γ-Fe2O3 Core Research Articles

High efficiency removal of organic and inorganic iodine with ferrate[Fe(VI)] through oxidation and adsorption

I− is a halogen species existing in natural waters, and the transformation of organic and inorganic iodine in natural and artificial processes would impact the quality of drinking water. Herein, it was found that Fe(VI) could oxidize organic and inorganic iodine to IO3−and simultaneously remove the resulted IO3− through Fe(III) particles. For the river water, wastewater treatment plant (WWTP) effluent, and shale gas wastewater treated by 5 mg/L of Fe(VI) (as Fe), around 63 %, 55 % and 71 % of total iodine (total-I) had been removed within 10 min, respectively. Fe(VI) was superior to coagulants in removing organic and inorganic iodine from the source water. Adsorption kinetic analysis suggested that the equilibrium adsorption amount of I− and IO3− were 11 and 10.1 μg/mg, respectively, and the maximum adsorption capacity of IO3− by Fe(VI) resulted Fe(III) particles was as high as 514.7 μg/mg. The heterogeneous transformation of Fe(VI) into Fe(III) effectively improved the interaction probability of IO3− with iron species. Density functional theory (DFT) calculation suggested that the IO3− was mainly adsorbed in the cavity (between the γ-FeOOH shell and γ-Fe2O3 core) of Fe(III) particles through electrostatic adsorption, van der Waals force and hydrogen bond. Fe(VI) treatment is effective for inhibiting the formation of iodinated disinfection by-products in chlor(am)inated source water.

SiO2 based nanocomposite for simultaneous magnetic removal and discrimination of small pollutants in water

A nanocomposite adsorbent material was synthetized in order to obtain an efficient system able to remove, by means of chemical adsorption, mainly aromatic analytes dissolved in aqueous phase. The adsorbing substrate is composed by a magnetic responsive iron oxide (γ-Fe2O3) core coated by a shell of SiO2. The adsorption process is mediated by the chemical interaction among amine and silanol groups on the surface of the nanocomposite adsorbent and the analyte π cloud. The paramagnetic core allows to remove the formed nanosystem-analyte adduct quickly and completely, representing a huge improvement in comparison of the most used gravimetric separation. The removal efficiency obtained using the proposed nanocomposite reaches about 93% for the dangerous pollutant 1,2-phenylenediamine in water solution, 70% for dinitrophenol, 60% for aniline. Further, the nano-adsorbent was decorated with plasmonic Ag nanoparticles without significantly affecting the ability to adsorb the aromatic compounds. The presence of the plasmonic nanoparticles on the SiO2 surface allows to obtain surface enhanced Raman scattering (SERS) of the signals of the adsorbed aniline and 1,2-phenylenediamine proposing this approach to remove and, concomitantly, discriminate the retrieved pollutants from water.

γ-Fe2O3@Ag-mSiO2[sbnd]NH2 magnetic Janus micromotor for active water remediation

Micromotors have hold great promise for environmental remediation. Herein, we reported a novel γ-Fe2O3@Ag-mSiO2NH2 magnetic Janus micromotor for dynamic removal of heavy metal ions and organic pollutants from water. The as-prepared Janus micromotors displayed unique core-shell structure composed of amino-functionalized meso‑SiO2 shell and γ-Fe2O3 magnetic core, and could be propelled by O2 bubbles generated by Ag-catalyzed decomposition of H2O2. This Janus micromotor could move with a high velocity of 203.06 ± 10.6 μm s−1 (about 253.8 body lengths s–1) in 10 wt.% H2O2 solution. γ-Fe2O3@Ag-mSiO2NH2 magnetic Janus micromotor showed much higher removal capacities for Cu2+ (15.59 mg g−1) and doxycycline (31.45 mg g−1) than its static control samples due to the synergy of self-propulsive movement and amino-functionalized porous core-shell structure. Furthermore, the magnetic γ-Fe2O3 cores enabled the remote magnetic control on the movement direction and magnetic recycling. This work provides a new strategy for environmental pollutants treatment.

Magnetic Hyperthermia on γ-Fe2O3@SiO2 Core-Shell Nanoparticles for mi-RNA 122 Detection

Magnetic hyperthermia on core-shell nanoparticles bears promising achievements, especially in biomedical applications. Here, thanks to magnetic hyperthermia, γ-Fe2O3 cores are able to release a DNA target mimicking the liver specific oncotarget miRNA-122. Our silica coated magnetic nanoparticles not only allow the grafting at their surface of a significant number of oligonucleotides but are also shown to be as efficient, by local heating, as 95 °C global heating when submitted to an alternative magnetic field, while keeping the solution at 28 °C, crucial for biological media and energy efficiency. Moreover, a slight modification of the silica coating process revealed an increased heating power, well adapted for the release of small oligonucleotides such as microRNA.

Mechanistic Insights into the Formation and Growth of Anisotropic-Shaped Wüstite–Spinel Core–Shell Iron Oxide Nanoparticles in a Coordinating Solvent

Wustite (FeO)–spinel (magnetite, Fe3O4/maghemite, γ-Fe2O3) core–shell iron oxide nanoparticles (IONPs) of shapes cuboctahedron, cube, and octopods were successfully synthesized by thermal decomposi...

MIL-53(Fe) derived MCC/rGO nanoparticles with excellent broadband microwave absorption properties

High efficient MIL-53(Fe) derived γ-Fe2O3 coated by carbon framework (MCC for short) and compound with reduced graphene oxide for broadband microwave absorption is prepared by facile hydrothermal method and gradient temperature calcination. The sheets/bowknot-shaped nanoparticles structure have better microwave absorption performance via uniting magnetic γ-Fe2O3 core, carbon skeleton and rGO sheets. Binary material calcined at 600°C has an optimal RL value −62.53dB under 2.66mm thickness. In addition, the ternary MCC/rGO of 700°C calcination has better performance with an 11.68GHz effective absorption bandwidth (from 6.32GHz to 18GHz) of a single thickness of 3.60mm, and a maximum RL of −43.13dB at 3.25mm thickness. The MOF framework enhances particle stability and internal scattering, while graphene provides a larger absorption surface, coupled with the good impedance matching rooted in suitable permittivity and permeability, the material is an ideal new type of absorbing material.

A magnetic γ-Fe2O3@PANI@TiO2 core-shell nanocomposite for arsenic removal via a coupled visible-light-induced photocatalytic oxidation-adsorption process.

Arsenic polluted groundwater impairs human health and poses severe threats to drinking water supplies and ecosystems. Hence, an efficient method of simultaneous oxidation of As(iii) to As(v), and removal of As(v) from water has triggered increasing attention. In this study, a magnetic γ-Fe2O3 core–shell heterojunction nanocomposite was synthesized by means of hydrothermal crystallization of TiO2 on the surface of the magnetic core–shell loaded with polyaniline (γ-Fe2O3@PANI@TiO2). As an efficient photocatalyst coupled with adsorption, γ-Fe2O3@PANI@TiO2 has a high light utilization and good adsorption capacity. Notably, the nanocomposite has excellent stability at various initial pH values with good reusability. Among the co-existing ions investigated, PO43− has the greatest competitive reaction. The photocatalytic oxidation of As(iii) on γ-Fe2O3@PANI@TiO2 is dominated by the synergy of several active substances, with superoxide free radicals and photogenerated holes being the major players.

Magnetic Pt single and double core-shell structures for the catalytic selective hydrogenation of cinnmaladehyde

Abstract This study reports the catalytic preparation, characterization, and evaluation of nanoscale core-shell structures with a γ-Fe2O3 core covered by a SiO2 monoshell or by a SiO2@TiO2 multishell as a support for Pt nanoparticles (NPs) to synthesize active and operationally stable catalysts for selective liquid-phase cinnamaldehyde hydrogenation. The structures were designed with a magnetic core so they could be easily recovered from the catalytic bed by simple magnetization and with a SiO2 monoshell or a SiO2@TiO2 multishell to protect the magnetic core. At the same time, this study details the effect of the shell on the catalytic performance. Moreover, the effect of particle size on the selective production of cinnamyl alcohol was studied by preparing two families of catalysts with metal loadings of 1 wt% and 5 wt% Pt with respect to the core-shell. The particle size effect enabled the Fe2O3@SiO2-5%Pt system, with an average particle size of 5.6 nm, to reach 100 % conversion of cinnamaldehyde at 300 min of reaction, producing cinnamyl alcohol with 90 % selectivity; this result differed greatly from that of the Fe2O3@SiO2-1%Pt (dPt = 3.5 nm) system, which reached a maximum conversion at 600 min with 49 % selectivity for the product of interest. However, the Fe2O3@SiO2@TiO2-x%Pt systems showed lower levels of conversion and selectivity compared to those of the Fe2O3@SiO2-x%Pt catalysts, which is attributed to the fact that average metal particle sizes below 5.0 nm were obtained in both cases. After reduction in H2 at 773 K, the Fe2O3@SiO2@TiO2-1%Pt catalyst showed deactivation, reaching 10 % conversion at 600 min of reaction and 60 % selectivity for the product of interest. However, the reduced Fe2O3@SiO2@TiO2-5%Pt system showed 98 % conversion with 95 % selectivity for cinnamyl alcohol at 24 h of operation; the increase in selectivity is attributed to the combined effects of the increase in average particle size (~7.5 nm) and the presence of strong metal-support interaction – SMSI – effects after reduction. Finally, the most selective systems were tested for operational stability, where the Fe2O3@SiO2@-5%Pt catalyst could be reused in three consecutive operating cycles while maintaining its activity and selectivity for cinnamyl alcohol – unlike the Fe2O3@SiO2@TiO2-5%Pt reduced system, which was deactivated after the third reaction cycle due to active phase leaching.

Structure, morphology and magnetic properties of flowerlike γ-Fe2O3@NiO core/shell nanocomposites synthesized from different precursor concentrations

The flowerlike γ-Fe2O3@NiO core/shell nanocomposites are synthesized by the two-step method. Their structure and morphology can be controlled by tuning the precursor concentration. Microstructural analysis reveals that all the samples have distinct core/shell structure without impurities, and the NiO shells are built of many irregular nanosheets which enclose the surface of γ-Fe2O3 core. As the precursor concentration decreases (i.e., more NiO content), the NiO grain grows significantly, and the thickness of NiO shells increases. Magnetic experiments are performed to analyze the influences of different microstructures on magnetic properties of samples and we have the following two results. First, at 5 K, along with increasing thickness of NiO shell, the saturation magnetization increases, while the residual magnetization decreases slightly. Second, the hysteresis loops under cooling field demonstrate that the value of exchange bias effect fluctuates between 13 Oe and 17 Oe. This is mainly because of the NiO shell that (i) is composed of irregular nanosheets with disordered orientations, and (ii) does not form a complete coating around γ-Fe2O3 core.

Low-friction behaviors of Ag-doped γ-Fe2O3@SiO2 nanocomposite coatings under a wide range of temperature conditions

In this paper, Ag-doped γ-Fe2O3@SiO2 nanocomposite coatings have been prepared by sol–gel method and deposited on steel substrate. The microstructure, surface topography, and high-temperature tribological properties of these coatings were measured and investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope with energy- dispersive spectrometer (SEM/EDS), transmission electron microcopy (TEM), and a high-temperature tribometer. The results show that the γ-Fe2O3 core is coated with an amorphous SiO2 shell and Ag nanoparticles are evenly distributed in the γ-Fe2O3@SiO2 nanocomposites. The tribological properties of the coatings against ZrO2 balls have been investigated by a tribometer at room temperature (RT), 100, 300, 500, and 600 °C, respectively. It is found that the nanocomposite coatings exhibit low and stable coefficients of friction (CoF) (in the range from 0.25 to ~0.06) from RT to 600 °C, respectively. CoF of the friction pair decreases with the increase of temperature. XRD, Raman spectroscopy, and SEM measurements show that the antifriction behaviors of nanocomposite coatings are owing to the soft phases of metal Ag and γ-Fe2O3. The presence of γ-Fe2O3 with high-temperature plasticity is beneficial to form low-shear interface and to achieve low and stable friction at high temperature. The core–shell microstructure of the nanocomposite coatings inhibits the soft γ-Fe2O3 phase, changing it into the α-Fe2O3 phase.

Synthesis of ferrofluids using a chemically induced transition method and their characterization

Using an altering chemically induced transition route, magnetic nanoparticles as well as nanoparticles modified with oleic acid have been prepared. The modified nanoparticles have been used to synthesize a high-quality kerosene-based ferrofluid, in which the mass fraction percentage of particles consisting of a γ-Fe2O3 core and an oleic acid coating, ϕm, amounted to 55%. Ferrofluids having lower concentrations of particles were obtained by diluting the mother ferrofluid. Magnetization measurements showed the as-synthesized ferrofluids to have excellent dispersity of the particles and field-induced inter-particle interactions. Optical transparency measurements confirmed that the ferrofluids showed a sensitive field-induced effect of chain-like aggregation, with redispersion of the particles after removing the magnetic field. According to results concerning both particle structure and ferrofluid density, the volume fraction percentage of particles, including both the γ-Fe2O3 core and the oleic acid coating, ϕ′v, as well as that of the γ-Fe2O3 alone, ϕv, can be deduced.

Stable Lithium Storage in Nitrogen-Doped Carbon-Coated Ferric Oxide Yolk-Shell Nanospindles with Preserved Hollow Space.

Iron oxide (Fe2 O3 ) is a promising anode material for next-generation high-energy lithium-ion batteries owing to its high theoretical specific capacity, but it suffers from unstable electrochemistry, as represented by a significant volume variation upon (de)lithiation and unstable solid-electrolyte interface. To target these issues, a double-coating synthetic route has been developed to prepare a yolk-shell-structured γ-Fe2 O3 /nitrogen-doped carbon composite, in which spindle-like γ-Fe2 O3 cores are encapsulated in the highly conductive carbon shell. Through precisely controlling the void space between the γ-Fe2 O3 core and the carbon shell, volume variation in γ-Fe2 O3 during (de)lithiation is well accommodated, while the composite maintains an intact and relatively dense structure, which stabilizes the solid-electrolyte interface and is beneficial for improving the practical energy density of the material. With a stabilized (de)lithiation electrochemistry and a synergistic storage effect between the two active components, the composite enables excellent lithium storage performance, in terms of reversible capacity, cycling ability, and rate capability.

Silver Nanoparticles Engineered β-Cyclodextrin/γ-Fe2O3@ Hydroxyapatite Composite: Efficient, Green and Magnetically Retrievable Nanocatalyst for the Aqueous Reduction of Nitroarenes

Ag nanoparticles incorporated β-cyclodextrin conjugated magnetic hydroxyapatite, γ-Fe2O3@HAp-CD.Ag was conveniently synthesized via the grafting of β-cyclodextrin moieties on the hydroxyapatite surface, followed by reacting of the nanocomposite, γ-Fe2O3, with silver nitrate and then its reduction with sodium borohydride. The cavity of β-cyclodextrin units as host material can stabilize the Ag nanoparticles (particles size: 12–14 nm) effectively and prevent their aggregation and separation from the surface. The nanocomposite obtained appears to have an organized structure, with a magnetic γ-Fe2O3 core surrounded by a layer-structured coating shell. The structure and composition of the nanocomposite were confirmed by FT-IR, FE-SEM, TEM, TGA, XRD, EDS, BET, and VSM. This catalytic system selectively reduces the nitro group even in the presence of other sensitive functional groups in good to excellent yields (85–98%).The organometallic nanocatalyst was easily removed from solution using an external magnet and was successfully examined for five runs, with a slight loss of catalytic activity.

Investigating Exchange Bias and Coercivity in Fe₃O₄-γ-Fe₂O₃ Core-Shell Nanoparticles of Fixed Core Diameter and Variable Shell Thicknesses.

We have carried out extensive measurements on novel Fe3O4–γ-Fe2O3 core–shell nanoparticles of nearly similar core diameter (8 nm) and of various shell thicknesses of 1 nm (sample S1), 3 nm (sample S2), and 5 nm (sample S3). The structure and morphology of the samples were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The direct current (DC) magnetic measurements were carried out using a superconducting quantum interference device (SQUID). Exchange bias and coercivity were investigated at several temperatures where the applied field was varied between 3 and −3 T. Several key results are obtained, such as: (a) the complete absence of exchange bias effect in sample S3; (b) the occurrence of nonconventional exchange bias effect in samples S2 and S1; (c) the sign-change of exchange bias field in sample S2; (d) the monotonic increase of coercivity with temperature above 100 K in all samples; (e) the existence of a critical temperature (100 K) at which the coercivity is minimum; (f) the surprising suppression of coercivity upon field-cooling; and (g) the observation of coercivity at all temperatures, even at 300 K. The results are discussed and attributed to the existence of spin glass clusters at the core–shell interface.

Ultrasmall iron oxide nanoparticles: Magnetic and NMR relaxometric properties

Ultrasmall iron oxide (USPIO) nanoparticles, with diameter mostly less than 3 nm dispersed in an organic carrier fluid were synthesized by polyol route. The evolution of ZFC-FC magnetization curves with temperature, as well as the shift of the ac susceptibility peaks upon changing the frequency, reveal that the nanoparticles in the fluid are non-interacting and superparamagnetic with the blocking temperature TB ∼10 K. The Mössbauer spectra analysis proposed the core/shell structure of the nanoparticles consisting of stoichiometric γ-Fe2O3 core and non-stoichiometric shell. The nanoparticle surface layer has a great influence on their properties which is principally manifested in significant reduction of the magnetization and in a large increase in magnetic anisotropy. Magnetic moments do not saturate in fields up to 5 T, even at the lowest measured temperature, T = 5 K. The average magnetic particle diameter is changed from 1.3 to 1.8 nm with increasing magnetic field from 0 to 5 T which is noticeably smaller than the particle sizes measured by TEM. The estimated effective magnetic anisotropy constant value, Keff = 2 × 105 J/m3, is two orders of magnitude higher than in the bulk maghemite. Measurements of the longitudinal and transverse NMR relaxivity parameters on water diluted nanoparticle dispersions at 1.5 T gave the values r1 = 0.028 mmol−1 s−1, r2 = 0.050 mmol−1 s−1 and their ratio r2/r1 = 1.8. Continuous increase of the T1-weighted MRI signal intensity with increasing Fe concentration in the nanoparticle dispersions was observed which makes this ferrofluid to behave as a positive T1 contrast agent.

Magnetic nanoparticles prepared by chemically induced transition: Structure and magnetization behaviors

The magnetic nanoparticles were prepared by chemically induced transition using an FeOOH/Mg(OH)2 precursor and an FeCl2 or FeCl2/NaOH treating solution. The morphology, bulk and surface chemical compositions, crystal properties, and specific magnetization of the magnetic nanoparticles were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, X-ray diffraction, and vibrating sample magnetometer. A self-consistent explanation of these characterization results was proposed. As a consequence, the particles' physical structure, including the chemical phases, microstructure, average density, and sizes (crystal, physical, and magnetic sizes), were determined. The apparent magnetization of magnetic nanoparticles system having magnetic interaction between particles can be described by a modified Langevin function. It is confirmed that as-prepared nanoparticles were composed of a γ-Fe2O3 core and a FeCl3⋅6H2O coating. The spins in the surface layer of the γ-Fe2O3 core could be disordered to weaken the apparent magnetization of the particle system. The difference in the magnetization of the nanoparticles prepared using different treating solutions is explained, and it is revealed that additional NaOH can stimulate the epitaxial growth of γ-Fe2O3 during the chemically induced transition. In addition, it was ascertained that the crystallite size determined by X-ray diffraction was the most probable crystallite size rather than the average crystallite size.

Removal of arsenic from gold processing circuits by use of novel magnetic nanoparticles

ABSTRACTArsenic adversely affects gold mining operations by interfering with the extraction of gold, as well as posing a significant health and environmental hazard. While a number of technologies are available for removing arsenic, none of them is effective under all conditions. Although adsorption is a promising approach, most methods focus on the purification of water under neutral or acidic conditions and tend to be less effective in gold mining process waters, operating under highly alkaline conditions. In this study, the removal of As(III) and As(V) from both arsenic-only solutions and simulated process waters using composite magnetic nanoparticles was investigated. The nanoparticles consisted of magnetite (Fe3O4) or maghemite (γ-Fe2O3) cores covered by various metal oxides with Langmuir adsorption capacities of As(III) and As(V) ranging from 31.4 to 79.1 mg g−1 and 10.2 to 25.5 mg g−1, respectively, in arsenic-only solutions at pH 9. The adsorption capacities were further characterised by adsorption tests conducted in simulated process waters. The ability to remove As(III) is of particular importance as it is harder to remove it from alkaline solutions than As(V). The magnetic cores allow simple and efficient magnetic recovery of the As-loaded nanoparticles.

Removal of arsenic from alkaline process waters of gold cyanidation by use of γ-Fe2O3@ZrO2 nanosorbents

Arsenic is a problem in gold mining, as it can adversely affect operations and poses a health hazard. Although a number of technologies has been developed for its removal, none of them is effective under all conditions. Adsorption in particular, is a promising approach, but most methods have concentrated on the purification of water under neutral or acidic conditions. In gold mining and metallurgical processing waters, these adsorbents tend to be less effective. In this study, the removal of As(III) and As(V) from simulated mining process waters by use of composite nanoparticles is considered. The particles consisted of γ-Fe2O3 cores coated with ZrO2. The maximum Langmuir adsorption capacities of As(III) and As(V) were 62.2mg/g and 18.3mg/g, respectively, at a pH of 9. In the alkaline process waters from a gold cyanide leaching plant, adsorption of 42.3mg/g for As(III) and As(V) collectively, remained satisfactory, despite the presence of multiple competitive ions. Moreover, the particles retained their capacities well after multiple cycles of regeneration.

Dipolar-Distribution Cavity γ-Fe2 O3 @C@α-MnO2 Nanospindle with Broadened Microwave Absorption Bandwidth by Chemically Etching.

Developing microwave absorption materials with ultrawide bandwidth and low density still remains a challenge, which restricts their actual application in electromagnetic signal anticontamination and defense stealth technology. Here a series of olive-like γ-Fe2 O3 @C core-shell spindles with different shell thickness and γ-Fe2 O3 @C@α-MnO2 spindles with different volumes of dipolar-distribution cavities were successfully prepared. Both series of absorbers exhibit excellent absorption properties. The γ-Fe2 O3 @C@α-MnO2 spindle with controllable cavity volume exhibits an effective absorption (<-10 dB) bandwidth as wide as 9.2 GHz due to the chemically dipolar etching of the core. Reflection loss of the γ-Fe2 O3 @C spindle reaches as high as -45 dB because of the optimized electromagnetic impedance balance between polymer shell and γ-Fe2 O3 core. Intrinsic ferromagnetism of the anisotropy spindle is confirmed by electron holography. Strong coupling of magnetic flux stray lines between spindles is directly imaged. This unique morphology and facile etching technique might facilitate the study of core-shell type microwave absorbers.

Functional magnetic porous silica for T1–T2 dual-modal magnetic resonance imaging and pH-responsive drug delivery of basic drugs

A smart magnetic-targeting drug carrier γ-Fe2O3@p-silica comprising a γ-Fe2O3 core and porous shell has been prepared and characterized. The particles have a uniform size of about 60 nm, and a porous shell of thickness 3 nm. Abundant hydroxyl groups and a large surface area enabled the γ-Fe2O3@p-silica to be readily loaded with a large payload of the basic model drug rhodamine B (RB) (up to 73 mg g−1). Cytotoxicity assays of the γ-Fe2O3@p-silica particles indicated that the particles were biocompatible and suitable for carrying drugs. It was found that the RB was released rapidly at pH 5.5 but at pH 7.4 the rate and extent of release was greatly attenuated. The particles therefore demonstrate an excellent pH-triggered drug release. In addition, the γ-Fe2O3@p-silica particles could be tracked by magnetic resonance imaging (MRI). A clear dose-dependent contrast enhancement in both T1-weighted and T2-weighted MR images indicated the potential of the γ-Fe2O3@p-silica particles to act as dual-mode T1 and T2 MRI contrast agents.