Chemical control on the size and properties of nano NiFe2O4 synthesized by sol–gel autocombustion method

Nickel ferrite nanoparticles have been synthesized by sol–gel auto combustion route. The significant role played by nitric acid added to the precursor solution in controlling the reaction rate phase purity, crystallinity, crystallite size, thermal and magnetic properties of nanoparticles was explored and reported. Also, the influence of annealing on the properties were studied. Samples of average crystallite size ranging from 10 nm to 40 nm have been obtained by controlling the HNO₃ concentration and by increasing the annealing temperature. The size-dependent structural, thermal and magnetic properties were investigated and reported. The Hopkinson peak was observed for all the crystalline samples near the Curie temperature. The highest value 47.3 emu/g of saturation magnetization was obtained for the sample prepared with higher concentration (6 mol/L) of HNO₃.     

Temperature induced evolution of structure/microstructure parameters and their correlations with electric/magnetic properties of nanocrystalline Nickel ferrite

Nickel ferrite nanoparticles were annealed in order to find dependence of electric/magnetic properties on crystallite size. The following correlations of crystallite size with physical parameters were found: (a) lattice parameter decreases with the increase in size and it reaches value for bulk counterpart approximately for crystallites bigger than 7 nm, (b) ac electrical resistivity at room temperature increases with the increase in crystallite size, (c) for crystallites of ~7 nm or smaller electrical resistivity have maximum value at 50 °C, (d) the real part of permittivity at selected frequency generally decreases with the increase in crystallite size and (e) magnetization increases with the increase in crystallite size. Deviation of stoichiometry, cation polyvalence, and cation redistribution with annealing are the main factors that influence physical properties of Nickel ferrite nanoparticles.     

Synthesis of MnFe2O4 nanocrystals by wet-milling under atmospheric conditions

This work reports an original method for synthesis of well-crystallized manganese ferrite (MnFe₂O₄) nanoparticles via a high energy wet milling technique under atmospheric conditions, starting from metallic Mn and Fe powders in the presence of distilled water. The effects of milling conditions on the formation and magnetic properties of MnFe₂O₄ nanoparticles were investigated in detail. Fully stoichiometric MnFe₂O₄ nanocrystals with an average crystallite size of 14.5 nm were produced after 24 h of milling. As-synthesized MnFe₂O₄ nanocrystals were found to show soft magnetic behavior at room temperature with saturation magnetization of 53 emu/g. Due to reduced thermal effects, the saturation magnetization increased to 68 emu/g at 5 K. Results show that this method is simple and efficient for the mass production of MnFe₂O₄ nanoparticles.     

Effects of magnesia addition on structural, morphological and magnetic properties of nano-crystalline nickel ferrite system

Nano-crystalline magnesia doped nickel ferrite powders have been synthesized by the combustion route. The structural, morphological and magnetic properties of the products were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy and vibrating sample magnetometer (VSM). X-ray analysis showed that all samples were cubic spinel. The increase in magnesia concentration resulted in a decrease in the average crystallite size, lattice constant, unit cell volume, X-ray density, ionic radii, the distance between the magnetic ions and bond lengths on tetrahedral sites and octahedral sites of the as prepared ferrite. The combustion method led to formation of spongy and fragile network structure. Increasing amounts of magnesia brought about remarkable changes in the microstructure and porosity of nickel ferrite. Doping of nickel ferrite by magnesia led to a decrease in its saturation magnetization. The minimum saturation magnetization value of nickel ferrite due to the doping 1 wt.% MgO attained 44.18 emu/g.     

Magnetic studies on one-step chemically synthesized nickel ferrite thin films

Nickel ferrite thin films were synthesized at room temperature using one-step electrodeposition solution processing. Reaction kinetics was also proposed. An effect of air baking on the structural, surface morphological and magnetic properties was investigated. As-deposited nickel ferrite thin films were cubic in crystal structure. Calculated grain size after annealing was increased from 30 to 48 nm in addition to formation of rough surface morphology. Due to decrease in defect levels after air baking the annealed nickel ferrite thin film showed saturation magnetization of 268 emu/cc, higher than non-annealed (230 emu/cc), when used in magnetic studies.     

Magnetic and Mössbauer behavior of the nanostructured MgFe2O4 spinel obtained at low temperature

This study investigated the solution combustion synthesis technique to obtain the nanostructured magnesioferrite (MgFe₂O₄) spinel powder. The reaction was performed in an electric muffle furnace. Considering the characteristics of the as-synthesized powders, the 30% fuel-deficient formulation was selected for synthesis temperature evaluation. This formulation was synthesized at different furnace temperatures. Powder characterization was carried out by X-ray diffraction (XRD) to evaluate crystallographic analysis and crystallite size; Transmission Electron Microscopy (TEM) was done to assess the morphology and crystallite size; and Mössbauer spectroscopy and vibrational sample magnetometer (VSM) were performed to obtain magnetic measurements. Crystallite sizes estimated from the XRD technique increased with furnace temperature values, which were consistent with the results obtained by TEM. The characterized samples of MgFe₂O₄ had an average crystallite size of 42.8 nm using the DRX method, average saturation magnetization of 25.6 emu/g and coercive field not higher than 11 Oe.     

Nanocrystalline gamma-alumina: A highly active catalyst for dimethyl ether synthesis

In this article, mesoporous nanocrystalline γ-Al₂O₃ with high surface area is synthesized by a simple sol-gel method with cationic surfactant as template. This sample is used for vapor-phase dehydration of methanol to Dimethyl ether. The synthesized catalyst showed a high surface area of 375 m² g^− 1 and a crystallite size of about 3.9 nm. NH₃-TPD analysis revealed that the sample with smaller crystallite size possesses higher concentration of medium acidic sites and consequently the catalytic activity.     

Structural, morphological, magnetic and optical properties of chromium substituted strontium ferrites, SrCrxFe12 − xO19 (x = 0.5, 1.0, 1.5, 2.0 and 2.5) annealed with potassium halides

Chromium substituted strontium ferrites SrCr_xFe_12 − xO₁₉ (x = 0.5, 1.0, 1.5, 2.0 and 2.5) have been synthesized via sol gel method and the dry gels obtained have been annealed with various inorganic template agents (KCl, KBr and KI). The powder X ray diffraction studies reveal a crystallite size of ~ 40-45 nm. The use of KCl as inorganic template agent leads to an increase in the crystallite size. This may be attributed to the fact that the coordination ability of Cl⁻ is maximum due to its larger charge to size ratio, which promotes crystal growth in one dimension leading to needle-like morphology. On the other hand, KI undergoes sublimation to form I₂ which gets entrapped in the strontium ferrite crystal leading to a bubble-like morphology. A systematic change in the lattice constants, a and c, is not observed because the radius of Cr³⁺ ion (0.63 Å) is similar to that of Fe³⁺ ion (0.64 Å). The saturation magnetization decreases with increase in the chromium concentration from 43.03 emu/g to 17.40 emu/g due to the substitution of Fe³⁺ ions by less magnetic Cr³⁺ ions in 2a and 12k sites of the lattice. The coercivity decreases with increase in the chromium concentration due to decrease in magnetocrystalline anisotropy. In the presence of KCl and KBr, both saturation magnetization and coercivity increase and the saturation magnetization has the maximum value in case of samples annealed with KBr. However, with KI, the values of both saturation magnetization and coercivity decrease sharply which may be due to lower crystallinity due to bubble-like morphology because of the decomposition of KI to I₂. The energy band gap for all the ferrite compositions is found to be ~ 2.2 eV and its value increases in the samples annealed with KI.     

Size-controlled high magnetization CoFe2O4 nanospheres and nanocubes using rapid one-pot sonochemical technique

Highly crystalline single phase spherical and monodisperse cobalt ferrite (CoFe₂O₄) nanoparticles (NPs) with uniform shape and size distribution have been synthesized by one pot-rapid sonochemical method. The effect of different solvents, such as aqueous, alcoholic, and a mix of water/ethanol in 1:1 volume ratio on the shape, size, and crystalline structure of CoFe₂O₄ NPs were studied using X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy. The size of CoFe₂O₄ nanoparticle was controlled in the range from 20 to 110 nm based on the solvent medium used in the synthesis process. Furthermore, the evolution from spherical to cubic morphology of cobalt ferrite NPs is achieved by simply changing the solvent medium from aqueous to alcoholic medium. The magnetic properties of all the synthesized CoFe₂O₄ NPs were studied by vibrating sample magnetometer (VSM) at room temperature. The magnetization value was found to be particle size dependent, and high magnetization (Ms) of 92.5 emu/g was obtained for the CoFe₂O₄ NPs sample synthesized in a mixed solution of water and ethanol. A possible reaction mechanism for the formation of cobalt ferrite NPs by the sonochemical technique was discussed. The facile method adopted in our study appears to be a promising route for synthesis of highly crystalline nanoparticles within short times and without the need for using any calcination process.     

Structural,morphological, and magnetic properties of ZnxCo1-xFe2O4 (0 ≤ x ≤ 1) prepared using a chemical co-precipitation method

In the present study, the chemical co-precipitation technique was adopted to synthesize Zn_xCo_1-xFe₂O₄ (ZCF) (0?≤ x?≤?1) ferrites. The thermogravimetric-differential thermal analysis results revealed that above 405?°C, the precursor had decomposed and ferrite formation had occurred. The structure and morphology of the prepared ferrite nanoparticles were investigated using X-ray diffraction, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy (FE-SEM). The synthesized polycrystalline nanoparticles had a cubic spinel structure and the crystallite size was in the range of 6.09–12.98?nm. The prepared ferrites appeared as nearly spherical nanoparticles with a particle size in between 0.13 and 0.23?µm, as confirmed using FE-SEM. The elemental composition was determined using the energy-dispersive X-ray spectroscopy technique. The influence of the Zn-substituted cobalt ferrites (ZCF) on the structural, morphological, and magnetic properties were studied. The magnetic properties of the ZCF samples such as saturation magnetization, remanence magnetization, and coercivity measured at room temperature were 0.387–2.065?emu/g, 0.057–1.282?emu/g, and 60–1834?Oe, respectively. It was confirmed from the nature of the hysteresis loops that the given ZCF samples can be considered as a soft magnetic material.     

Magnetically retrievable nanoscale nickel ferrites: An active photocatalyst for toxic dye removal applications

Nickel ferrite (NiFe₂O₄) nanoparticles were synthesized through the sol-gel auto-combustion method using urea and glycine as mixed fuel. The prepared nanoparticles were investigated for their structural, optical, and magnetic characterizations. Rietveld refined X-ray diffraction (XRD) patterns revealed the development of single-phase cubic spinel. The crystallite size was calculated by using Modified Scherrer's method and the W-H plot was found in the order of 26.6 nm and 25.4 respectively which are nearly the same. The infrared spectrum showed the typical characteristic absorption bands in the range of 400 cm^-1 to 600 cm^-1 belonging to cubic spinel structure. Scanning electron microscopy images showed the spherical nature of the nanoparticles along with agglomeration to some extent. As per the optical study, the prepared nanoparticles have an optical bandgap of 2.59 eV. The magnetic properties were studied through the M − H hysteresis curve showing superparamagnetic nature, the value of saturation magnetization (M_s), coercivity (H_c) was observed 46.20 emu/gm, and 383.2 Oe respectively. The photocatalytic activity of nickel ferrite was studied based on the degradation of methylene blue (MB) dye as a model compound, where the result showed that prepared nanoparticles possessed a good photocatalytic activity against dye degradation. Up to four times catalyst exhibits nearly the same reutilization.     

Synthesis of high magnetization hydrophilic magnetite (Fe3O4) nanoparticles in single reaction—Surfactantless polyol process

High magnetization hydrophilic magnetite nanoparticles have been synthesized in two different batches with mean particle sizes of 32.3 and 9.2 nm by inexpensive and surfactant-free facile one-pot modified polyol method. In the synthesis, polyethylene glycol was used as a solvent media and it has been found to play a key role to act as a reducing agent as well as a stabilizer simultaneously. It was shown that the size of the nanoparticles can be effectively controlled by modifying the reaction parameters such as reaction temperature, time and polyol/metal precursor ratio. X-ray diffraction and energy dispersive spectroscopy studies confirm the formation of a pure magnetite phase without the presence of any other phases. Transmission electron microscopy and the Fourier transform infrared spectroscopy results reveal that the particle size and surface adsorption properties are very much dependent on reaction parameters. The magnetic properties of the samples measured by physical property measurement system have shown that the as-synthesized magnetite nanoparticles possess a high magnetization of 85.87 emu/g at 300 K and 91.7 emu/g at 5 K with negligible coercivities. The structural and magnetic characterizations of these polyol coated, hydrophilic, monodisperse, superparamagnetic nanoparticles clearly indicate that they are suitable for biomedical applications.     

The impact of microwave-assisted sintering on fabrication of cobalt ferrite nanostructure foams for gas-sensing

This study employed the Pechini-type sol-gel method to synthesize single-phase cobalt ferrite nanoparticles with almost spherical morphology and an average size of ～50 nm. The Pechini sol-gel is based on the polysterification reaction between citric acid and ethylene glycol and the formation of colloidal nanoparticles due to the polymerization of an iron-cobalt complex. Foam samples were prepared from the obtained nanoparticles by using urea as the progenic agent and subsequent conventional or microwave sintering. The average grain size values for the microwave and conventionally sintered foam samples were 90 and 280 nm, respectively. Microwave sintering has successfully hindered grain growth regarding the initial ～50 nm size of the cobalt ferrite nanoparticles. The microwave sintered foam sample showed an approximately two-fold increase in the surface area value compared to its conventionally sintered counterpart. The pore volume for the conventionally and microwave sintered samples was measured at 0.007 and 0.026 cc/g, respectively. Also, the pore diameter values were measured to be less than 2.5 nm in both samples. The pore size distribution within the microwave sintered sample was unimodal, while the conventionally sintered sample showed a bimodal one. The gas-sensing properties of the samples were examined in pure ethanol, acetone, and liquefied petroleum gas (LPG) atmospheres at different temperatures. The results indicated that for all the samples and in all the three atmospheres, the best working temperature is 300 °C. The microwave sintered foam sample showed the highest sensitivity and the shortest response time. This sample was more selective towards ethanol than the other two gases.     

Magnetic enrichment behavior of monodispersed MFe2O4 nanoferrites (M= Mg,Ca, Ni,Co, and Cu)

The magnetic enrichment behavior of monodispersed MFe₂O₄ (M = Mg, Ca, Ni, Co, and Cu) ferrite nanoparticles with different size (10–130 nm) on the surface of a 15 mm o.d. NdFeB-N40 magnetic rod has been investigated. The materials were synthesized by a modified sol-gel method. They were characterized by XRD, TEM, and VSM. The magnetic field of the rod was modelled numerically using a finite element analysis software to obtain the input data for the magnitude of magnetic force. Three adsorption models can be used to describe the enrichment mechanism of ferrite nanoparticle depending on the magnetic permeability: (i) Freundlich adsorption model at low magnetic permeability (<10 μemu/Oe) which leads to the enrichment percentage below 50%, (ii) mixed (multilayer) adsorption model at intermediate permeability (10–50 μemu/Oe), and (iii) a monolayer adsorption at high permeability (>100 μemu/Oe) leading to the enrichment percentage above 90%.     

Structural,magnetic, and electrical evaluations of rare earth Gd3+ doped in mixed Co–Mn spinel ferrite nanoparticles

The controlled and stable crystal structure, reduction in Curie temperature and semiconducting nature of oxide materials are the key factors for magnetoelectrical applications. Therefore, Co_0.6Mn_0.4Gd_xFe_2-xO₄ where x = 0, 0.033, 0.066 and 0.10 were synthesized to analyse the structural, morphological, magnetic, and electrical properties using a sol-gel autocombustion approach. The X-ray diffraction pattern reveals that the cubic crystallite size decreases with increasing smaller content of Gd³⁺ oxides without any secondary phase. Field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) study explain the complete morphology, agglomeration and dense structure of rare earth-doped Gd oxide in the mixed Co–Mn spinel ferrite nanoparticles. Fourier transform infrared spectra confirms the formation of a spinel structure with absorption bands below 1000 cm^?1. The magnetic analysis shows that the saturation magnetization (59.20 emu/g - 49.71 emu/g) and coercivity (985.21 Oe – 254.11 Oe) of the synthesized samples decreased with increasing content of Gd³⁺ ions. The increase in DC conductivity with increasing temperature verifies the semiconducting nature of the synthesized samples, and a higher DC conductivity of the Co_0.6Mn_0.4Gd_0.10Fe_1.90O₄(CMGF3) samples was observed at approximately 0.0362 S/cm at 973 K temperature.     

Effect of heat treatment on structural,morphological, dielectric and magnetic properties of Mg–Zn ferrite nanoparticles

Green combustion was used to prepare a ferrite composition of Mg_0.4Zn_0.6Fe₂O₄ using a blend of fresh lemon juice as a natural fuel-reductant. Effect of heat treatment on phase, morphological, dielectric, and humidity sensor properties is discussed. The formation of a cubic spinel ferrite has been established by XRD-diffraction and vibrational spectroscopic studies. The experimental lattice parameter ranges from 8.3721 to 8.3631 Å. The broadening of octahedral band (υ₂) in the vibrational spectra is an identification for the existence of ferrite nanoparticles in various sizes. The typical crystallite size ranges from 10.2 to 36.9 nm. Using micrographs obtained from field-effect scanning electron microscopy (FESEM), researchers observed a spherical-shaped microstructure with agglomerated nanoparticles. Dielectric investigations have shown that the current ferrite composition has typical dielectric dispersion. The highest reported value for saturation magnetization (M_s) in the present study is 33 emu/g. Magnetic behaviour is primarily influenced by magnetocrystalline anisotropy, cation distribution, and crystallite size. The existence of void spaces in the sintered samples, as well as their porous nature, rendered them suitable for humidity sensor applications. Sintered samples have good sensing capability at 900 °C. The current findings are integrated in terms of cation distribution and magnetocrystalline anisotropy, assuming fine size effects of ferrite nanoparticles.     

Effect of sintering temperature on magnetic and electrical properties of nano-sized Co2W hexaferrites

Nano-sized and single phase W-type hexaferrite (BaCo₂Fe₁₆O₂₇) powders synthesized by sol-gel autocombustion method have been investigated. The samples were sintered in a temperature range of 1000-1200 °C for 5 h. The thermal decomposition behavior of as-prepared powder was studied by thermogravimetry (TG), differential thermal analysis (DTA) and infrared spectra (IR). The structural and magnetic properties of powders were investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The grain size calculated by Scherer equation was found in the range of 36-47 nm which is small enough to obtain a suitable signal-to-noise ratio in high density recording media. Hysteresis loop measurements show that the coercivity values lie in the range of 210.61-1602.6 Oe with increasing sintering temperature. Magnetization studies show a significant increase in the values from 15 to 22 emu/g. The dc electrical resistivity is observed to decrease up to a certain value as the temperature increases and then rises at higher temperature.     

Structural,magnetic, and antimicrobial properties of zinc doped magnesium ferrite for drug delivery applications

In this study, drug loading and release ability of the ferrite nanoparticle coated with PEG (polyethylene glycol) have been investigated for biomedical applications. The zinc-magnesium ferrite (Zn_xMg_(1-x)Fe₂O₄) was synthesized using sol-gel route. The doping concentration of Zn was gradually increased from zero to maximum (x = 1). XRD (X-ray diffraction) analysis of the samples shows the single phase with a cubic spinel structure. The Debye-Scherer formula has been used to calculate the average crystallite size (30.51 nm). The dumbbell and spherical shaped morphology (40–50 nm average particle size) have been investigated from the secondary electron images of FESEM (Field Emission Scanning Electron Microscopy). The antimicrobial assay has been carried out against E. coli bacteria by gentamicin (drug) loaded ferrite nanoparticles. The significant zone of inhibition might suggest that the drug-loaded ferrite nanoparticles can be used in drug delivery applications. PL (Photoluminescence) of the spinel ferrite shows that all the samples are in the visible range, and peaks at around 430 nm. The result reveals the synthesis of high purity ferrite nanoparticles with significant potential for drug delivery applications.     

Synthesis of manganese ferrite from non-standard raw materials using ceramic technique

Manganese ferrite spinel has been synthesized by using mill scale and fines of manganese ore sinter as sources of iron oxide and manganese oxide, respectively. The magnetic and physico-mechanical properties of the produced sample are largely dependent not only on the sintering condition but also on the Mn:Fe mole ratio. The effect of silica (which is one of the constituents of the fines of manganese ore sinter) on the properties of the sintered samples is investigated. The results show that a single phase of manganese ferrite spinel with weak magnetic properties is obtained in a sample containing a Mn:Fe mole ratio of 1.4:2 and sintered at 1300 °C for 2 h. On the other hand, a maximum saturation magnetization (62 emu/g) with reasonable physico-mechanical properties is obtained for a sample containing a Mn:Fe mole ratio of 1.3:2 and sintered at the same sintering conditions.     

Simple synthesis of mesoporous carbon with magnetic nanoparticles embedded in carbon rods

Magnetically separable ordered mesoporous carbon containing magnetic nanoparticles embedded in the carbon walls was synthesized using a simple synthetic procedure. The resulting magnetically separable mesoporous carbon was denoted as M-OMC (magnetically separable ordered mesoporous carbon) poly(pyrrole) with residual Fe²⁺ ions in the mesoporous channel was converted to carbon material containing superparamagnetic nanoparticles. The size of the magnetic nanoparticles obtained was restricted by the channel size of the SBA-15 silica template, which resulted in the generation of superparamagnetic nanoparticles embedded in the carbon rods. The blocking temperature of M-OMC is 110 K. Pore size and textural property of M-OMC is similar to that of hexagonally ordered mesoporous carbon fabricated using SBA-15 silica as a template. The saturation magnetization of M-OMC is ca. 30.0 emu/g at 300 K, high enough for magnetic separation.