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

Abstract

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 80nm, were obtained by annealing the TiO2 powders at 700°C. The crystallite sizes of anatase phase TiO2 increases from 8 to 11nm and band gap energy ranges from 2.49 and 3.26eV, 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 339nm, 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 385nm with the change in the rate of hydrolysis. TiO2 nanoparticles synthesized at slow hydrolysis rate (6ml 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.