Adsorption of a Styrylpyridinium Dye on Silica and Modified Silica Surfaces from Some Binary Solvent Mixtures-Should We Call It Solvent-Induced Preferential Adsorption?

A styrylpyridinium dye with a dodecyl cleft and a N,N-dimethyl amino substituent (C-12-NMe2) has been adsorbed on unmodified silica (UnMS), graphene oxide-modified silica (GOMS), and sodium dodecyl sulfate-modified silica (SDSMS) surfaces from three binary solvent mixtures: EtOH-dioxane, EtOH-toluene, and dioxane-toluene. The extent of adsorption is observed to be changing remarkably with the percent of cosolvent in the binary mixtures. Besides, the overall polarity of the mixtures has a profound effect on the adsorption process. The saturation time of adsorption, effect of temperature, and thermodynamics and kinetics of adsorption lead to an impression of preferential adsorption, which may be acting as a reverse process of well-known preferential solvation. Logical explanations and suitable models have been extended to record such a development, which, in fact, looks like a preferential adsorption phenomenon from binary solvent mixtures.