Search

Microwave sintering is a key technology for future lunar habitats, which has been verified by various lunar soil simulant experiments. However, nanophase iron (np-Fe0), a unique component of the real lunar regolith, has been ignored in previous studies of the microwave sintering of lunar soil simulants. In this study, microwave-sintering experiments of lunar soil simulant CLRS-2 with and without np-Fe0 at different temperatures were conducted. A comparison of the microstructure and chemical composition of sintered products indicates that all products of samples with 1.0 wt% np-Fe0 exhibit better properties than those without np-Fe0 after heating at equivalent temperatures. Adding np-Fe0 to the lunar soil simulant CLRS-2 couples well with microwaves, which may increase the real heating temperature in a sample, resulting in the product being solidified at 700 °C and a relatively dense product forming at 900 °C, thus improving the sintering efficiency. This study suggests that microwave sintering is an effective potential technology for future lunar habitats and road hardening because of the wide distribution of np-Fe0 in the lunar regolith. The technical parameters given in this study can provide an important guide for future lunar construction by microwave sintering. [ABSTRACT FROM AUTHOR]

Wheat plants are ubiquitously simultaneously exposed to salinity and limited iron availability caused by soil saline‐alkalisation. Through this study, we found that both low Fe and NaCl severely inhibited the growth of seminal roots in wheat seedlings; however, sufficient Fe caused greater growth cessation of seminal roots than low Fe under salt stress. Low Fe improved the root meristematic division activity, not altering the mature cell sizes compared with sufficient Fe under salt stress. Foliar Fe spray and split‐root experiments showed that low Fe‐alleviating the salinity‐induced growth cessation of seminal roots was dependent on local low Fe signals in the roots. Ionomics combined with TEM/X‐ray few differences in the root Na+ uptake and vacuolar Na+ sequestration between two Fe levels under salt stress. Phytohormone profiling and metabolomics revealed salinity‐induced overaccumulation of ACC/ethylene and tryptophan/auxin in the roots under sufficient Fe than under low Fe. Differential gene expression, pharmacological inhibitor addition and the root growth performance of transgenic wheat plants revealed that the rootward auxin efflux and was responsible for the low Fe‐mediated amelioration of the salinity‐induced growth cessation of seminal roots. Our findings will provide novel insights into the modulation of crop root growth under salt stress. Summary statement: We found that low Fe ameliorated the salinity‐induced growth cessation of wheat seminal roots, and our findings will provide novel insights into the understanding of Fe involved nutrient interactions and the modulation of crop root growth under salt stress. [ABSTRACT FROM AUTHOR]

A 2-D framework composed of a chair-like {Fe6} cluster and BTC linkers, [Fe6(BTC)2(HCOO)6(DMF)6] (1, BTC = 1,3,5-benzenetricarboxylate), has been synthesized under solvothermal conditions and characterized by elemental analysis, infrared spectroscopy, thermal gravimetric analysis, and single-crystal X-ray diffraction analysis. The {Fe6} cluster contains six iron ions and six formate ligands, with each formate coordinating with three iron ions to construct the hexa-nuclear iron wheel. The {Fe6} wheels are further connected via BTC ligands resulting in the first example of a 2-D framework based on {Fe6} clusters and BTC linkers. A magnetic study indicates that intramolecular antiferromagnetic interactions exist in the hexa-nuclear iron cluster. [ABSTRACT FROM AUTHOR]

Hepcidin is a peptide hormone that regulates iron homeostasis and acts as an antimicrobial peptide. It is expressed and secreted by a variety of cell types in response to iron loading and inflammation. Hepcidin mediates iron homeostasis by binding to the iron exporter ferroportin, inducing its internalization and degradation via activation of the protein kinase Jak2 and the subsequent phosphorylation of ferroportin. Here we have shown that hepcidin-activated Jak2 also phosphorylates the transcription factor Stat3, resulting in a transcriptional response. Hepcidin treatment of ferroportin-expressing mouse macrophages showed changes in mRNA expression levels of a wide variety of genes. The changes in transcript levels for half of these genes were a direct effect of hepcidin, as shown by cycloheximide insensitivity, and dependent on the presence of Stat3. Hepcidin-mediated transcriptional changes modulated LPS-induced transcription in both cultured macrophages and in vivo mouse models, as demonstrated by suppression of IL-6 and TNF-alpha transcript and secreted protein. Hepcidin-mediated transcription in mice also suppressed toxicity and morbidity due to single doses of LPS, poly(I:C), and turpentine, which is used to model chronic inflammatory disease. Most notably, we demonstrated that hepcidin pretreatment protected mice from a lethal dose of LPS and that hepcidin-knockout mice could be rescued from LPS toxicity by injection of hepcidin. The results of our study suggest a new function for hepcidin in modulating acute inflammatory responses. [ABSTRACT FROM AUTHOR]

Abstract: Batch tests were conducted to investigate nitrite reduction in a zerovalent iron (Fe0) system under various conditions. Nitrite at 1.4mM initial concentration was slowly reduced to nitrogen gas in the first stage (days 1–6), which was mediated by an amorphous, Fe(II)-rich iron oxide coating. The second stage (days 7–14) featured a rapid reduction of nitrite to both ammonia and nitrogen gas and the formation of a more crystalline, magnetite form iron oxide coating. Water reduction by Fe0 occurred concurrently with nitrite reduction from the beginning and contributed significantly to the overall iron corrosion. Nitrite at 14mM was found to passivate the surface of Fe0 grains with respect to nitrite reduction. Adding aqueous Fe2+ significantly accelerated reduction of nitrite by Fe0 to nitrogen gas with lepidocrocite as the main iron corrosion product. Substantially, though still substoichiometrically, 0.55mol of Fe2+ were concomitantly consumed per 1.0mol nitrite reduction, indicating that Fe0 was the main electron source. In the presence of Fe2+, nitrite reduction out-competed water reduction in terms of contributing to the overall iron corrosion. Results of this study help understand complicated interactions between water reduction and nitrite reduction, the roles of surface-bound Fe2+, and the evolution of the iron corrosion coating. [Copyright &y& Elsevier]

Abstract: Rapid oxidation of Fe0 by O2 occurred when Fe0 grains were bathed in 0.54mM FeCl2 solution saturated with dissolved oxygen (DO), forming a substantial corrosion coating on Fe0 grains. A sonication method was developed to strip the corrosion coating off the iron grains layer by layer. The transformation of the constituents and the morphology of the corrosion coating along its depth and over reaction time were investigated with composition analysis, X-ray diffraction and scanning electron microscopy. Results indicate that the sonication method could consistently recover >90% iron oxides produced by the Fe0-DO redox reaction. Magnetite (Fe3O4) and lepidocrocite (γ-FeOOH) were identified as the corrosion products. Initially, lepidocrocite was the preferential product in the presence of DO. As the oxide coating thickened, the inner layer transformed to magnetite, which retained as the only stable corrosion product once DO was depleted. The study confirms the phase transformations between γ-FeOOH and Fe3O4 within a stratified corrosion coating. The sonication technique exemplifies a new approach for investigating more complicated processes in Fe0/oxides/contaminants systems. [Copyright &y& Elsevier]

Nitrate reduction in an iron/nitrate/water system with or without an organic buffer was investigated using multiple batch reactors under strict anoxic conditions. Nitrate reduction was very limited (<10%) at near-neutral pH in the absence of the organic buffer. However, nitrate reduction was greatly enhanced if the system: (1) had a low initial pH (∼2–3); (2) was primed with adequate aqueous Fe2+; or (3) was in the presence of the organic buffer. In Cases (1) and (3), nitrate reduction usually was involved in three stages. The first stage was quick, and H+ ions directly participated in the corrosion of iron grains. The second stage was very slow due to the formation of amorphous oxides on the surface of iron grains, while the third stage was characterized by a rapid nitrate reduction concurrent with the disappearance of aqueous Fe2+. Results indicate that reduction of nitrate by Fe0 will form magnetite; Fe2+ (aq.) can accelerate reduction of nitrate and will be substoichiometrically consumed. Once nitrate is exhausted in the system, no more Fe2+ will be consumed. In the presence of nitrate, Fe2+ (aq) will be adsorbed onto the surface of iron grains or iron oxides; the surface-complexed Fe(II) (extracted by acetate with pH=4.1) might be oxidized and become structural Fe(III), resulting in a steadily increasing ratio of Fe(III)/Fe(II) in the oxides formed. The transformation of nonstoichiometric amorphous iron oxides into crystalline magnetite, a nonpassive oxide, triggers the rapid nitrate removal thereafter. [ABSTRACT FROM AUTHOR]

The effects of three selected Good’s pH buffers on the performance of an Fe0/nitrate/H2O system were evaluated. The Good’s pH buffer itself did not reduce nitrate directly. Nitrate reduction by iron powder at near-neutral pH was negligible in an unbuffered system, but it was greatly enhanced with the presence of the buffer. A significant amount of aqueous Fe2+ (or Fe3+) was released after adding the Good’s pH buffer into the Fe0/H2O system with or without nitrate. In general, the pH of the buffered solution increased from the initial pH (=∼4.6–5.3, depending on buffer’s pKa) to near-neutral pH. After the initial pH hiking, the pH in the system was more or less stable for a period of time (∼5–10 h, usually concurrent with a fairly stable aqueous Fe2+). The pH then drifted to ∼7.1 to 8.6, depending on the buffer’s initial concentration, the buffer’s pKa, and the consumption of Fe2+ concurrent with nitrate reduction. While a common assumption made by researchers is that Good’s pH buffers do not directly participate in reaction processes involved in contaminant remediation, this study shows that as side effects, the Good’s pH buffer may react with iron powder. [ABSTRACT FROM AUTHOR]

The effect of low pH (2–4.5) on nitrate reduction in an iron/nitrate/water system was investigated through batch experiments conducted in a pH-stat. The results showed that nitrate could be rapidly reduced to ammonium at pH 2–4.5. A black coating, consisted of both Fe(II) and Fe(III), was formed on the surface of iron grains as an iron corrosion product. X-ray diffractometry indicated that the black coating was poorly crystalline, and its spectrum could not be matched with commonly known iron oxides/hydroxides/oxide hydroxides or green rust I/II. The black coating does not inhibit the reactivity of Fe0 (at least at pH <3). The black coating was unstable and evolved with time into other oxides under certain conditions. A kinetic model incorporating the effects of pH on nitrate reduction and Langmuir adsorption of nitrate was proposed, and the parameters were estimated by nonlinear curve fitting. Based on this model, the two major effects of pH on the kinetics of nitrate reduction are that: (a) H+ ions directly participate in the redox reaction of nitrate reduction following first-order kinetics; and (b) H+ ions affect the nitrate adsorption onto reactive sites. [Copyright &y& Elsevier]

Although considerable research has been conducted on nitrate reduction by zerovalent iron (ZVI), the process kinetics at near neutral pH has not been studied thoroughly. In this study, a kinetic model with a double-Langmuir-adsorption formulation was developed to represent site saturation effects of aqueous Fe[sup 2+] and NO[sub 3][sup -] on nitrate reduction in a ZVI system at near neutral pH. Both an analytical solution and a numerical solution of the proposed model were developed. The kinetic parameters were evaluated based on batch experiments with two types of ZVI. Sensitivity analysis indicates that it is rather difficult and unreliable to estimate the parameters of the proposed multivariable nonlinear kinetic model from a single test curve. A better strategy is to obtain reliable parameters by designing specific experiments to target one parameter each time. The results indicate that, although the values of the kinetic parameters might change with different types of iron powder, the kinetic model can fit the experimental data very well, and therefore is consistent with the proposed mechanism. [ABSTRACT FROM AUTHOR]

Finding a good sorbent for phosphorus (P) recovery from the aquatic environment is critical for preventing eutrophication and providing P resources. The activated iron system (mainly consisted of zero-valent iron (ZVI), Fe 3 O 4 and Fe 2+ ) has been reported to exhibit a favorable performance towards various contaminants in wastewater, but its effect on P recovery has not been studied systematically. In this study, we used Fe 2+ -nitrate pretreatment reaction to prepare the activated iron system and then applied it to P recovery. Results show that more than 99% P was removed from water in 60 min; co-existing anions (NO 3 − , Cl − and SO 4 2− ) and natural organic matter (NOM) had little effect on P removal. The P removal capacity of activated iron system is very high compared with currently reported sorbents. Externally-supplied Fe 2+ plays an important role on P removal in the system. Regeneration study shows that the activated iron system exhibited stable P recovery ability by using 0.1 M NaOH solution. Various methods were applied to characterize the ZVI and iron corrosion, and results conclude that sorption precipitation, and co-precipitation contribute to P removal. This method will be promising and have an application potential in the field for efficient and cost-effective recovery of P with cheap microscale zero valent iron. [ABSTRACT FROM AUTHOR]

[Display omitted] • Yudongzi BIFs were formed at ca. 2.8 Ga, and suffered two-stage metamorphism. • Yudongzi BIFs were formed on the back–arc basin setting. • Yudongzi complex combined to Yangtze Block later than Paleoproterozoic. The Yudongzi banded iron formations (BIFs) are widely spread in the Neoarchean Yudongzi Group of the Bikou Terrane, Central China. Their sedimentary and metamorphic ages, however, remain controversial, either their forming or reworking processes. In this contribution, we conducted an integrated study of zircon U-Pb-Hf isotope geochemistry, as well as mineral and bulk-rock geochemistry on the Heishan'gou iron deposit, the largest iron deposit of the Yudongzi BIFs, to constrain their formation and metamorphism ages, source of ore-forming material and tectonic setting. Mineral chemistry analysis indicates that the amphibolite, host-rock of the Heishan'gou deposit suffered amphibolite facies metamorphism. LA-ICP-MS U-Pb dating of zircon grains from orthometamorphic host-rocks suggests that the Heishan'gou deposit was formed at the early Neoarchean (2781 ± 43 Ma for amphibolite and 2776 ± 43 Ma for plagioclase-hornblende schist), and metamorphosed at ca. 2480 ± 26 Ma and 1818 ± 44 Ma, respectively. The low contents of aluminum, titanium and high field strength elements in BIFs suggest that they are detritus-free marine chemical precipitates. The rare earth elements (REE) and Y patterns of BIFs display seawater-like signatures with light REE depletion, and positive La and Y anomalies. Meanwhile, their positive Eu anomalies suggest that submarine hydrothermal fluid might also be involved in the precipitation of BIFs. Combined with zircon Hf isotope data and geochemical compositions of amphibolites, it is proposed that the Yudongzi BIFs should be formed at back-arc basin setting. Compared with the representative Archean continent nucleus of the Yangtze Block (Kongling Complex), the Yudongzi Complex experienced distinct crustal evolutionary history. It indicates that the Yudongzi Complex might represent the accretionary block combined to the Yangtze continental nucleus later than the Paleoproterozoic. [ABSTRACT FROM AUTHOR]

· Mn(VII)-Fe(III)/PMS process showed excellent coagulation and oxidation performance. · NOM in raw water can mediate the redox cycle of iron. · The synergistic effect of NOM, Fe and Mn can promote the activation of PMS. · SO 4 •− was the main active species in the Mn(VII)-Fe(III)/PMS process. To improve the performance of the conventional coagulation process, a permanganate (Mn(VII)) pre-oxidation combined with Fe(III)/peroxymonosulfate (PMS) coagulation process (Mn(VII)-Fe(III)/PMS) that can significantly improve the removal of dissolved organic carbon (DOC), turbidity, and micropollutants is proposed in this study. Compared with conventional Fe(III) coagulation, the Mn(VII)-Fe(III)/PMS process can also significantly enhance the removal of iohexol and sulfamethoxazole in raw water. During this process, the primary reduction product, Mn(IV), after Mn(VII) pre-oxidation was adsorbed on the floc surfaces and involved in the Fe(III)/PMS process. The natural organic matter (NOM) in raw water mediated the redox cycle of iron. The synergistic effect of NOM, Fe, and Mn facilitated the redox cycle of Mn(III)/Mn(IV) and Fe(III)/Fe(II) to promote the activation of PMS. The sulfate radical (SO 4 •−) played an important role in the degradation of micropollutants. The formation potential of the detected volatile disinfection by-product (DBP) during the subsequent chlorination was reduced by 21.9% after the Mn(VII)-Fe(III)/PMS process. This study demonstrated the promising application of the Mn(VII)-Fe(III)/PMS process for coagulation and micropollutant control and illustrated the reaction mechanism. This study provides guidance for improving conventional drinking water treatment processes. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract A novel dicarboxyl-functionalized iron cryptate with a 2,2-pyridine unit has been synthesized, which displays outstanding electrochemical properties in water as a potential biosensing probe. Taking the silver ion (Ag+) as an example, we report a novel Ag+ assay by recording the electrochemical signals of Fe cryptate. In summary, a hairpin-structured DNA probe is designed and modified with the synthesized Fe cryptate. In the absence of Ag+, this is absorbed on the surface of a reduced graphene oxide modified electrode and a significant electrochemical response is obtained. In the presence of Ag+, cytosine–cytosine mismatches in the DNA probe recognize target ions and it is transformed into a conformation which cannot resist digestion by exonuclease III. As a result, Fe cryptate is released and Ag+ is recycled for continuous DNA digestion. By analyzing the reduced electrochemical signals of Fe cryptate, it is possible to quantify the target ions. Graphical abstract Unlabelled Image Highlights • A novel dicarboxyl-functionalized iron cryptate is synthesized. • Fe cryptate is modified with a DNA probe and the electrochemical response is studied. • A sensitive and selective method for Ag+ assay is developed. [ABSTRACT FROM AUTHOR]

[Display omitted] • ECS as a substrate for S-nZVI can effectively avoid agglomeration. • S-nZVI@ECS can effectively remove Cd(II), Cu(II) and Pb(II) in a wide pH range. • The mechanisms include reduction, complexation, and precipitation. • Cu(II) and Pb(II) removal are almost unaffected in the presence of Cd(II). Exhausted copper slag (ECS) is an industrially utilized secondary waste, and due to its large volume and potential environmental risks, the utilization of ECS in a safe manner is required. In this study, a novel synthetic composite (S-nZVI@ECS) was prepared by loading sulfidized nanoscale zerovalent iron (S-nZVI) onto ECS for the removal of Cd(II), Cu(II), and Pb(II) from aqueous solutions. The composite not only provides a new idea for utilizing ECS but also prevents S-nZVI particles from agglomerating. The optimized S-nZVI@ECS can achieve efficient removal of the three heavy metals over a wide pH range without being affected by coexisting ions (Na+, K+, Mg2+, Ca2+). With the respective maximum adsorption capacities of these three cationic heavy metals being as high as 173.01, 93.81, and 338.98 mg/g (based on the Langmuir model), the elimination of S-nZVI@ECS for these three cationic heavy metals could be fitted with the Langmuir and Freundlich models well, and the associated mechanisms (including redox reactions, complexation, and precipitation) were elucidated. The novel S-nZVI@ECS composites prepared in this study using secondary waste as a substrate have good potential for removing cationic heavy metals from aqueous solutions. [ABSTRACT FROM AUTHOR]

In present research, Fe-doped brushite bone cements were synthesized. The setting time, microstructure and antibacterial property of samples were investigated. The results showed that the setting time of cements was retarded to about 20 min and 123 min, respectively, as iron doping content increasing from 1 mol% to 5 mol% in β-TCP powder. Moreover, Fe-doped cements had much bigger crystal particles and calcium iron phosphate was identified in them. Furthermore, Fe-doped cements performed well in inhibiting the growth of Staphylococcus aureus and Pseudomonas aeruginosa, and larger inhibition halo was obtained with more iron content. Nevertheless, the Fe-loaded cements were not so sensitive to Escherichia coli as to the other two bacteria. [ABSTRACT FROM AUTHOR]

Aerosol soluble iron (Fe) is crucial in the biogeochemical cycle and atmospheric processing. In this study, soluble Fe and their solubility in fine particles (PM 2.5) were investigated over Xi'an, China to insight the iron sources and the roles in aerosol formation. Our results showed that most Fe in PM 2.5 was insoluble (Fe solubility: 25.5 ± 11.3%). Seasonal variations exhibited that the highest soluble Fe(II) showed in winter (308.9 ng m−3) and the highest Fe(III) levels were in summer (116.3 ng m−3). Source identification of soluble Fe illustrated that industrial coal combustion contributed most in summer, whereas mineral dust, biomass burning, and coal combustion dominated in spring, autumn, and winter, respectively. Moreover, strong correlations between soluble Fe and water-soluble inorganic ions suggested soluble Fe is related to not only primary sources but also secondary formations. Furthermore, a negative correlation (R = −0.56) was observed in winter between Fe(III) and SO 4 2−, indicating that the oxidation pathway of Fe(III) catalysis should play a vital role in sulfate formation in winter. In addition, secondary brown carbon presented positive correlations with soluble Fe(II), while negatively correlated with soluble Fe(III), potentially suggested an important pathway for the formation of secondary BrC. Our study provides a broader understanding of Fe solubility and their roles in atmospheric chemical processing. [Display omitted] • Field observation was conducted to reveal the role of soluble Fe in secondary aerosol formations. • Fe(II) was the highest in winter, while the highest Fe(III) was in summer. • Both biomass burning and coal combustion contributed to soluble Fe. • Fe-chemistry played a vital role in winter sulfate and secondary BrC formations. [ABSTRACT FROM AUTHOR]

In female, inadequate iron supply is a highly prevalent problem that often leads to iron-deficiency anemia. This study aimed to understand the effects of pregnancy and lactation on iron metabolism. Rats with different days of gestation and lactation were used to determine the variations in iron stores and serum iron level and the changes in expression of iron metabolism-related proteins, including ferritin, ferroportin 1 (FPN1), ceruloplasmin (Cp), divalent metal transporter 1 (DMT1), transferrin receptor 1 (TfR1), and the major iron-regulatory molecule—hepcidin. We found that iron stores decline dramatically at late-pregnancy period, and the low iron store status persists throughout the lactation period. The significantly increased FPN1 level in small intestine facilitates digestive iron absorption, which maintains the serum iron concentration at a near-normal level to meet the increase of iron requirements. Moreover, a significant decrease of hepcidin expression is observed during late-pregnancy and early-lactation stages, suggesting the important regulatory role that hepcidin plays in iron metabolism during pregnancy and lactation. These results are fundamental to the understanding of iron homeostasis during pregnancy and lactation and may provide experimental bases for future studies to identify key molecules expressed during these special periods that regulate the expression of hepcidin, to eventually improve the iron-deficiency status. [ABSTRACT FROM AUTHOR]

Geobacter species are of great interest for environmental and biotechnology applications as they can carry out direct electron transfer to insoluble metals or other microorganisms and have the ability to assimilate inorganic carbon. Here, we report on the capability and key enabling metabolic machinery of Geobacter metallireducens GS-15 to carry out CO2 fixation and direct electron transfer to iron. An updated metabolic reconstruction was generated, growth screens on targeted conditions of interest were performed, and constraint-based analysis was utilized to characterize and evaluate critical pathways and reactions in G. metallireducens. The novel capability of G. metallireducens to grow autotrophically with formate and Fe(III) was predicted and subsequently validated in vivo. Additionally, the energetic cost of transferring electrons to an external electron acceptor was determined through analysis of growth experiments carried out using three different electron acceptors (Fe(III), nitrate, and fumarate) by systematically isolating and examining different parts of the electron transport chain. The updated reconstruction will serve as a knowledgebase for understanding and engineering Geobacter and similar species. [ABSTRACT FROM AUTHOR]

Nanoscale zero-valent iron (nZVI) has been extensively used to remove various pollutants. However, the rapid deactivation due to aggregation and surface passivation severely limits its practical application. In this study, a novel composite with nZVI supported by pinecone biochar (nZVI-PBC) was successfully synthesized and used for the removal of high concentration Cr(VI) from aqueous solution in the presence of Shewanella oneidensis MR-1 (MR-1). The results showed that the nZVI-PBC coupling with MR-1 (nZVI-PBC/MR-1) exhibited an excellent removal performance for high concentration Cr(VI) compared to the nZVI-PBC alone. Under optimal conditions, 100 mg/L Cr(VI) could be removed completely by nZVI-PBC/MR-1 within 48 h, while only 39.50% of Cr(VI) was removed by nZVI-PBC alone. The improvement of Cr(VI) removal is due to the dissolution of the surface passivation layer of nZVI-PBC, formation of sorbed Fe(II) in the presence of MR-1, and an important role of extracellular polymeric substance (EPS) derived from MR-1. X-ray photoelectron spectroscopy (XPS) and Cr K-edge X-ray absorption near-edge structure spectra (XANES) confirmed that most Cr(VI) was reduced to insoluble Cr(III) and formed Cr 2 O 3 , Cr x Fe 1-x (OH) 3 and FeCr 2 O 4 precipitates, and a small amount of unreduced Cr(VI) was immobilized through adsorption and complexation. The results suggest that nZVI-PBC/MR-1 can effectively overcome the limitations of nZVI and achieve highly efficient removal of high concentration Cr(VI). [Display omitted] • nZVI-PBC coupling with MR-1 exhibited an excellent capacity for Cr(VI) removal. • Sorbed Fe(II) could act as a strong reductant to reduce Cr(VI) to Cr(III). • The EPS derived from MR-1 play an important role in Cr(VI) removal. • nZVI-PBC coupling with MR-1 overcomes the aggregation and passivation of nZVI. • The mechanism of Cr(VI) removal by nZVI-PBC coupling with MR-1 was proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high-efficiency process for Cr(VI) reduction/removal was developed. • MR-1 can promote dissolution of the passivation layer and maintain the nZVI reactivity. • The EPS play a crucial role in removing the passivation layer and reducing Cr(VI). • The mechanisms for MR-1 enhancing Cr(VI) reduction by ZVI were proposed. The surface passivation of nZVI is considered one of the most challenging in successfully applying nZVI to environmental remediation. Shewanella oneidensis MR-1 (MR-1) are widely distributed in the various aquatic environments, which can use Fe(III) (hydr)oxides as electron acceptor, converting Fe(III) to Fe(II). In this study, the nZVI coupling with MR-1 process is proposed for efficient reduction/removal of high concentration of hexavalent chromium [Cr(VI)]. By studying the experimental conditions such as initial Cr(VI) concentrations, nZVI dosages, and cell concentrations, the optimal experimental conditions for Cr(VI) removal were obtained. Under the conditions of nZVI dosage of 1.32 mM, cell concentration of 3 × 107 cells/mL and Cr(VI) concentration of 80 mg/L, the removal efficiency of Cr(VI) and total chromium [Cr(total)] can reach 98.65% and 98.23% within 6 days, respectively. The key point of this study is to demonstrate that the addition of MR-1 can promote dissolution of the passivation layer on the nZVI surface and prolong its reactivity, significantly improving Cr(VI) reduction/removal efficiency. In this process, most Cr(VI) is reduced to Cr(III), which then is removed by forming Cr 2 O 3 and Cr(CH 3 C(O)CHC(O)CH 3) 3 complexes, and a small amount of the unreduced Cr(VI) is removed through adsorption and complexation with oxygen-containing functional groups. The extracellular polymeric substances (EPS) derived from MR-1 play a crucial role in removing the passivation layer on the nZVI surface and Cr(VI) removal. This method may have great potential application for reduction and detoxification of Cr(VI) in the aqueous environment. [ABSTRACT FROM AUTHOR]