Fabrication of TiO 2 nanospheres by template replication in porous carbon networks
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S.B. Yoon and J-S. Yu Department of Chemistry, Hannam University, Daejon 306-701, Korea (Received 1 October 2002; accepted 27 December 2002)
A silica-colloidal template approach was used to prepare monodisperse nanospheres of TiO2. Close-packed arrays of silica spheres were infiltrated with a sucrose precursor used as a source of carbon. The infiltrated sucrose was carbonized by calcination at 800 °C in flowing argon. After removal of the silica spheres by washing with HF, a porous carbon replica remained. The resulting pores in the replica were then filled with a chloroform solution of titanium alkoxide. Nanospheres of TiO2 approximately 200 nm in diameter were obtained after calcination of the organic component at 600 °C in an argon atmosphere and subsequent sintering in air at 700 °C.
I. INTRODUCTION
Recently, nanocrystalline TiO2 materials have attracted a great deal of attention, largely because they have a wide range of applications in many technologies, such as solar cell,1,2 photocatalysis,3 and photonic bandgap materials.4,5 In particular, monodisperse nanospheres of TiO2 are a promising class of such materials that have many potential applications because of their size and shape. However, the direct synthesis of uniform and monodisperse spherical TiO2 is very difficult, although nanocrystalline powders with various diameters have been prepared by various techniques.6– 8 Only silica and polymer colloidal crystals have thus far been prepared with a very narrow size distribution. Thus, one alternative approach for creating monodisperse and spherical TiO2 materials is to use monodisperse silica or polymer colloidals as templates.9 This template method has been successfully applied to produce various nanoporous materials.10 For instance, macroporous polymers replicated from silica templates were used as templates to generate inorganic oxide materials.9 One disadvantage, however, is that the polymer replica has a carbon residue even after sintering at high temperature. In this paper, we describe a template synthesis of spherical TiO2 nanocrystals within a highly ordered nanoporous carbon matrix. With colloidal silica, SiO2, as a template, a porous carbon replica was produced after the removal of the core silica. The uniform and spherical voids of the carbon replica were then used as a a)
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J. Mater. Res., Vol. 18, No. 4, Apr 2003 Downloaded: 12 Jun 2014
microreactor to grow spherical TiO2 nanocrystals. An important feature of this method is that the voids are well ordered and highly uniform over long distances. Since neighboring voids are three-dimensionally interconnected through small channels and the carbon framework exhibits long-range order, the pores can be completely filled with the metal alkoxide precursor and the physical dimensions of the colloids formed within the voids are preserved. It is shown that this template approach is relatively straightforward but widely applicable in producing vario
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