Synthesis of nanoparticulate anatase and rutile crystallites at low temperatures in the Pluronic F127 microemulsion syst
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Hirotoshi Furusho Structural Chemistry, Department of Materials and Environmental Chemistry, Stockholm University, SE 106 91 Stockholm, Sweden
Osamu Terasaki Structural Chemistry, Department of Materials and Environmental Chemistry, Stockholm University, SE 106 91 Stockholm, Sweden; and Graduate School of EEWS (WCU), KAIST, Daejeon 305-701, Republic of Korea
Anders E.C. Palmqvistb) Applied Surface Chemistry, Dept. of Chemical and Biological Engineering, Chalmers University of Technology, SE 412 96 Göteborg, Sweden (Received 1 May 2010; accepted 7 September 2010)
A low-temperature synthesis method for preparing nanosized TiO2 crystallites has been developed based on a Pluronic F127 microemulsion system. Both anatase and rutile polymorphs can be prepared, and there exists a temperature window between 40 and 50 °C where the formation of rutile is favored over anatase. At 60 °C and above, anatase is kinetically favored and only very slowly transforms to rutile at 60 °C. The results differ from previous observations regarding formation kinetics and temperature range for rutile formation as well as in the microscopic aggregation of the formed nanoparticles. This development of a low-temperature synthesis of crystalline titania nanoparticles within the Pluronic block copolymer system is an important and enabling step toward devising a direct synthesis route for the formation of ordered mesoporous and crystalline titania. I. INTRODUCTION
Titania (TiO2) is a photoactive compound of great importance for photophysical and photochemical applications. In 1972, Fujishima and Honda showed that TiO2 can be used to photocatalytically split water to hydrogen and oxygen using solar light, a topic of great current societal interest and intense research.1 The strong photocatalytic oxidation capacity of TiO2 is also used for degradation of organic contaminants in water and air.2 In this area, selfcleaning coatings of titania are saving large amounts of energy.3 More recently, titania has been increasingly studied for its great potential as an active component in solar cells as demonstrated by Oregan and Grätzel.4 Titania occurs as a common compound in the earth’s crust where its three most common polymorphs are brookite, anatase, and rutile. Rutile is thermodynamically stable, whereas anatase and brookite are metastable. The polymorphs have somewhat different electronic and optical properties and hence different areas of application. Anatase has been reported to exhibit higher photocatalytic activity than rutile.2,5 However, there are studies that show Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2010.5 288
J. Mater. Res., Vol. 26, No. 2, Jan 28, 2011
http://journals.cambridge.org
Downloaded: 11 Mar 2015
that rutile nanoparticles synthesized at low temperatures show similar activity but may catalyze different reaction paths compared with anatase.6–8 A way of further improving the effectiveness of crystalline titania for photocatalytic oxidation is to
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