Thermally grown Zn-doped hematite (α-Fe2O3) nanostructures for efficient adsorption of Cr(VI) and Fenton-assisted degradation of methyl orange

This work presents a facile method of growing zinc-doped alpha-hematite (Zn-doped alpha-Fe2O3) nanostructures via thermal oxidation of Fe sheet in the presence of Zn2+ mist. Both undoped and Zn-doped alpha-Fe2O3 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 alpha-Fe2O3 lattice. However, excessive Zn2+ (0.01 M) promotes the formation of large Zn hydroxide chloride particles on top of the alpha-Fe2O3 nanoblades. The undoped alpha-Fe2O3 nanostructures prepared at 650 degrees 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 Zn2+ mist is also efficient in the Fenton-assisted photodegradation of methyl orange with >90% removal even after five degradation cycles.