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Materials 2015, 8(9), 5702-5714; doi:10.3390/ma8095270

In Situ Anodization of WO3-Decorated TiO2 Nanotube Arrays for Efficient Mercury Removal

Nanotechnology & Catalysis Research Centre (NANOCAT), Institute of Postgraduate Studies (IPS), University of Malaya, Kuala Lumpur 50603, Malaysia
These authors contributed equally to this work.
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Author to whom correspondence should be addressed.
Academic Editor: Luciano Feo
Received: 20 June 2015 / Revised: 16 July 2015 / Accepted: 6 August 2015 / Published: 28 August 2015
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Abstract

WO3-decorated TiO2 nanotube arrays were successfully synthesized using an in situ anodization method in ethylene glycol electrolyte with dissolved H2O2 and ammonium fluoride in amounts ranging from 0 to 0.5 wt %. Anodization was carried out at a voltage of 40 V for a duration of 60 min. By using the less stable tungsten as the cathode material instead of the conventionally used platinum electrode, tungsten will form dissolved ions (W6+) in the electrolyte which will then move toward the titanium foil and form a coherent deposit on the titanium foil. The fluoride ion content was controlled to determine the optimum chemical dissolution rate of TiO2 during anodization to produce a uniform nanotubular structure of TiO2 film. Nanotube arrays were then characterized using FESEM, EDAX, XRD, as well as Raman spectroscopy. Based on the FESEM images obtained, nanotube arrays with an average pore diameter of up to 65 nm and a length of 1.8 µm were produced. The tungsten element in the samples was confirmed by EDAX results which showed varying tungsten content from 0.22 to 2.30 at%. XRD and Raman results showed the anatase phase of TiO2 after calcination at 400 °C for 4 h in air atmosphere. The mercury removal efficiency of the nanotube arrays was investigated by photoirradiating samples dipped in mercury chloride solution with TUV (Tube ultraviolet) 96W UV-B Germicidal light. The nanotubes with the highest aspect ratio (15.9) and geometric surface area factor (92.0) exhibited the best mercury removal performance due to a larger active surface area, which enables more Hg2+ to adsorb onto the catalyst surface to undergo reduction to Hg0. The incorporation of WO3 species onto TiO2 nanotubes also improved the mercury removal performance due to improved charge separation and decreased charge carrier recombination because of the charge transfer from the conduction band of TiO2 to the conduction band of WO3. View Full-Text
Keywords: WO3 decorated TiO2 nanotubes; electrochemical anodization; mercury removal; fluoride content; active surface area WO3 decorated TiO2 nanotubes; electrochemical anodization; mercury removal; fluoride content; active surface area
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Lee, W.H.; Lai, C.W.; Hamid, S.B.A. In Situ Anodization of WO3-Decorated TiO2 Nanotube Arrays for Efficient Mercury Removal. Materials 2015, 8, 5702-5714.

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