Preparation of Nano-TiO₂ by a Surfactant-Free Microemulsion-Hydrothermal Method and Its Photocatalytic Activity

The TiO₂ nanoparticles with high photocatalytic activity were prepared by the surfactant-free microemulsion (SFME)-hydrothermal method at lower temperatures using oil-in-water SFME systems as templates. The phase diagram of the SFME ethyl acetate (EA)/propan-2-ol/water was determined by electrical conductivity and UV-visible spectroscopy. The synthesized TiO₂ nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, and N₂ adsorption-desorption techniques. They were all assigned to the anatase phase and showed type IV adsorption-desorption isotherms with type H2 hysteresis loops. As the EA content () of the SFME decreases, the Brunauer-Emmett-Teller (BET) specific surface area (S_BET) of the TiO₂ nanoparticles increases. This results in an increase in the photocatalytic activity of the TiO₂ nanoparticles. With an increase in temperature, the photocatalytic activity of the TiO₂ nanoparticles increases significantly, whereas the S_BET values decrease and the crystal size increases. Under the same conditions, the degradation rate of the TiO₂ prepared at 190 °C reaches 97%, which is significantly higher than that of Degussa P-25 (66%). This may be due to the use of the SFME system to synthesize the TiO₂ nanoparticles, which avoids the blocking effects of surfactant molecules on the active sites of the nanoparticles.