Electrochemically assisted photocatalysis on self-organized TiO2 nanotubes (original) (raw)
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Some critical factors for photocatalysis on self-organized TiO2 nanotubes
Journal of Solid State Electrochemistry, 2012
In the present work, different intrinsic and extrinsic parameters are investigated that affect the photocatalytic activity of self-organized TiO 2 nanotube layers. Particularly, the influence of annealing temperature and annealing atmosphere, the influence of different gas purging in the electrolyte, and the effect of applied voltage on the photocatalytic degradation rates of acid orange (AO7) are discussed. We find that the effect of the reducing gas atmosphere dominates over the anatase/rutile ratio in activating the nanotube layers. Moreover, we show that the effect of different gas purging (Ar and O 2) of the electrolyte affects the reaction rate twofold: (1) by providing electron acceptor states and also by (2) a different change in the red-ox potential, i.e., the band bending in TiO 2. By an external anodic voltage, the reaction rates can be increased drastically due to increased band bending. Nevertheless, the magnitude of the effect is also affected by the presence or absence of O 2 in the electrolyte.
Applied Surface Science, 2014
We report the significance of crystallinity on photoelectrochemical and the photocatalytic degradation of methyl orange of titanium dioxide (TiO 2) nanotube arrays. The TiO 2 nanotube arrays are fabricated by electrochemical anodization of titanium substrates in fluoride based aqueous electrolyte for various anodization time. The degree of crystallinity and phase purity (anatase) is confirmed from X-ray diffraction and Raman spectra. High resolution scanning electron microscope is used to analyze the surface morphology of forming nanotubes. The UV-visible absorption spectrum shows the enhanced absorption in the visible region which is further confirmed using photoluminescence spectra. The photoelectrochemical properties of the prepared samples are studied from linear sweep photovoltammetry measurements and a maximum photocurrent density of 1.32 mA/cm 2 is observed. The enhanced photoelectrochemical activity is attributed to the higher crystallinity which increases the charge carrier separation and extends its light absorption from ultraviolet to visible region owing to lower band gap of 2.751(7) eV.
A systematic study of titanium dioxide (TiO 2 ) nanotube arrays grown by electrochemical anodisation in an ethylene glycol electrolyte containing 0·5 wt-% ammonium fluoride has been carried out, with a range of anodisation voltage of 15-60 V for 1 hour. Among all of the applied anodisation voltages, 60 V resulted in the highest aspect ratio TiO 2 nanotube arrays with the tube length of approximately 2 μm and pore size of 105 nm. The diameter and length of nanotubes were found to be increased with anodisation voltage because of the high electric field dissolution at the barrier layer of nanotubes. Besides, the anatase phase of TiO 2 could be detected from the X-ray diffraction patterns after subjecting the annealing process at 400°C in argon atmosphere for 4 hours. Based on the photocatalytic studies, it was observed that TiO 2 nanotube arrays with the highest aspect ratio (length/pore's size) exhibited preferably high photocatalytic activity among the samples owing to the larger active surface area to generate more photo-induced electron-hole pairs. This condition will enhance the photocatalytic degradation efficiency of methyl orange.
Small, 2012
Photocatalytic approaches, that is the reaction of lightproduced charge carriers at a semiconductor surface with their environment, currently attract an extremely wide scientifi c interest. This is to a large extent due to the high expectations: i) to convert sunlight directly into an energy carrier (H 2 ), ii) to stimulate chemical synthetic reactions, or iii) to degrade unwanted environmental pollutants. Since the early reports in 1972, TiO 2 has been the most investigated photocatalytic material by far; this originates from its outstanding electronic properties that allow for a wide range of applications. Not only the material, but also its structure and morphology, can have a considerable infl uence on the photocatalytic performance of TiO 2 . In recent years, particularly 1D (or pseudo 1D) structures such as nanowires and nanotubes have received great attention. The present Review focuses on TiO 2 nanotube arrays (and similar structures) that grow by self-organizing electrochemistry (highly aligned) from a Ti metal substrate. Herein, the growth, properties, and applications of these tubes are discussed, as well as ways and means to modify critical tube properties. Common strategies are addressed to improve the performance of photocatalysts such as doping or band-gap engineering, co-catalyst decoration, junction formation, or applying external bias. Finally, some unique applications of the ordered tube structures in various photocatalytic approaches are outlined.
To improve the photo-catalytic degradation of salicylic acid, we reported the fabrication of ordered TiO2 nanotube arrays by a simple and effective two-step anodization method and then these TiO2 nanotubes treated in a methanol solution under UV light irradiation. The TiO2 nanotubes prepared in the two-step anodization process showed better photo-catalytic activity than TiO2 nanotubes prepared in one-step anodization process. Also, compared with TiO2 nanotubes without the UV pretreatment, the TiO2 nanotubes pretreated in a methanol solution under UV light irradiation exhibited significant enhancements in both photocurrent and activity. The treated TiO2 nanotubes exhibited a 5-fold enhancement in photocurrent and a 2.5-fold increase in the photo-catalytic degradation of salicylic acid. Also the effect of addition of persulfate and periodate on the photo-catalytic degradation of salicylic acid were investigated. The results showed that the degradation efficiency of salicylic acid increased with increasing persulfate and periodate concentrations. These treated TiO2 nanotubes are promising candidates for practical photochemical reactors.
Fabrication of TiO 2 Nanotube by Electrochemical Anodization: Toward Photocatalytic Application
Research Article, 2020
In this study, a self-organized nanotubular titanium dioxide (TiO 2) array was successfully produced by anodizing pure titanium in a mixture of glycerol, distilled water (8% vol.), and ammonium fluoride using a dual electrode system. The size control and distribution of the nanopores were performed in a DC voltage range varying from 30 V to 60 V. The diameter of TiO 2 nanopores varies from 59 to 128 nm depending on the anodizing voltage. Energy-dispersive X-ray spectroscopy (EDX) analysis reveals that the as-prepared films are essentially composed of TiO 2. According to the X-ray diffraction (XRD) and Raman spectroscopy analysis, the nanotubular arrays of TiO 2 annealed at 600°C for 2 hours are composed of a phase mixture of anatase and rutile. Mott-Schottky analysis showed that the TiO 2 nanotubes are consistent with an n-type semiconductor with a donor density of about 10 17 cm-3. Preliminary results on the photocatalytic degradation of a pharmaceutical pollutant showed that the TiO 2 nanotubes can be used as a promising material for application in wastewater treatment.
Energy Procedia, 2011
In this study, titanium dioxide nanotube (TNT) were prepared by anodization method. The effects of voltage and addition of water in electrolyte solution that contains 0.5 %wt. HF and 0.3 %wt. NH4F were investigated. Photocatalytic activity of the TNT films were evaluated in terms of the degradation of methylene blue under UV light. The results showed that the 20 V of voltage and addition 2 vol% of water in electrolyte solution were the best condition on anodization.process.
Influence of Anodization-Electrolyte Aging on the Photocatalytic Activity of TiO2 Nanotube Arrays
The Journal of Physical Chemistry C, 2020
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 (Φ90 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, the pH of the electrolyte, and with the resulting morphology, structure, composition and the 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. Subsurface chemical composition was evaluated by 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.
Titanium Dioxide - Material for a Sustainable Environment
This book chapter reports some spectacular and interesting 1D nanostructures of TiO 2 , which are grown by the anodic oxidation. Under suitable conditions, conventional onestep anodic oxidation is available to grow TiO 2 nanotube arrays (TNAs) and TiO 2 nanowires/nanotubes; meanwhile, two-step anodic oxidation allows fabricating some novel TNAs with spectacular morphologies such as highly ordered TNAs, bamboo-type TNAs, and lotus root-shaped TNAs. The formation mechanisms of these nanostructures during the anodic oxidation processes are elusive via studying effects of several key parameters such as oxidizing voltage, processing time, and electrolytes. In addition, the photocatalytic activity of the TNA-based nanomaterials is characterized by the degradation of pharmaceutical model, methylene blue, or the photoelectrochemical effect.