Study of the adsorption of organic molecules on clay colloids by means of a fluorescent probe

Viaene, Karel; Crutzen, M.; Kuniyma, B.; Schoonheydt, Robert A.; Schryver, F. C. De

doi:10.1007/bfb0114200

Cited by 5 publications

(1 citation statement)

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“…For [3-(1-pyrenyl)propyl]trimethylammonium, Viaene et al (1987Viaene et al ( , 1988 showed that the reorganization of the molecule over the surface occurred on a time scale of 500-1000 s. In the present case, spectral changes are observed on a time scale of days. This indicates that clay particle rearrangement is the major phenomenon.…”

Section: Discussionsupporting

confidence: 47%

Clay adsorbed dyes: methylene blue on Laponite

Schoonheydt¹,

Heughebaert²

1992

Clay miner.

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The adsorption of methylene blue (MB) from aqueous solution on Laponite (a synthetic 2:1 layer-silicate) exchanged with Na +, Cs + and tetraethylammonium ions has been studied. At low loadings the monomer form predominates, but as the loading increases dimers and trimers (or higher aggregates) are formed, the latter being the most important species when the loading is equal to, or larger than, the Na+-CEC. The distribution of the molecules over the surface is time-dependent due to changes in the aggregation of the clay particles. On Cs+-Laponite, and to a lesser extent on Na+-Laponite, a small amount of MB is protonated by cation-coordinated water molecules. In similar work where adsorption was from ethanolic solution, MB is adsorbed as monomers and dimers only at small loadings and precipitates on the surface of the clay aggregates at high Ioadings. These precipitates can be broken up by sonication.The adsorption (by ion exchange) of dyes such as methylene blue (MB) and proflavine (PF) on clays in aqueous suspension leads to a concentration of the dyes in a small volume around the clay particles. The effective concentration of the dyes in this surface region is much higher than in solution and the dye molecules aggregate. Dimers, trimers and higher aggregates are formed, each with their own spectroscopic signature (Cenens & Schoonheydt, 1988;Cenens & Schoonheydt, 1990;Yariv et al., 1990). The relative concentration of the various forms of the dyes on the surface depends on (1) the type of dye, (2) the solvent, (3) the clay, i.e., its particle size, the type of exchangeable cation, surface heterogeneity and all other factors which influence the dispersion of the clay.In our previous work (Cenens & Schoonheydt, 1988;Cenens & Schoonheydt, 1990) low loadings were investigated in order to obtain maximum spectral resolution and maximum stability of the aqueous clay suspensions. Two questions remain: (1) are the spectroscopic properties of adsorbed dyes time-dependent? If yes, is the time dependence due to reorganization of adsorbed molecules or to changes in the degree of aggregation of the clay particles? (2) What is the spectroscopic signature of adsorbed dyes in a less hydrophilic (or more organophilic) environment?In an attempt to obtain answers to these questions, we measured the absorption spectra of MB adsorbed on Laponite (LAP) at different loadings, including loadings exceeding the cation exchange capacity (CEC), in the presence of different exchangeable cations and with water and ethanol as solvents. EXPERIMENTAL Sample preparationLaponite B (Laporte Industries) in the Na+-form was transformed to the Cs +-and tetraethylammonium (TEA+)-forms by exchange in dialysis membranes with 0.1 M aqueous 9 1992 The Mineralogical Society

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Section: Discussionsupporting

confidence: 47%