Intercalation in clays

Quenching mechanism. Steady state measurements of the luminescence quantum yield of Ru(byp)3 intercalated in clay films brings about more detailed information with respect to the possible role of electron transfer in luminescence quenching. The quantum yield is dependent upon the amount of co-adsorbed water and s strongly depleted by transition metal impurities, such as Fe5 or Cr in the lattice (28). 

E Ruiz-Hitzky, P Aranda. Electroactive Polymers Intercalated in Clays and Related Solids. Chapter 2. In TJ Pinnavaia, GW Beall, eds. Polymer-Clay Nanocomposites. West Sussex. UK Wiley, 2000 19-46. 

FIGURE 25 Grafting of mercaptopropylsilane groups to the inner and outer walls of mesostructured silica intercalated in clay. (From Ref. 118.)... 

Bio-nanocomposites based on layered clay can be stained with Safranine O by ion-exchange. Safranine O, a fluorescent dye, contains alumimun ion. Aluminum ion enables this dye to intercalate in clay galleries dming ion-exchange. Confocal microscopy can then be used to determine the extent of dispersion of clay during mixing or sonication (Yoonessi et al., 2004). 

Y. V. Kudryavtsev, E. N. Govorun, A. D. Litmanovich, and H. R. Fischer. Pol5mier melt intercalation in clay modified by diblock copolymers. Macro-molecular Theory and Simulations, 13 5 (2004), 392-399. 

Phosphonium cations can also intercalate in clays. Different studies were reported on the interaction of different phosphonium cations with bentonites and montmorillonites. The use of... 

Ruiz-Hitzky E and Aranda P (2000) Electroactive polymers intercalated in clays and related solids, in Polymer-Clay Nanocomposites (Eds. Pinnavaia T J and Beall G W), Wiley, Chichester, UK, Ch. 2, pp. 19-46. 

Ogata et al. (1997) first prepared PLA/ organoclay (OMMT) blends by dissolving the polymer in hot chloroform in the presence of dimethyl distearyl ammonium modified MMT (2Ci8MMT). XRD results show that the silicate layers forming the day could not be intercalated in the PLA/MMT blends, prepared by the solvent-cast method. Thus, the clay existed in the form of tactoids, consisting several stacked silicate monolayers. 

Recently a lot of attention is being given to the field of latex-based nanocomposites. Various organoclays as well as pristine clays have been intercalated in aqueous medium with NR latex, SBR latex, NBR latex, as well as carboxylated nitrile mbber (XNBR) latex [184—187], to achieve a good degree of dispersion. 

Polyimide-clay nanocomposites constitute another example of the synthesis of nanocomposite from polymer solution [70-76]. Polyimide-clay nanocomposite films were produced via polymerization of 4,4 -diaminodiphenyl ether and pyromellitic dianhydride in dimethylacetamide (DMAC) solvent, followed by mixing of the poly(amic acid) solution with organoclay dispersed in DMAC. Synthetic mica and MMT produced primarily exfoliated nanocomposites, while saponite and hectorite led to only monolayer intercalation in the clay galleries [71]. Dramatic improvements in barrier properties, thermal stability, and modulus were observed for these nanocomposites. Polyimide-clay nanocomposites containing only a small fraction of clay exhibited a several-fold reduction in the... 

Pillared clays (MELS) are aLso covered in this review. MELS have three-dimensional network structure like zeolites, and, unlike clays, which have two-dimensional layered structures, pillared cationic and anionic clays have been studied. Phthalocyanins intercalated in anionic clays have given interesting results for wastewater purification (Vaccari, 1998). 

The intercalated catalysts can often be regarded as biomimetic oxidation catalysts. The intercalation of cationic metal complexes in the interlamellar space of clays often leads to increased catalytic activity and selectivity, due to the limited orientations by which the molecules are forced to accommodate themselves between sheets. The clays have electrostatic fields in their interlayer therefore, the intercalated metal complexes are more positively charged. Such complexes may show different behavior. For example, cationic Rh complexes catalyze the regioselective hydrogenation of carbonyl groups, whereas neutral complexes are not active.149 Cis-Alkenes are hydrogenated preferentially on bipyridyl-Pd(II) acetate intercalated in montmorillonite.150 The same catalyst was also used for the reduction of nitrobenzene.151... 

The positively charged phosphonium ligand was intercalated in the hectorite and was used to catalyze olefin hydroformylation.156 Cu(II)-exchanged clays were tested as catalysts in the cyclopropanation reaction of styrene with... 

The biochemical activity and accessibility of biomolecule-intercalated AMP clays to small molecules was retained in the hybrid nanocomposites. For example, the absorption spectrum of the intercalated Mb-AMP nanocomposite showed a characteristic soret band at 408 nm associated with the intact prosthetic heme group of the oxidised protein (Fe(III), met-myoglobin) (Figure 8.9). Treatment of Mb with sodium dithionite solution resulted in a red shift of the soret band from 408 to 427 nm, consistent with the formation of intercalated deoxy-Mb. Reversible binding of CO under argon to the deoxy-Mb-AMP lamellar nanocomposite was demonstrated by a shift in the soret band from 427 to 422 nm. Subsequent dissociation of CO from the heme centre due to competitive 02 binding shifted the soret band to 416nm on formation of intercalated oxy-Mb. 

Systems that react in this manner fall into two classes. In the first of these the framework that dominates the crystal structure scarcely participates in the reaction. This is the case, for example, in the reaction of an organic molecule intercalated in graphite or a clay, or of a guest molecule held in a clathrate of urea or thiourea. Some cases of this sort will be treated in the next section. 

Organic polymers are widely used in modified electrodes [220], but inorganic materials such as zeoHtes, clays or microporous solids are attractive as replacements since they have much better stability, tolerance to high temperatures and oxidizing conditions, and chemical inertness. Due to the capability of clays to exchange intercalated ions, clay modified electrodes have been extensively studied. 

Intercalation in layered solids is a long-established phenomenon. It has been suggested [ 1 ] that the first example, dating from over two thousand years ago, involved intercalation in kaolinite (an aluminosilicate clay) and explains the secret behind the production of fine Chinese porcelain, hi modern times, many thousands of papers have been devoted to intercalation chemistry in clays, graphite and other materials. 

It is important to distinguish these novel reactions, which take place between the individual sheet silicates and involve the intercalation of one or more of the reactants, from those catalysed by clay mineral surfaces. While details of the mechanism of reactions involving intercalation in sheet silicates are not fully understood, it is generally known that acid sites present in sheet silicates (Bronsted, as well as Lewis) are involved in the reactions. Protonated intermediates such as carbonium or oxonium ions play a crucial role in such reactions. 

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