Porous TiO 2 with a controllable bimodal pore size distribution from natural ilmenite Tao Tao, ab Alexey M. Glushenkov, * a Qiyuan Chen, b Huiping Hu, b Dan Zhou, cd Hongzhou Zhang, cd Markus Boese, d Sanly Liu, e Rose Amal e and Ying Chen a Received 13th August 2010, Accepted 11th October 2010 DOI: 10.1039/c0ce00533a Ilmenite (FeTiO 3 ) is an inexpensive abundant natural mineral and it would be a perfect precursor for the production of porous TiO 2 if a suitable synthesis method was developed. A new method combining a series of processing steps of ball milling, high-temperature annealing, selective chemical leaching and ﬁnal calcining in air is proposed in this paper. The resulting TiO 2 is a porous material with a bimodal pore structure. The pore size distribution has two clear maxima corresponding to small mesopores (2–30 nm) and large meso- and macropores (centered at around 50–80 nm). It was found that the duration of the annealing step could alter the contribution of each type of pores. A short annealing time (0.5 h) lead to the preferential formation of pores within 2–30 nm while pores centered at 50–80 nm dominated the pore size distribution after a relatively long annealing (1.5 h). The obtained porous rutile TiO 2 shows a better photocatalytic activity than that of a commercial rutile TiO 2 powder. 1. Introduction Porous titania (TiO 2 ) has applications in solar cells, photo- catalysts, and lithium-ion batteries. 1–4 The porous structure plays an important role in these applications because it provides a larger surface area and often a well-deﬁned characteristic pore size. For example, it has been reported that the photoelectric conversion efﬁciency of a dye-sensitised solar cell prepared using mesoporous TiO 2 nanoparticles as an electrode material was 10.1%, exceeding the efﬁciency of the reference cell based on P25 (nonporous TiO 2 nanopowder) by 3.8%. 2 Hierarchically micro-/ nano-porous TiO 2 ﬁlms have an improved photocatalytic activity in mineralizing gaseous acetaldehyde and liquid-phase phenol with respect to that of non-porous ﬁlms, because the continuous pore channels in the porous TiO 2 ﬁlm enhance the transportation of reactants, products and O 2 within the catalytic framework. 3 A number of synthetic methods have been proposed for obtaining porous titanium dioxide. They often involve the use of templates and include (but are not limited to) hydro- and solvothermal methods, sol–gel synthesis, evaporation-induced self-assembly and application of ionic liquids. 5–12 In many cases the titanium precursors or templates used for preparing porous TiO 2 (for example, tetraisopropyl-orthotitanate, 13 titanium tet- raisopropoxide, 14 cetyltrimethylammonium bromide (CTAB), 15 mesoporous silicas SBA-15 or KIT-6 16 ) are not readily available or expensive materials. Ilmenite (FeTiO 3 ), naturally occurring iron titanate, is cheap, abundant, and suitable for producing titanium dioxide. The US Geological Survey 17 states that the world total reserves of ilmenite are above 680 million tons (containing about 350–400 million tons of TiO 2 ) and the deposits of ilmenite can be found in different parts of world – North America (USA, Canada), South America (Brazil), Australia, Asia (China, India, and Vietnam), Europe (Norway, Ukraine) and Africa (South Africa, Mozam- bique). According to the same source, the price of ilmenite is low and was ﬂuctuating between 80 and 107 USD per ton between 2004 and 2008. At present, ilmenite is commonly used in industry for making white pigment via a sulfate or chlorine route. 18,19 It would be very desirable to adapt the existing industrially appli- cable techniques to the preparation of porous TiO 2 suitable for advanced applications. In the current paper we demonstrate a method capable of preparing TiO 2 with porous structure from ilmenite. The method includes carbothermal reduction, ball milling and acid leaching. Carbothermal reduction is a process in which ilmenite is reduced by carbon to yield metallic iron and titanium oxide at high temperatures. Ball milling is capable of reducing the temperature needed for carbothermal reduction of ilmenite and increasing the rate of this reaction. 20 Chen et al. have reported that a ball milled mixture of FeTiO 3 and activated carbon can react and produce rutile TiO 2 at a temperature as low as 760  C. 21 The effects of the pre-treatment of ilmenite by ball milling on its reﬁnement can be attributed to the creation of crystal defects and lattice distortions, the decrease in particle sizes and the increase of surface areas. 21,22 A parametric study of the mechanically activated carbothermal reduction of ilmenite has been published by Welham. 23 Recently, single-crystalline TiO 2 nanorods have also been produced using the ball milling and annealing process. 24 The low temperature treatment in hydrogen atmosphere activates a Institute for Technology Research and Innovation, Deakin University, Waurn Ponds, VIC 3217, Australia. E-mail: alexey.glushenkov@deakin. edu.au; Fax: +61 3 52271103; Tel: +61 3 52272931 b College of Chemistry and Chemical Engineering, Central South University, Changsha, 410083, China c School of Physics, Trinity College Dublin, Dublin 2, Republic of Ireland d Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Dublin 2, Republic of Ireland e School of Chemical Engineering, ARC Centre of Excellence for Functional Nanomaterials, The University of New South Wales, Sydney, NSW 2052, Australia 1322 | CrystEngComm, 2011, 13, 1322–1327 This journal is ª The Royal Society of Chemistry 2011 PAPER www.rsc.org/crystengcomm | CrystEngComm Downloaded by Trinity College Dublin on 02 April 2012 Published on 05 November 2010 on http://pubs.rsc.org | doi:10.1039/C0CE00533A View Online / Journal Homepage / Table of Contents for this issue