A simple low-cost synthesis of brookite TiO 2 nanoparticles
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A new low-cost synthesis of brookite TiO2 nanoparticles using isopropanol as both the solvent and ligand is described here. Other ligands can be bound to the titania surface during or postsynthesis to tailor the particles’ functionality. The often extremely rapid hydrolysis of titanium isopropoxide has been successfully controlled so that nanoparticle growth is achieved. The resulting 4-nm particles are nonagglomerated, stable in solution, and have a low polydispersity. The synthesis is scalable and enables the simple fabrication of large amounts of titania nanoparticles that do not scatter visible light and are highly suited for incorporation into optical composites. I. INTRODUCTION
Wide band gap metal oxides, like TiO2, have a wide range of uses, particularly if they can be synthesized in nanoparticle form. Titania nanoparticles have proven to be very useful across a broad range of applications and have been intensively studied. For example, TiO2 nanoparticles are excellent precursors for the formation of mesoporous semiconductor layers in dye-sensitized solar cells and recently in many solid-state polymer solar cells.1,2 Titania nanoparticles also find applications as catalysts,3 photocatalysts,4–7 pigments,8 as a possible electrode material in rechargeable lithium batteries,9,10 and in many optical devices.11–13 Here, we present a simple room temperature synthesis for nonagglomerated crystalline titania (TiO2) nanoparticles without the use of expensive organic surfactants or high temperature processing. The synthesis requires only three inexpensive widely available chemicals (titanium isopropoxide, isopropanol, and water) and produces very high quality nanoparticles that are well dispersed. Different ligands can be bound to the titania surface during or postsynthesis to further modify the particles’ functionality. The particles described here are well suited for use in optical devices and other applications. Due to its high utility, a variety of different synthetic techniques have been used to fabricate TiO2 nanoparticles. A common method of synthesizing commercially available titania nanoparticles is through oxidation of titanium tetrachloride (TiCl4) in a methane–oxygen flame.14,15 This approach is high yield and cost-effective yet it produces particles with a very high size dispersity. These particles also tend to agglomerate since they have high surface area and are synthesized without any ligands. Two other less common synthesis techniques used for commercial TiO2 a)
Address all correspondence to this author. e-mail: [email protected] b) Present address: Department of Chemistry, University of Washington, Seattle, Washington 98195 DOI: 10.1557/jmr.2012.358
involve ultrasonic irradiation4 and chemical vapor deposition,16 which both result in particles that suffer from similar issues as oxidation of TiCl4. Many research groups have fabricated titania nanoparticles on a smaller scale using wet chemistry techniques. A common approach is to synthesize the particles by hydrolyzing alkoxide or halide titanium pr
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