engleski

Formation of iron oxides in a highly alkaline medium in the presence of rhodium ionsNS

The effect of the presence of rhodium ions on the formation of iron oxides in a highly alkaline precipitation system was investigated using X-ray powder diffraction (XRPD), Mössbauer and FT-IR spectroscopies, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Acicular α-FeOOH particles precipitated in a highly alkaline medium with the addition of tetramethylammonium hydroxide (TMAH) were used as reference material. The initial addition of rhodium ions to that precipitation system had a significant effect on the formation of iron oxide phases and their properties. Characterization of α-FeOOH samples formed in the presence of rhodium ions showed thinner particles, smaller mean crystallite size, decreased average hyperfine magnetic field and a shift in the position of IR absorption bands in comparison with the reference sample. In the presence of higher concentrations of rhodium ions a small fraction of α-Fe2O3 was also formed. By additional autoclaving at 160 °C of the precipitation system, α-FeOOH precipitated in the presence of rhodium ions was transformed to α-Fe2O3 crystals in the form of hexagonal bipyramids via a dissolution-reprecipitation mechanism with a simultaneous formation of metallic rhodium nanoparticles. These rhodium nanoparticles acted as a catalyst for the reductive dissolution of α-Fe2O3 particles and the formation of Fe3O4 crystals in the form of octahedrons

iron oxides ; rhodium ; Mössbauer spectroscopy ; XRD ; FE-SEM

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