Copper-incorporated titania nanotubes for effective lead ion removal Srimala Sreekantan a,n , Syazwani Mohd. Zaki a , Chin Wei Lai b , Teoh Wah Tzu c a School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia Engineering Campus, 14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia b Nanotechnology & Catalysis Research Centre (NANOCAT), Institute of Postgraduate Studies (IPS), University of Malaya, 3rd Floor, Block A, 50603 Kuala Lumpur, Malaysia c Department of Civil and Environmental Engineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2118, Japan article info Available online 18 June 2014 Keywords: Cu-loaded TiO 2 nanotubes Wet impregnation Heavy metals Photocatalytic Lead(II) ions abstract Small copper (Cu 2 þ ) dopant levels were successfully diffused into titanium dioxide (titania or TiO 2 ) nanotube lattice via an incipient wet impregnation technique. This study investigated the optimum Cu 2 þ dopant content to be incorporated into the TiO 2 nanotubes to achieve an effective lead ion (Pb(II)) removal system. The exciton states of the PL intensities varied in the following order: pure TiO 2 40.6 M Cu–TiO 2 40.1 M Cu–TiO 2 40.06 M Cu–TiO 2 40.01 M Cu–TiO 2 . The significant quenching of the PL intensity indicates that incorporation of the appropriate amount of Cu 2 þ dopants into the TiO 2 lattice markedly enhanced the charge-carrier separation and transport. The photocatalytic ability of the samples was evaluated by the removal of the Pb(II) ions under UV illumination. The results show that the Cu dopants in the TiO 2 lattice at the optimum concentration (0.8 at%) acted as photoinduced electron mediators and thus increased the Pb(II) ion removal efficiency. The maximum Pb(II) ion removal rates for the 0.01 M Cu–TiO 2 nanotubes and after five hours of UV illumination were approximately 56.3% and 79.5% at pH 5 and pH 11, respectively. The generation of strong oxidizing agents (dOH radicals) effectively reduces the toxic Pb(II) ions into PbO/PbOH. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction The rapid growth of electronic waste (e-waste) volumes in the Association of Southeast Asian Nations (ASEAN) region has increasingly gained international attention. Economies face huge demands for electrical and electronic products, whereas governments are confronted with diffi- culties in dealing with the increasing volumes of e-waste [1]. In addition, economic growth and higher living stan- dards has led to a rapidly increasing demand for electrical and electronic equipment (EEE) [1]. As a consequence, large volumes of waste and pollution are discharged into streams, rivers, or seas. In a scientific report, Goosey [2] showed that the volumes of e-waste are growing three times faster than that of average solid waste. In addition, at least 50 million tons of e-waste are produced each year [3]. The U.S. Environmental Protection Agency (U.S. EPA) estimates that only 15–20% of e-waste is recycled; the rest of these electronics go directly into landfills and incinera- tors [4]. Thus, initiatives and strategic measures must be immediately implemented to remove toxic heavy metal ions from e-waste. Among various types of semiconductor photocatalysts, titanium dioxide (TiO 2 ) has the most promising photocatalysts Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/mssp Materials Science in Semiconductor Processing http://dx.doi.org/10.1016/j.mssp.2014.05.034 1369-8001/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. Tel.: þ60 45995255; fax: þ60 45941011. E-mail addresses: srimala@usm.my (S. Sreekantan), cwlai@um.edu.my (C.W. Lai). Materials Science in Semiconductor Processing 26 (2014) 620–631