γ-Fe2O3 Nanoparticles Research Articles

The maximum absorption capacities of γ-FeOOH, α-FeOOH, γ-Fe2O3 and α-Fe2O3 nanoparticles for As(V) and As(III)

γ-FeOOH, α-FeOOH, γ-Fe2O3 and α-Fe2O3 nanoparticle adsorbents for As(V) and As(III) removal were prepared by a chemical coprecipitation method. In the XRD diagrams the oxides appeared in the form of γ-FeOOH, α-FeOOH, γ-Fe2O3 and α-Fe2O3. These typical SEM images of the prepared samples were shown, which reveal that the nanoparticles were about 15 –30 nm. The maximum adsorption capacities of α- FeOOH for As(V) and As(III) were 77.28 and 78.65 mg/g; and γ-FeOOH were 63.75 and 88.99 mg/g respectively and higher than those of γ-Fe2O3 and α-Fe2O3 at pH= 6.0. The adsorption data accorded with Langmuir and Freundlich isotherms. The high adsorption capability and good performance on other aspects make the FeOOH nano particles being a promising adsorbent for the removal of As(V) and As(III) from groundwater.

Formation of bifunctional conglomerates composed of magnetic γ-Fe2O3 nanoparticles and various noble metal nanostructures

Bifunctional conglomerates made of magnetic and noble metal nanoparticles have many applications in the fields of catalysis, chemical analysis, biology, and medicine. Therefore, it is very important to find a way to synthesize such conglomerates that makes it possible to easily control the size and shape of the attached noble metal nanoparticles. In this contribution, we propose a method of synthesizing such conglomerates in which the noble metal nanoparticles are prepared before being bound to the magnetic nanostructures, and in which the initial size and shape of the noble metal nanoparticles does not change during the process of the formation of the conglomerates with magnetic γ-Fe2O3 nanoparticles. The proposed synthesis is based on directly binding the metal and γ-Fe2O3 nanoparticles by means of molecules of (3-aminopropyl)trimethoxysilane (APTMS). Functionalization with APTMS leads to the formation of nanostructures (methoxy groups of APTMS react with the surface of the Fe2O3 nanoparticles, forming strong FeOSi bonds) with a terminal amine group. The noble metal nanoparticles are then attached to the amine-terminated γ-Fe2O3 nanoparticles. This binding process has been successfully tested for decahedral Ag, cubic Ag, hollow Au, and hollow Pt nanoparticles. As far as we know synthesized composites are the first examples of magnetic composites containing such anisotropic metallic nanostructures. The magnetic-plasmonic conglomerates obtained have been used as materials for easily producing very homogeneous substrates for surface-enhanced Raman scattering (SERS) measurements. Conglomerates with Pt nanoparticles have been tested as catalysts for reducing 2-nitrophenol. We found that, after a relatively quick decomposition of the weakly bonded γ-Fe2O3-Pt nanostructures in the reaction mixture, the stability of the remaining conglomerates was large enough for them to be recycled in a magnetic field after the reaction and reused. This process may be repeated effectively many times.

High Frequency Hysteresis Losses on γ-Fe₂O₃ and Fe₃O₄: Susceptibility as a Magnetic Stamp for Chain Formation.

In order to understand the properties involved in the heating performance of magnetic nanoparticles during hyperthermia treatments, a systematic study of different γ-Fe2O3 and Fe3O4 nanoparticles has been done. High-frequency hysteresis loops at 50 kHz carried out on particles with sizes ranging from 6 to 350 nm show susceptibility χ increases from 9 to 40 for large particles and it is almost field independent for the smaller ones. This suggests that the applied field induces chain ordering in large particles but not in the smaller ones due to the competition between thermal and dipolar energy. The specific absorption rate (SAR) calculated from hysteresis losses at 60 mT and 50 kHz ranges from 30 to 360 W/gFe, depending on particle size, and the highest values correspond to particles ordered in chains. This enhanced heating efficiency is not a consequence of the intrinsic properties like saturation magnetization or anisotropy field but to the spatial arrangement of the particles.

Enhancement of Image Quality in LCD by Doping γ-Fe₂O₃ Nanoparticles and Reducing Friction Torque Difference.

Improving image sticking in liquid crystal display (LCD) has attracted tremendous interest because of its potential to enhance the quality of the display image. Here, we proposed a method to evaluate the residual direct current (DC) voltage by varying liquid crystal (LC) cell capacitance under the combined action of alternating current (AC) and DC signals. This method was then used to study the improvement of image sticking by doping γ-Fe2O3 nanoparticles into LC materials and adjusting the friction torque difference of the upper and lower substrates. Detailed analysis and comparison of residual characteristics for LC materials with different doping concentrations revealed that the LC material, added with 0.02 wt% γ-Fe2O3 nanoparticles, can absorb the majority of free ions stably, thereby reducing the residual DC voltage and extending the time to reach the saturated state. The physical properties of the LC materials were enhanced by the addition of a small amount of nanoparticles and the response time of doping 0.02 wt% γ-Fe2O3 nanoparticles was about 10% faster than that of pure LC. Furthermore, the lower absolute value of the friction torque difference between the upper and lower substrates contributed to the reduction of the residual DC voltage induced by ion adsorption in the LC cell under the same conditions. To promote the image quality of different display frames in the switching process, we added small amounts of the nanoparticles to the LC materials and controlled friction technology accurately to ensure the same torque. Both approaches were proven to be highly feasible.

γ-Fe2O3 nanoparticles embedded in porous carbon fibers as binder-free anodes for high-performance lithium and sodium ion batteries

A facile strategy of electrospinning has been employed to fabricate freestanding anodes of γ-Fe2O3/porous carbon fibers (γ-Fe2O3/PCF) for both lithium and sodium ion batteries, in which γ-Fe2O3 nanoparticles ranging from 50 to 150 nm were in-situ formed and embedded in the porous carbon fibers. The thus obtained composite delivers highly reversible discharge capacities of 980 mAh g−1 in lithium ion batteries and 291 mAh g−1 in sodium ion batteries, corresponding to high capacity retentions of 97 and 78%, respectively. The superior electrochemical performance of the binder-free anodes can be attributed to the unique composite structure with γ-Fe2O3 nanoparticles homogenously dispersed in the porous carbon fibers, which should help alleviate the volumetric fluctuation, promote the wettability of electrolyte, and enhance the electronic conductivity, demonstrating a promising candidate as the flexible anode material for high-performance energy storage devices.

Specific loss power measurements by calorimetric and thermal methods on γ-Fe2O3 nanoparticles for magnetic hyperthermia

Abstract Specific loss power has been measured on γ-Fe2O3 nanoparticles dispersed in water by means of several techniques, i.e. heat flow in a calorimeter, hyperthermia, and static and dynamic hysteresis loops. Static hysteresis loops as a function of the maximum applied field underestimate the power losses as dynamic effects are not exploited, but turned out to be a valuable tool to prove the consistency of specific loss power measurements obtained by the other techniques over a wide range of applied magnetic field intensities. A temperature-dependence of the specific loss power has been taken into account in hyperthermia measurements performed with a fully modelled non adiabatic experimental setup. Simple mean-field theoretical models (interacting superparamagnetic, modified Stoner-Wohlfarth) have been exploited to reproduce the static energy losses of the particles.

Gamma-ferric oxide nanoparticles decoration onto porous layered double oxide belts for efficient removal of uranyl

Layered double oxides (LDO) and γ-Fe2O3 have been demonstrated to be promising adsorbents to remove radioactive elements from aqueous media. Herein, magnetic γ-Fe2O3 nanoparticles decoration onto porous layered double oxides belts (γ-Fe2O3/LDO) were fabricated by in situ solid-state thermolysis technique combined with Fe(III)-loaded layered double hydroxides as a precursor. The microstructure, chemical composition, and magnetic properties of γ-Fe2O3/LDO were characterized in detail. The as-obtained γ-Fe2O3/LDO was employed as an adsorbent for the elimination of U(VI) from water. The adsorption process followed the Langmuir model with the maximal adsorption capacity of U(VI) onto γ-Fe2O3/LDO being 526.32 mg·g−1 at 303 K and pH 5, which surpassed pristine LDO and many other materials. The Fourier transformed infrared spectra and the X-ray photoelectron spectra analysis suggested that the interaction mechanism was mainly controlled by the surface complexation and electrostatic interactions. All in all, the γ-Fe2O3/LDO with remarkable adsorption capacity, excellent regeneration, and easy magnetic separation opens a new expectation as a suitable material for the cleanup of U(VI) from contaminated water.

Adaptive Neuro-fuzzy Inference System Prediction of Zn Metal Ions Adsorption by γ-Fe2o3/Polyrhodanine Nanocomposite in a Fixed Bed Column

This study investigates the potential of an intelligence model namely, Adaptive Neuro-Fuzzy Inference System (ANFIS) in prediction of the Zn metal ions adsorption in comparision with two well known empirical models included Thomas and Yoon methods. For this purpose, an organic-inorganic core/shell structure, γ-Fe2O3/polyrhodanine nanocomposite with γ-Fe2O3 nanoparticle as core with average diameter of 15 nm and polyrhodanine as shell with thickness of 3 nm, was synthesized via chemical oxidation polymerization. The properties of adsorbent were characterized with transmission electron microscope (TEM) and Fourier transform infrared (FT-IR) spectroscopy. Sixty seven experimental data sets including the treatment time (t), the initial concentration of Zn (Co), column height (h) and flow rate (Q) were used as input data to predict the ratios of effluent-to-influent concentrations of Zn (Ct/C0). The results showed that ANFIS model with the R coefficient of 0.99 can predict Ct/C0 more accurately than empirical models. Also it was found that the result of the Thomas and Yoon methods with R coefficient of 0.828 and 0.829, respectively were so close to each other. Finally, performance of our ANFIS model was compare to Thomas and Yoon methods in two different conditions, i.e. variable initial influent concentration and variable column height. High performance of ANFIS model was proved by the comparitive results.

Magnetic field intensity and [formula omitted] concentration effects on the dielectric properties of magnetodielectric tissues

Microfiber-based tissues are prepared by impregnation of an absorbent cloth with silicone oil mixed with carbonyl iron and various volume concentrations of γ-Fe2O3 nanoparticles. Plane capacitors are manufactured having the microfiber tissues as dielectric materials. The equivalent capacitance (Cp) and resistance (Rp) are measured without a magnetic field, and respectively with a magnetic field superimposed on a medium-frequency electric field. From the measured values of Cp and Rp we determine the absorption-dispersion characteristics, the Cole-Cole diagrams, static and optical relative permittivities, and relaxation times of the tissues. We show that in the presence of the magnetic field superimposed on the electric one, the dielectric properties of the tissues are sensibly influenced by the concentration of γ-Fe2O3 nanoparticles.

Maghemite (γ-Fe2O3) nanoparticles enhance dissimilatory ferrihydrite reduction by Geobacter sulfurreducens: Impacts on iron mineralogical change and bacterial interactions

Microbially mediated bioreduction of iron oxyhydroxide plays an important role in the biogeochemical cycle of iron. Geobacter sulfurreducens is a representative dissimilatory iron-reducing bacterium that assembles electrically conductive pili and cytochromes. The impact of supplementation with γ-Fe2O3 nanoparticles (NPs) (0.2 and 0.6 g) on the G. sulfurreducens-mediated reduction of ferrihydrite was investigated. In the overall performance of microbial ferrihydrite reduction mediated by γ-Fe2O3 NPs, stronger reduction was observed in the presence of direct contact with γ-Fe2O3 NPs than with indirect contact. Compared to the production of Fe(II) derived from biotic modification with ferrihydrite alone, increases greater than 1.6- and 1.4-fold in the production of Fe(II) were detected in the biotic modifications in which direct contact with 0.2 g and 0.6 g γ-Fe2O3 NPs, respectively, occurred. X-ray diffraction analysis indicated that magnetite was a unique representative iron mineral in ferrihydrite when active G. sulfurreducens cells were in direct contact with γ-Fe2O3 NPs. Because of the sorption of biogenic Fe(II) onto γ-Fe2O3 NPs instead of ferrihydrite, the addition of γ-Fe2O3 NPs could also contribute to increased duration of ferrihydrite reduction by preventing ferrihydrite surface passivation. Additionally, electron microscopy analysis confirmed that the direct addition of γ-Fe2O3 NPs stimulated the electrically conductive pili and cytochromes to stretch, facilitating long-range electron transfer between the cells and ferrihydrite. The obtained findings provide a more comprehensive understanding of the effects of iron oxide NPs on soil biogeochemistry.

Fluorescent magnetic PEI-PLGA nanoparticles loaded with paclitaxel for concurrent cell imaging, enhanced apoptosis and autophagy in human brain cancer.

Magnetic nanoparticles are regarded as a promising drug delivery vehicle with the improved efficacy and lowered side effects for antitumor therapy. Herein, the poly lactic-co-glycolic acid (PLGA) modified magnetic nanoplatform was synthesized using superparamagnetic γ-Fe2O3 nanoparticles (MNPs) as a core, and then labelled with polyethylenimine (PEI)-conjugated fluorescein isothiocyanate (FITC), and simultaneously loaded with antitumor drug paclitaxel (PTX) for theranostic analysis of antitumor effects investigated in human brain glioblastoma U251 cells. As a result, the prepared PEI-PLGA-MNPs showed a relatively round sphere with an average size of 80 nm approximately, and the FITC-labeling PEI-PLGA-MNPs were efficiently endocytosed by the U251 cells for cellular imaging. Moreover, the fabricated PEI-PLGA-PTX-MNPs also demonstrated an inhibition of the targeted cell proliferation and migration, and a programmed cell death, via both apoptosis modulating by a burst of reactive oxygen species (ROS) and autophagy with accumulation of autophagosomes and LC3-II signals detected in the treated glioblastoma U251 cells after uptaking. Therefore, the constructed nanoplatform could be effectively applied for simultaneous cellular imaging and drug delivery in human brain glioblastoma treatment in future.

Solvent evaporation driven entrapment of magnetic nanoparticles in mesoporous frame for designing a highly efficient MRI contrast probe

The present work reports a novel strategy of assembling maghemite (γ-Fe2O3) nanoparticles (NPs) in mesoporous silica host for developing a highly efficient MRI contrast probe. Shrinkage of hydrophobic environment due to the continuous evaporation of chloroform from Chloroform-in-Water emulsions pushes the hydrophobic γ-Fe2O3 NPs towards the hydrophobic pores of silica spheres resulting in a water soluble dense assembly structure. Mesoporous silica only with straight pores is found to be suitable for this particular entrapment process, while with curved and twisted pores, NPs are found to be seated on the surface only. So-developed assembly system has retained the superparamagnetic behaviour of its comprising NPs and exhibited high colloidal stability and biocompatibility. A significant enhancement in MRI transverse relaxivity to 386.2 mM−1 s−1 from 191.8 mM−1 s−1 of isolated primary γ-Fe2O3 NPs, has been obtained due to the strong magnetic field generated by the large number of NPs packed in the porous channels and consequent faster relaxation process. The fabrication strategy can be extended for the development of designed secondary nanostructures with new magnetic effects and physical properties.

Reduced surface spin disorder in ZrO2 coated γ-Fe2O3 nanoparticles

Surface spin disorder in microwave plasma synthesized zirconium dioxide (ZrO2) coated maghemite (γ-Fe2O3) nanoparticles have been studied by using AC and DC magnetic measurements. The inverse spinel structure of γ-Fe2O3 was confirmed by X-ray diffraction. The calculated average crystallite size of γ-Fe2O3 and ZrO2 phase was about 13 and 6 nm, respectively. Zero field cooled/field cooled measurements revealed average blocking temperature at 65 K. The fitted value of Keff deduced from simulation was higher than that of bulk γ-Fe2O3 magneto-crystalline anisotropy which is mainly due to surface spin disorder. However, it was lower than the reported value for uncoated γ-Fe2O3 nanoparticles, which is due to reduction in surface effects and interparticle interactions in ZrO2 coated nanoparticles. Below 25 K, a sharp increase in saturation magnetization was observed which is due to extra contribution of frozen surface spins to magnetism at low temperatures. The coercivity also showed a sharp increase below 25 K, which is due to presence of strong core-surface interactions at low temperatures. For AC susceptibility, Arrhenius law fit revealed weak interactions among the nanoparticles which were not strong enough to create a spin-glass state. In summary, ZrO2 coated γ-Fe2O3 nanoparticles showed reduced surface spin disorder and weak interparticle interactions which is due to non-magnetic ZrO2 coating.

A Tribological Study of γ-Fe2O3 Nanoparticles in Aqueous Suspension

In this work, the nano- and macroscale tribological properties of maghemite (γ-Fe2O3) nanoparticles in aqueous solution are compared and contrasted for alumina contacts as a function of nanoparticle concentration. A quartz crystal microbalance (QCM) technique was used for nanotribology measurements and a ball-on-disk method was used to measure macroscale friction coefficients. Statistical methods were employed to identify significant associations between the QCM and ball-on-disk measurements, employing selected candidate performance factors for each system. In particular, the macroscale response was parameterized by % reduction in the friction coefficient while candidate QCM “bulk” and “surface” performance factors were selected from functions of the frequency f and resistance Rm shifts upon addition of nanoparticles to the water surrounding the QCM. Incremental increases in concentration were performed and reductions in friction and drag forces were observed for concentrations up to 0.6 wt%, after which further reductions were not observed. The factor δRfilm/δffilm exhibited a linear correlation with the reduction in macroscale friction coefficient, defined as the ratio of the shift in resistance to the shift in frequency attributable to interfacial effects and changes in the glide plane location. Atomic force microscopy was also utilized to both qualitatively and quantitatively determine surface roughness before and after particle uptake, leading to the observations that particles are easily removed from the surface and do not significantly alter surface morphology.

γ-Fe2O3 nanoparticles aligned in porous carbon nanofibers towards long life-span lithium ion batteries

A freestanding γ-Fe2O3/carbon nanofiber composite as the anode of lithium ion batteries has been prepared with γ-Fe2O3 nanoparticles aligned in the tubular channels of the nanofibrous carbon matrix. Innovatively, a large amount of voids are generated for confining a very high active mass content by facilely verifying the ratio of carbon source and the sacrificing pore-forming agent, poly(methyl methacrylate). The best electrochemical performance at an active mass ratio of 70% is obtained with a high discharge capacity of 1088 mAh g−1 retained after 300 cycles at 0.2 C. Good rate capability and long life-span performance are further achieved at 0.5 and 2 C for 600 and 1000 cycles, respectively. In situ X-ray patterns further reveal better exploitation of the active materials for this γ-Fe2O3/carbon nanofiber composite electrode. The enhanced electrochemical performance of lithium ion batteries can be ascribed to the well-dispersed γ-Fe2O3 nanoparticles within the porous carbon matrix, as well as the cross-linked fiber morphology. Consequently, this study provides a superior electrode architecture for constructing flexible anodes of high-performance lithium ion batteries.

Tenacic Acids: A New Class of Tenacious Binders to Metal Oxide Surfaces.

The backbone of 2-hydroxyisophthalic acid was identified as a potential metal oxide anchor because of the perfect alignment of all three of its donor groups for binding to inorganic surfaces. It can therefore be used in the design of organic linkers for metal oxide based hybrid materials. Optimized and scalable methods for the synthesis of 2-hydroxyisophthalic acid (1) and its 5-substituted derivatives: 5-bromo- (2), 5-sulfooxy- (3), 5-hydroxy- (4), and 5-PEG600 (5) are presented. Dynamic light scattering (DLS) demonstrated that compound 2 inhibits Fe(OH)3 precipitation when FeIII aqueous solutions are titrated with NaOH, while similar titrations in the presence of the structurally-related isophthalic and salicylic acids, both missing the third donor group, show turbidity at pHs as low as 2.3 and 3.5, respectively. The adduct synthesized from 4.5 nm γ-Fe2 O3 nanoparticles and 5 is water-, alcohol- and CH2 Cl2 -soluble, and forms stable aqueous colloids in the pH range of 4.4-8.7. Moreover, at a pH close to neutral these colloids survive at 100 °C, demonstrating the high practicality of 2-hydroxyisophthalic acid for nanoparticulate inorganic/organic hybrid material design.

Tailoring nanostructured surfaces with plasmonic/magnetic multifunctional response

In this work, we present an innovative way to functionalize large surfaces combining both plasmonic and magnetic nanoparticles on a substrate, by the growth of bilayers and a subsequent single annealing. In particular, we show here the formation of Au and γ-Fe2O3 nanoparticles using this route. Thermal treatments promote the nanostructuration of the film plus a partial oxidation of Fe to form ferrimagnetic oxides. For this purpose, annealing conditions and the structure of the bilayer must be selected to achieve an optimal nanostructuration, avoiding the full oxidation of Fe to form antiferromagnetic hematite.

Comparison of Cd(II) preconcentrations by using magnetized Pleurotus erygnii and Coprinus micaceus and its determination in real samples

The utilization of the magnetized Pleurotus erygnii and Coprinus micaceus with γ-Fe2O3 nanoparticles as biosorbents for magnetic solid phase extraction (MSPE) of Cd(II) were investigated in details. The surface structures of magnetized P. erygnii and C. micaceus were investigated by the Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM) and energy dispersive X-ray (EDX). The best process conditions were tested and determined as pH 5, 3 mL min−1 flow rate, 100 mg of P. erygnii and C. micaceus on 75 mg of γ-Fe2O3 nanoparticles, 5 mL of 1 mol L−1 HCl as eluent, and 400 mL of sample volume for both biosorbents. The limit of detections (LOD) were achieved as 0.054 ng mL−1 and 0.040 ng mL−1 for magnetized P. erygnii and C. micaceus, respectively. Preconcentration factors were determined as 80 for both magnetized biosorbents. The recommended methods were validated using certificated reference materials. Cd(II) in different real samples were determined by ICP-OES (inductively coupled plasma optical emission spectrometry) after preconcentration with developed methods.

Catalyst Support Effect on the Activity and Durability of Magnetic Nanoparticles: toward Design of Advanced Electrocatalyst for Full Water Splitting.

Earth-abundant element-based inorganic–organic hybrid materials are attractive alternatives for electrocatalyzing energy conversion reactions. Such material structures do not only increase the surface area and stability of metal nanoparticles (NPs) but also modify the electrocatalytic performance. Here, we introduce, for the first time, multiwall carbon nanotubes (MWNTs) functionalized with nitrogen-rich emeraldine salt (ES) (denoted as ES-MWNT) as a promising catalyst support to boost the electrocatalytic activity of magnetic maghemite (γ-Fe2O3) NPs. The latter component has been synthesized by a simple and upscalable one-step pulsed laser ablation method on Ni core forming the core–shell Ni@γ-Fe2O3 NPs. The catalyst (Ni@γ-Fe2O3/ES-MWNT) is formed via self-assembly as strong interaction between ES-MWNT and Ni@γ-Fe2O3 results in NPs’ encapsulation in a thin C–N shell. We further show that Ni does not directly function as an active site in the electrocatalyst but it has a crucial role in synthesizing the maghemite shell. The strong interaction between the NPs and the support improves notably the NPs’ catalytic activity toward oxygen evolution reaction (OER) in terms of both onset potential and current density, ranking it among the most active catalysts reported so far. Furthermore, this material shows a superior durability to most of the current excellent OER electrocatalysts as the activity, and the structure, remains almost intact after 5000 OER stability cycles. On further characterization, the same trend has been observed for hydrogen evolution reaction, the other half-reaction of water splitting.

Pulverized Sponge Iron, a Zero-Carbon and Clean Substitute for Fossil Coal in Energy Applications

The direct combustion of recyclable metals has the potential to become a zero-carbon energy production alternative, much needed to alleviate the effects of global climate change caused by the increased emissions of the greenhouse gas CO2. In this work, we show that the emission of CO2 is insignificant during the combustion of pulverized sponge iron compared to that of pulverized coal combustion. The emissions of the other harmful pollutants NOx and SO2 were 25 and over 30 times lower, respectively, than in the case of pulverized coal combustion. Furthermore, 96 wt % of the solid combustion products consisted of micrometer-sized, solid or hollow hematite (α-Fe2O3) spheres. The remaining 4 wt % of products was maghemite (γ-Fe2O3) nanoparticles. According to thermodynamic calculations, this product composition implies near-complete combustion, with a conversion above 98%. The results presented in this work strongly suggest that sponge iron is a clean energy carrier and may become a substitute to pulverized c...