Spectroscopic characterization of the adsorption of rhodamine 3B in hectorite

The adsorption of the cationic dye rhodamine 3B in the clay hectorite is studied using electronic absorption and fluorescence emission spectroscopy. The results show the presence of various dye monomers, dimers, and higher aggregates and their interconversion subject to variations in loadings and stirring times. The growth of metachromasy related to generation of dye aggregates is interpreted with the help of exciton theory. Dimers are found to be J-type aggregates whose geometrical parameters are deduced. In some conditions the increase of stirring time leads to a loss of metachromasy that is related to the dye deaggregation. All the observations are interpreted in terms of stacking of clay platelets containing bound monomeric dye to form tactoids followed by dye migration within the large internal framework of the tactoids.