Heterogeneous photocatalytic degradation of diazinon in water using nano- TiO2: Modeling and intermediates

In this study, photocatalytic degradation of diazinon was investigated using commercial nano-TiO2as a photocatalyst the operational parameters such as adsorption, aeration, pH and nano-TiO2 dosage were investigated. Dispersive liquid-liquid microextraction (DLLME) technique was used to extract and preconcentration of residual diazinon and by-products from the liquid samples and the analysis was applied by gas chromatography with flame ionization detector. The amount of diazinon mineralization was quantified by chemical oxygen demand (COD) experiment. The intermediates formed during the photocatalytic treatment were identified by using gas chromatography with mass spectrometric detection (GC/MS). Based on models and the related constraint conditions, numerical optimization with the help of Design Expert software version 7.0.0.1 considering each value of response, the best condition for diazinonphotodegradation (100%) was achaived on pH value of 6 and nano-TiO2 concentration (0.55 g/L) with irradiation time of 95 min under UV irradiation and aeration and the best condition for COD removal (65.7%) was determined in pH value of 6 and nano-TiO2 concentration (0.51 g/L) with irradiation time of 92 min under UV irradiation and aeration. Maximumremoval of diazinon and COD were due to UV irradiation (71%, 41%), exposuretime (16%, 39%), aeration (7%, 4%) and increase concentration of nano-TiO2 (0.4%, 2%) respectively. The main by-products, which were identified during diazinon photo-oxidation,were 2isopropyl-6-methyl-pyrimidin-4-ol (IMP), 2-isopropyl-6-methylpyrimidin-4-yl phosphate (diazoxon) and hydroxydiazinon, which some of them were less toxic than its parent compound. Generally, based on the results, the photocatalytic degradation could be useful method for the removal, mineralization and detoxification of wastewaters containing diazinon.