Synthesis and Photochemical Properties of Au-Attached Titania Nanotubes Arrays
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1211-R07-04
Synthesis and Photochemical Properties of Au-Attached Titania Nanotubes Arrays Ragen McAdoo, Mohamed Abd Elmoula, Latika Menon Northeastern University, Physics Department Boston, MA, 02115, U.S.A. ABSTRACT Au nanoparticles have been attached to the surface of titania nanotube arrays by means of a deposition-precipitation method. We demonstrate a high deposition density of the gold particles over the nanotube surface and also good control over the size of the gold nanoparticles. Photocurrent measurements using such Au attached titania nanotubes as photoanodes have been measured and compared with blank titania nanotubes. INTRODUCTION Modification of titania nanostructures by various functional groups has been a subject of active research interest. It has been reported by Haruta et al. [1] that Au particles attached to oxide surfaces, such as TiO2 have enhanced catalytic properties in CO oxidation, and predicted by Aurora et al. [2] that Au attached TiO2 nanotubes will also have enhanced catalytic properties in photoelectrochemical (PEC) hydrogen production. It is expected that attachment of the Au particles to titania nanotubes will have additional advantages with respect to catalysis due to the enhanced surface area. In a previous work [3], we have shown that Au nanoparticles can indeed be attached uniformly to nanotube surfaces using a modified deposition-precipitation method originally pioneered by Moreau et al.[4] Very good control over the gold nanoparticle diameters (in the range of 2-7 nm) was shown in our previous work [3] and coverage percentage (up to 70%) was demonstrated by adjusting the soaking time. In this work, we report the increase and decrease of particle coverage density as a function of the concentration of HAuCl4. We show that these gold particles are incompatible with liquid I2 solar cell dyes due to absorption of the gold particles into the electrolyte. Finally, we compare the behavior of gold modified TiO2 nanotubes to blank TiO2 nanotubes in a PEC cell for hydrogen production in two electrode and three electrode configurations. EXPERIMENTAL RESULTS For attachment of Au nanoparticles, titania nanotube arrays were fabricated by anodization in a hydrofluoric acid solution, a method pioneered by Gong et al.[5] Commercially available titanium foil (Alfa Aesar, 99.99%, 45 x 25 x 0.032 mm) was cleaned by sonication for 20 minutes, then rinsed with ethanol, de-ionized water, and dried in air. A 45 x 20 mm active area was immersed in a beaker containing 0.25 M HF, and anodized for 35 minutes under constant bias (15 or 20 V), the result being the formation of an ordered array of nanotubes (diameter depending on the anodization voltage, and several hundreds of nanometers long) on both sides of the samples. Asformed nanotubes were amorphous, and crystallization to anatase was obtained by annealing in oxygen for 1h at 400°C, with heating and cooling rates of 1°C per minute.
Gold Deposition In order to deposit gold nanoparticles [3], the TiO2 nanotube samples were soaked in a mixture of HAuC
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