Spherical Ferrite Nanoparticles Research Articles

The synthesis of a monodisperse quaternary ferrite (FeCoCrO4) from the hot injection thermolysis of the single source precursor [CrCoFeO(O2CtBu)6(HO2CtBu)3

Monodisperse cobalt chromium ferrite (FeCoCrO4) nanoparticles have been synthesised using the trimetallic pivalate cluster [CrCoFeO(O2CtBu)6(HO2CtBu)3]. The precursor was thermolysed in oleylamine and oleic acid, with diphenyl ether as the solvent at 260 °C. The effect of time and the concentration of the precursor on the stoichiometry of the phase formed and/or the morphology of the nanoparticles was studied. The reaction time was investigated by withdrawing aliquots at different times. No products were formed after 5 minutes and aliquots withdrawn at reaction times of less than 1 hour contain traces of iron oxide (Fe2O3); only cubic cobalt chromium ferrite (FeCoCrO4) was obtained after one hour. Transmission Electron Microscopy (TEM) showed that more monodisperse spherical ferrite nanoparticles (4.0 ± 0.4 nm) were obtained at higher precursor concentrations. Magnetic measurements revealed that all the ferrite particles are superparamagnetic at room temperature but showed large hysteresis at low temperature. The nanoparticles were characterised by Powder X-Ray Diffraction (p-XRD) and Transmission Electron Microscopy (TEM). A Superconducting Quantum Interference Device (SQUID) was used to analyse the magnetic properties of the nanoparticles.

Thermal behavior of MnFe2O4 and MnFe2O4/C nanocomposite synthesized by a solvothermal method

A new solvothermal method for MnFe2O4 nanoparticles and MnFe2O4/C nanocomposite synthesis is reported. Manganese ferrite nanoparticles thus sinthesized are not stable at thermal treatment in oxidizing atmosphere, due to Mn(II) oxidation to Mn(III), evidenced at 640°C by thermal analysis. The FTIR spectroscopy also confirmed the oxidation of Mn(II) to Mn(III). XRD analysis has revealed the complete decomposition of manganese ferrite around 700°C. The specific surface area of the composite with activated carbon was much higher (253m2g−1), in comparison with that of the naked ferrite (65m2g−1). Scanning electron microscopy and transmission electron microscopy images evidenced the obtaining of nearly spherical ferrite nanoparticles, with diameters within the range 10nm − 30nm, loaded on the surface of activated carbon in case of the composite. The magnetization of the synthesized composite (30emug−1) was below the one of naked manganese ferrite (40emug−1), but sufficient to insure a facile magnetic separation of the composite from aqueous solution, in case of its use as adsorbent for pollutant removal.

Ni0.5Zn0.5Fe2O4 nanoparticles dispersed in a SiO2 matrix synthesized by sol–gel processing

Abstract (Ni 0.5 Zn 0.5 Fe 2 O 4 )x/(SiO 2 )(100 − x) (x = 5, 20 and 50 wt.%) nanocomposites are synthesized by a sol–gel method using tetraethylorthosilicate (TEOS) and metallic nitrates as precursors, and by further annealing the powders for 1 h at 1273 K. X-ray diffraction (XRD), transmission electron microscopy (TEM), room temperature vibrating sample magnetometry (VSM) and SQUID measurements are employed for structural, morphological and magnetic sample characterization. For all the concentrations analyzed, the powder nanocomposites actually consist of spinel NiZn ferrite nanoparticles, dispersed in an amorphous silica matrix. TEM studies reveal different particle size distributions and particle morphologies for the three ferrite contents. The 20 wt.%-NiZn ferrite samples consist of nearly spherical nanoparticles, of about 8 nm, mainly superparamagnetic, well-dispersed in the amorphous silica matrix, while the 5 wt.%-NiZn ferrite samples exhibit a bimodal particle size distribution (5 and 30 nm) of single-domain nanoparticles embedded in the silica. In the 50 wt.%-NiZn ferrite samples, two particle families are observed: small round superparamagnetic nanoparticles of about 8 nm embedded in the amorphous silica matrix and large, non-spherical, ferrimagnetic ones, forming agglomerates outside the matrix. In all the synthesized samples, thickness fringes are observed inside some of the ferrite nanoparticles in dark field images. This contrast is explained using the theory of electron diffraction in a weak beam dark field (WBDF) condition and considering spherical ferrite nanoparticles. A large range of tailored magnetic properties varying the fraction, dispersion and mean size of the ferrimagnetic NiZn ferrite particles is obtained. Room temperature saturation magnetization values are found in the range 3.0–30.4 Am 2 /kg for the different concentration samples. Coercivity values, between 1.9 and 7.6 mT, are more than 50% higher than those measured in powders of pure stoichiometric NiZn ferrite nanoparticles and somewhat higher than those reported for similar NiZn ferrite/SiO 2 nanocomposites also synthesized by sol–gel processes. A correlation between the nanocomposite microstructure and the observed magnetic properties is established.

Aqueous synthesis and transmission electron microscopy observation of seed-grown spherical ferrite nanoparticles

Uniform-sized spherical iron ferrite nanoparticles grew on seed crystals in an aqueous solution containing sucrose. Using the seed crystals which were highly dispersed in acidic or alkaline seed-crystal suspension without relation to pH of the suspension, we widely controlled the particle diameter in the range 20–200 nm by changing the additive amount of the seed crystals. By transmission electron microscopy observation and X-ray diffraction analysis, it indicated that the particles were highly crystalline but not amorphous. Selected area diffraction patterns of the particles by using transmission electron microscope revealed that the particles were composed of one to several crystals. Thus we provided the evidence that the particles grew on clusters composed of one to several seed crystals to which those of several dozen seed crystals were disintegrated.

Continuous Synthesis of Spherical Ferrite Nanoparticles with Narrow Size Distribution by Flow Tubular Reactor Method

By tubular reactor method, spherical ferrite nanoparticles with 210±30 nm diameter and composition intermediate between Fe3O4 and γ-Fe2O3 were synthesized from an aqueous solution. A reaction solution of FeCl2 and an oxidizing solution of NaOH and NaNO3 added with sucrose, which shapes spheres, together with ferrite seed crystals, which narrow the size distribution, were mixed and injected into a flow tubular reactor kept at 90°C. The tubular reactor had 3 mm inner diameter, 4 mm outer diameter, and 50 m length. We extended the method to a sequential flow process by which we could fabricate ferrite nanoparticles coated with citrate; the output stream of the tubular reactor containing the as-synthesized ferrite particles was mixed with a trisodium citrate solution, which was then injected into another tubular reactor at room temperature. The obtained ferrite particles coated with citrate were stably dispersed in a distilled water for as long as 24 hours. They were separated from the water by a magnet in two minutes. Since the yield of the flow tubular reactor method is easily multiplied by multiplying the number of the reactors, producing ferrite particles by the flow tubular reactor method will give new impetus to mass production of ferrite particles.