Estudo da influência da temperatura na síntese de nanopartículas magnéticas de CoFe2O4 para aplicações em eletrodos bifuncionais

Abstract

With globalization, numerous concerns have arisen regarding resources for energy generation and the damage that is caused during the exploration, use and transport of these materials. Therefore, research has focused on several applications, in this work we emphasize energy storage devices and catalysts for advanced oxidative processes. In order to add to these studies, this research has successfully synthesized CoFe2O4 nanoparticles by the synthesis route of proteic gel sol, the calcination of this material was carried out at three temperatures: 600, 800 and 1000 °C in order to understand the influence of the thermal tract on the physical, morphological and structural, which consequently act on the efficiency of the bifunctional electrodes prepared with the synthesized materials. The results of the XRD pattern confirmed the formation of CoFe2O4 with the presence of a second residual phase of αCo-Fe in calcined materials at low temperature, through Raman spectroscopy it was possible to reaffirm that the CoFe2O4 powder with spinel type structure was obtained efficiently by the method of sol-gel proteic route in the three materials and is a promising material for applications that require good kinetics and diffusion of charges. The FTIR spectra showed strong absorption bands in the range of 440 and 650 cm-1, related to the Fe-O and Fe-Co bonds. SEM images showed that the cobalt ferrite nanoparticles exhibit a porous structure, formed by a hexagonal morphology and diffuse reflectance spectroscopy showed a reduction in the band-gap energy with thermal tract. Magnetic analyzes show that one more property is altered with the thermal treatment of the materials, its magnetic hysteresis the saturation magnetization values for cobalt ferrite ceramics increased according to the calcination temperature increase. These differences can be attributed to the non formation of a complete reverse spinel ferrite, that is, a partially inverted spinel ferrite, which leads to the decrease in the saturation magnetization value, which again, collaborates with the results obtained at from other characterizations. It was possible to observe that the increase in the calcination temperature resulted in more crystalline materials, better organized and with less energy required for electronic excitation. Such characteristics resulted in a capacity of 76.52, 14.74 and 6.58 mA h g-1 at the current density of 1 A.g-1. This was the best result obtained for the electrodes of 600, 800 and 1000 °C, respectively. It was also observed that 75% of the initial capacitance is maintained after 5000 cycles of continuous cyclic voltammetry at the scan rate of 100 mV.s-1. For the second application, the efficiency as a catalyst resulted in 60, 90 and 100% degradation of the methylene blue dye for the electrodes of 600, 800 and 1000 °C, respectively, which confirms the superior performance of the electrode prepared at 1000 ° C both as storage material for energy and catalyst for photocatalytic degradation reactions.