Photocatalytic oxidation of organic pollutants in water

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 TiO2 and FeCl3 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 how 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 TiO2. When FeCl3 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 FeCl3; 100% in 20 min with TiO2 and 100% in 2 min with TiO2 and FeCl3. Approximately the same performance obtained for dimethoate was completely oxidized in 20 min after irradiation of slurry solution of TiO2 with FeCl3. 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 FeCl3 or TiO2 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 FeCl3 and TiO2 together, the rate increased about 10 times more. Also, deactivation of catalyst was studied by X-ray diffraction, TG and DTA methods. (C) 1998 Elsevier Science B.V.