Morphology Control of TiO2 Nanoparticle in Microemulsion and Its Photocatalytic Property

TiO2 nanoparticles with controlled morphology and high photoactivity were prepared using a microemulsion-mediated hydrothermal method in this study, and the particles were characterized by means of TEM, XRD, BET, and BJH analysis. As the hydrothermal temperature is elevated, mean pore diameter, crystalline size, and crystallinity of the particles increase gradually, while the surface area decreases significantly, and the morphology changes from a spherical into a rod-like shape. The morphology transition mechanism of the TiO2 crystal has been put forward based on a decrease in intensity of the microemulsion interface and an increase in collision efficiency between droplets with increasing the hydrothermal temperature. The photocatalytic activity of the TiO2 particles synthesized at 120–200 °C is relatively low due to their weak crystallinity, though they have high surface area of 146–225 m2/g and small crystalline size of 6–10 nm. However, the TiO2 samples prepared at 250–350 °C with low surface area (28–90 m2/g) exhibit high activity on the degradation of Rhodamine B (RhB), which is comparable or higher than that of the commercial P-25. The reason is ascribed to their high crystallinity that determines material activity in this temperature region. This study reveals that the effects of the surface area, crystallinity, and crystalline size on TiO2 activity are interdependent, and the balance between these factors is important for improving the photoactivity of the catalyst.