PHOTOCATALYTIC DEGRADATION OF THE ORGANOPHOSPHORUS PESTICIDE FENTHION IN AQUEOUS SUSPENSIONS OF TiO2 UNDER UV IRRADIATION

In present study the photocatalytic degradation of the organophosphorus pesticide fenthion, under UV irradiation in the presence of titanium dioxide (TiO2) photocatalyst, in aqueous suspensions has been investigated and compared with the photodegradation by hydrogen peroxide (H2O2) solution as an oxidant agent. The experiments were carried out in a 250mL pyrex UV laboratory-constructed photoreactor equipped with four 18W low pressure mercury lamps emitting irradiation at 365nm, whereas the maximum light intensity of the irradiation system was 14.5mW cm(-2) at a distance of 15cm. Remaining concentration of fenthion was determined by Gas Chromatography and Nitrogen Phosphorus Detector (GC-NPD) means. The degradation kinetics were studied under different experimental conditions, such as the amount of the photocatalyst, the initial concentration of fenthion, the illumination time, the presence of H2O2 as an oxidant/electron acceptor and the oxidant's initial concentration. Acquired results showed that the photocatalytic degradation of fenthion was strongly influenced by these parameters and the best conditions for its heterogeneous photocatalysis were obtained. Photolysis of fenthion in the absence of catalyst or oxidant was a very slow process and far from resulting in complete mineralization. On the contrary, according to the obtained photodegradation efficiencies the process of photodecomposition of target organophosphorus compound occurred significantly fast in UV-TiO2 and UV-TiO2-H2O2 systems. Fenthion was effectively degraded in the presence of TiO2 in employed UV-TiO2 system. Furthermore a synergistic effect was observed when the oxidant H2O2 was added in the TiO2 suspensions increasing the reaction rate of photodegradation of fenthion by a factor of similar to 18. In all cases examined the reduction process appeared to follow pseudo first order kinetics described by the Langmuir-Hinshelwood model. Finally the extent of pesticide mineralization was assessed through TOO measurements. Evolution of inorganic heteroatoms (SO42- and PO43-) as final products provided evidence that pesticide degradation occurred. Finally both of the occupied systems utilized UV light that simulated solar radiation (lambda<390nm) in view of eventual application of sunlight as energy source, proved to be adequate for water treatment and therefore they have good potential to be used in small scale applications.