Influence of the gas atmosphere on the obtention of cobalt and iron based nanocomposites and core/shell nanoparticles by calcination in the presence of chitosan

Abstract

In this work, CoFe2O4/CoFe2 nanoparticles with core/shell structure were synthesized by carbothermic reduction using chitosan beads impregnated with Fe3þ and Co2þ ions. The samples were synthesized at 400, 550, 650 and 750 C, during intervals of 30, 90 and 120 min and under air, N2 and H2 gases. To apply the carbothermic method, chitosan was thermally decomposed in presence of N2 gas. The structural and magnetic properties were studied using X-ray powder diffraction, transmission electron microscopy, vibrating sample magnetometry and Mossbauer € spectroscopy. The results showed that the Co–Fe impregnated chitosan beads thermally treated, firstly, in air at a given temperature and afterwards treated at 400 and 550 C in H2 for 30 and 90 min led to the formation of CoFe2O4/CoFe2 nanoparticles, the samples treated at higher temperatures were single phase of CoFe2. However, the Co–Fe chitosan beads treated in N2 for 120 min at 550, 650 and 750 C favored the formation of a core/shell (CoFe2O4/CoFe2) nanoparticles with CoFe2 concentration ranging from 75.5 to 35.0 Wt %, the amount of CoFe2 increased with the increase of temperature. The highest saturation magnetization of 227.7 emu/g was achieved for the sample treated at 550 C under N2 atmosphere.