Direct growth of TiO2 nanotubes with well-morphology and high {001} facets exposure ratio by H3PO4/HF-assisted anodic oxidation

It is challenging to develop well-designed photocatalysts with high activity. In this work, TiO 2 nanotubes (TiO 2 -NTs，TNT) with well-morphology and high {001} facets exposure ratio were directly synthesized by H 3 PO 4 /HF-assisted two-step anodic oxidation. The results show that the addition of 3 wt% H 3 PO 4 and 0.5 wt% HF into the electrolyte facilitates the preparation of TiO 2 -NTs with an average crack density of 0 % and {001} facets exposure ratios up to 80.00 %. Moreover, the PO 4 3- and HPO 4 2- in the anode effectively hinder the generation of electron current and release of oxygen bubbles on the surface of Ti substrate, which reduces the surface cracks of TiO 2 -NTs. The F - in the electrolyte is adsorbed on the {001} facets of the TiO 2 -NTs, which decreases the energy of the O-Ti-O, thus achieving the purpose of high {001} facets exposure ratio. Ultimately, the excellent optical properties, in conjunction with the synergistic effect of {001} facets-selective orientation and O V , significantly enhanced the photocatalytic activity of TiO 2 -NTs, resulting in the removal of 90.32 % Rhodamine B in 120 min under visible light illumination. This work could shed light on the new approach to the rational design of high-efficiency TiO 2 -NTs-based photocatalysts. • Well-morphology TiO2-NTs with high {001} facets exposure ratio were directly prepared. • PO43- is the main reason for reducing electron current generation and oxygen release. • Beneficial oxygen vacancies (OV) were constructed on TiO2-NTs by F-. • Degradation efficiency of RhB by the optimized TiO2-NTs up to 90.32 % within 120 min.