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 comb ination 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 parat hion under different conditions. The addition of TiO2 or iron compound s in combination with hydrogen peroxide was effective in the detoxific ation of parathion. The k(obs) and initial rate constants increased wi th 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 c an enhance the degradation rate of parathion in the order of ClO2- > I O3- > BrO3- > ClO3-. The existence of oxygen increased the initial rat e of parathion in a TiO2-amended system, but has little effect on k(ob s). Also, the addition of iron compounds is a promising technique for the photodegradation of parathion. The rate constants for parathion ra nged from 0.029 to 0.033 min(-1) in the iron-amended system, which cor responds to 3-fold increase relative to UV/H2O2 system. Diethylphospho ric acid, p-nitrophenol, diethylmonothiophosphoric acid, O,O-ethyl p-n itrophenyl monothiophosphoric acid and oxalate were identified as inte rmediates and shown to be oxidized further. Moreover, oxalate and 4-ni trophenol were found to be the major intermediates in the degradation of parathion. (C) 1998 Elsevier Science S.A. All rights reserved.