DECOMPOSITION OF ORGANOPHOSPHORUS COMPOUNDS ON PHOTOACTIVATED TIO2 SURFACES

Aqueous solutions of the organophosphorus compounds 4-nitrophenyl diethylphosphate (Paraoxon or 4-NPDEP), diethyl-p-nitrophenyl thiophosphate (Parathion or 4-NPDETP), O,O-dimethyl-S-(1,2-dicarbethoxyethyl)-phosphorodithioate (Malathion or DM-S-DCPT), 4-nitrophenylethylphenyl phosphinate (4-NPEPP) and 4-nitrophenylisopropylphenyl phosphinate (4-NPIPP) are totally decomposed into CO2 and the corresponding mineral acids by irradiation in a solar simulator in the presence of dispersed particles of the n-type semiconductor, TiO2 (anatase, B.G. = 3.23 eV). Addition of strongly oxidizing species such as K2S2O8, H2O2, NaIO4 and KBrO3 to these solutions enhances dramatically the rate of catalytic activity by inhibition of the electron and hole back-reaction as well as direct oxidation of the substrate species by the strong oxidants themselves. A mechanism of degradative oxidation on the TiO2 particles involving epoxidation by surface peroxo species and direct hole oxidation is proposed. © 1990.