Green synthesis and characterization of superparamagnetic Fe3O4 nanoparticles

In this paper, we have first demonstrated a facile and green synthetic approach for preparing superparamagnetic Fe₃O₄ nanoparticles using α-d-glucose as the reducing agent and gluconic acid (the oxidative product of glucose) as stabilizer and dispersant. The X-ray powder diffraction (XRD), X-ray photoelectron spectrometry (XPS), and selected area electron diffraction (SAED) results showed that the inverse spinel structure pure phase polycrystalline Fe₃O₄ was obtained. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results exhibited that Fe₃O₄ nanoparticles were roughly spherical shape and its average size was about 12.5 nm. The high-resolution TEM (HRTEM) result proved that the nanoparticles were structurally uniform with a lattice fringe spacing about 0.25 nm, which corresponded well with the values of 0.253 nm of the (3 1 1) lattice plane of the inverse spinel Fe₃O₄ obtained from the JCPDS database. The superconducting quantum interference device (SQUID) results revealed that the blocking temperature (T_b) was 190 K, and that the magnetic hysteresis loop at 300 K showed a saturation magnetization of 60.5 emu/g, and the absence of coercivity and remanence indicated that the as-synthesized Fe₃O₄ nanoparticles had superparamagnetic properties. Fourier transform infrared spectroscopy (FT-IR) spectrum displayed that the characteristic band of Fe-O at 569 cm⁻¹ was indicative of Fe₃O₄. This method might provide a new, mild, green, and economical concept for the synthesis of other nanomaterials.     

An easy and novel approach for the decoration of graphene oxide by Fe3O4 nanoparticles

A new and relatively general route was developed to fabricate graphene oxide (GO)-Fe₃O₄ hybrid. X-ray diffraction, transmission electron morphology, X-ray photoelectron spectroscopy (XPS) and energy-dispersive spectrum were used to demonstrate the successful attachment of iron oxide nanoparticles to GO sheets. Transmission electron microscopy observation indicates that the size of the Fe₃O₄ nanoparticles was about 2.7 nm with narrow size distribution. Moreover, this hybrid shows superparamagnetic property and allows the rapid separation under an external-magnetic field. In addition, the method could be extended to further development of graphene-based nanoelectronics.     

Fabrication, characterization and measurement of thermal conductivity of Fe3O4 nanofluids

Magnetite Fe₃O₄ nanoparticles were synthesized by a co-precipitation method at different pH values. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electronic microscopy. Their magnetic properties were evaluated on a vibrating sample magnetometer. The results show that the shape of the particles is cubic and they are superparamagnetic at room temperature. Magnetic nanofluids were prepared by dispersing the Fe₃O₄ nanoparticles in water as a base fluid in the presence of tetramethyl ammonium hydroxide as a dispersant. The thermal conductivity of the nanofluids was measured as a function of volume fraction and temperature. The results show that the thermal conductivity ratio of the nanofluids increases with increase in temperature and volume fraction. The highest enhancement of thermal conductivity was 11.5% in the nanofluid of 3 vol% of nanoparticles at 40 °C. The experimental results were also compared with the theoretical models.     

Microwave synthesis of magnetic Fe3O4 nanoparticles used as a precursor of nanocomposites and ferrofluids

Methods to synthesize magnetic Fe₃O₄ nanoparticles and to modify the surface of particles are presented in the present investigation. Fe₃O₄ magnetic nanoparticles were prepared by the co-precipitation of Fe³⁺ and Fe²⁺, NH₃·H₂O was used as the precipitating agent to adjust the pH value, and the aging of Fe₃O₄ magnetic nanoparticles was accelerated by microwave (MW) irradiation. The obtained Fe₃O₄ magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The average size of Fe₃O₄ crystallites was found to be around 8–9 nm. Thereafter, the surface of Fe₃O₄ magnetic nanoparticles was modified by stearic acid. The resultant sample was characterized by FT-IR, scanning electron microscopy (SEM), XRD, lipophilic degree (LD) and sedimentation test. The FT-IR results indicated that a covalent bond was formed by chemical reaction between the hydroxyl groups on the surface of Fe₃O₄ nanoparticles and carboxyl groups of stearic acid, which changed the polarity of Fe₃O₄ nanoparticles. The dispersion of Fe₃O₄ in organic solvent was greatly improved. Effects of reaction time, reaction temperature and concentration of stearic acid on particle surface modification were investigated. In addition, Fe₃O₄/polystyrene (PS) nanocomposite was synthesized by adding surface modified Fe₃O₄ magnetic nanoparticles into styrene monomer, followed by the radical polymerization. The obtained nanocomposite was tested by thermogravimetry (TG), differential scanning calorimetry (DSC) and XRD. Results revealed that the thermal stability of PS was not significantly changed after adding Fe₃O₄ nanoparticles. The Fe₃O₄ magnetic fluid was characterized using UV–vis spectrophotometer, Gouy magnetic balance and laser particle-size analyzer. The testing results showed that the magnetic fluid had excellent stability, and had susceptibility of 4.46×10⁻⁸ and saturated magnetization of 6.56 emu/g. In addition, the mean size d (0.99) of magnetic Fe₃O₄ nanoparticles in the fluid was 36.19 nm.     

Chemical synthesis of spinel nickel ferrite (NiFe2O4) nano-sheets

The present investigation is related to the deposition of single-phase nano-sheets spinel nickel ferrite (NiFe₂O₄) thin films onto glass substrates using a chemical method. Nano-sheets nickel ferrite films were deposited from an alkaline bath containing Ni²⁺ and Fe²⁺ ions. The films were characterized for their structural, surface morphological and electrical properties by means of X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and two-point probe electrical resistivity techniques. The X-ray diffraction pattern showed that NiFe₂O₄ nano-sheets are oriented along (3 1 1) plane. The FT-IR spectra of NiFe₂O₄ films showed strong absorption peaks around 600 and 400 cm⁻¹ which are typical for cubic spinel crystal structure. Microstructural study of NiFe₂O₄ film revealed nano-sheet like morphology with average sheet thickness of 30 nm. The room temperature electrical resistivity of the NiFe₂O₄ nano-sheets was 10⁷ Ω cm.     

High temperature ferromagnetism of the vacuum-annealed (In1−xFex)2O3 powders

(In_1−xFe_x)₂O₃ (x = 0.02, 0.05, 0.2) powders were prepared by a solid state reaction method and a vacuum annealing process. A systematic study was done on the structural and magnetic properties of (In_1−xFe_x)₂O₃ powders as a function of Fe concentration and annealing temperature. The X-ray diffraction and high-resolution transmission electron microscopy results confirmed that there were not any Fe or Fe oxide secondary phases in vacuum-annealed (In_1−xFe_x)₂O₃ samples and the Fe element was incorporated into the indium oxide lattice by substituting the position of indium atoms. The X-ray photoelectron spectroscopy revealed that both Fe²⁺ and Fe³⁺ ions existed in the samples. Magnetic measurements indicated that all samples were ferromagnetic with the magnetic moment of 0.49-1.73 μ_B/Fe and the Curie temperature around 783 K. The appearance of ferromagnetism was attributed to the ferromagnetic coupling of Fe²⁺ and Fe³⁺ ions via an electron trapped in a bridging oxygen vacancy.     

Exchange coupling behavior in bimagnetic CoFe2O4/CoFe2 nanocomposite

In this work we report a study of the magnetic behavior of ferrimagnetic oxide CoFe₂O₄ and ferrimagnetic oxide/ferromagnetic metal CoFe₂O₄/CoFe₂ nanocomposite. The latter compound is a good system to study hard ferrimagnet/soft ferromagnet exchange coupled. Two steps were followed to synthesize the bimagnetic CoFe₂O₄/CoFe₂ nanocomposite: (i) first, preparation of CoFe₂O₄ nanoparticles using a simple hydrothermal method, and (ii) second, reduction reaction of cobalt ferrite nanoparticles using activated charcoal in inert atmosphere and high temperature. The phase structures, particle sizes, morphology, and magnetic properties of CoFe₂O₄ nanoparticles were investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) with applied field up to 3.0 kOe at room temperature and 50 K. The mean diameter of CoFe₂O₄ particles is about 16 nm. Mossbauer spectra revealed two sites for Fe³⁺. One site is related to Fe in an octahedral coordination and the other one to the Fe³⁺ in a tetrahedral coordination, as expected for a spinel crystal structure of CoFe₂O₄. TEM measurements of nanocomposite showed the formation of a thin shell of CoFe₂ on the cobalt ferrite and indicate that the nanoparticles increase to about 100 nm. The magnetization of the nanocomposite showed a hysteresis loop that is characteristic of exchange coupled systems. A maximum energy product (BH)_max of 1.22 MGOe was achieved at room temperature for CoFe₂O₄/CoFe₂ nanocomposites, which is about 115% higher than the value obtained for CoFe₂O₄ precursor. The exchange coupling interaction and the enhancement of product (BH)_max in nanocomposite CoFe₂O₄/CoFe₂ are discussed.     

Ag-deposited silica-coated Fe3O4 magnetic nanoparticles catalyzed reduction of p-nitrophenol

In this paper, a novel approach was successfully developed for advanced catalyst Ag-deposited silica-coated Fe₃O₄ magnetic nanoparticles, which possess a silica coated magnetic core and growth active silver nanoparticles on the outer shell using n-butylamine as the reductant of AgNO₃ in ethanol. The as-synthesized nanoparticles have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared spectra (FT-IR), vibration sample magnetometer (VSM), and have been exploited as a solid phase catalyst for the reduction of p-nitrophenol in the presence of NaBH₄ by UV-vis spectrophotometry. The obtained products exhibited monodisperse and bifunctional with high magnetization and excellent catalytic activity towards p-nitrophenol reduction. As a result, the as-obtained nanoparticles showed high performance in catalytic reduction of p-nitrophenol to p-aminophenol with conversion of 95% within 14 min in the presence of an excess amount of NaBH₄, convenient magnetic separability, as well as remained activity after recycled more than 6 times. The Fe₃O₄@SiO₂-Ag functional nanostructure could hold great promise for various catalytic reactions.     

Biosynthesis and magnetic properties of mesoporous Fe3O4 composites

Magnetic Fe₃O₄ materials with mesoporous structure are synthesized by co-precipitation method using yeast cells as a template. The X-ray diffraction (XRD) pattern indicates that the as-synthesized mesoporous hybrid Fe₃O₄ is well crystallized. The Barrett-Joyner-Halenda (BJH) models reveal the existence of mesostructure in the dried sample which has a specific surface area of 96.31 m²/g and a pore size distribution of 8-14 nm. Transmission electron microscopy (TEM) measurements confirm the wormhole-like structure of the resulting samples. The composition and chemical bonds of the Fe₃O₄/cells composites are studied by Fourier transform infrared (FT-IR) spectroscopy. Preliminary magnetic properties of the mesoporous hybrid Fe₃O₄ are characterized by a vibrating sample magnetometer (VSM). The magnetic Fe₃O₄/cells composites with mesoporous structure have potential applications in biomedical areas, such as drug delivery.     

Synthesis and magnetic properties of hard magnetic (CoFe2O4)-soft magnetic (Fe3O4) nano-composite ceramics by SPS technology

CoFe₂O₄/Fe₃O₄ nano-composite ceramics were synthesized by Spark Plasma Sintering. The X-ray diffraction patterns show that all samples are composed of CoFe₂O₄ and Fe₃O₄ phases when the sintering temperature is below 900 °C. It is found that the magnetic properties strongly depend on the sintering temperature. The two-step hysteresis loops for samples sintered below 500 °C are observed, but when sintering temperature reaches 500 °C, the step disappears, which indicates that the CoFe₂O₄ and Fe₃O₄ are well exchange coupled. As the sintering temperature increases from 500 to 800 °C, the results of X-ray diffractometer indicate the constriction of crystalline regions due to the ion diffusion at the interfaces of CoFe₂O₄/Fe₃O₄ phases, which have great impact on the magnetic properties.     

Preparation and magnetic properties of the conductive Co(1−x)NixFe2O4/polyaniline microsphere composites

Core-shell Co_(1−x)Ni_xFe₂O₄/polyaniline nanoparticles, where the core was Co_(1−x)Ni_xFe₂O₄ and the shell was polyaniline, were prepared by the combination of sol-gel process and in-situ polymerization methods. Nanoparticles were investigated by Fourier transform spectrometer, X-ray diffraction diffractometer, Scanning electron microscope, Differential thermal analysis and Superconductor quantum interference device. The results showed that the saturation magnetization of pure Co_(1−x)Ni_xFe₂O₄ nanoparticles were 57.57 emu/g, but Co_(1−x)Ni_xFe₂O₄/polyaniline composites were 37.36 emu/g. It was attributed to the lower content (15 wt%), smaller size and their uneven distribution of Co_(1−x)Ni_xFe₂O₄ nanoparticles in the final microsphere composites. Both Co_(1−x)Ni_xFe₂O₄ and PANI/Co_(1−x)Ni_xFe₂O₄ showed superparamagnetism.     

Synthesis and characterization of TiO2/Fe2O3 core-shell nanocomposition film and their photoelectrochemical property

TiO₂/Fe₂O₃ core-shell nanocomposition film has been fabricated via two-step method. TiO₂ nanorod arrays are synthesized by a facile hydrothermal method, and followed by Fe₂O₃ nanoparticles deposited on TiO₂ nanorod arrays through an ordinary chemical bath deposition. The phase structures, morphologies, particle size, chemical compositions of the composites have been characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and ultraviolet-visible (UV-vis) spectrophotometer. The results confirm that Fe₂O₃ nanoparticles of mean size ca. 10 nm coated on the surface of TiO2 NRs. After depositing Fe₂O₃, UV-vis absorption property is induces the shift to the visible-light range, the annealing temperature of 600 °C is the best condition for UV-vis absorption property of TiO₂/Fe₂O₃ nanocomposite film, and increasing Fe content, optical activity are enhanced one by one. The photoelectrochemical (PEC) performances of the as-prepared composite nanorods are determined by measuring the photo-generated currents under illumination of UV-vis light. The TiO₂ NRs modified by Fe₂O₃ show the photocurrent value of 1.36 mA/cm² at 0 V vs Ag/AgCl, which is higher than those of unmodified TiO₂ NRs.     

Synthesis of nanocrystalline Zn0.5Mn0.5Fe2O4 via in situ polymerization technique

Nanocrystalline Zn_0.5Mn_0.5Fe₂O₄ was synthesized through the pyrolysis of polyacrylate salt precursors prepared via in situ polymerization of the metal salts and acrylic acid. The pyrolysis behavior of the polymeric precursors was studied by use of thermal analysis. The as-obtained product was characterized by powder X-ray diffraction (XRD), transmission electron microscope (TEM), electron diffraction (ED) pattern, scanning electron microscopy (SEM) and electron dispersive X-ray (EDX) analysis. The results revealed that the particle size is in the range of 15–25 nm for Zn-Mn ferrites with good crystallinity. Magnetic properties of the sample at 300 K were measured using a vibrating sample magnetometer, which showed that the sample exhibited characteristics of superparamagnetism.     

Synthesis and characterization of Fe3O4@C@Ag nanocomposites and their antibacterial performance

We synthesized Fe₃O₄@C@Ag nanocomposites through a combination of solvothermal, hydrothermal, and chemical redox reactions. Characterization of the resulting samples by X-ray diffraction, Fourier-transform infrared spectroscopy, field-emission scanning and transmission electron microscopy, and magnetic measurement is reported. Compared to Fe₃O₄@Ag nanocomposites, the Fe₃O₄@C@Ag nanocomposites showed enhanced antibacterial activity. The Fe₃O₄@C@Ag nanocomposites were able to almost entirely prevent growth of Escherichia coli when the concentration of Ag nanoparticles was 10 μg/mL. Antibacterial activity of the Fe₃O₄@C@Ag nanocomposites was maintained for more than 40 h at 37 °C. The intermediate carbon layer not only protects magnetic core, but also improves the dispersion and antibacterial activity of the silver nanoparticles. The magnetic core can be used to control the specific location of the antibacterial agent (via external magnetic field) and to recycle the residual silver nanoparticles. The Fe₃O₄@C@Ag nanocomposites will have potential uses in many fields as catalysts, absorbents, and bifunctional magnetic-optical materials.     

Influence of substrate temperature in BiFeO3-CoFe2O4 nanocomposites deposited on SrTiO3 (0 0 1)

BiFeO₃-CoFe₂O₄ epitaxial nanocomposites have been deposited on SrTiO₃ (0 0 1) substrates by pulsed laser deposition. We present here a study of the influence of the deposition temperature (T_S), in the 550-800 °C range, on the film composition, morphology and microstructure. Electron-probe microanalysis shows strong reduction of the Bi content in the films when increasing T_S. Films prepared at T_S=750 °C and above are virtually Bi-free. X-ray diffraction (XRD) data show that, due to the volatility of Bi, there is a progressive reduction in the amount of BiFeO₃. The deposition temperature and the concomitant presence of Fe_xO_y spurious phases in the nanocomposites grown at high temperature promote radical changes in film morphology and magnetization. It thus follows that a temperature range suitable for controlled modification of nanocomposites morphology would be extremely narrow.     

Effect of Li2O and CoO-doping of CuO/Fe2O3 system on its surface and catalytic properties

Physicochemical, surface and catalytic properties of pure and doped CuO/Fe₂O₃ system were investigated using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), nitrogen adsorption at −196 °C and CO-oxidation by O₂ at 80-220 °C using a static method. The dopants were Li₂O (2.5 mol%) and CoO (2.5 and 5 mol%). The results revealed that the increase in precalcination temperature from 400 to 600 °C and Li₂O-doping of CuO/Fe₂O₃ system enhanced CuFe₂O₄ formation. However, heating both pure and doped solids at 600 °C did not lead to complete conversion of reacting oxides into CuFe₂O₄. The promotion effect of Li₂O dopant was attributed to dissolution of some of dopant ions in the lattices of CuO and Fe₂O₃ with subsequent increase in the mobility of reacting cations. CoO-doping led also to the formation of mixed ferrite Co_xCu_1−xFe₂O₄. The doping process of the system investigated decreased to a large extent the crystallite size of unreacted portion of Fe₂O₃ in mixed solids calcined at 600 °C. This process led to a significant increase in the S_BET of the treated solids. Doping CuO/Fe₂O₃ system with either Li₂O or CoO, followed by calcination at 400 and 600 °C decreased its catalytic activity in CO-oxidation by O₂. However, the activation energy of the catalyzed reaction was not much affected by doping.     

Effect of Fe/Sr mole ratios on the formation and magnetic properties of SrFe12O19 microtubules prepared by sol-gel method

The sol was obtained by sol-gel method. Then, the sol was dripped onto the absorbent cotton template. The gel was obtained after the evaporation of water. Strontium ferrite microtubules were prepared after carrying out calcination process at different temperatures. The phase, morphology and particle diameter and the magnetic properties of samples were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM), respectively. The effects of Fe³⁺/Sr²⁺ mole ratio and calcination temperature on the crystal structure, morphology and magnetic properties of ferrite microtubules were studied. The external diameters of obtained SrFe₁₂O₁₉ microtubules were found to range between 8 and 13 μm; the wall thicknesses ranged between 1 and 2 μm. When the Fe³⁺/Sr²⁺ mole ratio and the calcination temperature were 11.5 and 850 °C, respectively, the coercivity, saturation magnetization and remanent magnetization for the samples were 7115.1 Oe, 70.1 and 42.4 emu/g, respectively. The mechanism of the formation and variation in magnetic properties of the microtubules were explained.     

Growth of nanocrystalline CuIn3Se5 (OVC) thin films by ion exchange reactions at room temperature and their characterization as photo-absorbing layers

Nanocrystalline CuIn₃Se₅ thin films have been grown on ITO glass substrates using chemical ion exchange reactions with CdS, in alkaline medium at pH 11. The as-deposited films were annealed in air at 200 °C for 30 min and characterized using X-ray diffraction (XRD), transmission electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy to study the structural, compositional and morphological properties. The XRD patterns reveal the nanoparticles size to be of 18-20 nm diameter, while from the SEM images the nanoparticles size is estimated to be 20-30 nm. It is observed that the annealed films contain nanocrystallites connected with each other through grain boundaries, with grain size of about 100-125 nm and have an overall n-type electrical conductivity and higher photoconductivity. The current-voltage (I-V) characteristics (in dark and light) of these films indicated the formation of a Schottky like junction between the n-CuIn₃Se₅ (OVC) and CdS/ITO layers.     

Synthesis of magnetic and lightweight hollow microspheres/polyaniline/Fe3O4 composite in one-step method

After hollow microspheres (HM) were surface modified, a layer of electromagnetic polyaniline/Fe₃O₄ composite (PAN/Fe₃O₄) was successfully grafted onto the surface of the self-assembled monolayer coated HM, resulting in HM/PAN/Fe₃O₄ composites. In this approach, γ-aminopropyltriethoxy silane was adopted to form a well-coating monolayer with amino groups for the graft polymerization of aniline, which played an important role in fabricating the core-shell structure. FeCl₃ was used as the oxidant not only for aniline to form PAN, but also for FeCl₂ to prepare the magnets. The structure, morphologies, and magnetic properties of the as-prepared samples were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and vibrating sample magnetometer. The results indicated that the HM/PAN/Fe₃O₄ composites possess low density (ρ < 1.0 g/cm³), controllable morphology, and good magnetic properties at room temperature (saturation magnetization Ms = 8.32 emu g⁻¹ and coercive force Hc ≈ 0).     

Morphology and magnetic properties of FeCo nanocrystalline powder produced by modified mechanochemical procedure

Properties of FeCo nanocrystalline intermetallic powders prepared by salt-matrix hydrogen reduction of a milled Fe₂O₃-Co₃O₄ mixture were investigated. The product of 72 ks ball-milling at 350 rpm was CoFe₂O₄ nanopowder. Reduction of this powder for 3.6 ks by hydrogen at 750 °C resulted in the formation of Fe_0.67Co_0.33 stoichiometric compound. Scanning electron microscopy, electron dispersive spectrometry, X-ray diffraction and vibrating sample magnetometry were used to characterize the nanopowder. Using a salt-matrix (NaCl as a dispersion medium) resulted in the decrease of the reduction temperature and improvement of the morphology and magnetic properties of the nanopowder. Dispersion of the ball-milled product in Hexan resulted in further improvements of the magnetic properties.