Short Communication Cu 2 O/TiO 2 heterostructure nanotube arrays prepared by an electrodeposition method exhibiting enhanced photocatalytic activity for CO 2 reduction to methanol Junyi Wang a , Guangbin Ji a, ⁎, Yousong Liu a , M.A. Gondal b , Xiaofeng Chang a a College of Material Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 211100, China b Laser Research Group, Physics Department, Center of Excellence in Nanotechnology, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia abstract article info Article history: Received 13 June 2013 Received in revised form 21 September 2013 Accepted 12 November 2013 Available online 20 November 2013 Keywords: Cu 2 O/TiO 2 heterostructures Electrodeposition CO 2 photocatalytic reduction to methanol Degradation of organic pollutants (dyes) Cu 2 O/TiO 2 composite nanotube arrays demonstrating enhanced photocatalytic performance were synthesized using an electrodeposition method to impregnate the p-type Cu 2 O into the n-type titanium dioxide nanotube arrays (TNTs). The morphological results confirmed that the TNTs are wrapped by the Cu 2 O nanoparticles and the UV–Vis absorption spectra showed that the Cu 2 O/TNTs display a better ability for visible light absorption compared to the pure TNTs. CO 2 photocatalytic reduction experiments carried out by using Cu 2 O/TNT nanocom- posites proved that Cu 2 O/TNTs exhibit high photocatalytic activity in conversion of CO 2 to methanol, while pure TNT arrays were almost inactive. Furthermore, Cu 2 O/TNTs also exhibited augmented activity in degradation of target organic pollutant like acid orange (AO) under visible light irradiation. The ultra enhanced photocatalytic activity noticed by using Cu 2 O/TNTs in CO 2 reduction and degradation of organic pollutant could be attributed to the formation of Cu 2 O/TiO 2 heterostructures with higher charge separation efficiency. © 2013 Elsevier B.V. All rights reserved. 1. Introduction In recent years, a lot of research has been carried out to study the solar-driven photocatalytic conversion of CO 2 into hydrocarbon fuels to achieve the primary objective of the cyclic utilization of CO 2 due to global warming and climate change [1,2]. So far, semiconductor photocatalysts like TiO 2 , ZnO [3], CdS [4], ZnGa 2 O 4 [5], Zn 2 GeO 4 [6,7], InTaO 4 [8], and WO 3 [9,10] have been widely investigated. Among them, TiO 2 has attracted considerable attention for its nontoxicity, low cost and stability in the field of photoelectric conversion and photo- catalysis. Compared with the traditional TiO 2 particles, TiO 2 nanotube arrays have been widely applied for their large surface areas, excellent controllability, superior electron transport properties and excellent per- formance [11,12]. However, the wide band gap of TiO 2 (3.2 eV) inhibits its use for solar energy applications as TiO 2 only absorbs light having wavelength shorter than 387 nm in the ultraviolet region [13,14]. The construction of interface structure, such as heterojunction [15], is con- sidered as an effective tool to improve the utilization of sun light and separation efficiency of the photo-generated electrons and holes. So far, the photocatalytic performance of the interface structures, such as CdS/TiO 2 [16], Fe 2 O 3 /TiO 2 [17], MoS 2 (WS 2 )/TiO 2 [18], and CdS (Bi 2 S 3 )/ TiO 2 [19], has been widely studied. Cu 2 O exhibits great potential for applications in the field of the conversion of solar energy because of its advantages such as low price, visible light absorption and adjustable band-gap [20–24]. Coupled Cu 2 O with TiO 2 to form Cu 2 O/TiO 2 hetero- junction may enhance the light absorption ability and photocatalytic activity in CO 2 reduction. In this paper, we used TiO 2 nanotube arrays as the matrix to prepare Cu 2 O/TNTs using electrodeposition method. The photoelectric proper- ties and the photocatalytic activity of the composite photocatalyst in CO 2 reduction into hydrocarbon like methanol and photodegradation of organic pollutant (acid orange dye) were investigated. 2. Experimental section 2.1. Materials' preparation and characterization Well-ordered TNTs were prepared by the anodization of Ti foil, as re- ported earlier [25]. The Cu 2 O/TNT composites were prepared using a simple electrodeposition method (the preparation process in detail has been presented in the supplementary material). The morphology of the prepared samples was studied with scanning electronic microsco- py (SEM, HITACHI-S4800). The crystal structure of the samples was examined by means of X-ray diffraction analysis (XRD, Bruker D8 ADVANCE with Cu-Kα radiation, λ = 1.5418 Å). UV–Vis absorption spectra of the Cu 2 O/TNT composites were obtained using a UV–Vis spec- trometer (Shimadzu UV-3600). Catalysis Communications 46 (2014) 17–21 ⁎ Corresponding author. Tel.: +86 25 52112902; fax: +86 25 52112900. E-mail address: gbji@nuaa.edu.cn (G. Ji). 1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.catcom.2013.11.011 Contents lists available at ScienceDirect Catalysis Communications journal homepage: www.elsevier.com/locate/catcom