Selective synthesis of nanosized TiO 2 by hydrothermal route: Characterization, structure property relation, and photoch
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A. Ramachandra Reddy Department of Physics, National Institute of Technology, Warangal, Andhrapradesh 506004, India (Received 9 January 2004; accepted 22 March 2004)
By variation of reaction temperature and time during the hydrothermal synthesis process, TiO2 nanoparticles in anatase, rutile, and mixture of rutile-anatase phases are formed without adding any mineralizer. Differential thermal analysis studies indicate the rutile phase crystallization at a comparatively lower temperature and a low weight loss. The material synthesized by hydrothermal reaction required no post-calcination for the crystallization. Transmission electron microscopy, selected-area diffraction, Brunauer–Emmett–Teller, and x-ray diffreaction studies confirmed the compositions to be anatase and rutile with the particle size ranging from 5 to 25 nm with surface area as high as 260 m2/g for the anatase and 65 m2/g for rutile. The prepared nanoparticles exhibited a blue shift of the absorption edge in the ultraviolet-visible spectrum greater than 10 nm. The particles with average size around 5 nm showed two band edges in the absorption spectra attributed to two different particle sizes. Simple photocatalytic reactions were tried to demonstrate the photochemical activity of the synthesized material. The synthesized nanoparticles exhibited an ultraviolet radiation simultaneous photoreduction of Cr(VI) to Cr(III) and oxidation of formic acid into carbon dioxide and water.
I. INTRODUCTION
Titanium dioxide possesses interesting optical, dielectric, and catalytic properties, which result in industrial applications such as pigments, dye sensitized solar cells, fillers for catalyst supports, and in photocatalysis.1,2 As a pure component and as a mixture with other oxides, TiO2 has been associated with improved sensitivity to humidity, oxygen,3 enhanced mechanical property,4 and catalytic activity,5 and it has also been used in membrane separations involving chemical reactions.6 Titania has been known to exist in several polymorphic forms, of which anatase and rutile have been widely studied. Rutile is the only stable phase, whereas anatase and brookite are metastable at all temperatures and transform to rutile on heating to temperatures above 700 °C.7 The rutile phase offers an attractive combination of physical properties which has made it the most widely used white pigment in the worldwide market due to its exceptional light scattering efficiency, high refractive index, hiding power,
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0335 J. Mater. Res., Vol. 19, No. 9, Sep 2004
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tinting strength, and chemical inertness.8,9 However, unlike anatase, it is found that the synthesis of ultrafine rutile particles is much more difficult.10 All the crystalline forms occur in nature as minerals, whereas methods adopted for the synthesis generally produce anatase at low temperatures.11,12 The anatase form is preferred for applications as membranes in dye
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