Solvent-controlled deposition of titania on silica spheres for the preparation of SiO2@TiO2 core@shell nanoparticles with enhanced photocatalytic activity

Controlled synthesis of SiO2@TiO2 core@shell particles is important for effectively exploiting the unique properties associated with core@shell architecture and obtaining photocatalysts with enhanced photoactivity. Herein, we propose an alternative, simple and rational solvent-based synthetic strategy for the reproducible and controlled coating of anatase nanocrystals ((similar to)5 nm) over submicron SiO2 spheres. This strategy is based on the fact that titanium (IV) isopropoxide (TiP), the TiO2 precursor, exists in oligomeric (less reactive) and monomeric (more reactive) forms in ethanol-rich and isopropanol-rich solvent, respectively. The different reactivity of TiP in mixed solvents with varying ethanol/isopropanol ratio thus allows a precise control over the rate of titania deposition or TiO2 loading as well as the resultant particle morphology through simple manipulation of isopropanol/ethanol ratio of the solvent mixture used in the sol-gel process. Based on a detailed characterization of the samples using an array of complementary characterization techniques, a comprehensive discussion on the relationship between solvent composition, particle morphology and their photoactivity is presented. Photocatalytic dye degradation assays reveal that SiO2@TiO2 particles with uniform morphology obtained by solvent-controlled deposition show enhanced activity per mass unit of TiO2, thus confirming the importance of controlled deposition of titania for the design of efficient core@shell photocatalytic systems. The solvent-based synthetic strategy proposed here is facile, general and effective in controlling the structure and composition of the SiO2@TiO2 particles which, in turn, allows one to tune the photocatalytic properties and obtain core@TiO2 composite photocatalysts with improved photocatalytic activity.