2:1 phyllosilicates

Sheet silicates, or phyllosilicates, are layered phases with infinite two-dimensional hexagonal arrays of silica and alumina tetrahedra (Si205) , (AlSi30jQ) , or (Al2Si20jo) . The simplest glass-ceramic crystals of this type 

Synthesis and Characterization of Organically Functionalized 2 1 Magnesium Phyllosilicates 

Metal cations Organic moieties covalently attached to phyllosilicate framework References 

Mg (3-methacryloxy)propyl, methyl, phenyl, 3-aminopropyl, 3-mercaptopropyl, [n-(2-aminoethyl)-3-aminopropyl], [(10-amino)-4,7-diazanonyl], hexadecyl, n-propyl-ethylenediamine, n-propyltriethylenediamine, 3-chloropropyl, 5 -amino-1,3,4-thiadiazol-2-thiol, (CH3CH20)Si(CH2)3NHC(0)NH-R (R = 3-propyl, 3-pentyl, 3-heptyl) [11-13,15,16,18,19,21-23,26,33] 

Al-Mg n-dodecyl, n-octyl, n-pentyl, (3-methacryloxy)propyl, isobutyl, phenyl, 3-mercaptopropyl [14,24,25,28,31,32] 

Ca methyl, ethyl, n-butyl, n-hexyl, n-octyl, n-dodecyl, phenyl, n-octadecyl [29] 

The silicates with bidimensional finite groups of tetrahedra form the 

The stratified structure results by the unlimited association of the bands. In these structures the tetrahedra are united through three common comers, the 0 Si ratio being equal to 2.5. The stmctural types of phyllo-silicates can be subdivided after the symmetry of the lattice s closures for the resulted planes and after the number of the layers that are framed by the cations which ensure the cohesion between the layers by ionic bonds. 

Considering the number of the bi-dimensional units united through 

An important stmcture is that of micas. The micas group has the formula R R2 [(0H)2AlSi30jJ where R is K+, and R stands for AF+, Fe,  

FIGURE 4.47 (a) Tetragonal and (b) hexagonal types of stratified phyllo-silicates structures after The Chemistry of Silicates (2003). 

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F. Paris, P. Bonnaud, J. Ranger, M. Robert, and F. Lapeyrie, Weathering of ammonium- or calcium-saturated 2 1 phyllosilicates by ectomycorrhizal fungi in vitro. Soil Biol. Biochein. 27 1237 (1995). 

Phyllosilicates, in addition to talc and silica, have recently been evaluated for their use as tableting excipients. These compounds include the smectites, pa-lygorskites, and sepiolites [85a]. Although they show some promise, current levels of metallic impurities are currently too high for use in pharmaceutical preparations. 

Cobalt is capable of substitution for Fe2+ and other transition metals in the phyllosilicates due to the similarity of ionic radii. On the other hand, cobalt (Co2+) is specifically adsorbed by Mn and Fe oxides, and concentrations of Co sorbed by Mn oxides are much greater than those by Fe oxides (Backes, et al., 1995). Traina and Donor (1985) suggested that the Mn release during Co2+ ion sorption resulted not only from the oxidation of... 

Fujii and coworkers reported the synthesis and detailed structural analyses of alkylammonium/magnesium phyllosilicate hybrids [88], which were prepared by hydrothermal reaction from a mixture ofoctadecyldimethyl(3-trimethoxysilylpropyl)-ammonium chloride, silica sol, and magnesium hydroxide Mg(OH)2. The structure of the hybrid compound was studied by XRD, TEM, electron diffraction, high-resolution solid-state NMR, TG-DTA/MS, and elemental analysis. The resulting analytical information confirmed the unit structure, which consists of a 2 1... 

Fig. 2.17 Three structure candidates (A, B, and C) of alkyl-ammonium/magnesium phyllosilicate hybrids. Reprinted with permission from [88], K. Fuji etal., Chem. Mater., 2003, 75,1189.

This chapter reviews recent work on the fabrication and characterization of bio-inorganic nanomaterials based on organically functionalized magnesium phyllosilicate materials. We begin with the general procedures used to synthesize and characterize these organodays (Section 8.2), and then describe how higher-order... 

Fig. 8.2 PXRD pattern of ethlyenediamine-functionalized magnesium phyllosilicate showing reflections indexed according to the 2 1 trioctahedral phyl losi I icate structure of talc.

Fig. 8.3 SEM images of hexadecyl-functionalized magnesium phyllosilicate showing (A) intact spheroids (scale bar = 20pm) and (B) fractured spheroid with foam like interior (scale bar = 20pm). (C) TEM image of a wall fragment showing lattice fringes corresponding to a periodic lamellar structure (scale bar = 50 nm).

Fig. 8.5 SEM images of (A) close packed array of latex beads (scale bar= 1 tm) and (B) macroporous aminopropyl-functionalized magnesium phyllosilicate monolith obtained after infiltration and extraction of colloidal template (scale bar= 1 pm).

Intercalation of Biomolecules within Organically Modified Magnesium Phyllosilicates... 

In the next section, we demonstrate how exfoliation and ordered restacking of aminopropyl-derivatized magnesium phyllosilicates in the presence of proteins, enzymes or DNA can be used to prepare new types of bio-inorganic layered nanocomposites. 

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]. 

In conclusion, we have highlighted in this and the preceding section two versatile synthetic strategies to bio-inorganic layered nanocomposites based on the self-assembly of organically functionalized magnesium phyllosilicates (Figure 8.18). 

Fig. 8.18 Schematic diagram showing the potential scope of organically functionalized magnesium phyllosilicate (shown in top centre of figure) for the preparation of functional bioinorganic nanomaterials. (A) biomolecule-induced co-assembly of exfoliated aminopro-pyl-functionalized organoclay sheets to produce layered nanocomposites containing functional protein molecules (top left) or DNA (bottom left). (B) molecular wrapping...

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