Montmorillonite basal spacing

Fig. 2. Diagram showing the intercalation of compact quaternary ammonium cations, such as trimethylphenylammonium (TMPA) into different smectites, giving rise to type I organoclays with a basal spacing of about 1.5 nm. SWa is a high-charge nontronite (iron-rich smectite) and SAz is a high-charge montmorillonite, while SAC is a low-charge montmorillonite. After Jaynes and Boyd (1991b).

The same evolution of the basal spacing (d 001) for the pillared montmorillonite in which the Li has been introduced after the Zr is illustrated in fig. 5. It has to be mentioed that, after saturation of the solids by ethylene glycol, the interlayer distance of the samples calcined at 400°C is always slightly higher than before saturation. 

A small increase of the (d 001) basal spacing is observed for the Li containing Zr pillared clays. However, the thermal stability of these solids drastically decrease. At high temperature, the collapse of the strucutre is also supported by the decrease of the surface area which is, at 700°C, almost identical to those measured for the montmorillonite. Different hypothesis may be proposed to explain the increase of the interlayer distance at low temperature (i) a better polymerization of the intercalated complex (ii) a modification of the distribution of the pillars (iii) a lower interaction between the pillar and the silica layer. The first hypothesis may easily be eliminated since the small variation of the height of the pillars (less than 1 A) cannot be explained by structural changes of the... 

Titanium-pillared montmorillonite may be used as a heterogeneous catalyst for the Sharpless asymmetric epoxidation of allylic alcohols (Scheme 20) (46). The enantiomeric purities of the epoxy products are comparable with those achieved using homogeneous Ti isopropoxide with molecular sieves as water scavengers (Chapter 4). Since basal spacing of the recovered catalyst after the reaction is unaltered, the catalyst can be recycled. 

The catalytic and structural properties of two chromia-pillared montmorillonites were compared in an effort to establish structure-reactivity relationships in these materials. The basal spacings of pillared products, prepared by reaction of Na+-montmorillonite with base-... 

Evidence that difference in reactivity for Cr3 53 and Crx 88-montmorillonite is due largely to differences in gallery accessibility is provided by the adsorption data in Figure 5. The Cr3 53 derivative, which retains a basal spacing near 21 A after reaction, is capable of rapidly adsorbing cyclohexane. However, the Cr1 88 derivative with a basal spacing near 13.7 A adsorbs very little cyclohexane. 

The cation exchange of layer silicates significantly influences some structural and colloid chemical properties. Depending on the charge of the cation, the interlayer space contains water in different quantities (Chapter 2, Section 2.1.2). So, the basal spacing (the distance between similar faces of adjacent layers) is different for monovalent, bivalent, and trivalent cations. For example, in monovalent montmorillonite, it is about 1.2 nm, and in bivalent and trivalent montmorillonite, it is about 1.5—1.6 nm. 

Some basic properties, such as basal spacing (d001), internal and total specific surface area, and cation-exchange capacity (CEC) of some natural montmorillonite or bentonite with high montmorillonite samples are listed in Table 2.1. Similar characteristics of different cation-exchanged montmorillonites are given in Section 2.3. 

The other type of transformation process of the interlayer cation is pillaring (Chapter 1, Section 1.3.5). In this process, metal oxide chains are formed in the interlayer space upon thermal treatment of different cation-exchanged mont-morillonites. As a result, the basal spacing, that is, the size of the interlayer space, increases. The pillared montmorillonites are widely applied in catalytic reactions, as evidenced by over 600 scientific publications in the last 10 years (e.g., Fetter et al. 2000 Johnson and Brody 1988 Perez Zurita et al. 1996). 

The structural parameters of cation-exchanged montmorillonites prepared from calcium-montmorillonite (Istenmezeje) are listed in Table 2.3. As seen in Table 2.3, the basal pacing of monovalent montmorillonite is approximately 1.25 nm, and the water content is approximately 1%. It means that there is one layer of water in the interlayer space. For bivalent montmorillonite, both basal spacing (>1.5 nm) and water content (>10%) are higher, showing two layers of water molecules in the interlayer space. The basal spacing of Pb-montmorillonite is 1.254 nm, which is similar to the value characteristic of monovalent montmorillonite (1.241 nm). However, it does not mean that lead is sorbed on the surface of montmorillonite as monovalent cation since the other parameters that are determined by the distance between the layers (hydration entropy, charge/ion radius value, water content in the interlayer space) lie between the values for bivalent and monovalent cations (Foldvari et al. 1998). 

The basal spacing of lanthanoid-montmorillonites is similar to other trivalent montmorillonites and varies between 1.5 and 1.6 nm. For example, the basal spacing of Fe(III)-bentonite is about 1.6 nm (Komlosi et al. 2007 Izumi et al. 2005 Kong et al. 2005), and that of Al-bentonite is 1.576 nm the ionic radius of Fe(III) and Al is, however, much smaller. For the lighter lanthanoids, this value is above... 

At the same time, the concentration of manganese ions remains the same. The basal spacing (d001) of montmorillonite determined by x-ray diffraction is very similar to the newly prepared (1.51 nm) and old (1.48 nm) samples. The distribution... 

Encapsulation chemistry similar to that described above (exchange of anilinium, followed by oxidation with peroxydisulfate) was foimd to produce polyaniline not only in zeolite Y, but also in montmorillonite clay. 5 Spectral features (UV-VIS, IR and EPR) of the products were indicative of emeraldine salt and base formation, respectively. The change in basal spacing of the montmorillonite upon intercalation provided additional evidence for the inclusion polymerization. 

Figure 15.21. Basal spacing of CH3(CH2)ii iNH montmorillonites vs. the number of carbon atoms. [Adapted, by permission, from Lan T, Kaviratna D, Pinnavaia T J, Chem. of Mat., 6, No.5, 1994, 573-5.]...

Figure 10. The mole fraction of benzene (xl) in the interfacial layer and the basal spacing (dL) in ethanol(l)- -cyclohexane(2) mixtures on hexadecylammonium-montmorillonite.

Posner, A.M. and Quirk, J.P., 1964. Changes in basal spacing of montmorillonite in electrolyte solutions. J. Colloid Chem., 19 798—812. 

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