Encapsulation of methyl red pH-indicator into a sol-gel matrix

Encapsulation of methyl red pH indicator into transparent monolithic silica matrices was made via the acid-catalyzed sol-gel reaction of tetraethylorthosilicate and methyl red indicator. The immobilized methyl red shows behavior similar to its solution counterpart. It retains its structure during the sol-gel reactions in terms of response to pH. Polarized light microscopy and the surface morphology indicated that methyl red molecules are strongly interacted within the host silica network.