In this study, hematite (α-Fe2O3) nanostructures were synthesized via thermal oxidation of Fe sheet in dry air and in water vapor. SEM images show nanoblades and nanowires growing on the surface of the sheet. Samples synthesized in water vapor generally produced larger nanostructures while samples oxidized in higher temperatures formed taller and slender nanostructures. The α-Fe2O3nanostructures were used as adsorbent for Cr (VI) in acidic medium. Chromium removal was highest with the samples synthesized at 650°C in water vapor with 95% efficiency. Kinetic and thermodynamic studies revealed that the adsorption process strongly followed pseudo-second order kinetics model and is endothermic. The process also follows the Langmuir adsorption isotherm model, suggesting that the process is described by homogeneous, monolayer adsorption. Adsorption of Cr (VI) onto hematite may be attributed to the electrostatic reaction between the positively charged hematite adsorbent and negative chromium ion.
This work presents a facile method of growing zinc-doped α-hematite (Zn-doped α-Fe 2 O 3) nanostructures via thermal oxidation of Fe sheet in the presence of Zn 2+ mist. Both undoped and Zn-doped α-Fe 2 O 3 nanostructures exhibit blade-like morphology mixed with some nanowires. In general, smaller yet denser nanostructures are formed at higher oxidation temperatures. On the other hand, misting (water vapor) enhances the oxidation rate, leading to larger nanoblades. Raman and energy dispersive X-ray spectroscopy reveal the successful incorporation of Zn in the α-Fe 2 O 3 lattice. However, excessive Zn 2+ (0.01 M) promotes the formation of large Zn hydroxide chloride particles on top of the α-Fe 2 O 3 nanoblades. The undoped α-Fe 2 O 3 nanostructures prepared at 650 °C in water vapor effectively adsorb hexavalent chromium [Cr(VI)] in aqueous solution with about 95% removal efficiency. The sample oxidized in 0.005 M Zn 2+ mist is also efficient in the Fenton-assisted photodegradation of methyl orange with > 90% removal even after five degradation cycles.
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