Coprecipitation

RESUMEN: Se sintetizó un nanocompuesto de ferrita de cobalto mediante el método de coprecipitación, usando nitratos cobaltoso y férrico como precursores metálicos. El compuesto sintetizado fue caracterizado mediante difracción de rayos-x, espectroscopia infrarroja por transformada de Fourier, microscopía electrónica de transmisión y magnetometría de muestra vibrante. Se determinó que las nanopartículas poseen un tamaño promedio de aproximadamente 4 nm, y cristalizaron en la estructura cúbica espinela, aunque se obtuvo una segunda fase cristalina de hematita. Las medidas de magnetización en función del campo magnético aplicado sugieren que el nanocompuesto sintetizado presenta un comportamiento antiferromagnético, como consecuencia de la abundante fase de hematita.

ABSTRACT: A cobalt ferrite nanocompound was synthesized by the coprecipitation method, using cobaltous and ferric nitrates as metallic precursors. The synthesized compound was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometry. It was determined that the nanoparticles have an average size of approximately 4 nm, and crystallized in the cubic spinel structure, although a second crystalline phase of hematite was obtained. Magnetization measurements as a function of the applied magnetic field suggest that the synthesized nanocompound has an antiferromagnetic behavior, as a consequence of the abundant phase of hematite.

A series of Cu–ZnO/ZrO2 catalysts (Znat/Cuat, 0–3; ZrO2, 42–44 wt.%) with markedly improved total (SA, 120–180 m2/g) and metal surface area (MSA, 9–63 m2/g) has been synthesized via the reverse co-precipitation under ultrasound field. Structure, adsorption properties and surface reactivity were probed by BET, XRD, TPR, N2O-titration and TPD measurements of H2, CO and CO2, while the activity pattern in the CO2 to CH3OH hydrogenation reaction (TR, 433–473 K; PR, 1.0 MPa) has been addressed. An optimum ZnO loading (Znat/Cuat, 0.3–0.8) ensures higher process productivity, while the apparent structure sensitive character of the title reaction relies on the synergism of metal hydrogenation and oxide basic sites (dual-site). The extent of the oxide/metal interface, probed by Cuδ+/Cu0 and oxide-to-metal surface area (OSA/MSA) ratios, is the key-parameter allowing the normalization of the catalytic specific activity in a wide range (3–60%) of metal dispersion and the consequent structure insensitive character of the CO2 hydrogenation reaction.

RESUMEN: Se sintetizaron dos nanocompuestos de magnetita mediante el método de coprecipitación, usando como agentes precipitantes los hidróxidos de sodio y amonio, para los compuestos Fe3O4-I y Fe3O4-II, respectivamente. Los nanomateriales sintetizados fueron caracterizados mediante espectroscopia infrarroja, difracción de rayos-x y magnetometría de muestra vibrante. En los dos materiales se obtuvo el óxido de hierro esperado, pero adicionalmente en el Fe3O4-I se formaron trazas de impurezas de compuestos de cloro. Ambos nanocompuestos cristalizaron en la estructura cúbica espinela. A temperatura ambiente, los dos compuestos nanoparticulados se encuentran en el régimen superparamagnético, aunque con interacciones magnéticas presentes entre las partículas.

ABSTRACT: Two nanocomposites of magnetite were synthesized by the coprecipitation method, using as precipitating agents sodium and ammonium hydroxides, for Fe3O4-I and Fe3O4-II, respectively. The synthesized nanomaterials were characterized by infrared spectroscopy, x-ray diffraction and vibrating sample magnetometry. In the two materials, the expected iron oxide was obtained, but traces of impurities of chlorine compounds were formed in Fe3O4-I. Both nanocompounds crystallized in the cubic-spinel structure. At room temperature, the two nanoparticulate compounds are in the superparamagnetic regime, although with magnetic interactions between the particles.

In this study, magnetite (Fe3O4) nanoparticles were synthesized at room temperature using FeCl3.6H2O (1.28 M), FeCl2.4H2O (0.64 M) and HCl (0.4 M) for preparing a solution as the iron source and NaOH (0.9-1.5 M) for to prepare a solution as the alkali source by the aqueous phase co-precipitation method under vigorous mechanical stirring (450 and 750 rpm) together with N2 gas flowing through the reaction medium during synthesis operation in closed system. The powder samples were characterized by the commonly used techniques of scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infra-red (FTIR), X-ray diffraction (XRD), vibrating sample magnetometry (VSM) and BET analyses. SEM was used to observe the morphology and agglomeration state of the powder. Size and morphology of the precipitated crystallites were examined with TEM. The prevalence of functional groups in the synthesized powders was ascertained by FTIR spectroscopy. The pure magnetite and other phases according to processing parameters were observed by XRD analysis. The magnetic properties of magnetite (Fe3O4) nanoparticles were examined using VSM. Finally, the specific surface area of nanoparticles was measured by BET technique. The results indicate that smaller particles can be synthesized by increasing stirring rate and decreasing the NaOH concentration, which in this case corresponded to 35 nm using 0.9 M NaOH at 750 rpm. The VSM analysis showed a saturation magnetization range of (82-96 emu/g) and coercivity of (83-119 Oe) for particles between (35-96 nm) respectively. Also, the highest specific surface area of 40 m2/g was obtained at 0.9 M NaOH at 750 rpm and the smallest value of 15 m2/g at 1.5 M of NaOH at 450 rpm using BET analysis.