Influence of the layer charge density of smectites on the interaction with methylene blue

Six Na-saturated smectites were isolated from bentonites of various deposits. Their H-forms were prepared using H–OH–H resins. The interaction of methylene blue (MB) (0.05 mmol g-1) with Na-saturated untreated and H-autotransformed clay samples was investigated by the VIS spectroscopy of their dispersions. The spectra provided information about the formation of protonated dye cations, dimers, and higher agglomerates on the clay surface. The amounts of various dye forms were compared with the distributions of negative layer charge of the used clays, obtained by the alkylammonium method. Formation of MB dimers and higher agglomerates reflected sensitively the layer charge density of the smectites. MB cations formed predominantly higher agglomerates at the surface of those smectites with high charge density. Suppressed dye agglomeration was observed for the samples of lower layer charge density and was caused by greater distances between the adsorbed MB cations. Due to the high sensitivity of MB agglomeration on the layer charge and the simplicity of the method, MB–clay interaction can potentially be utilized for the layer charge characterization of smectites.