Bi25FeO40-Fe3O4-Fe2O3 composites: Synthesis, structural characterization, magnetic and UV-visible photocatalytic properties

In this work a series of Bi25FeO40- Fe3O4-Fe2O3 composite samples were prepared directly through the solid state reaction process using bismuth and iron based minerals. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible spectroscopy. A series of samples was prepared, varying the calcination temperature between 550 degrees C and 750 degrees C. XRD results show the formation of composites, consisting of the phases Bi25FeO40, magnetite (Fe3O4) and hematite (Fe2O3). The percentage of the Bi25FeO40 phase in the samples ranged from 60% to 85% according to the calcination temperature. SEM micrographs show that the particles making up these materials have lamellar, spherical and cylindrical structures. Magnetic measurements show that the saturation magnetization decreases with the percentage of magnetite. The coercive field (H-c = 210 Oe) remains constant for all samples calcined in the temperature range between 550 - 700 degrees C. The sample calcined at 750 degrees C presents an atypical behavior, with an increase of 3x in the value of the coercive field and a low saturation magnetization value, M-s = 0.40 emu/g. UV-visible spectroscopy results show that samples calcined between 550 - 750 degrees C show absorption of ultraviolet and visible light. These results indicate that the powders of the composite Bi25FeO40- Fe3O4-Fe2O3 have photocatalytic properties which can be easily recycled by magnetic separation. (C) 2019 Elsevier B.V. All rights reserved.