Adsorption and degradation of the cationic dyes over Co doped amorphous mesoporous titania–silica catalyst under UV and visible light irradiation

Cobalt doped amorphous mesoporous titania–silica with Ti/Si mass ratio of 0.8 (Co–TiO₂–SiO₂) was synthesized and used for the photodegradation of six cationic dyes (gentian violet, methyl violet, methylene blue, fuchsin basic, safranine T, and Rhdamine B) under UV and visible light illumination. The catalyst was characterized by a combination of various physicochemical techniques, such as N₂ physisorption, diffuse reflectance UV–vis, X-ray diffraction, and FT-IR.Co–TiO₂–SiO₂ exhibited activity under UV light and had better activity under visible light when compared with that of Degussa P25 TiO₂. The activity of Co–TiO₂–SiO₂ was also compared with that of Co-MCM-41, Co doped mesoporous titania with a crystalline framework (Co–MTiO₂) and titania-loaded Co doped MCM-41 (TiO₂/Co-MCM-41) for the degradation of gentian violet under visible light irradiation. It was also found that the degradation rates of Co–TiO₂–SiO₂ for gentian violet, methyl violet, methylene blue, fuchsin basic and safranine T were greater in alkaline media than in acid and neutral media, while it did not exhibit any significant activity for the photodegradation of Rhdamine B in alkaline media or in acid media under visible light irradiation.