Optimizing hydrothermal synthesis of titanium dioxide nanotubes: Doehlert method and desirability function approach

Design of experiments is a powerful planning technique that optimizes processes and reduces experimental variability. This research aims to optimize the hydrothermal synthesis of TiO₂ nanotubes with a high specific surface area (SSA). A 2² factorial design was applied to investigate the influence of temperature and time on nanotube formation, achieving SSA above 350 m² g⁻¹. A Doehlert design combining SSA with morphology reveals closely related responses and a defined maximum surface. Microscopy shows that nanotube formation is favored at lower temperatures and longer treatment times, with the optimal condition at 120 °C for 36 h. Higher temperatures yield cauliflower-like nanostructures and provide insight into how synthesis conditions affect the morphology and nanoparticle properties. XRD and Raman spectroscopy analysis revealed that, although the anatase phase played a vital role in nanotube formation, the materials exhibited a combination of crystalline phases, including the discovery of an unidentified phase.