Controlled nanostructuring of TiO2 nanoparticles: a sol–gel approach

The ever increasing interest in titanium oxide (titania) is motivated by its applications in solar cells, biomaterials and photo-catalytic activities. Nanocrystalline titania is preferred in these applications due to chemical stability, mechanical hardness, high refractive index and excellent transmission in the visible region. Titania exists in three different crystallographic phases i.e. anatase, rutile and brookite, amongst which brookite is the most difficult to synthesize. Anatase and rutile crystallize in tetragonal phase whereas brookite has orthorhombic phase. In the present work, titania nanoparticles are synthesized following sol–gel approach. TiCl4 is used as precursor and ammonia as a gelation agent. pH of the sol is varied in the range of 1–11. Nanostructures and hollow core titania nanoparticles with mean diameter of 120 and 70 nm respectively have been synthesized without the use of any hard/soft template. At pH 1 the nanoparticles show amorphous behavior whereas increasing the pH induces crystallinity in nanoparticles. The presence of (020), (202) and (321) confirms the formation of pure brookite phase at a low temperature of 60 °C. The presence of absorption bands in fourier transform infrared spectroscopy in the range of 450–700 cm−1 correspond to infrared active mode of Ti–O–Ti stretching indicating the formation of titania. Detailed Spectroscopic analyses indicate that these nanoparticles are highly transmitting in the visible and infrared region with band gap in the range of 2.96–3.03 eV. Cauchy Model used for fitting the experimental spectroscopic data gives a high value of refractive index with low extinction coefficient.