Iron Oxide Samples Research Articles

A structural, magnetic and colloidal stability study of uncoated and silica coated iron oxide samples prepared in two different surfactants

The discovery of new magnetic materials of interest in the biomedicine field is a relevant topic in current research. For years, our research group has been investigating the obtaining and study of nanostructured magnetic samples that behave superparamagnetically to enable their transport in living organisms. We present here a study that summarizes the structural characteristics, magnetic behavior and stability of two Fe3O4 samples synthesized by coprecipitation that were dispersed using two different surfactants (oleylamine, OL, and oleic acid, OA), and two others prepared from the previous ones by reaction with tetraethyl orthosilicate (TEOS). The relationships between the surfactant used in the synthesis, the presence of a certain maghemite (γ-Fe2O3) content, the influence of silica shell thickness and magnetic behaviour of all samples were systematically studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), Mössbauer spectroscopy and H vs. M loops. Rietveld refinements of the XRD profiles confirmed a partial oxidation of the non-silica-coated samples and FTIR spectra of the uncoated samples showed a very strong broad metal-oxygen band and additional sets of bands from the different organic chains of the two surfactants. Individual particles with a mean diameter of 7 and 9 nm were distinguished in TEM images of uncoated magnetic samples. Mössbauer data indicated the presence of non-stoichiometric magnetite in all samples, in agreement with XRD refinements. Magnetic measurements confirmed the superparamagnetic behavior of all the samples. Highest negative zeta potential values are found for the silica covered samples in both acidic and basic medium, being Fe3O4-AO@SiO2 the best suited for the purposes of its dispersibility in future applications. Low polydispersity index (PDI) values confirmed the best stability and dispersibility of all samples investigated in tetrahydrofuran (THF).

Determination and study of correlations of relative sensitivity factors in metal and metal oxide samples by glow discharge mass spectrometry

The determination of relative sensitivity factor (RSF) plays a crucial role in achieving accurate quantitative analysis in glow discharge mass spectrometry (GD-MS). In this study, the RSF of typical elements in 14 metal and metal oxide matrices were determined, and their correlation with discharge parameters, matrix effects, the first ionization energies and sample shapes were investigated. It was found that discharge gas flow exerted a minor influence on RSF values in a nickel (Ni) metal sample, whereas discharge current significantly affected RSF, with variations up to 57.00 % for cobalt (59Co). The results revealed that matrix effects were more pronounced in metal oxides, with the relative standard deviation (RSD) of RSF for typical elements ranging from 25.17 % to 101.04 %. RSF values for the same element across different metal oxides showed a correlation with lattice binding energy (U0). Particularly, RSF values for 12 elements including 23Na, 27Al, 28Si, 45Sc, 52Cr, 56Fe, 59Co, 88Sr, 130Te, 138Ba, 139La and 140Ce within 7 metal oxides showed a significant correlation with U0 of the metal oxides. In terms of sample shape, pin samples generally yielded higher RSF values than flat samples in both metals and oxides. RSF accuracy was confirmed with standard samples of zirconium (Zr 73 MR10002 and Zr IARM 705–18) and iron oxides (Fe2O3-1 and Fe2O3-2) with relative errors within 17.50 % except for 12C. Subsequently, these RSF values were effectively utilized for the quantitative analysis of samples collected from the China Space Station (CSS). This comprehensive analysis elucidates the multifaceted influences on RSF values, enhancing the precision of trace element quantification in GD-MS.

Multifunctional application of different iron oxide nanoparticles

Abstract Iron oxide nanoparticles have found wide applications in different fields of biomedicine and advanced catalytic applications. Several studies have suggested using iron oxide nanoparticle (Fe2O3-NPs) be a potential candidate for antibacterial activity assessment. Iron oxide nanoparticles, apart from being available extensively and cheap, also plays a vital part in multiple biological processes, making it an interesting choice of selection. The aim of the present study revolves around synthesis and characterization of iron oxide Fe2O3-NPs, followed by assessment of its antimicrobial activities and its catalytic behaviour. Synthesis of Fe2O3-NPs was performed by co-precipitation approach, and commercial iron oxide samples were studied for the comparison. The silver nanoparticles were also doped to the iron oxide nanoparticles and studied for the synergic effect. The samples characterization was done by UV-visible, X-ray diffraction (XRD), Scanning electron microscopy (SEM) with EDS and transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), Raman Spectroscopy (RAMAN). Antimicrobial activity was checked by agar diffusion assay against Gram positive and Gram negative bacteria. The electrode performance of the iron oxide samples was done by cyclic voltammetry to explore their application in the energy storage and sensor.

Nanocrystalline Iron Oxides with Various Average Crystallite Size Investigated Using Magnetic Resonance Method

A series of nanocrystalline iron oxide samples (M1–M5) which differ from each other in average crystallite size (from 26 to 37 nm) was studied. The raw material was nanocrystalline iron with an average crystallite size equal to 21 nm promoted with hardly reducible oxides: Al2O3, CaO, K2O (in total, max. 10 wt%). Nanocrystalline iron was subjected to oxidation with water vapor to achieve different oxidation degrees (α = 0.16–1.00). Metallic iron remaining in the samples after the oxidizing step was removed by etching. Magnetic resonance spectra of all samples were obtained at room temperature. All resonance lines were asymmetric and intense. These spectra were fitted by Lorentzian and Gaussian functions. All spectral parameters depend on the preparation method of the nanoparticles. We suppose that the Lorentz fit gives us a spectrum from larger agglomerated sizes whereas the Gaussian fit comes from much smaller magnetic centers. For the nanocrystalline samples with the largest size of iron oxide nanocrystallites, the highest value of total integrated intensity was obtained, indicating that at smaller sizes, they are more mobile in reorientation processes resulting in more settings of anti-parallel magnetic moments. The magnetic anisotropy should also increase with the increase in size of nanocrystallites.

Novel mesoporous iron oxide synthesized from naturally occurring magnetic sand: A potential and promising catalyst for chemical processes

This paper presents the synthesis of iron oxide from natural magnetic sand that was obtained from Michika, Adamawa State, Nigeria. Characterization of the raw magnetic sand and the synthesized iron oxide was performed to investigate the effect of the synthesis method on functional groups, morphology, composition, crystallinity, acidity and surface area/pore distribution using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy – energy dispersive X-ray (SEM – EDX), X-ray fluorescence (XRF), X-ray diffraction (XRD), BET and pyridine FTIR, respectively. The XRF analysis of the two samples revealed a significant variation in oxide composition. The raw magnetic sand had an iron oxide content of 64.69 wt%, which increased to 85.20 wt% after synthesis. Furthermore, the SEM-EDX analysis indicated a decrease in average particle size from 114.6 and 36.8 µm for the respective samples. The XRD patterns revealed that the crystallinity increased after synthesis. FTIR showed the associations of functional groups present in the sample. The wavebands in the range 550 – 630 cm−1, which correspond to the Fe – O bond, improved clearly in the synthesized iron oxide sample, particularly at 582 cm−1. The pyridine FTIR depicts that the overall acidic site is higher in the synthesized sample. The N2 adsorption–desorption procedure shows an increased BET surface area from 9.394 m2/g (raw) to 24.851 m2/g (synthesized). Overall, the results showed that the synthesized mesoporous iron oxide exhibits properties similar to materials that have a high potential for application as catalysts in chemical processes.

Evolution of sample optical pathlength during diffuse reflectance FT-IR analyses

In situ and operando diffuse reflectance FT-IR (DRIFTS) studies are often carried out over samples that may undergo changes in optical properties due to stronger absorptivity (darkening), for instance when coking or being reduced. The variation of IR optical pathlength of two Fe and Co-based Fischer-Tropsch catalysts treated at different temperatures was investigated through the use of an internal standard CaCO3 that was physically mixed with the catalyst. The CaCO3 overtone band at 1795 cm-1 was used, exhibiting an integral molar absorption coefficient ε = 2.68 × 105 cm mol-1. The IR penetration depth was negligible over the iron oxide sample once reduced above 400 °C, due to the formation of a strongly absorbing material. A reduction of the cobalt sample up to 350 °C revealed large changes of optical pathlength (dropping four-fold from 66 to 16 µm), likely related to the onset of cobalt oxide deep reduction. These data indicate that changes in optical pathlength should be considered when attempting quantitative DRIFTS analyses and that mixing a small concentration of CaCO3, e.g. 2 wt%, is a suitable way of doing so.

Analysis and characterization of opto-electronic properties of iron oxide (Fe2O3) with transition metals (Co, Ni) for the use in the photodetector application

There are several uses for ultraviolet photodetectors, including in the scientific, military, and industrial sectors. In this sense, UV photodetectors must have high responsiveness, be insensitive to visible light, and be inexpensive to produce. For this purpose, we report the development of Co and Ni based iron oxide nanoparticles via the cost effective low temperature sol–gel auto-combustion process. XRD study approves the cubic crystal structure of iron oxide (Fe2O3) with predominant orientation along (311) direction. A sharp and strong peak is obtained at 583 cm−1 and 594 cm−1 for both samples in FT-IR spectra assigned to metal oxide Fe–O network system which approves the formation of iron oxide. Raman spectroscopy analysis reveals the presence of two A1g and five Eg phonon modes in the case of both samples. Absorption study exhibits the strong absorption peaks for the iron oxide sample doped with cobalt and nickel, while poor absorption was noticed from the pure iron oxide nanoparticles. The large and low energy band gap values are found to be 2.77 eV and 1.68 eV for pure Fe2O3 and cobalt and nickel doped Fe2O3 nanoparticles, respectively. Stone and cloud-like shape morphology was observed from SEM analysis. The EDX spectra reveal the presence of essential elements, like Fe and O in the case of pure iron oxide while Fe, O, Co and Ni in the case of transition metals doped iron oxide nanoparticles. The photoluminescence (PL) spectroscopy technique was recorded the luminescent properties which reveals the decrease in PL intensity that confirms the decline in electron–hole recombination. Therefore, I–V characterization analysis reveals that electrical conductivity increases with the addition of metals due to decrease in electron–hole recombination with the co-doping of metals. These modified opto-electronic properties of the developed Fe2O3 by metals co-doping make it suitable candidate for the use in photodetector application.

Characterization of Iron Oxide Samples Using Mössbauer Spectroscopy and Hysteresis Loops

In this work, we used Mössbauer spectroscopy and magnetometry at room temperature to investigate the magnetic properties of four different iron oxide samples (α-FeOOH, γ-Fe2O3, or Fe3O4 and α-Fe2O3) before and after annealing at 1000°C for one hour. We found that after annealing, all four samples exhibited the same properties as hematite (α-Fe2O3). These results show that the iron oxides in this study underwent phase transformations from an initial phase of either α-FeOOH, γ-Fe2O3, or Fe3O4 to a single final phase of α-Fe2O3.

Waste toner-derived porous iron oxide pigments with enhanced catalytic degradation property

‘Wealth from Waste’ is an emerging concept, since it leads an effective waste treatment and waste recyclability. On the other hand, cost effective production iron oxide (IO) nanomaterials is still needed to develop, owing to their wide applications. Herein, we proposed a simple direct calcination method to prepare porous IO (Fe3O4 and Fe2O3) nanomaterials from waste toner powder. Characterization techniques reveal that a structural change happened from Fe3O4 to γ-Fe2O3 and γ-Fe2O3 to α-Fe2O3 at the calcination temperature of 500 °C and 700 °C respectively. Consequently, optical (band gap) and magnetic parameters of IO samples were significantly varied. The pigment characteristics of the IO samples were evaluated using Commission Internationale de l’Eclairage (CIE) analysis. IO900 sample has shown good brown-red coloration (L* = 43.11, a* = 13.26 and b* = 5.69) and it also exhibited good stability in acidic and basic conditions. Practical applicability of IO pigments were also tested by mixing with plaster of paris (PP) powder. Further, porous IO samples were also used as catalysts in the reductive degradation of methyl orange (MO) dye in presence of excess sodium borohydride (NaBH4). IO, prepared at 900 °C exhibited ∼99.9% reduction efficiency within 40 min. Recycling experiments indicated that IO900 possess good stability up to seven cycles. The present porous IO samples will become potential in pigment and environmental remediation.

Investigations on the structural, electrical, magnetic and 57Fe Mössbauer studies of YFeO3

Yttrium iron oxide (YFeO3) sample is prepared by sol-gel method. X-ray diffraction (XRD) graph shows highly defined peaks showing that the compound possess crystalline nature. The Rietveld refined XRD data revealed that the sample has orthorhombic structure with Pbnm space group. The experimental data of structural parameters is in accordance with DFT calculated theoretical structural parameters.Fourier Transform Infrared Spectroscopy (FTIR) shows that a pure phase of YFeO3 isbeen formed. Scanning electron micrograph of YFeO3 reveals that the sample has non uniform grain structure with slight porosity in it. The grains have an average grain size of about 200 nm. Raman spectroscopic studyconfirms the structure and phase purity of the sample. The M-H curve of YFeO3shows a hysteresis loop, with a coercive field of 61 Oe and a residual magnetization of 0.516 emu/gm. Weak ferromagnetic nature of YFeO3 is attributed to the remnant magnetization value, which suggests that Fe+3 spins are slightly canted but not perfectly anti parallel. Room temperature P-E measurement of YFeO3 shows lossy ferroelectric nature of the sample.Positive Up Negative Down (PUND) measurementsdone on YFeO3 sample gives the trueswitchable polarization to be0.002 C/cm2.From the ln J versus ln E plot, the slope of the line is found to be 1.25, indicating Ohmic conduction in the sample. At 300 K, 57Fe Mössbauerspectra of YFeO3 exhibit a single magnetic sextet, confirming the presence of a single Fe site and the absence of any magnetic impurities. The value of Isomer shift is0.37 mm/s, quadrupole splitting is found to be 0.01 mm/s, Line width (Г) = 0.47 mm/s and hyper fine magnetic field (Bhf) of 49.8 T are being calculated from 57Fe Mössbauer measurements.

Hydrogen production and photocatalytic activity of HTAB assisted titanium doped α-Fe2O3 nanoparticles treated by microwave irradiation process

• Ti doped Iron oxide nanoparticles prepared by Microwave irradiation method. • Impact of different weight percentage of Ti doped hematite nanoparticles tuned the bandgap energy. • The spherical, granules, hexagonal blocks, platelets and foam like structures are formed in lower to higher doping of Ti in iron oxide nanoparticles. • Mainly, photocatalytic degradation percentages of Ti doped iron oxide nanoparticles were measured. The present work influence of titanium doping on morphology, optical, stoichiometry, electrical and photocatalytic efficiency of α-Fe 2 O 3 nanoparticles which were synthesized via the microwave irradiation process. Titanium doped iron oxide nanoparticles are synthesized at different doping wt % of Ti. The increase of Titanium doping level in the iron oxide nanoparticles influences more on particle size and it increases from 38 nm for lower Ti level to 58 nm at higher Ti level. The band gap values from 2.49 eV to 2.34 eV especially in the visible light region. The valence band top resulting in decreases of band gap of α-Fe 2 O 3 , considering tuneable bandgap of Ti doped hematite nanoparticles for photocatalytic activity and MB dye degradation process performed under sunlight irradiation for hydrogen production. The morphological changes like spherical, granules, rhombus and platelet shapes are confirmed from FESEM images. The XPS results shows peaks like Ti 2p 3/2 and Ti 2p 1/2 of Ti doped iron oxide samples. The binding energy of 532 eV is almost indicated oxygen environment of α-Fe 2 O 3 . The HRTEM images are supported for morphological transformation. Overall incorporation of TiO 2 on iron oxide nanoparticles offer possibilities for utilizing this inexpensive and earth-abundant oxide materials in the pollution controlling areas.

Microstructural analysis of iron ore samples with bitumen as a binder

In the present investigation, the direct reduction of magnetite and hematite powder with and without 5% bitumen at various temperatures has been studied in a hydrogen atmosphere. The prepared samples were fired in the temperature range of 673–1373 K to observe the weight loss and to find the effect of the bitumen in the samples. The microstructural results show that bitumen mixed with iron ore powder exhibited a more porous structure with cracks after reduction at 773 K and 973 K respectively. At temperatures above 1073 K, the carbon present in bitumen contributed to an enhanced rate of reduction of iron oxide samples. It was observed that, the reactivity of samples was affected by the level of impurities, crystal structure, binder, and composition of the reducing agent.Graphical

Synthesis of nanostructured iron oxides and study of the thermal crystallization process using DSC and in situ XRD experiments

Using a coprecipitation route in aqueous medium with different precipitating agents (NH4OH and NaOH), iron-oxide nanostructures were prepared with distinct structural and magnetic properties. X-ray diffraction (XRD), 57Fe Mössbauer spectroscopy and N2 sorption experiments indicated that the sample synthesized with NaOH had nanocrystalline goethite as the dominant phase, with a specific surface area (SSA) of 80 m2/g, whereas the sample synthesized with NH4OH was X-ray amorphous, with SSA = 270 m2/g. The crystallization process of the amorphous material was investigated in detail, using in situ XRD experiments combined with differential scanning calorimetry (DSC). The X-ray diffractograms recorded at high temperatures for this sample showed first the formation of maghemite, which was then converted into hematite as the heat treatment temperature increased. DSC curves recorded at different heating rates allowed the assessment of the kinetics of the crystallization process, with identification of two consecutive steps (formation of maghemite and conversion of maghemite into hematite) and the determination of the corresponding activation energies (166 and 273 kJ/mol, respectively). From the magnetic viewpoint, the nanostructured iron oxide samples showed non zero magnetization values, indicating a strong contribution form the uncompensated iron spins at the particle surfaces, leading to a superparamagnetic regime (i.e., magnetically non-blocked state) observed for temperatures above 50 K for both samples. These results evidenced how the chemical composition and the structural features of nanostructured iron oxides can be controlled by the conditions employed in the synthesis and the posterior thermal treatments performed on these materials.

Analysis of the influence of iron source and its occurrence state on the color of celadon glaze

Using different iron sources of industrial iron oxide, loess, slag, and golden soil, iron elements were introduced into the formula respectively, and celadon samples were prepared in a reducing atmosphere. To reveal the influence of iron source on glaze color, the celadon samples were analyzed by Spectrophotometer, X-ray fluorescence spectroscopy, X-ray diffractometer, scanning electron microscope, and X-ray photoelectron spectrometer. The results show that the glaze color of the samples is quite different, samples using iron oxide and golden soil as iron source raw materials are sky-green, the loess sample is olive green, and the slag sample is similar to the bean green. There are many quartz crystals in the glaze of iron oxide samples, and the turbidity is high. The liquid-liquid phase separation size close to the quartz crystal is large, and far away from the crystal is small. Industrial iron oxide is the easiest to reduce, followed by goethite in golden soil, and reduction of hematite in slag and the iron in loess in the form of isomorphic is successively more difficult. The difference in the form of occurrence of iron is the most essential factor that causes the difference in glaze color.

One-step solution auto-combustion process for the rapid synthesis of crystalline phase iron oxide nanoparticles with improved magnetic and photocatalytic properties

We report the solution auto-combustion (AC) process for the rapid synthesis of Fe3O4 nanoparticles derived from the sol–gel (SG) process. The citric acid (CA) and tartaric acid (TA) is used as gelling agents in the SG process, where the citric acid turns into a fuel that combusts the gel and yields a highly magnetic crystalline phase Fe3O4 nanoparticles in one step with an average particle size of 50 nm. In contrast, the citric acid at different concentrations and tartaric acid at any concentrations do not lead to any combustion process and yield amorphous iron oxides. Upon annealing, these CA and TA derived iron oxide samples are turned to crystalline phase α-Fe2O3 particles. In contrast, the as-synthesized AC sample (i.e. Fe3O4) is oxidized to γ-Fe2O3 phase, which is confirmed from their respective XRD, Rietveld refinement and XPS studies. All the synthesized iron oxide phases showed broad visible light absorption. The room temperature M−H hysteresis curves obtained from VSM revealed that the Fe3O4 and α-Fe2O3/γ-Fe2O3 phases exhibit super-paramagnetic and ferromagnetic properties, respectively. The photocatalytic efficiencies of the samples are found to be in the order of Fe3O4 > γ-Fe2O3 > α-Fe2O3 with 98, 87, 79/73% degradation of rhodamine B dye at the end of 3 h and H2 evolution rate over these systems is found to be 2.1, 1.3 and 0.92/0.89 mmol/h/g, respectively under simulated solar light irradiation. The photocatalytic recycle studies demonstrated that all the synthesized photocatalysts possess excellent chemical and photo-stabilities.

Heterophase synthesis of ferrite cobalt Elena E. Nikishina

Objectives. The study aimed to develop new methods for the synthesis of cobalt ferrite (CoFe2O4), which is a precursor for the synthesis of CoFe2O4-based functional materials, as well as to study the physicochemical properties of the obtained phases.Methods. Two methods were used for the synthesis of CoFe2O4: (1) heterophase interaction of hydrated iron oxide with cobalt(II, III) oxide and (2) heterophase interaction of hydrated iron oxide with an aqueous solution of cobalt(II) sulfate (CCo = 0.147 mol/L, solid/liquid = 1:43). In both cases, the precursor was hydrated iron oxide (Fe2O3, 84.4 wt %), which was obtained by the heterophase interaction of iron(III) chloride with a concentrated ammonia solution (6.0–9.5 mol/L). The resulting intermediate products were subjected to thermal treatment at 750 °C (synthesis 1) and at 900 °C (synthesis 2) for 10–30 h in increments of 10 h. The synthesized phases and products of their thermolysis were studied by differential thermal analysis and differential thermogravimetry (DTA–DTG), X-ray diffraction analysis (XRDA), and granulometry.Results. The hydrated iron oxide sample remained amorphous even up to the crystallization temperature of 445 °C, which corresponds to the exothermic effect on the DTA curve. Further heating led to the α-modification of iron(III) oxide of the hexagonal system (a = b = 5.037 ± 0.002 Å; c = 13.74 ± 0.01 Å), which has an average particle size of 1.1 μm. XRDA results showed that a synthesis temperature of 750 °C (synthesis 1) and a heat treatment duration of 30 h were sufficient for the formation of a single-phase cobalt ferrite (a = 8.388 ± 0.002 Å) with an average particle diameter of 1.9 μm. For synthesis 2, a higher temperature of 900 °C was used because sample weight loss (about 12.5%) was observed in the temperature range of 720–810 °C based on the DTA results, which was due to the removal of SO2 and SO3. Moreover, when synthesis temperature and duration were at 900 °C and 30 h, respectively, CoFe2O4 with a = 8.389 ± 0.002 Å was formed. The results of the granulometric analysis showed that particles of different diameters were formed. The smallest particle size (1.5 μm) of cobalt ferrite was obtained by the heterophase interaction of hydrated iron(III) oxide (Fe2O3, 84.4 wt %) with an aqueous solution of cobalt sulfate with CCo = 0.147 mol/L. Conclusions. Depending on the method used for the synthesis of cobalt ferrite, particles of different diameters are formed. The smallest particle size of cobalt ferrite was obtained from the heterophase interaction of hydrated iron(III) oxide with an aqueous solution of cobalt(II) sulfate.

Natural tannic acid (green tea) mediated synthesis of ethanol sensor based Fe3O4 nanoparticles: Investigation of structural, morphological, optical properties and colloidal stability for gas sensor application

A green tea mediated combustion synthesis route is implemented to prepare iron oxide nanoparticles. Chemical ferric nitrate and natural tannic acid extracted from green tea are used to prepare iron oxide nanoparticles, and the prepared sample is annealed at 350 °C. The crystal structure and phase of iron oxide nanoparticles have been analyzed using X-ray Diffraction (XRD). The crystallite size (D) and lattice constant (a) of the prepared and annealed samples are calculated. The mean crystallite size is found to be 23.4 nm for the prepared sample and 30.1 nm for the annealed sample. The morphological and compositional analysis are characterized through scanning electron microscopy (SEM) and EDX. The particle shape and size are recorded through tunneling electron microscopy (TEM) and the average grain size is 25 nm for as-prepared and 32 nm for annealed samples. The stability of colloidal systems of iron oxide nanoparticles has been assessed using the zeta potential. The as-prepared sample has a decent stability value of − 58.3 mV, whereas the annealed sample has an exceptional value of − 60.1 mV. The optical band gap of the samples is calculated from ultra-violet (UV–vis) spectra, and the energy band gap of the as-prepared samples is 2.24 eV, and the annealed sample is 2.78 eV. The gas sensing behavior of as-prepared and annealed iron oxide samples is analyzed for different aspects related to operating temperature, gas concentration, response-recovery time, and different gases.

Magnetic Properties and SAR for Gadolinium-Doped Iron Oxide Nanoparticles Prepared by Hydrothermal Method

This study is an attempt to produce gadolinium-doped iron oxide nanoparticles for the purpose of utilization in magnetic fluid hyperthermia (MFH). Six gadolinium-doped iron oxide samples with varying gadolinium contents (GdxFe3−xO4,x=0, 0.02, 0.04, 0.06, 0.08, 0.1) were prepared using the hydrothermal method at 180 °C and high vapor pressure to incorporate gadolinium ions in the iron oxide structure. The samples were indexed as GdIO/x, with x varying from 0.0 to 0.1. The results reveal that gadolinium ions have a low solubility limit in the iron oxide lattice (x = 0.04). The addition of gadolinium caused distortion in the produced maghemite phase and formation of other phases. Based on X-ray diffraction (XRD) analysis and photoelectron spectroscopy (XPS), it was observed that gadolinium mostly crystalized as gadolinium hydroxide, Gd (OH)3 for gadolinium concentrations above the solubility limit. The measured magnetization values are consistent with the formed phases. The saturation magnetization values for all gadolinium-doped samples are lower than the undoped sample. The specific absorption rate (SAR) for the pure iron oxide samples was measured. Sample GdIO/0.04, pure iron oxide doped with gadolinium, showed the highest potential to produce heat at a frequency of 198 kHz. Therefore, the sample is considered to hold great promise as an MFH agent.

Cobalt Iron Oxides Prepared by Acidic Redox-Assisted Precipitation: Characterization, Applications, and New Opportunities.

The microscopic homogeneity of mixed metals in a single-phase oxide is a critical issue in improving material performance. Aqueous alkaline precipitation is the most common approach but it has the limits of microscopic inhomogeneity because of intrinsically different precipitation rates between metal cations. Herein, we demonstrate a new preparation of uniformly structural substituted cobalt iron oxides via acidic redox-assisted precipitation (ARP) upon the interaction of CoII and K2FeO4. This low-pH synthesis features the redox process between Co and Fe, presumably through the formation of inner-sphere complexes such as [(H2O)5CoII-O-FeVIO3]. With the nucleation starting from such complexes, one obtains a product with predominantly mixed-metal Co-O-Fe moieties, which improves the electrical conductivity of the product. This work further analyzes how the properties of the product species evolve during the hydrothermal synthesis step in the ARP process. We see that the Co/Fe ratio slowly increases from about 1:1 to a final value of 2:1, but does not reach the expected redox stoichiometry of 3:1. At the same time, the magnetization also increases, reaching a value of 16.9 emu g-1 for the final superparamagnetic product, which is three times higher than the value of monometallic Co3O4 and Fe2O3. The cobalt iron oxide samples obtained from ARP also possess superior oxygen evolution activity (307 mV overpotential at 10 mA cm-2 μg-1) compared to a mixture of Co3O4 and Fe2O3 (422 mV) or pure cobalt oxide (350 mV), highlighting the structure-induced enhancement of the catalytic activity. The difficult synthesis of evenly blended trinary/quaternary metals in a single-oxide phase may become possible in the future via ARP.

Magnetic interactions in graphene decorated with iron oxide nanoparticles

We present the studies of structural and magnetic properties of graphene composites prepared with several quantities of α-Fe2O3 dopant of 5%, 25% and 50% made with either ethanol or acetone. Our studies showed the presence of a weak magnetic order up to room temperature and saturation magnetization close to 0.2 emu g−1 in pure commercial graphene. With regard to magnetic properties of our graphene + iron oxide samples, the solvent used during the preparation of the composite had a significant influence on them. For graphene + Fe2O3 samples made with acetone the magnetic properties of pure graphene played a major role in the overall magnetic susceptibility and magnetization. On the other hand, for graphene + iron oxide samples made with ethanol we observed the presence of superparamagnetic blocking at T < 110 K which was due to the additional appearance of γ-Fe3O4 nanoparticles. Changes in the synthesis solvent played a major role in the magnetic properties of our graphene + Fe2O3 nanocomposite samples resulting in much higher saturation magnetization for the samples made with ethanol. Both the shape and the parameters characterizing magnetization hysteresis loops depend strongly on the amount of iron oxide and changes in the preparation method.