Amorphous/crystalline phase control of nanotubular TiO2 membranes via pressure-engineered anodizing

One-step fabrication of fully amorphous vertically-aligned TNTs can have many applications. To control the phase and quality of membrane-like structures, this study introduces a novel method of the pressure-engineered electrochemical process (PEEP). The isostatic pressure on the electrolyte was examined to have a critical effect on the phase of TiO2 nanotubes (TNTs) and a distinctive difference in the quality of TNTs was observed under negative pressure condition (P-n: 10(-2) mbar) compared with other pressures of ambient (P-a: atmospheric) and positive pressure (P-p: 5 bar). SAED showed at P-a and P-p on the surface of nanotubes crystallites grew on {101) planes owing to the lower surface free energy of these crystal planes. Similarly, the current density vs. time profile of the PEEP showed the current consumed at P-n was more than P-p or P-a conditions. In respect of bubble mould theory, it could be concluded that the number of sucked oxygen molecules increased at P-n, generating larger nanotubes in diameter. Ion chromatography (IC) test also proved that the fluorine ion (fluoride, F-) in the electrolyte did not react with those elements leached from the substrate to form (TiF6)(2-). A newly practiced method of PEEP is capable of the scalable fabricating high-quality membrane to be used in optoelectronics, photocatalytic, and photoelectrochemical platforms. (C) 2020 The Authors. Published by Elsevier Ltd.

Automated summary

A novel pressure-engineered electrochemical process (PEEP) method was introduced in this study to fabricate high-quality TiO2 nanotubes by controlling the pressure of the electrolyte. It was found that under negative pressure condition, the TiO2 nanotubes produced were of better quality and larger in diameter compared to ambient and positive pressure conditions.