Stabilization of a hydrophobic natural dye by intercalation into organo-montmorillonite

The stability of the naturally occurring annatto dye against irradiation with visible light was enhanced by intercalation into octyl trimethylammonium and dodecyl trimethylammonium montmorillonite. The intercalated dye exhibited improved light fastness. The effect of the stability enhancement was more distinct with dodecyl trimethylammonium montmorillonite. The reason of the improvement was proved to be the hindrance from the contact with the atmospheric oxygen because the dye molecules were incorporated in the interlayer space. The amount of the adsorbed dye could be increased more than ten times when an aqueous ethanolic solution was used instead of pure ethanol as solvent in the adsorption process.

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► Hydrophobic annatto dye was intercalated in alkyl trimethylammonium montmorillonite.
► The intercalated annatto dye showed enhanced stability against visible light.
► Using ethanol–water mixtures in the adsorption process increased the dye adsorbed.