Layered double hydroxide materials for environmental applications: insights on key properties from synthesis and structure

Layered double hydroxides (LDHs) are layered materials of increasing interest for environmental applications due to their tunable chemical composition, structure, and adjustable physicochemical properties. This review presents a critical synthesis of recent advances in LDH-based materials, highlighting the close links between synthesis methods, structural characteristics, and key properties controlling their environmental performance. The main synthesis strategies are discussed in relation to their influence on crystallinity, morphology, specific surface area, metal cation distribution, and the nature of structural defects. Particular attention is paid to the effect of cationic composition, interlayer anions, and structural modifications (doping, exfoliation, composite formation) on adsorption, ion exchange, redox activity, and heterogeneous photocatalysis mechanisms. Environmental applications of LDHs are systematically examined, including the adsorption of inorganic and organic pollutants, the photodegradation of emerging contaminants under UV and visible irradiation, and water treatment. LDH-derived materials, particularly mixed metal oxides and LDH/semiconductor composites, are also discussed due to their improved photocatalytic performance and increased stability. Finally, current challenges and future prospects are addressed, with a particular focus on the recyclability, durability, and scaling up of LDH-based materials for advanced environmental applications.