Montmorillonite-water systems

Buswell and associates (34) studied the effect of variation in drying conditions on the spectrum of montmorillonite-water systems. The use of infrared to study the state of water in minerals had previously been suggested and briefly explored by Coblentz (35). The effect of drying on the... 

The spatial extent of adsorbed water on smectite surfaces is a matter of some controversy. Infrared spectroscopy, NMR relaxation, and X-ray and neutron diffraction experiments all point to a thickness of the adsorbed water film of around 1.0 nm. However, certain thermodynamic data, summarized for Na-montmorillonite in Table 2.5, suggest a thickness as great as 10 nm or more." These data are for partial and apparent specific properties of montmorillonite-water systems whose variation with water... 

P. F. Low, Nature and properties of water in montmorillonite-water systems, Soil Sci. Soc. Am. J. 43 651 (1979). J. L. Oliphant and P. F. Low, The relative partial specific enthalpy of water in montmorillonite-water systems and its relation to the swelling of these systems, J. Colloid Interface Sci. 89 366 (1982). 

Interlayer Molecular Structure and Dynamics in Li-, Na-, and K-Montmorillonite-Water Systems... 

Fu MH, Zhang ZZ, Low PF (1990) Changes in the properties of a montmorillonite-water system during the adsorption and desorption of water hysteresis. Clays Qay Miner 38 485 92 Fujii K, Nakano M (1984) Chemical potential of water adsorbed to bentonite. Trans Japanese Soc Irrigation Drainage Rural Eng 112 43-53 (in Japanese)... 

Roderick, G. L., D. Senich, and T. Demirel, 1969. X-ray diffraction and adsorption isotherm studies of the montmorillonite-water system. Proc. 3rd Int. Clay Conf, AIPEA (Tokyo) 1 659-668. 

Onium salts, such as tetraethylammonium bromide (TEAB) and tetra-n-butylammonium bromide (TBAB), were also tested as PTCs immobilized on clay. In particular, Montmorillonite KIO modified with TBAB efficiently catalyzed the substitution reaction of a-tosyloxyketones with azide to a-azidoketones, in a biphasic CHCI3/water system (Figure 6.13). ° The transformation is a PTC reaction, where the reagents get transferred from the hquid to the solid phase. The authors dubbed the PTC-modified catalyst system surfactant pillared clay that formed a thin membrane-hke film at the interface of the chloroform in water emulsion, that is, a third liquid phase with a high affinity for the clay. The advantages over traditional nucleophilic substitution conditions were that the product obtained was very pure under these conditions and could be easily recovered without the need for dangerous distillation steps. 

Kenawy 64) immobilized ammonium and phosphonium peripheral functionalized dendritic branches on a montmorillonite supported chloromethylstyrene/methyl methacrylate copolymer (74-75). These polymer/montmorillonite-supported dendrimers were used as phase transfer catalysts (PTC) for the nucleophilic substitution reaction between -butyl bromide and thiocyanate, cyanide, and nitrite anions in a toluene or a benzene/water system. These PT catalysts could be recycled by filtration of the functionalized montmorillonite from the reaction mixture. Generally,... 

The present chapter is an attempt at conceptual synthesis concerning smectite-water systems, designed to help sharpen the experimental issues that should be addressed in the next generation of laboratory investigations. The focus of our discussion is on Li-, Na-, and K-montmorillonite, based on the results of our previous simulation studies carried out separately for these homoionic smectites (16-18). The emphasis in our present analysis is on comparison with respect to the type of interlayer cation, in order to respond more definitively to the question of whether the aqueous phases in low-order montmorillonite hydrates are essentially two-dimensional ionic solutions (7, 2). 

Zhang et al. [31] used a Calvet calorimeter to measure as a function of S, the apparent adsorption, for the adsorption from aqueous solution of several different organic compounds on Na-montmorillonite. The apparent adsorption is the difference between the amount of organic compound actually present in the system per unit mass of montmorillonite and that which would be present if the concentration of the compound in the equilibrium solution persisted up to the montmorillonite/water interface. Their results are reproduced in Fig. 15. Observe from this figure that Q, was negative for some of the... 

The clay-water system. II. Water adsorption and cation exchange in montmorillonite. 

FIG. 4 Lamellar reflections in the XRD spectra of HDTABr/n-pentanol/water system before and after addition of Na-montmorillonite. (IX amount of surfactant corresponding to the cec of the montmorillonite 3. IX, 4.3X, 6.5X amount of surfactant corresponding to 3.1, 4.3, 6.5 times the value of cec. The basal distances are denoted in the figure.)... 

Liquid crystalline cationic surfactant/pentanol/water systems were investigated. The influence of water and pentanol contents on the swelling properties of lamellar systems was studied. Liquid crystalline systems were mixed with montmorillonite, resulting in the formation of a swollen organ-ocomplex that retained its ordered lamellar structure. It can be assumed that the driving force for maximal swelling and the corresponding adsorption is the development of a liquid crystalline system of ordered structure in the interlamellar space between the silicate lamellae. Silver nanoparticles were... 

FIG. 13 Reduction of the relative permeability coefficient is dependent on the clay platelet aspect ratio in the system of polyimide-clay hybrid with water vapor as the permeate. Each hybrid contains 2 wt% clay. The aspect ratios for hectorite, saponite, montmorillonite, and synthetic mica are 46, 165, 218, and 1230, respectively. (From Ref. 71.)... 

Fewer controlled experiments have been carried out for purely aquatic systems. Montmorillonite complexes with benzylamine at concentrations below 200 pg/L decreased the extent of mineralization in lake-water samples, although a similar effect was not noted with benzoate (Snbba-Rao and Alexander 1982). Even in apparently simple systems, general conclusions cannot therefore be drawn even for two structurally similar aromatic compounds, both of which are readily degradable nnder normal circumstances in the dissolved state. 

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