Kinetic Model for UV/H2O2 Degradation of 5-Methoxypsoralen

Abstract

The influence of H₂O₂ on the photodegradataion of 5-methoxypsoralen (5-MOP) in ethanol and in waterethanol solutions upon exposure to KrCl excilamp radiation (λ_rad = 222 nm) and XeBr excilamp radiation (λ_rad = 283 nm) is investigated. A kinematic model of photodegradation of the investigated molecule is constructed. The addition of H₂O₂ resulted in a weak increase of the decay rate of 5-MOP in ethanol exposed to KrCl excilamp radiation. In water-ethanol solutions the addition of H₂O₂ altered the mechanism of decay of 5-MOP irradiated by the KrCl excilamp in comparison with irradiation by the XeBr excilamp. It has been shown that upon exposure to XeBr excilamp radiation in the presence of H₂O₂, the primary photoproduct of the transformation of 5-MOP in the reaction corresponding to the first-order kinetic model is formed both in ethanol and in the water-ethanol solutions. Maximum removal of 5-MOP takes place for the ratio of initial concentrations [5-MOP]:[H₂O₂] = 1:3 after 60 min irradiation. It is found that irradiation by the XeBr excilamp the decay rate of 5-MOP is 5 times higher in the water-ethanol solutions in comparison with ethanol. Upon exposure to KrCl excilamp radiation the mechanism of 5-MOP decay corresponds to a pseudo-firstorder kinetic model. The nature of the dependence of the decay rate of 5-MOP on the irradiation time for the ratio of initial concentrations [5-MOP]:[H₂O₂] = 1:24 indicates that during decay of the initial compound a photoproduct appears in the system which decays during the irradiation time into secondary compounds. Efficient removal of 5-MOP under this irradiation takes place for the ratio of initial concentrations [5-MOP]:[H₂O₂] = 1:10 after 60 min irradiation.