Synthesis of visible-light-active nanosize rutile titania photocatalyst by low temperature dissolution–reprecipitation process

doi:10.1016/S1010-6030(03)00289-2

Journal of Photochemistry and Photobiology A: Chemistry

Volume 163, Issues 1–2, 15 April 2004, Pages 1-8

https://doi.org/10.1016/S1010-6030(03)00289-2 Get rights and content

Abstract

Titania nanocrystals were prepared by a “low temperature dissolution–reprecipitation process” (LTDRP) in liquid media. The crystallization of amorphous precursor could proceed at low temperature around room temperature, which was much lower than those of conventional calcination and hydrothermal reactions. The thermodynamically stable rutile formed at low temperature below 70 °C, while the metastable anatase formed at higher temperature. The phase composition, microstructure, morphology, and specific surface area of titania changed significantly depending on the reprecipitation temperatures. Needle-like rutile titania and spherical anatase titania crystals with high specific surface areas were prepared. Well-crystallized needle-like nanosize rutile crystals possessed higher photocatalytic activities than those of anatase crystals under visible light irradiation of wavelength >400 and/or >510 nm.

Introduction

Titania is the most effective photocatalyst and widely applied in purification of air and water, solar system, etc. [1], [2]. Three polymorphs, rutile, anatase, and brookite have been occurred in nature. In photocatalysis research, anatase titania is usually considered to be more active than rutile crystalline [3], [4]. The enhancement is ascribable to the differences of the Fermi level and the extents of surface hydroxylation of the solid [4]. In addition, rutile usually showed harder agglomeration and larger particle size than those of anatase since rutile is normally prepared by calcination of anatase at high temperatures. Rutile is a thermodynamically stable phase and possesses a smaller band gap than that of anatase phase. Consequently, rutile titania possesses better photo-absorption property in visible light wavelength range (>400 nm). In the present research, titania crystal was prepared from titanium tetraisopropoxide precursor by the low temperature dissolution–reprecipitation process (LTDRP) [5], [6] in liquid media under mild conditions. By this novel process, the thermodynamically stable rutile phase with fine particle size and high specific surface area can be prepared even around room temperature. The phase composition, microstructure, morphology, and specific surface area of titania prepared under various conditions were examined in detail. The hydrogen evolution activity and nitrogen monoxide destruction ability of prepared titania under visible light irradiation were investigated.

Section snippets

Experimental

Amorphous TiO₂ gel was prepared by slowly adding 0.125–0.250 mol of titanium tetraisopropoxide to 1000 cm³ of distilled water at room temperature. Transparent acidic TiO₂ colloid solution was obtained by adding hydrochloric acid in the fresh prepared amorphous slurry and stirring at room temperature for 4 h. After aging at desired temperature (25–220 °C) for desired time, fine crystals of titania were produced. The phase constitution of the products was determined by X-ray diffraction (XRD)

Results and discussion

It was found that fresh prepared amorphous titania could be dissolved as transparent titania gel in stirred acidic solutions, and then fine particles reprecipitated after a long time (48 h) aging at room temperature. At higher temperatures, the reprecipitation could be realized within 4 h. The precipitation yields of prepared samples were about 20–30%. In order to investigate the effect of co-existed ions, a washing operation was also carried out before and after LTDRP followed by hydrothermal

Conclusions

Based on the experimental results the following conclusions may be drawn:

(1)
Crystallization of rutile and anatase titania was realized at very low temperature by the LTDRP.
(2)
The phase compositional and morphological control of titania powders could be realized by applying washing operation and/or hydrothermal treatment to LTDRP process.
(3)
A formation mechanism of titania nanocrystals prepared by LTDRP was suggested.
(4)
Well-crystallized nanosize rutile titania possessed higher hydrogen evolution activity

Acknowledgements

This work was partly supported by a grant in aid for Scientific Research, No. 14750660, from the Ministry of Education, Science and Culture.

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Synthesis of visible-light-active nanosize rutile titania photocatalyst by low temperature dissolution–reprecipitation process

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgements

Electrochim. Acta

J. Solid State Chem.

Mater. Chem. Phys.

Nature

Nature