Cation-exchanged montmorillonites

Clay materials show a different behavior. They are either cation-poor or cation-rich sheet silicates. They can swell by taking up varying amounts of water between the sheets. If the intercalated cations are hydrated as in montmorillonite, they act as cation exchangers. Montmorillonite, especially when it has intercalated Ca2+ ions, has thixotropic properties and is used to seal up drill holes. The effect is due to the charge distribution on... 

Interestingly, the use of Sc(OTf)3 as the promoter gave hydroxyalkyl-6,7-dihydrobenzofuran-4(57/)-one derivatives 17 from D-ribose (9), whereas scandium cation-exchanged montmorillonite (Sc -mont) afforded hydroxyalkyl-3,3,6,6,-tetramethyl-3,4,5,6,7,9-hexahydro-l//-xanthene-l,8(27/)-dione (18) in good yield [97] (Scheme 3). 

Quantifying Iron and Surface Water in a Series of Variably Cation-Exchanged Montmorillonite Clays... 

Cation exchange Montmorillonite, silica 4-A-methylpyridiumyl-substituted porphyrin Cooke et al (104), Battioni et al. (108), Barloy et al (109)... 

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 synthesis of cation-exchanged montmorillonite is performed through the following reactions. 

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 Structural Parameters of Cation-Exchanged Montmorillonites Prepared from Calcium-Montmorillonite (Istenmezeje, Hungary)... 

Sometimes, to achieve a particular objective, the conditions of the correct preparation of cation-exchanged montmorillonites can be neglected. For example, Fe(III)-montmorillonite has been prepared for application in the deep geological repository of high-level nuclear wastes (Manjanna et al. 2009). Acidic pH has been applied, destroying the crystal lattice however, a part of iron(III) ion has been precipitated as oxide and hydroxide, desirable for the sorption of radioactive matter. 

Acid-Base Properties of Cation-Exchanged Montmorillonites... 

The publications on amino acid adsorption on clay minerals before 1974 are summarized in the book by Theng (1974). It provides information on the adsorbed quantity of different amino acids on cation-exchange montmorillonites and the characteristic IR bands of amino acid-montmorillonites adsorption compounds. Usually, only the adsorbed quantity of amino acids on montmorillonites is shown, and no adsorption mechanism is usually hypothetized (e.g., Friebele et al. 1981 Rak and Tarasevich 1982), except in Stadler and Schindler (1993a) where the adsorption is evaluated by the surface-complexation model, and the possible surface complexes are given for p-alanine. 

Here, the adsorption of valine on different cation-exchanged montmorillonites is described (Nagy and Konya 2004). A discussion of the kinds of interactions that are possible in the ternary system of montmorillonite/valine/metal ions will be presented, and a description how the metal ions can affect these interactions. The interlayer cations (calcium, zinc, copper ions) were chosen on the basis of the stability constants of their complexes with valine. The adsorption of valine on montmorillonite is interpreted using a surface-complexation model. 

Tateiwa, J. I., H. Horiuchi, K. Hashimoto, and T. Kamauchi. 1994a. Cation-exchanged montmorillonite-catalyzed facile Friedel-Crafts alkylation of hydroxy and methoxy aromatics with 4-hydroxybutan-2-one to produce raspberry ketone and some pharmaceutically active compounds. J. Org. Chem. 59 5901-5904. 

Tateiwa, J. I., T. Nishimura, H. Hiriuchi, and S. Ulmura. 1994b. Rearrangement of alkyl phenyl ethers to alkylphenols in the presence of cation-exchanged montmorillonite (Mn" -mont)../. Chem. Soc. Perkin 3367-3371. 

---