Layered Double Hydroxides: Synthesis and Catalytic Applications

Layered double hydroxides (LDHs) are a class of two-dimensional anionic clays characterised by positively charged metal hydroxide layers and exchangeable interlayer anions. Their general formula, [M2+1–xM3+x(OH)2]A n– x/n·mH2O, allows a broad range of metal combinations (for example Mg–Al, Ni–Fe, Zn–Cr) and interlayer species (such as carbonate, nitrate or organic anions). Synthetic routes include co-precipitation under controlled pH, hydrothermal crystallisation, sol–gel methods and urea hydrolysis. Post-synthetic modifications—anion exchange, pillaring with metal oxides or organic molecules, metal doping and exfoliation into single-layer nanosheets—further tailor porosity, surface chemistry and electronic properties.

In catalysis, LDHs serve both as active materials and as precursor templates for mixed oxide catalysts. Their tunable basicity makes them effective in base-catalysed reactions such as transesterification, aldol condensation and Knoevenagel condensations. Redox-active LDHs incorporating transition metals (for instance Ni, Co, Fe) display promising performance in oxygen evolution, CO oxidation and selective oxidation of organic substrates. Photocatalytic applications exploit band-gap engineering via metal substitution or composite formation, enabling visible-light-driven degradation of pollutants, CO2 reduction and water splitting. The ability to exfoliate LDHs into few-layer nanosheets enhances active site exposure, while magnetic LDH hybrids facilitate catalyst recovery. Global significance lies in their role in green chemistry, environmental remediation and renewable energy conversion.

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Technical terms

Layered double hydroxide (LDH): A lamellar material composed of mixed divalent and trivalent metal hydroxide layers with exchangeable interlayer anions.

Co-precipitation: A synthesis method in which metal salts are precipitated simultaneously by adding a base under controlled pH to form mixed hydroxides.

Hydrothermal synthesis: A crystallisation technique conducted in sealed vessels at elevated temperatures and pressures to yield well-defined LDH crystals.

Anion exchange: A post-synthetic process replacing original interlayer anions with desired functional anions to modulate properties.

Pillaring: The insertion of rigid inorganic or organic species between layers to increase interlayer spacing and stabilise the structure.

Photocatalysis: A light-driven catalytic process in which photon absorption generates electron–hole pairs that initiate redox reactions on the catalyst surface.

References

1. Layered double hydroxide nanostructures and nanocomposites for biomedical applications. Journal of Materials Chemistry B (2019).
2. Structural transformation of layered double hydroxides: an in situ TEM analysis. npj 2D Materials and Applications (2018).
3. Magnetic Fe3O4 based layered double hydroxides (LDHs) nanocomposites (Fe3O4/LDHs): recent review of progress in synthesis, properties and applications. Journal of Nanostructure in Chemistry (2018).
4. Layered Double Hydroxide Materials: A Review on Their Preparation, Characterization, and Applications. Inorganics (2023).