DOI : 10.2240/azojomo0295

Synthesis and Characterization of Ru Doped TiO2 Nanoparticles by A Sol-Gel and A Hydrothermal Process

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Nov 9 2010

Hyun-Ju Kim, Sung Bin Bae and Dong- Sik Bae

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AZojomo (ISSN 1833-122X) Volume 6 November 2010

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Abstract
Keywords
Introduction
Experimental
Results and Discussions
Conclusions
Acknowledgments
Reference
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Abstract

Ru doped TiO₂ nanoparticles were prepared under high temperature and mild pressure conditions(0.1 MPa) by mixture from metal chloride solution and TiO₂ sol. Ru doped TiO₂ particles were reaction at the temperature range of 170°C-210°C for 6 h. The microstructure and phase of the synthesized particles were studied by TEM and XRD. Thermal properties of the synthesized powder were studied by TG-DTA analysis. X-ray diffraction pattern shows that the synthesized particles were crystalline. The effects of synthesis parameters, such as the concentration of starting solution, reaction temperature are discussed.

Keywords

Ru doped TiO₂ nanoparticles, Anatase, Rutile, Sol-Gel Process, Hydrothermal Process

Introduction

Titanium dioxide is an important material for a variety of applications such as catalytic devices, solar cells, and other optoelectronic devices [1–3]. Especially, TiO₂ is used in wide range of environmental photocatalyst because of its unique properties: it is a semiconductor with band gap about 3.2 eV possessing strong oxidative ability and non-toxicity. Titania is a well known n-type inorganic metal oxide semiconductor that is transparent to visible light and has a high refractive index. Due to its unique optical property and chemical stability, titania may be used in the splitting of water [4] and in the photo-oxidation[5] processes. Solar cells demonstrating rather high photovoltaic efficiencies are studied in the frame of structures containing transparent conductive oxide (TCO)/dye sensitized titania/electrolyte systems which include the dye-sensitized nanocrystalline TiO₂ solar cell [6]. However, there are some disadvantages of its use in photocatalytic applications, namely the light adsorption in UV light spectrum region only and the high electron (e–) – hole (h+) recombination rate. Many attempts to improve the performance of TiO₂ as a photocatalyst under UV illumination, and to improve its light absorption and conversion capacity in visible range of the solar spectrum, have been described in the literature in recent years [7, 8]. In this context, a large number of metal ions, particularly transition metal ions such as ruthenium, iron, chromium and cobalt, have been used as TiO₂ dopants [9-11]

The coordination environment of the dopants is affected not only by the nature of the dopant such as ionic radii and concentration but also by the synthesis method [12]. In this work, Ru3+ were used as dopants for TiO₂ based materials to improve their properties, namely to extend the light absorption into the visible light region, to reduce the recombination of the photogenerated e– and h+ and to increase the surface area. Ru doped TiO₂ powder has been obtained by sol–gel and hydrothermal method by a mixture from metal nitrates solution and TiO₂ sol. Hydrothermal processes have the potential for the direct preparation of crystalline ceramic powders and offer a low-temperature alternative to conventional powder synthesis techniques in the production of oxide powders [13]. This process can produce fine, high-purity, stoichiometric particles of single and multi-component metal oxides. Furthermore, if process conditions such as solute concentration, reaction temperature, reaction time and the type of solvent are carefully controlled, the desired shape and size of the particles can be produced [14-15]. A uniform distribution of the particles is important for optimal control of grain size and microstructure to maintain high reliability. It has been demonstrated that such powders are composed of much softer agglomerates and sinter much better than those prepared by calcination decomposition of the same oxides [16]. These powders could be sintered at low temperature without calcination and milling steps [17-18].

The object of this study was to prepare Ru doped TiO₂ nanoparticles by a combination of sol-gel and hydrothermal methods.

Experimental

Titanium(IV) isopropoxide (Ti[OCH(CH₃)₂]₄, JUNSEI Chemicals, 98%), Ruthenium chloride (RuCl₃ •3H₂O, KOJIMA Chemicals, 99%) and hydrochloric acid (HCl, Daejung Chemicals 35%) were used for the hydrothermal preparation. First, TiO₂ sol was prepared metal alkoxide hydrolysis and condensation. Titanium (IV) isopropoxide was used as a precursor. It was slowly added to the ethanol(99.9%) as a solvent , with distilled water added for hydrolysis reaction. Finally, a small amount of hydrochloric acid was slowly added to the solution with stirring. After condensation reaction and crystallization, transparent suspended TiO₂ sol was obtained. Ru solution (0.16 mol) was prepared by dissolving of RuCl₃ •3H₂O in distilled water. The weight percentage of the Ru:TiO₂ precursor mixtures was kept to 1:39 mL. The resulting suspension was placed in a 1000 mL stainless steel pressure vessel. The vessel was then heated to the 170-210°C range at a rate of 5°C/min for 6 h. The resulting powder was washed with distilled water until pH 7 and then dried at 80°C for 24 h. The phase identification of synthesized powders was recorded by x-ray diffractometer (Philips X’pert MPD 3040). The structure, size and morphology of the resulting composites were examined by transmission electron microscopy (FETEM, JEOL 2100CF). For TEM studies, samples were prepared by adding drops of freshly prepared cluster solution on a carbon film supported on a Cu grid. Thermal decomposition behavior of the synthesized powder was studied by TG-DTA analysis (TA5000/SDT 2960 DSC Q10).

Results and Discussions

Fig. 1 shows an X-ray diffraction pattern of the Ru doped TiO₂ particles as a function of reaction temperature. From the X-ray analysis, synthesized particles reveals the coexistence of anatase (JCPDS number 84-1286) and rutile (JCPDS number 01-1292) phases in the reaction temperature from 170°C to 210°C for 6 h. The intensity of rutile phase on Ru doped TiO₂ particles increased with increasing reaction temperature. The amount of rutile phase on the synthesized particles increased with decreasing Ru concentration in solution because the less a content of the transposition metal, the easier to phase transition in the same temperature condition. The TEM microstructure of the synthesized Ru doped TiO₂ particles as a function of reaction temperature is shown in Fig. 2. The average size of the synthesized Ru doped TiO₂ particles increased with reaction temperature increased from 170°C to 210°C. Microstructure of synthesized particles shows a small particles size about 10-60nm and size distribution was unclear and broad. The Fig. 3 shown the spectrum of Ru doped TiO₂ nanoparticles by TEM–EDS analysis. The peak of titanium, Ru and oxygen shows on the spectrum. From the TG-DTA analysis (Fig. 4) of Ru doped TiO₂ nanoparticles, the overall reduction in weight was about 4.2% up to ~700°C and water of crystallization was dehydration at 242°C. Also it shows that transition of phase from anatase to rutile at almost 561°C. Specific Surface Area of synthesized particles as a function of Ru concentration in TiO₂ by combination of a sol-gel and a hydrothermal process. BET surface areas of synthesized particles by a hydrothermal process were found to be larger than that of pure TiO₂ from synthesized by a sol-gel process (about 50 m2/g). The surface of synthesized particles increased with increasing Ru concentration in TiO₂ sol.

Figure 1. X-ray diffraction patterns of the synthesized particles as a function of reaction temperature synthesized powders : anatase (A) and rutile (R). (JCPDS number 84-1286, 01-1292)

Figure 2. TEM micrographs of the synthesized particles as a function of reaction temperature synthesized powders by combination a sol-gel process and a hydrothermal process : (a) 170°C, 6 h (b) 190°C, 6 h (c) 210°C, 6 h

Figure 3. EDS (Energy Dispersive Spectroscopy) spectrum of the synthesized Ru doped TiO₂ particles by combination a sol-gel process and a hydrothermal process.

Figure 4. TG-DTA analysis of the synthesized Ru doped TiO₂ nanoparticles by combination a sol-gel process and a hydrothermal process.

Conclusions

Ru doped TiO₂ particles have been synthesized by a combination of a sol-gel and hydrothermal process. Nanosized Ru doped TiO₂ particles were obtained in the temperature range of 170°C-210°C for 6 h. Microstructure of synthesized particles shows a small particles size around 10-60nm and size distribution was unclear and broad. The average size of the synthesized particles increased when reaction temperature increased. The crystalline phase of the synthesized Ru doped TiO₂ particles shows the coexistence of anatase and rutile reaction at the temperature range of 170°C to 210°C for 6 h.

Acknowledgments

This research was financially supported by the Korea Sanhak Foundation(2008).

Reference

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