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Our previous studies have revealed that a ”hybrid” structure of the amorphous and crystalline phases is formed in the outermost surface region of the austenitic stainless steel tubes of steam generators (SGs) as an undesired consequence of the industrial application of the AP-CITROX (AP: alkaline permanganate; CITROX: citric and oxalic acid) decontamination technology. The formation of this mobile oxide-layer increased the amount of the corrosion products in the primary circuit significantly, resulting in magnetite deposition on fuel assemblies. Owing to the fact that there is no investigation method available for the in-situ monitoring of the inner surfaces of heat exchanger tubes, a research project based on sampling as well as on ex-situ electrochemical and surface analytical measurements was elaborated. Within the frame of this project, comprehensive investigation of the general corrosion state and metallographic features of 36 stainless steel specimens, cut out from various locations of the 21 steam generators of the Paks NPP in the time period of 2000-2007 has been performed. The present work gives a brief overview on the general corrosion state of the heat exchanger tubes of SGs, concerning the long-term effects of the AP-CITROX procedure on the chemical composition and structure of the protective oxide-layer.

The development of an efficient and stable photo(electrochemical) catalyst is a very challenging task because its catalytic activity depends directly on the electronic structure and the charge carrier transfer through the catalyst/electrolyte interface. Therefore, the main objective of this study was to optimise the semiconducting properties of the electrospun α- Fe2O3 fibres by Ru3+ and Pt4+ doping, to determine the effect of these cations on magnetic and optical properties, as well as on the photocatalytic and photoelectrochemical activity of α-Fe2O3 fibres. Increased temperature of the Morin transition, enhanced remanent magnetization, lower coercivity and narrower optical band gap in hematite fibres by Pt4+ and Ru3+ doping was observed. Electrochemical measurements revealed n- type conductivity of all fibres, while increased donor density and anodic shift of the flatband potential were registered for the doped fibres. The photoactivity of fibres, which was tested for the degradation of rhodamine B, depended on the dopant used.

Nanoscroll formation by casacade intercalation–exfoliation method was investigated for a high iron-content kaolin and after the removal of its iron-bearing mineral constituents (goethite, hematite) by 11 M HCl treatment. Hindered kaolinite nanoscroll formation was observed by TEM in both cases, where the 11 M HCl treatment only slightly improved the occurrence of nanoscrolled shapes. The presence of minor amounts of well-dispersed, resilient Fe was observed after the exfoliation of 11 M HCl-treated sample, which was identified as structural Fe3+/Fe2+ in the octahedral sheet of kaolinite by Mössbauer and X-ray absorption spectroscopy. Iron substitution in the nanokaolinite TO layers was probed by computational chemistry. The computational results indicate inner coordination changes and elongation of bonds in the iron-substituted TO structure, and the increased curvature values offer an explanation for the observed experimental results for hindered nanoscroll formation. Graphical abstract

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.

Pure and doped iron oxide and hydroxide nanoparticles are highly potential materials for biological, environment, energy and other technological applications. On demand of the applications, single phase as well as multiple phase of different polymorphs or composites of iron oxides with compatible materials for example, zeolite, SiO

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.

A simple one-pot synthesis was utilized to prepare Mn-doped maghemite nanoparticles. A homogenized mixture of Mn- and Fe-acetylacetonates was heated in air atmosphere at 300 °C to produce Mn-doped maghemite. XRD showed only the presence of a spinel crystal structure with a linear increase of the unit-cell volume up to 20 mol% of the Mn dopant. Possible structural changes with increased Mn doping are briefly discussed.57Fe Mossbauer spectra recorded at 77 K were fitted with two sextets of lines corresponding to Fe3+ ions at A-tetrahedral and B-octahedral sites in maghemite. FE SEM images showed that Mn-doped maghemite nanoparticles were of good uniformity, with the crystallite size varying from 24 to 35 nm, as determined by XRD.

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

The glass samples with the composition of 40Fe2O3-xAl2O3-(60−x)SiO2 were prepared by sol-gel method. The samples were characterized by XRD, 80 K 57Fe Mossbauer spectroscopy, TEM, FTIR and impedance spectroscopy. In the glass samples with less than 10% alumina, fayalite and hematite were crystallized by addition of hercynite. Whereas nanoparticles of hematite (α-Fe2O3) and maghemite (γ-Fe2O3) doped with Al were confirmed with the increase of alumina contents (15% and 20%). The glass samples exhibit the electronic conduction which is explained by the polaronic conduction mechanism. It is noticed that the catalysts containing a mixture of hematite and maghemite nanoparticles showed higher photocatalytic degradation of Rhodamine B dye than those containing hematite alone. It is suggested from the characterizations of newly developed iron-containing aluminosilicate glass samples that the materials with several bandgaps and without dissolving itself should be developed in the future for water purification under visible light irradiation.

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

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).

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.

Nanoparticles of e-Fe2O3 in an amorphous silica matrix were prepared by the sol–gel method without using a precursor. X-ray diffraction patterns reflect a completely amorphous state for the samples even after heat-treated up to 600 °C, while at higher temperatures the formation of crystalline iron oxide phases was observed. Transmission electron microscopy analysis showed a wide size distribution of nanoparticles from 3±0.5 to 46±0.8 nm. The occurrence of e-Fe2O3 particles depends on several factors like annealing temperature, particle size and iron concentration in initial chemicals. Based on the 57Fe Mossbauer spectra, three octahedral and one tetrahedral iron site were identified for e-phase. The optimized conditions for the preparation of e-Fe2O3 rich sample were confirmed and ~ 90% of the e-Fe2O3 phase was obtained with the particle size of 15±0.6 nm. The high coercivity of ~ 1.18 T at room temperature was confirmed for our nanoparticle system.

The research investigated three iron carbonate (siderite) sedimentary concretions from Nagykovacsi, Uri and Delegyhaza, Hungary. To identify possible source rocks and effects of the glaze-like exposed surface of the concretions, we carried on comparative petrological, mineralogical, geochemical and isotopic studies. The samples were microbially mediated siderite concretions with embedded metamorphous and igneous mineral clasts, and had specific rim belts characterized by semi-concentric outer Fe-oxide layers, fluffy pyrite-rich outer belts and siderite inner parts. We investigated the cross section of the Fe-carbonate concretions by independent methodologies in order to identify their rim effects. Their surficial oxide layers showed evidence of degassing of the exposed surface caused most probably by elevated temperatures. The inner rim pyrite belt in the concretions excluded the possibility of a prolonged wet surface environment. Microtextural and mineralogical features did not support desert varnish formation. 10Be nuclide values of the Nagykovacsi and Uri concretions were far above the level of terrestrial in-situ cosmogenic nuclides, but they were consistent with the lowest levels for meteorites. Though the data were not conclusive to confirm any kind of known origin, they are contradictary, and open possibilities for a scenario of terrestrial meteorite origin.

The interaction between Lanthanides (Ln) - ions and Ca-bentonite and the structural changes accompanying were studied. Ln -exchanged bentonites were prepared from Ca-bentonite (Istenmezeje, Hungary) by ion exchange in three consecutive washings with lanthanide solutions. Scanning Eletronmicroscopy Energy Dispersive X-ray spectroscopy (SEM-EDX) studies showed even distribution of Ln s and other components of bentonite. The natural bentonite and the lanthnide exchanged bentonites were characterized by X-ray diffraction (XRD), which revealed the same mineral composition, and the increase of the basal spacing of montmorillonite from 1.465 (Ca 2+ ) to 1.577 nm (REE 3+ ). The d 001 basal spacing of lanthanide montmorillonite increases as the ion radius of the lanthanide cation increases. The Fe 3+ , and Ln s 3+ amount on the bentonite were determined by X-ray-fluorescence spectrometry (XRF) elemental analysis. The amount of exchanged Ln s were determined by washing the Ln -bentonite with 1 M ammonium-acetate, and measuring the amount of Ln released, using inductively coupled plasma optical emission spectrometry (ICP-OES). In most Ln -bentonites, the quantity of the exchanged Ln ions was about 80–90% of the cation exchange capacity (CEC) of the bentonite. In case of some lanthanides bentonite (La 3+ , Ce 3+ , and Gd 3+ ), however, the sorbed quantity of lanthanum ions was higher than the cation exchange capacity. In case of lanthanum-bentonite, the lanthanide quantity is as high as 136% of CEC. Moreover, the iron(III) content of lanthanum bentonite is less than that of the original Ca-bentonite. Mossbauer spectra of the La-, Ce-, and Gd-exchanged samples at 78 K revealed an unexpected magnetically split component that was absent from the Ca-bentonite. This component may belong to interlayer Fe. This iron can be released from the octahedral positions crystal lattice.

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.

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.

Radioactive liquid wastes containing large amounts of nitric acid (approx. 4–7 M) generated in the nuclear fuel cycle are very undesirable by-products. Denitration of highly acidic radioactive liquid wastes with organic reducing agents has sev - eral advantages, such as a significant pH increase, possibility of separation of radioisotopes which can be utilized in other technologies, reduction of volatility of radioisotopes and fixation of certain mono- and divalent radioisotopes with zeolite. In the present work some aspects of denitration of simulated radioactive liquid wastes at laboratory level were investigated. Denitration of HNO 3 with formic acid was investigated for different [HCOOH]/[HNO 3 ] ratios. The changes in the induction time, pH increase and volume reduction were determined. It was shown that by the denitration of simulated radioactive liquid waste high pH values could be achieved which in real systems would create more possibilities in radioactive waste manage- ment. Analysis of solid phases formed after the oxidation of excess HCOOH with H 2 O 2 showed the presence of amorphous fraction as well as goethite and hematite phases, which could remove different radioactive cations from the liquid phase. The immobilization of simulated solid radioactive waste with borosilicate glass matrix was also shown.

Magnetic interaction of the magnetite (Fe3O4) nanoparticles grown on zeolite has been studied. XRD patterns show that in the presence of 25–75 mg of zeolite the average particle size of Fe3O4 decreases to ≈6 nm, but with the increase of zeolite content (75 mg

57 Fe conversion electron Mossbauer spectroscopy was used to study the effect of swift heavy ion irradiation on electrochemically deposited metallic pure α-iron. We succeeded in preparing superparamagnetic iron by irradiating the electrochemically prepared thin α-iron films using 247 MeV Kr ions with a fluence of 1×10 13 ion cm −2 which converted 50% of crystalline α-iron into amorphous and superparamagnetic phases, the latter being >20%. The results are discussed in terms of the thermal spike model for the formation of the amorphous phase which could be essential for the formation of superparamagnetic iron.

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.

Glass samples with composition xFe2O3・yAl2O3・(100-x-y)SiO2 abbreviated as xFyAS for photo-Fenton catalyst were prepared by a sol-gel method and heat-treated at 1000 °C for 100 min. It was found that when alumina was added to the Fe2O3 + SiO2 glass matrix, the photo-Fenton activity tested with methylene blue degradation increased, so did the photoactivity with visible light. From Mossbauer and XRD results, it was noticed that hercynite phase appeared that showed higher photoactivity even for the samples having lower hematite content and that the Fe+3 (Td) content increased with Al2O3 content. In these samples, the more Fe+3 (Td) found, the more effective was the photo-Fenton degradation.

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.

A relationship between structure and visible light-activated photocatalytic activity of iron-containing soda lime aluminosilicate (15Na2O⋅15CaO⋅40Fe2O3⋅xAl2O3⋅(30−x)SiO2) glass (xNCFAS) was investigated by means of 57Fe-Mossbauer spectroscopy, X-ray diffractometry (XRD) and UV–visible light absorption spectroscopy (UV–VIS). The 57Fe-Mossbauer spectrum of 11NCFAS glass measured after heat-treatment at 1000 °C for 100 min was composed of a paramagnetic doublet due to FeIII(Td) and two magnetic sextets due to regular hematite (α-Fe2O3) and hematite with larger internal magnetic field. X-ray diffraction patterns of heat-treated xNCFAS samples resulted in decrease of α-Fe2O3 and increase of Ca2Fe22O33 or CaFe2O4 with alumina content. A quick decrease in methylene blue (MB) concentration from 15.6 to 4.7 μmol L−1 was observed in the photocatalytic reaction test with 40 mg of heat-treated 11NCFAS glass under visible light-exposure. The largest first-order rate constant of MB decomposition (k) was estimated to be 9.26 × 10−3 min−1. Tauc’s plot yielded a band gap energy (Eg) of 1.88 eV for heat-treated 11NCFAS glass, which is smaller than previously reported Eg of 2.2 eV for α-Fe2O3. These results prove that addition of Al2O3 into iron-containing soda lime silicate glass is favorable for the preparation of improved visible light-photocatalyst with ‘ubiquitous’ elements.

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.

A new method is developed to synthesize magnetic carbon microspheres decorated with carbon nanofibers and iron nanoparticles (nanofurry microspheres) for separation techniques in chemistry and biology. Microspheres are synthesized by carbonizing polystyrene–divinylbenzene-based, iron-loaded ion exchange resins. The phase composition, magnetic properties, and surface area and morphology of these materials are characterized by various techniques. It is detected that superparamagnetic (SPM) magnetite is present in microspheres exclusively upon carbonization at 400–500 °C, elemental iron, both α- and γ-Fe, is the major component at 600 °C, and cementite dominates between 700 and 1000 °C. Nanofiber formation is observed to be pronounced at high temperatures. The synthesized carbon microspheres have high surface area (100–300 m2 g−1) and can be separated easily by a magnet or by filtration. Saturation magnetization of selected samples is obtained between 5 and 28 emu g−1, depending on the phase composition. The novel microcomposites are expected to be effective adsorbents or support materials in various chemical processes, for example in water and air cleaning, catalysis, and biotechnological separations. Preliminary experimental studies for Cr(VI) removal from water and for platinum deposition are provided.

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.

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.