Simple route to prepare different core–shell structured silica-based microspheres

Different core-shell structured silica-titania (SiO₂-TiO₂) nanocomposites were successfully synthesised in two successive stages. In the first stage, the core was synthesised by preparing poly[oligo(ethylene glycol)monomethyl ether methacrylate] (POEOMA) on the modified surface of silica nanoparticles (SiO₂-POEOMA). In the second stage, the shell was formed by depositing or coating tetrabutyl titanate (TBT) with SiO₂-polymer to obtain cauliflower-like, cauliflower-pomegranate-like and pomegranate-like SiO₂-POEOMA-TiO₂ microspheres; the weight ratio of added SiO₂-POEOMA to TBT (1:0.146, 0.293 and 0.439) was then adjusted. Later, the polymer layer was removed to obtain the cauliflower-like, cauliflower-pomegranate-like and pomegranate-like core-shell structured SiO₂-TiO₂ microspheres (CMs, CPMs and PMs). X-ray diffraction results showed that the TiO₂ shell was a pure anatase phase. SiO₂-TiO₂ microspheres were also characterised by N₂ adsorption-desorption; the results showed that a pore structure was found in the porous shell. Extensive porosity was generated in the shell because POEOMA was used as a template and pore-forming agent; the structure of CMs, CPMs and PMs remained almost unchanged. These results also showed that pore volumes and specific surface areas of the final products derived from N₂ sorption decreased as the content of TBT increased. PMs with the highest content of TiO₂ showed the most efficient photocatalytic activity.