Selective electrodeposition of Ni into the intertubular voids of anodic TiO 2 nanotubes for improved photocatalytic prop
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Hui Li Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong; Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China; and USTC-CityU Joint Advanced Research Centre, Suzhou, Jiangsu 215123, China
Shiwei Shu and Hua Cheng Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong
Yang Yang Lia) Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong; and USTC-CityU Joint Advanced Research Centre, Suzhou, Jiangsu 215123, China (Received 8 May 2012; accepted 23 October 2012)
We report on Ni-modified TiO2 nanotubes with improved photocatalytic properties. Using the as-anodized TiO2 nanotubes as templates, Ni was electrodeposited using pulsed current waveforms. It was found that the Ni deposition was first initiated at the bottoms of the intertubular voids and then grew upward, resulting in a Ni/TiO2 coaxial nanostructure with Ni wrapping around the TiO2 nanotubes. Moreover, the tube inside was kept empty and tube openings unclogged for the fabricated Ni/TiO2 nanocomposites. Further photodegradation tests using methyl red revealed that the fabricated Ni/TiO2 nanocomposites possess higher photocatalytic efficiency than the counterparts of pristine TiO2 nanotubes. The observed improved photocatalytic efficiency is ascribed to the Schottky barriers formed between Ni and TiO2.
I. INTRODUCTION
Self-organized TiO2 nanotube arrays grown by facile anodic oxidation of Ti foils have attracted wide interest due to their great potential in energy- and environmentrelated applications, such as dye-sensitized solar cells,1–3 pollutant degradation,4 water photosplitting,5,6 lithium-ion batteries,7 supercapacitors,8 and smart windows.9–11 To further improve their performance and diversify their functionalities, anodic TiO2 are often used as host for other substances, e.g., metals, semiconductors, or polymers. For example, nickel oxide-embedded TiO2 nanotube arrays have been utilized as anode materials for lithium-ion batteries.12 Anodic TiO2 nanotubes decorated with CdS nanoparticles are shown with efficient solar light harvesting in the visible light region with an 8- to 9-fold of enhancement in photoactivity compared with pristine TiO2 nanotubes.13 Foreign species are generally introduced to anodic TiO2 by hydrothermal treatments,14 dip coating,15 chemical vapor deposition,16 or electrodeposition17 to form nanocomposites. Among various fabrication methods, electrodeposition is particularly attractive due to its simplicity and convenience, as demonstrated by the pioneering studies. For example, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.380 J. Mater. Res., Vol. 28, No. 3, Feb 14, 2013
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Schmuki et al.17 have developed a facile self-doping electrodeposition technique to deposit Cu nanorods inside the anodic TiO2 nanotube array. Choi et al.18 have used alternating soaking and ele
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