters, soil, and ground waters. In recent years, attention has been focused on the use of metallic iron (Fe0) for the abatement of CrVI polluted waters. Despite a great deal of research, the mechanisms behind the efficient aqueous CrVI removal in the presence of Fe0 (Fe0/H2O systems) remain deeply controversial. The introduction of the Fe0-based filtration technology, at the beginning of 1990s, was coupled with the broad consensus that direct reduction of CrVI by Fe0 was followed by co-precipitation of resulted cations (CrIII, FeIII). This view is still the dominant removal mechanism (reductive-precipitation mechanism) within the Fe0 remediation industry. An overview on the literature on the Cr geochemistry suggests that the reductive-precipitation theory should never have been adopted. Moreover, recent investigations recalling that a Fe0/H2O system is an ion-selective one in which electrostatic interactions are of primordial importance is generally overlooked. The present work critically reviews existing knowledge on the Fe0/CrVI/H2O and CrVI/H2O systems, and clearly demonstrates that direct reduction with Fe0 followed by precipitation is not acceptable, under environmental relevant conditions, as the sole/main mechanism of CrVI removal in the presence of Fe0.

Biological treatment of wastewater with high concentrations of zinc and sulfate ions from zinc pyrithione synthesis

Abstract An enriched and domesticated bacteria consortium of sulfate-reducing bacteria (SRB) was used to treat wastewater from zinc pyrithione (ZPT) production, and the effects of different reaction parameters on sulfate reduction and zinc precipitation were evaluated. The single-factor experimental results showed that the removal rates of Zn2+ and SO42− decreased with an increased ZPT concentration ranging from 3.0 to 5.0 mg/L. Zn2+ and SO42− in wastewater were effectively removed under the conditions of 30–35 °C, pH 7–8 and an inoculum concentration of 10%–25%. The presence of Fe0 in the SRB system enhanced Zn2+ and SO42− removal and may increase the resistance of SRB to the toxicity of Zn2+ and ZPT in wastewater. A Box–Behnken design was used to evaluate the influence of the main operating parameters on the removal rate of SO42−. The optimum parameter values were found to be pH 7.45, 33.61 °C and ZPT concentration of 0.62 mg/L, and the removal rate of SO42− reached a maximum of 91.62% under these optimum conditions.

Nano FexZn1−xO as a tuneable and efficient photocatalyst for solar powered degradation of bisphenol A from aqueous environment

Currently, the photocatalytic nanomaterials performing under solar radiation have gained worldwide attentions due to increasing environmental deterioration. For utilizing the sunlight for degradation of emerging pollutants it is important to develop visible active photocatalysts. This laboratory scale work reports magnetic and optically active nano-photocatalyst FexZn1−xO(x = 0.01, 0.03, 0.05) synthesized by solution combustion method. High resolution transmission microscopy suggests a slight degradation in the crystallite structure with Fe doping. X-ray photoelectron spectroscopy analysis shows the presence of intrinsic defects in the crystal structure. Zn resides in +2 and and Fe in +3 oxidation state. Optical band gap studies were made with band structure for each doped sample. The photoctalytic activity of the samples was tested by solar degradation of noxious pollutant Bisphenol A. 99.1% of bisphenol was degraded in 90min in presence of Fe0.03Zn0.97O under synergistic adsorption and photocatalysis. The results were analyzed in terms of total organic carbon, chemical oxygen demand, effect of scavengers, gas chromatography-mass spectrometry and reusability. In presence of Fe0.03Zn0.97O, 45.3% of total organic carbon was removed and chemical oxygen demand was reduced to 11.2%. A possible mechanism with structures of the intermediates has been given. Effect of scavengers reveal that hydroxyl radicals are major reactive oxygen species involved which is also supported by the band edge positions. The research work promises to design highly photo-active tuneable magnetic photocatalysts for solar powered degradation of contaminants of emerging concern with a simple and cost-effective approach.

The use of positrons to survey alteration layers on synthetic nuclear waste glasses

In order to safeguard society and the environment, understanding radioactive waste glass alteration mechanisms in interactions with solutions and near-field materials, such as Fe, is essential to nuclear waste repository performance assessments. Alteration products are formed at the surface of glasses after reaction with solution. In this study, glass altered in the presence of Fe0 in aqueous solution formed two alteration layers: one embedded with Fe closer to the surface and one without Fe found deeper in the sample. Both layers were found to be thinner than the alteration layer found in glass altered in aqueous solution only. For the first time, Doppler Broadening Positron Annihilation Spectroscopy (DB-PAS) is used to non-destructively characterize the pore structures of glass altered in the presence of Fe0. Advantages and disadvantages of DB-PAS compared to other techniques used to analyze pore structures for altered glass samples are discussed. Ultimately, DB-PAS has shown to be an excellent choice for pore structure characterization for glasses with multiple alteration layers. Monte Carlo modeling predicted positron trajectories through the layers, and helped explain DB-PAS data, which showed that the deeper alteration layer without Fe had a similar composition and pore structure to layers on glass altered in water only.

Synthesis and properties of ZnO-HMD@ZnO-Fe/Cu core-shell as advanced material for hydrogen storage

In this paper, a new synthetic strategy towards functionalized ZnO-HMD@ZnO-Fe/Cu core-shell using sol-gel process modified by chemical grafting of hexamethylenediamine (HMD) on the core and in-situ dispersion of Cu0/Fe0 as metallic nanoparticles (M-NPs) on the shell. The as-prepared core-shell materials were fully characterized by transmission electron microscopy, X-ray powder diffractometry, diffuse reflectance and FT-IR spectrophotometery, photoluminescence, and complexes impedance spectroscopy measurements. The XRD patterns agreed with that of the ZnO typical wurtzite structure, indicating good crystallinity of ZnO-HMD@ZnO-Fe/Cu, with the presence of Fe0 and Cu0 phases. Hexamethylenediamine grafting and M-NPs insertion were highly activated and enhanced the core and shell interface by the physiochemical interaction. After functionalization, luminescence intensities and electrical properties of both core and core-shell nanoparticles are improved, indicating the effects of the surface groups on the charge transfer of ZnO-HMD@ZnO-Fe/Cu. The hydrogen capacity retention was depended strongly on the composition and structure of the obtained core-shell. Iron/Copper-loaded ZnO-HMD@ZnO materials exhibited the highest capacity for hydrogen storage. The excellent stability and performance of the ZnO-HMD@ZnO-Fe/Cu core-shell make it an efficient candidate for hydrogen storage.

Biphasic reduction model for predicting the impacts of dye-bath constituents on the reduction of tris-azo dye Direct Green-1 by zero valent iron (Fe0)

Influence of common dye-bath additives, namely sodium chloride, ammonium sulphate, urea, acetic acid and citric acid, on the reductive decolouration of Direct Green 1 dye in the presence of Fe0 was investigated. Organic acids improved dye reduction by augmenting Fe0 corrosion, with acetic acid performing better than citric acid. NaCl enhanced the reduction rate by its ‘salting out’ effect on the bulk solution and by Cl− anion-mediated pitting corrosion of iron surface. (NH4)2SO4 induced ‘salting out’ effect accompanied by enhanced iron corrosion by SO42− anion and buffering effect of NH4+ improved the reduction rates. However, at 2g/L (NH4)2SO4 concentration, complexating of SO42− with iron oxides decreased Fe0 reactivity. Urea severely compromised the reduction reaction, onus to its chaotropic and ‘salting in’ effect in solution, and due to it masking the Fe0 surface. Decolouration obeyed biphasic reduction kinetics (R2>0.993 in all the cases) exhibiting an initial rapid phase, when more than 95% dye reduction was observed, preceding a tedious phase. Maximum rapid phase reduction rate of 0.955/min was observed at pH2 in the co-presence of all dye-bath constituents. The developed biphasic model reckoned the influence of each dye-bath additive on decolouration and simulated well with the experimental data obtained at pH2.

Application of on-line FTIR methodology to study the mechanisms of heterogeneous advanced oxidation processes

On-line FTIR-methodology was used to study the routes of 1,4-dioxane degradation in heterogeneous photocatalysis with titanium dioxide (TiO2) and heterogeneous photo-Fenton with zero valent iron (Fe0). To determine the multiple decomposition mechanisms of this environmental pollutant, heterogeneous Fe0-catalyst was compared with a homogenous iron catalyst and different photocatalytic systems with UV radiation and solar light were studied. In addition, the influence of H2O2 addition profile was assessed to optimize of the reagent dose and reaction time. Complete removal of 1,4-dioxane and 85% mineralization of TOC were achieved by UV photo-Fenton with Fe0, while solar light could work as cost-effective alternative, achieving 65% removal of 1,4-dioxane. Although constant addition of H2O2 was crucial for the rapid oxidation of organic matter, significant degradation was reached by only half of the stoichiometric amount of H2O2. Meanwhile, apparently similar treatment efficiencies were observed in both UV-assisted and solar photocatalysis (almost 60% of 1,4-dioxane removal). The degradation routes for 1,4-dioxane in both advanced oxidation processes were established and presented based on extensive chromatography analysis, whereas FTIR monitoring served as a powerful tool for on-line reaction monitoring. Ethylene glycol diformate was detected as the major primary intermediate in TiO2-photocatalysis, whereas ethylene glycol was found as the main initial by-product in Fe0-based photo-Fenton. An alternative route of 1,4-dioxane degradation through methoxyacetic and acetic acids was observed, being more pronounced in photo-Fenton processes and accentuated further in the presence of Fe0.

Characterization of the enhancement of zero valent iron on microbial azo reduction.

BackgroundThe microbial method for the treatment of azo dye is promising, but the reduction of azo dye is the rate-limiting step. Zero valent iron (Fe0) can enhance microbial azo reduction, but the interactions between microbes and Fe0 and the potential mechanisms of enhancement remain unclear. Here, Shewanella decolorationis S12, a typical azo-reducing bacterium, was used to characterize the enhancement of Fe0 on microbial decolorization.ResultsThe results indicated that anaerobic iron corrosion was a key inorganic chemical process for the enhancement of Fe0 on microbial azo reduction, in which OH−, H2, and Fe2+ were produced. Once Fe0 was added to the microbial azo reduction system, the proper pH for microbial azo reduction was maintained by OH−, and H2 served as the favored electron donor for azo respiration. Subsequently, the bacterial biomass yield and viability significantly increased. Following the corrosion of Fe0, nanometer-scale Fe precipitates were adsorbed onto cell surfaces and even accumulated inside cells as observed by transmission electron microscope energy dispersive spectroscopy (TEM-EDS).ConclusionsA conceptual model for Fe0-assisted azo dye reduction by strain S12 was established to explain the interactions between microbes and Fe0 and the potential mechanisms of enhancement. This model indicates that the enhancement of microbial azo reduction in the presence of Fe0 is mainly due to the stimulation of microbial growth and activity by supplementation with elemental iron and H2 as an additional electron donor. This study has expanded our knowledge of the enhancement of microbial azo reduction by Fe0 and laid a foundation for the development of Fe0-microbial integrated azo dye wastewater treatment technology.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0419-3) contains supplementary material, which is available to authorized users.