Saponite cations

Except for the PBS/SAP-qC16 (n-hexadecyl tri-n-butyl phosphonium cation modified saponite) system, the degree of degradation is the same for other samples. This indicates that MMT or alkylammonium cations, and at the same time other properties, have no effect on the biodegradability of PBS. The accelerated degradation of PBS matrix in the presence of SAP-qC16 may be due to the presence of alkylpho-sphonium surfactant. This kind of behavior is also observed in the case of PLA/MMT-based nanocomposite systems. 

After the experiments, significant quantities of newly formed minerals were observed at the cold extremity of the tube, pointing to a fast material transport by diffusion from the hot to the cold end of the tube. The following spatial distribution of newly formed phases, reflecting the temperature profile, was observed in both runs (Fig. 8) quartz + K-feldspar + plagioclase + Mg-rich saponites (hot extremity) quartz + K-feldspar + plagioclase (middle of the tube) and alkaline or Ca-rich clays + quartz + plagioclase (cold extremity). The cation composition of the phyllosilicates was similar in both experiments. Some newly fonned quartz crystals... 

Cetylmethylammonium (CTMA) as the clay exchange cation and decylamine as the co-surfactant were used to form a PCH. A 1.0 wt % suspension of previously prepared saponite was allowed to react at 50°C with a 0.3 M aqueous cetylmethylammonium bromide solution in two fold excess of the clay cation exchange capacity. After a reaction time of 24h, the product was washed with ethanol and water to remove excess surfactant and... 

The cation exchange capacity (CEC) of the saponite was determined from the ammonium content in solution after exchange with NaOH using an ammonia selective electrode. 

After evacuation at 25°C (spectrum C), the physisorbed fraction of acetonitrile-d3 and also the H-bonding effects with the silica surface -OH have disappeared, while the Bronsted acidity is still present (2309 cm 1). Subsequent evacuation at 60°C does not change the intensity of the Bransted acidity (spectrum D). Even at 120°C and at 150°C Bransted acid sites are still detected (spectra E, F). Therefore, it can be concluded that the Al-PCH is characterized by an important Bransted surface acidity. This type of acidity is expected since the initial Na+ ions on saponite have been replaced by surfactant cations and then by protons upon destruction of the surfactant through calcination. Besides, by the grafting of Al-species onto the support, Si-(OH)-Al bonds have been created, giving rise to the band at 2309 cm 1 indicative of Bransted acidity [10]. 

Figure 30. Schematic illustration of the packing of stilbazolium cations inside a magnesium-rich saponite clay. Stereoselective dimerization takes place to give the syn head-to-tail dimer. [Reproduced with permission from K. Takagi, H. Usami, H. Fukaya, and Y. Sawaki, J. Chem. Soc., Chem. Commun. 1174 (1989).]...

In montmorillonite some of the Al3 + in the octahedral sublattice are replaced by Mg2+ ions, and in hectorite some of the Mg2 + in the octahedral sublattice are replaced by Li+ ions. With beidellite and saponite, however, the isomorphous substitution takes place in the tetrahedral sublattice with Al3 + replacing some of the Si4+ ions. The residual negative charges in the layers on montmorillonite, hectorite, beidellite, and saponite are counterbalanced in the natural state by coexisting interlamellar, hydrated cations, usually Na+,... 

Table XXXVIII). Brindley (1955) has suggested that stevensite is a mixed-layer talc-saponite however, Faust et al. (1959) considered it to be a defect structure with a random distribution of vacant sites in the octahedral sheets. A small proportion of domains with few or no vacancies would then be present having characteristics of talc. The layer charge in stevensite is due to an incompletely filled octahedral sheet (Faust and Murata, 1953). This deficiency is minor (0.05—0.10) and the resulting cation exchange capacity is only about one-third that of the dioctahedral montmorillonites (100 mequiv./lOO g.).

The interest in LDHs is much more recent than their cationic equivalents (cationic clays such as montmorillonite and saponite). This is, in part, because cationic clays are much more abundant in nature and have an important role in many soil processes, for example. It is clear, however, that the potential for creating novel supramolecular structures, either directly as intercalates or for orienting organic molecules at reactive surfaces, is likely to increase. 

Saponite is a naturally occurring phyllosilicate clay of the smectite (montmorillonite) group. It is a magnesium-rich hydrated aluminum silicate and is present as a component of some commercial magnesium aluminum silicate clays. Saponite is a mineral with an approximate empirical formula owing to the variability in cation substitution see Table I. 

In these formulas, X denotes a monovalent cation such as Na" and/or Ca ", occupying interlayer exchange sites. The formulas show that beidellite is magnesium-free and montmorillonite magnesium-rich. Other smectite minerals include nontronite, hectorite, saponite, and sauconite (Table 9.1). All the smectites (and vermiculites) have swelling properties. 

Smectite 2 1 low hydrated cation (may tri- saponites saponite, hectorite... 

M. M. Mortland and K. V. Raman, Surface acidity of smectites in relation to hydration, exchangeable cation, and structure, Clays and Clay Minerals 16 393 (1968). See also J. D. Russell, Infrared study of the reactions of ammonia with montmorillonite and saponite, Trans. Faraday Soc. 61 2284 (1965), andM. M. Mortland, Protonation of compounds at clay mineral surfaces, Trans. 9th Int. Cong. Soil Sci. (Adelaide) 1 691 (1968). 

This study deals with the pillaring of a natural clay, a saponite from Ballarat, by polyhydroxoaluminum cations provided by a commercially available solution of Chlorhydrol. Interest of these starting materials may be briefly listed. 

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