Mechanism of thermal decomposition of K 2 FeO 4 and BaFeO 4 : A review
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Mechanism of thermal decomposition of K2 FeO4 and BaFeO4 : A review Virender K. Sharma1,2 · Libor Machala2
© Springer International Publishing Switzerland 2016
Abstract This paper presents thermal decomposition of potassium ferrate(VI) (K2 FeO4 ) and barium ferrate(VI) (BaFeO4 ) in air and nitrogen atmosphere. M¨ossbauer spectroscopy and nuclear forward scattering (NFS) synchrotron radiation approaches are reviewed to advance understanding of electron-transfer processes involved in reduction of ferrate(VI) to Fe(III) phases. Direct evidences of FeV and FeIV as intermediate iron species using the applied techniques are given. Thermal decomposition of K2 FeO4 involved FeV , FeIV , and K3 FeO3 as intermediate species while BaFeO3 (i.e. FeIV ) was the only intermediate species during the decomposition of BaFeO4 . Nature of ferrite species, formed as final Fe(III) species, of thermal decomposition of K2 FeO4 and BaFeO4 under different conditions are evaluated. Steps of the mechanisms of thermal decomposition of ferrate(VI), which reasonably explained experimental observations of applied approaches in conjunction with thermal and surface techniques, are summarized. Keywords High-valent iron species · Ferrate · Synchrotron radiation · Nuclear forward scattering · M¨ossbauer spectroscopy · Hyperfine interactions
This article is part of the Topical Collection on Proceedings of the 2nd Mediterranean Conference on the Applications of the M¨ossbauer Effect (MECAME 2016), Cavtat, Croatia, 31 May-3 June 2016 Virender K. Sharma
[email protected] 1
Department of Environmental and Occupational Health, School of Public Health, Texas A&M University, 1266 TAMU, College Station, Texas 77843, USA
2
Regional Centre of Advanced Technologies and Materials, Departments of Experimental Physics and Physical Chemistry, Faculty of Science, Palacky University, Olomouc, Czech Republic
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Hyperfine Interact (2016) 237:128
1 Introduction Iron as an element is present in numerous oxidation states ranging from zero to + 6 oxidation states in natural and synthetic compounds [1–4]. An interest in various iron oxides is due to their applications in nanotechnology, biocatalysis, energy, and remediation [5–9]. For example, high-valent tetra-oxy iron(VI) species (FeVI O2− 4 , ferrate(VI)) have shown their importance in greener synthesis of organic compounds, high energy density rechargeable batteries, and remediation and disinfection purification of water and wastewater [10–15]. In numerous uses of ferrate(VI), the reduction of this high-valent species to either Fe(II) or Fe(III) ions becomes imperative because this process defines the oxidation capacity of ferrate(VI) (i.e., four-oxidation equivalent versus three-electron equivalent) [11, 16, 17]. Furthermore, learning of the involvement of intermediate species during the reduction species, Fe(V) and Fe(IV) either through one-electron reduction or two-electron transfer process is also of utmost important in the evaluating the oxidation capacity of ferrate(VI) species. There
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