Kinetics rate model of the photocatalytic oxidation of trichloroethylene in air over TiO 2 thin films

Abstract

The photocatalytic oxidation of trichloroethylene (TCE) over a TiO 2 thin film was investigated in a flow-through photocatalytic reactor. The effects of TCE concentration and water vapor concentration on the oxidation rates were investigated. Rate models based on variations of the Langmuir–Hinshelwood kinetic model were found to represent the results unsatisfactorily. Therefore, a general rate equation for the oxidation of TCE was derived from an elementary reaction mechanism of TCE photocatalytic oxidation over TiO 2. The model, based on chlorine atom attack of the TCE molecule, yields a relatively complex equation including the explicit dependence on water vapor concentration, TCE concentration, photon flux and quantum yield. The rate equation yields half-order dependence on the photon flux at high photon fluxes and first-order dependence at low photon fluxes and reduces to first-order dependence on TCE and inverse dependence on water vapor under specific conditions. The kinetic parameters of the photocatalytic oxidation of TCE on TiO 2 thin film were estimated by fitting the model to the experimental results. The approach demonstrated in this paper represents a more rational method of kinetic analysis than the mechanical adoption of a Langmuir–Hinshelwood type rate equation often reported in the literature.