Layered double hydroxides (LDHs) are a class of ionic lamellar compounds made up of positively charged brucite-like layers with an interlayer region containing charge compensating anions and solvation molecules. Delamination of LDHs is an interesting route for producing positively charged thin platelets with a thickness of a few atomic layers, which can be used as nanocomposites for polymers or as building units for making new designed organic-inorganic or inorganic-inorganic nanomaterials. The synthesis of nanosized LDH platelets can be generally classified into two approaches, bottom-up and top-down. It requires modification of the LDH interlamellar environment and then selection of an appropriate solvent system. In DDS intercalated LDHs, the aliphatic tails of the DDS- anions exhibit a high degree of interdigitation in order to maximize guest-guest dispersive interactions. Bellezza reported that the LDH colloids can also been obtained by employing a reverse microemulsion approach.

Recent advances in the synthesis and application of layered double hydroxide (LDH) nanosheets.

Preparation of layered double hydroxides and their applications as additives in polymers, as precursors to magnetic materials and in biology and medicine

Layered double hydroxides: A brief review from fundamentals to application as evolving biomaterials

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

Layered hydroxide salts: Synthesis, properties and potential applications

Synthesis of layered double hydroxide anionic clays intercalated by carboxylate anions

Immobilized penicillin G acylase (PGA) has been assembled in the interlayer galleries of a layered double hydroxide (LDH) by a three-step process. Glutamate-pillared LDH was first prepared by a novel process involving dissolution of an LDH-carbonate precursor in aqueous glutamic acid, followed by precipitation of the product by addition of base. This method avoids the problem of competitive intercalation by nitrate ions observed with conventional methods involving precipitation of LDHs from solutions of metal nitrate salts. The glutamate ions are strongly held in the interlayer region of the LDH by virtue of the electrostatic interaction between their carboxylate groups and the cationic layers, and act as carriers for the introduction and retention of free amino groups in the interlayer galleries. Subsequent reaction of the amino groups of the immobilized glutamate ions with a glutaraldehyde linker followed by addition of PGA affords the immobilized enzyme (IME). The intermediate and final materials, which can be termed bioinorganic nanocomposites, have been characterized by FT-IR spectra, powder X-ray diffraction (XRD) and thermal analysis. The activity, thermal stability, pH stability and operational stability of the IME have been assayed. After 10 recycles, carried out in succession in a discontinuous reactor, the IME displayed 90% activity retention, with the expressed activity remaining above 430 U/g.

Immobilization of penicillin G acylase in layered double hydroxides pillared by glutamate ions

A new type of support, calcined layered double hydroxides (CLDH), has been used to immobilize penicillin G acylase. The effect of varying the composition of the layered double hydroxide precursor and the calcination temperature on the activity of the immobilized enzyme has been studied. The activity of the immobilized enzyme decreased with increasing Mg/Al molar ratio of the CLDH. Mg/Al-CLDH had a higher affinity for the enzyme than Zn/Al-CLDH, but a lower percentage expressed activity. The activity of the immobilized enzyme was a maximum when the calcination temperature was between 450 and 550°C. The amount of enzyme adsorbed by the support shows a close correlation with its surface area. Immobilization of the enzyme on the support increases the acid resistance of the former.

Some factors affecting the immobilization of penicillin G acylase on calcined layered double hydroxides

A anionic laminated material immobilized enzyme is prepared through intercalating the moleculae of object containing carboxy and amino groups between the layers of quasi-hydrotalcite as anionic laminated material, adding cross-linking agent and enzyme, and forming covalent bond between the amino groups on object and enzyme moleculae under the action of cross-linking agent to immobilize the enzymemoleculae between layers of quasi-hydrotalcite, so obtain layer column. Its advantage is high stability of enzyme moleculae.

Anionic type laminated material immobilized enzyme and its preparation method

An anionic laminar material immobilized enzyme(IME) and preparation method thereof. The said immobilized enzyme is obtained through using guest molecule and crosslinking agent to fix the enzyme molecule among Layered Double Hydroxides (LDHs).The said method include setting the guest molecule among anionic laminar material-LDHs by intercalation method, which the said guest molecule contains carboxyl group and amino-group and its amount of carboxyl group greater than amount of amino-group, then adding crosslinking agent and enzyme to make the amino-group of guest and amino-group of enzyme molecule form covalent bond, so the IME laminar material is acquired by fixing the said enzyme molecule among LDHs. The said IME is restricted by geometrical structure of plywood, when it response, the substrate and product can transform orderly on reaction platform which constructed by laminar material, and the enzyme molecule doesn't run off and it has favorable stability.

Lingling Ren

Papers

Synthesis of layered double hydroxide anionic clays intercalated by carboxylate anions

Immobilization of penicillin G acylase in layered double hydroxides pillared by glutamate ions

Some factors affecting the immobilization of penicillin G acylase on calcined layered double hydroxides

Anionic type laminated material immobilized enzyme and its preparation method

A anionic laminar material immobilized enzyme and preparation method thereof