Anodized TiO 2 nanotubes coated with Pt nanoparticles for enhanced photoelectrocatalytic activity
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TiO2 nanotubes have been demonstrated with promising future in photoelectrocatalytic (PEC)_ applications and deposition of Pt nanoparticles on TiO2 has been widely used to enhance their PEC activities. However, those Pt nanoparticles are normally randomly deposited on the surface of TiO2 nanotubes. Selective deposition of Pt nanoparticles is important to achieve better charge separation. In this study, we reported an electrochemical activation step to prepare TiO2 nanotubes deposited with Pt nanoparticles on their open ends. The “activation step” played a key role in achieving a clean surface of the TiO2 nanotubes, thus ensuring the uniform growth of Pt nanoparticles and efficient photogenerated electrons transportation. The Pt-A-TiO2 films have photocatalytic activities in hydrogen generation and methyl orange degradation with a high hydrogen generation rate of 0.74 mL/h/cm2, three times that of the pure TiO2 nanotubes (0.24 mL/h/cm2). Thus, this study demonstrated an effective method for improving the performance of Pt/TiO2 photocatalyst.
I. INTRODUCTION
Titanium dioxide (TiO2) has been extensively investigated and regarded as one of the most promising solardriven photocatalysts for hydrogen generation and water cleaning.1–5 However, its large band gap energy of 3.2 eV limits its solar-to-hydrogen efficiency for photoelectrochemical application, as the ultraviolet (UV) light only accounts for less than 5% of the entire solar spectrum. In the semiconductor-based photocatalytic process, photo-excited electrons and holes are first generated after the semiconductor absorbs light, they separate and migrate to the surface of the semiconductor to perform photoreduction and/or photooxidation to produce hydrogen from water or remove organic pollutants in water. The overall photocatalytic efficiency is proportional to the efficiency of each step in the photocatalytic process. Specifically, the larger the amount of the sunlight absorbed by the photocatalyst, the higher the photocatalytic efficiency is expected, as more photoexcited electrons and holes will be produced. On the other side, the more electrons and holes reaching on the surface of the photocatalyst, the higher efficiency is expected as well, as more charges can participate in the photooxidation or photoreduction reactions. The number of photoexcited electrons and holes on the surface equal to the number produced by the light absorption minus the Contributing Editor: Xiaobo Chen a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.462
number is consumed by various charge trapping or recombination processes before the charges come to the surface. Moreover, the photocatalytic activity depends on the surface area and surface facet of the photocatalyst. The larger the surface area of TiO2, the higher the photocatalytic activity is expected. And the more active surface facet exposed, the higher the photocatalytic activity. Thus, fabrication of the photocatalyst is crucial to its photocatalytic performance.6–8 Vertically oriented T
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