CoFe2O4@SiO2@TiO2 core-shell nanoparticles for photocatalytic water decontamination

Abstract

In the present work is reported, following a facile process, the synthesis of cobalt ferrite nanoparticles covered with a shell of SiO2, and then, covered with a shell of TiO₂. In the first step, cobalt ferrite nanoparticles were prepared by coprecipitation of Co⁺²and Fe ⁺²ions in basic medium, followed by a simple controlled oxidation process carried out by nitrate ions in basic medium with inert atmosphere at 95°C for 24h. In the second step, SiO₂ particles were deposited by heterogeneous nucleation onto the surface of the ferrite in alcohol medium by alkalinization of tetraethylortosilane solutions, finally, in the third step, the TiO₂shell film is deposited by using sol-gel technique. Characterization techniques were performed to determine the particle morphology and size distribution (Scanning electron microscopy), crystalline structure (X-ray diffraction). Results showed that cobalt ferrite nanoparticles can be obtained following this synthesis route without using surfactants as size drivers, which is a common reagent in nanoparticle preparation, giving a size distribution of 162 ± 30 nm and a polyhedral geometry. Also, it was observed that SiO₂ is homogeneously distributed onto the surface of the cobalt ferrite, and that TiO₂ shell films covered well, creating a catalyst that also presents magnetic response. This kind of catalyst nanomaterial, presents a magnetic response, and is a stable and environmentally safe, then could be separated easily from the aqueous medium at the end of the purification process by applying an external magnetic field.