Mechanism of formation of the complex oxide Gd<Subscript>2</Subscript>SrFe<Subscript>2</Subscript>O<Subscript>7</Subscript>

The mechanism of formation of the perovskite-like layered structure of the oxide Gd₂SrFe₂O₇ was studied. The limiting stages are those of formation of phases with perovskite (GdFeO₃, SrFeO_3?x ) and K₂NiF₄ (GdSrFeO₄) structures. The Mössbauer study has shown that iron atoms exist in a heterovalent state (Fe³⁺ and Fe⁴⁺) only in the structure of SrFeO_3?x ).     

Nonstoichiometric Zn Ferrite and ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Composite Spheres: Preparation,Magnetic Properties,and Chromium Removal

Monodisperse and porous nonstoichiometric Zn ferrite can be prepared by a solvothermal method. Such non-Zn ferrite was used to be the precursor for synthesis of ZnFe₂O₄/Fe₂O₃ composite via calcination at 600°C for 3 h in air. X-ray powder diffractometer (XRD) and Energy Dispersive Spectrometer (EDS) proved the nonstoichiometry of Zn ferrite synthesized by solvothermal method and the formation of ZnFe₂O₄/Fe₂O₃ composite via calcination. TEM image showed that non-Zn ferrite spheres with wormlike nanopore structure were made of primary nanocrystals. BET surface area of non-Zn ferrite was much higher than that of ZnFe₂O₄/Fe₂O₃ composite. Saturation magnetization of non-Zn ferrites was significantly higher than that of ZnFe₂O₄/Fe₂O₃ composites. Calcination of non-Zn ferrite resulted in the formation of large amount of non-magnetic Fe₂O₃,which caused a low magnetization of composite. Because of higher BET surface area and higher saturation magnetization, non-Zn ferrite presented better Cr⁶⁺ adsorption property than ZnFe₂O₄/Fe₂O₃ composites.     

Electroswitchable binding of [Co(dipy)<Subscript>3</Subscript>]<Superscript>3+</Superscript> and [Fe(dipy)<Subscript>3</Subscript>]<Superscript>2+</Superscript><Emphasis Type="Italic">n</Emphasis>-sulfonato(thia)calix[4]arenas

The methods of cyclic voltammetry, electrolysis, and spectrophotometry were used to study electrochemical properties of (TCAS + Fe³⁺ + dipy), (CCAS + Fe³⁺ + dipy), and (CCAS + Fe³⁺ + [Co(dipy)₃]³⁺) triple systems (where TCAS is n-sulfonatothiacalix[4]arene, CCAS is tetracarboxylate n-sulfonatocalix[4]arene, and dipy = α,α′-dipyridyl) in an aqueous solution. One-electron reduction of Fe(III) in the (TCAS + Fe³⁺ + dipy) system at pH 2.5 results in electroswitching of iron ions from the lower TCAS ring to the upper ([Fe(dipy)₃]²⁺). Reverse electrochemical switching of the system is impossible due to mediator ([Fe(dipy)₃]^2+/3+) oxidation of TCAS. Reverse electroswitching of Fe(III) ions from unbound to bound state as ([Fe(dipy)₃]²⁺) with CCAS has been revealed in the system (CCAS + Fe³⁺ + dipy) (pH 1.7) upon single-electron transfer, whereas reversible electroswitching by the upper rim of CCAS from one complex ion ([Co(dipy)₃]³⁺) to another ([Fe(dipy)₃]²⁺) has been demonstrated in the system ([Co(dipy)₃]³⁺ + CCAS + Fe³⁺ upon double-electron transfer. In all systems, electric switching was accompanied by synchronous color switching.     

Thermal behavior of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> mesoporous gels

Summary Titania-based photocatalytic materials were prepared by sol-gel method using Fe³⁺ and polyethyleneglycol (PEG₆₀₀) as additives. Thermogravimetry (TG), differential thermal analysis (DTA) and evolved gas analysis (EGA) with MS detection were used to elucidate processes that take place during heating of Fe³⁺ containing titania gels. The microstructure development of the Fe₂O₃/TiO₂ gel samples with and without PEG₆₀₀ admixtures was characterized by emanation thermal analysis (ETA) under in situ heating in air. A mathematical model was used for the evaluation of ETA results. Surface area and porosity measurements of the samples dried at 120&deg;C and the samples preheated for 1 h to 300 and 500&deg;C were compared. From the XRD measurements it was confirmed that the crystallization of anatase took place after thermal heating up to 600&deg;C.     

Behavior of silver sulfide in the system Ag<Subscript>2</Subscript>S-Fe(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>-HNO<Subscript>3</Subscript>-H<Subscript>2</Subscript>O

Behavior of silver sulfide in the system Ag₂S-Fe(NO₃)₃-HNO₃-H₂O was studied at 25, 55, and 80°C using the method of the simplex-lattice experiment design. The quantitative dependences of Ag₂S oxidation on the concentrations of the acid and Fe³⁺ were determined. The isoconcentration diagrams were obtained.     

Adsorption behavior of <Superscript>99</Superscript>Tc on Fe,Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>

Summary The adsorption of ⁹⁹Tc on the adsorbers Fe, Fe₂O₃ and Fe₃O₄ was studied by batch experiments under aerobic and anoxic conditions. The effects of pH and CO₃^2- concentration of the simulated ground water on the adsorption ratios were also investigated, and the valences of Tc in solution after the adsorption equilibrium were studied by solvent extraction. The adsorption isotherms of TcO₄- on the adsorbers Fe, Fe₂O₃ and Fe₃O₄ were determined. Experimental results have shown that the adsorption ratio of Tc on Fe decreases with the increase of pH in the range of 5-12 and increases with the decrease of the CO₃^2- concentration in the range of 10^-8M-10^-2M. Under aerobic conditions, the adsorption ratios of ⁹⁹Tc on Fe₂O₃ and Fe₃O₄ were not influenced by pH and CO₃^2-concentration. When Fe was used as adsorbent, Tc existed mainly in the form of Tc(IV) after equilibrium and in the form of Tc(VII) when the adsorbent was Fe₂O₃ or Fe₃O₄ under aerobic conditions. The adsorption ratios of Tc on Fe, Fe₂O₃ and Fe₃O₄ decreased with the increase of pH in the range of 5-12 and increased with the decrease of the CO₃^2- concentration in the range of 10^-8M-10^-2M under anoxic conditions. Tc existed mainly in the form of Tc(IV) after equilibrium when Fe, Fe₂O₃ and Fe₃O₄ was the adsorbent under anoxic conditions. The adsorption isotherms of TcO_4- on the adsorbers Fe, Fe₂O₃ and Fe₃O₄ are fairly in agreement with the Freundlich’s equation under both aerobic and anoxic conditions.     

High-yield preparation of rod-like CaSO<Subscript>4</Subscript>/Fe<Superscript>0</Superscript> magnetic composite for effective removal of Cu<Superscript>2+</Superscript> in wastewater

In this study, a simple approach was described for the fabrication of CaSO₄/Fe⁰ composite used as a novel adsorbent for the reductive removal of Cu²⁺ from aqueous solutions. The magnetic CaSO₄/Fe⁰ composite was prepared by a solid state reaction at 550 °C in the H₂ atmosphere using CaSO₄·2H₂O/α-FeOOH as a precursor. The structure and morphology of the as-synthesized magnetic composite were characterized by X-ray diffraction, field emission scanning electron microscopy and a superconducting quantum interference device, respectively. Results showed that the CaSO₄/Fe⁰ composite with a rod-like shape could be easily acquired from the CaSO₄·2H₂O/α-FeOOH precursor with the ratio of 1:0.5 at 550 °C in the H₂ atmosphere for 1 h. The CaSO₄/Fe⁰ composite exhibited enhanced performance relevant to the reductive removal of Cu²⁺. The removal amount of Cu²⁺ increased linearly with increasing of concentration of Cu²⁺ in wastewater. Possible removal mechanisms were proposed as follows: (1) the formation of Cu₂O by fast reduction of Cu²⁺ with Fe⁰ nanoparticles on interface of CaSO₄/Fe⁰ composite, (2) proper adsorption of Cu²⁺ on the surface of CaSO₄/Fe⁰ composite, (3) the hydrous iron oxide (HIO) such as Fe (OH)₃ and FeOOH in situ generated on the rest of CaSO₄/Fe⁰ composite could further adsorb Cu²⁺ from wastewater.     

Transition metal salts of H<Subscript>4</Subscript>PMo<Subscript>11</Subscript>VO<Subscript>40</Subscript> for efficient H<Subscript>2</Subscript>S removal in the liquid redox process

Several transition metal (Cu²⁺, Fe³⁺, Zn²⁺, Mn⁴⁺, and Cr⁶⁺) salts of H₄PMo₁₁VO₄₀ were prepared and their solutions were used initially for H₂S removal in the liquid redox process. H₂S removal tests were performed by dynamic absorption experiments. Among these polyoxometalates, that with the Cu²⁺ cation was found to have pronounced H₂S removal performance with the removal efficiency of up to 98%. The relevant oxidative desulfurization mechanism and the role of Cu²⁺ were studied.     

Iron(II) complexes [Fe(DfgH)<Subscript>2</Subscript>(3-CONH<Subscript>2</Subscript>-Py)<Subscript>2</Subscript>] and [Fe(DfgH)<Subscript>2</Subscript>(4-COOC<Subscript>2</Subscript>H<Subscript>5</Subscript>-Py)<Subscript>2</Subscript>]: Synthesis and structures

The complexes [Fe(DfgH)₂(3-CONH₂-Py)₂] (I) and [Fe(DfgH)₂(4-COOC₂H₅-Py)₂] (II), where DfgH₂ is α-benzyl dioxime, were obtained and examined by X-ray diffraction analysis. The equatorial planes of the coordination octahedra of the metal ions consist of two monodeprotonated α-benzyl dioxime residues united through intramolecular hydrogen bonds O-H…O into a pseudomacrocyclic system. The neutral molecules 3-CONH₂-Py and 4-COOC₂H₅-Py are coordinated to the Fe²⁺ ion through the N atom of the heterocycle. Structure I is layered and structure II is molecular. Intermolecular interactions N-H…O are responsible for the formation of layers in crystal structure I.     

Preparation and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>composite particles

Using Fe₃O₄ nano-particles as seeds, a new type of Fe₃O₄/Au composite particles with core/shell structure and diameter of about 170 nm was prepared by reduction of Au³⁺ with hydroxylamine in an aqueous solution. Particle size analyzer and transmission electron microscope were used to analyze the size distribution and microstructure of the particles in different conditions. The result showed that the magnetically responsive property and suspension stability of Fe₃O₄ seeds as well as reduction conditions of Au³⁺to Au⁰are the main factors which are crucial for obtaining a colloid of the Fe₃O₄/Au composite particles with uniform particle dispersion, excellent stability, homogeneity in particle sizes, and effective response to an external magnet in aqueous suspension solutions. UV-Vis analysis revealed that there is a characteristic peak of Fe₃O₄/Au fluid. For particles with d(0.5)=168 nm, the λmax is 625 nm.     

Study of Fe-doped V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> catalyst for an enhanced NH<Subscript>3</Subscript>-SCR in diesel exhaust aftertreatment

Selective catalytic reduction (SCR) with ammonia has been considered as the most promising technology, as its effect deals with the NO_X. Novel Fe-doped V₂O₅/TiO₂ catalysts were prepared by sol–gel and impregnation methods. The effects of iron content and reaction temperature on the catalyst SCR reaction activity were explored by a test device, the results of which revealed that catalysts could exhibit the best catalytic activity when the iron mass ratio was 0.05%. It further proved that the VTiFe (0.05%) catalyst performed the best in denitration and its NO_X conversion reached 99.5% at 270 °C. The outcome of experimental procedures: Brunauer–Emmett–Teller surface area, X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and adsorption (H₂-TPR, NH₃-TPD) techniques showed that the iron existed in the form of Fe³⁺ and Fe²⁺ and the superior catalytic performance was attributed to the highly dispersed active species, lots of surface acid sites and absorbed oxygen. The modified Fe-doped catalysts do not only have terrific SCR activities, but also a rather broad range of active temperature which also enhances the resistance to SO₂ and H₂O.     

Synthesis,Structure and Isomerism of the [Fe<Subscript>3</Subscript>Pt(μ<Subscript>4</Subscript>-Q)(CO)<Subscript>9</Subscript>(dppm)] Clusters (Q = Se,Te; dppm = Ph<Subscript>2</Subscript>PCH<Subscript>2</Subscript>PPh<Subscript>2</Subscript>)

The reaction of K₂[Fe₃(μ₃-Q)(CO)₉] (Q = Se (K₂[1a]), Te (K₂[1b])) with [(dppm)PtCl₂] leads to the addition of a [(dppm)Pt]²⁺ unit to a Fe₂Q face of the initial cluster. By this way new heteronuclear clusters [Fe₃Pt(μ₃-Q)(CO)₉(dppm)] were obtained possessing a butterfly-shaped cluster core bridged by a μ₄-Q unit. It has been found that the resulting Fe-Pt clusters exist as equilibrium mixtures of two isomeric forms in solution differing by the dppm coordination mode: as a chelate ligand coordinated to Pt or as a bridging ligand coordinated to Pt and Fe atoms. The mixtures of isomers can be separated by chromatography and the pure isomers can be isolated as stable crystalline phases. Solutions of both isomers attain equilibrium at normal conditions in about 1 month as found by NMR. Dedicated to Professor Dieter Fenske in the occasion of his 65th birthday.     

Facile synthesis of Fe@Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> core-shell nanowires as O<Subscript>2</Subscript> electrode for high-energy Li-O<Subscript>2</Subscript> batteries

Fe@Fe₂O₃ core-shell nanowires were synthesized via the reduction of Fe³⁺ ions by sodium borohydride in an aqueous solution with a subsequent heat treatment to form Fe₂O₃ shell and employed as a cathode catalyst for non aqueous Li-air batteries. The synthesized core-shell nanowires with an average diameter of 50–100 nm manifest superior catalytic activity for oxygen evolution reaction (OER) in Li-O₂ batteries with the charge voltage plateau reduced to ～3.8 V. An outstanding performance of cycling stability was also achieved with a cutoff specific capacity of 1000 milliampere hour per gram over 40 cycles at a current density of 100 mA g^?1. The excellent electrochemical properties of Fe@Fe₂O₃ as an O₂ electrode are ascribed to the high surface area of the nanowires’ structure and high electron conductivity. This study indicates that the resulting iron-containing nanostructures are promising catalyst in Li-O₂ batteries.     

Obtaining of Ni<Subscript>0.65</Subscript>Zn<Subscript>0.35</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposites by thermal decomposition of complex compounds embedded in silica matrix

This article presents the results of our investigation on the obtaining of Ni_0.65Zn_0.35Fe₂O₄ ferrite nanoparticles embedded in a SiO₂ matrix using a modified sol–gel synthesis method, starting from tetraethylorthosilicate (TEOS), metal (Fe^III,Ni^II,Zn^II) nitrates and ethylene glycol (EG). This method consists in the formation of carboxylate type complexes, inside the silica matrix, used as forerunners for the ferrite/silica nanocomposites. We prepared gels with different compositions, in order to obtain, through a suitable thermal treatment, the nanocomposites (Ni_0.65Zn_0.35Fe₂O₄)_x–(SiO₂)_100–x (where x=10, 20, 30, 40, 50, 60 mass%). The synthesized gels were studied by differential thermal analysis (DTA), thermogravimetry (TG) and FTIR spectroscopy. The formation of Ni–Zn ferrite in the silica matrix and the behavior in an external magnetic field were studied by X-ray diffraction (XRD) and quasi-static magnetic measurements (50 Hz).     

Deoxygenation of Nitrosobenzene by the Electrogenerated Pd<Subscript>3</Subscript>(dppm)<Subscript>3</Subscript>(μ<Subscript>3</Subscript>-CO) Cluster

The 2-electron reduction of the unsaturated Pd₃(dppm)₃(CO)²⁺ cluster ([Pd₃]²⁺) affords the highly reactive neutral cluster [Pd₃]⁰, which reacts with nitrosobenzene (PhNO) yielding the organic azoxybenzene product (PhN(O)NPh) via the formation of “triplet” nitrene “PhN”. The formation of [Pd₃(μ₃-O)] as a possible (relatively unstable) intermediate is also postulated based on MALDI-TOF findings, but not formally demonstrated. Concurrently, no reaction between [Pd₃]⁰ and OPPh₃ occurs. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. This paper is dedicated to Professor Dieter Fenske.     

Thermal dissociation of SmMn<Subscript>2</Subscript>O<Subscript>5</Subscript>

Measurements on a circulation static setup with subsequent XRD analysis of quenched solid phases were used to study phase equilibria implicated in the thermal dissociation of SmMn₂O₅over the temperature and pressure ranges from 973 to 1123 K and from 10^?3 to 10^?16 Pa, respectively. The thermal dissociation of SmMn₂O₅ results in the sequential formation of constant-composition phases: SmMn₂O₅ → SmMnO₃ + Mn₃O₄ + O₂ → SmMnO₃ + MnO + O₂ → Sm₂O₃ + MnO + O₂. The temperature dependence of the equilibrium oxygen pressure for the observed monovariant phase equilibria was used to calculate the thermodynamic characteristics of dissociation and formation of SmMn₂O₅ and SmMnO₃ from the elements.     

The influence of structural factors on the gas-sensitive properties of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-SnO<Subscript>2</Subscript>

The influence of the dispersity and structural and phase state of oxide materials based on Fe₂O₃ and SnO₂ on the gas-sensitive properties of these materials used as sensitive layers in chemical sensors was considered. It was found that high-dispersity Fe₂O₃-SnO₂ (Fe: Sn = 9: 1) ceramic layers possessed high sensitivity to ethanol vapor in both dry and humid atmosphere and low sensitivity to CO and CH₄. The maximum response to ethanol vapor in humid atmosphere was characteristic of layers with structures of substitution-interstitial solid solutions of Sn⁴⁺ in α-Fe₂O₃.     

Electrochemical properties of <Emphasis Type="Italic">n</Emphasis>-sulfonatothiacalyx[4]arene complexes with Fe<Superscript>3+</Superscript> and [Co(dipy)<Subscript>3</Subscript>]<Superscript>3+</Superscript> ions

The electrochemical properties of n-sulfonatothiacalyx[4]arene (H₄XNa₄) complexes with [Co(dipy)₃]³⁺ and Fe³⁺ ions were studied by means of cyclic voltammetry in aqueous solution at pH 2.5. The observed single-electron reduction of [Co(dipy)₃]³⁺ bound extraspherically to the upper rim and Fe³⁺ ion bound intraspherically to the lower rim of n-sulfonatothiacalyx[4]arene in binary [Co(dipy)₃]³⁺ · H₃X^5?, H₃X^5? · Fe³⁺, and ternary [Co(dipy)₃]³⁺ · H₃X^5? · Fe³⁺ heterometal complexes was more difficult than in the free state. The reversible single-electron transfer to the metal ion results in lower binding energy ([Co(dipy)₃]³⁺, ΔΔG ₀ = 3.9 kJ/mol) or in full fast dissociation of the complex (Fe³⁺). The ternary complex in the solution forms the aggregates, in which inner encapsulated Fe(III) and Co(III) ions are not reduced on the electrode. Their quantitative reduction takes place by the relay mechanism of intra- and intermolecular electron transfer through electrochemically generated [Co(dipy)₃]²⁺ outer ions.     

Magnetic properties of a dinuclear complex (2,3-Me<Subscript>2</Subscript>C<Subscript>5</Subscript>H<Subscript>3</Subscript>N)<Subscript>2</Subscript>Fe<Subscript>2</Subscript>(μ-OOCCMe<Subscript>3</Subscript>)<Subscript>4</Subscript> with “China lantern” structure

Magnetic characteristics of the dinuclear complex (2,3-Me₂C₅H₃N)₂Fe₂(μ-OOCCMe₃)₄ (1) were studied in the temperature interval 2–300 K. The magnetic behavior of complex 1 was interpreted in terms of the orbital-dependent exchange theory with allowance for the temperature dependence of the populations of the split ⁵T_2g ground-state components of the Fe^II ions. The calculated values of the orbital-dependent exchange parameters are in good agreement with the results reported for dinuclear carboxylates of other 3d-transition metals and suggest the existence of strong ferromagnetism in some types of heterodinuclear carboxylates.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2035–2039, October, 2004.     

A Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript>@graphene quantum dot core-shell structured nanomaterial as a fluorescent probe and for magnetic removal of mercury(II) ion

The authors describe the synthesis of a multifunctional nanocomposite with an architecture of type Fe₃O₄@SiO₂@graphene quantum dots with an average diameter of about 22 nm. The graphene quantum dots (GQDs) were covalently immobilized on the surface of silica-coated magnetite nanospheres via covalent linkage to surface amino groups. The nanocomposite displays a strong fluorescence (with excitation/emission peaks at 330/420 nm) that is fairly selectively quenched by Hg²⁺ ions, presumably due to nonradiative electron/hole recombination annihilation. Under the optimized experimental conditions, the linear response to Hg²⁺ covers the 0.1 to 70 μM concentration range, with a 30 nM lower detection limit. The high specific surface area and abundant binding sites of the GQDs result in a good adsorption capacity for Hg²⁺ (68 mg?g^?1). The material, due to its superparamagnetism, can be separated by using a magnet and also is recyclable with EDTA so that it can be repeatedly used for simultaneous detection and removal of Hg²⁺ from contaminated water.

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Graphical abstract A schematic view of preparation process for the Fe₃O₄@SiO₂@graphene quantum dots nanocomposite (denoted as Fe₃O₄@SiO₂@GQDs). The graphene quantum dots were covalently immobilized on the surface of silica-coated magnetite nanospheres (Fe₃O₄@SiO₂) via covalent linkage to surface amino groups.