The continuous hydrothermal synthesis of nano-particulate ferrites in near critical and supercritical water (original) (raw)
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Ferrites nanoparticles MFe2O4 (M = Ni and Zn): hydrothermal synthesis and magnetic properties
Boletín de la Sociedad Española de Cerámica y Vidrio, 2008
MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained samples were characterized by X-ray and electron diffraction, Scanning and Transmission Electron Microscopy and Mössbauer spectroscopy. The transmission images show homogeneous shape and particle size ranging from 10 to 40 nm, depending on the nature of the M cation. Mössbauer spectroscopy yields to a ratio of occupancy between the A and B sites of 0.7 in the case of NiFe 2 O 4 oxide. DC magnetization (2-300 K) measurements reveal a superparamagnetic behaviour for the ZnFe 2 O 4 sample with a blocking temperature of 20 K. By contrast, in the case of the NiFe 2 O 4 ferrite the blocking temperature appears to be above 300 K and at lower temperature, it shows a ferrimagnetic behaviour arising from the superexchange interactions that take place in this inverse spinel. Mössbauer spectroscopy results confirm the bulk magnetic measurements.
Ferrites nanoparticles MFe2O4 (M = Ni and Zn): Hydrothermal synthesis and magnetic properties
Boletin de la Sociedad Espanola de Ceramica y Vidrio
MFe 2 O 4 (M = Ni and Zn) nanoparticles were prepared by the hydrothermal method. The obtained samples were characterized by X-ray and electron diffraction, Scanning and Transmission Electron Microscopy and Mössbauer spectroscopy. The transmission images show homogeneous shape and particle size ranging from 10 to 40 nm, depending on the nature of the M cation. Mössbauer spectroscopy yields to a ratio of occupancy between the A and B sites of 0.7 in the case of NiFe 2 O 4 oxide. DC magnetization (2-300 K) measurements reveal a superparamagnetic behaviour for the ZnFe 2 O 4 sample with a blocking temperature of 20 K. By contrast, in the case of the NiFe 2 O 4 ferrite the blocking temperature appears to be above 300 K and at lower temperature, it shows a ferrimagnetic behaviour arising from the superexchange interactions that take place in this inverse spinel. Mössbauer spectroscopy results confirm the bulk magnetic measurements.
Preparation and magnetic properties of nano size nickel ferrite particles using hydrothermal method
Chemistry Central Journal, 2012
Background: Nickel ferrite, a kind of soft magnetic materials is one of the most attracting class of materials due to its interesting and important properties and has many technical applications, such as in catalysis, sensors and so on. In this paper the synthesis of NiFe 2 O 4 nanoparticles by the hydrothermal method is reported and the inhibition of surfactant (Glycerol or Sodium dodecyl sulfate) on the particles growth is investigated. Methods: For investigation of the inhibition effect of surfactant on NiFe 2 O 4 particles growth, the samples were prepared in presence of Glycerol and Sodium dodecyl sulfate. The X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM) and inductively coupled plasma atomic emission spectrometer (ICP-AES) techniques were used to characterize the samples. Results: The results of XRD and ICP-AES show that the products were pure NiFe 2 O 4 and also nanoparticles grow with increasing the temperature, while surfactant prevents the particle growth under the same condition. The average particle size was determined from the Scherrer's equation and TEM micrographs and found to be in the range of 50-60 nm that decreased up to 10-15 nm in presence of surfactant. The FT-IR results show two absorption bands near to 603 and 490 cm-1 for the tetrahedral and octahedral sites respectively. Furthermore, the saturated magnetization and coercivity of NiFe 2 O 4 nanoparticles were in the range of 39.60 emu/g and 15.67 Q e that decreased for samples prepared in presence of surfactant. As well as, the nanoparticles exhibited a superparamagnetic behavior at room temperature. Conclusions: Nanosized nickel ferrite particles were synthesized with and without surfactant assisted hydrothermal methods. The results show that with increasing of temperature, the crystallinity of nanoparticles is increased. In the presence of surfactants, the crystallinity of NiFe 2 O 4 nanoparticles decreased in comparison with surfactant-free prepared samples. All of the nickel ferrite nanoparticles were superparamagnetic at room temperature.
Hydrothermal growth of fine magnetite and ferrite crystals
Journal of Crystal Growth, 2016
In the present work, magnetite (Fe 3 O 4 , avg. ~ 70 nm) synthesis employing Azadirachta indica (neem) leaf extract is reported originally using hydrothermal conditions and the results obtained were compared with that of D-glucose. Fourier transform infrared spectroscopy confirms the presence of polysaccharides and proteins in the extract which act as both surfactants and reducing agents, aided the formation of magnetite nanostructures. Authors also reported the selective doping of Zn, Cu and Co on nickel ferrite for the enhancement of adsorptive dye removal property, adopting and investigating the use of eloquent one-step green hydrothermal approach (T=180⁰C, t=4 hr, pH=12) with sodium dodecyl sulphate as surfactant. Xray diffraction studies reveal that all the materials synthesized are isometric spinel structures and furthermore, morphological evidences using scanning electron microscopy are accounted. Adsorptive dye removal ability of synthesized materials was investigated using trypan blue as a probe. It was evident from the results that magnetite using neem extract showed enhanced adsorption ability (75%) than that of D-glucose (62%). Also, exponential increase in dye removal efficiency from 55% to 81% due to the presence of copper in nickel ferrite was duly noted.
Hydrothermally prepared nanocrystalline Mn–Zn ferrites: Synthesis and characterization
Microporous and Mesoporous Materials, 2008
Nanocrystalline particles of Mn x Zn 1Àx Fe 2 O 4 were prepared by chemical precipitation of hydroxides, followed by hydrothermal processing and freeze-drying. The synthesis involves the hydrolysis of aqueous metal precursors by using ammonia as precipitating agent. The chlorine ion concentration in the solution and the pH of the precipitation, are shown to play a crucial role in retaining the initial stoichiometry of the solution to the nanoparticles. The obtained products exhibited some interesting and unique features: they consisted of nanoparticles with sizes ranging from 5 to 25 nm, they had surface areas between 60 and 110 m 2 g À1 and pore sizes in the mesopore region (i.e. 8-20 nm). The produced materials were examined by powder X-ray diffraction for crystalline phase identification, scanning electron microscopy for grain morphology, high resolution transmission electron microscopy for particle size distribution and nitrogen sorption for surface area, pore volume and pore size distribution determination. The sintering of the ferrite powders was also studied by thermogravimetric analysis and dilatometry of the powders mixed with an organic binder to improve their compaction properties.
Journal of Materials Chemistry, 2001
Fine CoFe 2 O 4 powders with monodisperse, almost equi-axial nanometer-sized particles were synthesised in a polyol medium by forced hydrolysis of ionic Co(II) and Fe(III) salts at 160 ³C. K(Co) XANES and 57 Fe Mo È ssbauer spectroscopy show that the structure of this ferrite is slightly deviated from an inverse spinel structure: 16% of cobalt atoms are in tetrahedral sites. The particles are superparamagnetic above 300 K and ferrimagnetic below this blocking temperature with, at low temperature, strong coercivity, a saturation magnetisation value close to the bulk value and high reduced remanence. The saturation magnetisation measured at 5 K is clearly enhanced with respect to CoFe 2 O 4 nanometer-sized particles previously prepared by other methods. These magnetic characteristics suggest that these particles have a high crystallinity which may result from this novel synthesis route.
In order to optimize the hydrothermally synthesized manganese ferrite nanoparticles, the nanoparticles were synthesized under different reaction conditions. The effects of reaction temperature and time were investigated in a wide range. The samples have additional phases (hematite, maghemite) at high temperatures, and the sample synthesized at 120 °C has two different types of nanoparticles. However, the pure manganese ferrite phase was obtained as the reaction time increased at 130 °C. Particle size increased from 16.1 ± 6.1 nm to 25.8 ± 7.4 nm and from 19.4 ± 8.4 nm to 25.8 ± 8.2 nm with the rise of reaction temperature and time, respectively. The saturation magnetization M s of the nanoparticles also increased with the increase of reaction temperature and time. Although the M s values and particle sizes are very close for the samples synthesized at high temperature (at 220 °C for 4 h) and long reaction time (16 h at 130 °C), pure phase of manganese ferrite with high M s (65 emu/g) was observed at low temperature and long reaction time.