Polymorphism of nanocrystalline TiO 2 prepared in a stagnation flame: formation of the TiO 2 -II phase

• Published in: Chemical science (Cambridge) 2019-02, Vol.10 (5), p.1342-1350
• Main Authors: Manuputty, Manoel Y, Dreyer, Jochen A H, Sheng, Yuan, Bringley, Eric J, Botero, Maria L, Akroyd, Jethro, Kraft, Markus
• Format: Article
• Language: English
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/C8SC02969E

A metastable "high-pressure" phase known as α-PbO -type TiO or TiO -II is prepared a single-step synthesis using a laminar premixed stagnation flame. Three other TiO polymorphs, namely anatase, rutile and TiO -B phases, can also be obtained by tuning the oxygen/fuel ratio. TiO -II is observed as a mixture with rutile under oxygen-lean flame conditions. To the best of our knowledge, this is the first time that this phase has been identified in flame-synthesised TiO . The formation of TiO -II in an atmospheric pressure flame cannot be explained thermodynamically and is hypothesised to be kinetically driven through the oxidation and solid-state transformation of a sub-oxide TiO intermediate. In this scenario, rutile is nucleated from the metastable TiO -II phase instead of directly from a molten/amorphous state. Mixtures containing three-phase heterojunctions of anatase, rutile, and TiO -II nanoparticles as prepared here in slightly oxygen-lean flames might be important in photocatalysis due to enhanced electron-hole separation.