Negatively Charged Clay Particles Influence Spectroscopic Properties of Anionic Organic Dyes in Aqueous Colloids

Aqueous colloids of smectite-type clays have been employed as heterogeneous media for photofunctional dyes, where negatively charged clay particles adsorb cationic and polar dye molecules through electrostatic immobilization. However, we herein demonstrate impacts of negatively charged hectorite clay particles on the spectroscopic behavior of anionic dyes. Anionic Eosin B dissolved in aqueous clay colloids exhibits spectroscopic behavior reflecting the coexisting clay particles. The absorption and fluorescence maxima are red-shifted and the fluorescence is intensified with increasing clay concentration. Removal of the clay particles by ultracentrifugation recovers the spectra of aqueous solution, indicating attractive interactions between the anionic dye molecules and negatively charged clay particles. Moreover, the spectroscopic impacts of the clay particles vary on both the dye species and clay mineral species; spectroscopic properties of Rose Bengal are not greatly affected by the clay particles, and synthetic saponite more influences the absorption and emission spectra of the dyes. Negatively charged colloidal particles of smectite clay impact the spectroscopic behavior of anionic dyes. Anionic Eosin B dissolved in clay colloids exhibits absorption and fluorescence maxima red-shifted from the aqueous solution, and the fluorescence is intensified with increasing clay concentration.