Jiang Zhiliang, Feng Zhongwei, Jiang Yimin, Ling Shaoming
(Institute of New Technology and Materials, Guangxi Normal University, Guilin 541004, China)

Received Oct. 16, 2000; Supported by the Natural Science Foundation of Guangxi and Guangxi Education Department.

Abstract Nanometer-sized TiO₂ particle has been prepared by a microwave high-pressure method. The influence of tetrabutyl titanate(TBTi) and water concentrations, microwave power and irradiation time was investigated by resonance scattering spectroscopy and spectrophotometry. The resonance scattering spectra shows that TiO₂ nanopartcles in liquid exhibits two peaks at 350nm and 700nm. The nanoparticle size is about 14nm. This work demonstrate that microwave high-pressure method is a good procedure for the preparation of nanoparticles in liquid, and resonance scattering spectroscopy is a very useful technique to examine nanoparticle property.
Keywords Microwave high-pressure synthesis, tetrabutyl titanate, titania, nanoparticle, resonance scattering spectroscopy.

1. INTRODUCTION         
Titania nanoparticles shows good chemical and physical properties. It is very interesting to chemists, physicists, environmentalists, materialists and medical scientists^[1-4]. Its synthesis, property and application have become one of focus study^[1-6]. Several methods including sol-gel and hydrothermal have been reported for the synthesis of titania nanoparticle^[5]. The common shortcomings is that the formation of TiO₂ particles is not simultaneous, owing to the concentration diffusion or heat conducting. Microwave is a heating technique by means of molecular vibration in very high speed. For fast and homogeneous advantages, this method has been utilized to many research fields^[7-9]. However, microwave high-pressure procedure has not been reported for the synthesis of titania nanoparticles and the resonance scattering spectroscopic property of the nanopaticles in liquid has not been studied to date^[10,11]. In this work, titania nanoparticles prepared in liquid has been proposed by microwave high-pressure method using the chemicals of tetrabutyl titanate. The resonance scattering spectroscopic properties of the nanoparticle have been also reported.

2. EXPERIMENTAL   
All chemicals are analytical grade. The tetrabutyl titanate solution was prepared as follows: 7.0g of tetrabutyl titanate was put into a 100ml dry beaker; 3g of triethanolamine was added to prevent hydrolysis. The solution was dissolved with alcohol, and transferred into a 50ml volume flask, diluted to the mark with the solvent. The microwave reactions were carried out in a microwave high-pressure reactor(the max pressure 12 atm) setting in Glanz microwave oven(Sunde China, 2450MHZ). The resonance scattering spectra (RS), absorption spectra and TEM were obtained on a shimadiu RF-540 spectrofluorphotometer (Kyoto Japan), Hitachi U-3400 spectrophotometer (Japan) and JEM-1200 TEM (Japan) respectively.

3. RESULTS AND DISCUSSION    
The effect of water volume on the hydrolysis shows that the microwave reaction is slow when the volume less than 0.5ml, the hydrolysis is speed up at room-temperature when the volume is more than 5ml. However the hydrolysis is slow down at room-temperature when the tetrabutyl titanate is less than about 10^-5 mol/L.The microwave power and irradiation time were also examined. The recommendation conditions are 3ml water-480W for 3min.
    Resonance scattering ( some time also called Rayleigh ligh-scattering) is a new spectroscopic technique. It has been applied to biochemical research, inorganic analysis and supramolecular chemistry ^[10,11]. Recently this technique has been used to estimate the properties of silver, gold and AgCl nanoparticles, (Ag)_m.nAu and (AgCl)_m.nAg supramolecules in our research group^[12-15] with satisfactory results. The shape, size, absorption and rigidity of superamolecular or nanoparticles are prime factors to affect the resonance scattering spectra. Different shape for supramolecule or nanoparticle has the different resonance scattering spectra. The intensity of resonance scattering is proportional to the cubic diameter of supramolecule under the condition of the same shape^[16]. Figure 1 shows the resonance scattering spectra of titania nanoparticles.

    There are two resonance scattering peaks at 350nm and 700nm. The former peak is more sensitive than the latter's. The I_350nm is linear to the tetrabutyl titanate concentration in the range of 2.05×10^-5-2.05×10^-3mol/L. It can be explained from Rayleigh scattering formula, that is, the numbers of the nanoparticle increase with the addition of tetrabrtyl titanate. The two peaks have same properties that can be seen from the emission spectra in Figure 2. The peak at 350nm is the resonance scattering peak, the peak at 700nm is the secondary scattering peak^{[17, 18]}.

Fig.2 The emission spectra for titania nanoparticle
lex=350nm, 1.02×10^-3mol/L TBTi

    Figure 3 indicates the reagent blank(unirradiated) exhibits stronger absorption at ultraviolet region. The titania nanoparticles display absorption in the range of 370-500nm. The A_400nm is proportional to the TBTi concentration in the range of 4.1×10^-4-8.2×10^-3mol/L. The regression coefficient is 0.998.

	Fig.3 the absorption spectra for titania nanoparticle A: 4.1×10-3mol/L TBTi; B: A unirradiated by microwave
	Fig.4 The transmission electron microscopy for titania nanoparticle

    The result of TEM (Fig.4) demonstrates that there are aggregations for titania nanoparticle owing to the nanoparticle possessing high surface energy . The mean diameter for un-aggregated TiO₂ nonparticles is about 14nm. The aggregates are spongy particles,and silver ions can be embeded into the aggregates. This work is still carried on.

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