Highly controlled crystallite size and crystallinity of pure and iron-doped anatase-TiO 2 nanocrystals by continuous flow supercritical synthesis

High purity anatase titanium dioxide (TiO 2 ) and iron (Fe)-doped TiO 2 nanocrystals were prepared by a continuous flow synthesis method using isopropanol-water mixtures as solvent in supercritical or near-critical conditions. The method allows complete control of size (5–20 nm) and crystallinity (10–100%) of the nanoparticles and provides quick synthesis with a residence time of ∼10 s that can be scaled up to commercial production. It is found that the average crystallite size can be easily controlled by adjusting the ratio between isopropanol and water in the solvent, whereas the crystallinity is mainly controlled by the reaction temperature. As-prepared Fe-doped TiO 2 nanoparticles appear to be single phase, but Fe 3+ ions most likely do not occupy the Ti 4+ sites in the anatase TiO 2 crystal structure.