The effect of rate of hydrolysis on structural and optical properties of the TiO2 nanoparticles prepared by a sol–gel method

• In this paper, we provide new insights on the influence of the rate of hydrolysis on the overall material properties of TiO2.
• This was achieved by controlling the molar ratio of H2O and annealing temperature on the crystalline structure and optical properties of TiO2 nanoparticles.
• The anatase to rutile percentage decreases when temperatures greater than 500 oC and evaluated from intensity of (101) and (110), respectively.

The nanocrystalline TiO2 powders with different crystallinity and phase structures were obtained by controlling hydrolysis rate and annealing temperature. Rutile phase TiO2 nanoparticles with crystallite sizes of about 80 nm, were obtained by annealing the TiO2 powders at 700 °C. The crystallite sizes of anatase phase TiO2 increases from 8 to 11 nm and band gap energy ranges from 2.49 and 3.26 eV, calculated using XRD pattern and UV–vis reflectance spectra, respectively. In agreement with change of the TiO2 band gap after different rate of hydrolysis the PL emission peak in the UV region shift slightly from 335 to 339 nm, which corresponds to the direct recombination between electrons in the conduction band and holes in the valence band. The defect related emission shifted from 376 to 385 nm with the change in the rate of hydrolysis. TiO2 nanoparticles synthesized at slow hydrolysis rate (6 ml of H2O) shows the attainment of best luminescence and maximum reflectance in the visible range. Therefore, these TiO2 nanoparticles can also be employed as coating material to develop reflectors with maximum diffuse reflectance.