ELSEVIER Solar Energy Materials and Solar Cells 38 (1995) 421-430 Solar Energy Materials and Solar Cells A rigorous kinetic approach to model primary oxidative steps of photocatalytic degradations C. Minero Dept. of Analytical Chemistry, University of Torino, Torino, Italy Abstract A kinetic model for the early stages of oxidation of an organic compound over irradiated semiconductors is presented. The model considers only the simpler cases, having the advantage of simplicity and of analytical solutions to the general differential equation. The obtained relationships are able to justify 0) the observed decays of Ci(t) versus time, (ij) the observed dependencies of the measured kinetic constants on initial substrate concentration, (iii) on the catalyst concentration, and (iv) on the light intensity. 1. Introduction Heterogeneous photocatalysis has recently been proposed for reduction of water pollution caused by organic contaminants [1]. The base mechanism of the photocatalytic process has been exhaustively reviewed (see, e.g., Refs. [2] and [3]). The applications of the process using Ti0 2 to the decontamination of industrial waste waters or real matrices have been appeared. Examples are the treatment of ore spills [4], of dyes [5], of degreasing effluents [6] and soils [7]. The advantages and limits of photocatalysis have been discussed [3,8,9] also by comparison with other Advanced Oxidation Processes (AOP). Unlike other AOP's based on addition or generation of chemical reagents and the usual kinetic behaviour for chemical transformations, in. photocatalysis the observed rate of degradation of the organic substrate usually increases as the concentration of the substrate decreases. This supports applications at low pollutant concentration and renders the process inefficient at high organic carbon content, suggesting for these applications some dilution before the treatment [5]. The kinetic modelling of the primary degradation steps is therefore essential for any practical application of the process. Some kinetic models describing photocatalytic oxidation on illuminated semi- conductors have been proposed [10-12]. This paper reports a simple kinetic model 0927-0248/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0927-0248(94)00234-7