Heterogeneous photocatalysis degradation of 4-CP in TiO2 aqueous suspensions

• Main Authors: Wu,Pine-Huan, 吳秉寰
• Other Authors: Lo,Shang-Lien
• Format: Others
• Language: zh-TW
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/86893860711513602431

碩士 === 國立臺灣大學 === 環境工程研究所 === 84 === The heterogeneous photocatalytic degradation of 4-chloro- phenol (4-CP) in TiO2 aqueous suspensions at .lambda.=254 nm and .lambda.=365 nm has been studied. The reaction rates of above systems are slower than the reaction rate of direct photolysis at .lambda.=254 nm. The energy of UV 254 nm is strong enough to break C-Cl and C-OH bond of 4-CP. The mineralization efficiency of direct photolysis at .lamba.=254 nm is near 30% in 8 hours, but the mineralization efficiency of UV 254 nm/TiO2 system is near 50% with the same illumination time. UV 365 nm does not have enough energy to destroy the chemical bond of 4-CP, but the UV 365 nm/TiO2 system can produce .bcdot.OH (OH radicals) which have the ability to attack 4-CP strongly and can destroy 4-CP. The optimal TiO2 dosage at pH=7 is 1.0 g/L, and with this dosage the optimal pH is 7. The rate constant of the UV 365 nm/TiO2 system decays with increasing 4-CP concentration. Aeration increases the reaction rates of the UV 254 nm/TiO2 system and the UV 365 nm/ TiO2 system. Para hydroxylation is the main pathway, in which 4-CP gives rise to hydroquinone and oxidation of hydroquinone forms p-quinone. Formation of pyrocatechol is a minor pathway in the degradation of 4-CP. From the experimental results, it can be seen that the photocatalytic reaction falls into the pseudo-first -order kinetics such that -d.lbrak.4-CP.rbrak./dt= k''.lbrak.4-CP .rbrak. where k'' is the pseudo-first-order rate constant.