Smectite clay colloids

Clays are colloidal layered hydrous aluminosilicates. There are relatively few examples of porphyrin intercalation into clays reported, mostly with either smectite clays or layered double hydroxides (LDH). Smectite clays consist of negatively charged layered aluminosilicate sheets. These sheets are separated by cations and water molecules. The... 

These examples illustrate that biomolecules may act as catalysts in soils to alter the structure of organic contaminants. The exact nature of the reaction may be modified by interaction of the biocatalyst with soil colloids. It is also possible that the catalytic reaction requires a specific mineral-biomolecule combination. Mortland (1984) demonstrated that py ridoxal-5 -phosphate (PLP) catalyzes glutamic acid deamination at 20 °C in the presence of copper-substituted smectite. The proposed pathway for deamination involved formation ofa Schiff base between PLP and glutamic acid, followed by complexation with Cu2+ on the clay surface. Substituted Cu2+ stabilized the Schiff base by chelation of the carboxylate, imine nitrogen, and the phenolic oxygen. In this case, catalysis required combination of the biomolecule with a specific metal-substituted clay. 

Suspended solid surfaces (particles or colloids) in waters play a prominent role in controlling the concentration of dissolved trace elements. Most of these elements are eliminated by sedimentation after incorporation on to or into particles, generally by complexation with the surface sites. The most common inorganic particles and colloids are non-clay silicates (quartz, potash feldspar, plagioclase, opaline silica (diatoms)) clays (illite, smectite) carbonates (calcite, dolomite) Fe-Mn oxides (goethite, magnetite) phosphates (apatite) sulfides (mackinawite). Particles and colloids in a water body may be classified as a function of their origin ... 

Bentonite occurs commercially as powders ranging in colors and tints from off white to pale brown to gray depending on the cations present in natural deposits. It comprises natural smectite clays consisting primarily of colloidal hydrated aluminum silicates of the montmorillonite or hectorite type of minerals with varying quantities of alkalies, alkaline earths, and iron. It is insoluble in water, in alcohol, in dilute acids, and in alkalies. 

The Nemst equation applies (if we neglect the activity coefficients of the ions, in keeping with PB theory) to the emf (electromotive force) of an electrochemical cell. The emf of such a cell and the surface potential of a colloidal particle are quantities of quite different kinds. It is not possible to measure colloidal particle with a potentiometer (where would we place the electrodes ), and even if we could, we have no reason to expect that it would obey the Nemst equation. We have been at pains to point out that all the experimental evidence on the n-butylam-monium vermiculite system is consistent with the surface potential being roughly constant over two decades of salt concentration. This is clearly incompatible with the Nemst equation, and so are results on the smectite clays [28], Furthermore, if the zeta potential can be related to the electrical potential difference deviations from Nemst behavior, as discussed by Hunter... 

Clays and particles of soil organic matter have negative charges and high CECs, as confirmed by the following values 150-500 meq/100 g for organic matter and 3-150 meq/100 g for clay minerals (as kaolinite and smectite). On the other hand, aluminum and iron hydroxide colloids tend to be hydrophobic, with surface positive charges, and, consequently, they are predominantly anion adsorbers. 

Initially in this study, it was planned to critically evaluate AG data for complex clays, including chlorite, illite, and the smectites. However, there is much evidence that these clays dissolve Incongruently so that the apparent equilibria in solution are determined by secondary phases, such as gibbsite, boehmite, amorphous silica, and ferric oxyhydroxldes. The smectites are frequently the dominant clays in the colloidal size fraction in natural sediments. They have very large exchange capacities, and exhibit wide chemical variations. Usually, one or more of these factors have not been considered in the experimental solubility work. Even if appropriate corrections could be made, it is uncertain whether a AG value so obtained would have applicability to natural systems. 

Figure 8.5. Viscosity of a 0.23-percent suspension of Na -smectite in water as a function of the amount of NaCl added to solution. (Adapted from H. van Olphen, 1977. An Introduction to Clay Colloid Chemistry. 2nd ed. New York Wiley.)...

P. Bar-On, I. Shainberg, and I. Michaeli, Electrophoretic mobility of montmorillonite particles saturated with Na/Ca ions, J. Colloid Interface Sci. 33 471 (1970). R. D. Harter and G. Stotzky, X-ray diffraction, electron microscopy, electrophoretic mobility, and pH of some stable smectite-protein complexes. Sod Sci. Soc. Am. J. 37 116 (1973). S. L. Swartzen-Allen and E. Matijevi6, Colloid and surface properties of clay suspensions. II Electrophoresis and cation adsorption of montmorillonite, /. Colloid Interface Sci. 50 143 (1975). 

In the LB technique, a monolayer of amphiphilic molecules, prepared at the air-water interface, is transferred to a substrate, thus giving a monomolecular film. The molecules must be solvable in a volatile, water-insoluble (organic) solvent, but not, or to a very limited extent, in water. Thus, when the solution of the molecules in the organic solvent is spread over the surface of water, the solvent evaporates, leaving a monolayer of molecules at the air-water interface. This monolayer can be compressed and transferred to a substrate. When the molecules are replaced by colloidal, nanosized particles, monolayers of these particles on a substrate are obtained. Smectites are especially well suited for the LB technique. The elementary clay sheets are about 1 nm thick and a few tens to hundreds nm wide and long. In the alkali- or alkaline earth form, they are hydrophilic, but by ion exchange with suitable amphiphilic cations, they become hydrophobic. There are then two ways to prepare mono-layers of smectite clay particles by the LB technique. 

Chem. Desaip. Complex colloidal magnesium aluminum silicate derived from natural smectite clays CAS 12199-37-0 EINECS/ELINCS 235-374-6 Uses Thickener, vise, modifier, emulsion stabilizer for emulsions, suspensions, sol ns., liqs., creams, pastes, cosmetics, toiletries, toothpaste, pharmaceuticals, paints, textile finishes, chemical specialties, industrial applies. suspending agent, binder, dispersant for powds. and pigments disintegrant in tablets spreading agent for lotions, creams, and ointments... 

The cation exchange ability of smectites is isutilized to incorporate [Ru(bpy)3] cations. The luminescence probe studies have been carried out mainly in colloidal clay systems in which an aqueous solution of [Ru(bpy)3] is mixed with an aqueous suspension of smectites. In some cases, a species that quenches the excited state of [Ru(bpy)3] is added (80,82). The concentrations of hosts, [Ru(bpy)3], and quenchers in the suspensions have been varied in order to see the dynamics of the reactions. The photoprocesses of the [Ru(bpy)3] -smectite systems have revealed that the steady-state and time-re-solved luminescence properties of [Ru(bpy)3] + are not simple, and various interpretations of the unusual properties have been proposed (80,83,91). 

Kuykendall and Thomas studied the photophysics of tetrakis(V-methylpyri-dyl)porphyrin adsorbed on colloidal smectite and proposed that the photophysics can be a convenient method to monitor the degree of dispersion or extent of deflocculation of a clay dispersion to produce primary particles or single sheets (156). 

In addition to their high absorptive eapacity hormite clays offer useful thickening properties. When dispersed in water they do not swell, as smectites do. Instead, their needle-like colloidal particles deagglomerate in proportion to the amoimt of shear applied and form a random colloidal lattice. This loosely cohesive structure thickens the water and imparts thixotropy, pseudoplasticity, and yield value. Because of their mechanically-based dispersion and colloidal structure building, hormite cl s are largely insensitive to the types and levels of acids, bases, and salts dissolved in the aqueous systems in which they are used. Since their dispersion is mechanically rather than ionically driven, as with smectites, they can be used in nonaqueous applications in much the same... 

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