Synthesis and characterization of silica core/nano-ferrite shell particles

Core/shell particles were synthesized by assembling oppositely charged ferrite (Fe₃O₄ or NiFe₂O₄) nanoparticles on the surface of monodispersed silica core particles (having size ～0.4 μm) prepared by hydrolysis and condensation of tetraethylortosilicate. Optimal conditions for synthesis of silica core/nano-Fe₃O₄ shell particles were found at pH ～ 5.4. The obtained particles have superparamagnetic behavior above a blocking temperature of ≈25 K, which make them very attractive for a broad range of biomedical and bioengineering applications. Incorporation of nickel into ferrite structure could not be achieved at lower pH value, so functionalization of core particles was required. Incorporation of nickel into ferrite structure was successful at pH above 7, however at higher pH the formation rate of nickel–ferrite particles becomes very fast and the self-aggregation dominates the competing formation of the nickel–ferrite shell. Because of that the self-aggregation was prevented by surface modification of nickel–ferrite nanoparticles with citric acid before their deposition on the functionalized silica core and homogenous and continuous NiFe₂O₄ shell was finally obtained.     

Pinning enhancement in MgB2 superconducting thin films by magnetic nanoparticles of Fe2O3

MgB₂ thin films were fabricated on r-plane Al₂O₃ ( ${1} \overline{{1}} {0} {2})$ substrates. First, deposition of boron was performed by rf magnetron sputtering on Al₂O₃ substrates and followed by a post-deposition annealing at 850 °C in magnesium vapour. In order to investigate the effect of Fe₂O₃ nanoparticles on the structural and magnetic properties of films, MgB₂ films were coated with different concentrations of Fe₂O₃ nanoparticles by spin coating process. The magnetic field dependence of the critical current density J _c was calculated from the M–H loops and magnetic field dependence of the pinning force density, f _p(b), was investigated for the films containing different concentrations of Fe₂O₃ nanoparticles. The critical current densities, J _c, in 3T magnetic field at 5 K were found to be around 2·7 × 10⁴ A/cm², 4·3 × 10⁴ A/cm², 1·3 × 10⁵ A/cm² and 5·2 × 10⁴ A/cm² for films with concentrations of 0, 25, 50 and 100% Fe₂O₃, respectively. It was found that the films coated with Fe₂O₃ nanoparticles have significantly enhanced the critical current density. It can be noted that especially the films coated by Fe₂O₃ became stronger in the magnetic field and at higher temperatures. It was believed that coated films indicated the presence of artificial pinning centres created by Fe₂O₃ nanoparticles. The results of AFM indicate that surface roughness of the films significantly decreased with increase in concentration of coating material.     

Photocatalytic degradation of methyl orange dye by NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles under visible irradiation: effect of varying the synthesis temperature

Nanoparticles of nickel ferrites (NiFe₂O₄) were synthesized at different temperature of synthesis (25, 50 and 80 °C) through the chemical co-precipitation method. The synthesized powders were characterized using X-ray diffraction for crystallite size and lattice parameter calculation. It reveals the presence of cubic spinel structure of ferrites with crystallite size between 29 and 41 nm. Transmission electron microscopy and scanning electron microscopy showed uniform distribution of ferrite particles with some agglomeration. The Fourier-transform infrared spectroscopy showed absorption bonds, which were assigned to the vibration of tetrahedral and octahedral complexes. Raman spectroscopy is used to verify that we have synthesized ferrite spinels and determines their phonon modes. The thermal decomposition of the NiFe₂O₄ was investigated by TGA/DTA. The optical study UV–visible is used to calculate the band gap energy. Magnetic measurements of the samples were carried out by means of vibrating sample magnetometer and these studies reveal that the formed nickel ferrite exhibits ferromagnetic behavior. Photoluminescence showed three bands of luminescence located at 420, 440 and 535 nm. The photocatalytic properties of nickel ferrite (NiFe₂O₄) nanoparticles were evaluated by studying the photodecomposition of methyl orange as organic pollutant models and showed a good photocatalytic activity.     

The Effect of EDTA on the Synthesis of Ni Ferrite Nanoparticles

Nanocrystalline nickel ferrite (NiFe₂O₄) was synthesized by chemical sol-gel method using Ethylenediamine tetra acetic acid (EDTA) as a complexing agent. The results show that by using EDTA, it is possible to prepare pure phase of nickel ferrite nanoparticles at the relatively low temperatures. The annealing temperature is found to have strong influence on size, structural, and magnetic properties of the synthesized samples. It was found that the values of saturation magnetization, M _s increases by the increasing of the annealing temperature. The largest value of M _s, was found to be 47?emu/g for the sample annealed at 1000?°C, which is close to the reported value for the multi-domain bulk samples of nickel ferrite (50?emu/g). Furthermore, as the particle size increases the coercivity starts to increase and reaches a maximum value; then it decreases. This effect can be attributed to the transition of the particle size from single-domain to the multi-domain magnetic structure.     

Magnetic Properties of ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanoparticles Synthesized by Starch-Assisted Sol–Gel Auto-combustion Method

In this paper, ZnFe₂O₄ spinel ferrite nanoparticles with different grain sizes at different annealing temperatures have been synthesized using the starch-assisted sol–gel auto-combustion method. The synthesized nanoparticles were characterized by conventional powder X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and vibrating sample magnetometer. The X-ray diffraction (XRD) patterns demonstrated that the ZnFe₂O₄ nanoparticles consist of single-phase spinel structure with crystallite sizes 4.81, 8.72, 12.06, 29.32, and 72.60 nm annealed at 400, 600, 800, 1000, and 1200 °C, respectively. Field emission scanning electron microscopy reveals that particles are of spherical morphology at lower annealing temperature and hexagonal-like morphology at higher temperature. An infrared spectroscopy study shows the presence of two principal absorption bands in the frequency range around 525 cm^?1 (ν ₁) and around 350 cm^?1 (ν ₂), which indicate the presence of tetrahedral and octahedral group complexes, respectively, within the spinel ferrite nanoparticles. Raman spectroscopy study also indicated the change in octahedral and tetrahedral site-related Raman modes in zinc ferrite nanoparticles with change of particle size. The nanocrystalline ZnFe₂O₄ samples (4.81, 8.72, 12.06, 29.32 nm) show ferrimagnetic behavior, and bulk sample (72.60 nm) shows paramagnetic behavior. This change in magnetic behavior is due to change of cation distribution in ZnFe₂O₄ nanoparticles with decrease of particle size.     

Preparation and characterization of nanosized cobalt ferrite particles by co-precipitation method with citrate as chelating agent

Cobalt ferrite (CoFe₂O₄) nanoparticles were synthesized by a facile novel co-precipitation method with citrate as chelating agent. The synthesized cobalt ferrite nanoparticles were calcinated at 400, 600 and 800 °C and characterized by using XRD and TGDTA. From XRD it confirms that CoFe₂O₄ nano particles belongs to spinel type lattice of space group Fd3m. The CoFe₂O₄ nano particles calcinated at 600 °C were further characterized by using FE-SEM with EDAX, FE-TEM with SAED pattern, DLS zeta potential and CV. The linear relationship between particle size and calcination temperatures of CoFe₂O₄ nanoparticles was noticed. The surface morphology of CoFe₂O₄ studied through FE-SEM and FE-TEM indicate that the particles are found crystalline and are in cubic shape. EDAX analysis revealed the presence of Co, Fe and O. Zeta potential exposes the good stability of the prepared CoFe₂O₄ nanoparticles. Capacitance value 609 F g^?1 was observed for the scanning rate of 2 mV s^?1 from the CV study and concluded it is suitable for super capacitor application.     

YBa2SnO5·5, a novel ceramic substrate for YBCO and BiSCCO superconductors

YBa₂SnO_5·5 has been synthesized and sintered as single phase material for its use as substrate for both YBCO and BiSCCO superconductors. YBa₂SnO_5·5 has a complex cubic perovskite (A₂BB’O₆) structure with the lattice constanta = 8·430 Å. The dielectric constant and loss factor of YBa₂SnO_5·5 are in a range suitable for its use as substrate for microwave applications. YBa₂SnO_5·5 is found to be chemically compatible with both YBCO and BiSCCO superconductors. The thick film of YBCO screen printed on polycrystalline YBa₂SnO_5·5 substrate gave aT _c(0) of 92 K and a critical current density (J _c) of 4 × 10⁴ A/cm² at 77 K. A screen printed BiSCCO thick film on YBa₂SnO_5·5 substrate gaveT _c(0) = 110 K and current density 3 × 10³ A/cm² at 77 K.     

Antimicrobial activity of composite nanoparticles consisting of titania photocatalytic shell and nickel ferrite magnetic core

Reverse micelle and hydrolysis have been combined to synthesize composite nanoparticles consisting of anatase–titania photocatalytic shell and nickel ferrite magnetic core. The average particle size of the composite nanoparticles was in the range of 10–15 nm. The photocatalytic shell of titania is responsible for the photocatalytic and anti-microbial activity and nickel ferrite magnetic core is responsible for the magnetic behavior, studied by superconducting quantum interference device. The anatase TiO2 coated NiFe₂O₄ nanoparticles retains the magnetic characteristics of uncoated nanocrystalline nickel ferrites, superparamagnetism (absence of hysteresis, remanence and coercivity at 300 K) and non-saturation of magnetic moments at high field. The magnetic measurements results encourage their application as removable anti-microbial photocatalysts. Bacterial inactivation with UV light in the presence of titania-coated NiFe₂O₄ nanoparticles is faster than the action with UV light alone.     

Preparation of nickel ferrite nanoparticles via a new route and study of their photocatalytic properties

Pure nickel ferrite (NiFe₂O₄) were prepared via sol-gel route in presence of different amino acids as a capping agent. The effect of different amino acids such as leucine, asparagine, and cysteine on the size, and morphology of NiFe₂O₄ nanoparticles were investigated. The magnetic properties of the samples were investigated using VSM analyze. We found that the NiFe₂O₄ nanoparticles synthesized at temperature of 800 °C exhibit a ferromagnetic behavior with a saturation magnetization of 34 emu/g and a coercivity of 100 Oe. Furthermore, the photocatalytic properties of as synthesized NiFe₂O₄ were evaluated by degradation of methyl orange as water contaminant. XRD, SEM, EDS, and UV–Vis spectroscopy were employed to characterize structural, morphological, and optical properties of NiFe₂O₄ nanoparticles.     

Exchange Bias, Memory and Freezing Effects in NiFe2O4 Nanoparticles

Single-phase NiFe₂O₄ nanoparticles embedded in SiO₂ matrix have been synthesized by sol-gel method. Average particle size lies in the range 8?C12 nm. Magnetic measurements are taken by SQUID-magnetometer with a maximum applied field of ??7 T and temperature down to 4.2 K. An exchange bias effect in nanoparticles is due to the existence of strong core-shell interactions and it vanishes as the particle size decreases (<4?nm). Spin disorder and frustration appear at the core-shell interface due to broken bonds on the surface. We have observed the exchange bias effect via hysteresis loop shift, when the sample is cooled in an applied field of 5?T. In both AC and DC fields, our system exhibit memory effects at the halted temperatures. Furthermore, a sharp increase of coercivity at low temperatures (<50 K) is observed, which is attributed to increased surface anisotropy at low temperatures. For saturation magnetization vs. temperature data, Bloch??s T ^3/2 law (M(T)=M(0)?(1?BT ^b )) is fitted well and yields: B=4??10^?05 K^?3/2 and b=1.53. All these measurements prove the presence of exchange bias (core-shell interactions), memory effects, validation of Bloch??s T ^3/2 law and freezing effects in nickel ferrite nanoparticles dispersed in SiO₂ matrix.     

Spin canting phenomenon in cadmium doped cobalt ferrites, CoCd x Fe2−x O 4 ( x = 0·0, 0·2, 0·4, 0·6, 0·8 and 1·0), synthesized using sol–gel auto combustion method

Synthesis of non-collinear (spin canted) ferrites having the formula, CoCd _x Fe_2???x O ₄ (x?= 0·0, 0·2, 0·4, 0·6, 0·8 and 1·0), has been carried out using the sol–gel auto combustion method. The ferrite samples show an interesting magnetic transition from Neel to Yafet–Kittel configuration, as the Cd^2?+? concentration is increased beyond x?= 0·4. The FT–IR spectra confirm the formation of the metal oxide bond as they exhibit two frequency bands in the range of ~595 cm^???1 and ~450 cm^???1, corresponding to the tetrahedral and the octahedral stretching vibrations of the metal oxide, respectively. The structural evolutions of the nanophase investigated using powder X-ray diffraction (XRD) technique show that the average crystallite size is ~ 35 nm. The magnetic studies reveal that the saturation magnetization, M _s , increases up to x?= 0·4 and decreases when the value of x is >0·4. It is proposed that the incorporation of Cd^2?+? ion takes place into the tetrahedral sites and up to x?= 0·4, Neel’s model is followed. But for x?> 0·4, canting of spins occurs, as explained by Yafet–Kittel (Y–K) model. The d.c. resistivity decreases as a function of temperature, indicating semiconducting nature of the ferrites and the positive value of Seebeck coefficient establishes p-type conduction behaviour for all the ferrite samples.     

Electrical conductivity and chemical stability of BaCe0·8 − x A x Gd0·2O3 − δ (A = In, Zr, Ta; x = 0, 0·1) ceramics

BaCe_0·8???x A _x Gd_0·2O_3???δ (A = In, Zr, Ta; x?=?0, 0·1) ceramics were synthesized by solid-state reaction method. Microstructure and electrical properties of BaCe_0·8???x A _x Gd_0·2O_3???δ ceramics were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance analysis at intermediate temperatures of 573–1073 K in different atmospheres. BaCe_0·8Gd_0·2O_3???δ , BaCe_0·7In_0·1Gd_0·2O_3???δ and BaCe_0·7Zr_0·1Gd_0·2O_3???δ ceramics exhibit a single cubic perovskite structure. BaCe_0·7In_0·1Gd_0·2O_3???δ ceramic has the highest conductivity of 4·6 × 10^???2 S·cm^???1 in air at 1073 K. BaCe_0·7In_0·1Gd_0·2O_3???δ and BaCe_0·7Zr_0·1Gd_0·2O_3???δ ceramics exhibit an excellent chemical stability against boiling water. Indium is a suitable doping element to promote the sintering densification and to enhance both electrical conductivity and chemical stability of Gd-doped BaCeO₃ at operating temperatures.     

Some electrical and magnetic properties of γ-Fe2O3

γ-Fe₂O₃ synthesized from FeC₄H₄O₄·4H₂O has been studied using various techniques. The phase transformation observed by electrical conductivity measurements agrees well with the initial magnetization measurement. The magnetic hysteresis values compare with those ofγ-Fe₂O₃ samples synthesized using established procedures.γ-Fe₂O₃ particles obtained were circular in shape showing a well resolved six narrow bands in Mössbauer spectrum. The presence of hydrogen ferrite phase was also confirmed by electrical and magnetic measurements.     

X-Ray Diffraction and Cation Distribution Studies in Zinc-Substituted Nickel Ferrite Nanoparticles

Structural and cation distribution studies on Ni_1?x Zn _x Fe₂O₄ (with x=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) ferrite nanoparticles by using X-ray diffraction analysis are reported. In this work the Nickel–Zinc ferrites nanoparticles are synthesized by sol–gel auto combustion using respective metal nitrates and citric acid as fuel for the auto combustion reaction. Formation of ferrite nanoparticles having single-phase spinel structure is evident from the obtained X-ray diffraction patterns. Lattice constant values of the Ni_1?x Zn _x Fe₂O₄ ferrite system are found to increase with increase of zinc substitution x. Broad and intense XRD peaks in the patterns indicate the nanocrystalline nature of the produced ferrite samples. Average particle size calculated from most intense Bragg’s reflection (311) using Debye–Scherrer’s formula is found to be 30 nm. The particle size is found to decrease with increase in zinc substitution x. Observed X-ray density is found to decrease with increase in zinc substitution x. Bulk density, porosity, and unit cell volume are also calculated from the XRD data. Distribution of metal cations in the spinel structure estimated from X-ray diffraction data show that along with Ni²⁺ ions most of the Zn²⁺ ions also occupy the octahedral [B] sites, which are attributed to nanosize dimensions of the ferrite samples.     

Hydrothermal synthesis and magnetic properties of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles and nanorods

NiFe₂O₄ nanoparticles and nanorods were synthesized by a facile hydrothermal treatment of Ni(DS)₂ (Nickel dodecyl sulfate), FeCl₃, and NaOH aqueous solution at 120 °C. The products were characterized by powder X-ray diffraction, transmission electron microscopy, and selected area electron diffraction. The magnetic properties were evaluated using a vibrating sample magnetometer. The probable mechanism of the formation of NiFe₂O₄ nanoparticles and nanorods was discussed.     

Mechanochemically activated synthesis of nanostructured NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>

Powdery NiFe₂O₄ has been obtained by mechanothermal treatment. Nickel and iron hydroxides are used as initial compounds. For comparison the initial compounds are calcinated without mechanical treatment (samples obtained by direct heating). The characterization of the samples is carried out by XRD analysis and Mössbauer spectroscopy. It is established that single phase NiFe₂O₄ is formed after mechanical activation (5 h) and calcination at 773 K. The ferrite synthesized at this temperature contains a smaller quantity of Fe³⁺ ions in tetrahedral position (31%) than is the case of conventional nickel ferrite (50%). The number of tetrahedrally coordinated iron ions increases with enhancement of the synthesis temperature, approaching the distribution of the tetrahedral and octahedral positions typical of conventional NiFe₂O₄. The samples obtained by direct heating contain unreacted NiO and α-Fe₂O₃ even after calcinations at 1073 K.     

Dielectric behaviour of nano-crystalline spinel Ni0·2Ca0·8Fe2O4 and their nano-composite with polypyrrole

The spinel ferrite nano-particles of chemical composition Ni_0·2Ca_0·8Fe₂O₄ have been prepared by sol-gel method. Subsequently, the nanoparticles are encapsulated with the intrinsically conducting polymer shell of polypyrrole. The X-ray diffraction patterns confirm the single phase cubic spinel structure of the materials. To understand the dielectric properties of the materials, frequency-dependent dielectric measurement has been performed at 300 K in the range of 100 mHz to 2 MHz. On polymerization, both the dielectric strength as well the dielectric loss is significantly increased. Also, the dielectric conductivity, which arises from the electron hopping mechanism, is considerably increased on polymerization.     

Paederia foetida Linn. promoted synthesis of CoFe2 O4 and NiFe2 O4 nanostructures and their photocatalytic efficiency

A facile method of synthesis of cobalt ferrite (CoFe₂ O₄) and nickel ferrite (NiFe₂ O₄) nanoparticles (NPs) was developed using urea as a hydroxylating agent and Paederia foetida Linn. (family: Rubiaceae) leaf extract as a bio‐template. The synthesised ferrite NPs were characterised in a detailed manner by powder X‐ray diffraction (XRD), transmission electron microscopy, Fourier transform‐infrared spectroscopy and vibrating sample magnetometer analysis. The XRD patterns revealed the formation of cubic face‐centred phase for both CoFe₂ O₄ and NiFe₂ O₄ NPs. These quasi‐spherical particles of CoFe₂ O₄ and NiFe₂ O₄ were shown to have sizes in the range of 10–80 and 5–50 nm, respectively. The photocatalytic activity of metal ferrites was evaluated in H₂ O₂ assisted oxidative degradation of methylene blue (MB) and rhodamine B (RhB) under irradiation of solar light. Both metal ferrite photocatalysts exhibited pronounced activity in degradation of MB and RhB, respectively, but relatively higher activity was observed for NiFe₂ O₄. After completion, the catalysts were recovered using an external magnet. Recycling of these recovered catalysts up to five times showed no noticeable change in the efficiency.Inspec keywords: nanoparticles, nanofabrication, photochemistry, catalysts, cobalt compounds, nickel compounds, ferrites, X‐ray diffraction, transmission electron microscopy, Fourier transform infrared spectra, crystal structure, dyesOther keywords: Paederia foetida Linn, nanostructures, photocatalytic efficiency, cobalt ferrite nanoparticles, nickel ferrite nanoparticles, hydroxylating agent, leaf extract, bio‐template, powder X‐ray diffraction, transmission electron microscopy, Fourier transform‐infrared spectroscopy, vibrating sample magnetometer analysis, cubic face‐centred phase, quasi‐spherical particles, photocatalytic activity, methylene blue, rhodamine B, size 5 nm to 80 nm, CoFe₂ O₄ , NiFe₂ O₄      

Preparation of sheet like polycrystalline NiFe2O4 nanostructure with PVA matrices and their properties

Sheet-like nickel ferrite (NiFe₂O₄) has been synthesised with PVA matrices using co-precipitation technique. The sheet is formed from the oriented aggregation of single crystalline NiFe₂O₄ nanoparticles with PVA as the structure directing template. The synthesised materials are characterised based on X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), high-resolution scanning electron microscopy (HRSEM), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometry (VSM). The XRD results show that the nanocrystal contains single phase spinel structure of Fd3m space group. The existence of PVA with nanoparticles has been confirmed by FTIR spectra. The room temperature ferromagnetic property is exhibited by the as synthesised sample with high saturation magnetisation.     

A comprehensive study on influence of Nd3 + substitution on properties of LiMn2O4

LiNd _x Mn_2???x O₄ samples are synthesized via co-precipitation technique. The activation energies computed from thermogravimetric analyses on the basis of Ozawa method have been observed to linearly increase with increase in dopant concentration. X-ray diffraction analyses indicate the cubic–spinel structure for all the samples. The lattice parameter has been observed to decrease with increasing concentration of Nd^3?+? doping. The octahedral site preference of neodymium dopant in the LiMn₂O₄ structure has been elucidated using XRD and FT–IR studies. The porosity and surface roughness obtained from SEM analysis have been observed to decrease with increase in Nd^3?+? dopant concentration in LiMn₂O₄ lattice. The electrochemical performances of the electrodes were analysed through cyclic voltammetry, chronopotentiometry and electrochemical impedance techniques. The specific capacity has been observed to decrease initially with increase in Nd^3?+? dopant concentration, whereas the capacity retention has increased with increase in dopant concentration. The observed percentage capacity retention after 50 cycles of the electrodes LiNd_0·05Mn_1·95O₄, LiNd_0·10Mn_1·90O₄ and LiNd_0·15Mn_1·85O₄ were 88·4%, 97·1% and 96·8%, respectively. The Li ion diffusion coefficient ascertained using electrochemical impedance spectroscopy was found to be higher for LiNd_0·10Mn_1·90O₄ around 3·74 × 10^???12 cm² s^???1.