Photocatalytic kinetics of phenol and its derivatives over UV irradiated TiO2

In recent years, photocatalytic degradation mediated by illuminated TiO2 has received considerable attention as an alternative for treating polluted water. In the present study, a new two-phase swirl-flow monolithic-type reactor was used to study the kinetics of heterogeneous photocatalytic processes. Photocatalytic degradation of phenol, 4-chlorophenol (4-CP) and 4-nitrophenol (4-NP) both in aqueous suspensions and over immobilized Degussa P25 TiO2 has been studied in laboratory scale. Experiments were conducted to investigate the effects of parameters such as catalyst dosage, pollutant concentration, temperature, partial pressure of oxygen, UV light intensity, catalyst-layer thickness, circulation flowrate and catalyst annealing temperature. Simple model for predicting the optimal catalyst dosage in aqueous suspensions for different photo-systems was proposed. Pseudo first-order kinetics with respect to all the parent compounds was observed. Experimental data obtained under different conditions were fitted with kinetic equation to describe the dependency of degradation rate as a function of the above mentioned parameters. Consequently, kinetic parameters were experimentally determined. Adsorptive properties of all the organics were also experimentally measured and fitted with Langmuir equation. The extreme low surface coverage of the organics on the catalyst may be one of the main factors that result in the low efficiency of the photocatalytic process. Besides, mass transfer of organics and oxygen in the photocatalytic process has also been discussed in detail. (C) 1999 Elsevier Science B.V. All rights reserved.