Characterization and photocatalytic activity of N-doped TiO 2 prepared by thermal decomposition of Ti–melamine complex M. Sathish, B. Viswanathan, R.P. Viswanath * Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, India Received 23 January 2007; received in revised form 28 February 2007; accepted 7 March 2007 Available online 15 March 2007 Abstract Nitrogen doped spherical TiO 2 has been prepared by thermal decomposition of Ti–melamine complex in air atmosphere. A clear shift in the onset light absorption from UV region (<400) to visible region (>520 nm) has been observed for the N-doped samples. It has been deduced from the optical absorption spectra that the higher calcination temperature results in the decrease in the amount of N-doping. The XRD results revealed the phase transition of TiO 2 from anatase to rutile crystalline phase, starting at calcination temperature 600 8C. The electron microscopic images reveal the formation of spherical and flakes of TiO 2 nanocrystals (25 nm). The chemical nature of N in the N-TiO 2 has been evolved through X-ray photoelectron spectroscopy. The presence of different types of N species have been observed corresponding to different oxidation states and the presence of Ti–N and O–Ti–N have been confirmed from the observed binding energy values. Photocatalytic decomposition of methylene blue has been carried out both in the visible region and UV + visible region. In the visible region, N-TiO 2 showed higher activity compared to the undoped commercial TiO 2 (Degussa P25). # 2007 Elsevier B.V. All rights reserved. Keywords: N-doped TiO 2 ; Anion doping; Photocatalysis; Visible light absorption 1. Introduction Titanium dioxide, the promising photocatalyst receives incessant attention so far from their earliest invention by the Japanese scientists in 1972 [1]. Though, it is active only in the UV region, the other properties like stability against photo- corrosion, moderate band gap and suitable band position, easy availability, safe and low cost, etc. makes this material as foremost one among the available photocatalysts. Recently, various attempts have been made to improve the visible light activity. Various noble/transition metal (or) metal ions have been doped into the TiO 2 lattice and the photocatalytic activity has been studied [2,3], but none of them has given satisfactory results. In particular, the stability, low inter particle electron transfer rate, photocorrosion of the dopant, and harmful nature of the doped materials are some of the drawbacks. It is conceived from the literature knowledge that the modification of the band structure is essential to alter the light absorption characteristics of the TiO 2 . With this in view, the research has been focused to modify its band structure in such a way that the electron-hole pair are created on the valence band (VB) and conduction band (CB) of the TiO 2 by absorbing the light from visible region. At the same time, it should be kept in mind that, the band edge position that is in the top of the valence band and bottom of the conduction position should not be altered exceedingly. This may diminish the reduction and oxidation capability of the TiO 2 photocatalyst. Among the various methods tried, the recent preliminary studies on doping of non- metals like N, S, C on TiO 2 lattice has opened a new door in the non-metal doping with significant expectation [4–20]. Also, it is presumed that the mixing of empty and filled orbital of the doped hetero atoms with the energetically coordinated valence and conduction band orbital results in the broadening of the VB and CB. Besides, there are a few theoretical reports including our recent theoretical results that demonstrate the doping of these non-metals on TiO 2 lattice results in broadening at the top of the valence band, due to the contribution of 2p or 3p orbital of doped hetero-atom [4,21–26]. Indeed, the position of hetero- atom in the lattice plays a major role in the band structure and position. In the case of TiO 2 , there are two different sites www.elsevier.com/locate/apcatb Applied Catalysis B: Environmental 74 (2007) 307–312 * Corresponding author. Tel.: +91 44 64540460; fax: +91 44 22574200. E-mail address: rpv@iitm.ac.in (R.P. Viswanath). 0926-3373/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2007.03.003