Behavior of immobilized Alizarin Red S into sol–gel matrix as pH sensor

The preparation of transparent monolithic silica doping with Alizarin Red S was carried out by acid catalyzed sol–gel reaction of tetraethylorthosilicate (TEOS) in the presence of Alizarin Red S. The immobilized Alizarin Red S pH indicator shows similar behavior as its solution counterpart. The UV/VIS spectra indicate that the Alizarin Red S retains its structure during the sol–gel reactions in terms of response to pH. Therefore, the Alizarin Red S can be regarded as uniformly distributed in the sol–gel matrix. Also, addition of the dye plus SDS into the sol–gel matrix modifies the structure of the net work and makes it more homogeneous and increases the surface area. These characteristics were justified by using polarized microscope technique.