Preparation of Undoped and Metal-Doped Titanium Dioxide Catalysts for Photodegradation of Phenols in Aqueous Suspension

• Main Authors: Chwei-Huann Chiou, 邱垂煥
• Other Authors: 莊瑞鑫
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/36675561979193020339

博士 === 元智大學 === 化學工程與材料科學學系 === 96 === Recently, the photocatalystic degradation methods have a talented process to treat the aquatic organic solution. In this thesis, the photocatalytic oxidation of phenol of oxygenated solution with suspensions of titanium dioxide powder has been investigated experiment. The photodegradation of phenol using TiO2 photocatalysts prepared by sol-gel, hydrothermal and emulsion methods was investigated. The photocatalytic activities of the TiO2 powders prepared via different synthesis methods were studied by comparing with that of the commercial Degussa P25 TiO2. In addition, analyses such as XRD, SEM/EDX, UV-Vis were adopted to characterize the prepared TiO2 photocatalysts. The photocatalytic processes of TiO2 prepared by sol-gel, hydrothermal and emulsion methods have been carried out. The activities of the TiO2 photocatalysts prepared by these three methods are very close, which are lower than that of Degussa P25.The TiO2 containing both anatase and rutile powders have higher activity than that of pure anatase or pure rutile powder. This indicates the existence of a synergistic effect between anatase and rutile powder. Furthermore, the photoactivity of the TiO2 powder having anatase phase is higher than that of rutile phase. The optimal TiO2 dosage is about 1-2 grams per liter of solution and an excess of TiO2 will result in a light shielding effect. The supply of oxygen (or air) is essential for the photocatalytic degradation reaction. When an oxygen flow rate of 1.0 liter/min was purged during the process, the phenol removal was increased by about 13%. Therefore, adding oxygen by bubbling certainly improves the degradation efficiency. The first part of the experiments describes the use of hydrogen peroxide (H2O2) to improve photodegradation of phenol by commercial Degussa P25 TiO2 powders. The phenol photodegradation efficiencies in direct photolysis (UV alone), H2O2/UV, TiO2/UV, and H2O2/TiO2/UV systems were compared. The influences of operating parameters such as catalyst dosage, light intensity, solution pH, initial phenol and H2O2 concentrations on photodegradation process were also examined. Finally, the role of H2O2 on the photodegradation of phenol in aqueous solution was discussed. Photocatalytic degradation of phenol in water was examined using Pr-doped TiO2 nanoparticles. These photocatalysts were synthesized by an acid-peptized sol-gel method from titanium tetra-isopropoxide with different concentrations of Pr (III) dopant and calcination temperatures. Several tools such as XRD, BET surface area, SEM, and EDX, were used to evaluate particle structure, size distribution, and composition. The optical absorption properties of the prepared particles were also measured. Photocatalytic activity of the particles was studied in a batch reactor containing phenol solution with 400-W UV irradiation. Parameters affecting photocatalytic process such as the catalyst crystallinity, light absorption efficiency, the dosage of catalyst, dopant and phenol concentrations were investigated. The Pr-doped TiO2 showed high activity for photocatalytic degradation of phenol. The presence of Pr ions in the TiO2 particles would cause a significant absorption shift towards the visible region. The degradation process was optimized using 1 g/L Pr-doped TiO2 with a Pr (III) concentration of 0.072 mol% after 2 h irradiation. It was shown that photodegradation followed a pseudo-first-order kinetics and the rate constant changed with phenol concentration. Photocatalytic degradation of single and binary phenol and m-nitrophenol (m-NP) in aqueous solutions by commercial TiO2 powders (Degussa P-25) under UV irradiation were examined. The influences of various operating parameters including the initial reactant concentration (0.13-0.71 mM), solution pH (4.1-12.7), and the presence of the second reactant on photodegradation were studied. The effect of TiO2 pre-wetting with aqueous solution on phenol photodegradation was also studied. It was shown that the degradation rates of phenol and m-NP decreased with increasing initial reactant concentrations. The optimal solution pH for the photodegradation of single phenol and m-NP was at around 7.4 and 8.9, respectively. Compared to the single systems, the photodegradation rates of phenol and m-NP in binary systems decreased, particularly when the second reactant was in excess. Moreover, the photodegradation of either single or binary reactants in aqueous solutions satisfactorily followed the pseudo-first-order kinetics.