Synthesis and characterization of nanostructured TiO2 with reverse Micelle technique and modified sol-gel method

Abstract

Nanostructured Titanium dioxide can be synthesized with different morphologies by modifying synthesis parameters. The sol-gel and reverse micelle methods of synthesizing TiO2 are studied in this dissertation. The as synthesized nanosized titanium dioxide samples are then investigated for magnetic and photocatalytic properties. Spherical titanium particles were synthesized with a modified sol-gel method. The concentration of titanium isopropoxide in ethylene glycol and the concentration of water in acetone both varied for the purpose of controlling the particle size in a wider range. With the addition of ice bath during the reaction procedure, relatively smaller particles with size of around 120nm were synthesized, compared to the prevalent size of around 250nm without the utilization of ice bath. Particles collected after annealing were found out to be agglomerations of smaller particles with the size around 15nm. The mechanism of the reverse micelle system for synthesizing titanium dioxide was studied in this dissertation. It was proven that not only the Wo ratio which is [H2O]/ [AOT] would affect the reaction degree but also the mixing sequences of reverse micelle solution and diluted titanium isopropoxide (TTIP) strongly influenced the hydrolytic process of TTIP. The predominance of either polymerization or hydrolysis determined the final appearances of the samples after reaction to be either gel or colloidal suspension with precipitations while Wo and R ratio determined the reaction rates. Differences between normal sol-gel method and reverse micelle system were also studied. It was found out that the existence of micelles formed by surfactant advanced hydrolysis by increasing the local concentration of water and also stabilized the products by obstructing the interactions between titanium intermediates. Cobalt doped titanium dioxide were synthesized both with the addition of ammonia and citric acid. Ammonia accelerated the hydrolytic process while citric acid obstructed the hydrolysis. The particle size of samples synthesized with ammonia varied from 10 to 27 nm with the change of WO ratio. Cobalt was doped into TiO2, substituting Ti4+ atoms in the anatase structure. Samples were characterized to be ferromagnetic which was determined to be intrinsic other than due to cobalt metallic clusters or second phase.