Electron beam-induced transformation of LDH and derived materials

Transmission electron microscopy (TEM) is a versatile tool for the characterization of (catalytic) materials on the nanoscale. This is very important for understanding the structure-function relationships of the investigated samples. However, TEM experiments can induce significant changes in materials due to the electron-beam irradiation which in turn can lead to misinterpretation of results. Here, we systematically investigate the effect of beam-induced damage on layered double hydroxides (LDHs) and derived materials, focusing on NiCuAl LDHs with different Ni:Cu ratios. Using electron diffractograms, we confirm that all LDH samples exhibit high sensitivity to electron irradiation, resulting in structural modifications, which are not always accompanied by observable morphological changes. Ni-containing LDHs transform into metal oxides, while the CuAl LDH shows more pronounced indications for the formation of metallic species. For the NiCu(4:1)Al LDH after thermal treatment, the results indicate the formation of structural voids in the calcined sample, while the reduced sample shows the partial formation of a spinel structure. Our systematic study reveals that the degree of damage decreases in the order: LDH > LDH-calcined > LDH-reduced sample. Our findings underscore the general importance of considering beam damage and performing systematic experiments to avoid misinterpreting electron microscopy data.