Fe 3 O 4 -TiO 2 : Gd nanoparticles with enhanced photocatalytic activity and magnetic recyclability

In this study, photocatalytic Fe3O4-TiO2: Gd berry-like pseudo-core-shell (BL-PCS) nanoparticles with various Gd doping content for wastewater treatment were prepared. Their characteristics were evaluated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), X-ray photoelectron spectroscopy (XPS). The results show that Gd3+ ions are incorporated in the TiO2 lattice. A secondary phase of FeTiO3 was observed for undoped and low Gd doping level, phase which is no longer present for high doping content. By TEM and XPS depth profile analysis it was showed that a BL-PCS structure is formed. All the samples have superparamagnetic behavior. The optimum concentration of Gd dopant which assures the best photocatalytic performance on the RhB degradation under visible light irradiation was obtained. The photocatalytic degradation was examined by varying the operational parameters such as: catalyst amount and irradiation time. The photocatalyst can be easily separated from solution due to its magnetic component and presents a good stability with a minor loss of efficiency after 4 repeated cycles. According to the analysis of the reaction intermediates and final products, a mechanism of photodegradation was proposed. Additionally, electron paramagnetic resonance (EPR) study on the ability of Fe3O4-TiO2: Gd to generate reactive oxygen species was conducted and shows that hydroxyl radical and superoxide anion radical are generated under light irradiation, radicals which are involved in the photocatalytic process.