The study of the control of the ratio of anatase/rutile phase formation in TiO2 by flat flame method and the influence on its visible-light photocatalytic efficiency

• Main Authors: Tse-Shan Lin, 林澤珊
• Other Authors: Yi-Jia Chen
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/52450996370972397556

碩士 === 國立東華大學 === 材料科學與工程學系 === 99 === In this study, we have successfully prepared the dual phase TiO2 nanopowder as visible-light photocatalyst using flat-flame chemical vapor condensation method. First, we found that the type of buffer gas has significant effect on the phase transformation. Due to higher specific heat of nitrogen than that of argon, nitrogen is more capable of maintaining particles at high temperature, and to promote the rutile formation. We also realized that the dual phase formation by partial phase transformation from anatase to rutile is critical in the enhancement of photocatalytic reaction. Second, the increase of gap distance increases the heating time and collision time for the particles, thus increases the rutile content of the particles. Third, we managed to proceed our experiment by fixing the acetylene flow rate at either 600 sccm or 800 sccm, while vary the acetylene/oxygen flow ratio for 1:3, 1:4, 1:5, and 1:6, for the flame. We found that at low temperature and oxygen-deficient condition, the rutile formation is at the expense of visible-light photonic center, while at high temperature and oxygen-rich condition, the rutile formation does not interfere with its visible-light absorption. At high temperature and oxygen-rich condition, the rutile formation is promoted by thermal energy, and does not necessarily need the nucleation agent, such as visible-light photonic center. From the TEM observation, this powder consists of majorly fine anatase particles and some scattered large rutile particles. The nanopowder produced under this condition has the highest visible-light absorption capability as well as methylene blue photocatalytic decomposition reactivity. Finally, we concluded that the defect level in anatase formed by carbon doping and related effect is responsible for the visible-light absorption, and the dual phase is responsible for the reduction of the electron-hole recombination. With both carbon doping and dual-phase formation, the visible-light photocatalytic ability of our powder is greatly enhanced.