Layered double hydroxides chemical structures

An original method to fabricate oxide nanostructured magnetic materials has been proposed in Ref. [328]. The method is based on chemical modification of ion-substituted layered double hydroxides. These structures are nanocomposites based on ferromagnetic y-Fe203 nanoparticles and diamagnetic matrix, which are stable in air and have sufficient coercive force and saturation magnetization of y-Fe203. 

A study is reported on the use of layered double hydroxides (LDH) with the hydrotalcite-type structure as fillers of composites and nanocponposites in a polyethylene matrix. The properties of the LDH are first described, as well as then-preparation procedures. Then the most common methods to prepare the composites and nanocomposites are described and discussed and finally the properties of these compounds, which define their apphcations in different fields (e. g., mechanical, thermal, electric, chemical, etc. properties) are discussed. 

In addition to MMT and other cationic clays, layered double hydroxides (LDHs) with the hydrotalcite-type structure are another family of layered materials [18] which, despite they have been used in a lesser extent than MMT (and structure-related materials) as nanocomposite polymer fillers, have shown enormous more potentially advantages than natiual clays, specially concerning their purity and crystallinity and particle size control in addition, they can be also easily functionalized in different ways with different agents, thus permitting a chemical modification of the layers environment to optimize their compatibility with the polymer [19,20]. 

Layered double hydroxides (LDH) are another emerging class of layered crystals due to their wide range of applications in catalysis, sorbent, ion exchangers, stablizer and fire retardance [81, 82]. The LDHs have a brucite-like structure, where divalent octahedrally coordinated M(II) ions are partially substituted by trivalent M(III) ions. As a result, the positively charged metal oxide/hydroxide layers are neutralized by other charge-balancing anions. The general chemical formula of LDHs is [M ", M " (0H)J i+(A ) -nH,0 where, M = Li+, Mg, Co, Zn, Ni, etc. M + = Al +, Cr , Fe, etc., and A = Cl, NOj, COj, , etc. [83]. The... 

Figure 1. The crystal structure of Zr2(0H)2(SO4)3(H2O)4> reprinted with permission from Ref. 5, copyright 1966, American Chemical Society. Zirconium atoms are shown as solid circles, oxygen atoms as open circles. The Pu compound is isomorphous, Zr being replaced by Pu. la shows the manner in which the bridging sulfates link Pu atoms to form layers, lb shows the manner in which layers are linked through the double hydroxide bridges.

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. 

What are the capacitances, resistances, optical properties, chemical compositions and electronic structures of the hydroxide films as the function of potential and of the electric double layer at che OCP ... 

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