Metallic Iron Nanoparticles Research Articles

Novel metallic iron/manganese–zinc ferrite nanocomposites prepared by microwave hydrothermal flash synthesis

Metallic iron (α-Fe)/manganese–zinc ferrite (Fe3−x−yMnxZnyO4) nanocomposites have been successfully synthesized for the first time using microwave hydrothermal treatment of alcoholic solutions of chloride precursors and sodium ethoxide. This new type of nanocomposites, never obtained by conventional synthesis, can now be produced in a short period (e.g. 15s). The powders were characterized by X-ray diffraction, transmission electron microscopy and magnetic properties were measured. In most cases, three classes of crystallites were observed; one of them is composed of grains of about 100nm in size where the metal is inserted into the oxide. For all samples, 20% of metallic iron was routinely obtained using the microwave flash synthesis. Consequently, the microwave heating appears to provide an efficient source of energy in producing metallic iron nanoparticles protected against oxidation by an oxide matrix.

Microstructural investigations on strongly stained olivines of the chassignite NWA 2737 and implications for its shock history

Olivines from the meteorite Northwest Africa 2737 (NWA 2737) show unique characteristics such as strong brownish staining, the occurrence of perpendicular sets of bright lamellae and the exsolution of metallic nanoparticles. These features were investigated by transmission electron microscopy and spectroscopic techniques to understand their formation and consequent implications for the shock history of NWA 2737. Areas showing optically an intense brown staining are characterised by the occurrence of finely dispersed metallic nanoparticles, an extreme high density (10 16 m − 2 ) of polygonised dislocations with Burgers vector [001] and a high abundance of trivalent iron (16%) as determined by electron energy loss spectroscopy. In contrast, the bright lamellae contain individual dislocation lines with Burgers vector [001] of a slightly lower density (10 14 m − 2 ), almost no metallic nanoparticles and significantly lower trivalent iron content. Model mass balance calculations suggest that the high content of trivalent iron can be incorporated as a laihunite component into the cores of polygonised dislocations. This is charge balanced by the formation of metallic nanoparticles. Trivalent iron is likely responsible for the intense brown colour, whereas nanoparticles darken these areas considerably and cause an intense red slope in the infrared range. The proposed diffusion of trivalent iron into the cores of polygonised dislocations and the associated exsolution of metallic iron nanoparticles are likely fundamental processes for intense olivine staining during meteoritic impacts in general. Detailed analyses of variously stained regions suggest that the bright lamellae have experienced slightly higher shock-induced strain causing a recrystallisation of olivine, which occurred simultaneously with the polygonisation and exsolution processes resulting in the olivine staining of adjacent areas. The existence of individual dislocations can be interpreted as the result of a two-stage shock history for NWA 2737. After a first impact, the material of NWA 2737 was likely embedded in a hot ejecta blanket. This would ensure sufficient time at elevated temperatures for the polygonisation of dislocations and the recrystallisation of bright lamellae. A second impact resulted in the emission of individual dislocations into recrystallised olivine and the ejection of that meteorite from Mars.

Size and composition control of core-shell structured iron/iron-oxide nanoparticles

Metallic iron nanoparticles with a crystalline iron oxide shell were synthesized by the thermal decomposition of iron pentacarbonyl [Fe(CO)5] in octadecene in the presence of oleic acid and oleylamine. The effect of different synthetic parameters was investigated in details including the refluxing time and temperature, the injection temperature of iron precursor and the surfactant concentrations. The particles size can be tuned by controlling the injection temperature of iron precursor. Particle composition was adjusted by controlling the refluxing time. Both XRD diffraction and magnetic measurements indicated that these particles are very stable against oxidation which was further evidenced by microstructure analysis.

Synthesis of Fe-Core/Au-Shell Nanoparticles under Ambient Pressure

Pure metal iron nanoparticles are unstable in the air. By a coating iron on nanoparticle surface with gold, these air-stable nanoparticles are protected from the oxidation and retain most of the favorable magnetic properties. However, it is difficult to prepare Fe-core/Au-shell (Fe@Au) nanoparticles under ambient pressure because iron nanoparticles are very easily to be oxidized in the air. In this study, we synthesized Fe@Au nanoparticles by modified reverse micelle method under ambient pressure and investigated them by X-ray diffraction, transmission electron microscopy (TEM), ultraviolet-visible absorption spectra, and magnetic susceptibility measurements. X-ray diffraction analysis shows that the pattern of iron is hidden under the pattern of gold. TEM image reveals that the core-shell structure is obviously observed and the average size of Fe@Au nanoparticles is about 12 nm, with about 8 nm diameter core and 2 nm shell. The absorption band of the Fe@Au nanoparticles shifts to a longer wavelength and broadens relative to that of the pure gold. The magnetic susceptibility of Fe@Au nanoparticles is measured with a SQUID magnetometer and found to be superparamagnetic with a blocking temperature Tb ~25 K.

Active catalysts of sonoelectrochemically prepared iron metal nanoparticles for the electroreduction of chloroacetates

A new methodology for the sonoelectro-deposition and stripping of highly reactive iron at boron-doped diamond electrodes has been studied. In aqueous 1 M NH4F iron metal readily and reversibly electro-deposits onto boron-doped diamond electrodes. The effects of deposition potential, FeF63− concentration, deposition time, and mass transport are investigated and also the influence of power ultrasound (24 kHz, 8 Wcm−2). Scanning electron microscopy images of iron nanoparticles grown to typically 20-30 nm diameters are obtained. It is shown that a strongly and permanently adhering film of iron at boron-doped diamond can be formed and transferred into other solution environments. The catalytic reactivity of iron deposits at boron-doped diamond is investigated for the reductive dehalogenation of chloroacetate. The kinetically limited multi-electron reduction of trichloroacetate is dependent on the FeF63− deposition conditions and the solution composition. It is demonstrated that a stepwise iron-catalysed dechlorination via dichloroacetate and monochloroacetate to acetate is feasible. This sonoelectrochemical methodology offers a novel, clean and very versatile electro-dehalogenation methodology. The role of fluoride in the surface electrochemistry of iron deserves further attention.

Mössbauer spectroscopy study of the EuO:Fe spintronic material

The states of iron and europium in the EuO:Fe composite spintronic material have been studied by means of room-temperature Mossbauer spectroscopy. In both cases, two sets of lines indicating the ferromagnetism and superparamagnetism of metallic iron nanoparticles in the composite and the appearance of a fraction of europium ions in the Eu3+ oxidation state in the matrix in addition to the main Eu2+ state have been observed in the respective spectra. In the europium case, the observation implies the possibility of a partial spin polarization of paramagnetic europium ions in Eu-Fe-O clusters and an increased specific magnetization of the composite.

Efficient Microwave Oxidation of Alcohols Using Low‐Loaded Supported Metallic Iron Nanoparticles

The iron revolution: Highly active and stable iron nanoparticles have been prepared on a range of supports using a facile and environmentally friendly microwave approach. The inexpensive metallic iron nanoparticles were found to be extremely active and selective in the oxidation of various alcohols, achieving excellent turnover numbers. Fe/MCM-41 was found to be highly reusable, preserving and even slightly increasing its activity after several uses.

Laboratory simulations of redeposition of impact ejecta on mineral surfaces

We present quantitative laboratory studies that simulate the effect of redeposition of impact-ejecta on mineral surfaces. We produced deposits of natural olivine (Fo90) and forsterite on olivine and forsterite powder samples by ns-pulsed laser ablation. The deposits produce changes in the optical reflectance (0.66–2.5 μm). We show that significant darkening and reddening of the surface occurs when the deposit is olivine but not if it is forsterite. This is attributed to the formation of metallic iron nanoparticles in the olivine deposits. We also characterized structural and chemical changes using scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS). In situ XPS measurements show that the olivine deposits are reduced, with 50% of the iron becoming metallic. Transmission electron microscope studies confirm the presence of 2–3 nm crystalline iron nanoparticles in the olivine deposits. The scanning electron microscope shows that both olivine and forsterite deposits smoothen the topography of the powder surface, which could have effects on processes such as exosphere–surface interactions and sputtering. We conclude that the effect of coatings produced by micrometeorite impacts will not be uniform on airless bodies but will depend on the composition of the terrain.

Shock-induced metallic iron nanoparticles in olivine-rich Martian meteorites

Magnetic anomalies observed by the Mars Global Surveyor mission are attributed to crustal remanence. SNC (Shergotty–Nakhla–Chassigny) meteorites are likely samples of the Martian crust and are amenable to mineralogical and magnetic measurements essential to the understanding of the origin of magnetic anomalies. The recently discovered chassignite NWA 2737 and lherzolitic shergottite NWA 1950 display unusual magnetic characteristics that argue for a different magnetic carrier than the oxides and sulfides previously invoked in SNC meteorites. NWA 2737, the second member of the chassignite group, is a dunite with unusually dark-brown olivines and large magnetic susceptibility while Chassigny contains green olivines and is nearly a pure paramagnet. Dark olivines are also found in NWA 1950, a lherzolitic shergottite, which has singular magnetic properties when compared with other shergottites. The dark olivine color is due to the presence of Fe and FeNi metal nanoparticles, identified both by TEM and by magnetic measurements. Their size distribution encompasses the superparamagnetic to single domain transition at 30 K (10 nm range) and explains the magnetic properties of the bulk rocks. The formation of these nanoparticles is attributed to heating during the shock events that affected NWA 2737 and NWA 1950. The production of metal particles by shock-induced reduction of olivine has been invoked on surfaces deprived of atmosphere but never observed on Earth or Mars. Therefore, metal formed by shock in the heavily cratered Noachian crust is a possible carrier for crustal magnetic remanence. Widespread surface formation of metal nanoparticles could provide the precursor for the oxidized particles (goethite, hematite) observed in the Martian soils.

Iron-Doped Carbon Aerogels: Novel Porous Substrates for Direct Growth of Carbon Nanotubes

We present the synthesis and characterization of Fe-doped carbon aerogels (CAs) and demonstrate the ability to grow carbon nanotubes directly on monoliths of these materials to afford novel carbon aerogel-carbon nanotube composites. Preparation of the Fe-doped CAs begins with the sol-gel polymerization of the potassium salt of 2,4-dihydroxybenzoic acid with formaldehyde, affording K+-doped gels that can then be converted to Fe2+- or Fe3+-doped gels through an ion exchange process, dried with supercritical CO2, and subsequently carbonized under an inert atmosphere. Analysis of the Fe-doped CAs by TEM, XRD, and XPS revealed that the doped iron species are reduced during carbonization to form metallic iron and iron carbide nanoparticles. The sizes and chemical composition of the reduced Fe species were related to pyrolysis temperature as well as the type of iron salt used in the ion exchange process. Raman spectroscopy and XRD analysis further reveal that, despite the presence of the Fe species, the CA framework is not significantly graphitized during pyrolysis. The Fe-doped CAs were subsequently placed in a thermal CVD reactor and exposed to a mixture of CH4 (1000 sccm), H2 (500 sccm), and C2H4 (20 sccm) at temperatures ranging from 600 to 800 degrees C for 10 min, resulting in direct growth of carbon nanotubes on the aerogel monoliths. Carbon nanotubes grown by this method appear to be multiwalled (approximately 25 nm in diameter and up to 4 microm long) and grow through a tip-growth mechanism that pushes catalytic iron particles out of the aerogel framework. The highest yield of CNTs was grown on Fe-doped CAs pyrolyzed at 800 degrees C treated at CVD temperatures of 700 degrees C.

Electro-deposition and stripping of catalytically active iron metal nanoparticles at boron-doped diamond electrodes

A new methodology for the electro-deposition and stripping of highly reactive iron nanoparticles at boron-doped diamond electrodes is proposed. In aqueous 1 M NH 4F iron metal readily and reversibly electro-deposits onto boron-doped diamond electrodes. The effects of deposition potential, FeF 6 3 - concentration, deposition time, and mass transport are investigated. Power ultrasound (24 kHz, 8 W cm −2) is employed to achieve enhanced mass transport conditions. Scanning electron microscopy images of iron nanoparticles grown to typically 20–30 nm diameter are obtained. It is shown that a strongly and permanently adhering film of iron at boron-doped diamond can be formed and transferred into other solution environments. The catalytic reactivity of iron nanoparticle deposits at boron-doped diamond is investigated for the reductive dehalogenation of trichloroacetate. The kinetically limited multi-electron reduction of trichloroacetate is dependent on the FeF 6 3 - deposition conditions and the solution composition. It is demonstrated that a stepwise iron catalysed dechlorination via dichloroacetate and monochloroacetate to acetate is feasible. This methodology in conjunction with power ultrasound offers a novel, clean, and very versatile electro-dehalogenation methodology. The role of fluoride in the surface electrochemistry of iron deserves further attention.

Controlled Growth of Silicon Oxide Nanowires from a Patterned Reagent

A new process to fabricate silicon oxide nanowires (NWs) from a patterned reagent is reported. Arrays of NWs grow on patterned nanodots containing exposed hydrogen silsesquioxane (HSQ)/Fe−SiO2 nanocomposites during annealing at 900 °C. The NWs were seeded by metallic iron nanoparticles, and the resulting microstructure and morphology of the NWs is directly related to the size of the individual iron nanoparticles. The growth process could be dominated by a solid-state transformation mechanism in which iron nanoparticles, originally embedded in a SiO2 matrix, diffuse to the surface and act as nucleation sites, the exposed HSQ being the source for the growing NWs.

Fluorescence From Metallic Silver and Iron Nanoparticles Prepared by Exploding Wire Technique

The observation of intense visible fluorescence from silver and iron nanoparticles in different solution phases and surface capping is reported here. Metallic silver and iron nanoparticles were obtained by exploding pure silver and iron wires in pure water. Bovine serum albumin protein adsorption on the silver nanoparticles showed an enhanced fluorescence. The presence of poly-vinyl pyrrolidone polymer in the exploding medium resulted in a stabilized growth of iron nanoparticles with enhanced fluorescence intensity. The fluorescence was found to be surface /interface dependant. The fluorescence is attributed to electronic transitions among characteristic interface energy bands. The magnetic nature of iron nanoparticles was confirmed from the hysteresis measurements.

Development of Magnetic Nanostructured Silica-Based Materials as Potential Vectors for Drug-Delivery Applications

Metallic iron nanoparticles were synthesized within micron-sized mesoporous molecular sieves (with 2.9-nm pores) and hollow silica microcapsules (pores of 2.7 and 15 nm) using several cycles of wet impregnation under vacuum, followed by drying, oxidation, and reduction steps. For iron-loaded MCM-48, SQUID measurements revealed ferromagnetic behavior at room temperature with a magnetic moment as high as 3.40 emu/g (measured at 2 T) after four deposition cycles. Iron-loaded hollow silica microcapsules (250-nm wall thickness) showed a magnetic moment of 2.40 emu/g (at 2 T) after three deposition cycles and a coercivity as low as 12.9 Oe.

Synthesis and properties of magnetic fluid based on iron nanoparticles prepared by a vapor-phase condensation process

Magnetic fluid containing metallic iron nanoparticles was successfully fabricated in this work. The iron nanoparticles were synthesized by chemical vapor condensation process and then dispersed in water-base solution (pH 11) with oleic acid as surfactant. More than 80% of iron nanoparticles were fully dispersed in the fluid and remained stable without any further oxidation over 200 h. Both the iron nanoparticles and the subsequent magnetic fluid exhibited typical ferromagnetic behavior.

X-ray magnetic circular dichroism study of iron/iron oxide granular nanostructures

We present a study of the local magnetic properties of an iron/iron oxide nanostructured granular system by X-ray magnetic circular dichroism. The samples investigated consist of metallic iron (α-Fe) nanoparticles embedded in a nanocrystalline oxide matrix composed by both magnetite (Fe3O4) and maghemite (γ-Fe2O3). Samples were obtained by the inert gas condensation technique.Thanks to the chemical and site selectivity of XMCD, we were able to distinguish the magnetic contributions of the metallic core and of the two oxide phases present in the matrix and independently study their behaviour as a function of iron particle size, applied magnetic field, sample temperature and magnetization history.

Synthesis of poly(methyl methacrylate) stabilized colloidal zero-valence metallic nanoparticles

Poly(methyl methacrylate) (PMMA) stabilized colloidal metallic iron nanoparticles without additional surfactant or stabilizer were fabricated by a wet chemical reduction method. The synthesized colloidal iron nanoparticles were found to be stable in tetrahydrofuran (THF) solution and the dried PMMA–Fe nanocomposites were ferromagnetic even at room temperature as illustrated by magnetometer measurement. The particle size increased with the decrease of the initial PMMA concentration and the magnetic properties also depended on the initial PMMA concentration.

Chemical Vapor Deposition and Synthesis on Carbon Nanofibers: Sintering of Ferrocene-Derived Supported Iron Nanoparticles and the Catalytic Growth of Secondary Carbon Nanofibers

The synthesis of homogeneously distributed carbon nanofibers with well-defined morphology on vapor-grown carbon nanofibers was achieved by a sequence of gas-phase steps, thus fully avoiding wet chemistry: first, carbon nanofibers were exposed to oxygen plasma to introduce oxygen-containing functional groups. Then, the chemical vapor deposition of ferrocene was carried out under oxidizing conditions, yielding nanofiber-supported iron oxide nanoparticles. Secondary carbon nanofibers with diameters in the range from 10 to 20 nm were subsequently grown from cyclohexane catalyzed by the sintered metallic iron nanoparticles under reducing conditions. XPS was applied to monitor the chemical changes of the surface composition and the sintering of the metallic iron particles in hydrogen. The morphology and the height distribution of the sintered iron oxide nanoparticles was derived by a unique combined application of scanning electron microscopy and scanning tunneling microscopy. The specific surface area of the ...

Advantages of Ferromagnetic Nanoparticle Composites in Microwave Absorbers

AbstractFor Abstract see ChemInform Abstract in Full Text.

Characterization and Properties of Metallic Iron Nanoparticles: Spectroscopy, Electrochemistry, and Kinetics

There are reports that nano-sized zero-valent iron (Fe0) exhibits greater reactivity than micro-sized particles of Fe0, and it has been suggested that the higher reactivity of nano-Fe0 may impart advantages for groundwater remediation or other environmental applications. However, most of these reports are preliminary in that they leave a hostof potentiallysignificant(and often challenging) material or process variables either uncontrolled or unresolved. In an effort to better understand the reactivity of nano-Fe0, we have used a variety of complementary techniques to characterize two widely studied nano-Fe0 preparations: one synthesized by reduction of goethite with heat and H2 (Fe(H2)) and the other by reductive precipitation with borohydride (Fe(BH)). Fe(H2) is a two-phase material consisting of 40 nm alpha-Fe0 (made up of crystals approximately the size of the particles) and Fe3O4 particles of similar size or larger containing reduced sulfur; whereas Fe(BH) is mostly 20-80 nm metallic Fe particles (aggregates of <1.5 nm grains) with an oxide shell/coating that is high in oxidized boron. The FeBH particles further aggregate into chains. Both materials exhibit corrosion potentials that are more negative than nano-sized Fe2O3, Fe3O4, micro-sized Fe0, or a solid Fe0 disk, which is consistent with their rapid reduction of oxygen, benzoquinone, and carbon tetrachloride. Benzoquinone-which presumably probes inner-sphere surface reactions-reacts more rapidly with FeBH than Fe(H2), whereas carbon tetrachloride reacts at similar rates with FeBH and Fe(H2), presumably by outer-sphere electron transfer. Both types of nano-Fe0 react more rapidlythan micro-sized Fe0 based on mass-normalized rate constants, but surface area-normalized rate constants do not show a significant nano-size effect. The distribution of products from reduction of carbon tetrachloride is more favorable with Fe(H2), which produces less chloroform than reaction with Fe(BH).