Small Amount Of Fe3 Research Articles

Effect of Fe on the activity of Au/FeO x -TiO2 catalysts for CO oxidation

A thorough characterisation of Au/TiO2 and Au/FeOx-TiO2 catalysts was conducted in order to get a better understanding of the effect of Fe on the Au/TiO2 catalysts and link it to differences observed in their activities for CO oxidation. Several techniques including HRTEM, temperature-programmed reduction (TPR), UV-Vis and temperature-programmed desorption (TPD) of isopropyl amine, CO and CO2 were used to characterise the catalysts. Au/FeOx-TiO2 (300 °C), which was found to be the most active catalyst for CO oxidation, had the highest number of Bronsted acid sites, although its concentration of Lewis acid sites was similar to all other tested catalyst systems. X-ray photoelectron spectroscopy (XPS) revealed that the Fe species on the Au/FeOx-TiO2 catalyst is Fe2+ with a very small amount of Fe3+. Fe2+ is comprised of both FeO and Fe3O4 species, and according to TPR, the ratio (FeO/Fe3O4) between these two species increases with increasing calcination temperature. The presence of Fe on the Au/TiO2 catalyst seems to stabilise the Au nanoparticles from agglomeration. The activation energy of desorption (Ed) of CO from Au/FeOx-TiO2 (300 °C) was 82.7 kJ/mol, whilst on Au/TiO2, the Ed for CO was 108.8 kJ/mol. On both catalysts, the Ed for CO2 was ca. 99 kJ/mol.

XAS analysis of iron and palladium bonded to a polysaccharide produced anaerobically by a strain of Klebsiella oxytoca.

Klebsiella oxytoca BAS-10 ferments citrate to acetic acid and CO2, and secretes a specific exopolysaccharide (EPS), which is able to bind different metallic species. These biomaterials may be used for different biotechnological purposes, including applications as innovative green biogenerated catalysts. In production of biogenerated Pd species, the Fe(III) as ferric citrate is added to anaerobic culture of K. oxytoca BAS-10, in the presence of palladium species, to increase the EPS secretion and improve Pd-EPS yield. In this process, bi-metallic (FePd-EPS) biomaterials were produced for the first time. The morphology of bi-metallic EPS, and the chemical state of the two metals in the FePd-EPS, are investigated by transmission electron microscopy, Fourier transform infra-red spectroscopy, micro-X-ray fluorescence, and X-ray absorption spectroscopy methods (XANES and EXAFS), and compared with mono-metallic Pd-EPS and Fe-EPS complexes. Iron in FePd-EPS is in the mineralized form of iron oxides/hydroxides, predominantly in the form of Fe(3+), with a small amount of Fe(2+) in the structure, most probably a mixture of different nano-crystalline iron oxides and hydroxides, as in mono-metallic Fe-EPS. Palladium is found as Pd(0) in the form of metallic nanoparticles with face-centred cubic structure in both bi-metallic (FePd-EPS) and mono-metallic (Pd-EPS) species. In bi-metallic species, Pd and Fe nanoparticles agglomerate in larger clusters, but they remain spatially separated. The catalytic ability of bi-metallic species (FePd-EPS) in a hydrodechlorination reaction is improved in comparison with mono-metallic Pd-EPS.

Structural study on nickel doped Li2FeSiO4

The effect of nickel doping on the structure of Li2FeSiO4 is examined by X-ray diffraction, Mossbauer spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectrometer, and magnetization measurements. Both, the pristine and nickel doped Li2FeSiO4, crystallize in a monoclinic structure with (P21/n) symmetry. Their lattice parameters are similar, which suggests that Ni2+ doesn’t destroy the lattice structure. Some small amounts of Fe3+ impurity phases and unreacted Li2SiO3 are detected. Samples doped with more than 10 mol% contain some magnetic impurity of Fe-Ni alloy. Magnetic measurements indicated that Li2FeSiO4 is paramagnetic and becomes antiferromagnetic below 23 K. Nickel dopant does not modify the paramagnetic nature of this material.

Effects of surface hydroxyl group density on the photocatalytic activity of Fe3+-doped TiO2

The aim of the work is to study the effects of oxygen vacancy and surface hydroxyl group density on the photocatalytic activity of Fe3+-doped TiO2, and to investigate how the titanium dioxide doped with different levels of the Fe3+ influenced their physical and chemical characterizations. The photocatalysts were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), electron spin resonance (ESR), X-ray photoelectron spectroscope (XPS) and Fourier transform infrared (FTIR) spectra. The results revealed that adsorbed hydroxyl group density significantly influenced the photocatalytic activity, and a small amount of Fe3+ can act as a photo-generated hole and a photo-generated electron trap and inhibit the electron–hole recombination. The 0.10%-Fe3+-TiO2 with the highest surface hydroxyl group density revealed the maximum rate constant of 0.716 and the optimal photocatalytic degradation of MB. As Fe3+ doping levels are larger than 0.10%, the cluster of FeTi′–V¨O–FeTi′ generated gradually. This implied that an excessive amount of Fe3+ doped into TiO2 is detrimental to the photocatalytic activity due to the formation of FeTi′–V¨O–FeTi′ clusters and enhances the recombination of photogenerated electrons and holes.

Highly effective degradation of sodium dodecylbenzene sulphonate and synthetic greywater by Fenton-like reaction over zerovalent iron-based catalyst

There is an increasing interest to recycle greywater for meeting non-portable water demand. However, linear alkylbenzene sulphonates (a form of anionic surfactants) that are commonly found in greywater are less biodegradable at moderate to high concentrations. A fenton-like system is a relatively economic advanced oxidation process that can potentially be used for surfactant degradation in greywater treatment. This study investigated the feasibility of zerovalent iron (ZVI)-mediated Fenton's oxidation of sodium dodecylbenzene sulphonate (SDBS) using Fe0/H2O2 and Fe2+/Fe0/H2O2 systems under a range of operating conditions. For the Fe0/H2O2 binary system, the initial pH value and Fe0 dosage played important roles in final degradation efficiency. For the Fe2+/Fe0/H2O2 ternary systems, a small amount of Fe2+ (0.5–1.7 mM) contributed a synergistic effect to promote iron recycling and SDBS degradation. Approximately, 90% of SDBS mineralization efficiency was accomplished within 15 min at a pH range from 3.0 to 6.5, using 18 mM Fe0 and 15 mM H2O2. However, the removal kinetics was rate-limited by Fe2+ dissolution from the ZVI surfaces. The Fenton-like process of the Fe2+/Fe0/H2O2 ternary system also presents a promising treatment method for synthetic greywater, in which 90% TOC removal was achieved within the first 10 min; 78% COD and 91% BOD5 were achieved after 120 min of reaction.

Investigation of some new hydro(solvo)thermal synthesis routes to nanostructured mixed-metal oxides

We present a study of two new solvothermal synthesis approaches to mixed-metal oxide materials and structural characterisation of the products formed. The solvothermal oxidation of metallic gallium by a diethanolamine solution of iron(II) chloride at 240°C produces a crystalline sample of a spinel-structured material, made up of nano-scale particles typically 20nm in dimension. XANES spectroscopy at the K-edge shows that the material contains predominantly Fe2+ in an octahedral environment, but that a small amount of Fe3+ is also present. Careful analysis using transmission electron microscopy and powder neutron diffraction shows that the sample is actually a mixture of two spinel materials: predominantly (>97%) an Fe2+ phase Ga1.8Fe1.2O3.9, but with a minor impurity phase that is iron-rich. In contrast, the hydrothermal reaction of titanium bis(ammonium lactato)dihydroxide in water with increasing amounts of Sn(IV) acetate allows nanocrystalline samples of the SnO2–TiO2 solid solution to be prepared directly, as proved by powder XRD and Raman spectroscopy.

Fe4O5 and its solid solutions in several simple systems

Experiments at high pressures and temperatures reveal the stability of a Fe4O5-type structured phase in several simple chemical systems. On the one hand, the Fe4O5 end-member is stable in the presence of SiO2-rich phases, including stishovite, but contains ≤0.01 Si cations per formula unit. This indicates that Si is essentially excluded from this phase. On the other hand, the Fe4O5 phase can form solid solutions with Mg and Cr and can coexist with silicate phases at the high P–T conditions expected in the transition zone of the mantle (i.e. >~9 GPa). It can coexist with both wadsleyite and Mg-rich ringwoodite and can contain at least 25 mol% Mg2Fe2O5 component. The Fe4O5 phase always contains the least amount of Mg in any given mineral assemblage. Cr-bearing Fe4O5 has been synthesised with up to 46 mol% Fe2Cr2O5 component and can coexist with spinel and/or hematite-eskolatite solid solutions. Substitution of Mg and Cr for Fe2+ and Fe3+, respectively, leads to variations in Fe3+/∑Fe from the ideal value of 0.5 for the Fe4O5 end-member composition, which can influence its redox stability. These cations also have contrasting effects on the unit-cell parameters, which indicate that they substitute into different sites. This initial study suggests that Fe4O5-type structured phases may be stable over a range of P–T–fO2 conditions and bulk compositions, and can be important in understanding the post-spinel phase relations in a number of chemical systems relevant to the Earth’s transition zone. Thus, the presence of even small amounts of Fe3+ could alter the expected phase relations in peridotitic bulk compositions by stabilising this additional phase.

Dielectric and Electrical Transport Properties of the Fe3+-doped CaCu3Ti4O12

CaCu3–xFexTi4O12 (x=0, 0.015, 0.03, 0.045, 0.06) ceramics were synthesized by sol–gel method. The electrical conduction and dielectric measurements show that the doping of a very small amount of Fe3+ ions greatly reduces the low-frequency dielectric constants and leakage, and enhances grain resistivity. For the doped samples, the appearance of the strong low-frequency peaks in the spectra of dielectric loss confirms that the doping of Fe3+ ions induces the contact-electrode effect on ceramic surface. These great changes of electrical properties may originate from the reduced amount of oxygen vacancies by doping Fe3+.

Mössbauer spectroscopic study of Fe-Mg tourmalines with different Fe contents

We studied four tourmalines with different Fe contents from Xinjiang, Sichuan, and Yunnan provinces of China using Mossbauer spectroscopy and single crystal X-ray diffraction. The valence and location of Fe in the four tourmalines and two heat-treated tourmalines have been investigated. The experimental results showed that Fe in the four tourmalines at room temperature had two valence states and two locations, i.e. Fe2+(Y), Fe2+(Z), Fe3+(Y). After being heated at 850°C for 48 and 72 h, Fe elements in tourmaline were nearly completely oxidized and mainly occupied Y sites, and a small amount of Fe3+ shifted to Z sites. Simultaneously, the amount of mixed valence state Fe2.5+ progressively increased with heating time, and electron delocalization occurred between the adjacent sites [Fe2+-Fe3+].

Effect of Iron (III)-Doping on the Photocatalytic Activity of Titanium Dioxide Catalysts for Methylene Blue Degradation

Iron-doped TiO2 photocatalyst powders were prepared by the sol–gel method and characterized by Brunauer–Emmett–Teller (BET)-specific surface area, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Ultraviolet–Visible (UV-Vis) spectroscopy. Fe3+ doping in the TiO2 decreases the crystal grain size, increases the specific surface areas of powders, extends the absorption to visible light regions (400~500 nm), and lowers the photocatalytic activity for methylene blue (MB) degradation under UV irradiation. The photocatalytic degradation of MB in water was investigated as a function of the Fe3+ content in TiO2. It was found that under the irradiation of visible light, a small amount of Fe3+ dopant in TiO22 powders could obviously enhance the photocatalytic activity. When the Fe3+ content was in the range of 0.03–0.1 mol%, the photocatalytic activity of the samples was higher than that of undoped TiO2. Appropriate content of Fe-doping is an effective means to improve the photocatalytic activity of TiO2 for MB degradation under visible light irradiation.

Safety Assessment on Hydrogen Peroxide for Storage and Transportation Based on Runaway Scenario

Hydrogen peroxide is a very versatile reagent for many industrial processes. Nevertheless, it is very sensitive to impurities that can catalyze its decomposition violently. Combining the recent year’s hydrogen peroxide explosion accidents, this paper seeks to establish the evaluation model for its safe storage and transportation. Firstly, the runaway scenario that can serve as a basis for the assessment of the thermal risk was briefly described. Secondly, the adiabatic temperature increase () and the pressure for closed systems were used as the severity of the assessment criteria. Both closed and open systems were discussed. Thirdly, the time to maximum rate (TMRad) was presented as the probability of occurrence of the scenario. Finally, the established model was exemplified by two examples both with and without contamination. The results show that at 20°C the severity of 30(wt.) % H2O2is critical and a small amount of Fe3+(12.7mg∙L-1) reduces theTMRadof 30(wt.) % H2O2by almost a factor of eleven. This approach can assess the safety of hydrogen peroxide for storage and transportation in advance.

Characterisation of High Temperature Phase Stability and Evaluation of Metallurgical Compatibility with SS 304L, of Indigenously Developed Alternate Shielding Material Ferro- Boron for Fast Reactor Applications

Abstract The high temperature phase stability and metallurgical compatibility of Ferro boron alloy which contain about 15 wt.% boron and some impurity elements like C(0.3),Si (0.29), P(0.006) etc, with 304 L SS have been evaluated using calorimetry and metallography. The X-ray diffraction of ferroboron revealed the presence of major FeB and minor Fe2B constituents, besides a small amount of Fe3(B, C). The thermal stability of this ferroboron alloy has been characterised up to melting by high resolution thermal analysis. In addition, the enthalpy increment measurements and hence specific heat estimates have been also made in the temperature range 400- 1200oC, using drop calorimetry. The high temperature metallurgical interaction between ferroboron and 304L SS clad has been simulated at temperatures 823 – 1073 K (550-800 oC) for reaction times up to 5000 h, using diffusion couples.

Effect of H2O2 on Nafion® properties and conductivity at fuel cell conditions

During PEM fuel cell operation, formation of H2O2 and material corrosion occurs, generating trace amounts of metal cations (i.e., Fe2+, Pt2+) and subsequently initiating the deterioration of cell components and, in particular, PFSA membranes (e.g., Nafion). However, most previous studies of this have been performed using conditions not relevant to fuel cell environments, and very few investigations have studied the effect of Nafion decomposition on conductivity, one of the most crucial factors governing PEMFC performance. In this study, a quantitative examination of properties and conductivities of degraded Nafion membranes at conditions relevant to fuel cell environments (30–100%RH and 80°C) was performed. Nafion membranes were pre-ion-exchanged with small amounts of Fe2+ ions prior to H2O2 exposure. The degradation degree (defined as loss of ion-exchange capacity, weight, and fluoride content), water uptake, and conductivity of H2O2-exposed membranes were found to strongly depend on Fe content and H2O2 treatment time. SEM cross-sections showed that the degradation initially took place in the center of the membrane, while FTIR analysis revealed that Nafion degradation preferentially proceeds at the sulfonic end group and at the ether linkage located in the pendant side chain and that the H-bond of water is weakened after prolonged H2O2 exposure.

Magnetic alignment of nonmagnetic silicates caused by paramagnetic anisotropy: Origin of polarization observed in planetary formation region

Possible dust alignment in dense regions due to paramagnetic anisotropy ΔχPARA is discussed based on the results of a laboratory experiment on ortho-pyroxene grains containing a small amount of Fe2+ ions (1.8 mol%). Ortho-pyroxene has been detected in circum-stellar regions by infrared emission spectroscopy. Our experiment was performed at room temperature using He gas as the dispersing medium. Although the grains do not contain strong magnetic moments, alignment was achieved at low field strength (<2000 G). The alignment efficiency of ortho-pyroxene was compared with those of various rock-forming minerals. The magnitude of diamagnetic anisotropy ΔχDIA, free of paramagnetic ions, is generally <10-8 emu/g for various silicates. In contrast, ΔχPARA increases considerably with increasing Fe2+ concentration, reaching 10-5 emu/g for many of the silicates when the concentration of Fe2+ is >1 mol%; this increasing ΔχPARA is the cause of the above-mentioned alignment obtained at the low field strength. Based on our observations, we infer the field intensity needed to obtain partial dust alignment of sufficient size to explain the observed polarization in astrophysical environments. Due to temperature dependences caused by a Curie Law and a rotational Brownian motion, the field intensity required to cause the alignment is expected to decrease considerably at low-temperature conditions assumed for a proto-planetary disk. The results of our experiment performed at room temperature provide a technical basis to reproduce grain alignment under such temperature conditions.

Photoemission and x-ray absorption studies of valence states in (Ni,Zn,Fe,Ti)3O4 thin films exhibiting photoinduced magnetization

By means of photoemission and x-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)3O4 thin films, which exhibits a cluster glass behavior with a spin-freezing temperature Tf of ∼230K and photoinduced magnetization (PIM) below Tf. The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent (Fe3+) and tetravalent (Ti4+), respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe2+ ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.

Mössbauer study of glasses in meteorites: the D'Orbigny angrite and Cachari eucrite

Mossbauer spectroscopy measurements at room temperature (RT) and at liquid helium temperature (4.2 K) were carried out on bulk and glass samples from the D'Orbigny (angrite) and Cachari (eucrite) meteorites. The RT Mossbauer spectrum of the bulk sample of D'Orbigny shows the presence of Fe2+ in olivine and pyroxene and that of bulk Cachari contains only pyroxene. Very small amounts of Fe3+ are also present in the bulk samples, but are attributed to surface contamination. The RT spectra of the D'Orbigny and Cachari glasses are fitted with three doublets, which are assigned to Fe2+ at three different octahedral positions. No Fe3+ was detected in the glass samples. The spectra of the glasses measured at 4.2 K show the presence of relaxation effects. The results suggest a certain degree of structural ordering in these glasses.

Fault-Hosted Palygorskite from the Serrata De Níjar Deformation Zone (SE Spain)

AbstractPalygorskite fibers growing along fault planes in the outcrops of a large fault zone in SE Spain (Carboneras Fault Zone: CFZ; Serrata de Níjar) were studied by X-ray diffraction, scanning electron microscopy-energy dispersive X-ray analysis, and transmission electron microscopy-analytical electron microscopy. The structural formulae, calculated per half unit-cell, is: Si7.95Al0.05O20(Al1.93Fe0.08Mg1.92) (OH)2(OH2)4Na0.09K0.01Ca0.034(H2O). The samples have minor tetrahedral substitutions, with Mg/Al ratios close to one, and contain very small amounts of Fe3+. The number of octahedral cations per half unit-cell is 3.93. The fault-hosted palygorskite shows macroscopic ductile features including incipient foliation. Based on field and laboratory observations, as well as on regional geological evidence indicating the existence of widespread hydrothermal processes along the Serrata de Níjar and surrounding areas, we suggest that palygorskite may have formed during ongoing deformation in the CFZ, as a precipitate from Mg-rich hydrothermal fluids.

Structural locations of the iron ions in cordierite: a spectroscopic study

A series of 21 cordierites with 0.06 E-5(g) transition of octahedral Fe2+. The integral intensity of the beta- and gamma -polarized nu (3) band correlates linearly with the concentration of non-octahedral Fe2+. Its high molar extinction coefficient, ca. 150 cm(-2) 1 mol(-1), and temperature independence are best explained by its assignment to dd transitions of Fe2+ in tetrahedral coordination. There occurs also a broad band at 18,000 cm(-1) polarized predominantly along b. Its properties are typical of a metal-metal charge transfer (CT) band involving Fe2+ on the octahedra and Fe3+ on the T(1)1-tetrahedra, the two of which are edge-shared. All spectroscopic data, including changes in the electronic spectra caused by heating at 1,000 degreesC in air, as well as crystal-chemical considerations, suggest that the ring-connecting T(1)1-tetrahedra contain small amounts of Fe2+.

Phase relations in the system fayalite-magnetite at high pressures and temperatures

The phase relations in the Fe2SiO4–Fe3O4 binary system have been determined between 900 and 1200 °C and from 2.0 to 9.0 GPa. At low to moderate pressures magnetite can accommodate significant Si, reaching XFe2SiO4=0.1 and 0.2 at 3.0 and 5.0 GPa respectively, with temperature having only a secondary influence. At pressures below 3.5 GPa at 900 °C and 2.6 GPa at 1100 °C magnetite-rich spinel coexists with pure fayalite. This assemblage becomes unstable at higher pressures with respect to three intermediate phases that are spinelloid polytypes isostructural to spinelloids II, III and V in the Ni-aluminosilicate system. The phase relations between the spinelloid phases are complex. At pressures above ≈8.0 GPa at 1100 °C, the spinelloid phases give way to a complete spinel solid solution between Fe3O4 and Fe2SiO4. The presence of small amounts of Fe3+ stabilises the spinel structure to lower pressures compared to the Fe2SiO4 end member. This means that the fayalite–γ-spinel transition is generally unsuitable as a pressure calibration point for experimental apparatuses. The molar volumes of the spinel solid solutions vary nearly linearly with composition, having a small negative deviation from ideal behaviour described by Wv=−0.15(6) cm3. Extrapolation yields V°(298) = 41.981(14) cm3 for the Fe2SiO4-spinel end member. The cell parameters and molar volumes of the three spinelloid polytypes vary systematically with composition. Cation disorder is an important factor in stabilising the spinelloid polytypes. Each polytype exhibits a particular solid solution range that is directly influenced by the interplay between its structure and the cation distributions that are energetically favourable. In the FeO–FeO1.5–SiO2 ternary system Fe7SiO10 (“iscorite”) coexists with the spinelloid phases at intermediate pressures on the SiO2-poor, or Fe3+-poor side of the Fe2SiO4–Fe3O4 join. On the SiO2 and Fe3+-rich side of the join, orthopyroxene or high-P clinopyroxene coexists with the spinelloids and spinel solid solutions. The assemblage pyroxene+spinel+SiO2 is stable over a wide range of bulk composition. The stability of spinelloid III is of particular petrologic interest since this phase has the same structure as (Mg,Fe)2SiO4–wadsleyite, indicating that Fe3+ can be easily incorporated in this important phase in the Earth's transition zone, in addition to silicate spinel. This has important implications for the redox state of the Earth's transition zone and for the depth at which the olivine to spinel transition occurs in the mantle, potentially leading to a shift in the “410 km” seismic discontinuity to shallower depths depending on the prevailing redox state. In addition, a coupled tetrahedral substitution of Fe3++OH for Si+O could provide a further mechanism for the incorporation of H2O in wadsleyite.

Cordierite I: The coordination of Fe2+

The incorporation of Fe2+ was investigated in four natural cordierite samples. 57Fe Mössbauer, single-crystal UV-VIS optical absorption, and X-ray absorption spectroscopies, as well as X-ray single-crystal diffraction were used. Mössbauer, optical, and XAS spectroscopy show that Fe2+ is incorporated on two different structural sites in two Mg-rich samples. Mössbauer measurements give the best quantitative measure of the amounts of Fe2+, but the optical spectra are the most sensitive for determinations at low concentrations and at high-bulk Fe2+ concentrations in cordierite. The spectroscopic data are most consistent with small amounts of Fe2+ (i.e., 0.02 of Fe2+ per formula unit) being located on a tetrahedral site rather than in the center (or off center) of the six-membered tetrahedral rings or in channel cavities. X-ray single-crystal refinements on two Mg-rich cordierites show a very small excess electron density on T11 and not in the channels. A third refinement on a slightly more iron-rich sample shows, in contrast, no excess electron density on T11. We interpret these data as indicating that small amounts of Fe2+ (0.01 to 0.02 atoms per formula unit) replace tetrahedral Al11 in cordierite, where charge balance is achieved by placing Na in the center of the six-membered rings. This substitution is consistent with the known chemistry of natural cordierites and with simple structural energetics. The identification and assignment of small amounts of Fe2+ on T11 requires spectroscopic determination or careful X-ray single-crystal refinements and cannot be achieved from composition data and structural formula calculations.