Characterization of Surface Properties of Clay Particles in Aqueous Suspensions by Electronic Spectroscopy of Adsorbed Dyes(Exfoliation)

概要

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The adsorption properties of clay particles in aqueous suspension can be characterized by UV/Vis absorption and fluorescence spectroscopies of dyes adsorbed on the clay surfaces. Rhodamine laser dyes are adequate molecular probes for this purpose since their photophysical properties depend on several factors such as the molecular structure, the dye aggregation, the polarity and acidity of the environment, H-bonding interactions, etc. The displacement of the absorption and/or fluorescence bands of the rhodamine monomer adsorbed at clay surfaces can give information about the polarity and acidity of both the interlayer space and the water/clay interface. These physicochemical properties can be correlated with the type and extent of the isomorphic substitution of the clay. Furthermore, monomers, dimers and higher-order aggregates of rhodamines can be spectroscopically identified in both external surface and the interlayer space of smectite-type clays in aqueous suspensions. The presence or predominance of these species is governed by the relative dye/clay concentration, the aging of the samples, the hydrophobic character of the dye, the nature of the clay, etc. The evolution of these species with the aging time can be used not only to characterize the clay surfaces but also to analyze dynamic aspects of the adsorption mechanisms.
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