"Design of a ferrimagnetic high-entropy oxide (Mn₀.₆Cr₀.₆Co₀.₆Fe₀.₆Al₀.₆)O₄ for efficient photo-Fenton degradation of organic dyes."

Equiatomic high entropy oxides (HEOs) have attracted considerable attention in the field of chemical catalysis owing to their remarkable functional characteristics, including a high density of active surface sites, adjustable surface area, stable crystalline framework, and distinctive electronic balancing features. In this work, we report the synthesis of a nanoscale HEO containing Mn, Cr, Co, Fe, and Al specifically, (Mn₀.₆Cr₀.₆Co₀.₆Fe₀.₆Al₀.₆)O₄ using a sol-gel method followed by high-temperature calcination. Structural analysis via X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the formation of a single-phase nanosized HEO, while X-ray photoelectron spectroscopy (XPS) provided detailed insights into the oxidation states of the constituent metal ions. Despite the individual oxides exhibiting varied magnetic behaviors such as ferrimagnetism, paramagnetism, or antiferromagnetism at room temperature, the resulting inverse spinel HEO displayed soft ferrimagnetic properties. Furthermore, the material demonstrated outstanding photo-Fenton catalytic efficiency in degrading the organic dye methylene blue (MB), achieving complete degradation within 90 minutes. The efficiency of MB degradation and subsequent mineralization through the photo-Fenton mechanism was confirmed by mass spectrometric analysis.In addition to the participation of all constituent metal ions in providing additional active redox sites for Fenton degradation, the production of electron-hole pairs under UV light is responsible for the observed high MB degradation activity. Recovery of this catalyst and recycling investigations are made easier by the magnetic property of the developed magnetic HEO.