The synthesis and understanding of TiO₂ nano-polymorphic have been a subject of intense interests in the last few years. Unlike its bulk counterpart, the control of crystallite phases (anatase and rutile) in TiO₂ nanoparticles is poorly understood, as the surface Gibbs energy in the latter becomes a dominant component in the overall free energy. Control over the crystallite phases has important implications given its wide photocatalytic applications such as environmental remediation, self-cleaning and superhydrophilic surfaces, dye-sensitised solar cells and water splitting.

In this paper, we present a systematic investigation on the control of these phases in a one-step flame spray pyrolysis (FSP). By carefully controlling the rapid synthesis of these nanoparticles in a controlled atmosphere, we show for the first time, that it is possible to vary the anatase/rutile content (from 8 to 96% anatase) without affecting their crystallite size. This is discussed on the basis of flame combustion process which impacts directly the preferential crystallography of TiO₂ nanoparticles. The effect of flame synthesis on the photo-electronic properties of these nanoparticles was further studied, with larger electron diffusion coefficients and longer electron lifetime observed with increasing anatase content. These measurements have direct implications on their performance in various light harvesting applications.