Ternary MIL-100(Fe)@Fe3O4/CA magnetic nanophotocatalysts (MNPCs): Magnetically separable and Fenton-like degradation of tetracycline hydrochloride

Today’s world, tetracycline hydrochloride (TC) is considered as a Compounds of Emerging Concern (CECs). Metal-organic frameworks MOFs with a microporous structure and holding larger pores indicating potential applications in the fields of environmental purification. Recently, carbon aerogel (CA) has also aroused great interest due to its larger specific surface area, low density, thermal stability, and non-toxicity. Herein, MIL-100(Fe) was synthesized under low temperature and combined with Fe₃O₄ and CA, respectively. The obtained MIL-100(Fe), MIL-100(Fe)@Fe₃O₄, MIL-100(Fe)@CA and MIL-100(Fe)@Fe₃O₄/CA were investigated as a photocatalyst for removal of TC from the water. The results indicated that the MIL-100(Fe)@Fe₃O₄/CA degrade TC up to 85%, which is much higher than MIL-100(Fe)@Fe₃O₄ (c.a. 42%), due to its high surface area 389?m²?g^?1, smaller pore size and pore volume 2.4?nm and 0.319?m³?g^?1, high separation of electron and hole, and lower band gap of 1.76?eV. The coupling of CA with MIL-100(Fe)@Fe₃O₄ considerably accelerate the transfer of photo-generated charge carriers and enhanced 1.6 times the performance of MIL-100(Fe)@Fe₃O₄. Furthermore, the stability and recyclability were enhanced due to the addition of Fe₃O₄, facilitating the environmentally friendly water purification processes.     

Application of multi-functional chestnut shell in one-step preparing Fe3O4@C magnetic nanocomposite with high adsorption performance

Chestnut shell (CS) acts as a multi-functional material in the one-step preparation of Fe₃O₄@C nanocomposite via hydrothermal method by using Fe(NO₃)₃ as Fe source without adding any other additives. The characterized results show that under required hydrothermal conditions, a proper amount of CS can reduce a certain amount of adsorbed/enriched Fe³⁺ to Fe²⁺ to ensure the 2:1 molar ration of Fe³⁺ to Fe²⁺ and the in-situ formation of goal phase Fe₃O₄ on the surface of the CS. Meanwhile, CS is carbonized to C material similar to graphene oxide. In the preparation process of the composite of Fe₃O₄@C, CS plays multiple roles, such as promoter, reductive agent, C-source, and template, to endow a certain morphology of the nanocomposite Fe₃O₄@C. The composite material shows good magnetic separability and adsorption property for methylene blue (MB) solution. Furthermore, the adsorptive kinetic behavior of the Fe₃O₄@C is investigated. The method is simple, fast, low cost and green and really realizes the full use of wasteful resource CS.     

Preparing particulate magnetites with pigment properties from suspensions of basic iron(III) sulphates with the structure of jarosite

The transformation of a suspension of hydronium jarosite, H₃O⁺Fe₃(SO₄)₂(OH)₆, into Fe₃O₄ (magnetite) of pigment quality is described. The process consists in the neutralization of the hydronium jarosite suspension in FeSO₄ aqueous solutions with NH₃ and subsequent thermal treatment of this mixture at controlled pH and temperature.     

Synthesis of nanostructured M/Fe3O4 (M = Ag,Cu) composites using hexamethylentetramine and their electrocatalytic properties

Nanoscaled Ag/Fe₃O₄ hybrids with different Ag contents and Cu/Fe₃O₄ nanoshpere and microsphere were successfully synthesized with assistance of sodium citrate and (CH₂)₆N₄ via a hydrothermal process. The as-prepared samples were identified and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS), respectively. All samples were used as electrocatalysts modified on a glassy carbon electrode for p-nitrophenol reduction in a basic solution. The catalytic activity of Ag/Fe₃O₄ samples increased first and then decreased by increasing Ag content from 0% to 8%, and the one with 6% Ag displayed the highest catalytic activity. All the Cu/Fe₃O₄ samples exhibited enhanced catalytic activity by comparison with a glassy carbon electrode, and the one prepared with the molar ratio of Cu²⁺, Fe³⁺, citrate anion, and (CH₂)₆N₄ with 1:1:3:5 exhibited the highest catalytic activity.     

Redox behavior and reduction mechanism of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–CeZrO<Subscript>2</Subscript> as oxygen storage material

Fe₂O₃–CeZrO₂ is a suitable oxygen storage material for the production of pure hydrogen by a cyclic water gas shift (CWGS) process which is based on the reduction of the material by syngas followed by the re-oxidation of the reduced material with water vapor. For identification of the reduction kinetics H₂-temperature programmed reduction experiments were performed. Several kinetic models were tested and the activation energy of reduction was calculated by the Kissinger method, by model-based curve fitting and by the isoconversional analysis method. The reduction of Fe₂O₃–CeZrO₂was found to occur in a four-step process including the reduction of Fe₂O₃,Fe₃O₄, and CeZrO₂. The overall process can be interpreted as phase-boundary controlled reduction of Fe₂O₃ to Fe₃O₄, and two-dimensional nucleation controlled reduction of Fe₃O₄ to Fe and of CeO₂ to Ce₂O₃. At higher oxygen conversion, the reduction of Fe₃O₄ and CeO₂ are significantly influenced by volume-diffusion in the solid bulk.     

Preparation of reduced graphene oxide-NiFe2O4 nanocomposites for the electrocatalytic oxidation of hydrazine

A reduced graphene oxide (RGO)-NiFe₂O₄ nanocomposite was synthesized by a simple one step hydrothermal approach and its application in the electrocatalytic oxidation of hydrazine was demonstrated. The as-synthesized nanocomposite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV–visible spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Thermogravimetric analysis, Field emission-scanning electron microscopy (FE-SEM), and Transmission electron microscopy (TEM). The FE-SEM and TEM image analyses revealed that the NiFe₂O₄ nanoparticles were uniformly distributed on the RGO sheets with a diameter and length of ∼10 and ∼100 nm, respectively. The XPS analysis confirmed the ionic states of Ni and Fe to be Ni³⁺ and Ni²⁺, and Fe²⁺ and Fe³⁺, respectively. Further, the electrochemical activity of the RGO-NiFe₂O₄ nanocomposite was investigated by studying the oxidation of hydrazine. The RGO-NiFe₂O₄ modified glassy carbon electrode (GCE) showed an outstanding electrocatalytic activity towards the oxidation of hydrazine as compared to the NiFe₂O₄ and RGO modified electrodes. The enhanced electrocatalytic activity is due to the synergistic effect between RGO and NiFe₂O₄. Using amperometry, the lowest detection limit of 200 nM was achieved with the RGO-NiFe₂O₄ modified GCE. Therefore, the RGO-NiFe₂O₄ modified GCE can be used for the electrochemical oxidation of hydrazine.     

Magnetic nanoparticles and nanoparticle assemblies from metallorganic precursors

Magnetic nanoparticles of -Fe₂O₃, Fe₂O₃SiO₂ composite and magnetite Fe₃O₄ have been prepared using novel metallorganic precursors Fe[NC(C₆H₄)C(NSiMe₃)₂]₂Cl, Fe₂[O₂Si(C₆H₅)₂]₃ and [Fe(OBu^t)₃Na(THF)]₂) by hydrolysis, sol-gel condensation and further ultrasound and thermal treatment of the samples. The nanoparticles have been investigated by X-ray powder diffraction, TEM, SEM and AFM.     

Ferromagnetism and Morphology of Annealed Fe2O3/CoXOY/ZnO Thin Films

We have studied thermal solid‐state reactions in the Fe₂O₃/Co_XO_Y/ZnO thin film systems grown using the atomic layer deposition technique. The compound produced after annealing at 700 °C is found to be a complex mixture of three different spinel phases: ZnCo₂O₄, CoFe₂O₄, and ZnFe₂O₄. The magnetic properties of the compound strongly depend on the atomic ratio of Fe³⁺ and Co²⁺ atoms, which can be set by choosing the corresponding thicknesses of the Fe₂O₃ and Co_XO_Y films. In addition, we also find a formation of 100 nm voids at the interface between Fe–Co–Zn–O compound and remaining ZnO film after 1h annealing at 700 °C in argon atmosphere. The formation of these voids shows indirectly the preferential outward diffusion of Zn²⁺ ions from ZnO into the Fe₂CoO₄ phase layer what we prove via our magnetic measurements.     

Direct synthesis of mesoporous Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> through citric acid-assisted solid thermal decomposition

A simple and inexpensive approach to synthesizing mesoporous Fe₃O₄ is developed by using citric acid-assisted solid thermal decomposition of ferric nitrate. The structure and magnetic property of mesoporous Fe₃O₄ were characterized by XRD, FT–IR, N₂ adsorption–desorption isotherms, TEM, and vibrating sample magnetometer. It was shown that the decomposition of citric acid results in the formation of the mesoporous structure and narrow pore-size distribution. The reducing atmosphere which created by the decomposition of the ferric nitrate–citric acid complex caused the partial reduction of Fe(III) to Fe(II) and in turn the formation of Fe₃O₄. Moreover, the strength of the coordination between carboxyl group and Fe³⁺ also affected the phase composition of the iron oxides.     

Chemical vapor deposition growth of Fe3O4 thin films and Fe/Fe3O4 bi-layers for their integration in magnetic tunnel junctions

A possible route for the synthesis of Fe₃O₄, Fe, and Fe/Fe₃O₄ bi-layers with chemical vapor deposition by employing the same Fe₃(CO)₁₂ carbonyl precursor is presented. The comprehensive structural, chemical, and morphological investigation of the as-deposited thin single films and bi-layers is performed by X-ray diffraction, X-ray reflectivity, Raman spectroscopy, and time-of-flight secondary ion mass spectrometry depth profiling. We present the possibility of performing the deposition of pure metallic Fe and Fe₃O₄/γ-Fe₂O₃ by adjusting the deposition pressure from 10^- 3/^- 4 Pa to 1 Pa, respectively. The integration of Fe₃O₄ thin films in a magnetic tunnel junction stack fully synthesized by in situ atomic layer and chemical vapor deposition processes is also presented, showing good stack stability and marginal interdiffusion.     

Fabrication of Fe3O4 Dots Embedded in 3D Honeycomb‐Like Carbon Based on Metallo–Organic Molecule with Superior Lithium Storage Performance

A novel metallo–organic molecule, ferrocene, is selected as building block to construct Fe₃O₄ dots embedded in 3D honeycomb‐like carbon (Fe₃O₄ dots/3DHC) by using SiO₂ nanospheres as template. Unlike previously used inorganic Fe₃O₄ sources, ferrocene simultaneously contains organic cyclopentadienyl groups and inorganic Fe atoms, which can be converted to carbon and Fe₃O₄, respectively. Atomic‐scale Fe distribution in started building block leads to the formation of ultrasmall Fe₃O₄ dots (≈3 nm). In addition, by well controlling the feed amount of ferrocene, Fe₃O₄ dots/3DHC with well‐defined honeycomb‐like meso/macropore structure and ultrathin carbon wall can be obtained. Owing to unique structural features, Fe₃O₄ dots/3DHC presents impressive lithium storage performance. The initial discharge and reversible capacities can reach 2047 and 1280 mAh g^?1 at 0.05 A g^?1. With increasing the current density to 1 and 3 A g^?1, remarkable capacities of 963 and 731 mAh g^?1 remain. Moreover, Fe₃O₄ dots/3DHC also has superior cycling stability, after a long‐term charge/discharge for 200 times, a high capacity of 1082 mAh g^?1 can be maintained (80% against the capacity of the 2nd cycle).     

Single Unit-Cell Layered Bi2Fe4O9 Nanosheets: Synthesis,Formation Mechanism,and Anisotropic Thermal Expansion

As an important multiferroic material, pure and low-dimensional phase-stable bismuth ferrite has wide applications. Herein, one-pot hydrothermal method was used to synthesize bismuth ferrite. Almost pure Bi₂Fe₄O₉, BiFeO₃, and their mixture were successfully obtained by controlling the KOH concentration in the hydrothermal solutions. The as-prepared Bi₂Fe₄O₉ products were crystalline with Pbam space group, had nanosheet morphology, and tended to aggregate into nanofloret or random stacking. Each Bi₂Fe₄O₉ nanosheet was a single crystal with (001) plane as its exposed surface. Single unit-cell layered Bi₂Fe₄O₉ nanosheets had a uniform thickness of 1 nm. The surface energies of various (100), (010), and (001) planes were 3.6–4.0, 5.6–15.1, and 1.7–3.0 J m⁻², respectively, in the Bi₂Fe₄O₉ crystal. The formation mechanism and structural model of the as-prepared single unit-cell layered Bi₂Fe₄O₉ nanosheets have been given. The growth of Bi₂Fe₄O₉ nanosheets was discussed. Thermal analysis showed that the Bi₂Fe₄O₉ phase was stable up to 1260 K. The thermal expansion behavior of the Bi₂Fe₄O₉ nanosheet was nonlinear. The thermal expansion coefficients of the ultrathin Bi₂Fe₄O₉ nanosheets on the a-, b-, c-axes, and on the unit-cell volume V were determined, showing an anisotropic thermal expansion behavior. This study is helpful for the controllable synthesis of ultrathin Bi₂Fe₄O₉ nanosheets.     

Modulation of Inverse Spinel Fe3O4 by Phosphorus Doping as an Industrially Promising Electrocatalyst for Hydrogen Evolution

Fe‐based oxides have been seldom reported as electrocatalysts for the hydrogen evolution reaction (HER), limited by their weak intrinsic activity and conductivity. Herein, phosphorus doping modulation is used to construct inverse spinel P‐Fe₃O₄ with dual active sites supported on iron foam (P‐Fe₃O₄/IF) for alkaline HER with an extremely low overpotential of 138 mV at 100 mA cm^?2. The obtained inverse spinel Fe–O–P derived from controllable phosphorization can provide an octahedral Fe site and O atom, which bring about the unusual dissociation mechanisms of two water molecules to greatly accelerate the proton supply in alkaline media. Meanwhile, the ΔG_H of the P atom in Fe–O–P as an active site is theoretically calculated to be 0.01 eV. Notably, the NiFe LDH/IF⁽⁺⁾||P‐Fe₃O₄/IF^(?) couple achieves an onset potential of 1.47 V (vs RHE) for overall water splitting, with excellent stability for more than 1000 h at a current density of 1000 mA cm^?2, and even for 25 000 s at 10 000 mA cm^?2 in 6.0 m KOH at 60 °C. The excellent catalyst stability and low‐cost merits of P‐Fe₃O₄/IF may hold promise for industrial hydrogen production. This work may reveal a new design strategy of earth‐abundant materials for large‐scale water splitting.     

Oxidation of ferritic steels dispersion strengthened with TiO2 and Y2O3 oxides in lead melt

We study the structure and composition of scales formed during the contact of Fe–13Cr–2Motype ferritic steels hardened with oxides TiO₂ and Y₂O₃ with oxygen-containing (10⁻³ mass% O) lead melt at 550°C for 1000 h. It is established that a Fe₃ O₄ – Fe (Fe_{1 − x} , Cr _x )₂ O₄ two-layer scale forms. Its upper layer (Fe₃ O₄) grows in the direction of the melt, and the internal layer (Fe (Fe_{1 – x} , Cr _x )₂ O₄) grows in the direction to the matrix. Oxide particles favor an increase in the porosity of the internal sublayer of the scale. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 5, pp. 38 – 44, September–October, 2008.     

Phase composition and magnetic properties of iron oxide nanoparticles obtained by impulse electric discharge in water

The chemical composition and the magnetic properties of iron oxide nanoparticles obtained by impulse electric discharge in water are investigated. The phase composition of the Fe₃O₄, Fe₂O₃, and Fe nanoparticles is determined. By means of the nuclear magnatiec resonance (NMR) technique, the magnetic moments of the nanoparticles are determined. The magnetic moment of the spherical nanoparticles equals to 2.39 × 10^–19 A m², and that of the cubical ones is 4.56 × 10^–19 A m².     

Heterovalent cation substitutions in the layered compound YBaCuFeO<Subscript>5 + δ</Subscript>

(Y,M)BaCuFeO_{5 + δ} (M = Ce, Ca, Na), Y(Ba,K)CuFeO_{5 + δ}, YBa(Cu,Co)FeO_{5 + δ}, YBaCu(Fe,M)O_{5 + δ} (M = Zn, Nb), (Y,Ca)BaCu(Fe,Zn)O_{5 + δ}, and (Y,Ca)(Ba,La)Cu(Fe,Zn)O_{5 + δ} solid solutions have been prepared by ceramic processing techniques and have been characterized by x-ray diffraction, IR absorption spectroscopy, and thermal expansion and electrical conductivity (σ) measurements in air at temperatures from 300 to 1100 K. It is shown that, in the range 650–700 K, the linear thermal expansion coefficient of the (Y,M)BaCuFeO_{5 + δ} phases rises from (11–12) × 10^?6 to (14–15) × 10^?6 K^?1, while that of the YBa(Cu,Co)FeO_{5 + δ} solid solution decreases from 18 × 10^?6 to 14 × 10^?6 K^?1. The conductivity data (an increase in σ upon Ca²⁺ → Y³⁺ and Zn²⁺ → Fe³⁺ substitutions and a reduction in σ upon Ce⁴⁺ → Y³⁺ and Nb⁵⁺ → Fe³⁺ substitutions) demonstrate that the transport properties of YBaCuFeO_{5 + δ} can be tuned by electron-hole doping.     

Inducing multiferroic behaviour in the diamagnetic Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The synthesis and characterization of Y_2−xFe_xO₃ (where x = 0–0.3) compounds has been carried out for their importance in the field of multiferroic materials. The powder X-ray diffraction reveal that the compounds Y_1.95Fe_0.05O₃, Y_1.9Fe_0.1O₃, Y_1.85Fe_0.15O₃ and Y_1.8Fe_0.2O₃ crystallize in tetragonal structure whereas Y_1.75Fe_0.25O₃ and Y_1.7Fe_0.3O₃ compounds crystallize in orthorhombic structure. The change in crystal system with respect to the concentration of Fe may be attributed to the variation in occupancy position of Fe³⁺ into the Y³⁺ site of Y₂O₃ system. Variation in crystal structure, surface morphology and composition was studied by micro-Raman analysis, SEM and EDX analysis. The shift in intense Raman signals from 426 to 385 cm⁻¹ confirms the change in the crystal structure of the prepared compounds. Further it is also identified that the E_g mode of vibration is the dominant in the Fe substituted compounds. The substitution of Fe in the Y₂O₃ system leads to the increase in the intensity of resonance band, which indicates a large polarisability variation in the Y_2−xFe_xO₃ compounds. Diffused reflectance studies show a red shift in energy gap values while increasing the concentration of Fe. The room temperature magnetization and electron paramagnetic resonance studies reveal that the incorporation of Fe in the Y₂O₃ system leads to magnetic phase change from diamagnetic to ferromagnetic. The electric polarization studies imply that the substitution of lower ionic radii element Fe³⁺ in the Y³⁺ site leads to distortion in the lattice and show the way to spontaneous dipole moment and it was found that the Y_1.8Fe_0.2O₃ compound exhibits the possibility of multiferroic behaviour. Therefore this paper explores the possibility of inducing ferromagnetic and ferroelectric behaviour in the Fe substituted yttrium oxide system.     

Effect of crystallite size on oxidation and reduction behavior of a manganesesubstituted magnetite of composition Mn0.67Fe2.33O4

Thermogravimetry and electrical conductivity were used to determine the effect of crystallite size on oxidation and reduction behavior of a manganese substituted magnetite Mn_0.67Fe_2.33O₄ containing several oxidizable cations. We have found that within the single-phase region of the spinel (below 550°C) oxidation and reduction temperatures increase with increase of particle size. A quantitative analysis of cations suggests that there exists a grain size of 45 nm above which the oxidation characteristics of three oxidizable cations (Fe²⁺,Mn³⁺,Mn²⁺) change. Above 600°C, the temperature of structural change spinel → corundum increases with decrease in particle size owing to stresses at the crystal lattice level.     

Preparation of spinel lithium ferrite by thermal treatment of spray-dried formates

The thermal decomposition of mixtures of complex ferric formate, /Fe₃(HCOO)₆(OH)₂/HCOO.4H₂O, and LiHCOO.H₂O prepared by spray-drying of their water solutions has been investigated. It was shown that the mixtures decompose at lower temperatures than the individual compounds in them. It was established that stoichiometric Li_O, ₅Fe₂, ₅O₄ can be prepared by slow and careful heating of formate mixture with lithium in excess to the stoichiometric amount (Li:Fe = 1:4, 4). The final product obtained is powdery Li_O, ₅Fe₂, ₅O4 with a large surface area.     

Synthesis, structural and magnetic characterization of iron-zinc-borate glass ceramics containing nanocrystalline zinc ferrite

Two different glass ceramics with the composition of the (Fe₂O₃)_x·(B₂O₃)_(60−x)·(ZnO)₄₀, where x = 12.5 and 15 mol%, have been synthesized using the melt-quench method. The X-ray diffraction (XRD) patterns show the presence of nanometric zinc ferrite (ZnFe₂O₄) crystals, with spinel structure, in a glassy matrix after cooling from melting temperature. The estimated amount of crystallized zinc ferrite varies between 16 and 35%, as a function of the chemical composition. Glass transition (T_g), crystallization (T_p) and melting (T_m) temperatures were determined by differential thermal analysis (DTA) investigations. Fourier transform infrared (FTIR) data revealed that the BO₃ and BO₄ are the main structural units of these glass ceramics network. FTIR spectra of these samples show features at characteristic vibration frequencies of ZnFe₂O₄. Electron paramagnetic resonance (EPR) measurements show the presence of isolated Fe³⁺ ions predominantly situated in rhombic vicinities and as well as the Fe³⁺ species interacting by dipole–dipole interaction or to their superexchange coupled pairs in clustered formations. The magnetic properties of the studied glass ceramics were investigated by vibrating sample magnetometer (VSM). From the magnetization curves for glass ceramic containing 15 mol% Fe₂O₃ it was found that the nanoparticles exhibit ferromagnetic interactions combined with superparamagnetism with a blocking temperature, T_B. For studied samples the hysteresis is present. The coercive field is dependent on composition and magnetic field being around 0.05 μ_B/f.u for measurements performed in maximum 0.4 T.