Avaliação das propriedades magnéticas, hipertérmicas e eletroquímicas de ferritas do tipo espinélio (mfe2o4, m = co, ni e cu) obtidas via método sol-gel proteico

Abstract

MFe2O4 (M = Ni, Co, Cu) ferrites are magnetic ceramic with spinel-type structure, in which the cations distribution can be given by the general formula (M2+1-δFe3+δ)[M2+δFe3+2-δ]O4. Due to their atomic arrangement, composition and possibility of obtaining by various synthesis methods, ferrites are considered multifunctional and versatile materials to be used in various applications. Among synthesis methods, the sol-gel method and its variations have been outstanding for allowing the preparation of single phase nanoparticles. The proteic sol-gel method, one of the variations of the conventional sol-gel route, is characterized by using organic agents to promote polymerization and chelation of metal ions. In this context, this work presents the synthesis of ferrite (MFe2O4, M = Cu, Co, Ni) by proteic sol-gel method using conventional gelatin (animal gelatin) and agar-agar (vegetable gelatin) and the evaluation of their magnetic, hyperthermic and electrochemical properties. The results confirmed the MFe2O4 (M = Ni, Co, Cu) monophasic powders with particle in nanoscale (21-176 nm) in a mixed spinel composition (0 < δ <1). Isothermal hysteresis showed the ferrimagnetic behavior of the samples with saturation magnetization and coercivity field in the range 31.7-99.2 emu/g and 6.2 x103-10.9x103 Oe, respectively. The prepared nanoparticles generate enough heat by reaching temperatures in the range 66-97 ºC, as well as specific absorption rate values in the range 9.22-16.01 W/g. In this way, magnetic hyperthermia properties of the samples are dominated, but not limited, by hysteresis loss.The electrochemical behavior of ferrites in alkain solution, for use in energy storage devices, allowed classification of the ferrites as battery-like electrodes. The enhanced electrochemical performance of CuFe2O4 (Qs = 183 C g-1 at 0.5 A g-1) showed be depends on the concentration of surface defects, especially oxygen vacancies, evaluated by X-ray photoelectron spectroscopy (XPS), and microstructural characteristics. CoFe2O4 powders obtained with agar-agar were studied as electrode material for evolution oxygen reaction in alkaline solution, reaching an overpotential of 360 mV. RHE to generate 10 mA cm-2. The good electrocatalytic performance of this material compared to electrodes in the literature is explained by microstructural characteristics that affect the charge and mass transport processes.