Layered double hydroxides (LDHs) have been investigated for many years as host materials for a range of anion exchange intercalation reactions. In this role they have been used extensively as ion-exchange materials, catalysts, sorbents and halogen absorbers. More recently, there have been a tremendous number of new developments using these materials to store and deliver biologically active materials in vivo. Significant advances have been made recently on the characterisation of these materials, including structural studies and on the mechanism of intercalation using in situ techniques.

Intercalation chemistry of layered double hydroxides: recent developments and applications

A wide variety of cation-exchangeable layered transition metal oxides and their relatively rare counterparts, anion-exchangeable layered hydroxides, have been exfoliated into individual host layers, i.e., nanosheets. Exfoliation is generally achieved via a high degree of swelling, typically driven either by intercalation of bulky organic ions (quaternary ammonium cations, propylammonium cations, etc.) for the layered oxides or by solvation with organic solvents (formamide, butanol, etc.) for the hydroxides. Ultimate two-dimensional (2D) anisotropy for the nanosheets, with thickness of around one nanometer versus lateral size ranging from submicrometer to several tens of micrometers, allows them to serve either as an ideal quantum system for fundamental study or as a basic building block for functional assembly. The charge-bearing inorganic macromolecule-like nanosheets can be assembled or organized through various solution-based processing techniques (e.g., flocculation, electrostatic sequential deposition, or the Langmuir-Blodgett method) to produce a range of nanocomposites, multilayer nanofilms, and core-shell nanoarchitectures, which have great potential for electronic, magnetic, optical, photochemical, and catalytic applications.

Nanosheets of oxides and hydroxides: Ultimate 2D charge-bearing functional crystallites.

Layered double hydroxides (LDH) intercalated with metal coordination compounds and oxometalates

Clays and catalysis: a promising future

Driven by the scientific challenges involved in the creation of nanostructures providing access to new materials with unusual properties, the study of hybrid materials based on Layered Double Hydroxides (LDHs) has developed considerably during the last decade. This feature article is intended to give a broad overview of organic–inorganic hybrid assemblies based on LDH materials including their synthesis and characterization, and pointing out their potential applications. The LDH interlayer gap supplies an interesting, constrained environment arising from the anisotropic accommodation of the guest molecule at the nanoscale. Particularly, this article underlines the importance of compatibility between the two components, i.e. the organic and inorganic parts, in terms of charge distribution and molecular size for the polymerization process of interleaved molecules. Exfoliation and staging phenomena are also described. Through several examples of the shape and function of interlayer organic anions, hybrid LDH materials are described for their potential properties in optic devices, as drug delivery systems, and also as nano- and macro-fillers in polymer nanocomposites and cements, respectively. Eventually, LDH hybrid materials merge into even more complex systems for which topical applications are listed.

Fine tuning between organic and inorganic host structure: new trends in layered double hydroxide hybrid assemblies

meso-Tetrakis(p-carboxyphenyl)porphyrin (pTCPP), the atropoisomer (αααα) of meso-tetrakis(o-carboxyphenyl)porphyrin (oTCPP), and the ammonium salt of the meso-tetrakis(p-sulfonatophenyl)porphyrin (noted pTSPP) were intercalated into [Zn−Al] layered double hydroxide (LDH) using different preparative methods. Coprecipitation at constant pH in a porphyrinic solution of zinc and aluminum salts or anionic exchange of pTCPP on a [Zn−Al−Cl] precursor led to pure LDH phases, while products obtained from the calcination−reconstruction method on a [Zn−Al−Cl] precursor contain a significant amount of ZnO. Powder X-ray diffraction and UV−visible diffuse reflectance spectroscopy of LDH intercalated with pTCPP, oTCPP, and pTSPP show complete intercalation. Interlayer spacing ranging from 18.54 A for [Zn−Al−oTCPP] to 22.91 A for [Zn−Al−pTSPP] and 22.73 A for [Zn−Al−pTCPP], determined from PXRD patterns, reveal different orientations of the anionic macrocyles between the hyroxylated layers. This selective arrangement is ...

S. Bonnet

Papers

Synthesis of Hybrid Organo−Mineral Materials: Anionic Tetraphenylporphyrins in Layered Double Hydroxides