The adsorption of methylene blue onto aluminum-containing mesoporous silica films was investigated. The mesoporous silica films were synthesized by rapid solvent evaporation method using tetramethoxysilane, aluminum tri(s-butoxide), and trimethyloctadecylammonium chloride as a silica source, alumina source and supramolecular template, respectively. Methylene blue was adsorbed effectively on the mesoporous silica films from solutions. The adsorbed amount increased with the increase in the aluminum content of the films, indicating that the added aluminum generated the adsorption sites (probably acidic sites) for methylene blue adsorption. The mesopore surface is not strongly acidic because the protonation of methylene blue did not occur. Adsorbed methylene blue exists as monomers in the mesopore. The dehydration of the films resulted in the aggregation of methylene blue, as evidenced by the visible absorption spectra.
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