Reduction and oxidation properties of Fe2O3/ZrO2 oxygen carrier for hydrogen production

Fe₂O₃ is a promising oxygen carrier for hydrogen production in the chemical-looping process. A set of kinetic studies on reduction with CH₄, CO and H₂ respectively, oxidation with water and oxygen containing Ar for chemical-looping hydrogen production was conducted. Fe₂O₃ (20 wt.%)/ZrO₂ was prepared by a co-precipitation method. The main variables in the TGA (thermogravimetric analyzer) experiment were temperatures and gas concentrations. The reaction kinetics parameters were estimated based on the experimental data. In the reduction by CH₄, CO and H₂, the reaction rate changed near FeO. Changes in the reaction rate due to phase transformation were observed at low temperature and low gas concentration during the reduction by CH₄, but the phenomenon was not remarkable for the reduction by CO and H₂. The reduction rate achieved using CO and H₂ was relatively faster than achieved using CH₄. The Hancock and Sharp method of comparing the kinetics of isothermal solid-state reactions was applied. A phase boundary controlled model (contacting sphere) was applied to the reduction of Fe₂O₃ to FeO by CH₄, and a different phase boundary controlled model (contacting infinite slab) was fit well to the reduction of FeO to Fe by CH₄. The reduction of Fe₂O₃ to Fe by CO and H₂ can be described by the former phase boundary controlled model (contacting sphere). This phase boundary controlled model (contacting sphere) also fit well for the oxidation of Fe to Fe₃O₄ by water and FeO to Fe₂O₃ by oxygen containing Ar. These kinetics data could be used to design chemical-looping hydrogen production systems.     

Electromagnetic interference shielding effectiveness of hybrid multifunctional Fe3O4/carbon nanofiber composite

Electromagnetic interference shielding effectiveness (EMI SE) of multifunctional Fe₃O₄/carbon nanofiber composites in the X-band region (8.2–12.4 GHz) is studied. Here, we examine the contributing effects of various parameters such as Fe₃O₄ content, carbonization temperature and thickness on total shielding efficiency (SE_total) of different samples. The maximum EMI SE of 67.9 dB is obtained for composite of 5 wt.% Fe₃O₄ (0.7 mm thick) with the dominant shielding by absorption (SE_A) of electromagnetic radiation. The enhanced electromagnetic shielding performance of Fe₃O₄/carbon nanofiber composites is attributed to the increment of both magnetic and dielectric losses due to the incorporation of magnetite nanofiller (Fe₃O₄) in electrically conducting carbon nanofiber matrix as well as the specific nanofibrous structure of carbon nanofiber mats, which forms a higher aspect ratio structure with randomly aligned nanofibers. Furthermore, we prove that the addition of elastomeric polydimethylsiloxane (PDMS) as a coating for carbon nanofiber composite strengthens the composite structure without interfering with its electromagnetic shielding efficiency.     

Large-scale fine structural alumina matrix ceramic guideway materials improved by diopside and Fe2O3

Diopside and Fe₂O₃ were introduced in alumina matrix ceramic materials. Large-scale fine structural alumina matrix ceramic guideway materials were fabricated by the technology of pressureless sintering, during which liquid phase sintering took place and new phases such as 3Al₂O₃·2SiO₂, CaO·Al₂O₃·2SiO₂ and CaO·6Al₂O₃ were produced by the chemical reactions taking place among alumina and the additives. The hardness, the fracture toughness and the bending strength of the guideway products were tested. The influences of diopside and Fe₂O₃ additions were studied by microstructural observations and mechanical properties evaluations. Meanwhile, the expected improvement of mechanical properties compared with pure alumina was indeed observed. The fracture mechanism and porosity of large-scale fine structural alumina matrix ceramic guideway materials were analyzed.     

An efficient electron transfer at the Fe/iron oxide interface for the photoassisted degradation of pollutants with H2O2

Fe-200 was synthesized through the calcination of iron powder at 200 °C for 30 min in air. On the basis of characterization by X-ray diffraction and X-ray photoelectron spectroscopy, Fe-200 had a core–shell structure, in which the surface layer was mainly composed of Fe₂O₃ with some FeOOH and FeO, and the core retained metallic iron. The kinetics and mechanism of the interfacial electron transfer on Fe-200 were investigated in detail for the photoassisted degradation of organic pollutants with H₂O₂. Under deoxygenated conditions in the dark, the generation of hydroxyl radicals in aqueous Fe-200 dispersion verified that galvanic cells existed at the interface of Fe⁰/iron oxide, indicating the electron transfer from Fe⁰ to Fe³⁺. Furthermore, the effects of hydrogen peroxide and different organic pollutants on the interfacial electron transfer were examined by the change rate of the Fe³⁺ concentration in the solution. The results indicated that hydrogen peroxide provided a driving force in the electron transfer from Fe²⁺ to Fe³⁺, while the degradation of organic pollutants increased the electron transfer at the interface of Fe⁰/iron oxide due to their reaction with OH.     

Electromagnetic properties of electrospun Fe3O4/carbon composite nanofibers

In order to develop multifunctional nanofibers, the electrical conductivity and magnetic properties of Fe₃O₄/carbon composite nanofibers have been examined. Polyacrylonitrile (PAN) is used as a matrix to produce magnetic composite nanofibers containing different amounts of magnetite (Fe₃O₄) nanoparticles. Electrospun composite nanofibers were thermally treated to produce electrically conductive and magnetically permeable composite carbon nanofibers. The composite nanofibers were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), Raman spectroscopy, four-point probe and Superconducting Quantum Interference Device (SQUID). Uniform nanofibers were obtained with successful transferring of magnetic properties of Fe₃O₄ into the as-spun composite nanofibers. The electromagnetic properties were tuned by adjusting the amount of Fe₃O₄ in the matrix and carbonization process. The electrical conductivity, magnetic moment and also magnetic hysteresis rise up by adding Fe₃O₄ and increasing carbonization temperature. The high surface area provided by the ultrafine fibrous structures, the flexibility and tuneable electromagnetic properties are expected to enable the expansion of the design options for a wide rage of electronic devices.     

Superior thermal stability of polymer capped Fe3O4 magnetic nanoclusters

In general, the technologically important ferrites nanoparticles, magnetite and maghemite, are converted from cubic to the more stable rhombohedral structure above 500°C‐700°C under air/vacuum/inert atmosphere. Here, we report, the superior thermal stability of polymer capped Fe₃O₄ (PCIO) nanocluster (synthesized using microwave‐assisted polyol approach) up to 1000°C under vacuum and inert atmosphere. Raman spectra of post annealed PCIO nanoclusters show the Fe₃O₄ phase with carbon signature due to the decomposition of polymer matrix. The carbon layer seems to act as a thermal shield and increases the activation energy thereby preventing the intrusion of heat, oxygen, volatiles mass into the magnetic core. The presence of carbon layer was further confirmed from the high‐resolution transmission electron microscopic image. After thermal annealing at 1000°C, PCIO nanoclusters showed superparamagnetic behavior with a saturation magnetization of 89 emu/g, close to the bulk saturation magnetization of Fe₃O₄ phase. In contrast, the uncoated Fe₃O₄ (UCIO) nanoclusters decompose at 700°C into α‐Fe₂O₃ and FeO phases under similar annealing conditions. Our findings open up new possibilities of stabilizing nanomaterials for high‐temperature applications.     

Transformations of Iron (III) Precursors in a Wave of Flameless RDX Combustion

Flameless combustion of 40% Fe₂O₃ – 40% RDX – 20% HDI (mix I) and 30% CoCO₃ – 15% iron formate – 40% RDX – 15% HDI (mix II) systems was explored by time-resolved X-ray diffraction (TRXRD). In case of mix I, the reaction was found to proceed via the formation of FeO intermediate: Fe₂O₃ → FeO → Fe₃O₄. Variation in the extent of iron reduction was associated with dynamic temperature change and a reductant content of the reaction zone. The reduction proceeded as a solid-state reaction, without amorphization of the structure. The process in system II involved the formation of CoO and FeO intermediates. Further reduction – up to metals – takes place behind the combustion front and yields a mixture of nanosized Co, Fe, and Co_0.7Fe_0.3 particles. Exposure of hot reaction products – nano-sized Co and Fe – to the air leads to their self-ignition and formation of Co₃O₄ and Fe₃O₄, respectively.     

Microwave-assisted solution combustion synthesis of Fe3O4 powders

Magnetite (Fe₃O₄) powders were synthesized by solution combustion method at different fuel to oxidant ratios (ϕ = 0.5, 0.75, 1 and 1.5) using conventional and microwave ignition. The ignition method and fuel content affected the phase evolution, microstructure and magnetic properties of Fe₃O₄ powders as characterized by X-ray diffractometry, infrared spectroscopy, N₂ adsorption–desorption, electron microscopy and vibrating sample magnetometry techniques. Single phase Fe₃O₄ powders were only obtained using conventional ignition at ϕ value of 1, while the impurity phases such as α-Fe₂O₃ and FeO together with Fe₃O₄ phase were formed by microwave ignition. The bulky microstructure of conventionally combusted powders with specific surface area of 71.5 m²/g was transformed to disintegrated structure (76.5 m²/g) by microwave heating. The microwave combusted powders showed the highest saturation magnetization of 86.5 emu/g at ϕ value of 0.5 and the lower coercivity than that of conventionally combusted powders at all ϕ values, due to their larger particles.     

Optimal synthesis and new understanding of P2-type Na2/3Mn1/2Fe1/4Co1/4O2 as an advanced cathode material in sodium-ion batteries with improved cycle stability

A sol-gel method with ethylene diamine tetraacetic acid and citric acid as co-chelates is employed for the synthesis of P2-type Na_2/3Mn_1/2Fe_1/4Co_1/4O₂ as cathode material for sodium-ion batteries. Among the various calcination temperatures, the Na_2/3Mn_1/2Fe_1/4Co_1/4O₂ with a pure P2-type phase calcined at 900 °C demonstrates the best cycle capacity, with a first discharge capacity of 157 mA h g^?1 and a capacity retention of 91 mA h g^?1 after 100 cycles. For comparison, the classic P2-type Na_2/3Mn_1/2Fe_1/2O₂ cathode prepared under the same conditions shows a comparable first discharge capacity of 150 mA h g^?1 but poorer cycling stability, with a capacity retention of only 42 mA h g^?1 after 100 cycles. Based on X-ray photoelectron spectroscopy, the introduction of cobalt together with sol-gel synthesis solves the severe capacity decay problem of P2-type Na_2/3Mn_1/2Fe_1/2O₂ by reducing the content of Mn and slowing down the loss of Mn on the surface of the Na_2/3Mn_1/2Fe_1/4Co_1/4O₂, as well as by improving the activity of Fe³⁺ and the stability of Fe⁴⁺ in the electrode. This research is the first to demonstrate the origin of the excellent cycle stability of Na_2/3Mn_1/2Fe_1/4Co_1/4O₂, which may provide a new strategy for the development of electrode materials for use in sodium-ion batteries.     

Porous Fe3O4/C microspheres for efficient broadband electromagnetic wave absorption

Porous Fe₃O₄/C microspheres, which were Fe₃O₄ nanocrystals (～8?nm) embedded in an open nanostructured carbon network, were successfully synthesized via a facile hydrothermal process. The porous Fe₃O₄/C microspheres possessed many distinct attributes that facilitate efficient broadband electromagnetic wave absorption (EMWA). EMWs were attenuated through multiple reflections and absorption in the 3D interconnected porous structure of the microspheres; these processes collectively improved the interaction between the EMWs and the absorber. Additionally, the carbon network and embedded Fe₃O₄ nanoparticles caused significant dielectric losses and magnetic losses, respectively, which also enhanced EMWA. The EMWA characteristics of the microspheres could be precisely tuned via changing the carbon content to achieve optimized impedance matching. Porous Fe₃O₄/C microspheres with a 71.5?wt% carbon content displayed particularly impressive EMWA properties: a maximum reflection loss (RL) value of ??31.75 across broad band frequencies in the range of 7.76–12.88?GHz (RL < ?10?dB) at an absorber thickness of 3.0?mm. These excellent EMWA properties may be attributed to both dielectric loss (carbon) and magnetic loss (Fe₃O₄). Additionally, the 3D interconnected porous structure of the Fe₃O₄/C microspheres is especially favorable for impedance matching.     

Enhanced cycling performance of Fe3O4-graphene nanocomposite as an anode material for lithium-ion batteries

Fe₃O₄-graphene nanocomposite was prepared by a gas/liquid interface reaction. The structure and morphology of the Fe₃O₄-graphene nanocomposite were characterized by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The electrochemical performances were evaluated in coin-type cells. Electrochemical tests show that the Fe₃O₄-22.7 wt.% graphene nanocomposite exhibits much higher capacity retention with a large reversible specific capacity of 1048 mAh g⁻¹ (99% of the initial reversible specific capacity) at the 90th cycle in comparison with that of the bare Fe₃O₄ nanoparticles (only 226 mAh g⁻¹ at the 34th cycle). The enhanced cycling performance can be attributed to the facts that the graphene sheets distributed between the Fe₃O₄ nanoparticles can prevent the aggregation of the Fe₃O₄ nanoparticles, and the Fe₃O₄-graphene nanocomposite can provide buffering spaces against the volume changes of Fe₃O₄ nanoparticles during electrochemical cycling.     

Mechanistic investigation of chemical looping combustion of coal with Fe2O3 oxygen carrier

The reaction of three Chinese coals with Fe₂O₃ oxygen carrier (OC) was performed in a thermogravimetric analyzer (TGA), with special focuses on the effects of varying heating rate and coal rank on reactivity. Fourier transform infrared spectroscopy (FTIR) was used to in situ detect the emitted gases from TGA. Field scanning electron microscopy/energy-dispersive X-ray spectrometry (FSEM-EDX) was used to study the morphology and elemental compositions of the reaction residues collected from TGA and the related phase evaluation was further identified by X-ray diffraction (XRD). Through all these experiments, it was found that the pyrolysis of coal samples without Fe₂O₃ OC under N₂ atmosphere underwent the dehydration and the ensuing primary and secondary pyrolysis stages. The increasing heating rate shifted the characteristic temperature (T_m) of the primary pyrolysis to a higher temperature and favored a more rapid generation of volatile matters. When the three coals reacting with Fe₂O₃ OC, TGA results demonstrated even over 200 °C, the reaction still experienced the partial pyrolysis at the relatively low temperature and the ensuing two reactions of Fe₂O₃ with the pyrolysis products at the primary and secondary stages. The coal of low rank with high volatile content should be preferred for the full conversion of coal into CO₂. Furthermore, the activation energy of Fe₂O₃ OC reacting with PDS at its primary pyrolysis stage was the largest, more than 70 kJ/mol. Finally, SEM-EDX and further XRD analysis of the residues from the reaction of PDS with Fe₂O₃ OC indicated the reduced counterpart of Fe₂O₃ was Fe₃O₄, and some inert iron compounds such as Fe₂SiO₄ and FeAl₂O₄ were also generated, which might deteriorate the reactivity of Fe₂O₃ OC.     

Synthesis and strengthened microwave absorption properties of three-dimensional porous Fe3O4/graphene composite foam

The three-dimensional porous Fe₃O₄/graphene composite foam as a new kind of absorbing composite with electrical loss and magnetic loss was successfully synthesized by a facile method. Fe₃O₄ was evenly attached on structure of graphene sheets which overlapped with each other to form three-dimensional porous graphene foam. The results revealed that when the mass ratio of graphene oxide (GO) and Fe₃O₄ was 1:1, the Fe₃O₄/graphene composite foam possessed the best absorption properties: the minimum reflection loss was up to ??45.08?dB when the thickness was 2.5?mm and the bandwidth below ??10?dB was 6.7?GHz when the content of the composite foam absorbents was just 8%. The micron-sized three-dimensional porous structure provided more propagation paths, enhancing the energy conversion of incident electromagnetic waves. The addition of Fe₃O₄ contributed to improving the impedance matching performance and magnetic loss. The three-dimensional porous Fe₃O₄/graphene composite foam was a kind of high-efficiency wave absorber, providing a new idea for the development of microwave absorbing materials.     

Magnetic-field-induced Fe3O4@CNTs/PES/SPSf composite membrane for efficient removal of methylene blue by adsorption and catalytic degradation

Novel composite membranes are successfully developed for adsorption and catalytic degradation of methylene blue (MB) by blending Fe₃O₄-coated CNTs (Fe₃O₄@CNTs) nanoparticles in polyethersulfone (PES) and sulfonated polysulfone (SPSf) matrix via nonsolvent-induced phase separation (NIPS) method assisted by magnetic field. Fe₃O₄@CNTs nanoparticles migrate to the separation layer under the induction of magnetic field, thus Fe₃O₄@CNTs/PES/SPSf composite membranes prepared under magnetic field exhibit a better dye removal ability compared with that without magnetic field. The MB removal ratio by Fe₃O₄@CNTs/PES/SPSf composite membrane containing 8 wt% Fe₃O₄@CNTs (M2−M) can reach up to 99% in 30 min under the conditions of 0.25 g composite membrane, 20 mg/L MB, 0.1 mol/L H₂O₂, pH = 3 and 80°C. Furthermore, the composite membranes show excellent recycling performance, as the MB removal capacity remains at 99% even after four cycles.     

Phase equilibria in the Fe-V-O system near “FeO”-V2O3 isopleth

Phase equilibria in the “FeO”-V₂O₃ system from 1273 to 1808 K and in the range of oxygen partial pressure from 10⁻¹⁵ to 10⁻⁴ atm are investigated. High-temperature quenching, XRD, SEM-EDS, and DSC are used to determine the phase relations. Stable regions of (FeO)_s.s., (V₂O₃)_s.s., and spinel phases are considerably effected by the oxygen partial pressure, and structural models are proposed as (Fe²⁺, Fe³⁺, V²⁺)_1-xO, (V²⁺, V³⁺, V⁴⁺, Fe³⁺)₂O_3+x, and (Fe²⁺, Fe³⁺, V³⁺)(Fe²⁺, Fe³⁺, V³⁺, Va)₂O₄. Continuous solid solution FeV₂O₄-Fe₃O₄ is formed. The nonstoichiometry of FeV₂O₄ is attributed to the appearance of vanadium vacancies for electroneutrality due to the oxidation of Fe²⁺. The standard Gibbs energy of formation for FeV₂O₄ and component activities in FeV₂O₄-Fe₃O₄ solid solution at 1623 and 1773 K are derived based on the equilibrium oxygen partial pressure. The cation distribution in FeV₂O₄ at different temperatures is obtained according to site preference energy.     

Preparation of Pt nanoparticle-loaded three-dimensional Fe3O4/carbon with high electro-oxidation activity

A three-dimensional (3D) Fe₃O₄/carbon material functionalized with amino and hydroxyl groups was synthesized by decomposing 2,4,5-trichlorophenol/ferrocene mixture in the presence of ammonia and polyethylene glycol in solvothermal conditions at 250 °C for 30 h by a one-step process. The 3D Fe₃O₄/carbon materials can be loaded with Pt nanoparticles without adding any reducing agent; Pt-loaded 3D Fe₃O₄/carbon hybrid materials have superior electrochemical catalytic activity toward methanol oxidation and the oxidation current density on them is nearly triple that on a commercial Pt/C catalyst.     

Synthesis of a TiO2 ceramic membrane containing SrCo0.8Fe0.2O3 by the sol-gel method with a wet impregnation process for O2 and N2 permeation

A SrCo_0.8Fe_0.2O₃ impregnated TiO₂ membrane (TiO₂-SrCo_0.8Fe_0.2O₃ membrane) was successfully prepared using a sol-gel method in combination with a wet impregnation process. The membrane was subjected to a single gas permeance test using oxygen (O₂) and nitrogen (N₂). The TiO₂ membrane was immersed in the SrCo_0.8Fe_0.2O₃ solution, dried and then calcined to affix SrCo_0.8Fe_0.2O₃ into the membrane. The effect of the acid/alkoxide (H⁺/Ti⁴⁺) molar ratio of the TiO₂ sol on the TiO₂ phase transformation was investigated. The optimal molar ratio was found to be 0.5, which resulted in nanoparticles with a mean size of 5.30 nm after calcination at 400 °C. The effect of calcination temperature on the phase transformation of TiO₂ and SrCo_0.8Fe_0.2O₃ was investigated by varying the calcination temperature from 300 to 500 °C. X-ray diffraction spectroscopy (XRD) and Fourier transform infrared (FTIR) analysis confirmed that a calcination temperature of 400 °C was preferable for preparing a TiO₂-SrCo_0.8Fe_0.2O₃ membrane with fully crystallized anatase and SrCo_0.8Fe_0.2O₃ phases. The results also showed that polyvinyl alcohol (PVA) and hydroxypropyl cellulose (HPC) were completely removed. Field emission scanning electron microscopy (FESEM) analysis results showed that a crack-free and relatively dense TiO₂ membrane (∼0.75 μm thickness) was created with a multiple dip-coating process and calcination at 400 °C. The gas permeation results show that the TiO₂ and TiO₂-SrCo_0.8Fe_0.2O₃ membranes exhibited high permeances. The TiO₂-SrCo_0.8Fe_0.2O₃ membrane developed provided greater O₂/N₂ selectivity compared to the TiO₂ membrane alone.     

Electrospun polyacrylonitrile nanocomposite fibers reinforced with Fe3O4 nanoparticles: Fabrication and property analysis

The manufacturing of pure polyacrylonitrile (PAN) fibers and magnetic PAN/Fe₃O₄ nanocomposite fibers is explored by an electrospinning process. A uniform, bead-free fiber production process is developed by optimizing electrospinning conditions: polymer concentration, applied electric voltage, feedrate, and distance between needle tip to collector. The experiments demonstrate that slight changes in operating parameters may result in significant variations in the fiber morphology. The fiber formation mechanism for both pure PAN and the Fe₃O₄ nanoparticles suspended in PAN solutions is explained from the rheologial behavior of the solution. The nanocomposite fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectrophotometer, and X-ray diffraction (XRD). FT-IR and XRD results indicate that the introduction of Fe₃O₄ nanoparticles into the polymer matrix has a significant effect on the crystallinity of PAN and a strong interaction between PAN and Fe₃O₄ nanoparticles. The magnetic properties of the nanoparticles in the polymer nanocomposite fibers are different from those of the dried as-received nanoparticles.     

Nanocomposite Fe2O3-Se as a new lithium storage material

The electrochemical properties of nanocomposite Fe₂O₃-Se thin film prepared by pulsed laser deposition (PLD) method have been investigated by cyclic voltammetry and charge/discharge measurements. A large reversible capacity of nanocomposite Fe₂O₃-Se thin film was found to be around 650 mAh g⁻¹. A new couple of reduction and oxidation peaks at 1.4 and 1.8 V were observed from cyclic voltammogram for the first time. Our data demonstrated that nanocomposite Fe₂O₃-Se exhibit larger capacity and better cycle performance than pure Fe₂O₃. The electrochemical reaction mechanisms of Fe₂O₃-Se with lithium were examined by X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED). The reversible conversions reaction of nanosized metal Fe with Li₂Se and Li₂O formed after initial discharge process into FeSe and Fe₂O₃ respectively were revealed.     

Selective synthesis of mixed alcohols from syngas over catalyst Fe2O3/Al2O3 in slurry reactor

The Fe₂O₃/Al₂O₃ catalyst was studied to selectively synthesize mixed alcohols from syngas in a continuously stirred slurry reactor with the oxygenated solvent Polyethylene Glycol-400 (PEG-400). The selectivity of mixed alcohols in the products reached as high as 95 wt.% and the C₂₊ alcohols (mainly ethanol) was more than 40 wt.% in the total alcohol products at the reaction conditions of 250 °C, 3.0 MPa, H₂/CO = 2 and space velocity = 360 ml/g_cat h. The hydrogen temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) measurements of the catalyst confirmed that the FeO phase was responsible for the high selectivity to mixed alcohols in the process. And the oxygenated solvent PEG-400 was also necessary for the selective synthesis of mixed alcohols in the reaction system.