Smectite surfaces

Laird DA, Barriuso E, Dowdy RH, Koskinen WC (1992) Adsorption of atrazine on smectites. Soil Sci Soc Am J 56 62-67 Laird DA, Fleming PD (1999) Mechanisms for adsorption of organic bases on hydrated smectite surfaces. Environ Toxicol Chem 18 1668-1672 Lambert SM (1967) Functional relationship between sorption in soil and chemical structure. J Agric Food Chem 15 572-576 Lambert SM (1968) Omega, a useful index of soil sorption equilibria. J Agric Food Chem 16 340-343... 

A plot of the Lennard-Jones 9-3 form of Equations 7 and 8 for ST2 water interacting with smectite and mica surfaces is shown in Figure 1. Values for the parameters used in Figure 1 are given in Tables II and III, and in reference (23). The water molecule is oriented so that its protons face the surface and its lone pair electrons face away from the surface, and the protons are equidistant from the surface. Note that the depth of the potential well in Figure 1 for interactions with the smectite surface and mica surface are... 

An interaction potential between the surface and ions may also be needed in simulating counterion diffusion for the smectite and mica surface models. The form of such an interaction potential remains to be determined. This may not pose a significant problem, since recent evidence (40) suggests that over 98% of the cations near smectite surfaces lie within the shear plane. For specifically adsorbed cations such as potassium or calcium, the surface-ion interactions can also be neglected if it is assumed that cation diffusion contributes little to the water structure. In simulating the interaction potential between counterions and interfacial water, a water-ion interaction potential similar to those already developed for MD simulations (41-43) could be specified. 

Chorover, I, and Amistadi, M. K. (2001). Reaction of forest floor organic matter at goethite, birnessite and smectite surfaces. Geochim. Cosmochim. Acta 65, 95-109. 

Figure 21.5 Possible interactions between hydrated smectite surfaces and a chlom-.v-triazine. (See Color Plate Section.)...

Laird, D.A. (1996). Interactions between atrazine and smectite surfaces. In M.T. Meyer and E.M. Thurman, eds., Herbicide Metabolites in Surface Water and Groundwater. ACS Symposium Series 630. Washington, DC American Chemical Society, pp. 86-100. 

Laird, D.A. and P.D. Fleming (1999). Mechanisms for adsorption of organic bases on hydrated smectite surfaces. Environ. Tox. Chem., 18 1668-1672. 

Plate 6 Possible interactions between hydrated smectite surfaces and a chloro-s-triazine. 

The values of Dt of (1.89 0.09) and (1.94 0.10) reported by Van Damme and Fripiat (1985) for pillared clays were derived from the multilayer capacities of nitrogen and various organic adsorptives. The fact that Dt 2 appeared to confirm that the basal smectite surface was smooth and that the pillars were regularly distributed. It was argued by Van Damme and Fripiat that a random distribution of the pillars would necessarily lead to some localized molecular sieving and that this in turn would result in D% > 2. 

Laird, D. A. 2004. Reactions of organic molecules with smectite surfaces in aqueous systems. Acta Mineralogica-Petrographics, Abstract Series 4, p. 64. University of Szeged, Hungary. 

SMECTITE GROUP MINERALS. The structuTe of Water adsorbed by smectite group minerals has been studied extensively in both its static (D structure) and dynamic aspects. As with water molecules on vermiculite, the behavior of water on smectite surfaces is conditioned sensitively on the type of exchangeable cation and on the location of isomorphic cation substitutions in the layer structure. In many respects, a discussion of the configuration of water molecules hydrating smectites is parallel to that for vermiculite. 

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... 

The definition of adsorbed water adopted in Sec. 2.3 requires an arrangement of water molecules that differs significantly from that in an appropriate reference aqueous phase. For water on the surfaces of kaolinite group minerals the reference phase is bulk liquid water, whereas for water on vermiculite and smectite surfaces the reference phase is an aqueous solution because of the presence of exchangeable cations on the 2 1 layer silicates. On the ba,si.s of this definition, the consensus developed in Sec. 2.3 is that the spatial extent of adsorbed water on a phyllosilicate... 

Another important chemical property of adsorbed water on vermiculite and smectite surfaces is its Br nsted acidity. This property should refer principally to the acidity of the solvated exchangeable cations, as described by the reaction... 

Degradation of Tetraphenylboron at Hydrated Smectite Surfaces Studied by Time Resolved IR and X-ray Absorption Spectroscopies... 

Figure 2. Representation of multiple reaction pathways of TPB catalyzed degradation at smectite surfaces that were monitored directly by non-invasive in situ spectroscopic techniques.

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