In this study, magnetically separable Fe3O4-SiO2-mesoTiO2 nanocomposite has been synthesized for photodegradation of Methylene Blue (MB) and Rhodamine B (RhB) cationic dyes which have complex aromatic structures and are difficult to degrade into harmless products. By XRD analysis, it was determined that the magnetite phase of Fe3O4 was protected after coating with SiO2 interlayer and mesoTiO2 shell, and the anatase phase of TiO2 was formed. According to the N2-adsorption/desorption and VSM results, Fe3O4-SiO2-mesoTiO2 nanocomposite has a surface area of 197.8 m2/g, pore volume of 0.34 cm3/g and a pore size of 3.4 nm and has 3.8 emu/g saturation magnetization and negligible remnant magnetization and coercivity, which indicates its mesoporous and superparamagnetic character. The adsorption ability of RhB (16.86%) is lower than MB (23.32%), nevertheless, the photodegradation activity of RhB (99.06%) is higher than that of MB (97.52%). Photodegradation kinetics follows the pseudo-first order and the rate constants of photocatalytic reactions were calculated as 0.0422 and 0.0719 min−1 for MB and RhB, respectively. While the lower adsorption feature of RhB was resulted from steric hindrance, the higher photodegradation rate was explained by more radical scavenging effect. MB prefers to face the photocatalyst surface, whereas RhB prefers to focus on the aqueous phase, and based on scavenge results, RhB is more likely to encounter photoactive species (H2O2, h+ and ·O2−) than that of MB with ·O2− being the dominant active species. The synthesized Fe3O4-SiO2-mesoTiO2 photocatalyst could be reused three times with negligible photocatalytic loss in the photodegradation of both dyes.
