Transformation of a Fe-Mn oxide into a ferromagnetic [alpha]-Fe.sub.2O.sub.3

• Published in: Journal of thermal analysis and calorimetry 2020-11, Vol.142 (3), p.1207
• Main Authors: Narvekar, Apurva A, Tilve, S. G, Fernandes, J. B
• Format: Article
• Language: English
• Subjects: Ferromagnetism; Peroxides
• ISSN: 1388-6150; 1588-2926
• DOI: 10.1007/s10973-019-09142-3

The present investigation concerns synthesis of a ferromagnetic Mn.sup.2+-doped [alpha]-Fe.sub.2O.sub.3 following a co-precipitation method. Thus, an aqueous solution containing Fe.sup.3+ and Mn.sup.2+ ions in a molar ratio of 2:1 was precipitated as hydroxides and then dried at 100 °C. The product was characterized by XRD, TEM and TG-DTA. XRD and TEM analysis revealed that the 'as-prepared' material was largely 'amorphous' containing mixed-phase nanoparticles of [alpha]-FeOOH and MnFe.sub.2O.sub.4. The TG showed mass loss up to 250 °C while the DTA profile exhibited a broad exothermic peak in the temperature range ~ 300-800 °C, suggesting structural transformation. Additional phases were also synthesized by calcination of the initial product, at various temperatures, which were 200 °C, 450 °C, 600 °C and 750 °C. It was observed that in the temperature interval 600-750 °C, the material was transformed to Mn.sup.2+-doped [alpha]-Fe.sub.2O.sub.3 nanorods and nanoparticles having wide oblong shapes. The results were compared with pure [alpha]-Fe.sub.2O.sub.3 which was similarly synthesized without the presence of Mn.sup.2+. It was observed that unlike pure [alpha]-Fe.sub.2O.sub.3 which was antiferromagnetic, the Mn.sup.2+([alpha]-Fe.sub.2O.sub.3) sample was ferromagnetic and showed much higher catalytic activity toward decomposition of hydrogen peroxide. The catalytic decomposition of H.sub.2O.sub.2 could be explained on the basis of Fenton and photo-Fenton effects.