Processing titania based materials in flame reactors: from dopants to nano-composites

J. Aerosol%;. Vol. 29, Suppl. I. pp. S1294130. 1998 8 1998 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0021-8502/98 $19.00 + 0.00

Pergamon

PROCESSING TITANIA BASED MATERIALS IN FLAME REACTORS: FROM DOPANTS TO NANO-COMPOSITES Guixiang

Yang’, Zhongming

Wang’,

‘Aerosol & Department of ’ Department of Electrical, University

Pratim Biswas’, Wayne Bresser’ and Punit Boolchand’ Air Quality Research Laboratory Civil & Environmental Engineering Computer Engineering and Computer of Cincinnati, OH 4522 l-007 1

Science

KEYWORDS Nanophase

Titania,

Iron oxide, Dopants,

uv Absorption

The synthesis of structures on an atomic to nanometer scale is receiving significant attention in materials processing. Flame reactors are used to process materials and have been successfully used to produce iron oxide - silica nanocomposites (McMiIlin et al., 1996). Titania is another versatile material with several different applications such as in environmental catalysis. In this work, we report the results of experiments at processing titania particles doped with varying concentrations of iron oxide. A detailed description of the system to produce titania nanoparticles has been provided by Yang et al. (1996). A list of experiments with resultant particle phase composition is listed in Table 1. Experiments were performed at varying ratios of Fe:Ti, to obtain doped titania and nano-composites of iron oxide and titania.

Table 1. List of Experiments Performed with Resultant Phase of Powders Powder Phase Composition y-phase

iron oxide

anatase titania 95% anatase, 5% rutile 70% anatase, 30% rutile and amorphous 50% anatase, 50% rutile and amorphous amorphous,

Fe-Ti-Ocrystal

amorphous,

Fe-Ti-Ocrystal

amorphous,

Fe-Ti-Ocrystal

amornhous.

Fe-Ti-Ocrvstal

By varying the iron dopant concentration, the phase composition is altered as listed in Table 1. When the molar ratio is less than 0.14, the iron is in small enough quantities that the titania is s129

s130

Abstracts of the 5th International Aerosol Conference

1998

predominantly in anatase form. This is the preferred form for use as a photocatalyst. On measuring the uv-vis absorption, a significant shift towards the visible is observed, indicating a reduction in the band gap energy (Figure 1). This is because the iron is substitutionally incorporated into the titania lattice, and provides several additional intermediate energy states for the excited electrons. Results of Raman and Mossbauer spectroscopy to further elucidate the structure of these doped titania particles will be presented. Another interesting effect is the role of decreasing grain size, and one may transition into the quantum regime. This will result in a slight increase in the band gap energy, or a resultant blue shift. However, due to enhanced interfacial charge transfer rates, they may be more effective catalytically than their bulk counterparts.

-

Pure titania, case 2 Fe/Ti = 0.06, case Fe/Ti = 0.14, case

--

Wavelength

Figure

(nm)

1. UV-Vis absorption spectra of titania with varvino iron concentrations

particles

doped

At higher iron feed concentrations, inclusions of iron oxide in the titania matrix are obtained, similar to the work of McMillin et al. (1996). Results of magnetization and low temperature Mossbauer spectroscopy clearly indicate that the as produced powder is superparamagnetic REFERENCES McMillin B.K., Biswas P. and Zachariah M.R. (1996) In Situ characterization of vapor phase growth of iron oxide-silica nanocomposites: Part I. 2-D planar laser induced fluorescence and Mie imaging, J. Muter. Res.,, 11, 1552-1560. Yang G., Zhuang H. and Biswas P. (1996) Characterization and sinterability of nanophase particles processed in flame reactors, NunoStructured Materials, 7, 675-689.

titania