Heterogeneous and homogeneous photocatalytic degradation of chlorophenols in aqueous titanium dioxide and ferrous ion

Photocatalytic degradation of 100 mg/l chlorophenols was studied using TiO ₂ and Fenton reagent as catalysts. 2-chlorophenol, 4-chlorophenol, and 2,4-dichlorophenol were selected as the target compounds. Results showed that direct photolysis of chlorophenols was faster than that in the TiO ₂-amended system. The photodegradation of 2CP followed a first-order rate relationship and the rate constants were 0.022 and 0.0103 min ^-1 in direct photolysis and TiO ₂/UV systems, respectively. The apparent-first-order reaction rate for decomposition of 4-chlorophenol was higher than that for 2-chlorophenol and 2,4-dichlorophenol under acidic conditions, while 2,4-dichlorophenol was higher than 2-chlorophenol and 4-chlorophenol in an alkaline medium. Both the TiO ₂ catalyst system and direct photolysis process were faster in basic medium than acidic and neutral medium processes. The Fenton system is excellent for the degradation of chlorophenols and its activity has become low in high pH medium.