Layered double hydroxides lamellar structure

Layered materials are of special interest for bio-immobilization due to the accessibility of large internal and external surface areas, potential to confine biomolecules within regularly organized interlayer spaces, and processing of colloidal dispersions for the fabrication of protein-clay films for electrochemical catalysis [83-90], These studies indicate that layered materials can serve as efficient support matrices to maintain the native structure and function of the immobilized biomolecules. Current trends in the synthesis of functional biopolymer nano composites based on layered materials (specifically layered double hydroxides) have been discussed in excellent reviews by Ruiz-Hitzky [5] and Duan [6] herein we focus specifically on the fabrication of bio-inorganic lamellar nanocomposites based on the exfoliation and ordered restacking of aminopropyl-functionalized magnesium phyllosilicate (AMP) in the presence of various biomolecules [91]. 

Layered double hydroxides (LDH), also referred to as anionic clays, are very useful materials due to their anion exchange properties. LDH display a layered structure built on a stacking of positive layers ([MII1 MIII (OH)2] +), separated by inter-lamellar domains constituted of anions and water molecules ([X e nH20]x ) [117]. 

Layered double hydroxides, also known as anionic clays, belong to a class of lamellar hydroxides with a structure related to that of brucite. A large number of these hydroxides are naturally available and many more have been synthesized in laboratories. The structure of brucite, Mg(OH)2, consists of sheets of edge-connected Mg(OH)6 octahedra, which are held together by means of Van der Waals forces. The sheets have the composition Mg(OH)2, and are electrically neutral. 

Although there are numerous families of lamellar solids, only a handful of them exhibit the kind of versatile intercalation chemistry that forms the basis of this book. In arriving at the content of this volume, the editors have accurately identified six classes of versatile layered compounds that are at the forefront of materials intercalation chemistry, namely, smectite clays, zirconium phosphates and phos-phonates, layered double hydroxides (known informally as hydrotalcites or anionic clays ), layered manganese oxides, layered metal chalcogenides, and lamellar alkali silicates and silicic acids. Graphite and carbon nanotubes have not been included, in part because this specialty area of intercalation chemistry is limited to one or two molecular layers of comparatively small guest species that are capable of undergoing electron transfCT reactions with the host structure. 

Lamellar double hydroxides are part of, or are precursors of, a more general family of compounds designated as pillared layered structures (PLS). We quote some terms used to describe them (Mitchell 1990 Van Damme 1990). Pillared Layered Structures are nanocomposite materials prepared by linking molecules or colloids to a layered host. They exhibit a remarkably broad spectrum of structural, chemical, electronic, ionic, optical and magnetic properties, and provide supermesh host structures in which chemical reactions or physical processes can proceed under gas-phase conditions, but at liquid/solid state densities. They can be shaped as powders, pellets, or supported or self-standing Aims, and can be dispersed in solid or liquid matrices. 

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