Visible light responsive TiO2 nanotubes synthesized by electrochemical anodization method (original) (raw)
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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.
Solar Energy Materials and Solar Cells, 2015
In this study, we demonstrate the evolution of morphology and band gap tuning of TiO 2 nanotube (TNT) arrays by an electrochemical anodization method. Both XRD and Raman spectra confirm the crystallinity of TNT arrays in a phase pure anatase form. The crystallinity of TNT increases up to the anodization time of 60 min and with further increase in time, the crystallinity decreases due to the destruction of tubular structures. By increasing the anodization time, the optical absorption of TiO 2 is extended up to the visible region. The well defined visible light photoluminescence emissions reveal the structural defects, oxygen vacancies (F or F 2 þ , F þ) and radiative recombination sites created within the band gap. The nanotubes fabricated at an anodization time of 60 min show the highest photoconversion efficiency of 11.86% in the potassium hydroxide (KOH) electrolyte containing ethylene glycol.
Anatase-type TiO 2 nanotube arrays (TiO 2-NTAs) were grown on Ti foil by anodic oxidation in CH 3 COOH/NH 4 F solutions followed by thermal treatment. The surface of TiO 2-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 TiO 2-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 3 h, only the 35% of anatase transforms into rutile. Finally, it was shown that the TiO 2-NTAs decorated with Pd(0.72 wt%) and Ag(1.26 wt%) particles show higher photocatalytic activity compared with nanotubes modified with single metal particles. It is believed that the high photoactivity of TiO 2 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.
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.
Synthesis and Characterization of TiO2 Nanotube Using Electrochemical Anodization Method
2018
In this study, Titaium dioxide (TiO2) nanotubes (TNTs) were synthesized by a simple electrochemical anodization method. TNTs were characterized by Field Emission Scanning Electron Microscope (FESEM), Transmission Electron Microscope (TEM), UV-Vis Diffuse Reflectance Spectra and Photoluminescence (PL) Spectra to identify the morphology, crystalline phase and photocatalytic activity under the visible light. . The morphological analyses revealed that the inner diameter, and tube length of the synthesized TNTs has an average value of 60 nm, and 900 nm, respectively. The wall thickness of the TNTs is of 11 nm. Theobserved TNTs have nanotubular shape. The absorption edge in the visible range at around 400-460 nm obtained from UV-Vis Diffuse Reflectance Spectrum analysis. In addition, the PL spectral peak identified at around 400nm and 590 nm. The finding shows thatthe synthesized TNTs made by electrochemical anodization method has photocatalytic properties and can be used as a photocataly...
Photochemical activity of TiO2 nanotubes
Oxide-Based Materials and Devices Iv, 2013
TiO 2 is well known as a low-cost, highly active photocatalyst of good environmental compatibility. Recently it was found that TiO 2 nanotubes promise to enable for high photocatalytic activity (PCA). In our experiments, we studied the photocatalytic activity and spectroscopic properties of TiO 2 nanotube arrays formed by the anodization of Ti. The PCA efficiency related to the decomposition of methylene-blue was measured. To obtain reliable data, the results were calibrated by comparing with standard materials like Pilkington Activ™ which is a commercially available self cleaning glass. The studies included a search strategy for finding optimum conditions for the nanotube formation and the investigation of the relationship between PCA and annealing temperature. TiO 2 nanotubes of different shapes and sizes were prepared by an anodization of Ti foil in different electrolytes, at variable applied voltages and concentrations. The photo-dissociation of methylene-blue was detected by UV-VIS spectroscopy. For the optimized material, an enhancement factor of 2 in comparison to the standard reference material was found. Furthermore, femtosecond-laser induced photoluminescence and nonlinear absorption of the material were investigated. Possibilities for a further enhancement of the PCA are discussed.
There are currently immense needs to optimize low-cost materials, such as TiO2, so they can efficiently split water photoelectrochemically into hydrogen and oxygen, thus providing a clean energy fuel. To this end, the nature of the crystalline phase and the dimension of the photocatalyst are of crucial significance. In this study, films of 7 μm long titania nanotube arrays were fabricated via anodization of titanium foil in formamide electrolytes containing NH4F and H3PO4. Upon annealing the as-anodized nanotubes, the anatase-to-rutile phase transformation was found to start at 550 °C, which is about 120 °C above the temperature observed for the 500 nm long nanotube films, with the nanotube films remaining stable up to 580 °C. Analysis of the variation of crystallite size with annealing temperature along with XPS analysis of the films was used to investigate the reason behind this observation. UV−vis measurements showed that the absorption edges of the annealed samples were red shifted from that of the as-anodized sample. The stabilization of the anatase phase up to 550 °C, while keeping the tubular structure in place, is very significant as anatase is the most photoactive polymorph of titania. Besides, the 7 μm long nanotubular structure provides a large surface medium for light utilization through scattering. Used as photoanodes to photoelectrochemically split water, the 580 °C crystallized nanotube arrays showed a three-electrode photoconversion efficiency of 10% under UV illumination (100 mW/cm2, 320−400 nm, 1 M KOH).
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.