Transformation of a Fe-Mn oxide into a ferromagnetic alpha-Fe sub(2) O sub(3)

Abstract

The present investigation concerns synthesis of a ferromagnetic Mn sup(2+) -doped alpha-Fe sub(2) O 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 degrees 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(2) O sub(4). The TG showed mass loss up to 250 degrees C while the DTA profile exhibited a broad exothermic peak in the temperature range approx 300-800 degrees C, suggesting structural transformation. Additional phases were also synthesized by calcination of the initial product, at various temperatures, which were 200 degrees C, 450 degrees C, 600 degrees C and 750 degrees C. It was observed that in the temperature interval 600-750 degrees C, the material was transformed to Mn sup(2+)-doped alpha-Fe sub(2) O sub(3) nanorods and nanoparticles having wide oblong shapes. The results were compared with pure alpha-Fe sub(2) O sub(3) which was similarly synthesized without the presence of Mn sup(2+). It was observed that unlike pure alpha-Fe sub(2) O sub(3) which was antiferromagnetic, the Mn sup(2+)(alpha-Fe sub(2) O sub(3)) sample was ferromagnetic and showed much higher catalytic activity toward decomposition of hydrogen peroxide. The catalytic decomposition of H sub(2) O sub(2) could be explained on the basis of Fenton and photo-Fenton effects.