Removal of Neonicotinoid Insecticides in a Flat-plate Photoreactor

Abstract

The aim of this study was to investigate the photolytic and photocatalytic degradation of neonicotinoids in an aqueous solution. Acetamiprid (ACE) and thiacloprid (TIA), two widely used insecticides, were used as model components. Experiments were performed in a flat-plate photoreactor under conditions of recirculation of the reaction mixture over an immobilised photocatalyst layer (TiO2 modified by urea) using two artificial lamps for simulation of solar irradiation (2.4 % UVB and 12 % UVA; 300–700 nm). The catalyst used was characterised by XRD, UV/Vis-DRS, BET, SEM/EDX, and CHNS analysis. All experiments were performed at room temperature and atmospheric pressure, at a recirculation flow rate of 200 cm3 min–1, and at an initial concentration of ACE and TIA of 10 mg dm–3. For most measurements, the reaction mixture was sonicated for 15 min immediately before charging the reactor. The study focused on the influence of the pH of the initial solution on the efficiency of photocatalytic and photolytic degradation. It was found that photocatalytic degradation of the two model components was most effective under acidic operating conditions, i.e., at pH 4.5, while photolysis resulted in their minimum degradation. It was also observed that pretreatment of the reaction mixture with ultrasound promoted photocatalytic degradation, while in the case of photolytic degradation, the application of ultrasound did not contribute to better degradation. Finally, photocatalytic degradation of TIA proved to be more successful than photodegradation of ACE (66.4 % vs. 25.8 %) under identical process conditions.

Keywords

• heterogeneous catalysis
• neonicotinoid insecticides
• acetamiprid
• thiacloprid
• flate-plate photoreactor