Mössbauer and esr studies on structural evolution of some iron (III) doped rare earth oxides

Fe (III) ions were coprecipitated as 3 wt % and 5 wt % with La (OH)₃, Pr (OH)₃ and Nd (OH)₃. These coprecipitates were heated for 4 hours to 24 hours in air at temperatures ranging from 100°C to 1100°C. Samples with 5 wt % of Fe (III) ions were investigated by Mössbauer resonance at 300 and 77 K and those with 3 wt % of Fe (III) ions were studied by ESR spectroscopy. Characterization of the valency, coordination and chemical identity of the iron ions in the initial and thermally treated coprecipitates permit to follow the nature of thermal and microstructural processes which lead to the formation of iron-doped rare earth oxides.     

Low spin Fe(IV) arising from electron transfer in a mixed-valence compound: A Mössbauer study

Co(en)₃Fe(CN)₆ a mixed-valence compound, where ‘en’ corresponds to ethylene diamine, exhibits a heteronuclear charge transfer between iron and cobalt ions; both the ions being in oxidation state III. An ⁵⁷Fe Mössbauer investigation confirms the creation of the rare species Fe(IV) as a result of charge transfer.     

Phenomena associated with diffusion of trivalent iron in amethyst quartz

In natural amethyst crystals from different locations changes in the EPR, optical and infrared spectra were measured as a function of annealing temperature. After heating to 650°C for two hours the concentration of Fe(III) on substitutional sites with alkali ions as charge compensators is equal in all crystals irrespective of its initial concentration. Establishment of a heterogeneous equilibrium due to formation of iron oxide particles (presumably Fe₂O₃) previously characterized by their EPR and optical spectra is thus confirmed. Initially unequal distributions of Fe(III) among the three equivalent sites of the quartz structure also become equal under this treatment. From comparison with literature data for MnCl₂ precipitates in NaCl the average particle size can be estimated to be about 100 nm allowing an estimate of the diffusion coefficient of Fe(III) at 650°C. In one amethyst with a high concentration of hydrogen a large amount of the substitutional Fe(III) is charge compensated by hydrogen. Thermal destruction of these centers does not correlate with the intensities of infrared absorption bands in the OH stretching vibration region.     

EPR investigation of the spin-spin interactions in a Cu(II)-Gd(III)-Fe(III) heterospin system

The spin-spin interactions in a system that contains three different spin carriers, [{LCu}Gd(H₂O)₃×{Fe(CN)₆}] _n ·4nH₂O (1) [L²⁻, N,N-propylenedi(3-methoxysalicylideneiminato)], were investigated by electron paramagnetic resonance spectroscopy. Additional information was obtained by analyzing the discrete heterobinuclear system [LCu(OH₂)Gd(O₂NO)₃] (2), which contains the Cu(II)-Gd(III) pair also existing in the structure of 1, and the compounds [{LCu}Gd(H₂O)₃{Co(CN)₆}] _n ·3.5nH₂O and [{LCu}La(H₂O)₃×{Fe(CN)₆}] _n ·4nH₂O, which are isostructural with 1 and in which the paramagnetic low-spin Fe(III) and Gd(III) ions were replaced by diamagnetic low-spin Co(III) and La(III), respectively. The investigations were carried out in the temperature range of 293–4 K in both X- and Q-bands and also using a dual-mode X-band. The experimental spectra of the Cu(II)-Gd(III) pairs in 2 were interpreted as the sum of spectra of the ground spin state with total S = 4 and the excited state with S = 3 appearing due to the ferromagnetic exchange interaction between Cu(II) and Gd(III) ions. By fitting the experimental and simulated spectra, the zero-field splitting parameters of the Gd(III) ion are estimated and it is shown that no influence of the anisotropic interaction is detected. The magnetic properties of 1 are discussed from the perspective of the interaction of the Cu(II)-Gd(III) binuclear fragments with the Fe(III) ions.     

Studies of Nanosized Iron-Doped TiO<Subscript>2</Subscript> Photocatalysts by Spectroscopic Methods

Iron-doped TiO₂ nanoparticles with iron content in the range of 0.005 < Fe/Ti < 0.3 were prepared using the flame spray pyrolysis method and investigated with CW X-band electron paramagnetic resonance (EPR), X-ray diffraction, and Fourier transform infrared spectroscopy. This allowed for the clarification of the internal organization of Fe–TiO₂ nanoparticles. Different types of Fe(III) centers were distinguished in the samples: isolated high-spin paramagnetic Fe(III) ions (S = 5/2) in rhombic ligand fields state at 0.005 < Fe/Ti < 0.05, and Fe(III) ferromagnetic clusters at Fe/Ti < 0.1. All Fe-doped samples had rather high activity for the photocatalytic mineralization of oxalic acid under visible light illumination (λ > 400 nm) at 25 °C. Correlations were made between EPR and photocatalytic activity results. The specific surface area [S] data allowed us to deduce that the isolated Fe(III) centers were responsible for the photomineralisation of oxalic acid, while the Fe(III) ferromagnetic aggregates decreased the total efficiency of the system.     

pH effect on the physicochemical characteristics and efficiency of electroflotation extraction of low-soluble iron subgroup metal compounds from aqueous solutions

This paper reports on our study of the pH effect of solutions on the average hydrodynamic diameter (d_av) of the particles of the disperse phase and the electrokinetic potential (ζ) of the particles of low-soluble iron subgroup metals compounds using Fe(II, III), Ni(II), and Co(II) compounds as an example. The pH effect of solutions on the efficiency of the electroflotation extraction of metal ions from aqueous solutions containing these ions in individual form or in mixture was studied. The efficiency of the electroflotation extraction of the low-soluble compounds of iron subgroup metals is directly related to the particle size and electrokinetic potential of the particles, which depend on рН. The maximum degree of particle extraction α reached 97–99% at рН values characterized by the maximum hydrodynamic diameter of particles (over 20 μm for Fe(II) and Co(II) compounds and over 50 μm for Fe(III) and Ni(II) compounds) at ζ potentials of up to–10 mV for systems approximated to real wastewater. In the case of the extraction of the disperse phase of the Fe(III)–Ni(II)–Co(II) multicomponent system, the synergic effect was observed: the coextraction of metals was more complete and effective, which may be due to suppressed negative charge. In the range of рН 10–11, the degree of extraction of the Fe(III) disperse phase did not exceed 74%; in the ternary system, it reached 94%.     

Europium-sensitized Chemiluminescence of System Tetracycline–H<Subscript>2</Subscript>O<Subscript>2</Subscript>–Fe(II)/(III) and Its Application to the Determination of Tetracycline

Chemiluminescence (CL) of the reaction system tetracycline–H₂O₂–Fe(II)/(III)–Eu(III) was used for the determination of tetracycline hydrochloride in water, pharmaceutical preparations, and honey. The CL spectrum registered for this system shows emission bands typical of Eu(III) ions, with a maximum at λ ∼ 600 nm, corresponding to the electronic transitions of ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂. A strong chemiluminescence intensity characteristic of europium(III) ions in the system tetracycline–H₂O₂–Fe(II)/(III)–Eu(III), as contrasted to the emission of the system tetracycline–H₂O₂–Fe(II)/(III) without Eu(III), proves that the Eu(III) ion plays the role of a chemiluminescence sensitizer, accompanying tetracycline oxidation in the Fenton system (H₂O₂–Fe(II)/(III)). A linear dependence was observed for the integrated CL light intensity on the tetracycline concentration in the range of 2 × 10⁻⁷ to 3 × 10⁻⁵ mol l⁻¹ with the detection limit of 5 × 10⁻⁸ mol l⁻¹ in aqueous solution.     

Magnetic interactions between Fe(III) ions in the solid solutions CuM1 − xFexS2 (M = Al,Ga, In) and AgM1 − xFexO2 (M = Al,Ga).

Magnetic properties of CuM_{1 ? x}Fe_xS₂ (M = Al, Ga, In) and β-AgM_{1 ? x}, Fe_xO₂ (M = Al, Ga) solid solutions have been studied by Mössbauer spectroscopy (only on CuGa _{1 ? x}Fe_xS₂), magnetization measurements and EPR spectroscopy.In the structures studied all ions have tetrahedral co-ordination.The magnetic interactions between Fe(III) ions are shown to be very strong for nn sites ($\text{J}\text{k}$～100 K). More distant exchange interactions are found to fall off rather slowly as the distance between Fe(III) ions increases and are suggested to depend essentially on the number of bonds traversed.     

57Fe Mössbauer study of Eu1−x Sr x FeO3−y

The samples of Eu_1–x Sr _x FeO_3–y (x=0.0–1.0) were prepared by the solid state reaction method. Their X-ray diffraction patterns and⁵⁷Fe Mössbauer spectra at room temperature were measured. It is found that Sr ions incorporate in the lattice of EuFeO₃, the change of crystal structure is related to the dopant.⁵⁷Fe Mössbauer spectra consist of one magnetic, one doublet and one single paramagnetic components. The Fe ions in the cubic phase are in intermediate valence state between Fe(III) and Fe(IV) and may participate in electron hopping.     

The structure of Ni(II)−Fe(III) hydroxy-chloride green rusts by Mössbauer spectroscopy and X-ray diffraction

The crystallographic structure of Ni(II)?Fe(III) hydroxy-chloride green rusts obtained by oxidation of a Fe_xNi_1?x(OH)₂ precipitate is isomorphous with that of the ferrousferric green rust one and independent of the value of P=Fe/Ni. Mössbauer spectra exhibit two quadrupole doublets after further oxidation of the compounds which correspond to a formula (3-x)Ni(OH)₂ · xFeOOH · Fe(OH)₂Cl. The Fe³⁺ ions are found to occupy preferentially the sites close to the Cl^? ions and the Ni²⁺ those far from them. However the ordering of the Fe³⁺ ions is not perfect.     

Low frequency sonocatalytic degradation of Azo dye in water using Fe-doped zeolite Y catalyst

Sonocatalytic degradation of acid red B (ARB) dye was investigated using Fe doped zeolite Y catalysts with the assistance of low frequency (20 kHz) ultrasonic irradiation. Low concentration of Fe ions from different precursors was loaded onto the zeolite using wet impregnation method. Catalytic degradation of ARB dye was found to be accelerated by the reaction between Fe (II) and Fe (III) ions and hydrogen peroxide (H₂O₂) generated in situ by the ultrasound-mediated dissociation of water molecules. Fe (II)/Y exhibited higher degradation efficiency at the beginning of the reaction but achieved almost similar degradation at the end of the process. The increase of pH significantly decreased the degradation efficiency of ARB dye and strongly affected the leaching and catalyst stability. The highest efficiency was achieved at an initial pH of 3 with nearly 100% degradation in less than 60 min. Both catalysts showed no significant changes in terms of their mean particle sizes before and after reaction. Finally, Fe (III)/Y showed better performance evaluated based on leaching of Fe and also catalyst reusability. Only minor physical changes occurred during the degradation process for four consecutive runs of reaction.     

Specific features of spin-variable properties of [Fe(acen)pic<Subscript>2</Subscript>]BPh<Subscript>4</Subscript> · <Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O

The [Fe(acen)pic₂]BPh₄ · nH₂O compound has been synthesized and studied in the temperature interval of 5–300 K by the methods of EPR and magnetic susceptibility. The existence of ferromagnetic interactions between Fe(III) complexes in this compound has been revealed, in contrast to unhydrated [Fe(acen)pic₂]BPh₄. The reduction in the integrated intensity of the magnetic resonance signal as the temperature decreases below 80 K has been explained by the transition of high-spin ions to the low-spin state. It has been shown that the phase transition temperature in the presence of intermolecular (ferromagnetic) interactions is lower than that in the case of noninteracting centers.     

Incorporation of Siderophore Binding Sites in a Dipodal Fluorescent Sensor for Fe(III)

A new fluorescent probe 3, has been developed for the detection of Fe(III) in water based samples. The design of 3 involved the incorporation of Fe(III) binding sites observed in naturally occurring Siderophores into a synthetic sensing assembly. The probe, containing two Schiff base receptors connected to a mesitylene platform, was prepared in two steps. The dipodal sensor displayed good selectivity for Fe(III) when tested against other physiological and environmentally important metal ions, in HEPES buffered solution at pH 7.0, through a quenching of the fluorescent intensity. Stern-Volmer analysis of this quenching interaction indicated a 1:1 (host : guest) binding stoichiometry between the probe and Fe(III). The association constant, K _a calculated using the Benesi-Hildebrand equation was found to be 3.8 × 10⁴ M⁻¹. Crucially, the sensor was capable of measuring Fe(III) competitively in solutions containing both Fe(III) and Cu(II). Thus, the adoption of Fe(III) binding sites found in nature, into synthetic luminescent assemblies has proven an effective design strategy for the development of new Fe(III) probes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Investigation of the electronic structure and chemical bonding of lead hexacyanoferrate(III)

The electronic structure of lead hexacyanoferrate(III) is calculated by the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method in the LSDA + U approximation. The influence of vacancies in the lead sublattice on the electronic spectrum, chemical bonding, and magnetic properties of the Pb_1.5Fe(CN)₆ phase is investigated. Analysis of the electronic spectrum shows that this compound is characterized by semiconductor conductivity. It is demonstrated that the semiconductor gap is associated with the charge ordering of iron(III) ions.     

Evaluation of cerium doped tin oxide nanoparticles as a sensitive sensor for selective detection and extraction of cobalt

Chemo-sensor technology demands to design a single, preconcentrator based sensing system having higher sensitivity, sufficient selectivity and efficient removal of metal ions with simple operating and recognition methodology. Here we effectively deliberated Ce doped SnO₂ nanoparticles based sensing system which can be exploited for the recognition and extraction of Co(II) ions in a single step by strong interaction between Ce doped SnO₂ nanoparticles and Co(II). The sensing ability of Ce doped SnO₂ nanoparticles were deliberated for a selective removal of cobalt using inductively coupled plasma-optical emission spectrometry. The sensing ability of Ce doped SnO₂ is studied for various metal ions, such as Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Ni(II) and Zn(II) but the designed sensor was most selective toward Co(II) which was 5000 time more sensitive to Co(II) rather than different interfering metal ions. In addition, the desorption study for regeneration of Ce doped SnO₂ nanoparticles was carried out. This novel approach provides a new route for simultaneous detection and removal of Co(II) in a single step and can be a time and cost alternative tool for environmental safety.     

Spectroscopic studies of lanthanide(III) ion complexes with diethyl(phthalimidomethyl) phosphonate

Complexation and photophysical properties of complexes of lanthanide ions, Ln(III), with diethyl(phthalimidomethyl)phosphonate ligand, DPIP, were studied. Interactions between Ln(III) and DPIP were investigated using Nd(III) absorption and Eu(III) and Tb(III) luminescence (emission and excitation) spectra, recorded in acetonitrile solution containing different counter ions (NO₃^-, Cl^- and ClO₄^-). Results of the absorption spectroscopy have shown that counter ions play a significant role in the complexation of Ln(III)/DPIP complexes. Studies of luminescence spectra of Eu(III) and Tb(III) ions proved that the formation of Ln(III)/DPIP complexes of stoichiometry Ln:L=1:3 is preferred in solution. Based on the results of elemental analysis, Nd(III) absorption spectra and IR and NMR data, it was shown that the DPIP ligand binds Ln(III) ions via oxygen from phosphoryl group, forming complexes of a general formula Ln(DPIP)₃(NO₃)₃·H₂O, in which the NO₃^- ions are coordinated with the metal ion as bidentate ligands. Luminescent properties and energy transfer, from the ligand to Ln(III) ions in the complexes formed, were studied based on the emission and excitation spectra of Eu(III) and Tb(III). Their luminescent lifetimes and emission quantum yields were also measured.     

Role of precursor alloy phases and intermediate oxides in the preparation of Raney and Urushibara iron

⁵⁷Fe Mössbauer spectroscopy and scanning electron microscopy measurements of precursor phases formed during catalyst preparation and of the catalysts, themselves, demonstrate that the preparation of Raney iron from iron aluminum alloys involves the formation of Fe(OH)₂ and Fe₃O₄ as intermediate phases. The metallic Fe is formed from subsequent reduction of Fe₃O₄ by hydrogen generated by the oxidation of aluminum metal by hydroxide ions. Precursors to Urushibara iron U?Fe (III) are found to consist of Fe?Zn alloys when Zn is used as a reductant and of epitaxial deposits of Fe on aluminum when Al is the reductant. The material resulting from the reduction of the iron salt by aluminum is not a hydrogenation catalyst; the absence of catalytic activity is related to the absence of any alloying of the iron and aluminum. A consideration of the preparation of Raney iron, Urushibara iron, ammonia synthesis and Fischer-Tropsch catalysts leads to the conclusions that catalytic activity is highly correlated to the existence of intermediate mixed-crystals phases and the presence of intimate mixtures of at least two phases in the final catalyst.     

A New Fluorescent Sensor for the Determination of Iron(III) in Semi-Aqueous Solution

A simple fluorescent sensor 1 has been developed for the recognition of Fe(III) in semi-aqueous solution at pH 7.0. The sensor, containing two Schiff base type receptors directly connected to naphthalene fluorophores, shows a concentration dependent decrease in emission intensity upon Fe(III) addition. The sensor was selective for Fe(III) over other metal ions and can measure Fe(III) ion concentration between 0.05 and 0.12 mM. The binding stoichiometry was established as 1:1 (host: guest) with a binding constant (Logβ) of 4.01. Furthermore, the addition of Fe(III) to a solution of 1 caused a colour change from light yellow to colourless meaning 1 is also capable of detecting Fe(III) by the naked eye.     

EPR Studies of DOPA–Melanin Complexes with Fe(III)

Paramagnetic centers in 3,4-dihydroxyphenylalanine–melanin and its complexes with Fe(III) were examined by electron paramagnetic resonance (EPR) spectroscopy. Paramagnetic centers of melanin play an important role in detoxification of environment and they reveal high activity in binding of metal ions. Two different signals were observed in EPR spectra: lines of o-semiquinone free radicals and lines of paramagnetic Fe(III). Amplitudes of EPR lines of both free radicals and iron ions decrease with increasing Fe(III) content in melanin–metal ion complexes. Free radical concentrations in the melanin samples, g-factors, amplitudes and line widths of EPR spectra were determined. It was stated that fast spin–lattice relaxation processes exist in both free radical system and paramagnetic iron ions in melanin complexes.     

A Mechanism of the influence of Gd(III) and other Ln(III) ions on sensitized luminescence of Eu(III) and Tb(III) ions in aqueous and ethanol solutions: The role of hydroxyl bridges

We studied sensitization of Eu(III) and Tb(III) ions by molecules of 1,10-phenanthroline and 2,2-bipyridil in D₂O and d ₆-ethanol and the influence of Nd(III), Pr(III), Sm(III), Gd(III), and Ho(III) ions on the luminescence intensity I _lum and lifetime τ_lum of Eu(III) and Tb(III) in solutions. The stability constants of complexes of Eu(III) and Gd(III) with 2,2′-bipyridil are measured by spectrophotometric and luminescence methods. It is shown that luminescence of Eu(III) is quenched by Gd(III) ions at the ion concentration equal to 10^?2–10^?1 M, which is caused by competing between these ions for a sensitizer. At the concentration of Ln(III) ions equal to 10^?6?10^?3 M, the sensitized luminescence of Eu(III) and Tb(III) was quenched and τ_lum decreased in the presence of Nd(III) ions, whereas in the presence of Gd(III) the luminescence intensity increased. It is proved that a bridge that connects the two ions upon energy transfer is formed by hydroxyl groups. The intensity of luminescence of Eu(III) and Tb(III) in aqueous solutions and its lifetime decreased in the presence of hydroxyl groups, while upon addition of Gd(III) to these solutions these quantities were restored. We also found that the addition of Gd(III) to deoxygenated ethanol solutions of 2,2′-bipyridil and Eu(III) slows down photochemical and thermal reactions between bipyridil and Eu(III), resulting in the increase in the luminescence intensity of Eu(III).