The photocatalytic degradation of dichlorvos under solar irradiation

The photocatalytic degradation of the organophosphorous pesticide dichlorvos (DDVP) in suspended TiO2 was studied under solar irradiation. It is completely oxidized following a pseudo-first-order kinetic with a characteristic half-life time t1/2. The mineralization product formation followed the same kinetic order, Cl− ion being totally released, whereas PO43− only partially, due to formation of phosphate organic stable intermediates.Starting from various initial DDVP concentrations we used Langmuir–Hinshelwood equation to calculate Kad the adsorption–desorption equilibrium constant, kr the rate of the oxidation reaction and t1/2* the corresponding half-life time. The variation of t1/2* and t1/2 versus DDVP concentration suggests that there is no competition between the parent pollutant and its oxidation byproducts for the OH radical consumption. The addition of low concentration of H2O2 enhanced the oxidation effect on DDVP degradation.