Kinetic Modeling of Photocatalytic Degradation of Alachlor using TiO2 (Degussa P25) in Aqueous Solution

A kinetic model was developed to simulate the solar photocatalytic degradation of alachlor (organo chlorine herbicide) in aqueous solution using TiO2 (Degussa P25) catalyst. The effect of temperature, pH, radiant flux, TiO2 loading, presence of various cations, anions, surfactants on the photocatalytic degradation of alachlor were studied and determined the optimum condition under which the degradation rate was maximum. The solar irradiated samples were analyzed by a validated HPLC method. The photoproducts were determined by using LC /MS /MS technique. Rapid dissipation of herbicide was observed by using 0.5g /l of TiO2 (Degussa P-25) catalyst. The rate of degradation was found to increase with the increase in the temperature from 40 degrees C to 70 degrees C. The influence of cations on the degradation rate was in the order Fe2+, Cu2+ > Zn2+> Ni2+ > Mn2+ > Co2+ and for anions Cl-, HClo(3)-> CO32-, So(4)(2-). The rate was decreased as the pH was increased from 4.0 to 8.0. But at very high alkaline condition (pH 10.0) the rate was found to be the maximum. Among the three surfactants used (Cetyltrimethylammonium bromide (CTAB), Sodium dodecyl sulphate (SDS) and Polyethylene (23) dodecanol (Brij-35)) Sodium dodecyl sulphate showed much influence and when the study was conducted at three different radiant flux (109 Lux, 655 x 10(1) Lux, 601 x 10(2) to 1074 x 102Lux) it was observed that the rate was faster under the day light flux 601 x 10(2) to 1074 x 10(2)Lux. The degradation rate of alachlor was found to follow the first order kinetics. Finally the optimized conditions or the kinetic model which showed maximum degradation rate was then applied for treating effluent and ground water.