Preparation of High-Entropy Layered Double Hydroxides with the Hydrotalcite Structure

High-entropy six-cation layered double hydroxides (LDHs) of cationic composition MgNiCoAlFeY were prepared by five different methods, namely, by coprecipitation at constant pH, coprecipitation at constant or variable pH followed by hydrothermal treatment, microwave-assisted solvothermal synthesis, hydrothermal synthesis, and mechanochemical synthesis followed by hydrothermal treatment. All samples, except for the one prepared by coprecipitation at variable pH, were phase-pure with a uniform distribution of cations. The samples were characterized by X-ray powder diffraction, IR spectroscopy, Raman spectroscopy, and transmission electron microscopy. Thermal transformations of the samples were studied. The synthesis method affected the characteristics of the samples. The sample prepared by hydrothermal synthesis at variable pH had magnetic properties. The largest particles having near-hexagonal shapes were formed by coprecipitation followed by hydrothermal treatment. The sample prepared by the microwave-assisted solvothermal method was distinguished by a lower thermal stability.