Microwave-assisted synthesis of iron(III) oxyhydroxides/oxides characterized using transmission electron microscopy, X-ray diffraction, and X-ray absorption spectroscopy

Microwave-assisted synthesis of iron oxide/oxyhydroxide nanophases was conducted using iron(III) chloride titrated with sodium hydroxide at seven different temperatures from 100 to 250 °C with pulsed microwaves. From the X-ray diffraction (XRD) results, it was determined that there were two different phases synthesized during the reactions which were temperature dependent. At the lower temperatures, 100 and 125 °C, it was determined that an iron oxyhydroxide chloride was synthesized. Whereas, at higher temperatures, at 150 °C and above, iron(III) oxide was synthesized. From the XRD, we also determined the FWHM and the average size of the nanoparticles using the Scherrer equation. The average size of the nanoparticles synthesized using the experimental conditions were 17, 21, 12, 22, 26, 33, 28 nm, respectively, for the reactions from 100 to 250 °C. The particles also had low anisotropy indicating spherical nanoparticles, which was later confirmed using transmission electron microscopy (TEM). Finally, X-ray absorption spectroscopy (XAS) studies show that the iron present in the nanophase was present as iron(III) coordinated to six oxygen atoms in the first coordination shell. The higher coordination shells also conform very closely to the ideal or bulk crystal structures.