Superparamagnetic high-magnetization composite microspheres with Fe3O4@SiO2 core and highly crystallized mesoporous TiO2 shell

We demonstrate a novel synthesis of sandwich structured superparamagnetic mesoporous microspheres with a silica-coated magnetite core and mesoporous titania shell using a block-copolymer-templating approach. The synthesis process is simple and facile, in which uniform magnetite particles were coated with silica through classical Stöber method. And then, a mesostructured P123/TiO2 composite was deposited on the silica-coated magnetite core by using Pluronic P123 block-copolymer as a template and tetrabutyl titanate (TBOT) as a precursor in ethanol aqueous solution. After calcination at 400 °C, the superparamagnetic microspheres with crystallized mesoporous titania shell were obtained. The sandwich structures of the obtained composite microspheres have been confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The TEM and SEM images show that the microspheres possess a uniform diameter of ∼420 nm and a homogeneous mesoporous shell of ∼40 nm. The XRD indicates that mesoporous shell is highly crystallized anatase titania. The obtained microspheres possess tunable specific surface areas of 50–100 m2/g, and controlled large mesopore sizes of 3.7–5.0 nm. Furthermore, the resulting superparamagnetic microspheres with a high saturation magnetization value of ∼34 emu/g could be enriched completely within 10 s under the application of a 0.2 T magnet.