PEROXIDASE-LIKE CATALYTIC ACTIVITY OF FERRITE AS FUNCTION OF CRYSTALLINE PHASE AND OXIDATION STATE

M. S. NADAL; TORRES, TEOBALDO E; TROIANI, HORACIO E.; WINKLER, ELIN L; A. A. DE ALMEIDA; M. E. SALETA; MORENO MALDONADO, ANA CAROLINA; ZYSLER, ROBERTO D; DINA TOBIA; MARIANA RAINERI; MARCELO VASQUEZ MANSILLA; V. DRAGO; ENIO LIMA JR.

Bariloche

Congreso; XV Reunión Anual de la Asociación Argentina de Cristalografía; 2019

Iron oxides and hydroxides belong to a numerous family of Fe-based compounds, with phases of different Fe oxidation states (ionic valance), electronic configuration and crystalline phases. These properties are interrelated and phase plots can reveal the interplay between their magnetic and crystalline properties, for example. The ferrites with general chemical formula Mx(Fe2+yFe3+1-y)3-xO4 (M=Zn, Co, Mn, Ni), with cubic crystalline structure (space group Fd ̅m) and ferrimagnetic order, are probably the most intensely studied iron-oxides because of their chemical, electronic and magnetic properties, turning them very attractive for different applications. It is known that the ferrite phases are involved in different bio-geological catalytic process in the environment. Among the most important catalytic activities of the ferrites are those related to Fenton-type reactions, where iron oxides can generate Oxygen-based free radicals, specifically ?OH and ?OOH, from the decomposition of the H2O2. These radicals are produced by different mechanisms, with a strong dependence on the active surface area of the oxide, Fe oxidation state and crystalline structure. In fact, the catalytic activity of oxides is critically dependent on the occupancy of the electronic orbitals and the affinity of the surface with the molecules involved in the reactions. A complete understanding on the dependence of the catalytic activity of ferrites with its crystallinity, composition and oxidation state, is critical for different applications, as well as for different research areas because their possible toxicity and their direct impact on the environment.In this work, we identify and quantify the free radicals produced by the catalytic activity of ferrite systems with different oxidation states and crystalline phases using electron paramagnetic resonance (EPR) and a Spin Trap (DMPO). We studied magnetite nanoparticles with d ~100-200 nm with well-crystalline surface and other ones others with amorphous layer; also well-crystalline ferrite M2+xFe3-xO4 (M=Fe,Zn) nanoparticles (d = 10 nm) with different oxidation states, and microparticles containing different relations of ferrite/hematite. X-ray diffraction and high-resolution transmission electron microscopy were used to characterize crystalographically the different phases of the systems. According to our results, the well-defined cubic phase is the most active concerning the peroxidase-like reactions, specifically the Fe ions present in the B site. Moreover, we found that the oxidation state also plays an important role in the kinetics and in the free radical species formed.