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Photodegradation of neonicotinoids on a TiO2-based photocatalysts - efficiency of reactive oxygen species

In our previous work, different methods were used to modify the photocatalytic properties of TiO2- based photocatalysts and improve their performance for the degradation of imidacloprid as a representative of neonicotinoids [1]. This work aims to investigate the efficiency of reactive oxygen species (ROS) generated by TiO2-based photocatalysts. The identification and quantification of ROS is very important for understanding the photodegradation mechanism, improving the degradation efficiency as well as for practical application. Photocatalytic degradation of imidacloprid (10 ppm) was carried out using aqueous suspensions of different TiO2- based photocatalysts (0.08 g) in an 80 mL batch reactor equipped with a UVP Pen Ray lamp (UVA, =365 nm). The generation of hydroxyl radicals (OH●), singlet oxygen (1O2) and superoxide radicals (O2-●) formed by the UVA irradiation were determined using appropriate quenchers such as isopropanol, sodium azide and p-benzoquinone. To test the possibility that degradation occurs via direct oxidation of the adsorbed reactant molecules with holes (h+) in the valence band, additional experiments were performed using EDTA- Na2 as a hole scavenger. The effect of H2O2 addition in different concentrations on imidacloprid degradation was also investigated. Finally, to detect the presence of the short- living ROS in the aqueous medium, the electron paramagnetic resonance (EPR) spin-trap technique was employed using 5, 5-dimethyl-1-pyrroline-N- oxide (DMPO) as a scavenger reagent. The spectra were recorded under the UVA irradiation at different reaction times. Based on the results obtained, conclusions were drawn about the major ROS responsible for the efficient degradation of imidacloprid.

photocatalysis ; TiO2 ; neonicotinoids ; reactive oxygen species (ROS)

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