Fe microenvironments in heat treated rare-earth exchanged montmorillonites

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Elektrokémiailag-, párologtatással, ionkeveréssel és gyorshűtéssel előállított, mikrokristályos, amorf és kristályos ötvözetbevonatok és másként előállított rokonanyagok összehasonlító vizsgálata Mössbauer-spektroszkópiával és egyéb módszerekkel = Comparative investigations of electrochemically prepared, evaporated, ion beam mixed, rapidly quenched and ball milled microcrystalline, amorphous and crystalline alloys and related compounds by Mössbauer spectroscopy and other methods

Sikerült elsőként eddig nem ismert Co-Sn-Fe ternér valamint új Sn-Fe binér ötvözeteket előállítani nagy áramsűrűséget, speciális adalékanyagot és nagysebességű elektrolit-áramoltatást alkalmazó elektrokémiai leválasztás útján, amely bevonatok a Li elektródú telepekben nagyhatásfokú elektródként valamint környezetbarát korrózióálló anyagokként lehetnek alkalmazhatók. Az ötvözeteknek a 57Fe valamint 119Sn Mössbauer-spektroszkópiai vizsgálata az előállítási paraméterek függvényében többek között azt mutatta, hogy az ötvözetek túlnyomó részben új, eddig nem ismert fázisokból állnak. Ezek termikus úton nem állíthatók elő és nem szerepelnek az egyensúlyi fázisdiagramban sem. A Sn-Co-Fe ternér és az Sn-Fe binér ötvözetek amorf szerkezetűek és ferromágnesesek. Sikerült olyan új elektrokémiai előállítási paramétereket találnunk metastabilis fázisokat tartalmazó, korrózióálló, szupravezető kompozit huzalokban alkalmazható Fe-Cr-Ni ötvözetbevonatok előállítására, amelyeknél ezen fémrétegek rövid távú kémiai rendezettsége, elem- és fázisösszetétele, morfológiája és mágneses paraméterei célszerűen és finoman beállíthatók az elektrokémiai paraméterek alkalmas megválasztásával. Az amorf vas képződését mutattuk ki elektrokémiailag leválasztott α-Fe bevonatokon nagyenergiájú nehézion besugárzás hatására első ízben. Azt is sikerült kimutatnunk a 57Fe Mössbauer-spektroszkópia segítségével, hogy nemcsak a nagyenergiájú (250 MeV) hanem a kisenergiájú (40 keV) nehézion besugárzás is részleges amorf Fe kialakuláshoz vezet párologtatott α-Fe vékonyrétegekben. | We have succeeded to prepare previously not known Co-Sn-Fe ternary and new Sn-Fe binary alloys by electrochemical depositions using high current density, special complexant and high speed of electrolyte circulation. These coatings can be applied as high performance electrodes in Li-batteries and environmentally acceptable corrosion resistant materials. 57Fe and 119Sn Mössbauer investigations of these alloys showed among others that the alloys consist dominantly of new, previously not known metastable phases which never occur in thermally prepared alloys and can not be expected from the equilibrium phase diagram. These Co-Sn-Fe and Sn-Fe alloys proved to be amorphous and ferromagnetic. We have succeeded to find electrochemical parameters for the preparation of corrosion resistant Fe-Ni-Cr and Ni-Cr alloy coatings containing metastable phases, which alloys can be applied as substrates in superconducting composite wires. The chemical short range order, elemental and phase composition, morphology and magnetic properties of the metal layers can be appropriately and finely adjusted by the help of suitably chosen electrochemical parameters. We have shown the formation of amorphous Fe in electrochemically deposited a-Fe coatings due to the irradiation with energetic heavy ions. By the help of Mössbauer spectroscopy we have also shown the partial formation of amorphous iron in evaporated a-Fe thin films not only due to the energetic (246 MeV) but also due to the low energy (40 keV) heavy ion irradiation

Photo-Fenton degradation of methylene blue using hematite-enriched slag under visible light

This study aims to find a suitable method to transform the amorphous iron oxides obtained from the incineration of combustible waste slag into hematite. The resulting samples were utilized as heterogeneous photocatalysts for the photo-Fenton degradation of methylene blue (MB) aqueous solution. A good correlation was found between the MB degradation and the amount of hematite phase as confirmed by XRD and Mössbauer measurements. The largest rate constant (k) was (4.1 ± 0.08) × 10−2 min−1 for MB decomposition under visible-light for the sample N5-50-800. The results are promising for both low-cost photocatalysts and recycling of combustible waste slags

Iron oxide nanoparticles for plant nutrition? A preliminary Mössbauer study

One of the most important micronutrients for plants is iron. We have prepared iron(III) oxyhydroxide and magnetite nanoparticles with the aim to use them as possible nutrition source for plants. The iron(III)-oxide/oxyhydroxide nanoparticles prepared under our experimental conditions as colloidal suspensions proved to be 6-line ferrihydritenanoparticles as verified by XRD,TEM/SAED and Mössbauer spectroscopy measurements. 57Fe Mössbauer spectra of magnetite nanoparticles prepared under different preparation conditions could be analyzed on the basis of a common model based on the superposition of four sextet components displaying Gaussian-shaped hyperfine magnetic field distributions

Iron uptake from manufactured nanomaterials: obscured mechanism, controversial effect

Transition metals in nanomaterials such as iron, manganese or zinc are essential microelements for plants. When these metals are present in suboptimal concentration for the plants, deficiency syndromes develop that causes reduced crop production or poor fruit quality. Low mineral content of plant products has a major role in human malnutrition. Most stable Fe-chelates for the correction of Fe deficiency are not biodegradable and expensive so applying manufactured nanomaterials may serve as a cheap and eco-friendly alternative. Newly designed, transition metal containing nanomaterials stabilized in colloid suspension have been characterised and then applied in hydroponic cultures to cucumber model plants in a wide range of concentration. The uptake and distribution of the elements from the nanomaterials and their utilization were investigated by microXRF mapping, ICP-MS, enzyme activity tests, gene expression measurements and the changes in some basic physiological parameters were followed. Nanoferrihydrite and nano-Mn-Zn-ferrite colloid suspensions with 3-8 nm particle size applied in 0.01-0.02 mM concentration and at slightly acidic pH proved to be a good source of Fe, Mn and Zn in various experimental conditions. Mn-Zn-ferrite has also been tested at pH 7.5 and Fe deficient cucumber plants showed a significant recovery after 3 days of application in terms of chlorophyll concentration and photosynthetic efficiency but not at pH 8.5. Mn and Zn deficient plants also showed recovery upon addition of the ferrite. Ferric chelate reductase assays showed that it is not the normal reduction-based uptake pathway that plays a role in the iron utilization of these nanoparticles. Analysis of root ferric chelate reductase expression pointed out a quick utilisation of Fe content of the nanoferrihydrite particles. Elevated concentrations of the nanoferrite at the millimolar range as compared to equal concentrations of micronutrient salts proved to be significantly less toxic. However, another nanomaterial, an insoluble nano FeCo powder applied to the nutrient solution of cucumber in high concentration causes severe chlorosis due to cobalt toxicity, pointing on that the composition of the nanoparticles is highly important for their bioactivity. Keywords: nanomaterial, ferrite, ferrihydrite, fertilizer, ferric chelate reductase, toxicity This work was supported by the National Research, Development and Innovation Office, Hungary (NKFIH) K115784, 115913, 124159 and VEKOP-2.3.3-15-2016-00008. Á. Solti was also supported by the Bolyai János Research Scholarship of the Hungarian Academy of Sciences (BO/00207/15/4)

The relationship between local structure and photo-Fenton catalytic ability of glasses and glass-ceramics prepared from Japanese slag

Local structure and the photo-Fenton reactivity of iron-containing glasses and glass-ceramics prepared from Japanese domestic waste slag were investigated. The largest rate constant (k) of (2.8 ± 0.08) × 10−2 min−1 was recorded for the methylene blue degradation test by using H2O2 with a heat-treated ‘model slag’. The 57Fe Mössbauer spectrum was composed of a paramagnetic doublet with isomer shift of 0.18 ± 0.01 mm s−1 attributed to distorted FeIIIO4 tetrahedra. These results indicate that the paramagnetic Fe3+ provided strong photo-Fenton catalytic ability, and that waste slag can thus be recycled as an effective visible-light activated photocatalyst

The structure of Fe(III) ions in strongly alkaline aqueous solutions from EXAFS and Mossbauer spectroscopy

To establish the structure of ferric ions in strongly alkaline (pH > 13) environments, aqueous NaOH solutions supersaturated with respect to Fe(III) and the solid ferric-hydroxo complex salts precipitating from them have been characterized with a variety of experimental techniques. From UV measurements, in solutions of pH > 13, only one kind of Fe(III)-hydroxo complex species was found to be present. The micro crystals obtained from such solutions were proven to be a new, so far unidentified solid phase. Mossbauer spectra of the quick-frozen solution and that of the complex salt indicated a highly symmetrical ferric environment in both systems From the EXAFS and XANES spectra, the environment of the ferric ion in these solutions (both native and quick-frozen) and in the complex salt was found to be different. In the complex salt, the bond lengths are consistent with an octahedral coordination around the ferric centres. In solution, the coordination geometry of Fe(III) is most probably tetrahedral. Our results demonstrate that in strongly alkaline aqueous solutions, ferric ions behave very similarly to other structurally related tervalent ions, like Al(III) or Ga(III)

Hydrothermal activity at Eolo Seamount (Tyrrhenian Sea): Evidence form minerological, geochemical and isotopic studies

International audienc

Hydrothermal nontronite formation at Eolo Seamount (Aeolian volcanic arc, Tyrrhenian Sea).

International audienceA sediment core containing a yellowish-green clay bed was recovered from an area of extensive hydrothermal deposition at the SE slope of the Eolo Seamount, Tyrrhenian Sea. The clay bed is composed of pure nontronite (described for the first time in the Tyrrhenian Sea), which appears to be the most aluminous nontronite ever found among the seafloor hydrothermal deposits. The high Al content suggests precipitation from Al-containing hydrothermal solutions. The REE distribution of the Eolo nontronite has a V-shape pattern. The heavy REE enrichment is in part due to their preferential partitioning in the nontronite structure. This enrichment was possibly further enhanced by the HREE preferential sorption on bacterial cell walls. The light REE enrichment is the result of scavenging uptake by one of the nontronite precursors, i.e., poorly-ordered Fe-oxyhydroxides, from the hydrothermal fluids. Oxygen isotopic composition of the nontronite yields a formation temperature of 30 °C, consistent with a low-temperature hydrothermal origin. The relatively radiogenicNd isotopic signature of the nontronite compared to the present-dayMediterranean seawater indicates that approximately half of Nd, and presumably the rest of the LREE, are derived from local volcanic sources. On the other hand, 87Sr/86Sr is dominated by present-day seawater Sr. Scanning electron microscopy investigation revealed that the nontronite is composed of aggregates of lepispheres and tube-like filaments, which are indicative of bacteria assisted precipitation. Bacteria inhabiting this hydrothermal site likely acted as reactive geochemical surfaces on which poorly-ordered hydrothermal Fe-oxyhydroxides and silica precipitated. Upon aging, the interactions of these primary hydrothermal precipitates coating bacterial filaments and cell walls likely led to the formation of nontronite. Finally, the well-balanced interlayer and layer charges of the crystal lattice of seafloor hydrothermal nontronite decrease its sorption capacity to zero