An external template-free route to uniform semiconducting hollow mesospheres and their use in photocatalysis

Solid amorphous TiO₂ mesospheres were synthesized by controlled hydrolysis of Ti-containing precursors. Subsequently, solid TiO₂ mesospheres were exploited as scaffolds and subjected to a one-step external template-free hydrothermal treatment, yielding intriguing hollow anatase TiO₂ mesospheres. The synthetic protocol was optimized by investigating the effect of buffer reagents and fluoride ions on the formation of hollow TiO₂ spheres. The diameter of hollow mesospheres, ranging from 308 to 760 nm, can be readily tailored by varying the precursor concentration. The average thickness of a shell composed of TiO₂ nanocrystals was approximately 40 nm with a mean crystal size of 12.4-20.0 nm. Such hollow TiO₂ mesospheres possessed a large surface area and were employed in photocatalytic degradation of methylene blue under UV irradiation. Interestingly, the synthetic conditions were found to exert a significant influence on the photocatalytic ability of hollow TiO₂ mesospheres. The correlation between the degradation ability of hollow TiO₂ mesospheres and the precursor concentration as well as the hydrothermal time was scrutinized. The optimal photocatalytic performance of hollow TiO₂ mesospheres was identified.