Fabrication of pseudo-crystal nanostructures of TiO ₂ particles under UV-irradiation

Colloidal titanium dioxide (TiO ₂) suspensions were synthesized by hydrolysis of titanium isopropox-ide in the presence of acetic acid. When TiO ₂ colloids were subjected to bandgap excitation (ultraviolet [UV] irradiation), the colloidal solution exhibited yellow coloration, leading to the trapping of holes and electrons on the particle surfaces. The absorption spectra indicated a distinct absorption band in the UV and visible region. Dried-drop film of the UV-irradiated TiO ₂ suspension on the mica surface was characterized by scanning electron microscopy (SEM). SEM images showed that "crystal-like" network structures of TiO ₂ nanoparticles had formed dramatically on the solid surface. The resulting networks ranged in size from 100 nm to 500 nm and had crystal-growth patterns, while also having almost similar rectangular shapes. It seems that the individual particles, with electron or hole scavengers such as oxygen in ambient conditions, make contact with a number of neighbors, thereby forming self-assembled three-dimensional nanoparticle-based pseudo-crystalline structures.