Nowadays, layered double hydroxides (LDH), sometimes referred as hydrotalcite-like compounds, have gained great attention since their composition and structure can be easily modified, so that they can be implemented in multiple fields. LDH-based composite materials based on LDH exhibit tremendously improved properties such as high specific surface area, which promotes the accessibility to a greater number of LDH active sites, considerably improving their catalytic, adsorbent and biological activities. Therefore, this review summarizes and discusses the synthesis methods of composites constituted by LDH with other inorganic compounds such as zeolites, cationic clays, hydroxyapatites, among many others, and describe the resulting characteristics of the resulting composites, emphasizing the morphology. Brief descriptions of their properties and applications are also included.

Hydrotalcites with heterogeneous distributions of anions between their layers were synthesized. Some synthesis parameters were studied to verify their influence on the anionic segregation properties of the hydrotalcites. The nature of the divalent cation and the crystallization method were most relevant. Zinc, in contrast to magnesium, assisted in discriminating carbonates and attracting nitrates to form hydrotalcites with heterogeneous distributions using microwave irradiation. Furthermore, the identification of this kind of hydrotalcite could be easily verified by determining the presence of a double reflection in the 003 X-ray diffraction (XRD) maximum, which definitively characterized a heterogeneous anion distribution. Finally, the reason as to why in some cases the hydrotalcite presented two reflections in the 003 XRD peak was elucidated.

A series of coumarin-3-carboxamides were synthesized via a three-component reaction involving salicylaldehyde, aliphatic primary/secondary amines, and diethylmalonate. Li–Al containing layered double hydroxides were utilized as an eco-friendly heterogeneous catalyst in this process. The materials were prepared using a straightforward co-precipitation method and were thoroughly characterized using techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. The catalysts exhibited commendable performance, attaining product yields of up to 90% in an ethanol environment. Moreover, the layered double hydroxide catalysts can be efficiently recovered and recycled up to four times without substantial loss of catalytic activity. This method offers the advantages of a simple and clean synthetic route, easy work-up and waste minimization.