Influence of Anodization-Electrolyte Aging on the Photocatalytic Activity of TiO₂ Nanotube Arrays

Abstract

TiO 2 nanotubular films prepared using the anodic oxidation process applied to various forms of metal titanium are promising materials for photocatalytic applications. However, during successive anodizations in batch-anodization cells, the chemical composition of the NH 4 F- and water-based ethylene glycol electrolyte changes with each subsequent anodization, which greatly affects the final photocatalytic properties of the annealed TiO 2 nanotubular films. In the present study, 20 titanium discs (Φ 90 mm) were sequentially anodized in the same anodization electrolyte. The chemical composition of the electrolyte was measured after each anodization and correlated with the anodization current density, temperature, electrical conductivity, and pH of the electrolyte and with the morphology, structure, composition, and photocatalytic activity of the resulting TiO 2 nanotube films. It was found that the length of the TiO 2 nanotubes decreased with the age of the electrolyte due to its lower conductivity. The subsurface chemical composition was evaluated by time of flight secondary ion mass spectrometry (ToF SIMS) analyses, and the integrated ToF SIMS signals over a depth of 250 nm for the TiO 2 nanotube films showed that the concentration of F – in the annealed TiO 2 film increased with each subsequent anodization due to the increased pH value of the electrolyte. As a consequence, the concentration of the OH – and O 2 – species decreased, which is a major reason for the reduced photocatalytic activity of the TiO 2 films. It is proposed that the length of the TiO 2 nanotubes does not play a decisive role in determining the photocatalytic activity of the TiO 2 nanotube films. Finally, the best measured degradation results of 60% for caffeine were thus achieved for the first anodized titanium discs. After that the efficiency gradually decreased for each subsequent anodized disc.

Toward Atomic-Scale Inorganic Double Helices via Carbon Nanotube Matrices—Induction of Chirality to Carbon Nanotubes

“…SnIP, as a 1.8 eV semiconductor, was successfully used to fabricate composites in inorganic matrices and 2D materials. Electrochemically etched nanotubular TiO 2 membranes, being a prominent photocatalyst, − and layered C 3 N 4 were used as effective matrices to accommodate SnIP. Heterojunction formation occurred in such hybrid systems resulting in effective water splitting catalysts. − Motivated by the heterostructure formation we therefore decided to evaluate if the formation of SnIP@CNT heterostructures might be possible.…”

“…TiO2 was used as a matrix to create effective photochemical materials for various catalytic applications. [23][24][25][26][27][28][29] Here, in some cases nano-sized arrays are formed by electrochemical etching, which are modified by semiconductors afterwards. The nanotube approach was first adopted by Üzer et al to SnIP to form an effective photocatalytic hybrid 30,31 for water splitting.…”

Self-Ordered Anodic Porous Oxide Layers as a High Performance Electrocatalyst for Water Oxidation

“…Step 1 : Perchloric acid with ethylene glycol-based electrolyte The following chemical reactions can elucidate the emergence of nanostructures during the second anodization process. , Fluoride ions exert two primary influences on the process of oxide formation. First, they give rise to water-soluble [MF x ] y‑ ions, effectively inhibiting the creation of hydroxides .…”

“…Second, they facilitate the erosion of the established metal oxides, resulting in the development of a nanotubular layer instead of a dense one. Due to their capacity to induce chemical dissolution reactions and their possession of a diminutive ionic radius, a minor proportion of fluoride ions can become integrated into the metal oxides. − When subjected to annealing in air, fluoride ions are released from the metal oxide film surface of hydrogen fluoride (HF) …”

Electrochemical Oxidation of Ti15Mo Alloy—The Impact of Anodization Parameters on Surface Morphology of Nanostructured Oxide Layers

“…Some groups also reported a usage of the ‘aged’ electrolyte as an alternative for the freshly prepared one [ 28 , 34 ]. However, it is not only a long-term and expensive procedure, but also may result in a significant deterioration of TiO 2 NT properties [ 41 ].…”