Ultrasonic preparation of mesoporous titanium dioxide nanocrystalline photocatalysts and evaluation of photocatalytic activity

doi:10.1016/j.molcata.2004.10.012

Journal of Molecular Catalysis A: Chemical

Volume 227, Issues 1–2, 1 March 2005, Pages 75-80

https://doi.org/10.1016/j.molcata.2004.10.012 Get rights and content

Abstract

Mesoporous titanium dioxide nanocrystalline powders were synthesized by ultrasonic-induced hydrolysis reaction of tetrabutyl titanate (Ti(OC₄H₉)₄) in pure water without using any templates or surfactants. The as-prepared samples were characterized with X-ray diffraction (XRD) and N₂ adsorption–desorption measurements. The photocatalytic activity of the samples was evaluated using the probe reaction: the photocatalytic oxidation of mixture of formaldehyde and acetone at room temperature. It was found that the as-prepared products by the ultrasonic method were composed of anatase and brooktie phases. The photocatalytic activity of the samples prepared by ultrasonic method is higher than that of commercial Degussa P25 and the samples prepared by conventional hydrolysis method.

Graphical abstract

The photocatalytic activity of mesoporous TiO₂ nanocrystalline powders prepared by ultrasonic method is higher than that of commercial Degussa P25 and the samples prepared by conventional hydrolysis method.

Introduction

In 1972, Fujishima and Honda discovered the photocatalytic splitting of water on TiO₂ electrodes [1]. This event marked the beginning of a new era in heterogeneous photocatalysis. Since then, the investigation of TiO₂ has become a hot issue. In recent years, in order to solve the increasingly serious problems of environmental pollution, various advanced techniques were applied in the fields of environmental protection. Heterogeneous photocatalysis is a popular technique that has great potential to control aqueous organic contaminates or air pollutants. Among various oxide semiconductor photocatalyst, titanium dioxide has proved to be the most suitable catalysts for widespread environmental application because of its biological and chemical inertness, strong oxidizing power, non-toxicity and long-term stability against photo and chemical corrosion [2], [3], [4], [5], [6], [7], [8]. However, the photocatalytic activity of TiO₂ must be further enhanced from the point of view of practical use and commerce [9]. To achieve this purpose, mesoporous TiO₂ has attracted much attention due to its high surface area and large uniform pores.

Various mesoporous materials have been synthesized via conventional approaches using surfactants as templates based on a liquid crystal template mechanism [10]. These methods often require a long time and multiple-step procedures. Sonochemistry has been proven to be an excellent method for the preparation of mesoporous materials [11], [12]. It arises from acoustic cavitations, the formation, growth, and implosive collapse of bubbles in a liquid. The collapse of bubbles generates localized hot spots with transient temperatures of about 5000 K, pressure of about 20 MPa, and heating and cooling rates greater than 10⁹ K s⁻¹ [13], [14]. These conditions accelerate the hydrolysis reaction.

In this work, the mesoporous TiO₂ nanocrystalline photocatalysts with bi-phase structure were prepared by sonochemical method without using any templates and surfactants at the room temperature. The as-prepared samples were characterized with X-ray diffraction (XRD) and N₂ adsorption–desorption measurements. The photocatalytic activity of the as-prepared samples was evaluated by the photocatalytic oxidation of the mixture of formaldehyde and acetone in air.

Section snippets

Synthesis

Tetrabutyl titanate (Ti(OC₄H₉)_4, TBOT) was used as a titanium source. TBOT (8.8 ml) was added dropwise to 40 ml pure water in a 100 ml beaker under irradiation with a high intensity ultrasonic horn (6.3 mm diameter Ti-horn, 20 kHz, and 1200 W/cm² at 50% efficiency) (KS-1200: Ningbo Kesheng Ultrasonic Equipment Co. Ltd., Zhejiang, China) for 45 min. The ultrasonic system is 2 s on and 2 s off in air during the whole reaction. After ultrasonic reaction, the precipitate was centrifuged and washed with

XRD study

XRD was used to investigate the phase structures and average crystallite size of the as-prepared TiO₂ powders. Fig. 1(a) shows the XRD patterns of the TiO₂ powder samples prepared by ultrasonic method and calcined at different temperatures. The diffraction peaks of all samples were indexed with the anatase and brooktie phase of TiO₂, which was consistent with our previous work [16], [17], [18]. With increasing calcination temperature, the peaks became sharp. This implied that the grain size of

Conclusion

1.
Highly photocatalytic active mesoporous nanocrystalline TiO₂ powder photocatalyst could be prepared using a sonochemical technique without using any templates or surfactants at low temperature. The sonication promoted the hydrolysis of TBOT, crystallization of TiO₂ and formation of mesopore.
2.
All the samples prepared by ultrasonic method showed better photocatalytic activities than Degussa P25 and the samples prepared by conventional hydrolysis method. This may be ascribed to the facts that the

Acknowledgements

This work was partially supported by the National Natural Science Foundation of China (50272049, 20473059). This work was also financially supported by the Excellent Young Teachers Program of MOE of China and Project-Sponsored by SRF for ROCS of SEM of China.

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Ultrasonic preparation of mesoporous titanium dioxide nanocrystalline photocatalysts and evaluation of photocatalytic activity

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis

XRD study

Conclusion

Acknowledgements

J. Photochem. Photobiol. C: Photochem. Rev.

Appl. Catal. A

J. Solid State Chem.

Appl. Catal. B

Atmos. Environ.

J. Catal.

J. Colloid Interf. Sci.

Appl. Catal. B

Nature

Langmuir

Chem. Rev.

Chem. Rev.