Increasing the number of cations in layered double hydroxides via mechanochemically complemented synthesis: the more the merrier, or not?†

A series of layered double hydroxides Mg/Al, MgNi/Al, MgNi/AlIn, MgNiCo/AlIn, MgNiCo/AlInSc, and MgNiCo/AlInScTm were obtained via mechanochemically complemented synthesis with subsequent hydrothermal treatment and additional crystallization. All the samples, except for the Mg/Al one, which was similar to the meixnerite structure, were phase pure. The samples were characterized via X-ray diffraction, FTIR spectroscopy, Raman spectroscopy, and transmission electron microscopy. The peroxidase-like activity of the samples was estimated, and the crystal lattice parameters were calculated. Samples with five, six, and seven cations were characterized by X-ray fluorescence, according to which the cation ratios of the samples and the values of configurational entropy were calculated, which allowed them to be classified as high-entropy materials. For the six-cation sample, elemental mapping was additionally performed, which revealed a uniform distribution of elements over the sample area, along with high-temperature X-ray diffraction, which was also carried out for the five-cation sample.