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Abstract: Nanostructured NiZn ferrites were synthesized using two different techniques: first, a precipitation procedure in the reverse micelles of a CTAB/1-hexanol/H2O microemulsion, and second, precipitation in a bulk aqueous solution. XRD measurements, magnetic measurements, TEM imaging, analytical measurements and thermal analyses were used in an attempt to reveal the chemical pathway that leads to the formation of NiZn ferrite in the microemulsion and in the bulk aqueous solution. It was found that reverse micelles do not act as inert nano-sized reactors that influence only morphological properties of the synthesized powders, but have a decisive influence on the identity of the final product when compared to the non-microemulsion procedure, and therefore present the molecular structures which are actively engaged in the chemical pathway according to which the herein presented room temperature synthesis of NiZn ferrite nanoparticles takes place. The influence of the initial pH on the chemical pathway of reverse-micellar synthesis and the morphology of the synthesized particles was discussed after initially it was found that the pH of the precipitation ought to be higher than 8 in order to obtain the desired ferrite as a final product. [Copyright &y& Elsevier]

The procedure for the preparation of NiZn-ferrite powder with average particle size of 10 nm and saturation magnetization of 50 emu/g by using precipitation reaction between acidified sulphate precursor salts and NH4OH as the precipitating agent in the water-in-oil domain of the microemulsion CTAB/1-hexanol/water at 45°C is presented herein. TEM measurements have revealed relatively uniform morphology of the particles, which are associated in coral-like agglomerates. EDS measurements have been used for qualitative analysis of the sample, whereby FAAS measurement has been performed in order to reveal the proportion of the cations in the sample — Ni : Zn : Fe = 0.17 : 0.18 : 2.64. [ABSTRACT FROM AUTHOR]

Abstract: Stoichiometric nanocrystalline nickel–zinc ferrites were synthesized by a reverse micelle method following a multi-microemulsion approach. Different pH values were chosen for the alkali precipitating reaction during the synthesis of different powders. Synthesized, as-dried and subsequently calcined powders were characterized in terms of their magnetic properties. XRD analyses and specific-surface area measurements were used to determine the average particle sizes of the synthesized samples. DCS and TGA measurements were performed to reveal the phase transitions within the samples at elevated temperatures, whereas TEM was used to view and record the microstructure of the nanosized ferrite samples. A possible mechanism of the formation of the synthesized NiZn-ferrite was also discussed. [Copyright &y& Elsevier]

Ferrites have found extensive uses in electrical, chemical and mechanical engineering, but their potential as biomaterials remains largely unexplored. Here we report on the use of a flash method based on urea decomposition to synthesize four different compositions of cobalt and zinc ferrite, including monophasic CoFe 2 O 4 , ZnFe 2 O 4 and Co 0.5 Zn 0.5 Fe 2 O 4 , and CoFe 2 O 4 /ZnFe 2 O 4 nanocomposite. Zn-ferrite nanoparticles were approximately the same size as those of Co-ferrite, but were better dispersed, rougher, more crystalline and less pronouncedly faceted. The mixed, monophasic Co 0.5 Zn 0.5 Fe 2 O 4 composition was morphologically most similar to single-phase Co-ferrite. In the biphasic mixture of CoFe 2 O 4 and ZnFe 2 O 4 , smooth and polydisperse Co-ferrite grains were coated by finer, cuboid and monodisperse Zn-ferrite nanoparticles. The porosity and the roughness of this composition were the highest, and so was its coercivity owing to the shielding of the ferrimagnetic Co-ferrite grains by the paramagnetic Zn-ferrite nanoparticles. Expectedly, the highest saturation magnetization (66.3 emu/g) was detected in Co-ferrite and the lowest (2.8 emu/g) in Zn-ferrite. Co-ferrite also exhibited the highest magneto-crystalline anisotropy, remanence and hysteresis loop area, while the highest exchange bias and susceptibility were found in the mixed, Co 0.5 Zn 0.5 Fe 2 O 4 composition. All four ferrite compositions were biocompatible with human fibroblasts, but they demonstrated different antibacterial activities against Gram-negative E. coli and Gram-positive S. aureus, with the biphasic mixture of CoFe 2 O 4 and ZnFe 2 O 4 being more effective than Co 0.5 Zn 0.5 Fe 2 O 4 , CoFe 2 O 4 or ZnFe 2 O 4. Further, all the compositions were more active against both bacterial species under visible light than in the dark, indicating the photocatalytic formation of electron-hole pairs and reactive oxygen species that exert a damaging effect on the bacterial cells as the prime mechanism of action. • Monophasic CoFe 2 O 4 , ZnFe 2 O 4 and Co 0.5 Zn 0.5 Fe 2 O 4 , and CoFe 2 O 4 /ZnFe 2 O 4 nanocomposite were synthesized and characterized. • CoFe 2 O 4 /ZnFe 2 O 4 nanocomposite contained Co-ferrite grains coated by Zn-ferrite nanoparticles, leading to high coercivity. • Biphasic mixture of CoFe 2 O 4 and ZnFe 2 O 4 had the highest antibacterial activity. • Photocatalytic formation of electron-hole pairs and reactive oxygen species is the prime mechanism of antibacterial action. • High biocompatibility of the examined compositions might encourage their use for numerous biomedical applications. [ABSTRACT FROM AUTHOR]