Quaternary ammonium base groups were introduced onto surfaces Of SiO2-covered TiO2 particles (SiO2-TiO2). Oxidation of p-toluenesulfuric acid on the surface-modified TiO2 powders proceeded more efficiently than that on SiO2-covered TiO2 particles without surface modification. On the other hand, the photocatalytic activity of surface-modified SiO2-TiO2 for oxidation of 1,4-dimethylpyridinium iodide was much lower than that of pure SiO2-TiO2 In addition, no difference in photocatalytic activity for oxidation of toluene was observed between surface-modified SiO2-TiO2 and pure SiO2-TiO2. The enhancement of the photocatalytic activity of surface-modified SiO2-TiO2 is due to electrostatic interaction between the substrate and functional groups introduced on SiO2-TiO2. (C) 2007 Elsevier B.V. All rights reserved.