An array of highly oriented anatase nanoparticles was successfully prepared from NH₄TiOF₃ with the assistance of polyetheleneglycol-400 at 450 °C. The study showed the stability of obtained layered TiO₂-anatase close to 1200 °C. This research confirmed for the first time that the transition of mesocrystalline anatase to the rutile phase occurs between 1000 °C and 1200 °C, which is more than 400 °C higher than the transition of bulk TiO₂ due to the used precursor. A small quantity of K-phase nanowhiskers, which issued after 800 °C in the composite based on TiO₂, stimulated a fourfold increase in photocatalytic performance. This study offers a new approach to the construction and preparation of effective nanocrystalline photocatalyst.