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. Fluorescence spectra suggest that the monomer is adsorbed at two different surfaces, the external and the internal. A monomer is intercalated in the interlamellar space at low loading of dye (<3% CEC), whereas the monomeric state of the dye seems to be at the solid-aqueous interface in suspensions with high loading (>12% CEC). The metachromatic effect observed in the absorption spectra, for the loading interval between 1% and 15% CEC of Laponite B, is attributed to the dimerization of the dye, which seems, from X-ray diffraction measurements, to be formed at the clay interlayer. The formation constant and the absorption spectrum of the aggregate were obtained and the dimer was structurally characterized by applying the Exciton Theory. The observed fluorescence quenching for loadings lower than 15% CEC is attributed to energy transfer from monomer to the dimer, which obeys the Perrin model.