Smectites structure

All samples prepared in this study showed XRD patterns atca. 20= 8°, 20°, 35°, 53° and 61° that are assigned to (001), (020, 110), (130, 200), (240, 310, 150) and (060, 330) diffraction peaks of smectite structure [6], The diffraction patterns derived from metal oxides (nickel, cobalt and zinc oxides) did not appear in XRD patterns of all samples after calcination at 873 K. 

Table 1 shows the properties of smectite-type materials prepared. Smectite materials prepared at lower pH had fewer sodium ions, higher surface areas, and larger pore volumes for a series of samples containing the same divalent cation species (nickel and cobalt) in the octahedral sheet. The adsorption of methylene blue on all the synthetic smectites shows that the smectite fragments are negatively charged. The Si M ratios of synthetic smectites were about 8 6, indicating that most of divalent cations exist in octahedral layers and small amount of divalent cations would exist as hydroxide or oxide cluster in smectite materials. However, the amounts of the hydroxide or oxide cluster were small, because only smectite structures were observed in XRD patterns and EXAFS Fourier transforms of synthetic smectites calcined at 873 K. 

The nitrogen adsorption-desorption isotherms at 77 K showed that the pore structures of smectite-type materials are of a bottle-neck type [3]. The surface areas of Ni-481 and Ni-359 treated at 873 K were 381 and 184 m2 g 1, respectively (Figure 2). The synthetic smectites have large surface areas because many small fragments with the same smectite structure are intercalated in the interlayer region [4]. 

Pyridine adsorption experiments have showed that the nickel containing smectites have Lewis acid sites and do not have Bronsted acid sites [9]. The Ni2+-substituted smectite catalysts have large surface areas even after 873 K treatment because many small fragments with the same smectite structure are intercalated in the interlayer region. The activities of the Ni2+ substituted catalysts are derived from Ni2+ Lewis acid sites located on the edge framework. 

The mixed-layer structure of illite and smectite was obtained by alternating layers of illite and smectite. To allow comparison to other 1.0-nm structures, a layer spacing of exactly 1.0 nm was used for muscovite and biotite, and a layer spacing of exactly 2.0 nm was used for the 2-layer illite/smectite structure. 

Figure 2. Structure of a typical chlorite-like hydroxy-interlayered clay in which the galleries of a 2 1 smectite structure are filled, or nearly so, with brucite-like sheets of mainly edge-shared Mg(OH) octahedra. Aluminum occasionally substitutes for magnesium in the brucite sheet to provide the charge balance necessary for electrical neutrality.

In the case of a smectite, each layer comprises two sublayers of tetrahedra with an inserted octahedral layer, where between the layers an interlayer space is formed in which the exchangeable cations are located (see Figure 9.3). That is, the smectite structure can be described on the basis of layers containing two sublayers of silica tetrahedra squeezed into a layer of an octahedra of Al3+ or Mg2+, that is, a 2 1 layered clay [34], The replacement of some of the Al3+ with Mg2+ or Li+, or the isomorphous replacement of tetrahedral Si4+ with Al3+, results in a certain amount of total negative charge on the layer, compensated in turn by the presence of hydrated cations in the interlayer region (see Figure 9.3). 

Figure 3.8. Schematic of the smectite structure showing one gibbsite sheet between two silicate sheets. The basic unit is repeated many times in the horizontal directions to produce layers. The basic unit with the 9.6 A c-axis spacing expands to 14 A when water enters between layers. The exchangeable cations located between the layers produce the counter charge for the isomorphous substitution. It occurs in the layers marked with an asterisk (from Taylor and Ashcroft, 1972, with permission).

Volzone, C. and Torres Sanchez, R.M.. Thennal and mechanical effects on natural and activated smectite structure. Colloids Surf. A, 81, 211, 1993. 

The XRD patterns of the samples obtained (Fig. 1) are consistent with those of synthetic and natural stevensites [7,8J, evidencing formation of the trioctahedral smectite structure, as indicated by the (060) reflection at about 1.52 A. However, intensities of the X-ray reflections vary for the particular solids, which is caused probably by differences in the crystallinity and/or in size and stacking of particles. All the samples show a typical smectite ability to swell in ethylene glycol and exhibit ion-exchange capacity comparable with that of the natural stevensite (of about 50 mequiv/g). 

Lindgreen H, Drits VA, Sakharov BA, Salyn AL, Dainyak LG (2000) lllite-smectite structural changes during metamorphism in black Cambrian Alum shales from the Baltic area. Am Mineral 85 1223-1238 Lindgreen H, Jacobsen H, Jacobsen HJ (1991) Diagenetic structural transformations in North Sea Jurassic illite/smectite. Clays Clay Minerals 39 54-69... 

According to Savin and Lee (1988) tetrahedral aluminium and iron in the smectite structure should influence isotopic fractionation. An Fe and A1 " free smectite compared to nontronite should provide a difference in 6 0 of nearly 5 °/m- The chemical variability of the Ishirini smectites is very small. Therefore, the chemical variability of smectites on isotope fractionation is assumed to be negligible. The... 

The basic smectite structure if formed by an alumina octahedral layer sandwiched between two siUca tetrahedral layers. These layers share the apical oxygen atoms... 

Metal Ions and Complexes Sorbed Onto Solids. - The Li and Na NMR spectra of clay suspensions in water have been used to show how the smectite structure and the nature of the alkali counterions modulate the quadrupolar interaction. The surface modihcation of Y-AI2O3 by Na+ has been studied by H/ Na double resonance NMR techniques. The organic functionalisation of mesoporous molecular sieves with Grignard reagents has been investigated by C and Si NMR spectroscopy. ... 

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