Photocatalytic kinetics of phenol and its derivatives over UV irradiated TiO2

In recent years, photocatalytic degradation mediated by illuminated TiO2 ha s received considerable attention as an alternative for treating polluted w ater. In the present study, a new two-phase swirl-flow monolithic-type reac tor was used to study the kinetics of heterogeneous photocatalytic processe s. Photocatalytic degradation of phenol, 4-chlorophenol (4-CP) and 4-nitrop henol (4-NP) both in aqueous suspensions and over immobilized Degussa P25 T iO2 has been studied in laboratory scale. Experiments were conducted to inv estigate the effects of parameters such as catalyst dosage, pollutant conce ntration, temperature, partial pressure of oxygen, UV light intensity, cata lyst-layer thickness, circulation flowrate and catalyst annealing temperatu re. Simple model for predicting the optimal catalyst dosage in aqueous susp ensions for different photo-systems was proposed. Pseudo first-order kineti cs with respect to all the parent compounds was observed. Experimental data obtained under different conditions were fitted with kinetic equation to d escribe the dependency of degradation rate as a function of the above menti oned parameters. Consequently, kinetic parameters were experimentally deter mined. Adsorptive properties of all the organics were also experimentally m easured 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 transfe r of organics and oxygen in the photocatalytic process has also been discus sed in detail. (C) 1999 Elsevier Science B.V. All rights reserved.