A Method for Fabrication of Pyramid-Shaped TiO2 Nanoparticles with a High {001} Facet Percentage

A new method is demonstrated for fabricating TiO2 nanoparticles. Transformation of TiO2 nanotubes to truncated pyramid-like-shaped nanoparticles with a high percentage of photocatalytically active {001} facets has been observed in titanium dioxide (TiO2) ordered nanotube arrays after thermal annealing in ambient fluorine. It was found that the nanotube-nanoparticle transformation resulted from catalytic reaction of fluorine ions (F-) from the electrolyte residues in long nanotubes grown by anodization in ethylene glycol + NH4F electrolyte. This transformation occurs at annealing conditions when evaporation of electrolyte residues in nanotubes is slow enough to remain until 500 degrees C, when this transition starts. The size of the formed TiO2 nanoparticles depends on the fluorine concentration and can be controlled from 20 to 500 nm. The crystal properties of nanoparticle layers are superior compared to those of nanotube arrays. This work demonstrates a simple method for producing high-quality anatase TiO2 nanoparticles and nanoparticle-based electrodes with a high ratio of reactive {001} facets.