Leaching of the anthraquinone dye Solvent Blue 59 incorporated into organically modified silica xerogels

The effects of preparation method and precursor composition on the leaching behavior of the anthraquinone dye Solvent Blue 59 incorporated into silica based xerogels have been studied. Xerogels were prepared under acidic cond itions from mixtures of 20 mol% of organically modified silicon alkoxides, R'-Si(OR)(3), in Si(OR)(4) (R = methyl or ethyl, R' = methyl, vinyl, phenyl ). The dye was added at the beginning of the sol-gel reaction. The reaction was carried out by either hydrolysis under acidic conditions or acidolysis by formic acid. The dye incorporated was leached with refluxing ethanol us ing a Soxhlet extraction procedure to simulate the long-term stability of t he samples prepared. With increasing size of organic substituent (methyl < vinyl < phenyl), the amount of dye leached decreases. Results from nitrogen adsorption experiments show that all samples characterized have about the same average pore diameter, but they differ in total pore volume and BET su rface area. With increasing size of the organic residue, the pore volume de creases by an order of magnitude. Therefore, it is concluded that the micro structure of the xerogels prepared determines the retention behavior of dye s incorporated during the sol-gel reaction.