Controllable Microemulsion Synthesis of Hybrid TiO2–SiO2 Hollow Spheres and Au-Doped Hollow Spheres with Enhanced Photocatalytic Activity

Hollow structures in TiO2 materials can enhance the photocatalytic properties by reducing the diffusion length and improving the accessibility of active sites for the reactants. However, existing approaches for preparing hollow TiO2 materials have 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 maintaining the small grain size in calcinated TiO2, which is crucial for enhancing photocatalytic activity. Herein, a simple, effective method is proposed that not only enables the preparation of hybrid TiO2-SiO2 hollow spheres without the template fabrication and removal process via microemulsion technology but also achieves both high crystallization and a small grain size in calcinated TiO2 at once through the calcination of amorphous TiO2 with organosilane at a high temperature of 850 °C. The prepared TiO2-SiO2 hollow spheres with tunable sizes demonstrate high photocatalytic activity with a maximum k value of 133.74 × 10-3 min-1, which is superior to commercial photocatalyst P25 (k = 114.97 × 10-3 min-1). In addition, Au can be doped in the hybrid TiO2-SiO2 shell to gain Au-doped hollow spheres that show a high k value of up to 694.14 × 10-3 min-1, which is 6 times larger than that of P25 and much better than that reported in the literature. This study not only provides an effective approach to stabilize and tune the grain growth of the TiO2 photocatalyst during calcination but also enables the simple preparation of hollow TiO2-based materials with controllable hollow nanostructures.