Intimately mixed copper, cobalt, and iron fluorides resulting from the insertion of fluorine into a LDH template.

The advancement of lithium-ion batteries (LIBs) with high performance is crucial across various sectors, notably in space exploration. This advancement hinges on the development of innovative cathode materials. Our research is dedicated to pioneering a new category of cathodes using fluorinated multimetallic materials, with a specific focus on diverging from the traditional Ni, Co, and Mn-based NMC chemistries by substituting nickel and manganese with copper and iron which are more sustainable elements. Our goal is also to enhance the robustness of cathodes upon cycling by substituting oxygen with fluorine as the metal-ligand. To achieve this, an intimate composite blend of CuF2 and FeF3, through the multi-metallic template fluorination (MMTF) methodology using a layered double hydroxide (LDH) as a precursor has been designed. Each of these components was carefully selected for its distinct attributes, including high redox potential, elevated energy density, substantial theoretical capacity, and improved cyclability. The composition denoted as (Cu1.5Co0.5)2+(Fe0.75Al0.25)3+ has been selected for fluorination because it maximizes Fe3+ and Cu2+ amount in the screened LDHs. Subsequently, this particular LDH was fluorinated through solid-gas fluorination at different temperatures (200, 350, and 500 °C) using gaseous molecular fluorine (F2). A comprehensive characterization of these materials using various techniques, including X-ray diffraction (XRD), 57Fe Mössbauer spectrometry, scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), and inductively coupled plasma analyses (ICP-AES) was conducted, and the evolution of LDH upon fluorination has revealed an intermediate porous texture particularly sensitive to hydration. Two original crystallographic phases are else obtained by fluorination: one formed by the hydration of the amorphous intermediate compound: Cu3Fe1.5Al0.5F12(H2O)12 an anti-perovskite structure and another stabilized through the combination of solid gas fluorination and LDH precursor yielding an original CoFeF5-type phase. Raman operando during cyclic voltammetry measurement applied on a sample fluorinated at 500 °C and used as a cathode in front of lithium metal was finally conducted to validate redox activity and mechanism.

A Microporous Multi-Cage Metal-Organic Framework for an Effective One-Step Separation of Branched Alkanes Feeds.

The improvement of the Total Isomerization Process (TIP) for the production of high-quality gasoline with the ultimate goal of reaching a Research Octane Number (RON) higher than 92 requires the use of specific sorbents to separate pentane and hexane isomers into classes of linear, mono- and di-branched isomers. Herein we report the design of a new multi-cage microporous Fe(III)-MOF (referred to as MIP-214, MIP stands for materials of the Institute of Porous Materials of Paris) with a flu-e topology, incorporating an asymmetric heterofunctional ditopic ligand, 4-pyrazolecarboxylic acid, that exhibits an appropriate microporous structure for a thermodynamic-controlled separation of hydrocarbon isomers. This MOF produced via a direct, scalable, and mild synthesis route was proven to encompass a unique separation of C5/C6 isomers by classes of low RON over high RON alkanes with a sorption hierarchy: (n-hexane≫n-pentane≈2-methylpentane>3-methylpentane)low RON≫(2,3-dimethylbutane≈i-pentane≈2,2-dimethylbutane)high RON following the adsorption enthalpy sequence. We reveal for the first time that a single sorbent can efficiently separate such a complex mixture of high RON di-branched hexane and mono-branched pentane isomers from their low RON counterparts, which is a major achievement reported so far.

Expanding the horizons of porphyrin metal-organic frameworks via catecholate coordination: exploring structural diversity, material stability and redox properties.

Porphyrin based Metal-Organic Frameworks (MOFs) have generated high interest because of their unique combination of light absorption, electron transfer and guest adsorption/desorption properties. In this study, we expand the range of available MOF materials by focusing on the seldom studied porphyrin ligand H10TcatPP, functionalized with tetracatecholate coordinating groups. A systematic evaluation of its reactivity with M(iii) cations (Al, Fe, and In) led to the synthesis and isolation of three novel MOF phases. Through a comprehensive characterization approach involving single crystal and powder synchrotron X-ray diffraction (XRD) in combination with the local information gained from spectroscopic techniques, we elucidated the structural features of the solids, which are all based on different inorganic secondary building units (SBUs). All the synthesized MOFs demonstrate an accessible porosity, with one of them presenting mesopores and the highest reported surface area to date for a porphyrin catecholate MOF (>2000 m2 g-1). Eventually, the redox activity of these solids was investigated in a half-cell vs. Li with the aim of evaluating their potential as electrode positive materials for electrochemical energy storage. One of the solids displayed reversibility during cycling at a rather high potential (∼3.4 V vs. Li+/Li), confirming the interest of redox active phenolate ligands for applications involving electron transfer. Our findings expand the library of porphyrin-based MOFs and highlight the potential of phenolate ligands for advancing the field of MOFs for energy storage materials.

Oxidation State and Structure of Fe in Nontronite: From Oxidizing to Reducing Conditions.

The redox reaction between natural Fe-containing clay minerals and its sorbates is a fundamental process controlling the cycles of many elements such as carbon, nutrients, redox-sensitive metals, and metalloids (e.g., Co, Mn, As, Se), and inorganic as well as organic pollutants in Earth's critical zone. While the structure of natural clay minerals under oxic conditions is well-known, less is known about their behavior under anoxic and reducing conditions, thereby impeding a full understanding of the mechanisms of clay-driven reduction and oxidation (redox) reactions especially under reducing conditions. Here we investigate the structure of a ferruginous natural clay smectite, nontronite, under different redox conditions, and compare several methods for the determination of iron redox states. Iron in nontronite was gradually reduced chemically with the citrate-bicarbonate-dithionite (CBD) method. 57Fe Mössbauer spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) spectroscopy including its pre-edge, extended X-ray absorption fine structure (EXAFS) spectroscopy, and mediated electrochemical oxidation and reduction (MEO/MER) provided consistent Fe(II)/Fe(III) ratios. By combining X-ray diffraction (XRD) and transmission electron microscopy (TEM), we show that the long-range structure of nontronite at the highest obtained reduction degree of 44% Fe(II) is not different from that of fully oxidized nontronite except for a slight basal plane dissolution on the external surfaces. The short-range order probed by EXAFS spectroscopy suggests, however, an increasing structural disorder and Fe clustering with increasing reduction of structural Fe.

Immobilisation of contaminants by 'green'-synthesized magnetite as a remediation approach to the phosphogypsum waste leachates model solution.

Contaminant removal from (waste)waters by magnetite is a promising technology. In the present experimental study, a magnetite recycled from the steel industry waste (zero-valent iron powder) was used to investigate the sorption of As, Sb and U in phosphate-free and -rich suspensions, i.e. as a remediation for the acidic phosphogypsum leachates derived from the phosphate fertilizer industry. The results showed up to 98% U removal under controlled pH conditions, while phosphate did not hinder this immobilisation. In contrast, the results confirmed the limited uptake of As and Sb oxyanions by magnetite in presence of phosphate as the competing anion, displaying only 7-11% removal, compared to 83-87% in the phosphate-free sorption experiments. To limit this wastewater problem, raw ZVI anaerobic oxidation was examined as mechanism to increase the pH and as a source of Fe2+ in a first step, and in a second step to remove phosphate via vivianite precipitation, therefore prior to the reaction with magnetite. UV-Vis, XRD and SEM-EDS showed that vivianite precipitation is feasible at pH > 4.5, mainly depending on the phosphate concentration. The higher the [PO43-], the lower is the pH at which vivianite precipitates and the higher the % removal of phosphate from solution. It is anticipated that an optimum 3-steps design with separate reactors controlling the conditions of ZVI oxidation, followed by vivianite precipitation and finally, reaction with magnetite, can achieve high contaminant uptake in field applications.

Hierarchical superparamagnetic metal-organic framework nanovectors as anti-inflammatory nanomedicines.

Among a plethora of drug nanocarriers, biocompatible nanoscale metal-organic frameworks (nanoMOFs) with a large surface area and an amphiphilic internal microenvironment have emerged as promising drug delivery platforms, mainly for cancer therapy. However, their application in biomedicine still suffers from shortcomings such as a limited chemical and/or colloidal stability and/or toxicity. Here, we report the design of a hierarchically porous nano-object (denoted as USPIO@MIL) combining a benchmark nanoMOF (that is, MIL-100(Fe)) and ultra-small superparamagnetic iron oxide (USPIO) nanoparticles (that is, maghemite) that is synthesized through a one-pot, cost-effective and environmentally friendly protocol. The synergistic coupling of the physico-chemical and functional properties of both nanoparticles confers to these nano-objects valuable features such as high colloidal stability, high biodegradability, low toxicity, high drug loading capacity as well as stimuli-responsive drug release and superparamagnetic properties. This bimodal MIL-100(Fe)/maghemite nanocarrier once loaded with anti-tumoral and anti-inflammatory drugs (doxorubicin and methotrexate) shows high anti-inflammatory and anti-tumoral activities. In addition, the USPIO@MIL nano-object exhibits excellent relaxometric properties and its applicability as an efficient contrast agent for magnetic resonance imaging is herein demonstrated. This highlights the high potential of the maghemite@MOF composite integrating the functions of imaging and therapy as a theranostic anti-inflammatory formulation.

Influence of Nd Substitution on the Phase Constitution in (Zr,Ce)Fe10Si2 Alloys with the ThMn12 Structure.

Iron-based compounds with a ThMn12-type structure have the potential to bridge the gap between ferrites and high performance Nd2Fe14B magnets. From the point of view of possible applications, the main advantage is their composition, with about 10 wt.% less rare earth elements in comparison with the 2:14:1 phase. On the other hand, the main issue delaying the development of Fe-rich alloys with a ThMn12-type structure is their structural stability. Therefore, various synthesis methods and stabilizing elements have been proposed to stabilize the structure. In this work, the influence of increasing Nd substitution on the phase constitution of Zr0.4-xNdxCe0.6Fe10Si2 (0 ≤ x ≤ 0.3) alloys was analyzed. X-ray diffraction and 57Fe Mössbauer spectrometry were used as the main methods to derive the stability range and destabilization routes of the 1:12 structure. For the arc-melted samples, an increase in the lattice parameters of the ThMn12-type structure was observed with the simultaneous growth of bcc-(Fe,Si) content with increasing Nd substitution. After isothermal annealing, the ThMn12-type structure (and the coexisting bcc-(Fe,Si)) were stable over the whole composition range. While the formation of a 1:12 phase was totally suppressed in the as-cast state for x = 0.3, further heat treatment resulted in the growth of about 45% of the ThMn12-type phase. The results confirmed that the stability range of ThMn12-type structure in the Nd-containing alloys was well improved by other substitutions and the heat treatment, which in turn, is also needed to homogenize the ThMn12-type phase. After further characterization of the magnetic properties and optimization of microstructure, such hard/soft magnetic composites can show their potential by exploiting the exchange spring mechanism.

Two-step single-reactor synthesis of oleic acid- or undecylenic acid-stabilized magnetic nanoparticles by thermal decomposition.

Different iron oxides (i.e., magnetite, maghemite, goethite, wüstite), particularly nanosized particles, show distinct effects on living organisms. Thus, it is of primary importance for their biomedical applications that the morphology and phase-structural state of these materials are investigated. The aim of this work was to obtain magnetic nanoparticles in a single reactor using Fe(III) acetylacetonate as the initial precursor for the synthesis of Fe(III) oleate or Fe(III) undecylate followed by their thermolysis in situ. We proposed a new approach, according to which the essential magnetite precursor (a complex salt of higher acids - Fe(III) alkanoates) is obtained in a solvent with a high boiling point via displacement reaction of acetylacetone with a higher acid from Fe(III) acetylacetonate during its elimination from the reaction mixture under vacuum conditions. Magnetic nanoparticles (NPM) were characterized in terms of morphology, hydrodynamic diameter, and composition via several techniques, such as transmission electron microscopy, dynamic light scattering, thermogravimetric analysis, Fourier-transform infrared spectroscopy/attenuated total reflectance, 57Fe Mössbauer spectroscopy, and X-ray diffraction. The effect of unsaturated oleic (OA) and undecylenic (UA) acids, which are both used as a reagent and as a nanoparticle stabilizer, as well as the influence of their ratio to Fe(III) acetylacetonate on the properties of particles were investigated. Stable dispersions of NPM were obtained in 1-octadecene within the OA or UA ratio from 3.3 mol to 1 mol of acetylacetonate and up to 5.5 mol/mol. Below the mentioned limit, NPM dispersions were colloidally unstable, and at higher ratios no NPM were formed which could be precipitated by an applied magnetic field. Monodisperse nanoparticles of iron oxides were synthesized with a diameter of 8-13 nm and 11-16 nm using OA and UA, respectively. The organic shell that enables the particle to be dispersed in organic media, in the case of oleic acid, covers their inorganic core only with a layer similar to the monomolecular layer, whereas the undecylenic acid forms a thicker layer, which is 65% of the particle mass. The result is a significantly different resistance to oxidation of the nanoparticle inorganic cores. The core of the particles synthesized using oleic acid is composed of more than 90% of maghemite. When undecylenic acid is used for the synthesis, the core is composed of 75% of magnetite.

Presence of Induced Weak Ferromagnetism in Fe-Substituted YFexCr1-xO3 Crystalline Compounds.

Fe-substituted YFexCr1-xO3 crystalline compounds show promising magnetic and multiferroic properties. Here we report the synthesis and characterization of several compositions from this series. Using the autocombustion route, various compositions (x = 0.25, 0.50, 0.6, 0.75, 0.9, and 1) were synthesized as high-quality crystalline powders. In order to obtain microscopic and atomic information about their structure and magnetism, characterization was performed using room temperature X-ray diffraction and energy dispersion analysis as well as temperature-dependent neutron diffraction, magnetometry, and 57Fe Mössbauer spectrometry. Rietveld analysis of the diffraction data revealed a crystallite size of 84 (8) nm for YFeO3, while energy dispersion analysis indicated compositions close to the nominal compositions. The magnetic results suggested an enhancement of the weak ferromagnetism for the YFeO3 phase due to two contributions. First, a high magnetocrystalline anisotropy was associated with the crystalline character that favored a unique high canting angle of the antiferromagnetic phase (13°), as indicated by the neutron diffraction analysis. This was also evidenced by the high magnetic hysteresis curves up to 90 kOe by a remarkable high critical coercivity value of 46.7 kOe at room temperature. Second, the Dzyaloshinskii-Moriya interactions between homogenous and heterogeneous magnetic pairs resulted from the inhomogeneous distribution of Fe3+ and Cr3+ ions, as indicated by 57Fe Mössbauer studies. Together, these results point to new methods of controlling the magnetic properties of these materials.

Selenium Nanowire Formation by Reacting Selenate with Magnetite.

The mobility of 79Se, a fission product of 235U and long-lived radioisotope, is an important parameter in the safety assessment of radioactive nuclear waste disposal systems. Nonradioactive selenium is also an important contaminant of drainage waters from black shale mountains and coal mines. Highly mobile and soluble in its high oxidation states, selenate (Se(VI)O42-) and selenite (Se(IV)O32-) oxyanions can interact with magnetite, a mineral present in anoxic natural environments and in steel corrosion products, thereby being reduced and consequently immobilized by forming low-solubility solids. Here, we investigated the sorption and reduction capacity of synthetic nanomagnetite toward Se(VI) at neutral and acidic pH, under reducing, oxygen-free conditions. The additional presence of Fe(II)aq, released during magnetite dissolution at pH 5, has an effect on the reduction kinetics. X-ray absorption spectroscopy analyses revealed that, at pH 5, trigonal gray Se(0) formed and that sorbed Se(IV) complexes remained on the nanoparticle surface during longer reaction times. The Se(0) nanowires grew during the reaction, which points to a complex transport mechanism of reduced species or to active reduction sites at the tip of the Se(0) nanowires. The concomitant uptake of aqueous Fe(II) and Se(VI) ions is interpreted as a consequence of small pH oscillations that result from the Se(VI) reduction, leading to a re-adsorption of aqueous Fe(II) onto the magnetite, renewing its reducing capacity. This effect is not observed at pH 7, where we observed only the formation of Se(0) with slow kinetics due to the formation of an oxidized maghemite layer. This indicates that the presence of aqueous Fe(II) may be an important factor to be considered when examining the environmental reactivity of magnetite.

Deciphering the Thermal and Electrochemical Behaviors of Dual Redox-Active Iron Croconate Violet Coordination Complexes.

Interest in coordination compounds based on non-innocent ligands (NILs) for electrochemical energy storage has risen in the last few years. We have focused our attention on an overlooked redox active linker, croconate violet, which has not yet been addressed in this field although closely related to standard NILs such as catecholate and tetracyanoquinodimethane. Two anionic complexes consisting of Fe(II) and croconate violet (-2) with balancing potassium cations were isolated and structurally characterized. By a combination of in situ and ex situ techniques (powder and single-crystal X-ray diffraction, infrared, and 57Fe Mössbauer spectroscopies), we have shown that their dehydration occurs through complex patterns, whose reversibility depends on the initial crystal structure but that the structural rearrangements around the iron cations occur without any oxidation. While electrochemical studies performed in solution clearly show that both the organic and inorganic parts can be reversibly addressed, in the solid state, poor charge storage capacities were initially measured, mainly due to the solubilization of the solids in the electrolyte. By optimizing the formulation of the electrode and the composition of the electrolyte, a capacity of >100 mA h g-1 after 10 cycles could be achieved. This suggests that this family of redox active linkers deserves to be investigated for solid-state electrochemical energy storage, although it requires the solving of the issues related to the solubilization of the derived coordination compounds.

A Comprehensive Study of Pristine and Calcined f-MWCNTs Functionalized by Nitrogen-Containing Functional Groups.

We present the study of pristine and calcined f-MWCNTs functionalized by nitrogen-containing functional groups. We focus on the structural and microstructural modification tuned by the previous annealing. However, our primary goal was to analyze the electronic structure and magnetic properties in relation to the structural properties using a multi-technique approach. The studies carried out by X-ray diffraction, XPS, and 57Fe Mössbauer spectrometry revealed the presence of γ-Fe nanoparticles, Fe3C, and α-FeOOH as catalyst residues. XPS analysis based on the deconvolution of core level lines confirmed the presence of various nitrogen-based functional groups due to the purification and functionalization process of the nanotubes. The annealing procedure leads to a structural modification mainly associated with removing surface impurities as purification residues. Magnetic studies confirmed a significant contribution of Fe3C as evidenced by a Curie temperature estimated at TC = 452 ± 15 K. A slight change in magnetic properties upon annealing was revealed. The detailed studies performed on nanotubes are extremely important for the further synthesis of composite materials based on f-MWCNTs.

Structure-Property-Function Relationships of Iron Oxide Multicore Nanoflowers in Magnetic Hyperthermia and Photothermia.

Magnetite and maghemite multicore nanoflowers (NFs) synthesized using the modified polyol-mediated routes are to date among the most effective nanoheaters in magnetic hyperthermia (MHT). Recently, magnetite NFs have also shown high photothermal (PT) performances in the most desired second near-infrared (NIR-II) biological window, making them attractive in the field of nanoparticle-activated thermal therapies. However, what makes magnetic NFs efficient heating agents in both modalities still remains an open question. In this work, we investigate the role of many parameters of the polyol synthesis on the final NFs' size, shape, chemical composition, number of cores, and crystallinity. These nanofeatures are later correlated to the magnetic, optical, and electronic properties of the NFs as well as their collective macroscopic thermal properties in MHT and PT to find relationships between their structure, properties, and function. We evidence the critical role of iron(III) and heating ramps on the elaboration of well-defined NFs with a high number of multicores. While MHT efficiency is found to be proportional to the average number of magnetic cores within the assemblies, the optical responses of the NFs and their collective photothermal properties depend directly on the mean volume of the NFs (as supported by optical cross sections numerical simulations) and strongly on the structural disorder in the NFs, rather than the stoichiometry. The concentration of defects in the nanostructures, evaluated by photoluminescence and Urbach energy (EU), evidence a switch in the optical behavior for a limit value of EU = 0.4 eV where a discontinuous transition from high to poor PT efficiency is also observed.

Unveiling the role of surface, size, shape and defects of iron oxide nanoparticles for theranostic applications.

Iron oxide nanoparticles (IONPs) are well-known contrast agents for MRI for a wide range of sizes and shapes. Their use as theranostic agents requires a better understanding of their magnetic hyperthermia properties and also the design of a biocompatible coating ensuring their stealth and a good biodistribution to allow targeting of specific diseases. Here, biocompatible IONPs of two different shapes (spherical and octopod) were designed and tested in vitro and in vivo to evaluate their abilities as high-end theranostic agents. IONPs featured a dendron coating that was shown to provide anti-fouling properties and a small hydrodynamic size favoring an in vivo circulation of the dendronized IONPs. While dendronized nanospheres of about 22 nm size revealed good combined theranostic properties (r2 = 303 mM s-1, SAR = 395 W gFe-1), octopods with a mean size of 18 nm displayed unprecedented characteristics to simultaneously act as MRI contrast agents and magnetic hyperthermia agents (r2 = 405 mM s-1, SAR = 950 W gFe-1). The extensive structural and magnetic characterization of the two dendronized IONPs reveals clear shape, surface and defect effects explaining their high performance. The octopods seem to induce unusual surface effects evidenced by different characterization techniques while the nanospheres show high internal defects favoring Néel relaxation for magnetic hyperthermia. The study of octopods with different sizes showed that Néel relaxation dominates at sizes below 20 nm while the Brownian one occurs at higher sizes. In vitro experiments demonstrated that the magnetic heating capability of octopods occurs especially at low frequencies. The coupling of a small amount of glucose on dendronized octopods succeeded in internalizing them and showing an effect of MH on tumor growth. All measurements evidenced a particular signature of octopods, which is attributed to higher anisotropy, surface effects and/or magnetic field inhomogeneity induced by tips. This approach aiming at an analysis of the structure-property relationships is important to design efficient theranostic nanoparticles.

Iron Stearate Structures: An Original Tool for Nanoparticles Design.

Iron carboxylates are widely used as iron precursors in the thermal decomposition process or considered as in situ formed intermediate precursors. Their molecular and three-dimensional (3D)-structural nature has been shown to affect the shape, size, and composition of the resulting iron oxide nanoparticles (NPs). Among carboxylate precursors, stearates are particularly attractive because of their higher stability to aging and hydration and they are used as additives in many applications. Despite the huge interest of iron stearates, very few studies aimed up to now at deciphering their full metal-ligand structures and the mechanisms allowing us to achieve in a controlled manner the bottom-up NP formation. In this work, we have thus investigated the molecular structure and composition of two iron stearate precursors, synthesized by introducing either two (FeSt2) or three (FeSt3) stearate (St) chains. Interestingly, both iron stearates consist of lamellar structures with planes of iron polynuclear complexes (polycations) separated with stearate chains in all-trans conformation. The iron content in polycations was found very different between both iron stearates. Their detailed characterizations indicate that FeSt2 is mainly composed of [Fe3-(µ3-O)St6·xH2O]Cl, with no (or few) free stearate, whereas FeSt3 is a mixture of mainly [Fe7(µ3-O(H))6(µ2-OH)xSt12-2x]St with some [Fe3(µ3-O)St6·xH2O]St and free stearic acid. The formation of bigger polynuclear complexes with FeSt3 was related to higher hydrolysis and condensation rates within the iron(III) chloride solution compared to the iron(II) chloride solution. These data suggested a nucleation mechanism based on the condensation of polycation radicals generated by the catalytic departure of two stearate chains from an iron polycation-based molecule.

A Detailed Investigation of the Onion Structure of Exchanged Coupled Magnetic Fe3-δO4@CoFe2O4@Fe3-δO4 Nanoparticles.

Nanoparticles that combine several magnetic phases offer wide perspectives for cutting edge applications because of the high modularity of their magnetic properties. Besides the addition of the magnetic characteristics intrinsic to each phase, the interface that results from core-shell and, further, from onion structures leads to synergistic properties such as magnetic exchange coupling. Such a phenomenon is of high interest to overcome the superparamagnetic limit of iron oxide nanoparticles which hampers potential applications such as data storage or sensors. In this manuscript, we report on the design of nanoparticles with an onion-like structure which has been scarcely reported yet. These nanoparticles consist of a Fe3-δO4 core covered by a first shell of CoFe2O4 and a second shell of Fe3-δO4, e.g., a Fe3-δO4@CoFe2O4@Fe3-δO4 onion-like structure. They were synthesized through a multistep seed-mediated growth approach which consists consists in performing three successive thermal decomposition of metal complexes in a high-boiling-point solvent (about 300 °C). Although TEM micrographs clearly show the growth of each shell from the iron oxide core, core sizes and shell thicknesses markedly differ from what is suggested by the size increasing. We investigated very precisely the structure of nanoparticles in performing high resolution (scanning) TEM imaging and geometrical phase analysis (GPA). The chemical composition and spatial distribution of atoms were studied by electron energy loss spectroscopy (EELS) mapping and spectroscopy. The chemical environment and oxidation state of cations were investigated by 57Fe Mössbauer spectrometry, soft X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). The combination of these techniques allowed us to estimate the increase of Fe2+ content in the iron oxide core of the core@shell structure and the increase of the cobalt ferrite shell thickness in the core@shell@shell one, whereas the iron oxide shell appears to be much thinner than expected. Thus, the modification of the chemical composition as well as the size of the Fe3-δO4 core and the thickness of the cobalt ferrite shell have a high impact on the magnetic properties. Furthermore, the growth of the iron oxide shell also markedly modifies the magnetic properties of the core-shell nanoparticles, thus demonstrating the high potential of onion-like nanoparticles to accurately tune the magnetic properties of nanoparticles according to the desired applications.

Influence of Silica Coatings on Magnetite-Catalyzed Selenium Reduction.

The reactivity of iron(II/III) oxide surfaces may be influenced by their interaction with silica, which is ubiquitous in aquatic systems. Understanding the structure-reactivity relationships of Si-coated mineral surfaces is necessary to describe the complex surface behavior of nanoscale iron oxides. Here, we use Si-adsorption isotherms and Fourier transform infrared spectroscopy to analyze the sorption and polymerization of silica on slightly oxidized magnetite nanoparticles (15% maghemite and 85% magnetite, i.e., ∼2 maghemite surface layers), showing that Si adsorption follows a Langmuir isotherm up to 2 mM dissolved Si, where surface polymerization occurs. Furthermore, the effects of silica surface coatings on the redox-catalytic ability of magnetite are analyzed using selenium as a molecular probe. The results show that for partially oxidized nanoparticles and even under different Si surface coverages, electron transfer is still occurring. The results indicate anion exchange between silicate and the sorbed SeIV and SeVI. X-ray absorption near-edge structure analyses of the reacted Se indicate the formation of a mixed selenite/Se0 surface phase. We conclude that neither partial oxidation nor silica surface coatings block the sorption and redox-catalytic properties of magnetite nanoparticles, a result with important implications to assess the reactivity of mixed-valence phases in environmental settings.

Rheological, Microstructural and Thermal Properties of Magnetic Poly(Ethylene Oxide)/Iron Oxide Nanocomposite Hydrogels Synthesized Using a One-Step Gamma-Irradiation Method.

Magnetic polymer gels are a new promising class of nanocomposite gels. In this work, magnetic PEO/iron oxide nanocomposite hydrogels were synthesized using the one-step -irradiation method starting from poly(ethylene oxide) (PEO) and iron(III) precursor alkaline aqueous suspensions followed by simultaneous crosslinking of PEO chains and reduction of Fe(III) precursor. -irradiation dose and concentrations of Fe3+, 2-propanol and PEO in the initial suspensions were varied and optimized. With 2-propanol and at high doses magnetic gels with embedded magnetite nanoparticles were obtained, as confirmed by XRD, SEM and Mössbauer spectrometry. The quantitative determination of -irradiation generated Fe2+ was performed using the 1,10-phenanthroline method. The maximal Fe2+ molar fraction of 0.55 was achieved at 300 kGy, pH = 12 and initial 5% of Fe3+. The DSC and rheological measurements confirmed the formation of a well-structured network. The thermal and rheological properties of gels depended on the dose, PEO concentration and initial Fe3+ content (amount of nanoparticles synthesized inside gels). More amorphous and stronger gels were formed at higher dose and higher nanoparticle content. The properties of synthesized gels were determined by the presence of magnetic iron oxide nanoparticles, which acted as reinforcing agents and additional crosslinkers of PEO chains thus facilitating the one-step gel formation.

Stabilization of a mixed iron vanadium based hexagonal tungsten bronze hydroxyfluoride HTB-(Fe0.55V0.45)F2.67(OH)0.33 as a positive electrode for lithium-ion batteries.

In our search for novel insertion compounds for Li-based batteries, we have identified a new mixed iron vanadium based Hexagonal Tungsten Bronze (HTB) type phase. Its synthesis involves two steps which consist first of preparing mixed metal hydrated fluoride Fe1.64V1.36F8(H2O)2 by a microwave assisted thermal process, followed by thermal treatment under air to obtain metastable HTB-(Fe0.55V0.45)F2.67(OH)0.33 hydroxyfluoride. 57Fe Mössbauer spectrometry demonstrates the presence of oxidation states Fe2+ and Fe3+ in Fe1.64V1.36F8(H2O)2 as opposed to only Fe3+ in HTB-(Fe0.55V0.47)F2.67(OH)0.33. Moreover, the Mössbauer spectra recorded at 77 K reveal that none of the compounds shows magnetic ordering owing to the presence of V3+ distributed over the crystallographic sites of Fe3+. Complementary X-ray spectroscopy and Rietveld refinement further confirm the successful synthesis of HTB-(Fe0.55V0.45)F2.67(OH)0.33. Electrochemically, the new HTB-(Fe0.55V0.45)F2.67(OH)0.33 shows a first discharge capacity of 181 mA h g-1 with 67% of this capacity remaining upon cycling. Unlike HTB-FeF2.66(OH)0.34, the structure remains stable after the first discharge confirming the positive effect of vanadium in the HTB network.

Synthesis of Magnetic Wires from Polyol-Derived Fe-Glycolate Wires.

Fe-glycolate wires with micrometer-scale lengths can be synthesized by the polyol process. Although the as-produced wires are in the paramagnetic state at room temperature, they are transformed into ferrimagnetic iron oxides and ferromagnetic metallic iron wires by reductive annealing. The shape of the wires is unchanged by reductive annealing, and it is possible to control the magnetic properties of the resulting wire-shaped ferri/ferromagnets by adjusting the annealing conditions. Consequently, the reductive annealing of polyol-derived Fe-glycolate wires is an effective material-processing route for the production of magnetic wires.