Abstract

Phase-pure anatase TiO₂ nanocrystallites ranging from 2 to 10 nm in size were synthesized directly from a TiCl₄ aqueous solution using citric acid as an additive. Citric acid was found to play a decisive role in stabilizing the TiCl₄ aqueous solution, leading to the selective formation of the anatase TiO₂ nanocrystallites in hydrothermal autoclaving. On the other hand, hydrothermal autoclaving of the rutile TiO₂ embryos prepared by room-temperature peptization of the TiCl₄ aqueous solution gave rod-like rutile TiO₂ nanocrystallites (14–17 × 22–33 nm) under neutral conditions. The presence of KCl or NaCl enhanced the crystal growth of the rutile embryos in the hydrothermal process.