Titanium oxide nanoparticles precipitated from low-temperature aqueous solutions: I. Nucleation, growth, and aggregation

Titanium oxide (TiO₂) thin films can be prepared by controlled hydrolysis of a titanium tetrachloride (TiCl₄) precursor in an aqueous solution at temperatures below 100°C. As part of an effort to understand the formation of such TiO₂ films, the kinetics of the nucleation, growth, and aggregation of TiO₂ nanoparticles in aqueous solutions of TiCl₄ were studied using dynamic light scattering and a transmission electron microscope (TEM). A higher degree of supersaturation, produced by a higher solution temperature, a higher concentration of TiCl ₄, or a higher pH, results in a shorter nucleation induction time, a faster initial growth/aggregation rate, and a larger aggregate size. The interfacial energy of TiO₂ nanoparticles was found to be 0.072 J/m² from the homogeneous nucleation theory. Further investigations by a high-resolution scanning electron microscope (SEM) and TEM for the as-deposited films showed the structure hierarchy organized from nanocrystalline particles precipitated in the supersaturated solution. As a result, the effect of solution conditions on the nucleation, growth, and aggregation of TiO ₂ nanoparticles can provide useful guidance for tailoring of microstructures of the TiO₂ films.