Controllable Microemulsion Synthesis of Hybrid TiO2-SiO2HollowSpheres and Au-Doped Hollow Spheres with EnhancedPhotocatalytic Activity

Hollow structures in TiO2materials can enhancethe photocatalytic properties by reducing the diffusion length andimproving the accessibility of active sites for the reactants.However, existing approaches for preparing hollow TiO2materialshave two drawbacks that restrict their engineering applicability:first, a heavy reliance on templates to form a hollow structure,which makes the preparation laborious, complicated, and costly;second, difficult-to-achieve high crystallization while maintainingthe small grain size in calcinated TiO2, which is crucial forenhancing photocatalytic activity. Herein, a simple, effectivemethod is proposed that not only enables the preparation ofhybrid TiO2-SiO2hollow spheres without the template fabricationand removal process via microemulsion technology but also achieves both high crystallization and a small grain size in calcinatedTiO2at once through the calcination of amorphous TiO2with organosilane at a high temperature of 850 degrees C. The prepared TiO2-SiO2hollow spheres with tunable sizes demonstrate high photocatalytic activity with a maximumkvalue of 133.74x10-3min-1,which is superior to commercial photocatalyst P25 (k= 114.97x10-3min-1). In addition, Au can be doped in the hybrid TiO2-SiO2shell to gain Au-doped hollow spheres that show a highkvalue of up to 694.14x10-3min-1, which is 6 times larger than thatof P25 and much better than that reported in the literature. This study not only provides an effective approach to stabilize and tunethe grain growth of the TiO2photocatalyst during calcination but also enables the simple preparation of hollow TiO2-based materialswith controllable hollow nanostructures