Influence of Electrolyte Composition on Morphology of Titanium Dioxide Films Obtained by Titanium Anodization in a Circulated Mixing Cell

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Abstract—Highly ordered films from individual TiO₂ nanotubes (NTs) with controlled geometric characteristics were obtained by potentiostatic anodization of titanium in an electrochemical cell with flow-through circulation of the solution and a cooling system for it placed outside the cell at a temperature of 25 ± 0.5°C. The study shows how a wide concentration range of water (0–15%) and ammonium fluoride (0.1–2.0%) in ethylene glycol (EG) influences the morphology and composition of the obtained TiO₂ NTs. It was found that the most ordered structure of TiO₂ NTs forms when the water content in the anodizing solution is 0.5–4.0% and the proportion of NTs in the hexagonal coordination reaches 75%. It is shown that fluoride ion and water concentration in EG do not affect the chemical state and concentration of elements in the resulting nanostructures. X-ray photoelectron spectroscopy revealed that titanium in the obtained samples is in the form Ti⁴⁺ and Ti³⁺ with a relative proportion of the latter of 8 ± 2%.