γ-Fe2O3 Particles Research Articles

Vacuum-annealing-tailored robust and flexible nanopore-structured γ-Fe2O3film anodes for high capacity and long life Na-ion batteries

Relatively high cost and limited resources are limiting the broad applications of Li-ion batteries. Na-ion batteries are one of the most promising replacement candidates because of abundant sodium resources, low price and similarity with Li insertion chemistry. For the first time, γ-Fe2O3 film was grown directly on a copper sheet with radio frequency magnetron sputtering as an anode for Na-ion batteries. Results show that the γ-Fe2O3 film annealed at 600 °C delivers a high reversible capacity of 450 mA h g−1 and nearly 100% capacity retention over 100 charge–discharge cycles, significantly outperforming all the previously reported examples. It is believed that the high performance of the Na-ion anode can be attributed to high temperature annealing producing nanopores for a large ion-inserting surface area and uniform γ-Fe2O3 particles firmly loaded on the surface of the Cu substrate to robustly retain the film structure during the Na-ion intercalation process for long cycle life. This work holds great promise for the fabrication of inexpensive and non-toxic Na-ion batteries for practical applications.

Formation of highly crystalline maghemite nanoparticles from ferrihydrite in the liquid phase

Fe5O7(OH)·4H2O ferrihydrite is a low-crystallinity antiferromagnetic material. γ-Fe2O3 (maghemite) magnetic nanoparticles were prepared from a ferrihydrite precursor, by chemically induced transformation in FeCl2/NaOH solution. The magnetization, morphology, crystal structure and chemical composition of the products were determined by vibrating sample magnetometry, transmission electron microscopy, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy (XPS). Ferrihydrite underwent aggregation growth and transformed into α-FeO(OH) (goethite) particles, which subsequently transformed into γ-Fe2O3 nanoparticles, that became coated with NaCl. The γ-Fe2O3 particles had a flake-like morphology, when prepared from 0.01 mol/L FeCl2 and a FeCl2:NaOH molar ratio of 0.4. The γ-Fe2O3 particles were more spherical, when prepared from a FeCl2:NaOH molar ratio of 0.6. The Fe content of the flake-like particles was lower than that of the spherical particles. Their magnetizations were similar, and the coercivity of the flake-like particles was larger. The differences in morphology and magnetization were attributed to the surface effect, and the difference in coercivity to the shape effect.

Transformation of ferrihydrite to goethite and then to maghemite in a mixed FeCl2/NaOH solution

Ferrihydrite (Fe5O7(OH)·4H2O) is poorly crystalline hydrated ferric oxyhydroxide. Using a treatment in a mixed FeCl2/NaOH solution, we attempted to prepare magnetic nanoscale particles from ferrihydrite. During the treatment, the concentration of FeCl2 was fixed at 0.1 M, and the concentration of NaOH was varied from 0.09 to 0.26 M. The as-prepared products were characterized using X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. The experimental results showed that under the FeCl2/NaOH solution treatment, the ferrihydrite transformed into nanoscale γ-Fe2O3 via an α-FeO(OH) intermediate phase. The as-prepared products contained rod-type α-FeO(OH), sphere-type γ-Fe2O3, and flake-type γ-Fe2O3 particles. A mechanism for a coupling of the aggregation and the transition was proposed to interpret the formation of highly crystalline nanoscale particles from the poorly crystalline smaller particles.

Synthesis and Morphology of Platelet α-FeOOH and γ-Fe2O3 Nanoparticles for Cancer Therapy Using Hysteresis-Loss Heating

The morphology of platelet α-FeOOH, a precursor for synthesizing γ-Fe2O3 particles for use in cancer therapy by hysteresis-loss heating, was investigated with the aim of reducing the size of γ-Fe2O3 particles. The α-FeOOH particles were synthesized by the precipitation of ferric ions in alkaline solution containing ethanolamine, and crystals were grown via hydrothermal treatment. The particle length of α-FeOOH was reduced on lowering the precipitation temperature and maintaining it in the range from −3°C to 6°C, whereas the ratio of the long and short axes was maintained. The axial ratio of the α-FeOOH particles was remarkably affected by the precipitant's aging temperature in the range of 4–60°C, and became smaller when the aging temperature was lowered. The addition of Si was effective for reduction of the particle length of α-FeOOH. Platelet α-FeOOH particles with a particle length of ~40 nm and an axial ratio of ~1.5 were obtained by using Si as an addictive and employing precipitation, aging, and hydrothermal treatment temperatures of −3.5°C, 4°C, and 150°C, respectively.

Removal Polyacrylamide from Oil Recovery Wastewater by γ-Fe2O3 Magnetic Particles

Polyacrylamide is of concern in oil recovery wastewater treatment because of its persistence and environment effects. A concept is proposed to synthesize γ-Fe2O3 particles with magnetic functionalization for polyacrylamide removal from aqueous media. Magnetic particles were synthesized by the sol-gel method, using NH4HCO3 and FeSO4·7H2O. These magnetic particles show high adsorption capacity for polyacrylamide. Because of the useful magnetic property, large specific surface area and fast magnetic separation, the synthesized materials will provide a convenient and highly efficient means to remove polyacrylamide from oil recovery wastewater.

Preparation and High Reusability of a Novel Acid-Resistant Magnetic Weak Acid Resin for Ni2+ Removal

A novel magnetic weak acid resin (MWA06) was successfully synthesized and characterized. To enhance the acid resistance and lipophilicity of the γ-Fe2O3 particles, a titanate coupling agent (TCA) was employed to modify the particle surface. Afterward, the resultant resin was obtained through copolymerization and hydrolysis reactions, with a specific saturation magnetization of 10.9 emu/g and weak acid cation exchange capacity of 8.44 mmol/g. Leaching tests in acid showed that the magnetic resin was stable at pH 2. The presence of Ca2+ in the solution had an obviously negative impact on the adsorption of Ni2+, whereas Na+ did not influence the adsorption process. The adsorption of Ni2+ was pH-dependent as the uptake capacity increased from 0.06 to 2.81 mmol/g with the pH rising from 2 to 6. The desorption efficiency was nearly 100% by using 0.01 M HCl solution as desorption agent. Moreover, MWA06 could maintain high adsorption capacities for at least 10 regeneration cycles, indicative of a good reusability.

Preparation of magnetic porous carbon from waste hydrochar by simultaneous activation and magnetization for tetracycline removal

In the present work, a novel magnetic porous carbon (MPC) with maghemite (γ-Fe2O3) particles is facilely prepared from hydrochar (a solid residue of hydrothermal carbonization of biomass) in one step through simultaneous activation and magnetization. The resultant MPC is characterized and utilized as an adsorbent for tetracycline (TC) removal from aqueous solutions. The BET surface area and micropore volume of the MPC are found to be 349 m(2)g(-1) and 0.16 cm(3)g(-1), respectively. The adsorption kinetics data could be well described by the pseudo-second-order model, and the TC adsorption onto MPC is an endothermic and spontaneous process. The enhanced surface area of the MPC, as well as its graphite-like structure, may contribute to the adsorption capacity of TC. After adsorption, MPC could be effectively separated by applying a magnetic field.

Encapsulation of human serum albumin in submicrometer magnetic poly(lactide-co-glycolide) particles as a model system for targeted drug delivery

Abstract Two types of iron oxide nanoparticles were synthesized by coprecipitation of Fe(II) and Fe(III) chlorides: water-dispersible γ-Fe2O3 and organic solvent-dispersible oleic acid-coated Fe3O4 particles. The nanoparticles, together with human serum albumin (HSA) serving as a model for a protein-type drug, were then incorporated in poly(lactide-co-glycolide) (PLGA) particles using double emulsion solvent evaporation technique. Morphology, size and particle size distribution of the resulting particles was analyzed by electron microscopy and dynamic light scattering. Iron oxide and HSA encapsulating efficiency was determined by Prussian Blue staining and micro-BCA assay, respectively.

Dependences of Specific Loss Power on Magnetic Field and Frequency in Elongated Platelet $\gamma$-Fe$_{2}$O$_{3}$ Particles Using Hysteresis-Loss Heating

Elongated platelet γ-Fe2O3 particles with particle sizes of about 30 to 100 nm were prepared for magnetic thermoablation using hysteresis-loss heating of the ferromagnetic particles. The coercive force was based on the shape anisotropy of the elongated shape. The dependences of specific loss power (SLP) on the magnetic field strength and frequency were examined for particles in the range of 133 to 640 Oe and 117 to 429 kHz, respectively. The dependence of SLP on the magnetic field was similar to that of areas in minor hysteresis loops and showed that the heat generation in the particles was almost entirely based on hysteresis loss. To realize effective hysteresis-loss heating a magnetic field about four times stronger than the coercive force of particles was necessary. The SLP increased linearly with increasing frequency. Particles with a coercive force of 153 Oe showed an SLP of 1670 W/g under a magnetic field of 500 Oe and at a frequency of 429 kHz.

Expanded graphite–nanoferrite–fly ash composites for shielding of electromagnetic pollution

Expanded graphite (EG) was incorporated into fly ash matrix along with nanoferrite γ-Fe2O3 particles so that the resultant conductive fly ash composite can be used for electromagnetic shielding in microwave range. Conductivity of composites lies in the range 0.34–32.86S/cm. TEM images show that fly ash particle (0.87μm) is covered by sheets of EG containing the magnetic nanoparticles. Complex parameters have been calculated from experimental scattering parameters (S11 and S21) using theoretical calculations given in Nicholson–Ross and Weir algorithms. The microwave absorption properties of the composites have been studied in the 8.2–12.4GHz (X-band) frequency range which shows a shielding effectiveness up-to 90dB, which strongly depends on dielectric loss and weight fraction of fly ash and γ-Fe2O3 in EG matrix.

A protected annealing process for the production of high quality colloidal oxidenanoparticles with optimized physical properties

Colloidal synthesis of inorganic materials is usually achieved in solvents under milder conditions of temperature than those usually used for the preparation of bulk compounds. As commonly shown on oxide nanoparticles with sizes of more than typically 20 nm, this leads to particles exhibiting an altered crystallinity with the presence of more or less extended defects that may impact the physical properties of the particles. Considering that post-annealing treatments on powders of nanoparticles inevitably lead to their sintering (i.e. growth and irreversible aggregation), the influence of these defects has rarely been discussed. For a few years, we have been investigating a post-synthesis process of “protected annealing”. The basic principle relies on thermal treatment of preformed particles that have been previously dispersed into a sol–gel silica matrix. After annealing at temperatures up to 1000 °C, the dissolution of the host matrix allows recovery of a suspension of particles with the same size as the pristine particles and an almost perfect crystallinity. Investigation of the physical properties of these particles permitted us to show their optimized properties, thus discriminating the influence of altered crystallinity compared to small size or surface effects and high surface area. Results are presented in the case of oxide phosphors (YVO4:Eu, YAG:Ce), photocatalytic TiO2 and magnetic γ-Fe2O3 particles. Finally, an extension of the process is shown in the case of a reactive protected annealing, when the thermal treatment is associated with a change of chemical composition of the particles, thus allowing the investigation of systems that are difficult to obtain through conventional colloid chemistry. This latter strategy is presented in the cases of Zn2SiO4:Mn nanophosphors, Co-doped γ-Fe2O3 and N-doped TiO2.

Preparation and characterization of a novel magnetic biochar for arsenic removal

A magnetic biochar based adsorbent with colloidal or nanosized γ-Fe2O3 particles embedded in porous biochar matrix was fabricated via thermal pyrolysis of FeCl3 treated biomass. The synthesized samples were studied systematically by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, selected-area electron diffraction pattern, scanning electron microscopy, energy-dispersive X-ray analysis, superconducting quantum interference device, and batch sorption measurements. The characterization analyses showed that large quantity of γ-Fe2O3 particles with size between hundreds of nanometers and several micrometers tightly grow within the porous biochar matrix. Biochar/γ-Fe2O3 composite exhibited excellent ferromagnetic property with a saturation magnetization of 69.2emu/g. Batch sorption experimental results showed that the composite has strong sorption ability to aqueous arsenic. Because of its excellent ferromagnetic properties, the arsenic-laden biochar/γ-Fe2O3 composite could be easily separated from the solution by a magnet at the end of the sorption experiment.

Magnetic nanohydroxyapatite/PVA composite hydrogels for promoted osteoblast adhesion and proliferation

This paper reports on the systematic investigation of novel magnetic nano-hydroxyapatite/PVA composite hydrogels through cyclic freeze–thawing with controllable structure, mechanical properties, and cell adhesion and proliferation properties. The content of the magnetic nano-hydroxyapatite-coated γ-Fe2O3 (m-nHAP) particles exhibited remarkable influence on the porous structures and compressive strength of the nanocomposite hydrogels. The average pore diameter of the nanocomposite hydrogels exhibited a minimum of 1.6±0.3μm whereas the compressive strength reached a maximum of about 29.6±6.5MPa with the m-nHAP content of around 10wt% in the nanocomposite hydrogels. In order to elucidate the influence of the composite m-nHAP on the cell adhesion and proliferation on the composite hydrogels, the PVA, γ-Fe2O3/PVA, nHAP/PVA and m-nHAP/PVA hydrogels were seeded and cultured with osteoblasts. The results demonstrated that the osteoblasts preferentially adhered to and proliferated on the m-nHAP/PVA hydrogels, in comparison to the PVA and nHAP/PVA hydrogels, whereas the γ-Fe2O3/PVA hydrogels appeared most favorable to the osteoblasts. Moreover, with the increasing m-nHAP content in the composite hydrogels, the adhesion density and proliferation of the osteoblasts were significantly promoted, especially at the content of around 50wt%.

Insights into the Mechanism Related to the Phase Transition from γ-Fe2O3 to α-Fe2O3 Nanoparticles Induced by Thermal Treatment and Laser Irradiation

The nature of the physical mechanisms related to the γ-Fe2O3 to α-Fe2O3 phase transition under laser irradiation and heat treatment has been investigated using in situ micro-Raman spectroscopy and X-ray powder diffraction (XRPD) analysis. Measurements were carried out on as-prepared γ-Fe2O3 nanoparticles of about 4 nm in size as a function of laser power and on annealed γ-Fe2O3 particles. Annealing temperature affects the relative fractions of the γ-Fe2O3 and α-Fe2O3 phases, and at 450 °C, the phase transition into α-Fe2O3 becomes complete with apparent crystallite size ⟨D⟩ of about 30 nm. The hematite nanoparticles increase then up to more than 180 nm at 1400 °C. The excellent agreement between evolution of the wavenumbers and bandwidths confirms that the heat treatment and laser irradiation produces the same effects on nanoparticles. Correlations between structure modifications occurring at the nanometric scale during grain coalescence and the evolution of Raman vibrational spectra were quantitatively examined, and a physical mechanism for the γ → α-Fe2O3 phase transition was proposed.

The magneto-optical behaviors modulated by unaggregated system for γ-Fe2O3–ZnFe2O4 binary ferrofluids

Under an external magnetic field, when circularly polarized light was transmitted through binary ferrofluids based on strongly magnetic γ-Fe2O3 and weakly magnetic ZnFe2O4 nanoparticles, the birefringence Δn and dichroism Δk arising from the chains of γ-Fe2O3 particles system were modulated and decreased by the unchained ZnFe2O4 particles. In our experiments, we used two types of ZnFe2O4 nanoparticles: one consisted of ZnFe2O4(1) particles with higher moments, and the other consisted of ZnFe2O4(2) particles with lower moments. Comparing the birefringence and dichroism of the γ-Fe2O3–ZnFe2O4(1) and γ-Fe2O3–ZnFe2O4(2) binary ferrofluids, it was found that the modulating action of the ZnFe2O4(2) particle system with lower moments was larger than that of the ZnFe2O4(1) particle system with higher moments. Using a model for a bi-dispersed system based on chained and unchained particles, the behavior of the modulating action was explained by an additional effective relative magnetic permeability, which depends on the background of the unchained ZnFe2O4 particles for the chained γ-Fe2O3 particles and a field-induced demixing phase transition. These results showed that for binary ferrofluids based on both strong and weak magnetic nanoparticles, the power of the modulation of the magneto-optical effects depends on the difference in magnetization between the particles.

Restructurings in the catalyst for methane vapor reforming resistant to sulfur hydride impurity: Configuration of catalytically active nanocomponents of a core (Invar FeNi)-shell (γ-Fe2O3) type

The evolution of a nickel-containing catalyst based on a mixed oxide substrate obtained from vermiculite etching solutions has been investigated using the methods of Moessbauer and EXAFS spectroscopy, XRD, and transmission electron microscopy. The catalyst manifests high activity in the process of methane vapor reforming (MVR) and is resistant to low sulfur hydride content. Upon the deposition of active components (Ni-La) and thermal treatment at 900°C, the phases of nickel oxide and superparamagnetic particles of γ-Fe2O3 distributed in the structure of the mixed spinel of a composition Mg(FeAl)O4 ± δ are formed on the catalyst surface. In the course of the preliminary reduction activation by hydrogen, the surface phases interact with the formation of hybrid systems of a core-shell type with a size of 15–17 nm. The core comprises particles of the reduced α-Fe, invar alloy: γ-FeNi and α-FeNi surrounded by a shell of superparamagnetic clusters of γ-Fe2O3 1–4 nm in size with a strong interaction with the nucleus and isostructural mixed oxide with the structure of spinel. After catalysis in the MVR process, at T = 790–820°C the particles of the catalyst containing 30 ppm of H2S become enlarged up to 40–45 nm without a change in shape. The particle enlargement occurs as a result of the increase in the core size, whereas the shell size remains unchanged. It is assumed that the shell decomposes sulfur hydride until elementary sulfur, whereas the system core manifests high activity in the MVR process.

Synthesis of Superparamagnetic Nanoporous Iron Oxide Particles with Hollow Interiors by Using Prussian Blue Coordination Polymers

Our recent work has demonstrated that well-defined hollow interiors can be created inside Prussian Blue (PB) nanoparticles through controlled chemical etching in the presence of poly(vinylpyrrolidone) (Angew. Chem., Int. Ed.2012, 51, 984). By calcination of these PB nanoparticles as starting precursors, we can successfully synthesize nanoporous iron oxides with hollow interiors. From scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the original hollow cavities of PB nanocubes are shown to be retained after crystal transformation to iron oxides. Also, the obtained hollow iron oxides show a very high surface area because of their nanoporous shells, as illustrated by N2 gas adsorption–desorption analysis. By tuning the applied calcination temperatures and selecting the PB nanoparticles with different hollow cavities, crystalline α-Fe2O3, and γ-Fe2O3 can be selectively formed in the products without formation of any impurity phases. Field-dependent magnetization measurements indicate that the nanoporous hollow iron oxides exhibit a very interesting superparamagnetic property at room temperature. Especially, nanoporous hollow γ-Fe2O3 particles with well-developed crystallinity possess sufficient saturation magnetization (Ms) value. Such reasonable Ms value, together with the superparamagnetic property, high specific surface area, and internal hollow cavity, makes our nanoporous iron oxides a very promising platform for future biomedical applications.

Phenolic resin-based composite sheets filled with mixtures of reduced graphene oxide, γ-Fe2O3 and carbon fibers for excellent electromagnetic interference shielding in the X-band

Composite sheets consisting of phenolic resin filled with a mixture of reduced graphene oxide (RGO), γ-Fe2O3 and carbon fibers have been produced by compression molding. Its electrical conductivity lies in the range 0.48–171.21S/cm. Transmission and scanning electron microscopy observations confirm the presence of nano particles of γ-Fe2O3 (∼9.8nm) and carbon fiber (∼1mm) which gives flexural strength to composite sheets. Thermogravimetric analysis show that the thermal stability of the sheets depend upon the amount of RGO and phenol resin in the composite. Complex parameters, i.e., permittivity (ε*=ε′−iε″) and permeability (μ*=μ′−iμ″) of RGO/γ-Fe2O3/carbon fiber have been calculated from experimental scattering parameters (S11 and S21) using theoretical calculations given in Nicholson−Ross and Weir algorithms. The microwave absorption properties of the sheets have been studied in the 8.2–12.4GHz (X-Band) frequency range. The maximum shielding effectiveness observed is 45.26dB, which strongly depends on dielectric loss and volume fraction of γ-Fe2O3 in RGO matrix.

The modification of the initial susceptibility of dilute binary ferrofluids based on γ-Fe2O3/ZnFe2O4 nanoparticles

In the dilute γ-Fe2O3–ZnFe2O4 binary ferrofluids, the magnetic interaction between γ-Fe2O3 nanoparticles is large enough to form aggregates. The magnetization behavior of the binary ferrofluids with ϕ γ =0.4 % and ϕ Zn=0.1 %, 0.2 %, or 0.4 % are investigated. The magnetism of ZnFe2O4 nanoparticles is very weak so the magnetization behavior of the binary ferrofluids results mainly from the γ-Fe2O3 nanoparticle system. Experimental results indicate that the initial susceptibility of the binary ferrofluids with ϕ Zn=0.4 % is the smallest, although that with ϕ Zn=0.2 % is larger than the one with ϕ Zn=0.1 %. In addition, at high field, the magnetization of the ferrofluid with ϕ Zn=0.4 % is greatest. These results show that both chain-like and ring-like aggregates of γ-Fe2O3 particles are stimulated by the ZnFe2O4 particle system. The contributions of the two types of aggregate in the magnetization process are different. The ratio of these aggregates varies nonmonotonically with ϕ Zn, so as ϕ Zn increases; the weak magnetic ZnFe2O4 particle system produces a nonmonotonic modification of the initial susceptibility of these binary ferrofluids.

Effect of contacts between γ-Fe2O3 nanoparticles on their phase-transition temperature

The effect of mechanical contacts between γ-Fe2O3 particles on the temperature of the γ-α structural transition in them is established by magnetic studies and differential thermal analysis (DTA). The sample in which γ-Fe2O3 particles had no mechanical contacts with one another remained in the ferromagnetic state up to TC = 630°C and had two exothermal DTA peaks. The first peak almost coincided with the Curie temperature, while the second peak attributed to the γ → α structural transition corresponded to 760°C. The magnetic transition for particles with a larger number of contacts was shadowed by the γ → α structural transition with a temperature lowered to 550°C.