A new class of photocatalysts that can be used for decontamination of aquatic environments from organic and chloroorganic contaminants is reported. The photocatalysts are comprised of homogeneous dispersion of TiO2 nanocrystals in organically modified SiO2. These composite materials were prepared by a two-step acid catalyzed sol-gel preparation protocol. The combination of the improved photocatalytic activity of homogeneous dispersion of segregated nanocrystalline TiO2 and the adsorption properties of organically modified silica increases the rate of decomposition of hydrophobic organic pollutants in aquatic environments. An additional advantage of these catalysts is their floating capability. This property provides a possibility of using them under solar illumination. The activity of the organically modified SiO2-TiO2 catalyst is compared with that of commercial nanocrystalline TiO2 and TiO2-SiO2 and TiO2 sol-gel derived xerogels, under solar light and UV lamp irradiation.