Efficient photo-Fenton degradation of an organic dye by reusable magnetic (Al0.6Mn0.6Fe0.6Co0.6Ni0.6)O4 high entropy oxides

Abstract

High entropy oxides (HEOs) have recently emerged as potential candidates for the catalytic degradation of organic dyes due to their interesting functional properties, such as high structural integrity and diversified elemental compositions. Herein, we report the development of an HEO nanostructure comprising Al, Mn, Fe, Co, and Ni with a chemical composition of (Al_0.6Mn_0.6Fe_0.6Co_0.6Ni_0.6)O₄ using the sol–gel method, followed by calcination at ∼700 °C in air. The formation of single-phased HEO nanostructures was evident from XRD and TEM analyses, whereas the presence of Al, Mn, Fe, Co, and Ni cations was confirmed by STEM-EDS, flame atomic absorption spectroscopy and XPS studies. This HEO nanostructure (average size of ∼25 nm) exhibited ferrimagnetic ordering behavior at room temperature (∼20 emu g⁻¹) with a specific surface area of 22.9 m² g⁻¹. The UV-visible DRS, Mott–Schottky and impedance results demonstrated the ability of the HEO nanostructure to degrade organic dyes through Fenton-type catalytic reactions, photon absorption, or photo-Fenton-type reactions. It is observed that the organic dye, Methylene Blue (MB), was degraded up to 94% within 90 min under the photo-Fenton catalytic process, while only 60% and 85% degradation of MB was observed under photocatalytic and Fenton-type reactions, respectively. The successful mineralization of MB into smaller molecules is evident from mass spectroscopic analysis. Specifically, the magnetic HEO with multivalent cations (Fe, Mn, Ni and Co) could make it a reusable catalyst for the photo-Fenton degradation of organic dyes.