[en] Full text: Methylene blue (MB), an organic blue dye, is a typical textile pollutant. Therefore, degradation of MB is of great importance in environmental issues. In the present work we show that irradiation with UV light of mesoporous silicates MCM-41 and SBA-15 grafted with the red dye 3,4,9,10-perylenediimide (PDI) results in the photobleaching of MB in aqueous solution. The materials were prepared by post-synthesis modification of MCM-41 and SBA-15. The mesoporous silicates were first reacted with 3-aminopropyltriethoxysilane in toluene, resulting in materials with the mesopores functionalized with amino groups (MCM-41-NH₂ and SBA-15-NH₂ ). Reaction of the resulting materials with 3,4,9,10-perylenetetracarboxylic dianhydride lead to PDI covalently grafted into the mesopores. The resulting powdered materials, which displayed the red color characteristic of the PDI dyes, were designated MCM-41-PDI and SBA-15-PDI. They were characterized by infrared, UV-visible (diffuse reflectance mode) and fluorescence spectroscopies, which confirmed the presence of the PDI dye in the materials. Further characterization was done by thermogravimetric analysis (TGA), small angle x-ray scattering and nitrogen adsorption isotherms. When suspensions of MCM-41-PDI and SBA-15-PDI in aqueous solutions of MB were irradiated with a mercury lamp (350 - 500 nm bandpass filter), bleaching of MB was observed, indicating the photodegradation of MB. The proposed mechanism involves reaction of photogenerated PDI radicals with oxygen, leading to the formation of singlet oxygen, which then attacks the MB molecule. The results show that the system has a great potential in the remediation of water polluted by textile dyes. (author)