Anatase nanocrystals coating on silica-coated magnetite: Role of polyacrylic acid treatment and its photocatalytic properties

Magnetic photocatalysts composed of titania catalyst and magnetic support are of great interest due to their easy recovery and recyclability by magnetic separation. By using layer-by-layer chemical technique, a core-shell structure of Fe ₃O ₄/SiO ₂/TiO ₂ composite was prepared by coating magnetite core particles with silica and photoactive titania. An amorphous silica shell was coated on magnetite nanoparticles firstly to form SiO ₂/TiO ₂ composite. In the next step of synthesis, we found that the polyacrylic acid treatment on silica surface played an important role in the coating of the anatase nanoparticles: no any anatase nanoparticles could be attached to the silica surface without the polyacrylic acid treatment. The structure and morphology of the as-prepared composites were characterized by X-ray diffraction, infrared spectroscopic analysis and transmission electron microscopy. Experimental results proved that the treatment of silica surface with polyacrylic acid contributed to the formation of covalent bond between titania nanocrystals and silica. The as-prepared photocatalyst presented good photocatalytic activities in the degradation of rhodamine B under UV illusion, while it could be easily separated by external magnetic field.