Anodically fabricated TiO 2 nanopores for electrocatalytic reduction of aldehydes K. Firoz Babu, K. Marxe, M. Anbu Kulandainathan ⇑ Electro Organic, Central Electrochemical Research Institute, Karaikudi, India article info Article history: Received 30 May 2011 Received in revised form 19 September 2011 Accepted 27 September 2011 Available online 17 October 2011 Keywords: Anodization Nanoporous TiO 2 Voltammetry Electrocatalysis Aldehyde reduction abstract Uniformly ordered titanium dioxide (TiO 2 ) nanopores surface was synthesized by anodizing the titanium at different applied voltages 20, 30 and 40 V for 8 h in an electrolyte consisting of 0.3 wt.% NH 4 F and 2 vol.% H 2 O in ethylene glycol. The pores diameter was found to increase with applied voltage. Scanning electron microscopic studies revealed that the fabricated TiO 2 nanopores have an average pore diameter of 100 nm approximately and increasing with applied voltage. X-ray diffraction, cyclic voltammetry (CV) and impedance spectroscopy studies were employed to characterize the TiO 2 nanoporous film and cur- rent increase in the CV studies confirmed the increase in surface area. Electrocatalytic behavior of Ti/ TiO 2 nanopores was investigated for the reduction of aldehydes using cyclic voltammetry. It was observed that the nanopores catalytically reduced the benzaldehyde and furfural to corresponding alco- hol. Bulk electrolysis studies were also carried out for the reduction of benzaldehyde and the product was confirmed by NMR. The two time constants in impedance study showed the involvement of pores in the reduction behavior. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Titanium dioxide (TiO 2 ) is a technologically very important semiconductive material that provides a broad range of specific properties. These make the materials applicable in photo catalysis [1], solar cells [2], photolysis [3], sensing [4], and electrochromic devices [5,6]. As these materials become very important in nano- technology for making very small functional devices with different purposes, it is of high scientific and technological interest to find different strategies, which allow production of nanostructures of these materials in a cheap, tunable and easily controllable manner. Classical approaches to produce for instance nonoporous or nanop- articulate TiO 2 layers include typically sol–gel or hydrothermal processes using alkoxides as a starting material [7]. Recently, self-organized TiO 2 nanotubes could be grown on Ti [8,9] using a relatively simple electrochemical approach, that is, anodization in an acidic electrolyte containing fluorides. In all these works, fluoride anions were used to establish conditions that mildly dissolve the anodic oxides while the anodic bias perma- nently provides new oxide growth. Several important applications have already been found for these structures, such as high photo electrochemical performance under UV and visible light illumina- tion [10], hydrogen sensing [11], catalysis [12], electrochromism [13], and biological applications [14]. Recently, Masuda and coworkers presented a striking alternative approach showing first experimental findings [15] by using electrolytes containing perchlorate anions and using a set of specific anodization condi- tions, it is possible to form bundles of high aspect ratio TiO 2 nano- tubes on Ti under very rapid growth conditions. Since electrochemical methods are simple and considerably avoid environmental pollution, many organic compounds are syn- thesized by such methods [16,17]. In recent years much effort has been directed towards the heterogeneous electro catalytic reduc- tion of organic compounds [18]. Metal ionic redox couples such as Ti(IV)/Ti(III), Mn(III)/Mn(II) were used as mediator or electron carrier [19,20]. TiO 2 nanoparticles notably possess properties such as excellent redox selectivity, non-toxicity, high thermal stability, low cost and easy preparation. Because of such properties it is a promising candidate for electrocatalytic applications [21,22]. Beck and co-worker have developed a titanium dioxide coated titanium electrode which functions as a stable Ti(IV)/Ti(III) redox electron carrier and the electrode has been used in the reduction of nitro compounds [23,24]. Electrocatalytic oxidation of hydroquinone, dopamine and ascorbic acid using TiC–TiO 2 nanoparticles were also surveyed [25]. Large surface area may enhance electron trans- fer of TiO 2 , which can be obtained by preparing nanoporous tita- nium dioxide [26,27]. Nanostructured materials can not only contribute the highly active surface to the element that is sparing of natural resources but also bring in unique catalytic properties to the materials [28,29]. In the present work, nanoporous TiO 2 with enhanced surface area were prepared by anodizing titanium surface at different ap- plied potential in fluoride medium with a small amount of water. The prepared film was characterized using scanning electron microscopy, X-ray diffraction method, impedance spectroscopy 1572-6657/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2011.09.022 ⇑ Corresponding author. Tel.: +91 4565 227772; fax: +91 4565 227713. E-mail address: manbu123@yahoo.com (M. Anbu Kulandainathan). Journal of Electroanalytical Chemistry 663 (2011) 79–83 Contents lists available at SciVerse ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem