Invited article Review of the progress in preparing nano TiO 2 : An important environmental engineering material Yan Wang 1 , Yiming He 1, 2 , Qinghua Lai 1 , Maohong Fan 1, ⁎ 1. Department of Chemical & Petroleum Engineering, University of Wyoming, Laramie, WY 82071, USA. E-mail: yanwang0523@gmail.com 2. Department of Materials Physics, Zhejiang Normal University, Jinhua 321004, China ARTICLE INFO ABSTRACT Available online 12 October 2014 TiO 2 nanomaterial is promising with its high potential and outstanding performance in photocatalytic environmental applications, such as CO 2 conversion, water treatment, and air quality control. For many of these applications, the particle size, crystal structure and phase, porosity, and surface area influence the activity of TiO 2 dramatically. TiO 2 nanomaterials with special structures and morphologies, such as nanospheres, nanowires, nanotubes, nanorods, and nanoflowers are thus synthesized due to their desired characteristics. With an emphasis on the different morphologies of TiO 2 and the influence factors in the synthesis, this review summarizes fourteen TiO 2 preparation methods, such as the sol–gel method, solvothermal method, and reverse micelle method. The TiO 2 formation mechanisms, the advantages and disadvantages of the preparation methods, and the photocatalytic environmental application examples are proposed as well. © 2014 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. Keywords: TiO 2 preparation Nanomaterial Formation mechanism Photocatalytic environmental application Contents Introduction ........................................................... 2140 1. TiO 2 preparation methods ................................................. 2140 1.1. Sol–gel method ................................................... 2140 1.2. Hydrothermal method ............................................... 2144 1.3. Solvothermal method ................................................ 2147 1.4. Anodic oxidation method .............................................. 2151 1.5. Microwave-assisted method ............................................ 2155 1.6. Hard template method ............................................... 2157 1.7. Reverse microemulsion method .......................................... 2158 1.8. Direct oxidation method .............................................. 2160 1.9. Non-hydrolytic sol–gel method ........................................... 2162 1.10. Sonochemical method ............................................... 2164 1.11. Chemical vapor deposition ............................................ 2165 1.12. Physical vapor deposition ............................................. 2167 JOURNAL OF ENVIRONMENTAL SCIENCES 26 (2014) 2139 – 2177 ⁎ Corresponding author. E-mail: mfan@uwyo.edu (Maohong Fan). http://dx.doi.org/10.1016/j.jes.2014.09.023 1001-0742/© 2014 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. Available online at www.sciencedirect.com ScienceDirect www.journals.elsevier.com/journal-of-environmental-sciences