Understanding and Tuning Fe-Doping on Zn–Fe Layered Double Hydroxide Particle and Photocatalytic Properties

Abstract

Zn-based layered double hydroxides (LDHs) are promising photocatalytic materials, but their synthesis faces environmental and economic challenges. Oxidative ionothermal synthesis (OIS) offers a green route for zinc oxide synthesis using ionic liquids. To reduce costs, the OIS method uses recovered zinc-containing mixed metal systems, such as electric arc furnace dust, instead of pure metallic Zn. Understanding the interaction of Zn with impure metals during oxidation is essential. This study employs 1-Butyl-3-methylimidazolium chloride ([BMIM]Cl) as the solvent and Fe-doped metallic Zn, the most common waste-stream metal, as the starting material. This study applies quartz crystal microbalance with dissipation to monitor product formation, and X-ray diffraction and scanning electron microscopy to characterize composition and morphology. Results show that FeCl₂ doping accelerates the reaction, transforming simonkolleite to Zn–Fe LDH with tunable morphologies. A reaction mechanism for Zn in [BMIM]Cl with FeCl₂ is proposed. Photocatalytic hydrogen production tests reveal a favorable hydrogen evolution rate of 20.9 μmol h⁻¹ g⁻¹ with 0.45 M FeCl₂ doping, attributed to improved surface structure and crystallinity of the hydrotalcite.