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Se(VI) was very refractory to be removed by zero-valent iron (ZVI), therefore weak magnetic field (WMF) was employed to achieve efficient Se(VI) removal by ZVI. Batch experiments showed that negligible Se(VI) (<4%) was removed by ZVI without the application of WMF within 72 h. The presence of WMF dramatically enhanced Se(VI) sequestration by ZVI and complete removal of 10.0 mg L −1 Se(VI) was achieved by ZVI in 90 min. The main portion of kinetics of Se(VI) removal by ZVI in the presence of WMF followed zero-order rate law and the rate constants of Se(VI) sequestration by ZVI increased progressively with increasing the ZVI dosage. Fe K -edge XAFS spectra and synchrotron radiation-XRD analysis revealed that ZVI was transformed to X-ray amorphous Fe 3 O 4 before finally transformed to lepidocrocite (γ-FeOOH). The LCF analysis of Se K -edge XANES spectra indicated that adsorptive removal of Se(VI) was minor but adsorption of Se(VI) to the corroded ZVI surface was the first step of Se(VI) removal. Se(VI) was rapidly reduced to Se(IV), which could be further transformed to Se(0). Comparison of the performance of Se(VI) removal in the literature suggested that employing WMF to enhance Se(VI) removal by ZVI under oxic conditions be a promising method. [ABSTRACT FROM AUTHOR]

The change of rust composition on weathering steel was consecutively monitored by in situ Raman spectroscopy during exposure to atmosphere under cyclic 4 h wet-4 h dry condition for 144 h in the presence of NaCl deposit. Raman spectra of the rust surface in the presence of NaCl deposit at 0.93 mg cm corresponded to those of lepidocrocite (γ-FeOOH) and magnetite (FeO) in the initial 12 h exposure. After 12 h exposure, akaganeite (β-FeOOH) started to form, and its molar ratio on the rust surface increased to 90 % at 30 h exposure. The Raman spectra further changed after 30 h exposure in which γ-FeOOH again emerged. The reappearance of γ-FeOOH is assumed to be caused by capture of chloride ions in β-FeOOH resulting in the decrease of free chloride ions in the surface solution layer. When the amount of NaCl deposit was decreased to 0.11 mg cm, the surface was covered with dark brown corrosion product which may be amorphous FeOOH and after repeated dry-wet cycles, yellow-brown spots emerged which consisted of β-FeOOH. [ABSTRACT FROM AUTHOR]

Efficient methods for the synthesis of layered structure nanomaterials (nanosheets), their complete exfoliation (delamination) into the layers of atomic thickness and design of organic-inorganic nanohybrids present important stages toward development of improved polymer-based nanocomposites and pillared heterostructureswith potential application in purification technologies such as photocatalysis. A rapid and efficient exfoliation process of protonated layered ferrititanates with lepidocrocite-like structure and formation of organic-inorganic nanohybrids is performed starting from the nanosheets composed of only a few host layers and nanometric lateral dimensions using quaternary ammonium compounds. These nanosheets are initially synthesized from a highly abundant precursor through an alkaline hydrothermal route. We demonstrated that dimethyldioctadecylammonium cations strongly interact with the exfoliated single host layers (0.75 nm thick) providing thermal stability (~500 °C) to the as-prepared organic-inorganic nanohybrid over the temperature range commonly applied for the processing of thermoplastic nanocomposites. [ABSTRACT FROM AUTHOR]

Ferrihydrite is commonly associated with silicate (Si) and manganese (Mn) in various geological settings. Here, we examined the effects of Fe(III) hydrolysis rate and dissolved Si concentration on ferrihydrite formation, as well as the effects of aqueous Mn(II) on the transformation of two-line ferrihydrite (2LFh). Results indicate that with decreasing Fe(III) hydrolysis rate, the products transition from 2LFh to six-line ferrihydrite (6LFh) and goethite. When the hydrolysis rate is very low, lepidocrocite is formed in addition to 6LFh and goethite. This can be attributed to a decrease in the concentration of hydrolyzed Fe(III) species as the hydrolysis rate decreases. With increasing Si concentration, the products of Fe(II) oxidation transition from an assemblage of lepidocrocite and goethite to a mixture of 6LFh with minor poorly crystalline lepidocrocite and goethite, and finally to 2LFh. The strong adsorption and polymerization of Si limit the nucleation and growth of hydroxychloride green rust during Fe(II) oxidation and precipitation, thereby hindering the formation of lepidocrocite and goethite. With aging at 60 °C and various pHs, 2LFh converts into goethite and hematite within 20–140 days, with the conversion rate increasing with increasing pH. In addition, a small amount of pre-formed goethite converts into hematite at pH 7, 9 and 12. The aging of 2LFh in 8 mM Mn(II) at pH 4, 5.5, and 7 overwhelmingly favors the formation of goethite over hematite. However, the transformation of 2LFh is largely inhibited in 24 mM Mn(II) due to the limited accessibility of surface sites caused by increasing Mn(II) adsorption. These data provide evidence that the formation and secondary mineralization of ferrihydrite largely depend on pH, coexisting silicate, and Mn(II). [ABSTRACT FROM AUTHOR]

Dissolution of iron from mineral dust particles greatly depends upon the type and amount of copresent inorganic anions. In this study, we investigated the roles of sulfate, chloride, nitrate, and perchlorate on the dissolution of maghemite and lepidocrocite in ice under both dark and UV irradiation and compared the results with those of their aqueous counterparts. After 96 h of reaction, the total dissolved iron in ice (pH 3 before freezing) was higher than that in the aqueous phase (pH 3) by 6-28 times and 10-20 times under dark and UV irradiation, respectively. Sulfuric acid was the most efficient in producing labile iron under dark condition, whereas hydrochloric acid induced the most dissolution of the total and ferrous iron in the presence of light. This ice-induced dissolution result was also confirmed with Arizona Test Dust (AZTD). In the freeze-thaw cycling test, the iron oxide samples containing chloride, nitrate, or perchlorate showed a similar extent of total dissolved iron after each cycling while the sulfate-containing sample rapidly lost its dissolution activity with repeating the cycle. This unique phenomenon observed in ice might be related to the freeze concentration of protons, iron oxides, and inorganic anions in the liquid-like ice grain boundary region. These results suggest that the ice-enhanced dissolution of iron oxides can be a potential source of bioavailable iron, and the acid anions critically influence this process. [ABSTRACT FROM AUTHOR]

This paper described the preparation of lepidocrocites (γ-FeOOH) via the photocatalytic oxidation of Fe(II) in the presence of trace citric acid under visible light irradiation. The experimental results showed that different crystallized lepidocrocites were obtained by controlling the concentrations of citric acid under visible light irradiation. The crystallization of lepidocrocite was found to gradually decrease with increase in the concentration of citric acid. During the γ-FeOOH formation, the Fe(II)-citrate complex could absorb light in the visible regions and produce oxidizing species, leading to the acceleration of the oxidation rate. The higher oxidation rate was favorable for the formation of low-crystalline γ-FeOOH. The as-prepared low-crystalline γ-FeOOH was easily dissolved in aqueous solution, which exhibited higher efficiency for the degradation of orange II by homogeneous photo-Fenton reaction, and the low-crystalline γ-FeOOH had large specific surface area, which showed higher adsorption and photocatalytic activity toward the photodegradation of orange II by heterogeneous photo-Fenton reaction. [ABSTRACT FROM AUTHOR]

Lepidocrocite ( γ-FeOOH), an important iron-bearing mineral found to exist with a relatively high abundance in the soils of the Chinese nuclear test sites, has rarely been studied for its sorption of transuranic elements from the nuclear wastes. This work develops a quantitative surface complexation model describing the sorption and speciation of Np(V) on synthetic lepidocrocite ( γ-FeOOH). Batch sorption experiments on γ-FeOOH were performed under a range of conditions (25 ℃, 0.1 M NaClO4, pH = 4 - 11, 5 μM Np(V), and atmospheric conditions). The Diffuse Layer Model (DLM) was applied to describe the surface-complexation reaction. The data were best-fitted with a single surface-complexation reaction, (≡XOH + NpO2+ = XONpO20 + H+) that occurred at the lepidocrocite/water interface to form an inner-sphere Np(V) complex with lepidocrocite. The results are complemented by the Np LIII-edge EXAFS data that show that Np(V) was absorbed on γ-FeOOH as monomeric neptunyl ions, with no observations of multinuclear surface complexes or surface precipitates. A prominent peak at ∼3 Å in the EXAFS Fourier Transform spectra can be attributed to a Np-Fe scattering path, consistent with the formation of an inner sphere Np(V)-lepidocrocite surface complex. Formation of aqueous NpO2(CO3) x1 -2 x complexes prevents Np(V) sorption at higher pH values but it is unclear if ternary lepidocrocite-Np-carbonate complexes may also form. These data indicate that there are subtle differences in Np(V) interactions with hematite, goethite, and lepidocrocite which is likely a manifestation of the differences in surface reactivity of the three minerals. [ABSTRACT FROM AUTHOR]

Background: In soils and sediments, manganese oxides and oxygen usually participate in the oxidation of ferrous ions. There is limited information concerning the interaction process and mechanisms of ferrous ions and manganese oxides. The influence of air (oxygen) on reaction process and kinetics has been seldom studied. Because redox reactions usually occur in open systems, the participation of air needs to be further investigated. Results: To simulate this process, hexagonal birnessite was prepared and used to oxidize ferrous ions in anoxic and aerobic aqueous systems. The influence of pH, concentration, temperature, and presence of air (oxygen) on the redox rate was studied. The redox reaction of birnessite and ferrous ions was accompanied by the release of Mn2+ and K+ ions, a signiicant decrease in Fe2+ concentration, and the formation of mixed lepidocrocite and goethite during the initial stage. Lepidocrocite did not completely transform into goethite under anoxic condition with pH about 5.5 within 30 days. Fe2+ exhibited much higher catalytic activity than Mn2+ during the transformation from amorphous Fe(III)-hydroxide to lepidocrocite and goethite under anoxic conditions. The release rates of Mn2+ were compared to estimate the redox rates of birnessite and Fe2+ under diferent conditions. Conclusions: Redox rate was found to be controlled by chemical reaction, and increased with increasing Fe2+ concentration, pH, and temperature. The formation of ferric (hydr)oxides precipitate inhibited the further reduction of birnessite. The presence of air accelerated the oxidation of Fe2+ to ferric oxides and facilitated the chemical stability of birnessite, which was not completely reduced and dissolved after 18 days. As for the oxidation of aqueous ferrous ions by oxygen in air, low and high pHs facilitated the formation of goethite and lepidocrocite, respectively. The experimental results illustrated the single and combined efects of manganese oxide and air on the transformation of Fe2+ to ferric oxides. [ABSTRACT FROM AUTHOR]

The oxidation of aqueous suspensions of chukanovite (Fe 2 (OH) 2 CO 3 ) obtained by mixing NaOH, FeCl 2 and Na 2 CO 3 solutions was studied for various [Fe 2+ ]/[OH − ] and [CO 3 2− ]/[OH − ] concentration ratios. The redox potential of a platinum electrode immersed in the suspension was monitored during the oxidation process which reveals the presence of a plateau corresponding to equilibrium conditions between chukanovite and a poorly crystallized Fe(III) oxyhydroxide. The end products were characterized by Infrared spectroscopy and X-ray diffraction. Carbonate favoured the formation of goethite while Fe 2+ aq favoured lepidocrocite. This effect is mainly due to the influence of these species on the pH of the solution. [ABSTRACT FROM AUTHOR]

Premagnetization was employed to enhance the reactivity of zerovalent iron (ZVI) toward As(III) sequestration for the first time. Compared to the pristine ZVI (Pri-ZVI), the rate of As(III) elimination by the premagnetized ZVI (Mag-ZVI) was greater over the pHini range of 4.0-9.0 and increased progressively with increasing intensity of the magnetic field for premagnetization. Mag-ZVI could keep its reactivity for a long time and showed better performance than Pri-ZVI for As(III) removal from synthetic groundwater in column tests. The Fe K-edge XAFS analysis for As(III)-treated ZVI samples unraveled that premagnetization promoted the transformation of ZVI to iron (hydr)oxides and shifted the corrosion products from maghemite and magnetite to lepidocrocite, which favored the arsenic sequestration. The arsenic species analysis revealed that premagnetization facilitated the oxidation of As(III) to As(V). ZVI pretreated with grinding was very different from Mag-ZVI with regard to As(III) removal, indicating that the improved reactivity of Mag-ZVI should not be associated with the physical squeezing effect of the ZVI grains during magnetization. The positive correlation between the remanence of Mag-ZVI and the rate constants of total arsenic removal indicated that the enhanced reactivity of Mag-ZVI was mainly ascribed to its magnetic memory, i.e., the remanence kept by Mag-ZVI. [ABSTRACT FROM AUTHOR]

Micro-Raman spectroscopy was used to characterize the rust formed on 1008 carbon steel exposed to marine test sites in Hawaii. Besides lepidocrocite in the outer rust layers and goethite in the inner rust layers, akaganeite was detected on all samples due to the presence of Cl- and increased in quantity in the rust layer with increasing Cl- deposition rate. The presence of Cl- did not affect the corrosion rate of carbon steel when the Cl- deposition rate was lower than a threshold of approximately 75 mg/m²/day, but significantly increased the corrosion rate when the Cl- deposition rate was higher than the threshold. This is likely due to akaganeite being a sink for Cl- by incorporating it into its tunnel structure when salt deposition is below a certain level. Once the akaganeite is saturated with Cl- and the akaganeite cannot take up any more Cl-, free Cl- can be available to accelerate corrosion at anodic sites. [ABSTRACT FROM AUTHOR]

Abiotic oxidation of Fe(II) is a common pathway in the formation of Fe (hydr)oxides under natural conditions, however, little is known regarding the presence of arsenate on this process. In hence, the effect of arsenate on the precipitation of Fe (hydr)oxides during the oxidation of Fe(II) is investigated. Formation of arsenic-containing Fe (hydr)oxides is constrained by pH and molar ratios of As:Fe during the oxidation Fe(II). At pH 6.0, arsenate inhibits the formation of lepidocrocite and goethite, while favors the formation of ferric arsenate with the increasing As:Fe ratio. At pH 7.0, arsenate promotes the formation of hollow-structured Fe (hydr)oxides containing arsenate, as the As:Fe ratio reaches 0.07. Arsenate effectively inhibits the formation of magnetite at pH 8.0 even at As:Fe ratio of 0.01, while favors the formation of lepidocrocite and green rust, which can be latterly degenerated and replaced by ferric arsenate with the increasing As:Fe ratio. This study indicates that arsenate and low pH value favor the slow growth of dense-structured Fe (hydr)oxides like spherical ferric arsenate. With the rapid oxidation rate of Fe(II) at high pH, ferric (hydr)oxides prefer to precipitate in the formation of loose-structured Fe (hydr)oxides like lepidocrocite and green rust. [ABSTRACT FROM AUTHOR]

The adsorption of arsenic to iron oxyhydroxides strongly depends on water chemistry. Iron(III) oxyhydroxides can also participate in the oxidation of As(III) to As(V), which changes arsenic’s toxicity and adsorption behavior. As(III) and As(V) adsorption to lepidocrocite (γ-FeOOH) were examined in batch experiments that explored the effects of lepidocrocite dose, pH, availability of dissolved oxygen, and the presence of aqueous Fe(II) on adsorption. Lepidocrocite is an iron oxyhydroxide found in soils, and it is one of the major products of iron electrocoagulation for water treatment. A surface complexation model was able to describe the adsorption of both As(III) and As(V) to lepidocrocite over a broad range of conditions. The concentration and oxidation states of arsenic in solution were measured over the course of the reactions. At both oxic and anoxic conditions, As(III) was oxidized to As(V) in systems that contained lepidocrocite together with Fe(II); this oxidation led to overall enhanced arsenic adsorption at near neutral pH. With oxygen the pH-dependent generation of oxidants from the Fenton reaction drove the As(III) oxidation. In the absence of oxygen the As(III) was probably oxidized by Fe(III) in lepidocrocite that had become more reactive upon reaction with Fe(II). [ABSTRACT FROM AUTHOR]

Understanding the processes involved in the control of arsenic (As) dynamics within soils has become a challenging issue for soil and water quality preservation. Interactions between mineralogical phases, organic ligands and bacterial communities — closely linked to the chemical conditions of the medium — were thus investigated through a geochemical and microbiological experimental study involving the reduction of As(V)-doped lepidocrocite within the soil. Reducing conditions were established as soon as the experiment started, followed by a release of dissolved organic carbon corresponding to a release of acetate. Scanning electron microscopy observations pointed out a large bacterial colonization occurring on the lepidocrocite leading to a 3-dimensionally shaped biodissolution of lepidocrocite. The taxonomic diversity evolved throughout the experiment, and thus it demonstrated the evolution of the metabolic activities of the bacteria. At the beginning, lepidocrocite was mainly colonized by bacteria belonging to the Geobacter genus (Deltaproteobacteria) (26%) and Bacillus and Oxalophagus fermentative related genera (Firmicutes) (72%). After two weeks, Geobacter spp. and Firmicutes represented 54% and 30% of the bacterial community, respectively. Although still dominated by Geobacter spp. (34%) at the end of the experiment, the bacterial diversity had increased. After 3 and 8 weeks of incubation, the presence of the arsB and ACR3(1) genes, encoding transporters involved in As detoxification processes, indicated that this community harbored As-resistant or As-transforming genera able to contribute to the transformation of As(V) into As(III). [ABSTRACT FROM AUTHOR]

Although substitution of aluminuminto iron oxides and oxyhydroxideshas been extensively studied, it is difficult to obtain accurate incorporationlevels. Assessing the distribution of dopants within these materialshas proven especially challenging because bulk analytical techniquescannot typically determine whether dopants are substituted directlyinto the bulk iron oxide or oxyhydroxide phase or if they form separate,minor phase impurities. These differences have important implicationsfor the chemistry of these iron-containing materials, which are ubiquitousin the environment. In this work, 27Al and 2H NMR experiments are performed on series of Al-substituted goethite,lepidocrocite, and 2-line ferrihydrite in order to develop an NMRmethod to track Al substitution. The extent of Al substitution intothe structural frameworks of each compound is quantified by comparingquantitative 27Al MAS NMR results with those from elementalanalysis. Magnetic measurements are performed for the goethite seriesto compare with NMR measurements. Static 27Al spin–echomapping experiments are used to probe the local environments aroundthe Al substituents, providing clear evidence that they are incorporatedinto the bulk iron phases. Predictions of the 2H and 27Al NMR hyperfine contact shifts in Al-doped goethite andlepidocrocite, obtained from a combined first-principles and empiricalmagnetic scaling approach, give further insight into the distributionof the dopants within these phases. [ABSTRACT FROM AUTHOR]

Anti skid material (AM) used to improve the traffic conditions could affect the particulate matter emissions during winter. The investigated AM sample contains silica particles to improve the friction coefficient between tires and road surface and crystalline sodium chloride as anti glaze agent. We found also some interesting rusty particles containing iron hydroxide (lepidocrocite and goethite) mixed with fine quartz sliver. Compression test shows that those particles have a low strength being able to be disintegrated in harsh traffic conditions. The powder resulted after crushing of rusty particles feature fine fractions with diameter in the range of 1 - 10 μm. Such fractions were found in the collected sedimenting particles (SP) proving their ability to be suspended in atmosphere. The monitoring performed with Automatic Monitoring Air Quality Stations shows the average values for PM2.5; PM10 and SP are below the maximum accepted limit. However the registered values were high in days with intensive car traffic and lower in other days. The situation could be improved by a proper sorting of rusty particles from re-circulated anti skid material. [ABSTRACT FROM AUTHOR]

The monochloroacetic, dichloroacetic and trichloroacetic acid (MCAA, DCAA and TCAA) removed by metallic iron under controlled dissolved oxygen conditions (0, 0.75, 1.52, 2.59, 3.47 or 7.09 mg/L DO) was investigated in well-mixed batch systems. The removal of CAAs increased first and then decreased with increasing DO concentration. Compared with anoxic condition, the reduction of MCAA and DCAA was substantially enhanced in the presence of O 2 , while TCAA reduction was significantly inhibited above 2.59 mg/L. The 1.52 mg/L DO was optimum for the formation of final product, acetic acid. Chlorine mass balances were 69–102%, and carbon mass balances were 92–105%. With sufficient mass transfer from bulk to the particle surface, the degradation of CAAs was limited by their reduction or migration rate within iron particles, which were dependent on the change of reducing agents and corrosion coatings. Under anoxic conditions, the reduction of CAAs was mainly inhibited by the available reducing agents in the conductive layer. Under low oxic conditions, the increasing reducing agents and thin lepidocrocite layer were favorable for CAA dechlorination. Under high oxic conditions, the redundant oxygen competing for reducing agents and significant lepidocrocite growth became the major restricting factors. Various CAA removal mechanisms could be potentially applied to explaining the effect of DO concentration on iron efficiency for contaminant reduction in water and wastewater treatment. [ABSTRACT FROM AUTHOR]

Goethite and lepidocrocite are considered the stable species of Fe oxyhydroxides formed from Fe 2 + oxidation in mildly acidic soil environments, while maghemite is formed in mildly alkaline conditions. Complexing ligands, especially humic acid (HA), can change the pathway formation of these iron oxyhydroxides from Fe 2 + oxidation. This research aimed to assess the influence of HA on Fe 2 + oxidation and its effect on crystalline Fe mineral products. Ferrous iron was added to HA at increasing initial COOH/Fe(II) charge ratios (R) at pHs of 5.0 and 8.0 and aged at 70 °C for 1 month and up to 8 years at room temperature. The precipitated products after aging were analysed using XRD, FT-IR, TEM and AFM. The results indicate that oxidation of Fe 2 + at pH 5.0, in the presence of large amounts of HA (R = 0.1) promoted the formation of goethite together with ferrihydrite. Oxidation of Fe 2 + in slightly alkaline conditions (pH 8.0) yielded maghemite with small amounts of goethite. Further, long-term aging of HA coprecipitated with Fe 2 + perturbed the stacking of the Fe hydroxyl sheets at pH 5.0, favouring the formation of ferrihydrite. At pH 8.0 the presence of humic acid does not influence the crystallinity of the precipitation products and maghemite was still stable after 8 years of aging. This research confirms that the oxidation of Fe 2 + in soil and its subsequent hydrolysis is a very common process of Fe hydroxides/oxide formation in acidic soil environments. The type of Fe oxide formed depends strictly on the pH and secondly on the rate of oxidation, especially on the presence and amount of organic compounds that inhibit crystal growth. Humic acid are the main organic molecules in soils, particularly in cool, humid weathering environments where they lead to a decrease in crystalline perfection and promote the formation of ferrihydrite instead of goethite or lepidocrocite. These results provide significant insights into the effect of the mobility of HA in association with Fe minerals. [ABSTRACT FROM AUTHOR]

Ephemeral green rust is formed seasonally in some hydromorphic soils. It consists of Fe(II)/Fe(III) layered double hydroxides with different types of interlayer anions and different oxidation degrees of iron ( x). In synthetized stoichiometric green rust, x = 0.25-0.33; in soil fougerite, it may reach 0.50-0.66. The mineral stability is provided by the partial substitution of Mg for Fe. The ephemeral properties of the green rust are manifested in the high sensitivity to the varying redox regime in hydromorphic soils. Green rust disappears during oxidation stages, which complicates its diagnostics in soils. For green rust formation, excessively moist mineral soil needs organic matter as a source of energy for the vital activity of iron-reducing bacteria. In a gleyed Cambisol France, where fougerite is formed in the winter, the index of hydrogen partial pressure rH is 7.0-8.2, which corresponds to highly reducing conditions; upon the development of oxidation, fougerite is transformed into lepidocrocite. In the mineral siderite horizon of peatbogs in Belarus, where green rust is formed in the summer, rH is 11-14, which corresponds to the lower boundary of reducing conditions ( rH = 10-18); magnetite is formed in these soils in the winter season upon dehydration of the soil mass. [ABSTRACT FROM AUTHOR]

This paper described the adsorption and degradation of rhodamine B (RhB) during lepidocrocite (γ-FeOOH) formation by air oxidation of Fe(OH) 2 under visible-light irradiation in the presence of trace ethylenediaminetetracetic acid (EDTA). The results showed that RhB could be adsorbed on a green rust II (GR II) intermediate and on the γ-FeOOH product surface during γ-FeOOH formation and be degraded via heterogeneous and homogeneous photo-Fenton-like reactions. Fe 2+ and H 2 O 2 coexisted in the reaction system, and Fe 2+ or H 2 O 2 both promoted the adsorption and degradation of RhB. As the reaction proceeded, the increase in acidity enhanced the efficiency of the photo-Fenton-like reactions, which led to an increase in RhB degradation. The adsorbed RhB exhibited desorption behaviors because of the transformation of GR II and growth of γ-FeOOH. A possible mechanism was suggested for the comprehensive effect of RhB degradation during the reaction. [ABSTRACT FROM AUTHOR]

Carbon coated K0.8Ti1.73Li0.27O4 (KTLO) has been synthesized by a facile flux method followed by ball-milling and gaseous carbon coating. The carbon coated KTLO delivers a reversible specific capacity of 119.6 mA h g−1 at 20 mA g−1 with no capacity loss after 250 cycles as an anode material in sodium ion batteries, exhibiting an improved rate capability of 66 mA h g−1 at 200 mA g−1. It was found that carbon coating of KTLO not only enhances its electronic conductivity, but also improves the structure stability, proving that the carbon coated KTLO is a promising anode material for sodium ion batteries. [ABSTRACT FROM AUTHOR]

We investigated the reduction of lepidocrocite (γ-FeOOH) by Shewanella oneidensis MR-1 in the presence and absence of Cd. The results showed that Cd retarded microbial reduction of γ-FeOOH and avoided formation of magnetite. The inhibitory effect on γ-FeOOH transformation may not result from Cd toxicity to the bacterium; it rather was probably due to competitive adsorption between Cd and Fe on γ-FeOOH as its surface reduction catalyzed by adsorbed Fe was eliminated by adsorption of Cd. [ABSTRACT FROM AUTHOR]

Bioreduction of As(V) and As-bearing iron oxides is considered to be one of the key processes leading to arsenic pollution in ground waters in South and Southeast Asia. Recent laboratory studies with simple aqueous media showed that secondary Fe(II)-bearing phases (e.g., magnetite and green rust), which commonly precipitate during bioreduction of iron oxides, captured arsenic species. The aim of the present study was to follow arsenic speciation during the abiotic Fe(ll)-induced transformation of As(lll)- and As(V)-doped lepidocrocite to magnetite, and to evaluate the influence of arsenic on the transformation kinetics and pathway. We found green rust formation is an intermediate phase in the transformation. Both As(III) and As(V) slowed the transformation, with the effect being greater for As(Ill) than for As(V). Prior to the formation of magnetite, As(lII) adsorbed on both lepidocrocite and green rust, whereas As(V) associated exclusively with green rust, When magnetite precipitated, As(lll) formed surface complexes on magnetite nanoparticles and As(V) is thought to have been incorporated into the magnetite structure. These processes dramatically lowered the availability of As in the anoxic systems studied. These results provide insights into the behavior of arsenic during magnetite precipitation in reducing environments. We also found that As(V) removal from solution was higher than As(lll) removal following magnetite formation, which suggests that conversion of As(lII) to As(V) is preferred when using As-magnetite precipitation to treat As-contaminated ground waters. [ABSTRACT FROM AUTHOR]

In this study, the kinetics of Fe(II) oxidation in the presence of the iron oxyhydroxides ferrihydrite, Si-ferrihydrite, schwertmannite, lepidocrocite and goethite are investigated over the pH range 4–5.5. Despite limited sorption of Fe(II), the rate of Fe(II) oxidation is up to 70-fold faster than in the absence of any Fe oxyhydroxide phase over pH 4.5–5.5. Enhanced Fe(II) oxidation was minor or negligible at pH 4 with undetectable amounts of Fe(II) adsorbed to the iron oxyhydroxides at this pH. Heterogeneous rate constants derived from kinetic modeling were normalized to the concentration of adsorbed Fe(II) and deviated by no more than 13.8% at pH 4.5, 5 and 5.5, indicating that oxidation is proportional to the concentration of adsorbed Fe(II). Average rate constants were found to be: 2.12 ± 0.20, 1.30 ± 0.09, 1.69 ± 0.22, 1.20 ± 0.08 and 0.68 ± 0.09 M −1 s −1 for ferrihydrite, goethite, lepidocrocite, schwertmannite and Si-ferrihydrite, respectively. The role of reactive oxygen species, such as hydrogen peroxide, the hydroxyl radical and superoxide, towards the overall oxidation of Fe(II) was examined but found to have only a minor impact on Fe(II) oxidation when compared to the effect of heterogeneous oxidation. [ABSTRACT FROM AUTHOR]

The structures of many important functional oxides contain networks of metal-oxygen polyhedral units i.e. MOn. The correlation between the configurations and connectivities of theseMOn to properties is essentially important to be well established to conduct the design, synthesis and application of newMOn-based functional materials. In this paper, we report on an atomic-scale solution-chemistry approach that for the first time enables TiO6 octahedral network control starting from metastable brookite TiO2 through simultaneously tuning pH values and interfering ions (Fe3+, Sc3+, and Sm3+). The relationship between solution chemistry and the resultant configuration/connectivity of TiO6 octahedra in TiO2 and lepidocrocite titanate is mapped out. Apart from differing crystalline phases and morphologies, atomic-scale TiO6 octahedral control also endows numerous defect dipoles for giant dielectric responses. The structural and property evolutions are well interpreted by the associated H+/OH- species in solution and/or defect states associated with Fe3+ occupation within TiO6 octahedra. This work therefore provides fundamental new insights into controlling TiO6 octahedral arrangement essential for atomic-scale structure-property design. [ABSTRACT FROM AUTHOR]

For the first time, lepidocrocite-granular activated carbon (γ-FeOOH-GAC) nano composite was prepared and characterized. The prepared composite was used in the decolorization of textile wastewater containing reactive orange 29 by photo Fenton-like process in a continuous reactor. The influence of wastewater flow rate, H2O2 concentration and pH in decolorization process was studied using response surface methodology. The optimum conditions were flow rate of 1.98 mL min-1, H2O2 concentration of 3.25 mM and pH of 1.98. The decolorization ability of γ-FeOOH-GAC/H2O2/UV process was compared with that of γ-FeOOH-GAC/UV, γ-FeOOH-GAC/H2O2, γ-FeOOH-GAC, H2O2/UV, and UV processes at the optimum conditions. The obtained results indicated that γ-FeOOH-GAC/H2O2/UV process was more effective than other processes in the decolorization of the wastewater. [ABSTRACT FROM AUTHOR]

Sulfidization of iron oxyhydroxides can be accompanied by a release of adsorbed uranium, thus enhancing the mobility of uranium in systems undergoing a shift in redox conditions. We investigated the phase distribution and redox state of uranium in batch experiments, in which lepidocrocite with adsorbed U(VI) was reacted with sulfide. The amount of added sulfide was varied in the experiments performed, at pH 8 and ionic strength of 0.1 M. Sulfide, when not added in excess, was removed from solution within less than 1 h of reaction time. Consumption of dissolved sulfide was accompanied by reduction of Fe(III) and formation of iron sulfide. Each addition of sulfide led to an instantaneous release of uranium into solution. This release is most likely caused by the exchange of hydroxide groups at the lepidocrocite surface by thiol groups which have a lower tendency to bind uranium. Along with the consumption of dissolved sulfide, part of the released uranium became reassociated with the solid phase. This can be explained by a reversal of the ligand exchange process at the solid surfaces. However, steady state concentrations of dissolved uranium remained higher than before sulfide addition, indicating that the product of lepidocrocite sulfidization has a lower affinity for uranium than the starting material. Reduction of U(VI) also contributed to the transfer of dissolved uranium back to the solid phase. X-ray absorption spectroscopy revealed that reduction of U(VI) occurred in all experiments. The extent of U(VI) reduction depended on sulfide addition, however, formation of UO 2 occurred within a period of 48 h only when sulfide was added in excess. This suggests that the presence of dissolved sulfide is a prerequisite for fast reduction of U(VI) and formation of UO 2 . This would imply that the fast reaction of lepidocrocite with sulfide outcompetes reduction of U(VI) and, by this, kinetically inhibits the thermodynamically more favorable reduction of U(VI) to uraninite. Our results demonstrate that the transition from oxic to sulfidic conditions can lead to intermittent mobilization of uranium which is not expected based on equilibrium thermodynamics. [ABSTRACT FROM AUTHOR]

Effects of mineral particle morphology and roughness on potential determining ion ( p.d.i .; H + , OH − ) loadings achieved at synthetic lepidocrocite (γ-FeOOH) surfaces were predominantly investigated by potentiometry and thermodynamic modeling. Nanosized rod- (RL) and lath-shaped (LL) particles exhibiting different proportions of the same predominant crystallographic faces acquired largely comparable pH, ionic strength and counterion (NaCl, NaClO 4 ) dependencies on p.d.i . loadings. These results supported previous claims that faces ideally containing proton silent sites only, are likely populated by additional proton active sites. This concept was supported further by results of roughened LL-like particles (LLR) also showing highly congruent pH-, ionic strength- and composition-dependent p.d.i . loadings with those of LL and RL. These loadings thereby correspond to maximal levels allowed by net attractive and repulsive forces at each solution composition, irrespective of particle morphology. Contrasting equilibration times required to achieve these loadings revealed considerably slower exchange of p.d.i . and electrolyte ions near the point of zero charge in the rough LLR than in the more idealized LL and RL particles. Thermodynamic modeling was used to test various concepts accounting for these results. The model made use of a novel framework capable of isolating electrostatic contributions from different faces, and of accounting for ion-specific double-layer properties within a single crystallographic face. These efforts made use of capacitance values for each electrolyte ions within the framework of a recently developed Variable Capacitance Model. Attempts at modeling all three particle types were used to suggest that the (0 1 0) face contains ∼0.9 site nm −2 of proton active sites, a value notably constrained by recently published Na + , Cl − , and ClO 4 − loadings derived by cryogenic X-ray photoelectron spectroscopy. The model presented in this work thus provides a means to predict p.d.i . loadings on multifaceted mineral particle surfaces, and can therefore be used to constrain further our understanding of mineral/water interface reactivity. [ABSTRACT FROM AUTHOR]

This study aimed to manipulate the texture and elemental composition of the novel sheaths produced by the iron-oxidizing bacterium Leptothrix in culture by altering components of the medium. When previously isolated strain OUMS1 was cultured in media (pH 7.0 throughout incubation) containing various levels of Si on a rotary shaker at 20 °C and 70 rpm for 14 days, the strain was able to reproduce in media with up to 300 ppm Si, and the hollow microtubular architecture of the sheath was maintained even at 300 ppm Si. The constitutional iron oxide phase changed from poorly crystalline lepidocrocite at 0 ppm Si to X-ray diffraction (XRD)-amorphous 2-line ferrihydrite at 100-300 ppm via their mixture phase with intermediate Si content (Si-30 and -50 ppm). The results strongly indicate that the chemical character and crystallinity of the sheath texture can be regulated by culture conditions, especially components of the medium. [ABSTRACT FROM AUTHOR]