Adsorption of rhodamine 3B dye on saponite colloidal particles in aqueous suspensions

Absorption and fluorescence spectroscopies were used to study the adsorption of Rhodamine 3B (R3B) dye on Saponite (Sap) particles in aqueous suspensions. Fluorescence data confirmed that the R3B monomer can be adsorbed in the interlayer space and at the water/clay interface of the Sap tactoids. From the evolution of the fluorescence band with the loading and the aging, it was concluded that the internally adsorbed R3B molecules were obtained by the migration of externally adsorbed species. The aggregation of the dye at the clay surfaces was studied by the metachromasy observed in the R3B absorption spectrum, and head-to-tail R3B dimers and trimers were identified. The molecular arrangement for the head-to-tail J-type R3B allows the incorporation of more monomeric units to reach trimers (and higher aggregates), even in the restricted interlayer space of Sap tactoids.