Recent advances in layered double hydroxides (LDH)-based materials: Fabrications, modification strategies, characterization, promising environmental catalytic applications, and prospective aspects

Abstract

Layered double hydroxides (LDHs) are clay networks with brucite (Mg(OH2)) layers that are coupled with anion between the produced layers. The building structure of LDHs follows the formula: [M2+1−xM3+x(OH)2]x+(An−)x/n•yH2O, where M3+ and M2 are trivalent and divalent cations in the structural units (sheets), x is the structure's M3+ to (M2++M3+) cation ratio, and An is the interlayer anion. LDHs can be created utilizing simple approaches that regulate the layer structure, chemical composition, and shape of the crystals generated by adapting the production parameters. The first method of modifying LDH composites is through intercalation, which involves inserting inorganic or organic precursors into its composition, which can then be employed for a variety of purposes. The next method is a simple physical mixing technique among the created LDHs as well as advanced materials such as activated carbon, graphene and its derivatives, and carbon nanotube to be utilized as base substances in energy storage, supercapacitors, photo- and electrocatalysts, water splitting, and toxic gas removal from the surrounding environment. The final strategy is the synthesis of polymer-LDH composites by inserting effective polymers during the manufacturing process of LDHs to create nano-composites utilized for energy, fire retardant, gas barrier, and wastewater cleaning. LDHs are a sort of fine chemical that can be designed to have the desired chemical structure and performance for usage in a variety of purposes such as redox reaction, the process of bromination, ethoxylation, aldol condensation, NOx and SOx elimination, as well as biofuel production. Because LDH substances are not harmful to the environment, the different applications that use them are unique in terms of green chemistry because they are recyclable and eco-friendly catalysts. The present review investigated the various methods used to create LDHs and the improvement of the produced composites by enhanced temperature calcination, intercalation of their structures by small-, medium-, and high-nuclear anions, and support by carbon compounds. The evaluation methods as well as the best prospective uses, such as biofuel generation, catalysis, water splitting, charge transfer, and wastewater treatment, were comprehensively reported according to the most current studies, and the potential sight of LDHs is highlighted.