Interlamellar sorption

When organic cations (e.g., cationic tensides) are employed, clay organo-complexes are formed, which can be used in organic solvents. A Pd-hexadecy-lammonium montmorillonite catalyst was prepared by the reduction of Pd(OAc)2 by ethanol in the interlamellar space. At small ethanol concentrations in toluene, selective interlamellar sorption of ethanol was established consequently, the reduction also occurred only in the interlamellar space.160 The catalyst was used for the hydrogenation of alkenes.161... 

As already indicated, the surface area of the dry clay appeared to be about 50m2g-1. The platy particles (the tactoids) were therefore about 20 layers thick during the first stage of water sorption, the particles were split into smaller tactoids of around six clay platelets (surface area of 105 m2 g-1). The external dimensions at p/p° > 0.25 remained fairly constant, but the interlamellar sorption was accompanied by swelling and the development of an accessible internal area (possibly as high as... 

Interlamellar sorption and expansion data on hydrophobic montmorillonite organoclays in me-thanol(l)and benzene(2)... 

The synthesis of Pd-hexadecylammonium montmorillonite (HDAM) samples was performed by the in situ reduction of Pd(OAc)2 in the interlamellar space, with a bulk composition of ethanol toluene = 5.95. The method of preparation was designed according to preliminary liquid sorption and XRD measurements. At small ethanol concentrations in toluene, the selective interlamellar sorption of ethanol was established, which ensured the diffusion of Pd ions from the bulk phase to the interlamellar space, where reduction to Pd" took place. Samples of 2.5, 4.2, 6.5 and 10.2% Pd loadings were synthesized and characterized by N2 adsorption, TEM, XRD and SAXS measurements. A detailed description of the preparation method and instrumental analysis has been published recently [10]. 

TABLE 5 Interlamellar Sorption and Swelling on Hydrophobic Montmorillonites in Metha-nol(l)-Benzene(2) Mixtures... 

The swelling of clays in water results from the extra hydration of the interlamellar cations (Fig. 77). This is the best known example of the important phenomenon of intercalation, which is simply the insertion of guest species into an accommodating host, usually, but not exclusively, a layered solid. The degree of swelling, however, is governed by the nature of the interlamellar cation and the sorption isotherm often exhibits steps, as so often occurs with clathrates. 

The results in Figure 11.7 were consistent with the movement of the c-axis spacing, dm at p/p° < 0.25, this remained close to the dry-state value of 0.96 nm, but as the water vapour pressure was increased, dmi underwent a stepwise change to c. 1.8 nm. The initial sharp increase in the region of p/p° = 0.25 confirmed that at 25°C this represented the threshold relative pressure (and corresponding chemical potential) for the sorption of water within the interlamellar space. 

With the two aromatic hydrocarbons, Barrer and Kelsey (1961) found that the dm spacing increased steadily with the increase in p p°, but with the alkanes there was very little change. In the former case, it appeared that most of the uptake was in the interlamellar region. As indicated by the shape of the Type Hb isotherms, the sorption of the other organic vapours probably included an appreciable amount of multilayer adsorption on, and between, the clay platelets (cf. Figure 11.5). 

The sorption of 1,3,5-trinitrobenzene (TNB) from aqueous suspension on kaolin-ite, illite, and smectite is shown in Figure 4A (5). Considerably more sorption of 1,3,5-TNB occurs on the K-montmorillonite compared to kaolinite or illite. Related sorption studies of NACs on clay minerals indicate that NAC sorption on smectites occurs in the interlamellar regions. Internal sorption sites are not available on kaolinite or illite as a consequence, considerably less sorption occurs. Smectites, in particular, show a high affinity for NACs from aqueous suspension. 

Site-specific interactions between the —NO2 groups of sorbed NAC molecules in the interlamellar region of smectites and exchangeable cations were first proposed to account for NAC sorption by Yariv and coworkers over 30 years ago (72,73). They found that the vibrational bands of the sorbed NACs were shifted relative to the neat compound. The spectral trends in this study were not conclusively related to the nature of the exchangeable cation because of differences in water content (73). More recently, evidence against site-specific interactions was reported by Weissmahr and coworkers based on spectral similarities between NACs sorbed on K - and Cs +-exchanged clays obtained using UV-visible, infrared, and NMR methods (6). They reported spectral shifts in the ATR-FTIR spectra of sorbed NACs relative to the NAC in aqueous solution. However,... 

The structure and the sorption properties of partially hydrophobized silicates (do-decylammonium and dodecyldiammonium vermiculites) were investigated in aqueous solutions of n-butanol. The alcohol is preferentially adsorbed on the surface. The interlayer composition is calculated from adsorption and X-ray diffraction data. In the air-dried state the organic cations lie flat on the interlamellar surface. In aqueous n-butanol solutions, the basal spacing of dodecylammonium vermiculite gradually increases with the extent of n-butanol adsorption because the chains increasingly point away from the surface. The basal spacing of dodecyldiammonium vermicuiite is virtually independent of the interlayer composition, because the expansion of the interlayer space is sterically restricted and a... 

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