Low Temperature Synthesis Of Nano-crystanlline TiO₂ Via Microwave Assisted Heating Process And Its Photocatalytic Activity

Since Fujishima and Honda published a thesis about Electrochemical Photolysis of Water in Nature magazine. Many works have concentrated on the preparation of nano titanium dioxide(TiO₂) with high photocatalyticactivity, multiphase photocatalytic mechanism, and enhancing quantum efficiency of TiO₂. At present, TiO₂-based products, such as TiO₂ powder and TiO₂ film are usually obtained from calcining at high temperature, which can not be widely used in the industry. So it is significant to prepare TiO₂ at lower temperature without calcination. Based on the past research, an approach to the low temperature preparation of nanocrystanlline TiO₂ sol was proposed in this paper.Using Ti(SO₄)₂ as precursor, water worked as the solvent, a white precipitation of Ti(OH)₄ was obtained by the addition of ammonia aqueous adjusting the pH as 7～8, H₂O₂ or HNO₃ was used as peptizer. Then, the mixture aqueous was microwave heated for different hours at low temperature for crystallization. Finally, nanocrystalline TiO₂ sol was obtained. The effects of microwave heating temperature and heating time on the crystal phase were investigation, the influence of pH on the crystal phase of TiO₂ sol was also studied when HNO3 as peptizer. The crystals structure and morphology of the as-prepared sols were characterized by X-ray diffraction analysis(XRD), Transmission electron microscope(TEM). The results indicated that the produced sols using H₂O₂ as the peptizer contained anatase or anatase and rutile phase with a partice size about 10 nm. And using HNO3 as the peptizer, the anatase and brookie TiO₂ particles with a partice size approximately 4～5 nm was obtained. The effects of preparation conditions on the microstructure and performance of TiO₂ sol studied by Infrared Spectroscopy(FT-IR),Thermogravimetry -Differential thermal analysis(TG-DTA), UV-vis spectrometer(UV-vis), and Zeta value tests was used to study the influence of pH on the stablility of the sol. To producec high quality crystalization TiO₂, the optimum preparation conditions were microwave heating for 1.5 h at 90℃, and pH was adjust to 1 when using HNO3 as peptizer.The photocatalytic activity of the sol was evaluated on the degradation of methylene orange under the UV irradiation. The results showed the TiO₂ sol had high photocatalytic activity. With the sol prepared under the optimized conditions, the degradation of the methylene orange reached 90% in 50 min. TiO₂ film was fabricated by dip-coating method from the as-prepared sol, it also exhibited high photocatalytic activity. The degradation of the methylene orange reached 91% in 90 min.Based on the data of the experiment and the theory analysis, compared to the conventional heating method, the mechanism of microwave assisted heating was analyzed, which explains rigorously that microwave assisted heating can evidently speed the crystallization of TiO₂ sol.