Preparation and Phase Transformation Kiunetics of Nanometered Titania Powders

• Main Authors: Ming-Chang Wen, 溫明璋
• Other Authors: Chung-Hsin Lu
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/24553789871050548722

碩士 === 國立臺灣大學 === 化學工程學研究所 === 90 === Recently photocatalytic technologies have attracted considerable attention in the scientific researches and industry because the global environmental pollution had become a serious problem. The thermal hydrolysis method was developed for synthesizing TiO2 powders with starting materials of titanium tetrachloride and NH3 in this study. The subsequent calcination process was performed to obtain the powders with different ratios of anatase and rutile phases. The pH value of the starting solution had significant effects on the phase transformation from anatase to rutile. The temperature and the activation energy of the phase transformation were varied with the different pH value of the starting solution. The conversion was calculated based on the ratio of diffraction intensity of anatase to that of rutile. In the kinetics analysis, the reaction of phase transformation from anatase to rutile was determined to be the three-dimensional phase boundary controlled process. The UV-vis spectroscope and XRD were performed to investigate the mechanism of phase transformation from anatase to rutile. The mechanism of the phase transformation was supposed as the core-shell model. The hydrothermal microemulsion process was performed to prepare the nano-sized titania particles with anatase phase. Aqueous micelles of water-in-oil with two microemulsions systems were used as microreactors to precipitate the precursor. The precursors were treated hydrothermally at 150℃for 1 h to produce ultrafine titania particles. The morphology and particle size were directly influenced by the pH value of the microemulsion solutions. The particles prepared at pH = 4-6 and 7 of microemulsions showed the spherical and plate-like morphology, respectively. Different mechanisms of the formation of particles also were also supposed in this study. The energy of band gap was estimated from UV-vis spectra, and showed the quantum size effect of the prepared powders. The photocatalytic activity of prepared particles was evaluated using the decomposition of methylene blue solution with titania photocatalyst. The sample prepared from the starting microemulsion at pH = 7 showed a relative maximum photocatalytic activity. The surface area of this sample was also the maximum value between the synthesized samples. The developed process successfully prepared nanosized titania with high photocatalytic activity.