SPECTROSCOPIC STUDY OF THE ADSORPT ION OF RHODAMINE 6G ON LAPONITE B FOR LOW LOADINGS

electronic absorption and emission spectroscopies. Fluorescence spectra suggest hat 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, o 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. Since the first half of this century, many scientific areas such as soil science, colloid science, petro-leum technology, etc. have been interested in the properties of clay-organic systems (Dixon & Weed, 1977; Theng, 1974; Newman, 1987). Nowadays, the interaction between organic matter and clay minerals is an important ool in heterogeneous catalysis (Dale Ortego et al., 1991; Laszto, 1991), in decontamination (Srinivasan & Fogler, 1990), and in agriculture (Margulies et al.