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Hybrid materials (HMs) combine the high diversity of functionalities of organic compounds with properties typical for inorganic materials, such as high mechanical strength or high thermal stability. Herein, HMs combining organic pigment molecules and TiO2 as inorganic component, with covalently linked components, i.e., so‐called class II HMs, are reported. The synthesis of such HMs is intrinsically challenging, as the apolar organic pigment component and the inorganic polar TiO2 component require different conditions for their respective formation. Herein, we circumvent this issue by employing solvothermal synthesis in superheated isopropanol, which through temperature tunability of the solvent properties allows for both generating and linking both components in one‐pot. First, it is shown that an organic benzimidazole‐based pigment molecule designed for readily binding to Ti can be synthesized solvothermally. Second, new class II titanium‐based HMs are generated from Ti(OiPr)4 and pigment precursors in a solvothermal reaction. The pigment@TiO2 HMs feature significant porosity and are structurally identified as layered structures of lepidocrocite‐like TiO2 linked via pigment molecules. These layered HMs assemble into hierarchical nanoflowers, and depending on the pigment segments, different interlayer spacings in between inorganic layers are observed. Third, the pigment@TiO2 materials are shown to be usable as electrode materials in lithium‐ion batteries. [ABSTRACT FROM AUTHOR]

Physicochemical properties and vertical distribution patterns of clay minerals were studied in the permafrost-affected soils from the tundra and sub-tundra larch open woodland of Tit-Ary Island. This unique complex is located in the Lena River Delta, Republic of Sakha (Yakutia). Despite the small size of the island and the fact that permafrost is close to the surface, several variants of pedogenesis determine the soil diversity in this area. The soils are characterized by various degrees of gleyic and stagnic properties due to sandy or loamy texture and location in the landscapes (top of the hills and steep or gentle slope). Mineral associations in the studied profiles are similar and are characterized by the predominance of two components: chlorite and illite. Iron hydroxide—lepidocrocite—occurs at the boundary of permanently frozen ground in the profile with pronounced spodic features. Smectitic clay identified in both horizons of this permafrost affected soil, as well as lepidocrocite, can be attributed to the result of modern pedogenesis. [ABSTRACT FROM AUTHOR]

The relevance of obtaining new samples of nanoscale materials and researching ways to control these processes is supported by constant progress in the fields of nanotechnology, semiconductors, biomedicine, wastewater treatment etc. The Fe0 (Steel3)-H2O-O2 system, which is considered promising for use in the specified industries, allows both obtaining a number of nanoscale phases of iron oxygen-containing compounds (IOCs), in particular magnetite, cobalt ferrous ferrite, iron(III) hydroxide oxides, and controlling these processes due to changes in the physicochemical conditions of the process. Taking into account the permanent change in the specified system of phase composition on the metal surface, the method of X-ray diffraction analysis (XRD) was applied using the created additional device for the goniometric attachment GP-13 for the in situ study of IOCs formation processes on the surface of a steel disc in the system Fe0 (St3)-H2O-O2. This made it possible to investigate the mechanisms and optimal conditions for the formation of individual ultradisperse and nanosized phases of IOCs under a number of physicochemical conditions. By calculating the area under the characteristic peaks on the in situ XRD patterns, quantitative ratios of IOCs formed under certain physicochemical conditions were found, and the average size of crystallites was calculated according to Scherer's formula, which provided additional information for the analysis of IOCs formation mechanisms. Along with this, the method of scanning electron microscopy (SEM) and the XRD without an additional in situ device were used. Based on the analysis of the obtained kinetic regularities, conclusions were made about the formation of IOCs by the formation of iron (II-III) hydroxycarbonate and hydroxysulfate layered double hydroxides I and II types, followed by their transformation to the final nanoscale phases of magnetite, cobalt ferrous ferrite, and iron(III) hydroxide oxides. The formation and accumulation of ferrous hydroxide phase was not recorded by the XRD in situ, however, in the Fe0 (St3)-H2O-O2 system, the formation of iron (II-III) layered double hydroxides based on its monolayers is not excluded. The preference of carbonate anions over chloride anions in the formation processes of iron layered double hydroxides is shown. [ABSTRACT FROM AUTHOR]

Hybrid materials (HMs) combine the high diversity of functionalities of organic compounds with properties typical for inorganic materials, such as high mechanical strength or high thermal stability. Herein, HMs combining organic pigment molecules and TiO2 as inorganic component, with covalently linked components, i.e., so‐called class II HMs, are reported. The synthesis of such HMs is intrinsically challenging, as the apolar organic pigment component and the inorganic polar TiO2 component require different conditions for their respective formation. Herein, we circumvent this issue by employing solvothermal synthesis in superheated isopropanol, which through temperature tunability of the solvent properties allows for both generating and linking both components in one‐pot. First, it is shown that an organic benzimidazole‐based pigment molecule designed for readily binding to Ti can be synthesized solvothermally. Second, new class II titanium‐based HMs are generated from Ti(OiPr)4 and pigment precursors in a solvothermal reaction. The pigment@TiO2 HMs feature significant porosity and are structurally identified as layered structures of lepidocrocite‐like TiO2 linked via pigment molecules. These layered HMs assemble into hierarchical nanoflowers, and depending on the pigment segments, different interlayer spacings in between inorganic layers are observed. Third, the pigment@TiO2 materials are shown to be usable as electrode materials in lithium‐ion batteries.

Sixteenth-century mural paintings of Nossa Senhora das Neves in Vilar de Perdizes (Galicia—North Portugal Euroregion) were analysed. An iconographic study has allowed us to understand the meaning of the seven scenes that constitute the mural painting. X-ray fluorescence (XRF) and Raman spectroscopies determined the compounds used in this mural painting, both in the original and in later repaintings. The black paint was bone black. Hydroxyapatite characteristic bands and those of the associated phosphates have been identified. White lime was used as white paint. Lepidocrocite and goethite were used to make yellows, and hematite was used to make red shades. Cinnabar has been used for a later red repaint. Carbon-based compounds and rutile were used to create different tonalities by darkening or lightening colours. It is of great significance to obtain accurate and reliable mural painting information through scientific means, since preservation, restoration, and repainting without detailed information can be harmful to mural paintings.

Sixteenth-century mural paintings of Nossa Senhora das Neves in Vilar de Perdizes (Galicia—North Portugal Euroregion) were analysed. An iconographic study has allowed us to understand the meaning of the seven scenes that constitute the mural painting. X-ray fluorescence (XRF) and Raman spectroscopies determined the compounds used in this mural painting, both in the original and in later repaintings. The black paint was bone black. Hydroxyapatite characteristic bands and those of the associated phosphates have been identified. White lime was used as white paint. Lepidocrocite and goethite were used to make yellows, and hematite was used to make red shades. Cinnabar has been used for a later red repaint. Carbon-based compounds and rutile were used to create different tonalities by darkening or lightening colours. It is of great significance to obtain accurate and reliable mural painting information through scientific means, since preservation, restoration, and repainting without detailed information can be harmful to mural paintings. [ABSTRACT FROM AUTHOR]

Vanadium (V) is a redox-sensitive trace metal that typically exists in one of three oxidation states (+3, +4 and +5) in natural waters; a feature increasingly used in paleoredox studies of ancient marine sediments. However, our knowledge of V geochemistry in low-oxygen marine environments is still limited, especially regarding interactions of V with reduced iron minerals such as green rust. Carbonate green rusts (GR CO3) are mixed FeII/FeIII-phases found in some modern ferruginous settings, such as Lake Matano (Indonesia), and were likely abundant in ancient ferruginous marine systems where they may have played an essential role in authigenic V enrichments in sediments. Here, we present an abiotic pathway of V removal from seawater via reduction and adsorption onto amorphous GR CO3. Suspensions of the freshly precipitated GR CO3 (1 g L−1) were added to vanadate (1 mg VV L−1 initial concentration) in anoxic synthetic seawater solutions. Vanadium removal by GR CO3 was rapid and efficient, with 92 – 99% of V removed in under 20 seconds. Synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy showed that VV adsorbed by GR CO3 was partially reduced to a mixture of VV and VIV, with the average oxidation state of adsorbed V increasing (+4.3 to +4.7) with increasing solution pH (7.5 to 8.5). Upon subsequent exposure to aerated seawater, V-bearing GR CO3 oxidized to lepidocrocite [γ–FeO(OH)] within 24 h, with concomitant reduction of all solid-phase VV to VIV. During oxidation, V was not released back into solution; rather, extended X-ray absorption fine structure (EXAFS) modeling revealed that VIV was structurally incorporated into lepidocrocite as octahedral vanadyl (VO2+). Our work further constrains the aqueous geochemistry of V, which has implications for understanding V cycling and removal mechanisms in both modern and ancient marine systems. [ABSTRACT FROM AUTHOR]

Some thermophilic bacteria from deep-sea hydrothermal vents grow by dissimilatory iron reduction, but our understanding of their biogenic mineral transformations is nascent. Mineral transformations catalyzed by the thermophilic iron-reducing bacterium Desulfovulcanus ferrireducens during growth at 55°C were examined using synthetic nanophase ferrihydrite, akaganeite, and lepidocrocite separately as terminal electron acceptors. Spectral analyses using visible-near infrared (VNIR), Fourier-transform infrared attenuated total reflectance (FTIR-ATR), and Mössbauer spectroscopies were complemented with x-ray diffraction (XRD) and transmission electron microscopy (TEM) using selected area electron diffraction (SAED) and energy dispersive X-ray (EDX) analyses. The most extensive biogenic mineral transformation occurred with ferrihydrite, which produced a magnetic, visibly dark mineral with spectral features matching cation-deficient magnetite. Desulfovulcanus ferrireducens also grew on akaganeite and lepidocrocite and produced non-magnetic, visibly dark minerals that were poorly soluble in the oxalate solution. Bioreduced mineral products from akaganeite and lepidocrocite reduction were almost entirely absorbed in the VNIR spectroscopy in contrast to both parent minerals and the abiotic controls. However, FTIR-ATR and Mössbauer spectra and XRD analyses of both biogenic minerals were almost identical to the parent and control minerals. The TEM of these biogenic minerals showed the presence of poorly crystalline iron nanospheres (50-200 nm in diameter) of unknown mineralogy that were likely coating the larger parent minerals and were absent from the controls. The study demonstrated that thermophilic bacteria transform different types of Fe(III) (oxyhydr)oxide minerals for growth with varying mineral products. These mineral products are likely formed through dissolution-reprecipitation reactions but are not easily predictable through chemical equilibrium reactions alone. [ABSTRACT FROM AUTHOR]

Some thermophilic bacteria from deep-sea hydrothermal vents grow by dissimilatory iron reduction, but our understanding of their biogenic mineral transformations is nascent. Mineral transformations catalyzed by the thermophilic iron-reducing bacterium Desulfovulcanus ferrireducens during growth at 55°C were examined using synthetic nanophase ferrihydrite, akaganeite, and lepidocrocite separately as terminal electron acceptors. Spectral analyses using visible-near infrared (VNIR), Fourier-transform infrared attenuated total reflectance (FTIR-ATR), and Mössbauer spectroscopies were complemented with x-ray diffraction (XRD) and transmission electron microscopy (TEM) using selected area electron diffraction (SAED) and energy dispersive X-ray (EDX) analyses. The most extensive biogenic mineral transformation occurred with ferrihydrite, which produced a magnetic, visibly dark mineral with spectral features matching cation-deficient magnetite. Desulfovulcanus ferrireducens also grew on akaganeite and lepidocrocite and produced non-magnetic, visibly dark minerals that were poorly soluble in the oxalate solution. Bioreduced mineral products from akaganeite and lepidocrocite reduction were almost entirely absorbed in the VNIR spectroscopy in contrast to both parent minerals and the abiotic controls. However, FTIR-ATR and Mössbauer spectra and XRD analyses of both biogenic minerals were almost identical to the parent and control minerals. The TEM of these biogenic minerals showed the presence of poorly crystalline iron nanospheres (50–200 nm in diameter) of unknown mineralogy that were likely coating the larger parent minerals and were absent from the controls. The study demonstrated that thermophilic bacteria transform different types of Fe(III) (oxyhydr)oxide minerals for growth with varying mineral products. These mineral products are likely formed through dissolution-reprecipitation reactions but are not easily predictable through chemical equilibrium reactions alone.

Marine sponges of the subclass Keratosa originated on our planet about 900 million years ago and represent evolutionarily ancient and hierarchically structured biological materials. One of them, proteinaceous spongin, is responsible for the formation of 3D structured fibrous skeletons and remains enigmatic with complex chemistry. The objective of this study was to investigate the interaction of spongin with iron ions in a marine environment due to biocorrosion, leading to the occurrence of lepidocrocite. For this purpose, a biomimetic approach for the development of a new lepidocrocite-containing 3D spongin scaffold under laboratory conditions at 24 °C using artificial seawater and iron is described for the first time. This method helps to obtain a new composite as "Iron-Spongin", which was characterized by infrared spectroscopy and thermogravimetry. Furthermore, sophisticated techniques such as X-ray fluorescence, microscope technique, and X-Ray diffraction were used to determine the structure. This research proposed a corresponding mechanism of lepidocrocite formation, which may be connected with the spongin amino acids functional groups. Moreover, the potential application of the biocomposite as an electrochemical dopamine sensor is proposed. The conducted research not only shows the mechanism or sensor properties of "Iron-spongin" but also opens the door to other applications of these multifunctional materials. [ABSTRACT FROM AUTHOR]

The main compositions of pipe deposits from water distribution networks are potential iron resources, which can be used as catalysts to activate the combined hydrogen peroxide (HP) and peroxymonosulphate (PMS) system to produce reactive oxidative species (ROSs) to degrade pollutants. As a result, the degradation efficiency of chloramphenicol (CAP) in the HP/PMS dual-oxidant system could reach as high as 75.21% within 100 min with hydroxylamine (HA) assistance, and the dual-oxidant method had a wide pH applied range. To explore the mechanism of the dual-oxidant system in detail, several main affecting factors were investigated. In addition, the hydroxyl radical(•OH) was identified as the predominant radicals by Electron paramagnetic resonance (EPR) and the Radical scavenger test (RST). According to the competition kinetics experiment, the reaction rate of CAP with •OH was 1.933(± 0.052) × 1010 M−1s−1 in the HP/PMS dual-oxidant system, which was higher than the HP single oxidant system (6.10(± 0.036) × 109 M−1s−1). And the role of HA was explored , including reduction and competition. Six degradation products were detected by the liquid chromatography-mass spectrometry (LC-MS) and their toxicity was analyzed by the ecological structure-activity relationship (ECOSAR) predictive model. These findings further provide a theoretical basis for the practical application of pipe deposits and advance the development of in-situ removal of pollutants in water distribution networks in the future promisingly. [ABSTRACT FROM AUTHOR]

The current laboratory experiments investigated the corrosion resistance of galvanized steel in artificial seawater (ASW). After the coupons were immersed in ASW for varying time durations (7 and 14 days) at room temperature, the corrosion rates based on the weight loss were determined. Following exposure to carbon steel for 7 and 14 days, corrosion rates were 0.1193mmpy and 0.1373mmpy, respectively. Methods of Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray (EDX) Analysis characterized the surface composition of their corrosion product. The visible corrosion product is hematite and lepidocrocite. This result allows us to understand the corrosion behavior of galvanized steel used in the marine environment. [ABSTRACT FROM AUTHOR]

Physicochemical properties and vertical distribution patterns of clay minerals in the weakly differentiated permafrost-affected soils of the Kolyma Lowland have been studied. These soils are developed under conditions of cold ultracontinental climate within a broad range of landscapes: coastal marsh, alas meadows on the plain composed of the ice complex deposits, and typical northern taiga. Despite the fact that weathering processes are weakly developed at high latitudes, certain features of pedogenic transformation of the initial chlorite–illite association have been identified. These are the presence of (i) vermiculite in the acidic soil horizons of the alas meadow and zonal northern taiga landscapes and (ii) iron hydroxide (lepidocrocite) in the profile of the marsh meadow soil. The soils of zonal taiga woodland are classified as cryozems according to the new Russian profile-genetic soil classification system; their classification position does not cause doubt. Oppositely, the classification of weakly differentiated and differently gleyed soils of intrazonal landscapes (alases and marsh meadows) is open to argument and should be further clarified. [ABSTRACT FROM AUTHOR]

Effectively facilitating Fe3+/Fe2+ cycles and expanding its operating pH range are keys to optimizing the traditional Fenton reaction. In this exploration, we used chitosan and ferrous sulfate as precursors to prepare a multicomponent magnetic Fe/C Fenton-like catalyst, which exhibited extraordinary catalytic properties and excellent stability performance in a pH range of 4~8. Besides, it could be easily separated from the solution by a magnet. The characterization showed that the supported Fe species include troilite-2H (FeS), lepidocrocite (FeOOH), and pyrrhotite-6T (Fe1 − xS) with a unique "core-shell structure." The presence of reductive iron sulfide core in the system can accelerate the reduction of Fe(III). Meanwhile, the graphite-like structure formed after calcination can adsorb and enrich priority pollutants near the active site through π–π coupling and strengthen electron transfer, which endows its high catalytic performance and enables it invulnerable to dissolved organic compounds. [ABSTRACT FROM AUTHOR]

Various biological, chemical, and physical technologies have been studied to effectively remove total phosphorus (T-P) from wastewater. Among them, some mineral suspensions and cations in the aqueous phase have shown great potential for promoting phosphorus removal via chemical precipitation. Herein, we investigated the efficiency of T-P removal using various chemical-based cations (Fe2+, Fe3+, Mg2+, and Al3+); ferric ions (Fe3+) showed the highest T-P-removal efficiency (33.1%), regardless of the type of anion (Cl−, NO3−, and SO42−). To prepare natural Fe3+-rich solutions, three different Fe(III)-rich minerals (hematite, lepidocrocite, and magnetite) were treated with various HCl concentrations to maximize the dissolved Fe3+ amounts. Lepidocrocite in 2 N HCl showed the most effective Fe3+-leaching ability (L-Fe dissolved solution). Almost no significant difference in Fe3+ leaching was observed between HCl and H2SO4, whereas lepidocrocite-2 N H2SO4 showed the highest T-P-removal ability (91.5%), with the formation of amorphous Fe(III)-P precipitates. The L-Fe dissolved solution exhibited a higher T-P-removal efficiency than polyammonium chloride under real wastewater conditions. Our results can provide fundamental knowledge about the effect of cations on T-P removal in wastewater treatment and the feasibility of using the Fe3+ leaching solution prepared from Fe(III)-containing minerals for efficient T-P removal via chemical precipitation. [ABSTRACT FROM AUTHOR]

We demonstrate the autonomous synthesis of iron (hydr)oxide (green rust, magnetite, and lepidocrocite) nanoparticles by precipitating iron(II) ions using hydroxide ions generated in situ with the methylene glycol-sulfite (MGS) reaction, a pH-clock. We show that the nature of the products can be predetermined by tuning the initial iron(II) concentration. [ABSTRACT FROM AUTHOR]

The FeOOH polymers commonly existing in nature are potential adsorbent materials for phosphate ions (P). In this work, five synthesized isomeric α-, β-, γ-FeOOH (goethite, akaganéite and lepidocrocite samples of Gth1 and Gth2, Aka1 and Aka2, and Lep, respectively) were used to investigate their P adsorption characteristics and mechanisms, under various times, the levels of phosphate and FeOOH, solution pH, temperatures, and coexisting anions. Under 1.0 g/L of dosage and 20 mg/L of P, Lagergren second order rate model could describe well kinetic behaviors of P adsorptions for FeOOH (R2 being 0.999) at pH 7. Phosphate adsorption behaviors could be described well by both Langmuir (R2 being 0.968 − 0.999) and Freundlich (R2 being 0.945 − 0.988). The maximum adsorption capacities (mg/g) were 8.09(Gth1), 6.5(Gth2), 5.49(Aka1), 12.9(Aka2), and 7.36(Lep). In addition, P adsorptions presented the better capacities in a pH range of 3 − 8. The SO42− had the stronger effects on P adsorptions, while the other anions (Cl−, NO3− and CO32−) had little effects. The possible P adsorption mechanisms by FTIR and XPS results for FeOOH mainly were electrostatic attractions and ion exchanges. It is obvious that isomeric FeOOH are the promising adsorbents for P removal. [ABSTRACT FROM AUTHOR]

Goethite and lepidocrocite, as the main compositions of pipe deposits in the water distribution network, could be used as a catalyst for advanced oxidation processes (AOPs). This research utilizes them to activate PDS/H2O2 and PMS/H2O2 degrading the 2,4,6-trichlorophenol, respectively. To describe the incomplete degradation of pollutants and reflect the induction period, a modified first-order model has been proposed and used to analyze degradation differences under several key affecting factors. The results revealed that the PDS/H2O2 system has a synergy effect in the 2,4,6-trichlorophenol degradation process. The possible degradation pathways and intermediate products were confirmed by gas chromatograph-mass spectrometry (GC–MS). The paper provides a new idea for the effective use of pipe deposits to remove chlorophenols from drinking water, which is of great significance to ensure water quality safety. [ABSTRACT FROM AUTHOR]

When a few drops of acid (hydrochloric, acrylic, propionic, acetic, or formic) are added to a colloid comprised of 1D lepidocrocite titanate nanofilaments (1DLs)-2 × 2 TiO 6 octahedra in cross-section-a hydrogel forms, in many cases, within seconds. The 1DL synthesis process requires the reaction between titanium diboride with tetramethylammonium (TMA + ), hydroxide. Using quantitative nuclear magnetic resonance (qNMR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC), the mass percent of TMA + after synthesis is determined to be ≈ 13.1 ± 0.1%. The TMA + is completely removed from the gels after 2 water soak cycles, resulting in the first completely inorganic, TiO 2 -based hydrogels. Ion exchanging the TMA + with hydronium results in gels with relatively strong hydrogen bonds. The hydrogels' compression strengths increased linearly with 1DL colloid concentration. At a 1DL concentration of 45 g L -1 , the compressive strength, at 80% deformation when acrylic acid is used, is ≈325 kPa. The strengths are ≈ 50% greater after the TMA + is removed. The removal of all residual organic components in the hydrogels, including TMA + , is confirmed by qNMR, Fourier-transformed infrared spectroscopy (FTIR), and TGA/DSC. The 1DL phase is retained after gelation, TMA + removal, and 80% compression., (© 2024 Wiley‐VCH GmbH.)

Marine sponges of the subclass Keratosa originated on our planet about 900 million years ago and represent evolutionarily ancient and hierarchically structured biological materials. One of them, proteinaceous spongin, is responsible for the formation of 3D structured fibrous skeletons and remains enigmatic with complex chemistry. The objective of this study was to investigate the interaction of spongin with iron ions in a marine environment due to biocorrosion, leading to the occurrence of lepidocrocite. For this purpose, a biomimetic approach for the development of a new lepidocrocite-containing 3D spongin scaffold under laboratory conditions at 24 °C using artificial seawater and iron is described for the first time. This method helps to obtain a new composite as “Iron-Spongin”, which was characterized by infrared spectroscopy and thermogravimetry. Furthermore, sophisticated techniques such as X-ray fluorescence, microscope technique, and X-Ray diffraction were used to determine the structure. This research proposed a corresponding mechanism of lepidocrocite formation, which may be connected with the spongin amino acids functional groups. Moreover, the potential application of the biocomposite as an electrochemical dopamine sensor is proposed. The conducted research not only shows the mechanism or sensor properties of “Iron-spongin” but also opens the door to other applications of these multifunctional materials.

In this study, bar-like maghemite (γ-Fe 2 O 3) was obtained through the oxidation of lepidocrocite (γ-FeO(OH)) synthesized by the co-precipitation method. Afterward, the nano-bar γ-Fe 2 O 3 performance as an anode for Li-ion batteries was studied. The formation of γ-FeO(OH) was confirmed by using Fourier transform infrared spectroscopy (FTIR). X-ray diffraction (XRD) results declared the formation of γ-Fe 2 O 3 as a single-phase after oxidation of γ-FeO(OH) at 200 °C for 2 h. Nitrogen adsorption-desorption (BET) and high-resolution transmission microscopy (HRTEM) results revealed the formation of bar-like maghemite with a high surface area (110 m2 g−1) and an average width of about 10 nm. The anode body was prepared by tape casting of a paste prepared of bar-like maghemite. Cyclic voltammetry results disclosed the reaction path of lithium and iron oxide through charging and discharging. In addition, galvanostatic charge-discharge cycling at a current density of 500 mA g−1 presented a reversible capacity of approximately 680 mAh g−1 after 50 cycles. Moreover, the cell showed acceptable stability even at the high current charge-discharge rates of 3000 mA g−1. The good performance of the anode can be due to the size and shape of the maghemite particles. Bar-like shapes ease the expansion and contraction of particles in two-direction with less destruction imposed. [ABSTRACT FROM AUTHOR]

A study on the influence of the composition of the model media of the soil electrolyte (NS1–NS2) on the corrosion rate of tubular steels 17G1S and 13G1S-U in a long-term experiment. The phase composition and structure of corrosion products were determined by X-ray analysis. using an X-ray diffractometer Shimadzu XRD-7000. It was found that, regardless of the steel grade, the composition of corrosion products in the environment of NS1 will be mainly characterized by the presence of lepidocrocite, and in the environment of NS2 – goethite. The corroding samples in both media will have a small amount of magnetite. During the exposure (609 days) of steel samples in the studied model media, the rate of corrosion processes depends on the component composition of the model media, steel grade and pH. The obtained results are important for predicting the behavior of underground pipelines in soils of different corrosive activity. [ABSTRACT FROM AUTHOR]

Iron oxide minerals control the environmental behavior of trace elements. However, the potential effects of electron transfer directions by iron oxides between organic acids and trace elements remain unclear. This study investigates the redox capacity of tartaric acid (TA) with chromate (Cr(Ⅵ)) or arsenate (As(V)) on lepidocrocite (Lep) from the perspective of electron transfer. The results demonstrated the configurations of TA (bidentate binuclear (BB)), As(V) (BB), and Cr(Ⅵ) (BB and protonated monodentate binuclear (HMB)) on Lep. Frontier molecular orbital calculations and X-ray photoelectron spectroscopy (XPS) binding energy shifts further indicated different electron transfer directions between TA and the oxyanions on Lep. The iron of Lep might act as electron acceptors when TA is adsorbed, whereas the iron and oxygen of Lep act as electron donors when As(V) is adsorbed. The iron of Lep might accept electrons from its oxygen and subsequently transfer these electrons to Cr(Ⅵ). Macroscopic validation experiments showed the reduction of Cr(VI), whereas no reduction of As(V). The XPS analysis showed a peak shift, with the possible formation of As–Fe–TA ternary complexes and electron transfer on Lep. These findings indicate that mineral interfacial electron transfer considerably influences the transport and transformation of oxyanions. [Display omitted] • Interfacial interactions between Lep and oxyanions (As(V) or Cr(VI)) in the presence of TA were studied. • Lep acts as an electron acceptor when TA is adsorbed. • Lep acts as an electron donor with different pathways when only Cr(Ⅵ) or As(V) is adsorbed. • The Lep–TA + Cr(VI) system reduced Cr(VI) to 30 % compared to 9 % in the presence of only TA. [ABSTRACT FROM AUTHOR]

Iron-oxyhydroxides are common in lake sediments, typically forming in oxidizing conditions near the sediment-water interface. However, in the mine-tailings-impacted sediment delta at Long Lake near Sudbury, Ontario, diagenetic Fe-oxyhydroxides are formed in suboxic-anoxic conditions. Geochemical and mineralogical techniques were applied to investigate the diagenetic transformations of tailings-derived oxidation products following burial in the sediment delta. Two sets of vertical cores were collected, one from a shallow-water location in the sediment delta near the lake shore and the other from a deeper-water location, approximately 90 m north from the mouth of the active channel. One core from each location was sectioned in the field into 0.1 m intervals using an anaerobic globe bag and porewater was extracted for aqueous geochemical analysis. The second core from each location was dried anaerobically and sub-sampled for solid-phase geochemical and mineralogical analyses. The aqueous concentrations of As, Fe, and SO 4 are elevated near the sediment-water interface at both locations but at the shallow location they decline to the lowest observed concentrations at depth in the natural sediment. The decline in their concentrations may be enhanced by bacterial SO 4 reduction and precipitation of Fe- and As-sulfides which were observed in mineralogical analysis. The mine-impacted sediment consists of numerous fragments of tailings-derived ferric-arsenate-cemented crusts. Compared to the cemented crusts that occur in the tailings, these fragments exhibit partial-dissolution features and SEM-EDS analyses demonstrate that they have relatively low As/Fe ratios, suggesting the occurrence of selective As(V) dissolution during diagenesis. Diagenetic Fe-oxyhydroxides occur throughout the mine-impacted sediment, including zones that contain diagenetic Fe- and As-sulfides, suggesting they may have formed in suboxic-anoxic conditions. They occur proximal to, but separate from, the fragments of tailings-derived crusts and display diverse morphologies, including what may be a previously unreported spherulitic form. Individual Fe-oxyhydroxides range in size from nm to μm but they mostly occur in delicate clusters suggesting they are autochthonous. Compared to the cemented crusts from the tailings, they contain very small amounts of As. Analysis of one spherule indicates it contains lepidocrocite microcrystals with amorphous SiO 2.nH 2 O in the interstitial spaces. The microcrystals contain a mixture of Fe(III) and Fe(II), with Fe(III)/ΣFe = approximately 0.8. We interpret them to have formed by burst nucleation from Fe(III)-supersaturated solution, with subsequent aggregation of crystallites to form spherules. • As dissolves preferentially from tailings-derived ferric-arsenate in lake sediment. • Diagenetic Fe(III)-oxyhydroxides form in suboxic to anoxic conditions. • Fe(III)-oxyhydroxides display spherulitic texture. • Lepidocrocite microcrystals contain a mixture of Fe(III) and Fe(II). [ABSTRACT FROM AUTHOR]

Weathering steels are widely used in civil engineering, architecture and contemporary art due to their mechanical properties, their enhanced resistance to atmospheric corrosion as well as their aesthetic properties. Artists and blacksmiths often apply chemical treatments to obtain the appealing colors of a patina in a shorter period of time. However, the development of an accelerated patina may have an effect on the final appearance and color of the surface. With the aim of evaluating differences in color and studying the evolution of the surface, eight accelerated patinas were made and exposed to the atmosphere for periods of time of up to 24 months and were compared to a natural patina. The characterization studies showed the presence of lepidocrocite on the surface. A close inspection of the X-ray diffraction patterns showed the displacement of the (020) lepidocrocite reflection and asymmetric broadening of selective lines of this phase that were associated to stacking and twins faults, respectively. These faults decrease with the exposure time and are related to a maximum at 630 nm in the reflectance spectrum and the stabilization of the b* coordinate (yellow color). The colors of the accelerated patinas differ from the natural patina at short exposure times. However, they tend to converge at longer exposure times. [ABSTRACT FROM AUTHOR]

Antimony (Sb) is a recognized priority pollutant with toxicity that is influenced by its migration and transformation processes. Oxidation of Fe(II) to Fe(III) oxides, which is a common phenomenon in the environment, is often accompanied by the formation of Mn(III/IV) and might affect the fate of Sb. In this study, incorporated Mn(III) and sorbed/precipitated Mn(III/IV) associated with lepidocrocite were prepared by adding Mn(II) during and after Fe(II) oxidation, respectively, and the effects of these Mn species on Sb fate were investigated. Our results indicated that the association of these Mn species with lepidocrocite obviously enhanced Sb(III) oxidation to Sb(V), while concomitantly inhibiting Sb sorption due to the lower sorption capacity of lepidocrocite for Sb(V) than Sb(III). Additionally, Mn oxide equivalents increased in the presence of Sb, indicating that Sb oxidation by Mn(III/IV) associated with lepidocrocite was a continuous recycling process in which Mn(II) released from Mn(III/IV) reduction by Sb(III) could be oxidized to Mn(III/IV) again. This recycling process was favorable for effective Sb(III) oxidation. Moreover, Sb(V) generated from Sb(III) oxidation by Mn(III/IV) enhanced Mn(II) sorption at the beginning of the process, and thus favored Mn(III/IV) formation, which could further promote Sb(III) oxidation to Sb(V). Overall, this study elucidated the effects of Mn(III/IV) associated with lepidocrocite arisen from Fe(II) oxidation on Sb migration and transformation and revealed the underlying reaction mechanisms, contributing to a better understanding of the geochemical dynamics of Sb. [Display omitted] [ABSTRACT FROM AUTHOR]

The significant accumulation of Pb from anthropogenic activities threatens environmental ecosystems. In the environment, iron oxides are one of the main carriers of Pb. Thus, the redox cycling of iron oxides, which is due to biotic and abiotic pathways, and which leads to their dissolution or transformation, controls the fate of Pb. However, a knowledge gap exists on the bioreduction in Pb-bearing ferrihydrites, secondary-mineral precipitation, and Pb partitioning during the bioreduction/oxidation/bioreduction cycle. In this study, Pb-bearing ferrihydrite (Fh_Pb) with various Pb/(Fe+Pb) molar ratios (i.e., 0, 2, and 5%) were incubated with the iron-reducing bacterium Shewanella oneidensis MR-1 for 7 days, oxidized for 7 days (atmospheric O2), and bioreduced a second time for 7 days. Pb doping led to a drop in the rate and the extent of the reduction. Lepidocrocite (23–56%) and goethite (44–77%) formed during the first reduction period. Magnetite (72–84%) formed during the second reduction. The extremely-low-dissolved and bioavailable Pb concentrations were measured during the redox cycles, which indicates that the Pb significantly sorbed onto the minerals that were formed. Overall, this study highlights the influence of Pb and redox cycling on the bioreduction of Pb-bearing iron oxides, as well as on the nature of the secondary minerals that are formed. [ABSTRACT FROM AUTHOR]

Iron (Fe) cycling exerts strong control on the mobility and bioavailability of the key nutrient phosphate (PO 4) in soils and sediments. Coprecipitation of PO 4 is known to alter the structure of Fe (oxyhydr)oxides (FeOx), however the environmental fate of PO 4 -bearing FeOx is not well-understood. Here, PO 4 -bearing FeOx with 9 mol% coprecipitated PO 4 were prepared by Fe(III) hydrolysis and Fe(II) oxidation in the presence of dissolved PO 4 , in addition to pure FeOx synthesized in PO 4 -free solutions. The pure and PO 4 -bearing FeOx were subsequently exposed to different concentrations of dissolved Fe(II) and sulfide (2 and 10 mmol L−1). Mineral transformations and the fate of PO 4 were tracked over 7–14 days with wet chemical techniques (including sequential Fe and S extraction) and synchrotron-based Fe K-edge X-ray absorption spectroscopy. Coprecipitation of PO 4 affected the rate and extent of FeOx transformation differently for Fe(II) and sulfide. Poorly-ordered PO 4 -bearing FeOx was preserved in the presence of dissolved Fe(II) while pure ferrihydrite was nearly completely transformed into goethite over 7 days. By contrast, coprecipitation of PO 4 rendered FeOx more reactive towards sulfide compared to pure FeOx. Reaction with dissolved sulfide resulted in the formation of non-sulfidized Fe(II) or Fe(II) sulfide under high and low Fe/sulfide ratio, respectively. Under low Fe/sulfide ratio, Fh and PO 4 -bearing, poorly-ordered FeOx were nearly completely sulfidized after 14 days. Sulfidation of FeOx led to efficient release of PO 4 into solution, and at low Fe/sulfide ratio more PO 4 was released than expected based on the extent of Fe sulfidation. The results suggest feedback mechanisms of environmental relevance: coprecipitation of strongly-sorbing species such as PO 4 disrupts FeOx structure, which affects FeOx reactivity and the overall nutrient or contaminant retention capacity of soils or sediments differently depending on the ambient redox conditions. Specifically, the switch from reducing to sulfidic conditions may be associated with the disproportionate release of nutrients and contaminants. [ABSTRACT FROM AUTHOR]

We demonstrate the autonomous synthesis of iron (hydr)oxide (green rust, magnetite, and lepidocrocite) nanoparticles by precipitating iron(II) ions using hydroxide ions generated in situ with the methylene glycol-sulfite (MGS) reaction, a pH-clock. We show that the nature of the products can be predetermined by tuning the initial iron(II) concentration.

This paper presents a study of the electrically conductive properties of ceramics based on phases crystallizing in the K2O–Fe2O3–TiO2 system, when using for their synthesis the method of pyrolysis of citrate-nitrate compositions. Both single-phase titanates and their mixtures are obtained. This paper presents studies of the morphology and structure of the compounds obtained. The value of their electrical conductivity is measured in the temperature range 150–700°C. It is found that the phase with the lepidocrocite structure exhibits the highest conductivity among the considered compositions in the entire temperature range (Eact. = 0.415 eV). [ABSTRACT FROM AUTHOR]

Iron oxyhydroxides (FeOOH) are common crystalline forms of iron that play a critical role in technology and the natural environment via a variety of important reduction-oxidation reactions, including electrical semiconduction as an aspect. However, a basic understanding of the electron transport properties of these systems is still lacking. We examine the electron mobility in goethite (α-FeOOH), akaganéite (β-FeOOH), and lepidocrocite (γ -FeOOH) polymorphs by means of density functional theory based (DFT+U) calculations.We show that room temperature charge transport should be dominated by the small-polaron hopping type, and that the attendant mobility should be highest for pure goethite and akaganéite. Hopping pathways through the various lattices are discussed in terms of individual electron exchange steps and rates for each. Given the usual occurrence of compositional impurities in natural iron oxyhydroxides, we also investigate the effect of common stoichiometric defects on the electron hopping activation energies such as Al and Cr substitutional cations in goethite, and Cl anions in the channels of akaganéite. [ABSTRACT FROM AUTHOR]

Herein, the self-assembly of one-dimensional titanium oxide lepidocrocite nanofilaments in 10 different water miscible organic solvents was investigated. The nanofilament snippets, with minimal cross sections of ∼5 × 7 Å 2 and lengths around 30 nm, begin as an aqueous colloidal suspension. Upon addition, and brief mixing, of the colloidal suspension into a given solvent, a multitude of morphologies─seemingly based on the hydrophilicity and polarity of the solvent─emerge. These morphologies vary between sheets, highly networked webs, and discrete fibers, all with no apparent change in the lepidocrocite structure. On the micro- and nanoscale, the morphologies are reminiscent of biological, rather than inorganic, materials. The results of this work give insight into the self-assembly of these materials and offer new pathways for novel macrostructures/morphologies assembled from these highly adsorbent and catalytically active low-dimensional materials.

The mobility and bioavailability of phosphate in paddy soils are closely coupled to redox-driven Fe-mineral dynamics. However, the role of phosphate during Fe-mineral dissolution and transformations in soils remains unclear. Here, we investigated the transformations of ferrihydrite and lepidocrocite and the effects of phosphate pre-adsorbed to ferrihydrite during a 16-week field incubation in a flooded sandy rice paddy soil in Thailand. For the deployment of the synthetic Fe-minerals in the soil, the minerals were contained in mesh bags either in pure form or after mixing with soil material. In the latter case, the Fe-minerals were labeled with 57 Fe to allow the tracing of minerals in the soil matrix with 57 Fe Mössbauer spectroscopy. Porewater geochemical conditions were monitored, and changes in the Fe-mineral composition were analyzed using 57 Fe Mössbauer spectroscopy and/or X-ray diffraction analysis. Reductive dissolution of ferrihydrite and lepidocrocite played a minor role in the pure mineral mesh bags, while in the 57 Fe-mineral-soil mixes more than half of the minerals was dissolved. The pure ferrihydrite was transformed largely to goethite (82-85%), while ferrihydrite mixed with soil only resulted in 32% of all remaining 57 Fe present as goethite after 16 weeks. In contrast, lepidocrocite was only transformed to 12% goethite when not mixed with soil, but 31% of all remaining 57 Fe was found in goethite when it was mixed with soil. Adsorbed phosphate strongly hindered ferrihydrite transformation to other minerals, regardless of whether it was mixed with soil. Our results clearly demonstrate the influence of the complex soil matrix on Fe-mineral transformations in soils under field conditions and how phosphate can impact Fe oxyhydroxide dynamics under Fe reducing soil conditions.

The formation conditions and stability fields of Fe-serpentines are still poorly understood in both terrestrial (natural or anthropic) and extraterrestrial environments. Knowledge of the effects of physical-chemical parameters on compositional and structural features of Fe-serpentines is lacking, and only a few thermodynamic parameters of these minerals are available in the literature. To fill these gaps, the synthesis of these minerals, while controlling all the physicochemical experimental parameters, was undertaken. Two hydrothermal syntheses were carried out at 90°C to investigate the effect of two different starting mineralogical mixtures on the nature of Fe-serpentines. The run products were identified by several analytical techniques (powder X-ray diffraction, transmission, and scanning electron microscopy). Berthierine crystals were synthesized from a starting mixture of kaolinite and metal iron. The berthierines synthesized show different morphologies and iron contents (~3–38 at.%). From a starting mineralogical mixture composed of quartz and metal iron, cronstedtite crystallizes. Most of the crystals are 1M polytypes. Magnetite is always associated with both berthierine and cronstedtite. Lepidocrocite was observed only in the experiment with kaolinite. These experimental results demonstrated that Fe enrichment in serpentines depends on the silicate precursor (kaolinite or quartz) of the starting mixture. The results are also in agreement with the geochemical equilibrium predicted by thermodynamic modeling, i.e. the formation of berthierine and cronstedtite in association with magnetite at the expense of metal iron and silicates. [ABSTRACT FROM AUTHOR]

Aluminum (Al) substitution into the lepidocrocite structure commonly occurs in redoximorphic soils. However, little is known about its effects on the local structure, morphology, and surface properties of lepidocrocite due to its metastability in the environment. In this study, a series of Al-substituted lepidocrocite samples was synthesized and the local structure and surface properties were characterized by X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) spectroscopy, high resolution transmission electron microscopy (HRTEM), zeta potential and phosphate (P) adsorption kinetics. With the substitution of Al into the lepidocrocite structure, the lepidocrocite unit cell volume decreased due to the smaller ionic radius of Al3+ (r = 0.535 Å) than Fe3+ (r = 0.645 Å), and both the corner-sharing (along c-axis) and edge-sharing (along a-axis) Me-Me (Me = Al, Fe) distances decreased, with a more significant decrease in corner-sharing Me-Me distances. In addition, hydrogen bonding in the interlayer regions of the mineral along the b- axis was weakened with Al substitution. These changes of the local structure led to a gradual evolution of the lepidocrocite morphology: the aspect ratio (length to width) decreased with increasing Al substitution, and the Al-substituted lepidocrocite crystals became thinner, resulting in a decrease in the final ratios of coherent scattering domain (CSD) sizes of face (020) to those of terminating face (200) and (002). Theorfore, with increasing Al substitution, the relative proportion of face (020) with doubly coordinated oxygens per specific surface area decreased, leading to an increase of active hydroxyls and P adsorption density at the surface. These results shed new insights on the evolution mechanism of local structure and morphology of Al-substituted lepidocrocite and provided important information for evaluating the surface reactivity and environmental behaviors of lepidocrocite in soils. [ABSTRACT FROM AUTHOR]

In situ Raman spectroscopic studies on carbon steel specimens immersed in aqueous solutions showed the presence of Fe hydroxy salt, specifically green rust (GR), as the initial corrosion product in acidic, neutral and alkaline conditions. With increasing exposure time, GR was transformed to oxy-hydroxides, predominantly lepidocrocite (γ-FeOOH) in the upper layer and magnetite (Fe3O4) in the oxygen-deficient lower layer. The stability of GRs and their transformation are found to be dependent on the pH of solutions and anions present. The de-convoluted Fe peak in the Fe 2p3/2 region of XPS spectra of the corrosion products, formed on CS specimen immersed in tap water for 80 h, indicate the presence of lepidocrocite phase (γ-FeOOH), which was also evident from the laminar morphologies seen in SEM micrograph. The predominance of lepidocrocite over magnetite phase, in the presence of sulfate ions and in the low pH conditions, was in good agreement with the highest corrosion rate observed. [ABSTRACT FROM AUTHOR]

Foreign and domestic software products designed for quantitative description of the flow accelerated corrosion (FAC) rate and modeling erosion–corrosion use physicochemical computational models based on the assumption that the oxide film that protects the surface of steel consists of magnetite. Investigations of the phase composition and structural characteristics of oxide films on the inner surfaces of pipelines and equipment of coolant-circulation circuits of the NPP power-generating units with RBMK high-power channel-type reactors or the third circuits of the BN-800 fast reactors in which correction-free or oxygenated water chemistry conditions are implemented have revealed the presence on the steels' surface of not only magnetite but also other iron oxide forms. At present, the presence of the forms of iron oxides and hydroxides other than magnetite is considered in the computational modeling of the FAC by the introduction of empirical dependences. In the work, thermodynamic analysis of the existence forms of solid iron oxide and hydroxide phases in contact with the aqueous coolant in neutral oxygen-containing solutions has been made for temperatures of 25–200°C. To solve the problem set, the method of minimization of free energies of the system was used that allows one to determine which of the solid phases—iron oxides or hydroxides—will be thermodynamically stable in aqueous process media. On the assumption that the free energy of a system is minimal in the equilibrium state, the method allows determining the composition of the solid phase that is thermodynamically stable under the given conditions. The dependence of the phase composition of the oxide film on the temperature and chemical composition of the aqueous medium in contact with the oxide in question is shown. It is suggested to use the calculated results for refining the physicochemical models of the dependence of the FAC on the temperature for estimation of changes in the solubility of the iron oxides on the temperature and the thermodynamic stability regions of the basic phases in which iron oxides exist in the presence of oxygen and hydrogen. [ABSTRACT FROM AUTHOR]

Unstable Fe-minerals, which change the color of gley after the sample extraction from soil and make less pronounced the features of gleying in the dry season, are important in hydromorphic soils parallel to stable Fe-minerals conventionally detected in dried soil. Two new parameters are proposed for the additional characteristic of Fe-minerals. The first one—index I—characterizes the interaction of active Fe-minerals with colloids and is determined as I = CEC/Fefree, where CEC is the cation exchange capacity. The second parameter is the change in the redness of gley after drying (Δа*) according to the CIE–L*a*b* optic system. In iron-enriched reduced gley (Gr) with low I ~ 0.1 and a strong increase in Δа* (≈9) after drying, the green rust is transformed into brown lepidocrocite. During a decrease in humidity, the transformation of reduced gley into oxidized one is accompanied by a rise in Δа* (≈3) and by a change in the composition of the green rust: the transformation of fougerite into trebeurdenite (Fe-ephemer with a higher oxidation rate of iron). When oxidized gley Go with I = 2–8 dries up, a slow increase in Δа* is caused by the inhibition of crystallization of Fe-hydroxides by colloids. In the deferruginated gley (Gdf) with high I = 6–27, the absence of a rise in the red color (Δа* ≈ 0) during drying is probably related to the inactivity of Fe-phyllosilicates. [ABSTRACT FROM AUTHOR]

Vanadium (V) is a promising paleoredox tracer in ancient marine sediments due its range of possible oxidation states (+3 to +5) and its unique redox-sensitivity. However, the interactions between V and the sulfide minerals common under ancient depositional conditions remain poorly studied. Iron monosulfide (FeS) is the first sulfide phase to form in anoxic-sulfidic waters and sediments, and an important precursor for sedimentary pyrite. Here we investigate the adsorption of dissolved VV by freshly precipitated FeS under conditions relevant to marine waters. We report near complete removal of aqueous V (94–98%; ∼2 × 10−5 M) by FeS (1 g L−1) in anoxic seawater within 24 h. Synchrotron-based X-ray absorption spectroscopy (XAS) at the V and Fe K -edges shows that aqueous VV was rapidly (<60 s) reduced to solid-phase VIII during reductive sorption by FeS. Iron K -edge and X-ray diffraction data show that the products of the subsequent oxidation of VIII-bearing FeS were elemental sulfur and lepidocrocite. Solid-phase V was oxidized within 24 h from +2.97 to +4.0, with no loss of V to solution. EXAFS analysis suggests, based on the predominance of V┄Fe backscatters at ∼3.0 Å, that octahedral VIV may have been incorporated in the structure of lepidocrocite during its formation. These results provide valuable insight into the relationship of V and FeS in marine environments, including the adsorption mechanism and V speciation relevant to the fate of V during early diagenesis in marine sediments. [Display omitted] • FeS rapidly adsorbs and reduces vanadate (VV) to VIII in anoxic seawater. • Upon oxidation, V co-precipitates with lepidocrocite and structurally incorporates. • Results suggest a new one-way path for V sequestration in euxinic environments. [ABSTRACT FROM AUTHOR]

Highlights • Fe 3 O 4 nanoparticles were synthesized under the influence of two magnets. • Fe 3 O 4 nanoparticles shapes change when an external magnetic field is applied. • α-Fe 2 O 3 and γ-Fe 2 O 3 nanoparticles with nanoflake shapes were also identified. Abstract Iron oxide nanoparticles (NPs) were synthesized at room temperature, using a method based on a chemical reaction of iron filings, white vinegar, hydrogen peroxide, and ammonium hydroxide, in the presence of an external magnetic field (EXMF) of 1200 G. X-ray diffraction (XRD) analysis indicates that magnetite (Fe 3 O 4) is the most predominant phase, with lepidocrocite (γ-FeO(OH)) in smaller proportion. The shape and average particle size is altered by the application of a magnetic field during NPs synthesis. The average size of crystallite calculated with Scherrer's equation were 30.30 nm without EXMF and 18.37 nm with EXMF. Using electron microscopy techniques (SEM, TEM), NPs with regular shapes were identified when the EXMF was applied. Meanwhile, irregular shapes were observed when the EXMF was not applied. Some NPs with nanoflake shapes and the crystalline phases γ-FeO(OH) were also identified. High-resolution transmission electron microscopy (HRTEM) showed that the NPs with regular shapes are of Fe 3 O 4. [ABSTRACT FROM AUTHOR]

Abstract Schwertmannite is a metastable Fe(III)-bearing mineral that can rapidly transform to more stable Fe(III) oxides upon Fe(II) sorption, via a dissolution-reprecipitation pathway. Phosphate (PO 4 3−) is a nutrient found in varying quantities in natural systems, but the influence of PO 4 3− on the Fe(II) induced transformation of schwertmannite is not well characterized. Here, we aim to quantify the aqueous and mineralogical effects of varied PO 4 3− loading, and subsequent Fe(II) loading, to schwertmannite at circumneutral pH. Phosphate was presorbed to schwertmannite at loadings of 0, 80, 400 and 800 μmoles g−1 in anoxic artificial groundwater. Fe(II) was then added at a final concentration of 12.5 mM and aqueous and mineralogical products were observed over 10 days. No transformation occurred before Fe(II) addition in the zero PO 4 3− treatment. In contrast, the three highest PO 4 3− treatments partially transformed to a microcrystalline Fe(III) oxyhydroxide before Fe(II) addition, possibly due to exchange of sulfate with the added PO 4 3−. Within 1 h of subsequent Fe(II) addition in the zero PO 4 3−treatment, all schwertmannite had transformed to goethite via the Fe(II)-induced transformation pathway. Increases in the level of PO 4 3− loading attenuated goethite precipitation via Fe(II)-induced transformation of the precursor schwertmannite and microcrystalline Fe(III) oxyhydroxide, with 65%, 34%, and 21% solid phase Fe as goethite at day 10 in the low (80 μmoles g−1), medium (400 μmoles g−1) and high (800 μmoles g−1) PO 4 3− treatments. Under low PO 4 3− loading, the addition of Fe(II) induced the transformation of the microcrystalline Fe(III) oxyhydroxide and schwertmannite to a mixture of lepidocrocite and goethite. In the medium and high PO 4 3− treatments, schwertmannite and the microcrystalline Fe(III) oxyhydroxide were instead stabilized by surface-complexation of PO 4 3− and did not extensively transform to more crystalline phases. Overall, the results show that PO 4 3− loadings can both drive rapid schwertmannite transformation to a new microcrystalline Fe(III) oxyhydroxide phase, and subsequently inhibit the Fe(II)-induced formation of lepidocrocite and goethite. Graphical abstract Unlabelled Image Highlights • Phosphate induces transformation to a microcrystalline Fe(III) oxyhydroxide. • Low phosphate loading stabilizes the precipitation of lepidocrocite. • Higher phosphate loadings inhibit the Fe(II)-accelerated transformation. • Aqueous phosphate and Fe(II) are sequestered in the solid phase. [ABSTRACT FROM AUTHOR]

Atmospheric corrosion of low carbon steel exposed in a coastal tropical zone of Manabí, Ecuador, was determined. Specimens were exposed at six outdoor exposure sites located at different distances from the sea. The atmosphere is classified as coastal. Wind speed threshold for an increase in chloride deposition rate was determined. The behavior of chloride deposition rate versus distance from the sea is anomalous due to the presence of an estuary. Corrosion by weight loss was evaluated up to 1 year of exposure. Only a slight difference in atmospheric corrosion rate is noticed between wet and dry periods. Chloride deposition interaction with RH–temperature complex and with wind speed shows significant statistical influence on atmospheric corrosion of low carbon steel. Corrosivity category of the atmosphere high (C4) is the most predominant classification level in the zone. Prediction indicates corrosivity category high (C4) will remain up to 20 years of exposure. Different morphologies of corrosion products were identified by SEM. Lepidocrocite, goethite, magnetite, and akaganeite are the main crystalline phases determined by XRD. Protective ability index previously proposed for rust layers is not useful to apply in coastal sites. Atmospheric corrosion of low carbon steel exposed in a coastal tropical zone of Manabí, Ecuador, was determined. Specimens were exposed at six exposure sites located at different distances from the sea. The atmosphere is classified as coastal. Chloride deposition interaction with RH–temperature complex and with wind speed show significant influence on atmospheric corrosion of low carbon steel. [ABSTRACT FROM AUTHOR]

Abstract In this study, iron is removed from aqueous solution using a fluidized-bed crystallizer. Homogeneous oxyhydroxide pellets (FeOOH) were recovered at various value of pH, surface loading (L), and initial ferrous concentration to assess the treatability of iron-containing water. The optimal conditions for treating initial ferrous concentrations of 100–300 mg/L were L = 0.6 kg/m2/h (with 29 m/h of upflow velocity), a bed expansion of 50% and pH = 6.5 yielding the total iron removal (TR) of more than 99% and a corresponding iron crystallization ratio (CR) of 85%. X-ray diffractometry (XRD) revealed that the pellets consisted of a mixture of goethite (α-FeOOH) and lepidocrocite (γ-FeOOH). Scanning electron microscopy (SEM) yielded images of pellets of up to 1 mm in diameter, which were assembled from FeOOH flakes with thicknessess of 0.2–0.4 µm. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

We reported herein the temperature-dependent dielectric properties of K0.8M0.4Ti1.6O4 (M = Ni, Zn) lepidocrocite titanate ceramics at the frequency f of 103, 104 and 105 Hz. This titanate is an example of layered alkali titanium oxides possessing two-dimensional (2D) sheets of edge-shared TiO6 octahedra, in contrast to other widely studied materials with mostly corner-shared TiO6 motifs. The giant dielectric constants ε′ ∼104 and the dielectric losses tan δ ∼ 0.5–2 were obtained upon heating from RT to 250 °C. These values in our water-free ceramics are comparable to those previously reported in lepidocrocite titanate and related structures containing up to 15%wt water. The results were explained considering (i) Maxwell-Wagner polarization of interlayer species, and (ii) the possible formation of internal barrier layer capacitors (IBLCs) via the oxidized surfaces. [ABSTRACT FROM AUTHOR]

Abstract In this study, nanoflaky maghemite (γ-Fe 2 O 3) was successfully prepared by heating of synthesized lepidocrocite (γ-FeO(OH)). Once maghemite obtained, the electrochemical performance of nanoflaky maghemite, as an anode for Li-ion batteries, was investigated. Synthesis of lepidocrocite was optimized by adjusting the heating time and ratio of ethylene glycol (EG) to water in solution. The results revealed that with equal ratio of EG to water, the obtained phase was crystalline lepidocrocite whereas in other ratios lepidocrocite was not the only emerged phase. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) results revealed that increasing heating time has no effect on morphology. This increment only led to the slight crystallite growth and agglomeration of precipitation. The optimized lepidocrocite were heated at 230 °C for 2 h to form maghemite, which was confirmed by using XRD. FESEM, high-resolution transmission electron microscopy, and nitrogen adsorption-desorption results disclosed that the particles have flaky morphology with thickness of less than 10 nm and surface area of 105 m2 g−1. Cyclic voltammetry results of anode body (prepared using nanoflaky maghemite) demonstrated reversible formation pathway of iron and lithium oxide through discharging and charging. Moreover, galvanostatic charge–discharge cycling showed a reversible capacity of about 480 mAh g−1 after 50 cycles at current density of 500 mA g−1. Good cyclability, and capacity retention of the anode is due to the nananometric size and flaky shape of the maghemite particles. These particles' shape made it easier for them to expand and contract in thickness direction with minimized destructions imposed. [ABSTRACT FROM AUTHOR]

Schwertmannite is an important sink for cadmium (Cd) in acid mine drainage (AMD) environments and is unstable when environmental conditions change. However, the release and redistribution of Cd during schwertmannite transformation with respect to pre-bound Cd are poorly understood. In this work, the transformation of cadmium-associated schwertmannite and subsequent Cd repartitioning behaviors were investigated. The way of schwertmannite associated with Cd was predominant by absorption, and the diffuse layer model (DLM) showed that Cd2+ existed as monodentate complexes ≡Fe(1)OCd+ and ≡Fe(2)OCd+ on schwertmannite surfaces. Kinetics of SO42− release and mineralogical characterization both showed that the mineral transformation rates decreased and more lepidocrocite aggregated with increasing adsorbed Cd levels. The shrinking core model revealed that Fe(II)-induced process would affect mineral dissolution by changing surface reaction-controlled step to internal diffusion-controlled step, and significantly promote the dissolution rate of Cd-adsorbed schwertmannite. Adsorbed Cd blocked the surface sites for later Fe(II) adsorption and the Fe(II)-Fe(III) electron transfer, then resulted in the decelerated transformation and the accumulation of intermediate phase lepidocrocite. The maximum release of aqueous Cd occurred after 1 mM Fe2+ addition, then over 69% of initial added Cd(aq) re-bound to solid-phase accompanying with mineral transformation, and finally, Cd was mainly associated with the secondary minerals by complexation with surficial OH groups. These findings are useful for developing the strategies for treating Cd contamination in AMD affected areas. [ABSTRACT FROM AUTHOR]