Journal of Mazandaran University of Medical Sciences (May 2024)
Sonocatalytic Removal of Diazinon from Aqueous Solutions Using Zinc Oxide Immobilized on Polyethylene Terephthalate
Abstract
Background and purpose: Pesticides are well-known for their carcinogenic, mutagenic, and teratogenic properties, and they exhibit resistance to environmental degradation. Organophosphorus compounds represent one of the largest and most diverse groups of pesticides globally. Diazinon, an organophosphorus pesticide widely used in agriculture, was selected as the target pollutant for the present study. Materials and methods: The co-precipitation method was employed to synthesize zinc oxide nanocomposites coated on polyethylene terephthalate (PET). Subsequently, the nanoparticle structure was analyzed using XRD, FT-IR, SEM, and EDX analyses. The efficiency of diazinon sonocatalytic removal by zinc oxide nanocomposites coated on PET was investigated, and the impact of various parameters, including pH (3-11), nanocomposite dosage (0.2-2.5 g/L), initial diazinon concentration (5-50 mg/L), contact time (5-60 min), hydrogen peroxide concentration (2-50 mM), different gases (oxygen and nitrogen gas (2 L/min)), organic compounds (folic acid, citric acid, humic acid, EDTA, oxalate acid, phenol), radical scavengers (ammonium oxalate as h+ scavenger, benzoquinone as scavenger, tert-butyl alcohol as •OH scavengers), various processes (PET, US, PET/US, ZnO, ZnO-PET, ZnO/US, ZnO-PET/US), and recycled experiment, was evaluated. Firstly, the pH optimum was acquired to be 5, with changing pH and constant nanocatalyst dosage and initial diazinon concentration. The effects of different parameters on the removal of diazinon were investigated at the constant value of pH. Diazinon residual concentration was measured by a spectrophotometer (UV/VIS, DR5000) at a wavelength of 295 nm. Results: FT-IR and XRD analyses confirmed the coating of ZnO nanorods onto PET. Under optimal conditions, initial diazinon concentration of 20 mg/L, pH of 5, and nanocomposite dosage of 2.5 g/L for 60 minutes the sonocatalytic removal efficiency of diazinon reached 99.81%. The removal efficiency decreased from 100 to 40.15% as the diazinon concentration increased from 5 to 100 mg/L. The first-order rate constant (kobs) decreased from 0.123 to 0.0086 min-1, while R2 decreased from 0.985 to 0.9152, and electrical energy per order (EEo) increased from 181.073 to 2589.77 kWh.m-3 with increasing diazinon concentration. The sonocatalytic removal of diazinon increased with rising H2O2 concentration up to 5 mM. However, the addition of organic compounds and nitrogen gas led to a decrease in diazinon removal efficiency. The effectiveness of processes for pesticide removal from drinking water decreased due to anions scavenger activity. Examination of radical scavengers revealed that •OH radicals were the most active in diazinon removal. Notably, proper sonocatalytic activity in diazinon removal was observed even after six successive cycles. Intermediate products identified by GC-MS in the sonocatalytic removal process included diazoxon, IMP, hydroxy-diazinon, and diazinon-methyl-ketone. Conclusion: The findings suggest that zinc oxide coated on polyethylene terephthalate, as an affordable, practical, and environmentally friendly material, exhibits satisfactory efficiency for the sonocatalytic removal of diazinon from water environments.
