Fe microenvironments in heat treated rare-earth exchanged montmorillonites

L

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

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

Etude par spectrométrie Mössbauer des chélates de fer à l etat solide et en solutions aqueuses

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

The kinetics of the complex formation between iron(III)–ethylenediaminetetraacetate and hydrogen peroxide in aqueous solution

The kinetics of the formation of the purple complex, [Fe III(EDTA)O 2] 3−, between Fe III–EDTA and hydrogen peroxide was studied as a function of pH and temperature in aqueous solutions using a stopped-flow method. The observed second-order rate constants, k obs decrease with an increase in pH. The significantly more labile aqua complex ([Fe(EDTA)H 2O] −) could account for the decrease in k obs with increasing pH. The kinetics of the formation of the purple complex [Fe III(EDTA)O 2] 3−, between Fe III–EDTA and hydrogen peroxide was studied as a function of pH (8.22–11.44) and temperature (10–40 °C) in aqueous solutions using a stopped-flow method. The reaction was first-order with respect to both reactants. The observed second-order rate constants decrease with an increase in pH and appear to be related to deprotonation of Fe III–EDTA ([Fe(EDTA)H 2O] − ⇔ Fe(EDTA)OH] 2− + H +). The rate law for the formation of the complex was found to be d[Fe IIIEDTAO 2] 3−/d t=[( k 4[H +]/([H +] + K 1)][Fe III–EDTA][H 2O 2], where k 4=8.15±0.05×10 4 M −1 s −1 and p K 1=7.3. The steps involved in the formation of [Fe(EDTA)O 2] 3− are briefly discussed

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)

Development of Electrically Conductive ZrO2-CaO-Fe2O3-V2O5 Glass and Glass-Ceramics as a New Cathode Active Material for Na-ion Batteries with High Performance

Glass-ceramics xZrO2•10Fe2O3•(90-x)V2O5 with ‘x’ between 0 and 30 mol% and yZrO2･(20-y)CaO･10Fe2O3･70 V2O5 glass with ‘y’ between 0 and 20 mol%, respectively abbreviated as xZFV and yZCFV, before and after heat treatment at 500 °C for 100 min, were evaluated as potential cathode-active materials for sodium-ion batteries (SIBs). Relationships between physical properties and local structure of xZFV and yZCFV glass-ceramics were investigated by 57Fe-Mössbauer spectroscopy, V K-edge X-ray absorption near edge structure (XANES), X-ray diffractometry (XRD), DC four-probe method and differential thermal analysis (DTA). SIBs containing heat-treated xZFV glass-ceramics showed the highest discharge capacity of 153 mA h g−1 under a current density of 50 mA•g−1, which exhibited a high electrical conductivity of 1.8 × 10−2 Scm−1. Precipitation of V0.05Zr0.95O2 and Fe2V4O13 nanoparticles were confirmed from the XRD pattern of the heat-treated 20ZFV glass, consistent with the lower energy of the pre-edge peak at 5467 eV in the V K-edge XANES spectrum. This result is associated with the reduction of vanadium ions from VV to VIV. It is concluded that the precipitation of stable vanadium bronze phases with high electrical conductivity and structural stability effectively enable the high SIB capacity of these materials