Sol-Gel Synthesis of Nanocrystalline Titanium Dioxide (TiO2) at Different pH Values and Temperatures.

Abstract

The applications and unique properties of TiO2 depend upon the method of synthesis. The sol-gel wet chemistry route provides control over particle size and morphology by using simple reaction conditions with simple experimental setup. TiO2 nanoparticles (3-13nm) were synthesized via sol-gel route by the reaction of titanium tetra chloride and water using HCl and NaOH as catalysts at room temperature. The precipitate obtained were washed, dried, and calcined for characterization using XRD, SEM, TEM, EDX and XRF for their elemental phase composition, structure, size, morphology and phase change. Change in synthesis parameters like temperature, pH etc. effect the particle size, morphology and phase composition. In alkaline conditions the particle size increase, as the samples synthesized in alkaline conditions need to be calcined at high temperatures to get crystalline phase, resulting in increased particle size. While in acidic conditions particle size decreased. The samples synthesized in acidic conditions become crystalline at very low temperatures and hence particle size remains very small (3-6 nm). It is observed that at low pH values (2-4) anatase TiO2 is formed with spherical morphology and maximum surface area. Surface area decreases with increase in crystallite size. But as the pH value increases, the nanoparticles grew in size and lost specific morphology. At low temperature (100ºC) the yield of anatase is low. At higher pH values (9-14) amorphous phase is obtained with irregular morphology. The samples calcined at lower temperatures (100ºC) showed mixed phases mostly anatase and brookite, as suggested in literature, but calcinations at relatively higher values (150- 250ºC) lead to formation of pure anatase. The XRD data showed very small crystallite size (3-13 nm) for obtained samples. The EDX and XRF results indicated presence of titanium and oxygen in appropriate ratios. The SEM and TEM results showed that the particles at low pH (2-4) values have spherical shape and at higher pH (5-14) values they show irregular morphology