Photocatalytic oxidation of organic pollutants in water

Abstract

The primary photo-oxidation at pollutant level concentration of dodecylbenzene sulfonate (DBS), azynphos-methyl and dimethoate in water has been studied in homogeneous and heterogeneous media by using a 400 W lamp with a solar spectral distribution, and TiO 2 and FeCl 3 as catalysts. Two different geometries of differential batch-recycled reactors were used: first, a concentric tubular reactor with the lamp placed at the tube axis and second, a flow through parallel-plate reactor. An incidence radial model and a linear source spherical emission (LSSE) model with a Monte-Carlo approach to account for scattering of light have been used for the light intensity distribution. Data showed a molar concentration reduction of 30% for DBS in 150 min with light and TiO 2. When FeCl 3 was used as photocatalyst, concentration of DBS was reduced by 70%. Similar behavior found for azynphos-methyl was reduced to 85% in 20 min after irradiation with FeCl 3; 100% in 20 min with TiO 2 and 100% in 2 min with TiO 2 and FeCl 3. Approximately the same performance obtained for dimethoate was completely oxidized in 20 min after irradiation of slurry solution of TiO 2 with FeCl 3. From these data kinetic equations were obtained by assuming a free-radical mechanism for oxidation of hydrocarbons. Pollutants present no activity to solar light, but when FeCl 3 or TiO 2 were used, pollutants were decomposed; being the value of kinetic constant of order 10 4 cm 2/einst. When the solution was irradiated with a FeCl 3 and TiO 2 together, the rate increased about 10 times more. Also, deactivation of catalyst was studied by X-ray diffraction, TG and DTA methods.