Photodegradation of parathion in aqueous titanium dioxide and zero valent iron solutions in the presence of hydrogen peroxide

The photocatalytic degradation of parathion using UV radiation in combination with hydrogen peroxide and titanium dioxide or iron compounds was studied. Apparent first-order rate constants (k(obs)) and initial rate constants were used to describe the degradation behavior of parathion under different conditions. The addition of TiO2 or iron compounds in combination with hydrogen peroxide was effective in the detoxification of parathion. The k(obs) and initial rate constants increased with the increase of TiO2 loading from 0.1 g l(-1) to 1 g l(-1). However, the degradation rates of parathion decreased when the TiO2 dose was increased to 2 g l(-1). No significant difference between buffered and unbuffered solutions was observed. The addition of oxyanion oxidant can enhance the degradation rate of parathion in the order of ClO2- > IO3- > BrO3- > ClO3-. The existence of oxygen increased the initial rate of parathion in a TiO2-amended system, but has little effect on k(obs). Also, the addition of iron compounds is a promising technique for the photodegradation of parathion. The rate constants for parathion ranged from 0.029 to 0.033 min(-1) in the iron-amended system, which corresponds to 3-fold increase relative to UV/H2O2 system. Diethylphosphoric acid, p-nitrophenol, diethylmonothiophosphoric acid, O,O-ethyl p-nitrophenyl monothiophosphoric acid and oxalate were identified as intermediates and shown to be oxidized further. Moreover, oxalate and 4-nitrophenol were found to be the major intermediates in the degradation of parathion. (C) 1998 Elsevier Science S.A. All rights reserved.