Short communication Photocatalytic H 2 production on self-decorated Au nanoparticles/TiO 2 nanotubes under visible light Kiyoung Lee, Robert Hahn, Patrik Schmuki ⁎ Department of Materials Science and Engineering, WW4-LKO, University of Erlangen-Nuremberg, Martensstrasse 7, D-91058 Erlangen, Germany abstract article info Article history: Received 15 March 2014 Received in revised form 2 April 2014 Accepted 3 April 2014 Available online 13 April 2014 Keywords: Au decoration TiO 2 nanotubes Plasmon resonance H 2 production In the present work we fabricate TiO 2 nanotubes that are self-decorated with Au nanoparticles by anodizing low concentration (0.02 and 0.2 at.% Au) TiAu alloys. After formation, the TiO 2 tube walls carry regularly dispersed self-decorated Au particles with ~5 nm in diameter which cause significant surface plasmon resonances. This plasmon resonance effect can be exploited to achieve visible photoresponse and can be used for photocatalytic H 2 production under visible light illumination. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Over the past 10 years self-organized TiO 2 nanotube layers have attracted wide attention in various fields of science and technology. This is due to their easy formation and their promising properties in a number of applications such as dye-sensitized solar cells (DSSCs), photoelectrochemical water splitting, self-cleaning and electrodes [1–3]. TiO 2 nanotube layers are typically formed by anodic oxidation of a Ti metal substrate in a fluoride containing electrolyte, and can be fab- ricated with a high control over geometry (length, diameter, wall thick- ness) and crystal structure (as-grown tubes are amorphous and can be easily crystallized to anatase or rutile by thermal treatments) [4,5]. Photoelectrochemical applications such as photocatalysis, are based on electron–hole pair creation in the semiconductive TiO 2 under proper light irradiation. TiO 2 has suitable band edge positions to form oxidative species in water as exploited for destruction of pollutants, or to form H 2 from aqueous environments. However, the wide band gap of ~3 eV im- poses limitations to the use of the materials under sunlight conditions, as only UV light is efficiently absorbed in the material. In order to extend the photoelectrochemical properties to the visible range, band gap engineering approaches have been explored that are often based on doping TiO 2 for instance with C [6],N [7], or transition metals [8]. On the other hand, noble metal (e.g., Ag, Au) nanoparticle decoration on TiO 2 surfaces has been considered a promising approach in regard to two main purposes. First, in view of visible light absorption such noble several metal nanoparticles may yield a surface plasmon resonance effect under visible light excitation. In this case, particles enhance the localized electric field neighboring the semiconductor for the facile formation of electron–hole pairs in the near surface region of TiO 2 [9]. Second, metal nanoparticles on TiO 2 also play a role as co- catalysts that may facilitate electron–hole separation and/or increase surface reactions (such as the recombination of H atoms to H 2 ) [10]. The effective plasmon resonance and the catalytic activity strongly depend on particle size, geometry and interspacing of decorated noble metals [11,12]. Several approaches were reported on how to decorate noble metals on TiO 2 surface effectively, such as photoassisted deposition [13,14], im- pregnation [15,16], or physical mixing [17]. Most recently, we reported on the decoration of Au nanoparticles on TiO 2 nanotubes using simple electrochemical anodization of a TiAu alloy [18]. In the present report, we investigate the visible light photoelectro- chemical properties of Au self-decorated TiO 2 nanotubes and find considerable photocurrent response and photocatalytic activity. 2. Experimental details For nanotube layer fabrication, Ti sheets (99.6% purity, Advent Mate- rials, UK) of 0.125 mm thickness at 0.02 at.% and 0.2 at.% Au containing Ti alloy (Hauner Metallische Werkstoffe, Germany) were used. Prior to anodization, samples were mechanically ground with a 4000 grit size SiC paper and polished with 9 μm polycrystalline diamond suspension and with a mixture composed of a non-crystallizing colloidal silica polishing suspension and H 2 O 2 (90:10 vol.%). Afterwards the samples were degreased by sonication in acetone, ethanol, and isopropanol, followed by rinsing with deionized water; finally the samples were Electrochemistry Communications 43 (2014) 105–108 ⁎ Corresponding author. Tel.: +49 9131 852 7575; fax: +49 9131 852 7582. E-mail address: schmuki@ww.uni-erlangen.de (P. Schmuki). http://dx.doi.org/10.1016/j.elecom.2014.04.002 1388-2481/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom