TIME-DEPENDENT SPECTROPHOTOMETRIC STUDY OF THE INTERACTION OF BASIC-DYES WITH CLAYS .1. METHYLENE-BLUE AND NEUTRAL RED ON MONTMORRILLONITE AND HECTORITE

The variation with time of the electronic spectra of the basic dyes methylene blue and neutral red in the presence of montmorillonite and hectorite clays has been studied to obtain information about the time-dependent processes involved in these interactions. After being mixed, the dyes are immediately adsorbed on the external surface of the clay particles, as induced aggregates or as monomers. Depending on the structure, conformation, and counterions of the clays, a slower desorption process takes place, which tends to take dye monomers to the interlamelar region of the clay particles. An acid-base equilibrium is rapidly established for the monomers due to their interaction with acid sites present in this region. There is no need to postulate J-aggregates, interactions of the O-layer of the clays with monomers, or dimers in the interlamelar regions to explain the observed behavior.