Synthesis of nanostructured iron oxides dispersed in carbon materials and in situ XRD study of the changes caused by thermal treatment

Abstract

Carbon-based magnetic nanocomposites are of large interest for applications in catalysis, magnetic separation, water cleaning, and magnetic resonance imaging, among others. This work describes the synthesis of nanocomposites consisting of iron oxides dispersed into a char (obtained from the carbonization at 700°C of a lignocellulosic precursor) and the study of the thermal transformations occurring in these materials as a consequence of heat treatments. The materials were prepared by impregnation of the char with iron nitrate in the presence of ammonium hydroxide in aqueous suspension. X-ray diffraction experiments performed using synchrotron radiation and Mössbauer spectroscopy showed that the as-prepared material was composed of amorphous Fe 3? oxides. Scanning electron microscopy images combined with energy-dispersive X-ray spectrometry indicated a homogeneous dispersion of iron oxides and of silica particles (naturally present in the lignocellulosic precursor) throughout the char. X-ray diffractograms recorded in situ during the heat treatment of the as-prepared material showed the presence of small hematite crystallites (average size *22 nm) starting from ca. 300°C. Further heating caused a progressive growth of the hematite crystallites up to ca. 500°C, when the conversion to magnetite (Fe 3 O 4 ) started to take place. At higher temperatures, wüstite (Fe 1-x O) was detected as an intermediate phase and austenitic iron (c-Fe) became the dominant phase at temperatures from 900°C. A steep weight loss was observed in the TG curve accompanying this last reduction stage; upon cooling, c-Fe was converted into a-Fe (ferrite), which was the dominant phase at room temperature in this heat-treated sample.

Production of an Efficient Magnetic Adsorbent From Babassu Coconut Endocarp and Ni Particles for Easy Dye Removal From Mimetic Contaminated Effluents

“…Moreover, it is possible that some obstruction of the porous structure of the activated carbon also contributes to the porosity reduction in the composite samples. It is also worth pointing out that the increase in the relative fraction of mesopores in the total pore volume of the hybrid BACNi-X samples can be associated with the surface contribution of the Nicontaining particles, similarly to what has been observed in other nanostructured systems (Gonçalves et al 2015). Particles morphology SEM and TEM images of the hybrid BACNi-10, BACNi-20 and BACNi-30 samples are shown in Fig.…”

“…It is important to note that these crystallite sizes are somewhat smaller than the Ni particle sizes observed in the SEM and TEM images shown in Fig. 3 (albeit they are all the same order of magnitude), thus suggesting a polycrystalline nature for those particles (Gonçalves et al 2015).…”