Aggregation and stability of 1,1′-diethyl-4,4′-cyanine dye on the surface of layered silicates with different charge densities

The aggregation and decomposition of 1,1′-diethyl-4,4′-cyanine dye (DEC) in dispersed layered silicates were studied using ultraviolet–visible (UV–VIS) spectroscopy. Series of reduced-charge montmorillonites (RCMs) and di- and trioctahedral smectites were used as silicate materials. DEC, unstable in aqueous solutions, was partially stabilized in the dispersions with layered silicates. The layer charge density significantly affected the spectral bleaching of the dye. Silicates with very low charge density suppressed dye aggregation only partially. The presence of layered silicates with moderate charge density led to dye aggregation, which stabilized the dye against decomposition. In contrast, layered silicates with very high charge densities induced very fast and irreversible decomposition of the DEC. In general, the extent of DEC decomposition was proportional to the charge density magnitude. The presence of the surfactant Triton X-100, which stabilizes the DEC in aqueous solutions, did not greatly affect dye spectral bleaching in silicate dispersions. The phenomenon of DEC bleaching and its relationship with the charge density can be used as a simple method for estimating the surface density of layered silicates and possibly other similar materials.