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

ABSTRACT: TiO₂ 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 NH₄F- and water-based ethylene glycol electrolyte changes with each subsequent anodization, which greatly affects the final photocatalytic properties of the annealed TiO₂ nanotubular films. In the present study, 20 titanium discs (? 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 TiO₂ nanotube films. It was found that the length of the TiO₂ 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 TiO₂ nanotube films showed that the concentration of F^- in the annealed TiO₂ film increased with each subsequent anodization due to the increased pH value of the electrolyte. As a consequence, the concentration of the OH^- and O₂ ^- species decreased, which is a major reason for the reduced photocatalytic activity of the TiO₂ films. It is proposed that the length of the TiO₂ nanotubes does not play a decisive role in determining the photocatalytic activity of the TiO₂ 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.

SUBMITTER: Suhadolnik L

PROVIDER: S-EPMC7737329 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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

Suhadolnik Luka L Marinko Živa Ž Ponikvar-Svet Maja M Tavčar Gašper G Kovač Janez J Čeh Miran M

The journal of physical chemistry. C, Nanomaterials and interfaces 20200121 7

TiO2 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 NH4F- and water-based ethylene glycol electrolyte changes with each subsequent anodization, which greatly affects the final photocatalytic properties of the annealed TiO2 nanotubular films. In the pre ...[more]

PMID: 33343787

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Project description:Nanotube/nanowire-structured TiO2 was formed on the Ti surface by an anodic oxidation method performed at different potential values (50 or 60 V) and for different times (3 or 5 h). The TiO2 photocatalysts were taken in powder form using the ultrasonic treatment from the Ti electrodes, calcined at different temperatures, and characterized by XRD and SEM techniques, and BET surface area analyses. Both the crystallinity and the size of the primary TiO2 particles increased by increasing the heat treatment temperature. While all the photocatalysts heat treated up to 500°C were only in the anatase phase, the particles heat-treated at 700°C consisted of both anatase and rutile phases. The BET specific surface area of the samples decreased drastically after heat treatment of 700°C because of partial sinterization. SEM analyses indicated that the prepared materials were structured in both nanotubes and nanowires. They were tested as photocatalysts for the selective oxidation of glycerol and 3-pyridinemethanol under UVA irradiation in water at room temperature and ambient pressure. Glyceraldehyde, 1,3-dihydroxyacetone, and formic acid were determined as products in glycerol oxidation, while the products of 3-pyridinemethanol oxidation were 3-pyridinemethanal and vitamin B3. Non-nanotube/nanowire-structured commercial (Degussa P25 and Merck TiO2) photocatalysts were used for the sake of comparison. Low selectivity values towards the products obtained by partial oxidation were determined for glycerol. On the contrary, higher selectivity values towards the products were obtained (total 3-pyridinemethanal and vitamin B3 selectivity up to ca. 90%) for the photocatalytic oxidation of 3-pyridinemethanol. TiO2 photocatalysts must be highly crystalline (calcined at 700°C) for effective oxidation of glycerol, while for the selective oxidation of 3-pyridinemethanol it was not necessary to obtain a high crystallinity, and the optimal heat treatment temperature was 250°C. Glycerol and its oxidation products could more easily desorb from highly crystalline and less hydroxylated surfaces, which would justifies their higher activity. The prepared photocatalysts showed lower activity than Degussa P25, but a greater selectivity towards the products found.

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

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Influence of Anodization-Electrolyte Aging on the Photocatalytic Activity of TiO<sub>2</sub> Nanotube Arrays.

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