Silver-decorated titanium dioxide nanotube arrays with improved photocatalytic activity for visible light irradiation
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lver-decorated titanium dioxide (Ag/TiO2) nanotube (NT) arrays were successfully prepared using a two-step synthesis route comprised of an anodic oxidation procedure followed by photochemical reduction using ultraviolet irradiation. The resulting Ag/TiO2 NT arrays were characterized using scanning electron microscopy, transmission electron microscopy, x-ray diffraction, and UV-vis diffusion reflectance spectrometry. The characterization results indicated that the silver decoration significantly enhanced the light absorption capability of the TiO2 NT arrays in the visible spectral range. The visible light photocatalytic activity of the subject NT arrays was investigated. The experimental results showed the photocatalytic activity of silver-decorated titanium dioxide Ag/TiO2 NT arrays to be dependent on the size of the silver particles. The improved visible light absorption can be attributed to plasmonic effects induced by particle size phenomenon. The Ag/TiO2 NT arrays exhibit promising application for photocatalytic degradation of dye solutions and pollutants in water using visible irradiation.
I. INTRODUCTION
Titanium dioxide nanotube arrays (TiO2 NT arrays) have received considerable attention because of their large surface area, robust photocatalytic activity, and vectorial charge transfer properties.1–6 However, practical application of these materials is restricted by the intrinsic wide band gap of TiO2 (3.0–3.2 eV), which limits its photocatalytic activity in the visible light region. An additional drawback of TiO2 NT arrays is the high recombination rate of photogenerated electron–hole pairs resulting in low photocatalytic efficiency. To surmount these problems, considerable efforts have been undertaken to extend the optical absorption of TiO2 NT arrays into the visible range and lower the recombination rate of electrons and holes. These remedial techniques have included metal or nonmetal ion doping,7,8 dye sensitization,9,10 narrow band gap semiconductor coupling,11 and noble metal modification.12–16 In particular, noble metal-modified TiO2 NT arrays have become the focus of many studies due to the surface plasmon resonance (SPR) effect.17,18 It has been reported that this approach may extend the visible light absorption by TiO2.19–21 Besides the noble metals, silver (Ag) may also be of an attractive modifier due to its strong resonance wave length of 400–550 nm and lower cost in comparison to noble metals (e.g., gold (Au), platinum (Pt)).22 Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2014.116 1302
J. Mater. Res., Vol. 29, No. 11, Jun 14, 2014
http://journals.cambridge.org
Downloaded: 11 Mar 2015
These advantages make Ag a good candidate for modification of TiO2 NT arrays. Modification of TiO2 NT arrays using Ag can enhance the visible light absorption and reduce the recombination rate of photogenerated electron– hole pairs in TiO2 NT arrays. Zhang et al.23 prepared Ag nanoparticles to n-dope TiO2 NT arrays (Ag/N-TiO2 NT arrays) u
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