Nanoferritas de níquel multifuncionais: produção, propriedades e aplicações
Spinels are magnetic semiconductor ceramics where the cationic distribution is given by the equation ( 1− 2+ 3+)[ 2+ 1− 3+ ] 2−4. Due to the variable atomic arrangement, determined by the type of cation present in the structure and the method of obtaining it, ferrites are multifunct...
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| Formato: | doctoralThesis |
| Idioma: | pt_BR |
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Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/handle/123456789/49154 |
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| Resumo: | Spinels are magnetic semiconductor ceramics where the cationic distribution is given
by the equation ( 1− 2+ 3+)[ 2+ 1− 3+ ] 2−4. Due to the variable atomic arrangement,
determined by the type of cation present in the structure and the method of obtaining it, ferrites
are multifunctional materials. The application of these materials in electrochemistry has been
growing over the years and the possibility of using ferrites as electrodes, either for charge
storage devices or in water splitting reactions, brings great opportunities for nanotechnology
researchers. In this work we present the synthesis of nickel ferrite nanoparticles (NiFe2O4) by
the combined EDTA-Citrate complexation method. We studied the influence of reaction pH (3,
5, 7 and 9) on powder properties and the influence of temperature on phase formation when the
reaction pH was set at 7. Structural, morphological, optical, magnetic and electrochemical
properties were evaluated. The results confirmed the obtaining of single-phase NiFe2O4
powders at all pH studied (3, 5, 7 and 9) with nanoscale particle size (15-93 nm). The
morphology of the powders was affected by the reaction pH and exhibited rounded shapes,
undefined shapes and triangles. UV-vis analysis reveals an inversely proportional relationship
between crystal size and band gap. The isothermal hysteresis at 5 K and 300 K showed
ferrimagnetic behavior for all samples obtained. The samples obtained without pH 3 and 9 were
tested in an electrochemical cell in alkaline solution and it was found that for the purpose of
use in energy storage devices the material was classified as battery-like electrodes. The
improved electrochemical behavior of the NF9 sample (Qs = 65 C g-1 in 3 A g-1) was attributed
to an increase in faradaic reactions driven by the porosity difference on the surface of the sample
agglomerates and the boundary limits of the grains responsible for lower resistance to charge
transfer. The NiFe2O4 powders, obtained at pH 7 at 400, 500 and 600 °C, were studied in
alkaline solution as electrodes in oxygen evolution reactions reaching an overpotential of 326
mV vs. RHE to generate a current density of 10 mA cm-2 for samples calcined at 400 °C. The
improved electrochemical behavior compared to literature data was attributed to the
microstructural characteristics that affect the charge and mass transport processes and to the
reduced particle size. Thus, the materials obtained are presented as magnetic semiconductors
and can be applied in devices that require soft ferrimagnetic materials, as well as electrodes in
storage devices or in OER reactions. |
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