Effect of anodization time on the morphological, structural, electrochemical, and photocatalytic properties of anodic TiO2 NTs

Abstract

Titanium dioxide nanotubes (TiO2 NTs) were prepared by electrochemical anodizing of a pure titanium foil in glycerol-distilled water containing ammonium fluoride. The diameters and tube length of TiO2 NTs are controlled by tailoring of the anodization time. Synthesized NTs have been characterized by using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and electrochemical impedance spectroscopy (EIS). The results revealed that the internal diameters of NTs can be adjusted from 30 to 130 nm. The length of NTs became longer progressively to reach a maximum of about 3.32 μm after 90 min. XPS analysis shows that the oxidation state of titanium is +4, which confirms the formation of TiO2. XRD and Raman spectroscopy revealed that the TiO2 NTs are composed of a mixture of anatase and rutile phases. The Mott-Schottky analysis showed that the TiO2 nanotubes are consistent with an n-type semiconductor. The photocatalytic performances of TiO2 NTs were tested by degradation of methylene blue (MB) in aqueous solution. The results revealed that the length of the NTs has an important effect on photocatalytic efficiency. The TiO2 NTs with 2.55 μm of length exhibited excellent photocatalytic efficiency of about 79.69% with a kinetic rat 0.0051 min−1. Increasing solution pH from 3 to 12 increases the degradation efficiency from 31.6 to 93.1%.