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

Abstract

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.

Formation of Dense and High-Aspect-Ratio Iron Oxide Nanowires by Water-Vapor-Assisted Thermal Oxidation and their Cr(VI) Adsorption Properties

“…The presence of water vapor during oxidation induced more densely packed nanostructures with a uniform distribution compared with those under dry-air conditions; however, this work was performed at lower temperatures (400°C-500°C). When iron is oxidized at high temperatures, it grows an oxide scale containing multilayered oxides, which are markedly different to the oxide phases formed below 570°C (Yu et al 2003;Aquino et al 2020); therefore, investigating these high-temperature oxidations further may result in novel and potentially useful nanostructures for various applications, including adsorption.…”