Showing papers on "Iron oxide published in 2019"

Overall electrochemical splitting of water at the heterogeneous interface of nickel and iron oxide

Abstract: Efficient generation of hydrogen from water-splitting is an underpinning chemistry to realize the hydrogen economy. Low cost, transition metals such as nickel and iron-based oxides/hydroxides have been regarded as promising catalysts for the oxygen evolution reaction in alkaline media with overpotentials as low as ~200 mV to achieve 10 mA cm−2, however, they are generally unsuitable for the hydrogen evolution reaction. Herein, we show a Janus nanoparticle catalyst with a nickel–iron oxide interface and multi-site functionality for a highly efficient hydrogen evolution reaction with a comparable performance to the benchmark platinum on carbon catalyst. Density functional theory calculations reveal that the hydrogen evolution reaction catalytic activity of the nanoparticle is induced by the strong electronic coupling effect between the iron oxide and the nickel at the interface. Remarkably, the catalyst also exhibits extraordinary oxygen evolution reaction activity, enabling an active and stable bi-functional catalyst for whole cell water-splitting with, to the best of our knowledge, the highest energy efficiency (83.7%) reported to date. Ni–Fe based compound are known as active electrocatalysts for oxygen evolution reaction, but not a good choice for the other half-reaction of water-splitting. Here the authors report a unique interface between Ni and γ-Fe2O3 that efficiently catalyzes the cathodic hydrogen evolution reaction.

Atomically dispersed iron hydroxide anchored on Pt for preferential oxidation of CO in H-2

Abstract: Proton-exchange-membrane fuel cells (PEMFCs) are attractive next-generation power sources for use in vehicles and other applications1, with development efforts focusing on improving the catalyst system of the fuel cell. One problem is catalyst poisoning by impurity gases such as carbon monoxide (CO), which typically comprises about one per cent of hydrogen fuel2-4. A possible solution is on-board hydrogen purification, which involves preferential oxidation of CO in hydrogen (PROX)3-7. However, this approach is challenging8-15 because the catalyst needs to be active and selective towards CO oxidation over a broad range of low temperatures so that CO is efficiently removed (to below 50 parts per million) during continuous PEMFC operation (at about 353 kelvin) and, in the case of automotive fuel cells, during frequent cold-start periods. Here we show that atomically dispersed iron hydroxide, selectively deposited on silica-supported platinum (Pt) nanoparticles, enables complete and 100 per cent selective CO removal through the PROX reaction over the broad temperature range of 198 to 380 kelvin. We find that the mass-specific activity of this system is about 30 times higher than that of more conventional catalysts consisting of Pt on iron oxide supports. In situ X-ray absorption fine-structure measurements reveal that most of the iron hydroxide exists as Fe1(OH)x clusters anchored on the Pt nanoparticles, with density functional theory calculations indicating that Fe1(OH)x-Pt single interfacial sites can readily react with CO and facilitate oxygen activation. These findings suggest that in addition to strategies that target oxide-supported precious-metal nanoparticles or isolated metal atoms, the deposition of isolated transition-metal complexes offers new ways of designing highly active metal catalysts.

An Unconventional Iron Nickel Catalyst for the Oxygen Evolution Reaction.

Abstract: The oxygen evolution reaction (OER) is a key process that enables the storage of renewable energies in the form of chemical fuels. Here, we describe a catalyst that exhibits turnover frequencies higher than state-of-the-art catalysts that operate in alkaline solutions, including the benchmark nickel iron oxide. This new catalyst is easily prepared from readily available and industrially relevant nickel foam, and it is stable for many hours. Operando X-ray absorption spectroscopic data reveal that the catalyst is made of nanoclusters of γ-FeOOH covalently linked to a γ-NiOOH support. According to density functional theory (DFT) computations, this structure may allow a reaction path involving iron as the oxygen evolving center and a nearby terrace O site on the γ-NiOOH support oxide as a hydrogen acceptor.

Oxygen Isotope Labeling Experiments Reveal Different Reaction Sites for the Oxygen Evolution Reaction on Nickel and Nickel Iron Oxides

Abstract: Nickel iron oxide is considered a benchmark nonprecious catalyst for the oxygen evolution reaction (OER). However, the nature of the active site in nickel iron oxide is heavily debated. Here we report direct spectroscopic evidence for the different active sites in Fe-free and Fe-containing Ni oxides. Ultrathin layered double hydroxides (LDHs) were used as defined samples of metal oxide catalysts, and 18 O-labeling experiments in combination with in situ Raman spectroscopy were employed to probe the role of lattice oxygen as well as an active oxygen species, NiOO- , in the catalysts. Our data show that lattice oxygen is involved in the OER for Ni and NiCo LDHs, but not for NiFe and NiCoFe LDHs. Moreover, NiOO- is a precursor to oxygen for Ni and NiCo LDHs, but not for NiFe and NiCoFe LDHs. These data indicate that bulk Ni sites in Ni and NiCo oxides are active and evolve oxygen via a NiOO- precursor. Fe incorporation not only dramatically increases the activity, but also changes the nature of the active sites.

Three-dimensionally ordered mesoporous iron oxide-supported single-atom platinum: Highly active catalysts for benzene combustion

Abstract: Single-atom catalysts are a kind of promising catalytic materials that can use the precious metal more efficiently. The KIT-6-templaing method was adopted to obtain three-dimensionally ordered mesoporous iron oxide (meso-Fe2O3). The meso-Fe2O3-supported single-atom Pt with a loading of x wt% (xPt1/meso-Fe2O3, x = 0.08, 0.15, and 0.25) catalysts were synthesized via a polyvinyl alcohol-protected reduction route. The 0.25 Pt1/meso-Fe2O3 sample showed much better catalytic activity than the meso-Fe2O3-supported Pt nanoparticle (0.25 PtNP/meso-Fe2O3) sample for benzene combustion, with the temperatures T10%, T50%, and T90% (corresponding to benzene conversions of 10, 50, and 90%) were 164, 186, and 198 °C at a space velocity of 20,000 mL/(g h), respectively. The TOFPt (2.69 s−1) obtained over 0.25 Pt1/meso-Fe2O3 at 160 °C was much higher than that (1.16 s−1) obtained over the 0.25 PtNP/meso-Fe2O3 sample at 160 °C. Furthermore, the 0.25 Pt1/meso-Fe2O3 and 0.15Pt1/meso-Fe2O3 samples exhibited better water-resistant ability than the 0.25 PtNP/meso-Fe2O3 sample, which was possibly due to formation of the active radicals and decomposition of carbonates in the presence of moisture. In situ DRIFTS results demonstrate that the phenolate and benzoquinone as well as cyclohexanone and maleate were the main intermediates in the oxidation of benzene. The good stability of the 0.15Pt1/meso-Fe2O3 and 0.25 Pt1/meso-Fe2O3 samples was associated with the strong interaction between Pt and meso-Fe2O3.

A review on nanotechnological application of magnetic iron oxides for heavy metal removal

Abstract: With increasing trend in industrialization, heavy metals possess a great threat to the environment due to their discharge in water and wastewater above permissible limits. Heavy metals have toxic effects on human and environment. However, advancement in newly budding and fangled nanotechnology offers better treatment techniques. Development of novel and cost-effective 0D, 1D, 2D and 3D nanomaterials for environmental remediation, pollution detection and other applications has attracted considerable attention. Zero valent iron and iron oxide nanoparticles are found to be the best candidates for heavy metal adsorption and removal. Various mechanical, optical and electrical properties of nanoparticles play important role in nanoparticle formation and interaction. Forms of iron oxide such as hematite (α Fe2O3) and magnetite (Fe3O4) nanoparticles of varied morphology and size (10 nm, 20 nm, 50 nm etc.) were synthesized by various methods like sol-gel, precipitation, hydrothermal processes and magnetic nano-composites with different iron precursors (iron acetate, iron nitrate, ferric chloride, ferrous sulphate etc.). Iron oxide nanoparticles (in a variety of chemical and structural forms) have already exhibited its diversity and potential in many frontiers of environmental area. Present review is focused on the application of iron and iron oxide nanoparticles towards heavy metal removal.

Surface Study of Fe3O4 Nanoparticles Functionalized With Biocompatible Adsorbed Molecules.

Abstract: Surfaces of iron oxide of ferrimagnetic magnetite (Fe3O4) nanoparticles (MNPs) prepared by Massart's method and their functionalized form (f-MNPs) with succinic acid, L-arginine, oxalic acid, citric acid, and glutamic acid were studied by dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR-S), UV-vis, thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and reflection electron energy loss spectroscopy (REELS). The XPS analysis of elements and their chemical states at the surface of MNPs and f-MNPs revealed differences in chemical bonding of atoms, content of carbon-oxygen groups, iron oxide forms, iron oxide magnetic properties, adsorbed molecules, surface coverage, and overlayer thickness, whereas the Auger parameters (derived from XPS and Auger spectra) and elastic and inelastic scattering probabilities of electrons on atoms and valence band electrons (derived from REELS spectra) indicated modification of surface charge redistribution, electronic, and optical properties. These modified properties of f-MNPs influenced their biological properties. The surfaces biocompatible for L929 cells showed various cytotoxicity for HeLa cells (10.8-5.3% of cell death), the highest for MNPs functionalized with oxalic acid. The samples exhibiting the largest efficiency possessed smaller surface coverage and thickness of adsorbed molecules layers, the highest content of oxygen and carbon-oxygen functionalizing groups, the highest ratio of lattice O2- and OH- to C sp2 hybridizations on MNP surface, the highest ratio of adsorbed O- and OH- to C sp2 hybridizations on adsorbed molecule layers, the closest electronic and optical properties to Fe3O4, and the lowest degree of admolecule polymerization. This high cytotoxicity was attributed to interaction of cells with a surface, where increased content of oxygen groups, adsorbed O-, and OH- may play the role of additional adsorption and catalytic sites and a large content of adsorbed molecule layers of carboxylic groups facilitating Fenton reaction kinetics leading to cell damage.

Liquid Nitrogen Activation of Zero-Valent Iron and Its Enhanced Cr(VI) Removal Performance.

Abstract: In this study, we report that liquid nitrogen treatment is a promising zero-valent iron activation method that does not remove the iron oxide shell; this can improve the apparent Cr(VI) removal rate constant of zero-valent iron by about 4-120 times, depending on the particle sizes and the suppliers of zero-valent iron. It was found that liquid nitrogen, with its low temperature of 77 K, could crack the iron oxide shell of zero-valent iron to produce abundant fractures because of the different thermal expansion coefficients of iron oxide and iron. These fractures provided suitable mass transfer channels for the inward transfer of water/oxygen molecules to the iron core and the subsequent in situ generation of Fe(II) for the reduction of Cr(VI) to Cr(III). More importantly, systematic characterizations confirmed the generation of an Fe(III)/Cr(III)/Cr(VI) composite on the surface of zero-valent iron during the removal, suggesting its environmental benignancy. This study provides a novel physical zero-valent iron activation method, sheds light on the importance of the iron oxide shell of zero-valent iron on Cr(VI) removal, and clarifies the intrinsic Cr(VI) removal mechanism of zero-valent iron.

One step green synthesis of larvicidal, and azo dye degrading antibacterial nanoparticles by response surface methodology.

Abstract: The present study explored the one step extracellular green synthesis of Iron oxide (FexOy) and manganese oxide nanoparticles (MnNPs) using aqueous extract of Acorus calamus rhizome. The organic chemicals including polyphenol compounds responsible for bio-reduction and stabilization from the polyphenol enriched microwave irradiated aqueous extract of Acorus calamus were studied using GC–MS analysis. Further, their synthesis conditions were optimized using response surface methodology (RSM) and central composite design (CCD) using three variables. The green synthesized Iron oxide and Manganese oxide NPs were characterized by UV, FTIR, XRD, TEM and SEM. Results indicated that the Iron oxide NPs and mixture of iron and manganese NPs showed photocatalytic excellent activities in reducing dyes like methylene blue (0.1%) and Congo red (0.25%) at 0.03% NPs. However, Mn NPs showed moderate activity. On a contrary, manganese showed better larvicidal activity compared to Iron oxide NPs against the phytopathogens commonly affecting the vegetable crops. The present finding showed that high mortality rate at 30 μg/ml concentration of manganese NPs was comparatively interesting. In addition, NPs overall had appreciable activity with P. aeruginosa being more sensitive to Iron oxide NPs (22 ± 2 mm zone of inhibition) and manganese NPs (13 ± 2 mm zone of inhibition) and Iron oxide NPs completely inhibited the growth of A. flavus at 40 μg/ml concentration.

Chitosan-Graphene Oxide Hydrogels with Embedded Magnetic Iron Oxide Nanoparticles for Dye Removal

Abstract: We report a facile design and synthesis of magnetic iron oxide (IO) incorporated chitosan-graphene oxide (CSGO) hydrogel nanocomposites (CSGOIO) by employing in situ mineralization of iron ions in ...

Self-assembled nanostructures of 3D hierarchical faceted-iron oxide containing vertical carbon nanotubes on reduced graphene oxide hybrids for enhanced electromagnetic interface shielding

Abstract: The self-assembled three dimensional (3D) hybrids nanostructure containing uniform growth of vertical carbon nanotubes (VCNTs) with faceted iron oxide nanoparticles (f-Fe3O4 NPs) on the surfaces of reduced graphene oxide nanosheets (rGO NSs) is achieved using microwave assisted approach. The formation of hierarchical 3D f-Fe3O4-VCNTs@rGO hybrids, using microwave method is a rapid, simple, and inexpensive synthetic route. First, the VCNTs grow with help of Fe NPs, and after oxidizing of Fe NPs in form of f-Fe3O4 NPs, the growth has terminated resulting in formation of small size (

Cotransport and Deposition of Iron Oxides with Different-Sized Plastic Particles in Saturated Quartz Sand

Abstract: The present study was designed to investigate the cotransport and deposition of different-sized plastic particle from nano- (0.02 μm) to micrometer-scale (0.2 and 2 μm) with goethite and hematite (two types of representative iron oxides abundant in natural environment) in porous media at both low (5 mM) and high ionic strength (25 mM) in NaCl solutions. We found that through different mechanisms (i.e., modification of surface properties of iron oxides, steric repulsion, or alteration in deposition sites on quartz sand), different-sized plastic particles induced different effects on the transport and deposition behaviors of iron oxides in quartz sand. Likewise, via different mechanisms such as change of surface properties or alteration in deposition sites on quartz sand, different transport behaviors for different sized plastic particles induced by the copresence of iron oxides were also observed. The results of this study suggested that cotransport of iron oxides and plastic particles in porous media is far more complex than those of individual colloid transport. Since both plastic particles and iron oxides are ubiquitous presence in natural environment, it is expected that they would interact with each other and thus alter the surface properties, leading to the change of transport behaviors in porous media.

Elucidating the Structural Composition of an Fe–N–C Catalyst by Nuclear- and Electron-Resonance Techniques

Abstract: Fe-N-C catalysts are very promising materials for fuel cells and metal-air batteries. This work gives fundamental insights into the structural composition of an Fe-N-C catalyst and highlights the importance of an in-depth characterization. By nuclear- and electron-resonance techniques, we are able to show that even after mild pyrolysis and acid leaching, the catalyst contains considerable fractions of α-iron and, surprisingly, iron oxide. Our work makes it questionable to what extent FeN4 sites can be present in Fe-N-C catalysts prepared by pyrolysis at 900 °C and above. The simulation of the iron partial density of phonon states enables the identification of three FeN4 species in our catalyst, one of them comprising a sixfold coordination with end-on bonded oxygen as one of the axial ligands.

Green Synthesis of Iron Oxide Nanoparticles Mediated by Filamentous Fungi Isolated from Sundarban Mangrove Ecosystem, India

Abstract: In the present study, biosynthesis of iron oxide nanoparticles (IONPs) was achieved using three manglicolous fungi, STSP10 (Trichoderma asperellum), STSP 19 (Phialemoniopsis ocularis) and STSP 27 (Fusarium incarnatum) isolated from estuarine mangrove sediment of Indian Sundarban. Synthesised IONPs were initially monitored by UV-Vis spectrophotometer and further characterised by Fourier transform infrared (FTIR) spectroscopy, which provides information regarding proteins and other organic residues involved with iron nanoparticle. The morphology of iron nanoparticle were found to be spherical with average particle size ranging between 25 ± 3.94 nm for T. asperellum, 13.13 ± 4.32 nm for P. ocularis and 30.56 ± 8.68 nm for F. incarnatum, which were confirmed by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Energy-dispersive x-ray analysis (EDX) analysis was performed during FESEM study to confirm the presence of elemental Fe in the sample. X-ray diffraction (XRD) pattern has shown that the IONPs are iron oxide in nature.

The geologic history of seawater oxygen isotopes from marine iron oxides.

Abstract: The oxygen isotope composition (δ18O) of marine sedimentary rocks has increased by 10 to 15 per mil since Archean time. Interpretation of this trend is hindered by the dual control of temperature and fluid δ18O on the rocks’ isotopic composition. A new δ18O record in marine iron oxides covering the past ~2000 million years shows a similar secular rise. Iron oxide precipitation experiments reveal a weakly temperature-dependent iron oxide–water oxygen isotope fractionation, suggesting that increasing seawater δ18O over time was the primary cause of the long-term rise in δ18O values of marine precipitates. The 18O enrichment may have been driven by an increase in terrestrial sediment cover, a change in the proportion of high- and low-temperature crustal alteration, or a combination of these and other factors.

A carbon nanotube-confined iron modified cathode with prominent stability and activity for heterogeneous electro-Fenton reactions

Abstract: Transition metal modified carbon materials as multifunctional cathodes for electro-Fenton (EF) reactions are supposed to be promising for generating H2O2in situ and catalyzing it to form hydroxyl radicals to degrade organic pollutants, but this process still faces the challenges of reduced heterogeneous catalyst activities and poor stabilities due to the continuous leaching of active metals. Herein, a heterogeneous cathode, in which iron is confined in the interior of carbon nanotube cavities, (Fe0-in-CNTs) with extremely low iron leaching levels was prepared, producing a much higher H2O2 yield and phenol removal rate (9.68 times faster) when compared with iron being confined externally on the walls of CNTs (Fe0-out-CNTs). It was found that the iron valence on the CNTs played an important role in determining the heterogeneous Fenton activity, suggesting that Fe0 was beneficial for H2O2 selectivity through a 2e− process (2.43 times higher) and the phenol removal rate (21.44 times faster) compared to iron oxide. It was confirmed that the CNT cavities could provide an isolated space for Fe0, and the iron leaching mass was only 3.21 × 10−3 mg cm−2, even at pH 3. Consequently, different mechanisms for phenol degradation via heterogeneous EF reactions on Fe0-in-CNT and Fe0-out-CNT cathodes were disclosed. This supported the idea that a heterogeneous Fenton-like reaction on the CNT surface, rather than a solution homogeneous Fenton reaction, played a decisive role in pollutant degradation. Furthermore, the cathode reusability was proved to be dependent on the Fe0 content and efficient conversion between FeIII and FeII. This work verified the importance of confinement catalysis in selectively controlling the positions and valences of iron on CNTs, which could effectively increase the heterogeneous EF activity and decrease the amount of leached iron to improve cathode stability. Thereby this could lead to a significant breakthrough in heterogeneous EF studies and shed light on confinement catalysis methods for organic pollutant degradation.

Strong Metal-Support Interactions between Copper and Iron Oxide during the High-Temperature Water-Gas Shift Reaction.

Abstract: The commercial high-temperature water-gas shift (HT-WGS) catalyst consists of CuO-Cr2 O3 -Fe2 O3 , where Cu functions as a chemical promoter to increase the catalytic activity, but its promotion mechanism is poorly understood. In this work, a series of iron-based model catalysts were investigated with in situ or pseudo in situ characterization, steady-state WGS reaction, and density function theory (DFT) calculations. For the first time, a strong metal-support interaction (SMSI) between Cu and FeOx was directly observed. During the WGS reaction, a thin FeOx overlayer migrates onto the metallic Cu particles, creating a hybrid surface structure with Cu-FeOx interfaces. The synergistic interaction between Cu and FeOx not only stabilizes the Cu clusters, but also provides new catalytic active sites that facilitate CO adsorption, H2 O dissociation, and WGS reaction. These new fundamental insights can potentially guide the rational design of improved iron-based HT-WGS catalysts.

High-performance α-Fe2O3/C composite anodes for lithium-ion batteries synthesized by hydrothermal carbonization glucose method used pickled iron oxide red as raw material

Abstract: The α-Fe2O3/C composites have been successfully synthesized by a facile hydrothermal carbonization glucose method using pickled iron oxide red as raw materials, which is the recycled product after treating the pickling wastewater. The NaOH is used as an additive to assist carbonization of glucose to obtain the high-quality carbon coating layer. X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscope are used to characterize the structure and morphology of the samples. To characterize the surface chemical composition and bonding configuration of α-Fe2O3/C, X-ray photoelectron spectroscopy is detected. The Electrochemical properties are optimized by the orthogonal tests, revealing that the hydrothermal reaction time has the most significant influence on the electrode capacity, followed by the hydrothermal reaction temperature, the amount of glucose added and the concentration of NaOH. As anode material for lithium ion battery, the initial discharge/charge capacity of α-Fe2O3/C electrode can reach 2640.1/2151.4 mAh g−1 with initial coulomb efficiency of 81.49% at a current density of 100 mA g−1, and even after 80 cycles maintain the capacity of 1529.5 mAh g−1, which far exceeds the theoretical capacity (1007 mAh g−1) of α-Fe2O3 electrode.

Facile synthesis of ternary graphene nanocomposites with doped metal oxide and conductive polymers as electrode materials for high performance supercapacitors.

Abstract: Supercapacitors (SCs) due to their high energy density, fast charge storage and energy transfer, long charge discharge curves and low costs are very attractive for designing new generation of energy storage devices. In this work we present a simple and scalable synthetic approach to engineer ternary composite as electrode material based on combination of graphene with doped metal oxides (iron oxide) and conductive polymer (polypyrrole) with aims to achieve supercapacitors with very high gravimetric and areal capacitances. In the first step a binary composite with graphene mixed with doped iron oxide (rGO/MeFe2O4) (Me = Mn, Ni) was synthesized using new single step process with NaOH acting as a coprecipitation and GO reducing agent. This rGO/MnFe2O4 composite electrode showed gravimetric capacitance of 147 Fg−1 and areal capacitance of 232 mFcm−2 at scan rate of 5 mVs−1. In the final step a conductive polypyrrole was included to prepare a ternary composite graphene/metal doped iron oxide/polypyrrole (rGO/MnFe2O4/Ppy) electrode. Ternary composite electrode showed significantly improved gravimetric capacitance and areal capacitance of 232 Fg−1 and 395 mFcm−2 respectively indicating synergistic impact of Ppy additives. The method is promising to fabricate advanced electrode materials for high performing supercapacitors combining graphene, doped iron oxide and conductive polymers.

Nanoporous iron oxide/carbon composites through in-situ deposition of prussian blue nanoparticles on graphene oxide nanosheets and subsequent thermal treatment for supercapacitor applications

Abstract: This work reports the successful preparation of nanoporous iron oxide/carbon composites through the in-situ growth of Prussian blue (PB) nanoparticles on the surface of graphene oxide (GO) nanosheets. The applied thermal treatment allows the conversion of PB nanoparticles into iron oxide (Fe2O3) nanoparticles. The resulting iron oxide/carbon composite exhibits higher specific capacitance at all scan rates than pure GO and Fe2O3 electrodes due to the synergistic contribution of electric double-layer capacitance from GO and pseudocapacitance from Fe2O3. Notably, even at a high current density of 20 A g-1, the iron oxide/carbon composite still shows a high capacitance retention of 51%, indicating that the hybrid structure provides a highly accessible path for diffusion of electrolyte ions.

Global Fe-O isotope correlation reveals magmatic origin of Kiruna-type apatite-iron-oxide ores

Abstract: Kiruna-type apatite-iron-oxide ores are key iron sources for modern industry, yet their origin remains controversial. Diverse ore-forming processes have been discussed, comprising low-temperature hydrothermal processes versus a high-temperature origin from magma or magmatic fluids. We present an extensive set of new and combined iron and oxygen isotope data from magnetite of Kiruna-type ores from Sweden, Chile and Iran, and compare them with new global reference data from layered intrusions, active volcanic provinces, and established low-temperature and hydrothermal iron ores. We show that approximately 80% of the magnetite from the investigated Kiruna-type ores exhibit δ56Fe and δ18O ratios that overlap with the volcanic and plutonic reference materials (> 800 °C), whereas ~20%, mainly vein-hosted and disseminated magnetite, match the low-temperature reference samples (≤400 °C). Thus, Kiruna-type ores are dominantly magmatic in origin, but may contain late-stage hydrothermal magnetite populations that can locally overprint primary high-temperature magmatic signatures

A Review on Iron Oxide‐Based Nanoarchitectures for Biomedical, Energy Storage, and Environmental Applications

Abstract: Iron oxide nanoarchitectures with distinct morphologies from 1D to 3D have been developed using various wet chemical methods. They have been employed for a wide range of applications, including energy storage, biomedical, and environmental applications. The functional properties of iron oxide nanoarchitectures depend on the size, shape, composition, magnetic properties, and surface modification. To overcome the limitations of pure iron oxide nanostructures, hybridizations with various inorganic materials (e.g., silica, metals, metal oxides) and carbon-based materials have been proposed. Herein, the recent advances in the preparation of various iron oxide nanoarchitectures are reviewed along with their functional applications in energy storage, biomedical, and environmental fields. Finally, the effects of various parameters on the functional performance of iron oxide nanostructures for these applications are summarized and the trends and future outlook on the development of iron oxide nanoarchitectures for these applications are also given.

Oxygen defect engineering in cobalt iron oxide nanosheets for promoted overall water splitting

Abstract: Transition metal oxides have attracted tremendous attention as active and stable electrocatalysts for hydrogen or oxygen evolution from water splitting. However, their application as bifunctional catalysts for overall water splitting is still hindered by their limited activity. In this paper, via the surface defect engineering strategy, a bifunctional electrocatalyst based on oxygen vacancy enriched CoFe2O4 (r-CFO) nanosheets was successfully fabricated, exhibiting desired overall water splitting activity. DFT calculations demonstrated that benefitting from the incorporation of oxygen vacancies, the adsorption energy (Eads) of H2O and the Gibbs free energy change for hydrogen adsorption (ΔGH*) are both well optimized, leading to the fine modulation of active site activity. Meanwhile, along with oxygen vacancy doping, the density of states across the Fermi level increased as well, which would be conducive to fast electron transportation. As expected, the r-CFO catalyst afforded obviously lower overpotentials of 280 mV and 121 mV to achieve a current density of 10 mA cm−2 for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. Furthermore, r-CFO exhibited excellent overall water splitting activity with a voltage of 1.53 V to reach a current density of 10 mA cm−2. This work highlights the vital role of surface defect engineering based on transition metal oxides toward advanced electrocatalysts.

Regulating Secretion of Extracellular Polymeric Substances through Dosing Magnetite and Zerovalent Iron Nanoparticles To Affect Anaerobic Digestion Mode

Abstract: Anaerobic digestion technology is a promising method to reduce the usage of fossil fuels by transforming organic waste into biogas. Nano zerovalent iron (nZVI) and nano iron oxide have been reporte...