Titanium oxide nanoparticles precipitated from low-temperature aqueous solutions: II. Thin-film formation and microstructure developments

We explored effects of the degree of supersaturation, which depends on solution concentration, pH, and temperature, on the development of microstructures of the TiO₂ thin films deposited from the controlled hydrolysis of TiCl₄ aqueous solutions. It was shown that, with precursor (TiCl₄) solution of low degree of supersaturation, a porous flower-like dendritic structure was synthesized, while a densely packed particulate nanostructure was obtained with that of high degree of supersaturation. The former morphology was attributed to the directional growth of TiO₂ crystals from the already-deposited films, whereas the latter to the bulk precipitated TiO₂ nanoparticles nucleated in the solution, followed by their attachment and self organization. By establishing the processing-microstructure relations, this study provided a means of generating a wide spectrum of reproducible TiO₂ microstructures using the low-temperature aqueous solution processing.