One-Step Synthesis of Anatase TiO₂ Nanoparticles Using a Nonmixing Continuous Flow Solvothermal Reactor

A nonmixing solvothermal flow reactor has been designed and commissioned to allow for precise control of residence time during synthesis of crystalline nanoparticles. Benchmarking of the reactor was performed against a conventional T-mixing flow reactor at 200, 250, 300, and 350 °C (P = 250 bar) by synthesizing phase-pure anatase TiO2 nanoparticles from an industrial-grade TiOSO4 precursor. Characterization was carried out using PXRD, TEM, UV–vis, and Raman spectroscopy revealing highly anisotropic particles with constant crystallite sizes of ∼10 nm in the (100) basal plane and decreasing sizes along the [001] direction with increasing temperatures (from ∼19 to ∼14 nm). A residence time study using the nonmixing reactor confirmed that the crystallite size in the (100) plane is invariant to temperature (250–350 °C), residence time, and reactor design. At 350 °C, the crystallite size along [001] was stable at 14 nm, while at 250 °C, larger nanoparticles (16–19 nm) formed with increasing residence time. This study highlights the new reactor’s capability for controlled synthesis of anisotropic anatase nanoparticles and its easy optimization of synthesis parameters.