Proteic sol-gel synthesis, structure and battery-type behavior of Fe-based spinels (MFe2O4, M = Cu, Co, Ni)

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“…It was found that with increasing the initial pH of the synthesis solution also increases the crystallite size while the cell parameter remains nearly constant [28]. The synthesis method we used proved to allow a better organization of cations in organometallic complexes, as a result of that high purity nanocrystalline materials are expected to be produced, even when the precursors are thermally treated at low temperatures [44] in comparison to other synthetic approaches that use higher temperatures to obtain NiFe2O4 [10,29,30,51]. The high degree of chelation of the metallic ions in the solution is thought to be responsible for the good homogeneity of metallic constituents in the precursors, which leads to the fore mentioned result [50].…”

“…Spinels with X 2+ and Fe 3+ magnetic cations have distinct properties such as high saturation magnetization, high ferrimagnetic transition temperature, high magnetic permeability, and a wide range of coercivity fields. The electrochemical performance of spinels ferrites has also been studied for their applications as supercapacitors [9] and battery-type electrodes [10]. These materials have also been studied as photocatalysts for water splitting [5,[11][12][13], gas sensors [14,15], electrocatalyis for the oxygen evolution reaction (OER) [16,17], degradation of organic compounds by heterogeneous Photo-Fenton reactions [18][19][20][21][22], and biomedical applications [23,24].…”

“…Within the spinel family of oxides, nickel ferrite (NiFe2O4) has attracted considerable scientific interest due to its physical and chemical properties allowing these materials to be applied in electrochemical devices [10,16,25]. Besides, nickel ferrites have a band gap in the visible light region [26] due to the electronic excitation of the O-2p level (valence band) to the Fe-3d level (conduction band) [27], which is an interesting property for application in photocatalysis.…”

“…Besides, nickel ferrites have a band gap in the visible light region [26] due to the electronic excitation of the O-2p level (valence band) to the Fe-3d level (conduction band) [27], which is an interesting property for application in photocatalysis. Nickel ferrites may crystallize in an inversed spinel structure [28], however, the literature also reports several examples where Ni cations occupy both tetrahedral and octahedral sites [8,10,[29][30][31], leading to a partial inverse spinel.…”

“…Several synthesis methodologies have already been used to produce ferrites including co-precipitation [14,32], proteic sol-gel [10], hydrothermal [33][34][35], solvothermal [36][37][38], conventional sol-gel [29], combustion [39], solid state reaction [40], solution blow spinning [16], and complexation [41]. The sol-gel process is one of the most accepted methods for producing ferrites where chelates are formed through a complexation reaction between multivalent ions and citric acid, a multidentate ligand [30,42].…”