Search

A highly efficient photo-Fenton catalyst iron silicate glass was successfully prepared by a simple sol–gel method. The characterization results (XRD, Mössbauer spectroscopy, TEM, and FT- IR) showed that fayalite, clinoferrosilite and hematite nanoparticles were precipitated in the glass system. The catalytic activity of the glass samples was evaluated by measuring the degradation efficiency for organic dyes as well as for a typical persistent organic pollutant phenol, under visible light irradiation, in the presence of hydrogen peroxide (H2O2). The chemical oxygen demand (COD) and total organic carbon (TOC) were measured to see the progress in degradation of phenol. The results showed that the catalyst containing 20% iron had good catalytic properties for the degradation of both types of organic contaminants with superior stability for the degradation of methylene blue dye even after six cycles. Finally, a possible photocatalytic mechanism was proposed.

Chemical stability and good biocompatibility under physiological conditions render nanoparticles made of the spinel oxide magnetite a favorable choice in biomedical diagnostic and therapeutic applications that benefit from high levels of magnetization and superparamagnetism. Under ambient atmosphere, however, magnetite nanoparticles are prone to undesired oxidation leading to an at least partially oxidized form of magnetite. In the present work Fe3-xO4 nanopowders (with a particle size of 10–50 nm) were prepared under different conditions via chemical co-precipitation method, resulting in samples with different oxidation levels. The effect of oxidation of the prepared samples on their morphological, structural, electronic and magnetic properties is followed, respectively, by the means of transmission electron microscopy (TEM), powder X-ray diffractometry (PXRD), 57Fe Mossbauer spectroscopy (MS) and electron magnetic resonance (EMR) spectroscopy measurements. A novel method is applied to decompose the heavily broadened room-temperature 57Fe Mossbauer spectra of the nanoparticles into signals of intermediate valence Fe2.5+ and that of Fe3+ iron species. The results indicate that the cubic lattice parameter of non-stoichiometric magnetite nanoparticles depends on the concentration as well as on the mean oxidation level of the intermediate valence iron species. At the same time, EMR spectra of the samples indicate that oxidation influences the magnetic anisotropy of the nanoparticles, with the magnitude of the nanoparticles' magnetic anisotropy field being correlated with the concentration of the intermediate valence iron species. Malic acid, used as coating agent for several of the samples, is shown to hinder the oxidation of magnetite nanoparticles.

Pure hematite nanorods and very long and thin cobalt-doped hematite nanorods (nanoneedles) were prepared by a combined precipitation and annealing method. The influence of the level of cobalt doping on different properties of hematite nanorods was investigated. Incorporation of cobalt in the form of low-spin Co3+ ions into the structure of hematite by substitution for high-spin Fe3+ ions was proved by determination of a significant unit cell contraction by powder X-ray diffraction (PXRD) and characteristic positions of the absorption edge in X-ray absorption near edge structure (XANES) spectra and peaks in X-ray emission (XES) spectra. Cobalt doping caused a gradual elongation and thinning of hematite nanorods – very long and thin 1D nanoparticles (nanoneedles) were formed in the presence of 10 and 12 mol% Co. Magnetic measurements showed a strong increase in low-temperature remanent magnetization and coercivity upon cobalt doping, as well as a disappearance of the Morin transition, which was also confirmed by Mössbauer spectroscopy. Cobalt doping significantly affected optical properties of hematite nanorods – absorption in the visible and NIR ranges increased, which was accompanied by narrowing of the optical band gap. Compared with pure hematite nanorods cobalt-doped hematite nanoneedles showed a significantly better electrocatalytic activity for the oxygen evolution reaction (OER). © 2020 Elsevier Ltd

Pure and Cr-doped hematite (α-(Fe1-xCrx)2O3, x = 0, 0.026, 0.039, 0.085 or 0.135) nanorods were prepared by a simple co-precipitation and calcination method. Influence of different levels of Cr doping on the change of properties of long and thin pure hematite nanorods was investigated. Cr3+-for-Fe3+ substitution in the crystal structure of hematite was proved by measuring a gradual contraction of the unit cell and a gradual decrease of the hyperfine magnetic field by increasing the Cr molar fraction. Cr doping induced an increase in the width and thickness of hematite nanorods, as well as a decrease in the overall surface area. Low temperature 57Fe Mössbauer spectroscopy showed that the Morin transition in hematite was suppressed by Cr doping to temperatures below 80 K. Magnetic measurements confirmed the suppression of the Morin transition in Cr-doped hematite down to 5 K. Infrared spectra of Cr-doped hematite samples showed shifts of IR bands by Cr3+-for-Fe3+ substitution. Optical properties of α-Fe2O3 nanorods changed significantly by Cr doping – the absorption edge was shifted to higher wavelengths, accompanied by a greater absorption in the visible range and narrowed direct and indirect optical band gaps. The improved visible light photocatalytic activity of hematite nanorods in the heterogeneous photo-Fenton process by moderate Cr doping was measured, which can be attributed to the modifications in electronic structure and optical properties. © 2020 Elsevier Ltd

Comparison of the Mossbauer spectra of the as-prepared native iron oxide nanoparticles (IONs) and the citrate-functionalized IONs demonstrates differences in the spectral shapes at room temperature and variations of the 57Fe hyperfine parameters at 80 K. The observed differences are claimed to result from capping the IONs with citrate, thus decreasing the particle-particle interaction while promoting interaction of the outer atomic layers of the IONs with the surface molecular coating.

We report the results of the complex study of the bulk interior of Bursa L6 ordinary chondrite using optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, electron microprobe analysis (EMPA), X-ray diffraction (XRD), magnetization measurements, and Mossbauer spectroscopy. The main and minor iron-bearing phases and their chemical compositions were determined by these techniques. The detected iron-bearing phases in the bulk interior of Bursa L6 are the following: olivine; orthopyroxene; Ca-rich clinopyroxene; troilite; chromite; hercynite; ilmenite; the alpha(2)-Fe(Ni, Co), alpha-Fe(Ni, Co), and gamma-Fe(Ni, Co) phases; and ferrihydrite resulting from meteorite terrestrial weathering. Using the EMPA, the values of fayalite and ferrosilite were obtained as similar to 25.2% and similar to 21.4%, respectively. The unit cell parameters for silicate crystals were determined from XRD, then the Fe2+ and Mg2+ occupations of the M1 and M2 sites in these crystals were estimated. Further calculations of the ratios of the Fe2+ occupancies in the M1 and M2 sites in olivine and orthopyroxene based on XRD and Mossbauer spectroscopy appeared to be in a good agreement. The temperatures of equilibrium cation distributions for olivine and orthopyroxene obtained from these techniques are consistent: 623 K (XRD) and 625 K (Mossbauer spectroscopy) for olivine and 1138 K (XRD) and 1122 K (Mossbauer spectroscopy) for orthopyroxene., Ministry of Science and Higher Education of the Russian Federation [FEUZ-2020-0060, AAAA-A18-118053090045-8, AAAA-A19-119071090011-6]; Act 211 of the Government of the Russian Federation [02.A03.21.0006]; Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [MFAG/113F035]; Ege University Scientific Research Projects Coordination UnitEge University [17-FEN-050]; Hungarian Ministry of Human Capacities [783-3/2018/FEKUTSRAT], The authors are grateful to G.A. Yakovlev (Ural Federal University, Ekaterinburg, Russian Federation) for the help with scanning electron microscopy. This work was supported by the Ministry of Science and Higher Education of the Russian Federation, project No FEUZ-2020-0060 and by Act 211 of the Government of the Russian Federation, contract No 02.A03.21.0006. O.U. was supported by the Scientific and Technological Research Council of Turkey (TUBITAK), project No MFAG/113F035 and by the Ege University Scientific Research Projects Coordination Unit, project No 17-FEN-050. D.A.Z. and A.A.M. were supported by the Ministry of Science and Higher Education of the Russian Federation, projects No AAAA-A18-118053090045-8 (D.A.Z.) and No AAAA-A19-119071090011-6 (D.A.Z. and A.A.M.). on behalf of two of us (~ A.Sz. and Z.D.), this work was completed in the ELTE Excellence Programme (783-3/2018/FEKUTSRAT) supported by the Hungarian Ministry of Human Capacities. This work was carried out within the Agreement of Cooperation between the Ural Federal University (Ekaterinburg) and the E_otv_os Lor~and University (Budapest).

A relationship between the local structure and the visible-light activated photocatalytic effect was investigated in the glass and glass ceramics prepared by recycling waste slag, which was discharged from a Tokyo Household Garbage Combustion Plant. For the preparation of a homogeneous sample of waste slag recycled glass, (WSRG), 10 wt% of Na2CO3 and 10–50 wt% of Fe2O3 were added. 57Fe-Mössbauer spectra of WSRG recorded at liquid nitrogen temperature showed three types of magnetic hfs; one due to FeII(O h) with δ of 1.21 mm s−1 and H int of 46.7 T, one due to FeIII(O h) with δ of 0.46 mm s−1 and H int of 44.1 T, and the other due to FeIII(T d) with δ of 0.38 mm s−1 and H int of 47.8 T. They were superimposed on a relaxation spectrum due to superparamagnetic hematite. Methylene blue (MB) degradation test with 40 mg of the heat treated WSRG (50 wt% Fe2O3), under the visible-light irradiation for 6 h showed a marked decrease in the concentration of MB from 20 to 7.7 μmol L−1 with a rate constant (k) of 2.7×10−3 min−1 which was close to the k, 9.26×10−3 min− 1, recently obtained in 15Na2O⋅15CaO⋅40Fe2O3⋅ 11Al2O3⋅19SiO2 glass.

The effect of coating with nine different carboxylic acids (glycolic, propionic, lactic, malic, tartaric, citric, mandelic, caproic and caprylic) on nanostructured magnetite (D ~ 10 nm) was studied by Raman and photoacoustic, magnetic and 57Fe Mossbauer measurements. Mossbauer spectra of frozen suspensions showed dominantly magnetically split envelopes at lower temperatures, which were evaluated by hyperfine field distribution method. Mossbauer and Raman spectroscopy indicated similar variation of relative occurrence of magnetite and maghemite phases. These results are discussed on the basis of the hypothesis that different carboxylic acids can promote either the oxidation or reduction of iron oxide nanoparticles.

In the emission (57Co) variant of Mossbauer spectroscopy (EMS), the 57Co radionuclide (with a half-life of 9months) is used that undergoes a nuclear decay 57Co→57Fe via electron capture followed by the emission of a γ-quantum, the energy of which is modified by the chemical state and the close coordination environment of the parent 57Co atom. While EMS has been used largely in materials science and nuclear chemistry, its high sensitivity can also be of great advantage in revealing fine structural features and for speciation analysis of biological complexes, whenever the 57Co2+ cation can be used directly as the coordinating metal or as a substitute for native cobalt or other metal ions. As such EMS applications are yet rare, in order to reliably interpret emission spectra of sophisticated 57Co2+-doped biosystems, model EMS studies of simple cobalt biocomplexes are necessary. In this work, EMS spectroscopic data are analysed and discussed for 57Co2+ complexes with a range of small biomolecules of different structures, including 4-n-hexylresorcinol, homoserine lactone and a few amino acids (spectra measured in rapidly frozen dilute aqueous solutions or in the dried state at T=80K). The EMS data obtained are discussed with regard to the available literature data related to the coordination modes of the biocomplexes under study.

Microbial cells are well known to be capable of remaining viable when desiccated, and a variety of beneficial microorganisms can thus be preserved for storage. For the ubiquitous widely studied soil bacterium Azospirillum brasilense (wild-type strain Sp7), which has a significant agrobiotechnological potential owing to its plant-growth-promoting capabilities perspective for its use in biofertilisers, Fourier transform infrared (FTIR) spectroscopy (in the diffuse reflectance mode, DRIFT) was used to control the state of biomass, together with 57Fe transmission Mossbauer spectroscopy to monitor intracellular iron speciation in live rapidly frozen cell suspension and in the lyophilised biomass (both measured at T = 80 K). It has been shown for the first time that a relatively large part of ferrous iron in live cells (22% of the whole cellular iron pool, represented by two high-spin Fe(II) forms, in the 18-h culture grown on 57Fe(III) complex with nitrilotriacetic acid as the sole source of iron) gets largely oxidised upon lyophilisation. The remaining part of iron(II) in the resulting dry biomass was found to be ca. 3% only. The major part of ferric iron in the dry biomass was shown to be comprised of ferritin-like ferric species (giving a typical magnetically split sextet at T = 5 K), while the iron(III) formed from cellular iron(II) by oxidation in air in the course of drying remained in a paramagnetic state even at T = 5 K. The possibility of intracellular iron(II) oxidation to iron(III) upon desiccation may be a specific natural strategy to avoid cell damage caused by Fenton-type reactions in dormant (frozen, dried) cells. The results obtained may have important implications related to iron speciation and redox transformations in dried bacterial preparations intended for long-term storage.

Zinc borosilicate glass with optimized chemical composition was synthesized and doped with 5 wt % α-Fe2O3. XRD, 57Fe Mössbauer, FT-IR, UV/Vis/NIR and FE SEM were used as the characterization methods. XRD showed the amorphous nature of the samples synthesized. 57Fe Mössbauer spectra confirmed the superposition of Fe3+ in tetrahedral and Fe2+ in octahedral positions. FT-IR spectra showed general features characteristic of different borosilicate glasses. The NIR band at 1116 nm in the UV/Vis/NIR spectrum was assigned to the Fe2+ transition, whereas the Fe3+ transition bands could not be assigned due to the overlapping of several spectral bands of different origin in the UV region centered at 282 nm and the Vis region between 415 to 496 nm. Zinc borosilicate glass as synthesized can be considered as a possible matrix in the immobilization of nonradioactive as well as radioactive wastes. This work is licensed under a Creative Commons Attribution 4.0 International License.

We report the hydrothermal synthesis and structure of FexCo1−x alloy nanoparticles with considerable stability against oxidation under ambient atmosphere. Powder X-ray diffractometry (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma mass spectrometry (ICP-MS), 57Fe Mossbauer spectroscopy and magnetization measurements are applied to characterize the composition, morphology, crystal structure, atomic order and magnetic properties of the nanoparticles. As-prepared samples are composed mainly of the bcc FexCo1−x alloy phase. TEM images of heat-treated samples confirm the nanoparticle nature of the original alloys. A consistent analysis of the experimental results leads to x ≈ 53% and x ≈ 62% Fe atomic ratio respectively in two analogous alloy samples, and suggests that the atomic level structure of the nanoparticles corresponds to that of a fully disordered (A2-type) alloy phase. Exploration of the effect of cobalt on the 57Fe hyperfine parameters of iron microenvironments suggests that in these alloys the electronic state of Fe atoms is perturbed equally and in an additive manner by atoms in their first two coordination spheres.

Iron sulfide (troilite) inclusion extracted from Sikhote-Alin IIAB iron meteorite was examined for its composition, structure and magnetic properties by means of several complementary analytical techniques such as: powder X-ray diffractometry, scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, magnetization measurements, ferromagnetic resonance spectroscopy and 57 Fe Mossbauer spectroscopy with a high velocity resolution. The applied techniques consistently indicated the presence of daubreelite (FeCr 2 S 4 ) as a minority phase beside troilite proper (FeS). As revealed by 57 Fe Mossbauer spectroscopy, the Fe atoms in troilite were in different microenvironments associated with either the ideal FeS structure or that of a slightly iron deficient Fe 1– x S. Phase transitions of troilite were detected above room temperature by ferromagnetic resonance spectroscopy. A novel analysis of 295 and 90 K 57 Fe Mossbauer spectra was carried out and the hyperfine parameters associated with the ideal structure of troilite were determined by considering the orientation of the hyperfine magnetic field in the eigensystem of the electric field gradient at the 57 Fe nucleus.

For the ubiquitous diazotrophic rhizobacterium Azospirillum brasilense, which has been attracting the attention of researchers worldwide for the last 35 years owing to its significant agrobiotechnological and phytostimulating potential, the data on iron acquisition and its chemical speciation in cells are scarce. In this work, for the first time for azospirilla, low-temperature (at 80 K, 5 K, as well as at 2 K without and with an external magnetic field of 5 T) transmission Mössbauer spectroscopic studies were performed for lyophilised biomass of A. brasilense (wild-type strain Sp7 grown with (57)Fe(III) nitrilotriacetate complex as the sole source of iron) to enable quantitative chemical speciation analysis of the intracellular iron. In the Mössbauer spectrum at 80 K, a broadened quadrupole doublet of high-spin iron(III) was observed with a few percent of a high-spin iron(II) contribution. In the spectrum measured at 5 K, a dominant magnetically split component appeared with the parameters typical of ferritin species from other bacteria, together with a quadrupole doublet of a superparamagnetic iron(III) component and a similarly small contribution from the high-spin iron(II) component. The Mössbauer spectra recorded at 2 K (with or without a 5 T external field) confirmed the assignment of ferritin species. About 20% of total Fe in the dry cells of A. brasilense strain Sp7 were present in iron(III) forms superparamagnetic at both 5 and 2 K, i.e. either different from ferritin cores or as ferritin components with very small particle sizes.

The relationship between the local structure and magnetic properties of iron phosphate glass xFe2O3 • (100-x) P2O5 abbreviated as xFeP prepared by a sol-gel method has been investigated. From the Mossbauer spectroscopy results, it was found that iron ions are present in FeIII(distorted octahedral) and FeII(octahedral) coordination. HAADF-STEM images and elemental mapping results revealed that iron and phosphorus are uniformly dispersed in the system. It is clear from the magnetic susceptibility results that only 50FeP glass heat-treated at 200°C shows spin glass behavior and all other glasses are superparamagnetic at low temperatures. The Weiss temperatures (θw) obtained for all the glasses were negative, suggesting that the interaction between the magnetic moments is antiferromagnetic. In these samples, the higher the proportion of FeIII ions, the higher the frustration of the entire system is. The [FeIII] / [Fetotal] molar ratio decreases as the heat-treatment temperature increased.

Iron-oxide nanoparticles were prepared by chemical coprecipitation method in inert gas atmosphere and also in air atmosphere in order to use them as possible nutrition source for plants. The samples were characterized by 57Fe Mossbauer spectroscopy, electron ¨ microscopy and PXRD measurements. The presence of considerable FeII contributions were indicated by 57Fe Mossbauer spectra. Furthermore TEM and XRD reflected nanomagnetite ¨ in washed and lyophilized samples prepared in inert gas atmosphere while the samples prepared in air atmosphere contained much higher amount of FeIII than characteristic of magnetite. In the case of samples prepared in inert gas, it was also shown that the immediate washing after the coprecipitation has a crucial influence on the FeII content of the nanomagnetites.

57Fe Mossbauer spectroscopy, XRD, and TEM were used to investigate the effect of mandelic- and salicylic acid coatings on the iron oxide nanoparticles. These two carboxylic acids have similar molecules size and stoichiometry, but different structure and acidity. Significant differences were observed between the Mossbauer spectra of samples coated with mandelic acid and salicylic acid. These results indicate that the occurrence of iron microenvironments in the mandelic- and salicylic acid-coated iron oxide nanoparticles is different. The results can be interpreted in terms of the influence of the acidity of carboxylic acids on the formation, core/shell structure, and oxidation of coated iron oxide nanocomposites.

Frozen aqueous solution of hyperalkaline tin(II)-hydroxide was analysed by 119Sn Mossbauer spectroscopy at low temperature in order to determinate the structure of the hydroxo complex formed under hyperalkaline (pH > 13) conditions. Interestingly, the quadrupole doublet characteristic of this complex in the 119Sn Mossbauer spectrum exhibited asymmetry in the line intensities. Analysis of the temperature dependence of the Mossbauer spectra demonstrated that this phenomenon can be rationalised by the Goldanskii–Karyagin effect. The effect emerges due to the vibrational anisotropy of bonds in the tin complex formed in hyperalkaline solution, similarly to what has been found earlier for SnF2 with analogous Sn bond structure.

In spite of numerous investigations on the various processes of the thermal decomposition and rehydration of layered double hydroxides (LDHs) by a variety sophisticated experimental means, many details are still unexplored and some contradictions are still unresolved. In this work, our efforts were focussed on clarifying the composition, structure and properties of thermally decomposed metaphases originating from CaFe–LDH, heat treated in the 373–973 K temperature range. The structure reconstruction ability of mixed metal oxide phases obtained after heat treatments was also investigated, mainly concentrating on the changes in the microenvironment of Fe(III), in the presence of controlled amount of water vapour (i.e., at different relative humidities). All samples were characterised by X-ray diffractometry, and the iron-containing phases were studied by 57 Fe Mossbauer spectroscopy.

Iron–polygalacturonate complexes have been synthesized from polygalacturonic acid by applying a novel preparation method in order to develop medicine suitable for the effective iron supplementation of the human body in the case of anemia. Since the iron uptake depends on the oxidation state of iron, 57Fe Mossbauer spectroscopy was used to study the occurrence of different valence states in the iron–polygalacturonate complexes prepared under different circumstances. The Mossbauer-spectra indicated the presence of iron both in FeII and FeIII states in the investigated iron–polygalacturonate compounds, the occurrence of which varied with the preparation parameters. A correlation of the relative occurrence of iron valence states with the pH has been found. The relative occurrence of FeIII was found to increase with increasing pH. The knowledge of this correlation can help find optimum preparation conditions of iron–polygalacturonates to cure human anemia.

A relationship between the photocatalytic effect and the local structure of 50Fe2O3⋅ (50−x)SiO2⋅xTiO2 glass abbreviated as 50FSxTi prepared by sol-gel method was investigated by 57Fe-Mossbauer spectroscopy (FeMS), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR) and ultraviolet-visible diffuse reflectance spectroscopy (UV-VIS). Mossbauer spectra of 50FSxTi glass before annealing showed a doublet with the isomer shift (δ) and quadrupole splitting (Δ) of 0.41±0.01 mm s−1 and 0.75±0.02 mm s−1, indicating that Fe3+ formed FeO6 octahedra (O h). A comparable δ of 0.36±0.02 mm s−1 and the larger Δ of 0.92±0.02 mm s−1 values were confirmed for 50FSxTi after annealed at 400 ∘ C for 3 h. These results indicates that the coordination number of iron polyhedra decreases from 6 to 4 due to annealing. UV-VIS diffuse reflectance spectra of 50FS10Ti yielded two optical band gap energies (E g’s) of 2.05 eV and 3.55 eV. This result implied that 50FS10Ti has two optical band gaps in the visible area and UV area. A bleaching test performed by 10 mL of MB aqueous solution and 40 mg of powder 50FS10Ti glass sample showed that MB absorbance decreased from 3.16 to 0.43 after UV-visible light irradiation for 2 h with the first order rate constant (k) of $1.6\times 10^{-2}~ \min ^{-1}$ . These results prove that titanium containing iron silicate glass with the composition of 50Fe2O3⋅40SiO2⋅10TiO2 has the UV and visible light responsive photocatalytic effect.

Constant current electrochemical deposition technique was used to obtain quaternary alloys of Sn-Fe-Co-Ni from a gluconate electrolyte, which to date have not been reported in the literature. For the characterization of electroplated alloys, 57Fe and 119Sn Conversion Electron Mossbauer Spectroscopy (CEMS), XRD and SEM/EDAX were used. XRD revealed the amorphous character of the novel Sn-Fe-Co-Ni electrodeposited alloys. 57Fe Mossbauer spectrum of quaternary deposit with composition of 37.0 at% Sn, 38.8 at% Fe, 16.8 at% Co and 7.4 at% Ni displayed a magnetically split sextet (B = 28.9T) with broad lines typical of iron bearing ferromagnetic amorphous alloys. Magnetically split 119Sn spectra reflecting a transferred hyperfine field (B = 2.3T) were also observed. New quaternary Sn-Fe-Co-Ni alloys were successfully prepared.

A series of novel [Fe(MeiPrGlyoxH)2(amine)2] complexes have been synthesized [(MeiPrGlyoxH2 = methylisopropylglyoxime, amine = 3,5-dimethylpyridine, 4-(dimethylamino)pyridine, 4-(phenylamino)phenol, 2-imidazolidone)] and characterized by 57Fe Mossbauer, FTIR, UV–Vis spectroscopy, mass spectrometry, AFM and thermoanalytical methods. Quantum chemical (DFT) computations of [Fe(MeiPrGlyoxH)2(3,5-dimethyl-Py)2] (Py = pyridine) complex were also performed. The square-planar structure of [Fe(MeiPrGlyoxH)2] moiety is similar to that of [Fe(MeEtGlyoxH)2]. The incorporation of branching alkyl chains (isopropyl) in the complexes alters the Fe–N bond length and results in high-spin iron(II) state.

Liquids trapped in the pores of certain silicate glasses (such as Corning Vycor ‘thirsty’ glass) were found to display frozen solutions like behavior at temperatures much higher than their actual freezing point. For example, recoilless γ-resonance absorption was observed for Mossbauer active solutes such as 119Sn and 57Fe salts at room temperature (i.e., without the need of quenching). Thus capillary Mossbauer spectroscopy (CMS) proved to be a new and useful experimental tool with great potential in solution chemistry. As part of a research project concerned with the hydrolysis of SnII salts, we attempted to perform 119Sn CMS measurements for solutions containing stannous ion in a range of aqueous environments. Somewhat surprisingly, we found that under ambient conditions, SnII aqueous liquid solutions, both the acidic and the basic systems, are essentially CMS-silent. This can be attributed to the strong temperature dependence of Lamb–Mossbauer factor of SnII species, which may result in the complete disappearance of Mossbauer pattern well below room temperature. These observations can also explain why previous publications concerned with the use of CMS dealt exclusively with SnIV and not with SnII containing liquids.

Magnetization and low temperature in-field 57Fe Mossbauer spectroscopy measurements have been performed on a Fe[C(SiMe3)3]2/ferrihydrite hetero-mixture. The results indicate the presence of ferromagnetic coupling of magnetic moments involving Fe[C(SiMe3)3]2 with a hyperfine magnetic field of about 151 T, attributable mainly to the non-frozen atomic orbital contribution. The present findings show the sensitivity of single-ion molecular magnets to local alterations of their lattice-environment and might explain and reconcile some of the differences found in the literature for the observed bulk magnetic properties of the title Fe[C(SiMe3)3]2 compound.

The identity of the predominating tin(II)-hydroxide complex formed in hyper-alkaline aqueous solutions (0.2

Iron(III)-containing aqueous solutions of 5-methylresorcinol (5-MR), 5-n-propylresorcinol (5-n-PR) and 4-n-hexylresorcinol (4-n-HR) at pH ~ 3 were studied by means of 57Fe transmission Mossbauer spectroscopy. Kinetic considerations were applied to the redox reactions. Density Functional Theory (DFT) calculations were performed for the alkylresorcinol (AR) molecules and their non-alkylated analogue (resorcinol). Mossbauer spectra consisted of quadrupole doublets assigned to high-spin Fe(III) and Fe(II) species. From changes in their relative spectral areas, a gradual reduction of Fe(III) by all the ARs studied was observed. However, significant differences were found for the reduction rates among the ARs. The following series of the reduction rates was established by means of Mossbauer spectroscopy: 4-n-HR ≫ 5-MR > 5-n-PR, supplemented by rate constants calculated using a kinetic model. DFT calculations resulted in the following series: 4-n-HR ≫ 5-n-PR > 5-MR ≫ resorcinol (the latter is not oxidised under the conditions applied). The reversed order of the experimentally observed 5-MR and 5-n-PR oxidation rates may be explained in terms of their different kinetic parameters related to their structure.

N-containing fully saturated (L-prolinate) or aromatic (indole-2-carboxylate) heterocyclic anions were immobilised in CaFe-layered double hydroxide with the dehydration-rehydration method from aqueous ethanol or acetone. The structure of the resulting organic-inorganic hybrids was characterised mainly with powder X-ray diffraction and 57Fe Mossbauer spectroscopy, and as supplementary analysis scanning electron microscopy, energy dispersive X-ray spectroscopy with elemental mapping and molecular modelling were also applied. It was found that the solvent mixture used for the synthesis caused enormous difference in the interlayer spacings of the obtained inorganic-organic hybrids.

Preliminary 57 Fe transmission Mossbauer spectroscopic data were ob- tained for the first time for live cells of the plant-growth-promoting rhizobacterium Azospirillum brasilense (wild-type strain Sp245) grown aerobically with 57 Fe III - nitrilotriacetate (NTA) complex as a sole source of iron. The results obtained have shown that live cells actively reduce part of the assimilated iron(III) to iron(II), the latter amounting up to 33 % of total cellular iron after 18 h of growth, and 48 % after additional 3 days of storage of the dense wet cell suspension in nutrient-free saline solution in air at room temperature (measured at 80 K). The cellular iron(II) was found to be represented by two quadrupole doublets of different high-spin forms, while the parameters of the cellular iron(III) were close to those typical for bacterioferritins.

Mossbauer spectroscopy has been used to investigate the nature of the Zinc-Iron alloys present within the Hot Dip Galvanized (HDG) layers of steel with a silicon content of 0.35 %. The investigation also studied the impact of the powder coating pretreatment on the nature of the alloy layers. The acid etching process within the pretreatment process in particular would be expected to have a significant impact on the HDG layer. This study utilized 57Fe Mossbauer spectroscopy to examine identically processed samples prior to and post pre treatment. XRD and 57Fe CEMS measurements were performed on hot galvanized S355J2 + N samples, forming sandwiched structure. Both XRD and CEMS reveal the presence of dominant steel phase in accordance with its estimated occurrence on the surface of the sandwiched samples. Minor Γ-Fe3Zn10, ζ-FeZn15 and solid solution Fe-Zn as well as minor Fe-Si phases could also be identified.

The effects of the Mg(II)/Fe(III) ratio on the structure and Fe microenvironments in MgFe LDH substances were investigated. The LDHs were prepared by the co-precipitation method with Mg(II)/Fe(III) ratios from 2:1 to 6:1. The materials were characterized by 57Fe Mossbauer spectroscopy and powder X-ray diffractometry. The 57Fe Mossbauer spectra exhibited asymmetric doublet corresponding to high-spin Fe(III) microenvironments in all LDH structure. It was found that the quadrupole splitting decreased with increasing Mg(II)/Fe(III)ratio reflecting change in the electric field gradient due to the incorporation of different amounts of iron into the Mg-containing layers.

As-quenched and stress field annealed FINEMET ribbons were irradiated with 246 MeV energy Kr, 470 MeV energy Xe and 720 MeV energy Bi ions and investigated by 57Fe Mossbauer spectroscopy and XRD methods. The change in relative areas of the 2nd and 5th lines in the Mossbauer spectra indicated significant changes in the magnetic anisotropy of both as-quenched and stress annealed FINEMET due to irradiation with swift heavy ions. Differences were observed between the effect of irradiations with various ions having different energy and fluence. The effect of irradiation on the magnetic orientation in FINEMET was explained in terms of radiation induced defects. The swift heavy ion irradiation can be applied to produce FINEMET ribbons with more favorable soft magnetic properties for technological applications.

K2Fe3(OH)2(SO4)3(H2O)2 was prepared by hydrothermal synthesis. The crystal structure is the isomorphous phase of K2Co3(OH)2(SO4)3(H2O)2. Mossbauer spectra of K2Fe3(OH)2(SO4)3(H2O)2 were measured at low temperatures between room temperature and 14 K, and the hyperfine interactions were analyzed. The Neel temperature is 39 K. Two paramagnetic Fe2 + species were observed in the Mossbauer spectrum at room temperature, and Mossbauer spectra measured below 38 K were decomposed into four magnetic subspectra. From the temperature dependence, it is found that the local electron density at each site is largely deviating at low temperatures, which may induce the giant coercivity.

The structures of tin(II)-oxalate, tin(IV)Na–EDTA and tin(IV)Na 8 -inositol hexaphosphate were investigated using XRD analysis. Samples were identified using the Mossbauer study, thermal analysis and FTIR spectrometry. The Mossbauer study determined two different oxidation states of tin atoms, and consequently two different tin surroundings in the end products. The tin oxalate was found to be orthorhombic with space group Pnma, a =9.2066(3) A, b =9.7590(1) A, c =13.1848(5) A, V =1184.62 A 3 and Z =8. SnNa–EDTA was found to be monoclinic with space group P2 1 /c 1 , a =10.7544(3) A, b =10.1455(3) A, c =16.5130(6) A, β =98.59(2)°, V =1781.50(4) A 3 and Z =4. Sn(C 6 H 6 Na 8 O 24 P 6 ) was found to be amorphous.

Fe(III)-doped TiO2 based heterogeneous photocatalysts were prepared by the sol-gel technique (S samples) or flame hydrolysis (F samples). In photocatalytic phenol decomposition, the undoped F-sample performed much better, than the undoped S one. However, for the S samples, photocatalytic activity first increased with the increasing Fe(III) concentration, and then passed through a maximum, while Fe(III)-doping in F samples significantly decreased it, even at the smallest dopant level. Since the same dopant caused opposite photocatalytic effects in the two series, their structure was systematically compared to identify the underlying chemical and/or physical reasons. The photocatalysts were first characterized by AAS, DRS, XRD and TEM methods and it has been shown that the differences in the photocatalytic activity cannot be explained by the minor variations in the bulk structural properties of TiO2. Mossbauer and XP spectroscopic measurements performed on representative samples qualitatively proved that the local structure of Fe(III) is different in the two series. To quantify these effects, Fe-K edge X-ray absorption measurements were performed. From the pre-edge and XANES region it was learnt that Fe(III) was present in a distorted octahedral environment in both series, however, the extent of distortion is much more significant within the S than within the F one. Information obtained from the EXAFS region indicated that the structure of Fe2O3 was much more ordered in the F-series then in the S one and vacancies were more abundant in the S than in the F series. Moreover, the geometry around Fe(III) systematically varied within the S-series, which could explain, why photocatalytic activity passed through a maximum with the increasing Fe(III) concentration in these samples. (C) 2011 Elsevier B.V. All rights reserved. (Less)

57 Fe conversion electron Mossbauer spectroscopy, XRD and AFM measurements were used to study the radiation effect of 246 MeV Kr, 470 MeV Xe and 710 MeV Bi ions on electrochemically deposited iron thin films. It was found that, in the irradiated electrochemically deposited crystalline ferromagnetic α-Fe coatings, partial amorphisation of Fe took place. The relative amount of the ferromagnetic amorphous phase increased with both ion energy and ion mass as well as with the fluence of irradiation.

Mossbauer spectroscopy was used to study iron(III) reduction by alkylresorcinols (ARs; i.e., chemical analogs of microbial autoregulators excreted by cells into the environment and involved in intercellular communication) in aqueous solutions simulating acidic soil conditions. The concomitant oxidation process for an AR (5-methylresorcinol) was monitored using UV spectrophotometry.

Double hydroxides of Ba(II) and Fe(III) were prepared by the co-precipitation method. Co-precipitation was facilitated by applying highly alkaline, carbonate free NaOH solutions with varying base concentrations (2-20 M). The substances, thus obtained, were characterised by thermal methods. XRD spectra of samples treated at various temperatures, Mossbauer and X-ray absorption spectroscopies. It was found that in extremely concentrated base solutions (>= 10 M) layered double hydroxides, most probably with intercalated OH ions, were formed, indeed, while at low base concentration the Fe(III) ions were precipitated as various oxyhydroxides and the Ba(II) ions remained dissolved. (C) 2009 Elsevier B.V. All rights reserved.

Using various methods different tin phosphate samples were prepared. One of them was amorphous, while the others were crystalline with monoclinic structure, having unit cell parameters as follows: a=4.586 A, b=13.618 A, c=5.818 A, β=99.61° [Sn (H2PO4)2] and a=8.612 A, b=4.964 A, c=15.860 A, β=98.87° [Sn(HPO4)2], respectively. The crystal water content and the method of thermal decomposition of the samples were determined. The chemical composition of the end products of preparations was determined by promt-gamma activation analysis and was found to be Sn:P=1:2 for all samples independent of their preparation method. The oxidation state of tin atoms in samples as determined by Mossbauer spectroscopy was mainly +2 in sample no. 2, while in some other samples it was +4.

57Fe Mossbauer spectroscopy was used to study the effect of iron concentration on the oxidation state and microenvironments of iron in Fe–polygalacturonate compounds prepared by a novel method from pectin. The iron concentration of the coordination compounds was determined by inductively coupled plasma optical emission spectrometry analysis. The Mossbauer spectra of the studied compounds could be decomposed into three markedly different quadrupole doublets referring to three microenvironments. Two of these have ferrous and one has ferric oxidation state. In the applied concentration range the relative occurrence of the ferric component was found to increase considerably with iron concentration. At the same time, with increasing iron concentration the relative occurrence characteristic of the three components showed saturation behaviour up to the iron concentration at which for each pair of galacturonic acid units there is on average one iron atom in the system, which iron concentration value is interpreted as to be related to the complete fill up of certain iron complexation sites of the polygalacturonate chains.

The compound Fe[C(SiMe3)3]2 has been prepared and investigated by the means of powder X-ray diffractometry and 57Fe Mossbauer spectroscopy. The compound’s unique geometry, in which iron is linearly coordinated by the two C(SiMe3)3 ligands, results in a unusual electronic structure of iron, which is visualized as an extreme high hyperfine magnetic field of 157.5(8) T as sensed by the 57Fe nucleus at T = 20 K. In order to obtain information on the electronic structure of iron and on the bonds to the ligands, DFT (density functional theory) calculations were carried out on Fe[C(SiMe3)3]2. The high-spin state of iron was found to be energetically favored: an Fe(II) electron configuration of 3d5.83 4s0.72 is predicted, where the 4s electron density is only slightly polarized, and most of the unpaired electrons have 3d character. By assuming a linear crystal field, and associated 3d level scheme as a starting point, it is suggested that the extreme high hyperfine magnetic field, observed along with an apparently negative quadrupole splitting, is perpendicular to the C–Fe(II)–C bond axis, and can be decomposed mainly into contact (B c ≈ 44 T), dipolar (B d ≈ 14 T), and orbital (B L ≈ 99 T) hyperfine magnetic field contributions.

Thermal degradation of the solid monomeric Na[FeEDTA(H2O)]·2H2O (EDTA = ethylenediaminetetraacetate anion) complex was studied in air by simultaneous thermogravimetry and differential thermal analysis (TG/DTA) coupled on-line with a quadrupole mass spectrometer for evolved gas analysis (EGA-MS). The solid products were analysed by Mossbauer spectroscopy. A four-step decomposition was observed until 500 °C by TG/DTA–EGA-MS, involving first the release of two molecules of crystal lattice water then one coordinated water molecule and above 200 °C, the release of CO2 as a result of degradation of a carboxylate arm of the EDTA ligand. While releasing CO2, reduction of the ferric iron to ferrous iron was observed by Mossbauer spectroscopy. Two ferrous species have been found to form simultaneously which are assumed to be configurational isomers since their aerial oxidation resulted in the formation of the same μ-oxo dimeric iron(III) species. Reaction pathway for this oxidation is proposed. Finally, the organic residues are burnt out rapidly accompanied by a very sharp exothermic heat effect between 280 and 330 °C; meanwhile magnetite is formed.

Distinct chemical species of iron were investigated by Mössbauer spectroscopy during iron uptake into cucumber roots grown in unbuffered nutrient solution with or without 57Fe-citrate. Mössbauer spectra of iron deficient roots supplied with 10-500 microM 57Fe-citrate for 30-180 min and 24 h and iron-sufficient ones, were recorded. The roots were analysed for Fe concentration and Fe reductase activity. The Mössbauer parameters in the case of iron-sufficient roots revealed high-spin iron(III) components suggesting the presence of FeIII-carboxylate complexes, hydrous ferric oxides and sulfate-hydroxide containing species. No FeII was detected in these roots. However, iron-deficient roots supplied with 0.5 mM 57FeIII-citrate for 30 min contained significant amount of FeII in a hexaaqua complex form. This is a direct evidence for the Strategy I iron uptake mechanism. Correlation was found between the decrease in Fe reductase activity and the ratio of FeII-FeIII components as the time of iron supply was increased. The data may refer to a higher iron reduction rate as compared to its uptake/reoxidation in the cytoplasm in accordance with the increased reduction rate in iron deficient Strategy I plants.

Local structure and thermal durability of semiconducting xBaO·(90 − x)V2O5 · 10Fe2O3 glasses (x = 20, 30 and 40), NTA glass TM, before and after isothermal annealing were investigated by 57Fe-Mossbauer spectroscopy and differential thermal analysis (DTA). An identical isomer shift (\(\mathit{\delta}\)) of 0.39 ± 0.01 mm s − 1 and a systematic increase in the quadrupole splitting (Δ) were observed from 0.70 ± 0.02 to 0.80 ± 0.02 mm s − 1 with an increasing BaO content, showing an increase in the local distortion of FeIIIO4 tetrahedra. From the slope of the straight line in the T g–Δ plot of NTA glass TM, it proved that FeIII plays a role of network former. Large Debye temperature (Θ D) values of 1000 and 486 K were respectively obtained for 20BaO · 70V2O5 · 10Fe2O3 glass before and after isothermal annealing at 400°C for 60 min, respectively. This result also suggests that FeIII atoms constitute the glass network composed of tetrahedral FeO4, tetrahedral VO4 and pyramidal VO5 units. The electric conductivity of 20BaO · 70V2O5 · 10Fe2O3 glass increased from 1.6 × 10 − 5 to 5.8 × 10 − 2 S cm − 1 after isothermal annealing at 450°C for 2,000 min. These results suggest that the drastic increase in the electric conductivity caused by heat treatment is closely related to the structural relaxation of the glass network structure.

Fe[C(SiMe3)3]2 compound, in which iron is coordinated by two carbons, was prepared using the reaction of FeCl2 with (Me3Si)3CLi, and investigated by XRD, 57Fe Mossbauer spectroscopy and DFT calculations. 157.5 T hyperfine magnetic field was found at the site of the iron nucleus of this compound at 20 K. DFT calculations predict the quintet states to be clearly favored energetically over the lower spin states. The population analysis reveals considerable 4s as well as large unpaired 3d electron contributions, which can be responsible for the extremely high hyperfine field.

Mossbauer study of La1 − x Sr x 57Fe0.025Co0.975O3 (0.15 ≤ x ≤ 0.25) perovskites below their magnetic ordering temperature shows cooperative electronic and magnetic phase separation for all compositions investigated. It is shown that the increase of the Sr concentration results in a transition from superparamagnetism to long range ferromagnetism of Co clusters between x = 0.18 and 0.2. In-field Mossbauer measurements revealed the existence of frustrated magnetic interactions at x = 0.22.