Interaction of methylene blue (MB) with reduced charge
Li−montmorillonites (RCM) in the aqueous
suspensions was investigated using visible absorption spectroscopy.
Dye cation agglomeration and protonation
at the clay surface depended very sensitively on layer charge density.
With increasing layer charge reduction,
the content of agglomerates of MB cations decreased in favor of
monomers and the protonated form of MB.
Lower negative charge density on the clay basal surface induces a
greater distance between neighboring MB
cations sorbed at the clay surfaces, which suppresses dye
agglomeration. Since each form of MB absorbs
visible light at a different wavelength, different layer charge
densities induce different colors of the resulting
clay−dye suspension. Therefore, visible spectra of MB−smectite
suspensions may be a simple but extremely
sensitive method for the detection of layer charge density of
smectites.