High-temperature stable anatase-type TiO2 nanotube arrays: A study of the structure–activity relationship

• Published in: Applied catalysis. B, Environmental Environmental, 2016-05, Vol.185, p.119-132
• Main Authors: Eskandarloo, Hamed, Hashempour, Mazdak, Vicenzo, Antonello, Franz, Silvia, Badiei, Alireza, Behnajady, Mohammad A., Bestetti, Massimiliano
• Format: Article
• Language: English
• Subjects: Anatase; Anodic oxidation; Noble metal deposition; Photoelectrocatalytic activity; Titania nanotubes
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2015.11.048

[Display omitted] •Anatase-type TiO2-NTAs was prepared via an anodic oxidation and thermal treatment.•Anodic oxidation in CH3COOH/NH4F provides high-temperature stable anatase structure.•TiO2-NTAs was further decorated by Pd and Ag via a chemical-reduction method.•Photoelectrocatalytic activity of TiO2-NTAs was studied toward the removal of PNP.•The structure–activity relationship was established by using various techniques. Anatase-type TiO2 nanotube arrays (TiO2-NTAs) were grown on Ti foil by anodic oxidation in CH3COOH/NH4F solutions followed by thermal treatment. The surface of TiO2-NTAs was further decorated by palladium and silver metal clusters through a chemical-reduction method and its photocatalytic activity was tested by investigating the degradation of p-nitrophenol (PNP) in aqueous solution under visible-light irradiation and electrical polarization. The effects of preparation variables both on microstructural properties of samples and photocatalytic activity were examined by using the 3D response surface and the 2D contour plots. The experimental investigations carried out by using XRD, SEM, HRTEM, EDS, XRF, ICP-AES, XPS, DRS, and PL, demonstrated a strong relation between the phase structure and the photocatalytic activity of TiO2-NTAs. Titania nanotubes grown in acetic acid solution and thermally post-treated have stable anatase crystal structure, to a point that by performing annealing at 800°C for 3h, only the 35% of anatase transforms into rutile. Finally, it was shown that the TiO2-NTAs decorated with Pd(0.72wt%) and Ag(1.26wt%) particles show higher photocatalytic activity compared with nanotubes modified with single metal particles. It is believed that the high photoactivity of TiO2 nanotubes decorated with Pd–Ag heterostructures is due to the prolonged lifetimes of photogenerated electron–hole pairs. The possible mechanism for the enhanced photocatalytic activity is discussed in detail.