Abstract
High aspect ratio of WO3-loaded TiO2 nanotube arrays have been successfully synthesized using the electrochemical anodization method in an ethylene glycol electrolyte containing 0.5 wt% ammonium fluoride in a range of applied voltage of 10–40 V for 30 min. The novelty of this research works in the one-step formation of WO3-loaded TiO2 nanotube arrays composite film by using tungsten as the cathode material instead of the conventionally used platinum electrode. As compared with platinum, tungsten metal has lower stability, forming dissolved ions (W6+) in the electrolyte. The W6+ ions then move towards the titanium foil and form a coherent deposit on titanium foil. By controlling the oxidation rate and chemical dissolution rate of TiO2 during the electrochemical anodization, the nanotubular structure of TiO2 film could be achieved. In the present study, nanotube arrays were characterized using FESEM, EDAX, XRD, as well as Raman spectroscopy. Based on the results obtained, nanotube arrays with average pore diameter of up to 74 nm and length of 1.6 µm were produced. EDAX confirmed the presence of tungsten element within the nanotube arrays which varied in content from 1.06 at% to 3.29 at%. The photocatalytic activity of the nanotube arrays was then investigated using methyl orange degradation under TUV 96W UV-B Germicidal light irradiation. The nanotube with the highest aspect ratio, geometric surface area factor and at% of tungsten exhibited the highest photocatalytic activity due to more photo-induced electron-hole pairs generated by the larger surface area and because WO3 improves charge separation, reduces charge carrier recombination and increases charge carrier lifetime via accumulation of electrons and holes in the two different metal oxide semiconductor components.
Highlights
The process of dyeing in the textile industry has resulted in the production of large amounts of wastewater with intense coloration which has to be eliminated before release into natural water streams
Fine pits or cracks form on the oxide surfaces which arise from chemical and field-assisted dissolution of the oxide at local points of high energy
As compared to WO3-loaded TiO2 nanotubes, pure TiO2 nanotube arrays showed a lower efficiency of methyl orange (MO) decomposition, where the MO concentration was reduced to 28% of initial MO concentration after 4 h
Summary
The process of dyeing in the textile industry has resulted in the production of large amounts of wastewater with intense coloration which has to be eliminated before release into natural water streams If left untreated, such dyes will remain in the environment for an extended period of time and cause serious environmental and health problems. To optimize the properties and performance of the nanotubes, anodizing conditions such as applied potential, anodization time, and electrolyte composition can be tailored to control the dimensions of the nanotubes such as length, pore diameter and wall thickness [11,12,13,14,15]. The influence of anodization voltage on the formation of WO3-loaded TiO2 nanotube arrays was investigated in this study with the aim to fabricate nanotubes with optimum length, wall thickness, and pore diameter for better photocatalysis application. Oxidation rate of Ti metal to form TiO2 layer and field assisted dissolution rate of Ti metal ions in the electrolyte [18]
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