Effect of silica capping on the oxidation of Fe_{3}O_{4} nanoparticles in dispersion revealed by x-ray absorption spectroscopy (original) (raw)
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Journal of Magnetism and Magnetic Materials, 2014
The synthesis of iron oxide nanoparticles, i.e., magnetite was attempted by using only ferrous ion (Fe 2 þ ) as a magnetite precursor, under an ambient atmosphere. The room temperature reverse co-precipitation method was used, by applying two synthesis protocols. The freshly prepared iron oxide was also immediately coated with Stöber silica (SiO 2 ) layer, forming the coreshell structure. The phase, stoichiometry, crystallite and the particle size of the synthesized powders were determined by using X-ray diffraction (XRD) and transmission electron microscope (TEM), while the magnetic and oxidation behaviors were studied by using the vibrating sample magnetometer (VSM) and Mössbauer spectroscopy. Based on the results, the bare iron oxide nanoparticles are in the stoichiometry between the magnetite and the maghemite stoichiometry, i.e., oxidation occurs. This oxidation is depending on the synthesis protocols used. With the silica coating, the oxidation can be prevented, as suggested by the fits of Mössbauer spectra and low temperature magnetic measurement.
Iron Oxide Nanoparticles: Synthesis, Characterization and Applications
2017
Iron oxide is a mineral compound which occurs in different forms like hematite, magnetite and maghemite. Fe-based nanoparticles act as new generation environmental remediation technologies, and provide cost-effective solutions to the most demanding environmental cleanup problems. The synthesis of magnetic iron oxide nanoparticles (IONPs) has been intensively developed not only for its fundamental scientific interest but also for its many technological applications, such as targeted drug delivery, magnetic resonance imaging (MRI), gas sensing, photocatalytic degradation of organic pollutant, etc. In this review, different methods like sol-gel, co-precipitation, micro-emulsion, thermal decomposition to prepare iron oxide nanoparticles have been described. Characterization of iron oxide nanoparticles is done by scanning electron microscopy(SEM), Transmission electron microscopy(TEM), X-ray powder diffraction(XRD), and Fourier transform infrared spectroscopy(FT-IR). Also various applica...
Synthesis and Characterization of Silica-Encapsulated Iron Oxide Nanoparticles
IEEE Transactions on Magnetics, 2014
The properties of magnetic core-shell nanoparticles greatly depend on their core sizes and shell materials. Silica shell can prevent the magnetic nanoparticles from corrosion and agglomeration. In addition, the hydrolyzed silica can provide silanol groups to facilitate surface biofunctionalization. In this paper, superparamagnetic Fe O nanoparticles coated with SiO shell were prepared by a one-pot water-in-oil microemulsion method. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM) were utilized to characterize the morphology and magnetic properties of the synthesized nanoparticles. The results indicated that by tuning the water/surfactant molar ratio (Wo) of the microemulsion system, core size of the resulting Fe O nanoparticles can be altered. The size-controllable silica-encapsulated Fe O superparamagnetic nanoparticles have great potential to be applied as multifunctional tracer materials for magnetic particle imaging (MPI).
Environmental science & technology, 2014
Oxidation behavior of nano-Fe(0) particles in an anoxic environment was determined using different state-of-the-art analytical approaches, including high resolution transmission electron microscopy (HR-TEM) combined with energy filtered transmission electron microscopy (EFTEM), X-ray absorption spectroscopy (XAS), and magnetic measurements. Oxidation in controlled experiments was compared in standard double distilled (DD) water, DD water spiked with trichloroethene (TCE), and TCE contaminated site water. Using HR-TEM and EFTEM, we observed a surface oxide layer (∼3 nm) formed immediately after the particles were exposed to water. XAS analysis followed the dynamic change in total metallic iron concentration and iron oxide concentration for the experimental duration of 35 days. The metallic iron concentration in nano-Fe(0) particles exposed to water, was ∼40% after 35 days; in contrast, the samples containing TCE were reduced to ∼15% and even to nil in the case of TCE contaminated sit...
Synthesis, Characterization and Applications of Iron Oxide Nanoparticles – a Short Review
Journal of Aerospace Technology and Management, 2015
Iron oxide is a mineral compound that shows different polymorphic forms, including hematite (α-Fe2O3), magnetite (Fe3O4) and maghemite (γ-Fe2O3). Solid propulsion technology nanoparticulate materials, such as hematite and maghemite, exhibit high performance on thermal decomposition of ammonium perchlorate. The enhanced catalytic effect of metallic iron oxide nanoparticles is attributed to their particle size, more active sites and high surface area, which promotes more gas adsorption during thermal oxidation reactions. Nowadays, metallic iron nanoparticles can be synthesized via numerous methods, such as co-precipitation, sol-gel, microemulsion, or thermal decomposition. Although there are data on these synthetic methods in the literature, there is a lack of details related to nanoparticulate oxides and to their characterization techniques. In this context, this short review based on scientific papers, including data from the last two decades, presents methods for obtaining nanoparticulate iron oxides as well as the main aspects of the different characterization techniques and also about the decomposition aspects of these nanomaterials. Morphologies and structures of iron oxides can be characterized through transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy. As for textural properties, they are usually determined by physical adsorption techniques.
Size-dependent oxidation in iron/iron oxide core-shell nanoparticles
Physical Review B, 2003
We report a detailed morphological and structural characterization of iron/iron oxide core-shell nanoparticles with x-ray diffraction and x-ray absorption spectroscopy performed at both the Fe and O K edges. Core-shell nanoparticles with core size ranging from 7 to 21 nm were synthesized using the inert gas condensation technique followed by 12 h of controlled surface oxidation. Rietveld analysis of diffraction patterns shows the presence of ␣-Fe nanoparticles surrounded by a 2-3 nm-thick oxide layer with a disordered cubic spinel structure. Magnetite (Fe 3 O 4 ) and maghemite (␥-Fe 2 O 3 ), two different iron oxides, share this lattice structure, but x-ray diffraction was not able to distinguish between the two. An analysis of the Fe and O x-ray absorption spectra in both the near-edge and the extended energy regions is described. The analysis of the extended spectra was performed using the ab initio calculation of all significant contributions to the absorption cross section. We show that there are size-dependent changes in the local structure and oxidation state of the oxide shell, the relative fraction of maghemite increasing at the expense of magnetite as the core dimensions decrease. This size/structure correlation has been explained in terms of morphological and structural disorder arguments
Synthesis and Characterization of Iron Oxide Nanoparticles by Solid State Chemical Reaction Method
Journal of Cluster Science, 2010
Iron oxide nanoparticles dispersed in aluminum (Al) or silicon (Si) oxides were prepared via a polymeric precursor derived from the Pechini method. The samples were characterized by thermogravimetric analysis, Fouriertransform infrared spectroscopy, X-ray diffraction, N 2 adsorption/desorption isotherms (Brunauer-Emmett-Teller, BET), Mössbauer spectroscopy, and vibrating sample magnetometry (VSM). BET analysis shows that the samples are mesoporous materials and have a high surface area. The size of the Fe 2 O 3 nanoparticles in Al 2 O 3 is smaller than that in SiO 2 . Mössbauer spectra of the samples show that the Fe 2 O 3 nanoparticles in Al 2 O 3 are non-magnetic at room temperature but magnetic below 50 K. The FeSi samples are magnetic at both room and low temperatures. The magnetic measurements with VSM confirmed this point.
Journal of Magnetism and Magnetic Materials, 2007
Synthesis of magnetite (Fe 3 O 4) nanoparticles under oxidizing environment by precipitation from aqueous media is not straightforward because Fe 2+ gets oxidized to Fe 3+ and thus the ratio of Fe 3+ :Fe 2+ ¼ 2:1 is not maintained during the precipitation. A molar ratio of Fe 3+ :Fe 2+ smaller than 2:1 has been used by many to compensate for the oxidation of Fe 2+ during the preparation. In this work, we have prepared iron oxide nanoparticles in air environment by the precipitation technique using initial molar ratios Fe 3+ :Fe 2+ p2:1. The phases of the resulting powders have been determined by several techniques. It is found that the particles consist mainly of maghemite with little or no magnetite phase. The particles have been suspended in non-aqueous and aqueous media by coating the particles with a single layer and a bilayer of oleic acid, respectively. The particle sizes, morphology and the magnetic properties of the particles and the ferrofulids prepared from these particles are reported. The average particle sizes obtained from the TEM micrographs are 14, 10 and 9 nm for the water, kerosene and dodecane-based ferrofluids, respectively, indicating a better dispersion in the non-aqueous media. The specific saturation magnetization (s s) value of the oleic-acid-coated particles ($53 emu/g) is found to be lower than that for the uncoated particles ($63 emu/g). Magnetization s s of the dodecane-based ferrofluid is found to be 10.1 emu/g for a volume fraction of particles j ¼ 0.019. Zero coercivity and zero remanance on the magnetization curves indicate that the particles are superparamagnetic (SPM) in nature.
Economically viable synthesis of Fe3O4 nanoparticles and their characterization
Polish Journal of Chemical Technology
Economically viable synthesis of Fe3O4 nanoparticles and their characterization Nano iron oxide particles (Fe3O4) were synthesized by coprecipitation of Fe2+ and Fe3+ by ammonia solution in the aqueous phase. Various instrumentation methods such as X ray Diffractometry (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) and Vibrating Sample Magnetometery (VSM) were used to characterize the properties of nanoparticles. The size of the nanoparticles was measured and was found to be between 10 to 15 nm. The value of saturation magnetization of the nanoparticles was found to be 55.26 emu/g. The BET surface area of nano iron oxide particles measured to be 86.55 m2/g.
The effect of carboxylic acids on the oxidation of coated iron oxide nanoparticles
Journal of Nanoparticle Research, 2018
57 Fe Mössbauer spectroscopy, XRD, and TEM were used to investigate the effect of mandelic-and salicylic acid coatings on the iron oxide nanoparticles. These two carboxylic acids have similar molecules size and stoichiometry, but different structure and acidity. Significant differences were observed between the Mössbauer spectra of samples coated with mandelic acid and salicylic acid. These results indicate that the occurrence of iron microenvironments in the mandelic-and salicylic acidcoated iron oxide nanoparticles is different. The results can be interpreted in terms of the influence of the acidity of carboxylic acids on the formation, core/shell structure, and oxidation of coated iron oxide nanocomposites.