Synthesis and Characterization of Dendrimer-Encapsulated Iron and Iron-Oxide Nanoparticles

In this paper, a series of iron (Fe) containing nanoparticles were prepared by employing PAMAM (Poly(amidoamine), dendrimers with different generations (G0?CG3) as templates and sodium borohydride as a reducing agent. The products have been characterized by TEM, FT-IR, XRD, VSM, TGA, and XPS. XRD analysis reveal low crystallinity of formed particles within the dendrimers, however, crystallinity of the nanoparticles was observed to increase with increasing generation of dendrimers. Dominant phases were determined as magnetite (Fe₃O₄ or maghemite, ??-Fe₂O₃). XPS analysis revealed the chemical composition of nanoparticles as iron oxide which indicated the oxidation of Fe species subsequent to the reduction process, in agreement with XRD analysis. The magnetization curves have superparamagnetic nonhysteretic characteristic at lower fields and with nonsaturation characteristic at high fields. Magnetic evaluation of samples with the 20:1?molar ratio of Fe:PAMAM showed decreasing superparamagnetic character and decreasing saturation magnetisation with increasing generation of dendrimers.     

Thermally induced changes in the magnetic properties of iron oxide nanoparticles under reducing and oxidizing conditions

Application of iron oxide nanoparticles in the fields of water purification, biomedicine or chemistry often requires controlled magnetic properties that can be modified by changing temperature and redox conditions. Therefore, this work investigates the changes in the magnetic properties of iron oxide nanoparticles in the FeOOH − Fe₂O₃ − Fe₃O₄ system (i.e. hematite, goethite, lepidocrocite, maghemite and magnetite) at heating under reducing and oxidizing conditions. The results show that heat treatment of hematite and goethite in the presence of a reducing agent (5% starch) leads to their conversion into high magnetic magnetite. The starting temperature of transformation is approximately 350 °C for both samples. The magnetization increases to 86 Am²/kg for hematite reduced at 700 °C and to 88 Am²/kg for goethite reduced at 900 °C. An intense reaction occurs within the first 10 min and then the conversion process decelerates. Thermal treatment of lepidocrocite under both oxidizing and reducing conditions leads to an increase in magnetization due to the formation of maghemite and magnetite, respectively. Regardless of the redox conditions, the formation of magnetic phase begins at a temperature of 250 °C and is associated with the formation of maghemite from lepidocrocite. Under oxidizing conditions, the magnetization begins to decrease at 350 °C, which is associated with the conversion of maghemite to hematite. On the contrary, under reducing conditions, the magnetization of lepidocrocite increases up to 900 °C, which is associated with the formation of magnetite. Maximum values of magnetization are 36 Am²/kg for maghemite obtained at 350 °C, and 88 Am²/kg for magnetite obtained at 900 °C from lepidocrocite. With the help of conventional heating, the magnetic properties of IONs can be altered by phase transformations in the FeOOH − Fe₂O₃ − Fe₃O₄ system. Temperature and redox conditions are the two most important factors controlling the transformation pathways and the magnetic properties of the resulting IONs.     

Preparation and application of calix[4]arene-grafted magnetite nanoparticles for removal of dichromate anions

Magnetic Fe₃O₄ nanoparticles were prepared by the chemical co-precipitation of Fe(III) and Fe(II) ions. Then, the nanoparticles were modified directly by 3-aminopropyltrimethoxy silane (APTMS) to introduce reactive groups onto the particles' surface, and diester derivative of calix[4]arene was immobilized onto the surface of modified-Fe₃O₄ nanoparticles by aminolysis reaction. The prepared magnetite nanoparticles (Calix-GM) were characterized by a combination of IR, TGA and TEM analyses. The extraction properties of the new material toward dichromate anions were also studied. It was observed that the prepared magnetite nanoparticles were an effective extractant for the removal of dichromate anions at pH 2.5–4.5.     

Synthesis of pyramidal,cubical and truncated octahedral magnetite nanocrystals by controlling reaction heating rate

Pyramidal, cubical and truncated octahedral magnetite nanocrystals have been synthesized by thermal de-composition of iron (III) acetylacetone (Fe(acac)₃) in the presence of oleic acid under various reaction rate controlled by heating rate. The magnetite nanocrystals were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). High-resolution transmission electron microscopy (HRTEM) was applied to reveal the structural information of single magnetite (Fe₃O₄) nanocrystals. Magnetization curves of the three types of magnetite nanocrystals show that the pyramidal crystals exhibit a slight hysteresis compared to the other two despite of the similar size range. The results suggest that in addition to the surfactant selective capping and varying reaction temperature, the reaction rate variation is also an effective means for controlling the morphology and functions of the magnetite nanocrystals.     

Influence of the precipitation pH of magnetite in the oxidation process to maghemite

The aim of this work is to study about the synthesis of maghemite starting from cubic magnetite, using a mathematical model, which not only includes factors associated to the oxidation process of magnetite, but also factors related with precursor characteristics, such as the precipitation pH for the Fe(OH)₂. Two samples of magnetite, obtained by oxidation of Fe(OH)₂ to pH 8–9 and pH > 11, respectively, were air-heated under different conditions, planned according to the fractional factorial design 2⁶⁻³. The experiment was done in two zones, one (zone 1) that considered the values reported in the literature and tentative experiments and another (zone 2), whose values are far removed from the first set. Based on the results of the statistical analysis, it was concluded that the model was adequate to zone 1 (M and N samples) where the relevant parameters are those corresponding to: the independent term, the air flow, the time, the mass, the pH (of the magnetite precipitation) and the interaction of the time and pH variables. In zone 2 (O and P samples) it was impossible to write a corresponding equation due to parameter interactions; also, the model proved inadequate. The oxidation process of Fe₃O₄ to γ-Fe₂O₃ also depends on the precursor characteristics. The magnetite obtained at pH between 8 and 9 is oxidized to maghemite more completely than magnetite synthesized at pH > 11.     

Dielectric and magnetic response of Fe3O4/epoxy composites

Magnetic and dielectric properties of Fe₃O₄/epoxy resin composites were studied as a function of Fe₃O₄ concentration. The Fe₃O₄ powder was milled using a planetary ball-mill in order to reduce the particle size. B.E.T. area of these particles was determined, and a structural characterization was performed by X-ray diffraction (XRD). Fe₃O₄/epoxy composites were prepared mixing the raw materials and pouring them into suitable moulds. Dielectric measurements were performed at different frequencies and temperatures, while magnetic properties were assessed at different temperatures. It was found that permittivity was strongly dependent on the filler concentration and frequency. Maxwell–Wagner–Sillars interfacial polarization, Intermediate Dipolar Polarization (IDE), and α relaxation process were responsible for the observed behavior. Magnetic measurements revealed the presence of magnetite nanoparticles in the composites, with a blocking temperature close to 170 K.     

Exchange-coupled Fe3O4/L10-FePt bilayer films by controlled oxidation of Fe/Pt multilayer

A Fe₃O₄/L1₀-FePt bilayer thin-film magnet was fabricated via a simple one-step process by annealing Fe/Pt multilayer thin films in a N₂ gas flow. X-ray diffraction and plane-view selected-area electron diffraction results are identified with magnetite phase (Fe₃O₄) and L1₀-FePt. Cross-sectional transmission electron microscopy images show the two phases form a bilayer structure. Magnetic hysteresis loops of the bilayer show single phase behavior which is interpreted as a result of the soft Fe₃O₄ phase exchange-coupled with the hard L1₀-FePt phase, consistent with micromagnetic simulation prediction. Such bilayer structure may have potential for coercivity control in high density magnetic recording application.     

Magnetic nanoparticles and nanoparticle assemblies from metallorganic precursors

Magnetic nanoparticles of -Fe₂O₃, Fe₂O₃SiO₂ composite and magnetite Fe₃O₄ have been prepared using novel metallorganic precursors Fe[NC(C₆H₄)C(NSiMe₃)₂]₂Cl, Fe₂[O₂Si(C₆H₅)₂]₃ and [Fe(OBu^t)₃Na(THF)]₂) by hydrolysis, sol-gel condensation and further ultrasound and thermal treatment of the samples. The nanoparticles have been investigated by X-ray powder diffraction, TEM, SEM and AFM.     

Mössbauer,xrd and positron annihilation studies on natural magnetite and hematite ore from Ari Dongri,central India

Natural magnetite and hematite samples taken from iron ore deposits associated with Precambrian banded iron-formation (BIF) at Ari Dongri (20°23′N:81°3°E), Bastar district in Central India have been studied by Mossbauer, XRD and positron annihilation techniques. Three magnetite samples show a genetic association with α-Fe₂O₃ with a wide range of variations in Fe₃O₄:α-Fe₂O₃ ratio. The fourth sample, a typical specular hematite, shows α-Fe₂O₃ content of the order of 90%, the rest being magnetite. The magnetite present in the samples was found to be stoichiometric. None of the samples contains maghemite (γ-Fe₂O₃). Some geological implications of the observed variation in the oxidation states of the samples are considered.     

A review of Fe3O4 thin films: Synthesis,modification and applications

Magnetite (Fe₃O₄) has been used for thousands of years as one of the important magnetic materials. The rapid developments of thin film technology in the past few decades attract the attention of material scientists on the fabrication of magnetite thin films. In this article, we present an overview of recent progress on Fe₃O₄ thin films. The widely used preparation methods are surveyed, and the effect of substrates is discussed. Specifically the modified Fe₃O₄ thin films exhibit excellent electrical and magnetic properties compared with the pure films. It is noteworthy that modified Fe₃O₄ thin films can be put into two categories: (1) doped films, where foreign metal ions substitute iron ions at A or B sites; and (2) hybrid films, where magnetite phases are mixed with other materials. Notably, Fe₃O₄ thin films show great potentials in many applications such as sensors and batteries. It is expected that the investigations of Fe₃O₄ thin films will give us some breakthroughs in materials science and technology.     

Synthesis of magnetic nanostructures: Shape tuning by the addition of a polymer at low temperature

We report a simple method for shape-controlled synthesis of iron oxide spinels such as magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃) nanostructures using a thermoresponsive polymer poly(vinyl methyl ether) (PVME) by the alkaline hydrolysis of iron salt at low temperature (20 °C). Microscopic analysis confirmed the formation of needle- and flower-shaped iron oxide nanostructures depending on reaction conditions. High-resolution transmission electron microscopic analysis of the needle- and flower-shaped nanostructures as well as their corresponding selected area electron diffraction patterns revealed that the formed nanostructures are crystalline in nature. X-ray diffraction study reveals the formation of well-crystalline pure Fe₃O₄ and γ-Fe₂O₃ nanostructures under different reaction conditions. Fourier transform Infra-red spectroscopic analysis confirms the adsorption of PVME on the surface of iron oxide nanostructures. Finally, the magnetic properties of γ-Fe₂O₃ and Fe₃O₄ nanostructures is studied that shows the superparamagnetic behavior of the formed iron oxide nanostructures.     

Fabrication of periodically micropatterned magnetite nanoparticles by laser-interference-controlled electrodeposition

This paper introduces a laser-interference-controlled electrochemical deposition method for direct fabrication of periodically micropatterned magnetite (Fe₃O₄) nanoparticles (NPs). In this work, Fe₃O₄ NPs were controllably synthesized on the areas where the photoconductive electrode was exposed to the periodically patterned interferometric laser irradiation during the electrodeposition. Thus, the micropattern of Fe₃O₄ NPs was controlled by interferometric laser pattern, and the crystallization of the particles was controlled by laser interference intensity and electrochemical deposition conditions. The bottom-up electrochemical approach was combined with a top-down laser interference methodology. This maskless method allows for in situ fabrication of periodically patterned magnetite NPs on the microscale by electrodeposition under room temperature and atmospheric pressure conditions. In the experiment, Fe₃O₄ NPs with the mean grain size below 100 nm in the pattern of 5-μm line array were achieved within the deposition time of 100 s. The experiment results have shown that the proposed method is a one-step approach in fabricating large areas of periodically micropatterned magnetite NPs.     

Fe3O4 on ZnO: A spectroscopic study of film and interface properties

Magnetite (Fe₃O₄) thin films have been grown epitaxially on zinc oxide (ZnO) substrates, using reactive molecular beam epitaxy. The film quality was found to be strongly dependent on the oxygen partial pressure during growth. For a uniform Fe₃O₄ film a certain pressure variation was needed during growth. Structural, electronic, and magnetic properties were analyzed utilizing low energy electron diffraction, Hard X-ray Photoelectron Spectroscopy (HAXPES), Magneto-Optical Kerr Effect (MOKE), and X-ray Magnetic Circular Dichroism (XMCD). Diffraction patterns show clear indication for growth of Fe₃O₄ in the [111] direction on ZnO(0001). Non-destructive depth profiling by HAXPES revealed uniform magnetite thin films. Both, MOKE and XMCD measurements show easy in-plane magnetization. The dichroic spectra clearly support the formation of Fe₃O₄.     

Facile synthesis of titania-encapsulated magnetites with controlled magnetism and surface morphology

Titania-encapsulated magnetites (A-Fe₃O₄@TiO₂) were facilely fabricated through the modified sol–gel reaction of APTMS-complexed Fe₃O₄ (A-Fe₃O₄) with tetraethyl orthotitanate (TEOT). The magnetism and surface morphology of A-Fe₃O₄@TiO₂ were controlled by adjusting the thickness of titania capsule layer. A-Fe₃O₄@TiO₂ exhibited the superparamagnetic characteristics of negligible remanence and coercity. Thermal analysis of A-Fe₃O₄@TiO₂ showed that the amorphous titania was transformed into crystalline phase at around 440 °C. The core–shell magnetite–titanium nanocomposites can be an attractive candidate for recyclable photocatalysts with magnetite core and/or active Fe₃O₄ electrode materials with buffering TiO₂ capsules.     

Fabrication of spherical magnetite particles by the flame fusion method

Fabrication of spherical magnetite powders was investigated in the propane-oxygen flame using sponge iron powders as a starting powder. Spherical particles produced by fusion, sphering and oxidation of iron powder were composed of residual Fe, FeO, Fe₃O₄ and -Fe₂O₃ in the case of particles collected by a cyclone. The amount of Fe₃O₄ in the products was strongly dependent on the propane/oxygen ration and the flow rate of carrier air, but weakly on the feed rate of iron powder. Injection of quenching gas was found to be effective to improve the yield of Fe₃O₄. Particle size of products reflected directly that of starting powders, indicating fairly easy control of particle size of products. The saturation magnetization of the produced powder under the optimum condition was 88 emu/g. These facts suggest that the fusion and oxidation treatment of iron powders in the propane-oxygen flame is a suitable process for the manufacture of the magnetic carrier for plain paper copy (PPC) on an industrial scale. Powders collected by a bag filter were found to be fine -Fe₂O₃ particles with a diameter of about 100 nm.     

Evaluation of CaO–SiO<Subscript>2</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Na<Subscript>2</Subscript>O–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> bioglass-ceramics for hyperthermia application

Magnetic bioglass ceramics (MBC) are being considered for use as thermoseeds in hyperthermia treatment of cancer. While the bioactivity in MBCs is attributed to the formation of the bone minerals such as crystalline apatite, wollastonite, etc. in a physiological environment, the magnetic property arises from the magnetite [Fe₃O₄] present in these implant materials. A new set of bioglasses with compositions 41CaO · (52 ? x)SiO₂ · 4P₂O₅  · xFe₂O₃ · 3Na₂O (2 ≤ x ≤ 10 mol% Fe₂O₃) have been prepared by melt quenching method. The as-quenched glasses were then heat treated at 1050°C for 3 h to obtain the glass-ceramics. The structure and microstructure of the samples were characterized using X-ray diffraction and microscopy techniques. X-ray diffraction data revealed the presence of magnetite in the heat treated samples with x ≥ 2 mol% Fe₂O₃. Room temperature magnetic property of the heat treated samples was investigated using a Vibrating Sample Magnetometer. Field scans up to 20 kOe revealed that the glass ceramic samples had a high saturation magnetization and low coercivity. Room temperature hysteresis cycles were also recorded at 500 Oe to ascertain the magnetic properties at clinically amenable field strengths. The area under the magnetic hysteresis loop is a measure of the heat generated by the MBC. The coercivity of the samples is another important factor for hyperthermia applications. The area under the loop increases with an increase in Fe₂O₃ molar concentration and the. coercivity decreases with an increase in Fe₂O₃ molar concentration The evolution of magnetic properties in these MBCs as a function of Fe₂O₃ molar concentration is discussed and correlated with the amount of magnetite present in them.     

Preparation and studies on surface modifications of calcium-silico-phosphate ferrimagnetic glass-ceramics in simulated body fluid

The structure and magnetic behaviour of 34SiO₂–(45 − x) CaO–16P₂O₅–4.5 MgO–0.5 CaF₂ − x Fe₂O₃ (where x = 5, 10, 15, 20 wt.%) glasses have been investigated. Ferrimagnetic glass-ceramics are prepared by melt quench followed by controlled crystallization. The surface modification and dissolution behaviour of these glass-ceramics in simulated body fluid (SBF) have also been studied. Phase formation and magnetic behaviour have been studied using XRD and SQUID magnetometer. The room temperature Mössbauer study has been done to monitor the local environment around Fe cations and valence state of Fe ions. X-ray photoelectron spectroscopy (XPS) was used to study the surface modification in glass-ceramics when immersed in simulated body fluid. Formation of bioactive layer in SBF has been ascertained using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The SBF solutions were analyzed using an absorption spectrophotometer. The magnetic measurements indicated that all these glasses possess paramagnetic character and the [Fe²⁺/Fe³⁺] ions ratio depends on the composition of glass and varied with Fe₂O₃ concentration in glass matrix. In glass-ceramics saturation magnetization increases with increase in amount of Fe₂O₃. The nanostructure of hematite and magnetite is formed in the glass-ceramics with 15 and 20 wt.% Fe₂O₃, which is responsible for the magnetic property of these glass-ceramics. Introduction of Fe₂O₃ induces several modifications at the glass-ceramics surface when immersed in SBF solution and thereby affecting the surface dissolution and the formation of the bioactive layer.     

Electromagnetic and microwave absorbing properties of magnetite nanoparticles decorated carbon nanotubes/polyaniline multiphase heterostructures

Magnetite nanoparticles decorated CNTs/PANI multiphase heterostructures were prepared by polymerization of aniline monomer and an additional process of the coprecipitation of Fe²⁺ and Fe³⁺. Scanning electron microscopy and transmission electron microscopy observation indicated that the monodispersed magnetite nanoparticles were uniformly decorated on the surface of CNTs/PANI. The formation of magnetite nanoparticles on CNTs/PANI was mainly through a preferentially position-selective precipitation process. More interestingly, a portion of Fe₃O₄ nanoparticles was found to form core–shell structures with PANI. The effects of different additional amounts of NH₂Fe(SO₄)₂·6H₂O reactant on the magnetic properties and microwave absorbing performances of CNTs/PANI/Fe₃O₄ heterostructures were investigated. The CNTs/PANI/Fe₃O₄ multiphase heterostructures were proved to be superparamagnetic. The microwave absorption measurement showed that the CNTs/PANI/Fe₃O₄ samples under 1.5 g of NH₂Fe(SO₄)₂·6H₂O condition exhibited much more effective absorption performance. These results suggested the novel CNTs/PANI/Fe₃O₄ multiphase heterostructures with PANI as the second phase may be potential candidate for microwave absorption systems.     

Fast microwave synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag magnetic nanoparticles using Fe<Superscript>2+</Superscript> as precursor

A simple and quick microwave method to prepare high performance magnetite nanoparticles (Fe₃O₄ NPs) directly from Fe has been developed. The as-prepared Fe₃O₄ NPs product was fully characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results show that the as-prepared Fe₃O₄ NPs are quite monodisperse with an average core size of 80 × 5 nm. The microwave synthesis technique can be easily modified to prepare Fe₃O₄/Ag NPs and these NPs possess good magnetic properties. The formation mechanisms of the NPs are also discussed. Our proposed synthesis procedure is quick and simple, and shows potential for large-scale production and applications for catalysis and biomedical/biological uses.     

Kinetic sorption study of Cerium (IV) on magnetite nanoparticles

Magnetite nanoparticles (Fe₃O₄) and humic acid-coated magnetite nanoparticles (Fe₃O₄/HA) were prepared by co-precipitation method for cerium ions removal from aqueous solution. The success of preparation in nanoscale was confirmed by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The TEM image shows that the size of Fe₃O₄ is around 15 nm and the presence of humic acid reduces the magnetite aggregation and stabilizes the magnetite suspension. Adsorption studies with respect to various process variables such as contact time, pH, and temperature were investigated by batch technique. The sorption kinetics and isotherms of Fe₃O₄ and Fe₃O₄/HA for Ce (IV) ions show that the sorption kinetics follow the pseudo-second-order and Langmuir isotherm models for both sorbents. The maximum capacities (Q_max) of Ce (IV) onto Fe₃O₄ and Fe₃O₄/HA were found to be 160 and 280 mg/g, respectively. The thermodynamic parameters (ΔG^o, ΔH^o and ΔS^o) were calculated, and the results revealed that the sorption process of Ce (IV) ions on both Fe₃O₄ and Fe₃O₄/HA are spontaneous, endothermic for Fe₃O₄ and exothermic for Fe₃O₄/HA.