Graphene oxide modified TiO 2 nanotube arrays: enhanced visible light photoelectrochemical properties Peng Song, a Xiaoyan Zhang, a Mingxuan Sun, a Xiaoli Cui * a and Yuehe Lin b Received 7th December 2011, Accepted 20th December 2011 DOI: 10.1039/c2nr11938b Novel nanocomposite films, based on graphene oxide (GO) and TiO 2 nanotube arrays, were synthesized by assembling GO on the surface of self-organized TiO 2 nanotube arrays through a simple impregnation method. The composite films were characterized with field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and UV–vis diffuse reflectance spectroscopy. The photoelectrochemical properties of the composite nanotube arrays were investigated under visible light illumination. Remarkably enhanced visible light photoelectrochemical response was observed for the GO decorated TiO 2 nanotube composite electrode compared with pristine TiO 2 nanotube arrays. The sensitizing effect of GO on the photoelectrochemical response of the TiO 2 nanotube arrays was demonstrated and about 15 times enhanced maximum photoconversion efficiency was obtained with the presence of GO. An enhanced photocatalytic activity of the TiO 2 nanotube arrays towards the degradation of methyl blue was also demonstrated after modification with GO. The results presented here demonstrate GO to be efficient for the improved utilization of visible light for TiO 2 nanotube arrays. 1. Introduction As a very famous semiconductor, TiO 2 has received much attention because of its long-term stability, no toxicity, low cost and broad functionality. Due to its outstanding physical and chemical properties, vertically oriented, highly ordered TiO 2 nanotube arrays have been extensively studied for their appli- cation in dye sensitized solar cells, 1–4 hydrogen generation by water photoelectrolysis 1 , and so on. Unfortunately, the wide band gap of TiO 2 (3.2 eV for anatase and 3.0 eV for rutile) makes light absorption occur only in the UV range, which accounts for only 4–5% of the spectrum of solar light. In order to utilize the solar light more efficiently, numerous approaches have been developed to promote the photoresponse of TiO 2 in the visible light region. Many researches have demonstrated that TiO 2 doped with non-metal elements, such as nitrogen, 5,6 boron, 7 fluorine, 8 sulphur 9 or carbon 10,11 and metal elements, such as iron 12 or niobium 13 show an improved response and higher photocatalytic activity in the visible light region. The coupling of TiO 2 to semiconductors has been proved to be another efficient method to enhance its photoresponse under visible light. Several semiconductors, such as CdS, 14,15 CdTe, 16,17 CdSe, 18,19 PbS, 20,21 NiO, 22 and SrTiO 3 23 have been adopted to improve the utilization of visible light for TiO 2 nanotube arrays. However, most of these sensitizers are either highly poisonous or expensive, thus limiting their practical applications. Besides, alternate absorption and rinse processes are often required for quantum dots sensitizers 14,21 and high temperature processing is often required for oxide sensitizers. 22,23 As one of the most promising precursors of graphene, which has attracted tremendous attention for its unique physicochem- ical properties, 24–28 graphene oxide (GO) is environmental friendly and cheap and has been widely studied in recent years. Inorganic materials modified with partially reduced GO have been reported to represent enhanced electrocatalytic 29 and pho- tocatalytic properties. 30 Nanocomposites based on graphene and TiO 2 nanoparticles have been widely investigated and their photocatalytic properties have been demonstrated. 31–33 We are highly interested in the photoelectrochemical properties of GO modified TiO 2 nanotube arrays, which have not been investi- gated so far. Herein, GO was assembled onto TiO 2 nanotube arrays by simple absorption in an attempt to improve the pho- toelectrochemical response of the array in the visible light region. The sensitizing effect of GO on the TiO 2 nanotubes was first studied by measuring the photoelectrochemical performance of the GO modified TiO 2 nanotube arrays under visible light irra- diation. Compared with previous strategies, our method presents a combination of advantages, such as a relatively high efficiency, an environmental friendly procedure, a low cost and a facile process. a Department of Materials Science, Fudan University, Shanghai, 200433, P. R. China. E-mail: xiaolicui@fudan.edu.cn; Fax: +86-21-65642682; Tel: +86-21-65642397 b Pacific Northwest National Laboratory, Richland, Washington, 99352, USA 1800 | Nanoscale, 2012, 4, 1800–1804 This journal is ª The Royal Society of Chemistry 2012 Dynamic Article Links C < Nanoscale Cite this: Nanoscale, 2012, 4, 1800 www.rsc.org/nanoscale PAPER Published on 04 January 2012. Downloaded by National Kaohsiung University of Applied Sciences on 08/07/2017 10:19:15. View Article Online / Journal Homepage / Table of Contents for this issue