Simple Procedure of Making Room Temperature Mesoporous TiO 2 Films with High Purity and Enhanced Photocatalytic Activity

A simple and benign procedure was developed to synthesize room-temperature titania (TiO₂) films consisting of nanoparticles. TiO₂ nanoparticles were synthesized using a sol-gel method employing the controlled hydrolysis and condensation reactions of titanium isopropoxide in the inner aqueous phase of reverse micellar solution of amphiphilic bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT). The organic–inorganic TiO₂ composite nanoparticles were deposited on glass substrates by dip coating, and all the organics including AOT in the sol-gel network were drifted with pure water instead of thermal treatment. Pure TiO₂ films consisting of nanoparticles were formed with a high surface area of 547 m²/g and a pore volume of 0.486 cm³/g. The thickness of the films was found to be dependent on AOT concentration and the particular time when the substrates were dipped in the sol as the polycondensation reaction was still in progress. The structural properties of the films were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffractometry, and porosimetry. The photocatalytic activity of the films dried at 150°C and calcined at 500°C was evaluated for the decomposition of methylene blue dye in water, and it was compared with that of immobilized Degussa P25 powder in films. The photocatalytic activity of the TiO₂ films synthesized using this method was significantly higher than that of P25 TiO₂ film. The reason for the high photocatalytic activity of the TiO₂ films is most probably due to the high surface area (in the range of 497 m²/g at 150 °C to 87 m²/g at 500°C), small crystallite size (less than 10 nm), high purity, and good anatase crystallinity of the TiO₂ material of the film.