Effects of radiation absorption and catalyst concentration on the photocatalytic degradation of pollutants

This study is dealing with the reaction rate dependence on catalyst concentration and light absorption in photocatalytic processes. Models relating the reaction rate to the absorbed radiation by the catalyst (titania in suspension) are proposed. To apply these models, the system is divided into layers and each layer is divided into cells, assuming that there is only one particle (agglomerate) of catalyst in each cell. The extensive reaction rate can be calculated as the sum of the reaction rate in each cell, being this proportional to the light absorbed by each particle. Two different models are proposed for light propagation through the reaction medium (exponential and probabilistic model). The extinction coefficients have been estimated by using transmittance measurements related to sedimentation rates changing according to catalyst concentration and pH. The integration of these models, taking into account the expression of the reaction rate, allows to obtain equations that can explain the trends observed in the photocatalytic treatment of Cr(VI) and phenol, by using TiO(2) (Degussa-P25) in suspension. (C) 2002 Elsevier Science B.V. All rights reserved.