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Behavior of glycerol concentration in a HCl electrolyte for obtaining Titania nanostructures by anodic oxidation
Abstract
In this work, the anodization of grade 2 titanium was performed using a HCl-based electrolyte in order to obtain Titania nanostructures. Different glycerol concentrations were added to the HCl electrolyte to study the effect it has on the shape and density of the nanostructures, additionally, anodization time and voltage was also varied. The anodized samples were observed by SEM microscopy and studied by Raman spectroscopy and X-ray diffraction. Raman spectroscopy and XRD showed the formation of the anatase phase of the TiO 2 . By SEM it was possible to observe several changes in the shape of the structures, by adding glycerol ball-like structures were visible, anodization time did not change the shape of the nanostructures. However, the voltage variation showed a clear control on the shape of the structures, forming nanotubes at higher voltages. It was concluded that a better control of the shape and density of the nanostructures is achieved by adding glycerol, however, in order to overcome the resistance that the electrolyte brings, higher voltages are required.
Currently, electrochemical anodizing is one of the most common processes in materials science, since, under the right conditions, it allows to modify the material surface without damaging it by means of redox reactions, generating an oxide layer that protects the material and improves its properties. In this paper, grade 2 titanium was anodized using a solution of hydrochloric acid, glycerol, and deionized water as electrolyte, and 0.5 M K 2 CrO 4 as doping agent, with a voltage of 30 V for 4.5 h. After anodizing with and without chromium, annealing was performed at different temperatures (500[Formula: see text]C, 600[Formula: see text]C and 700[Formula: see text]C) to promote structural and microhardness changes. The samples were analyzed by FE-SEM observing that the formation of nanostructures changes according to the heat treatment, where samples at 700[Formula: see text]C with chromium begin to form nanorods and, compared to those without chromium, the nanorods are longer. The presence of Cr in anodized TiO 2 at different temperatures was confirmed by EDS technique. Using XRD, the microstructure of TiO 2 anodized with and without Cr was analyzed and anatase and rutile phases were found, with greater presence of anatase for samples with Cr. Finally, a maximum hardness of up to 10.27 GPa was obtained from the sample at 700[Formula: see text]C without chromium, which is higher compared to the values of coatings with Cr. However, the anatase phase could be stabilized at higher temperatures making it suitable for medical applications since the anatase phase is the most biocompatible.
Recently, we reported the discovery of new high-aspect ratio titania nanotubes. These nanotubes were synthesized by means of anodization in an oxalic acid electrolyte containing chlorine ions and were found to have significant carbon content. In this article, the synthesis of similar titania nanotubes in oxalic, formic, trichloroacetic, gluconic, hydrochloric, and sulfuric acid is reported. Differences in carbon content and morphology are analyzed, which in turn provides information on the chemistry of the formation of these nanotubes. Our results suggest that the carbon content in the nanotubes can be controlled by the use of an appropriate organic acid.
The preparation of nanotubular arrays on different substrates and nanoporous structures on titanium foil by means of electrochemical anodization of titanium layer has been investigated. Highly aligned nanotubes of TiO2 on flexible, rough and flat substrates are reported. Modification of anodization conditions of titanium on specific substrates such as polyethylene terephthalate (PET), conducting glass and granular alumina was found to affect the morphology of TiO2nanotubes. Two different kinds of aqueous electrolytes have been applied, containing either glycerol or H2SO4, in order to investigate the effect of ion mobility on anodization process. Galvanostatic and potentiostatic anodization modes have been investigated: transition from nanotubes to nanoporous structures has been highlighted in galvanostatic mode, depending on the intensity of anodization current density. These results pave the way for massive production of TiO2nanotubes over, in principle, whatever substrate, enabling exploitation of new functional properties derived from the combination of tubes and substrates.
We have completed a detailed experimental investigation into the recently discovered synthesis of titania nanotubes in chloride-ion-containing media. We show that the role of the chloride ions is catalytic and it has a strong effect in increasing the reactivity of the solution, while the nature of cations has no visible role. We have identified the critical parameters for optimal growth and fast production of nanotubes, and a basic growth mechanism for the tubes is proposed. This opens routes for significant improvements of the method toward uniformity and/or better overall yield, making it a viable alternative to the present established methods.
Highly ordered TiO2 nanotube arrays (TNs) are prepared by electrochemical anodization of titanium foil in a mixed electrolyte solution of glycerol and NH4F and then calcined at various temperatures. The prepared samples are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The photocatalytic activity is evaluated by photocatalytic degradation of methyl orange (MO) aqueous solution under UV light irradiation. The production of hydroxyl radicals (OH) on the surface of UV-irradiated samples is detected by a photoluminescence (PL) technique using terephthalic acid (TA) as a probe molecule. The transient photocurrent response is measured by several on–off cycles of intermittent irradiation. The results show that low temperatures (below 600°C) have no great influence on surface morphology and architecture of the TNs sample and the prepared TNs can be stable up to ca. 600°C. At 800°C, the nanotube arrays are completely destroyed and only dense rutile crystallites are observed. The photocatalytic activity, formation rate of hydroxyl radicals and photocurrent of the TNs increases with increasing temperatures (from 300 to 600°C) due to the enhancement of crystallization. Especially, at 600°C, the sample shows the highest photocatalytic activity due to its bi-phase composition, good crystallization and remaining tubular structures. With further increase in the calcination temperature from 600 to 800°C, the photocatalytic activity rapidly decreases due to the vanishing of anatase phase, collapse of nanotube structures and decrease of surface areas.
In this paper, anatase type titania nanotube arrays were direct fabricated by anodization in dimethyl sulfoxide electrolyte containing 1wt% HF solution at above 50°C without subsequently annealing. The length of the nanotubes decreases with increasing anodization temperature from about approximately 15μm at 40°C to approximately 4.5μm at 60°C. High resolution transmission electron microscope images and selected area electron diffraction pattern confirm the polycrystalline anatase specimen consisting of many nanocrystals with a random orientation.
The stability of titanium oxide nanotube arrays at elevated temperatures was studied in dry oxygen as well as dry and humid argon environments. The tubes crystallized in the anatase phase at a temperature of about 280 °C irrespective of the ambient. Anatase crystallites formed inside the tube walls and transformed completely to rutile at about 620 °C in dry environments and 570 °C in humid argon. No discernible changes in the dimensions of the tubes were found when the heat treatment was performed in oxygen. However, variations of 10% and 20% in average inner diameter and wall thickness, respectively, were observed when annealing in a dry argon atmosphere at 580 °C for 3 h. Pore shrinkage was even more pronounced in humid argon environments. In all cases the nanotube architecture was found to be stable up to approximately 580 °C, above which oxidation and grain growth in the titanium support disrupted the overlying nanotube array.
Raman spectra of anatase have been observed in natural and synthetic crystals. Both crystals show the same spectral features. The Raman band occurring at 516 cm−1 at room temperature is split into two peaks centred at 519 cm−1 and 513 cm−1 at low temperature (73 K). The six Raman active fundamentals predicted by group theory are all observed and assigned. The spectra are analyzed by a simple model considering only short-range forces and the calculated vibrational frequencies are in good agreement with the observed Raman frequencies.
Titanium dioxide (TiO2) nanotube arrays were prepared by electrochemical anodization of titanium sheets in the glycerol 176 mL/H2O 44 mL/NH4F 0.5 wt% electrolytes modified with H2SO4 and NaAc addition. The surface morphologies, average inner diameter, and the length of the nanotube arrays changed with the solution pH in the range from 5.6 to 4.0 by adding H2SO4. A uniform surface morphology of the nanotubes with average inner diameter of ∼80 nm and a length of ∼1000 nm was obtained when the solution pH was 5.0. The growth rates of the nanotubes were remarkably enhanced by NaAc addition in the range of 0.04–0.14M. With NaAc addition of 0.10M, the length of the nanotube arrays reached 4.16 μm after an 8-h anodization, increasing 3.23 μm compared with no NaAc addition. The relationship between solution pH and growth of TiO2 nanotubes was analyzed by current–time curves, solution electrical conductivities, and scanning electron microscopy (SEM), and the role of NaAc was also discussed based on SEM and solution electrical conductivities.
Described is the synthesis of TiO 2 nanotube array thin films by anodization of Ti foil in an aqueous HCl electrolyte. This process represents an alternative electrolyte that can be utilized instead of fluoride-containing electrolytes. Nanotube arrays up to 300 nm in length, 15 nm inner pore diameter, and 10 nm wall thickness were obtained by using a 3 M HCl aqueous electrolyte for anodization potentials between 10 and 13 V. An anodization voltage of up to 20 V could be used if it was increased stepwise with a resulting nanotube length of approximately 600 nm; however, the resulting nanotubes are not as well-ordered as those fabricated by a constant anodization voltage. The addition of a low concentration of H 3 PO 4 as a buffering medium in the concentration range 0.01-0.1 M expands the anodization voltage up to 14 V but the architectures formed more closely resemble rods than tubes.
Norek Małgorzata , Michalska-Domańska Marta , Król Artur
- Stȩpniowski Wojciech
- Forbot Dominika
- C Veiga
- J P Davim
C. Veiga, J.P. Davim, A.J.R. Loureiro. Rev. Adv. Mater. Sci, 32, 133-148, (2012).
- K Nageh
- Craig A Allam
- Grime
Nageh K. Allam, Craig A. Grime. J. Phys. Chem. C, 111, 13028-13032, (2007).
- Afya Sahib
- Diab Al-Radha
Afya Sahib, Diab Al-Radha. International Journal of Science and Research 6, 2000-2004,
(2015).
- K Oomman
- Dawei Varghese
- Maggie Gong
- Craig A Paulose
- Grimes
Oomman K. Varghese, Dawei Gong, Maggie Paulose, Craig A. Grimes. Journal of Materials
Research, 18, 1, 156-165, (2003).