Phase selection and visible light photo-catalytic activity of Fe-doped TiO 2 prepared by the hydrothermal method Lin Wan a , Yun Gao a , Xiao-Hong Xia a,b, *, Quan-Rong Deng a,b , G. Shao b a Faculty of Physics & Electronic Technology, Hubei University, Wuhan 430062, China b Institute for Materials Research and Innovation, University of Bolton, Bolton BL3 5AB, UK 1. Introduction Nanocrystalline TiO 2 , particularly the anatase phase, has been extensively exploited as a major photo-catalyst to clean the living environment. In addition to its high catalytic activity, TiO 2 is low- cost, abundant in resources, nontoxic, and of long-term stability. Among various environmental applications, TiO 2 has attracted increasing attention for photo-catalytic degradation of water pollutants [1,2]. However, the photo-catalytic property of TiO 2 can be activated only by the ultraviolet (UV) light with wavelength shorter than 387 nm due to its large band gap (3.2 eV). The UV light accounts for merely 4% of the solar spectrum, and worse still, it can be readily filtered even by clear glass and pure water. It is thus necessary to develop a TiO 2 based photo-catalyst that efficiently absorbs visible light to activate their desiring catalytic functionality. Recently, various studies have been directed towards shifting the optical absorption edge of TiO 2 from the UV to visible range by doping with metallic cations (V, Mn, Cr, Ag, Pt, Co and Fe) [3–13] and non-metallic anions (C, N, S, F, P and I) [14–21] or co-doping with several ions [22–24]. Among the various doping ions, Fe 3+ was proven to be a useful dopant. It has been reported that a proper concentration of Fe 3+ ions in TiO 2 is not only beneficial to electron–hole separation, but also to narrowing the band gap of TiO 2 to permit the utilization of visible light [25–29]. Further- more, iron is inexpensive and rich in resource, which will be potentially advantageous for sustainable low-cost commercial exploitation. In addition to desirable reduction of the TiO 2 band gap, microstructure properties such as phase type (anatase or rutile), grain size, and morphology of the nanocrystals are also very important to the photo-catalytic activity of TiO 2 . The hydrothermal method has been shown to be more effective in tuning the size and crystalline structures, via controlling processing parameters including temperature, pressure and concentration of the chemical species [30], than other methods such as sol–gel, metal organic chemical vapor deposition, and metal plasma ion implantation. Although the phase selection of pure titanium dioxide under hydrothermal conditions has been widely investigated [31,32],a systematic study of the various processing factors on phase selection and structural control of Fe-doped TiO 2 is yet lacking. In the present work, we have carried out a systematic study of the effects of some important processing parameters on phase selection and microstructure development in Fe-doped TiO 2 photo-catalysts. It has been demonstrated that the Fe-doped TiO 2 catalysts are able to absorb most of the visible light to induce improved photo-catalytic performance, with anatase being more photoactive than its rutile counterpart. Materials Research Bulletin 46 (2011) 442–446 ARTICLE INFO Article history: Received 11 February 2010 Received in revised form 24 October 2010 Accepted 18 November 2010 Available online 1 December 2010 Keywords: A. Nanostructures B. Chemical synthesis C. X-ray diffraction D. Catalytic properties ABSTRACT It is necessary to extend the absorption range of TiO 2 based materials from the ultraviolet to the visible light region for most photo-catalytic applications of TiO 2 under solar irradiance or indoor lighting. Also, the ability to control the structural evolution, particularly the competition and transformation between different phases (anatase or rutile), is extremely important for the preparation of high efficiency TiO 2 based photo-catalysts. In this work, we have systematically studied the effects of various processing factors on the phase selection process/outcome of nanocrystalline Fe-doped TiO 2 , which includes the level of doping ions, annealing temperature, solution pH and the addition of acidic anions, using a low temperature hydrothermal method. Both Fe-doped rutile and anatase TiO 2 phases were obtained via varying the processing conditions. The visible-light photo-catalytic activity of doped materials was significantly improved over that of the pure TiO 2 nanopowders, which was demonstrated by effective degradation of methylene blue under visible light. ß 2010 Elsevier Ltd. All rights reserved. * Corresponding author at: Faculty of Physics & Electronic Technology, Hubei University, Wuhan 430062, China. Tel.: +86 27 88663797; fax: +86 27 88663797. E-mail address: xhxia@hubu.edu.cn (X.-H. Xia). Contents lists available at ScienceDirect Materials Research Bulletin journal homepage: www.elsevier.com/locate/matresbu 0025-5408/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2010.11.032