SPECTROSCOPIC STUDY OF THE ADSORPTION OF RHODAMINE-6G ON LAPONITE-B FOR LOW LOADINGS

The adsorption of Rhodamine 6G in aqueous suspension on Laponite B was investigated by electronic absorption and emission spectroscopies. Fl uorescence spectra suggest that the monomer is adsorbed at two differe nt surfaces, the external and the internal. A monomer is intercalated in the interlamellar space at low loading of dye (<3% CEC), whereas th e monomeric state of the dye seems to be at the solid-aqueous interfac e in suspensions with high loading (>12% CEC). The metachromatic effec t observed in the absorption spectra, for the loading interval between 1% and 15% CEC of Laponite B, is attributed to the dimerization of th e dye, which seems, from X-ray diffraction measurements, to be formed at the clay interlayer. The formation constant and the absorption spec trum of the aggregate were obtained and the dimer was structurally cha racterized by applying the Exciton Theory. The observed fluorescence q uenching for loadings lower than 15% CEC is attributed to energy trans fer from monomer to the dimer, which obeys the Perrin model.