Separation and Purification Technology 67 (2009) 152–157 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur A mesoporous TiO 2−x N x photocatalyst prepared by sonication pretreatment and in situ pyrolysis Guisheng Li a , Jimmy C. Yu a,∗ , Dieqing Zhang a , Xianluo Hu a , Woon Ming Lau b a Department of Chemistry and Environmental Science Programme, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China b Surface Science Western, University of Western Ontario, London, Ontario N6A 5B7, Canada article info Keywords: Titanium dioxide Nitrogen doping Pyrolysis Chelation Sonication abstract A novel method for preparing a visible-light-driven mesoporous TiO 2−x N x photocatalyst has been devel- oped. It involves the in situ pyrolysis of the product from a chelation reaction under sonication between TiCl 4 and ethylenediamine in an ethanol solution of the triblock copolymer F127. The as-prepared pho- tocatalysts exhibit very strong photoactivity in the photocatalytic oxidation of methylene blue under irradiation in the visible spectral region. The samples were characterized by spectroscopic techniques including ultraviolet–visible light reflectance (UV–vis), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission elec- tron microscopy (TEM). The effects of ultrasound on the physicochemical properties and photoactivity of mesoporous TiO 2−x N x are discussed based on the characterization results. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The application of TiO 2 photocatalyst for degradation of various kinds of organic and inorganic pollutants has been extensively stud- ied [1]. A major limitation of TiO 2 is that with a band gap of 3.2 eV it can only be activated by UV radiation [2]. A great deal of effort has been made to develop the visible-light-responsive materials by narrowing the band gap of TiO 2 . These include substituting the lattice Ti ion with various kinds of transition-metal ions [3,4] and doping of TiO 2 with impurities such as carbon, nitrogen, fluorine, or sulfur [5–10]. Surface area and crystallinity are important fac- tors that affect the activity of a photocatalyst. A highly crystalline mesoporous TiO 2 with a large surface area is obviously advanta- geous [11,12]. Surprisingly, reports on the preparation of N-doped mesoporous TiO 2 are scarce. Non-mesoporous N-doped TiO 2 mate- rials are usually prepared by treating TiO 2 under NH 3 atmosphere at very high temperatures, such as 500 ◦ C. Such an approach is energy intensive and the resulting products tend to have low sur- face area owing to agglomeration. We have developed recently a method to fabricate mesoporous TiO 2−x N x through thermal treat- ment of NH 3 -absorbed TiO 2 hydrous gels. The undesirable crystal growth during calcination was effectively inhibited by the addition of ZrO 2 as a structure stabilizer [13]. Herein, we describe a novel route to N-doped mesoporous TiO 2 without adding any stabilizers. This is done by in situ pyrolysis of the product of a chelation reac- ∗ Corresponding author. Tel.: +852 2609 6268; fax: +852 2603 5057. E-mail address: jimyu@cuhk.edu.hk (J.C. Yu). tion between TiCl 4 and ethylenediamine in an ethanol solution of surfactant under ultrasound irradiation. The use of ultrasound to enhance the rate of reaction has become a routine synthetic tech- nique for many homogenous and heterogeneous chemical systems [14,15]. Sonochemistry has been used to prepare various oxides and amorphous metal powders [15–17]. In the present work, ultrasonic irradiation can help disperse the TiO 2 particles, increase the sur- face area, enlarge the pore volume, and incorporate a relatively high concentration of nitrogen into the TiO 2 framework. 2. Experimental 2.1. Catalyst preparation To synthesize mesoporous TiO 2−x N x , we used titanium tetra- chloride (Aldrich) as a titanium source, a triblock copolymer F127 (EO 106 PO 70 EO 106 , Aldrich) as a structure direction agent, and ethylenediamine as a source of nitrogen. In a typical synthesis, an amount of 1.84g of F127 was dissolved in 60ml ethanol (EtOH). To this clear solution, 0.0125 mol TiCl 4 was added dropwise with vigor- ous stirring at room temperature. The product was labeled Solution A. A second solution was prepared by mixing 5.2 ml ethylenedi- amine with 20 ml ethanol. This mixture was added dropwise to Solution A under sonication for 1 h in an ultrasonic cleaning bath (Bransonic ultrasonic cleaner, model 3210E DTH, 47kHz, 120W, USA). The reaction mixture was aged for 24h in a closed autoclave at 180 ◦ C to form mono-dispersed TiO 2−x N x precursor particles. The particles were filtered and dried at 100 ◦ C in air in order to vaporize the residual alcohol, and then calcined at 350 ◦ C or 450 ◦ C 1383-5866/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2009.03.022