engleski

PHOTOCATALYTIC DEGRADATION OF IMIDACLOPRID IN A FLAT-PLATE REACTOR

The increase in the concentration of toxic contaminants in wastewater has led to increasingly stringent environmental legislation. The existing water treatment processes cannot remove persistent organic compounds sufficiently, which is why the advanced oxidation processes are increasingly explored as an alternative to conventional methods. In this work, the efficiency of the photocatalytic degradation of neonicotinoid insecticide imidacloprid (1-[(6-Chloro-3-pyridinyl)methyl]-N-nitro-1H-imidazol-2-amine) using immobilized commercial TiO2 P25 and TiO2 catalyst with enhanced activity under simulated sunlight was examined. Imidacloprid was chosen as a model compound because it represents a risk to the aquatic environment and is currently included in the watch list of substances for Union-wide monitoring in the field of water policy, established by the European Commission Implementing Decision 2018/840 pursuant to Directive 2008/105/EC. Despite many advantages of photocatalysis for wastewater purification and extensive laboratory research done in this field, there are several challenges preventing the application of this technology at the commercial scale, especially development of high efficiency photocatalysts, photoreactor design and light source optimization (Odling and Robertson, 2019). The experimental set-up consisted of: home made flat-plate reactor with upper quartz sheet plate, recirculation pump, reservoir containing the reaction mixture and two Arcadia natural sunlight lamps (8 W), which emit the whole sun spectrum. The photoactivation of commercial TiO2 (P25 Degussa/Evonik) under the visible light (λ>400 nm) was achieved using pretreatment of TiO2 with UVC irradiation. As shown previously in the literature, such kind of pretreatment leads to reduction of TiO2 and extend its photoresponse from the UV to the visible light region (Panayotov et al., 2005). Reduced TiO2 was immobilized on different support materials using sol-gel route and a TEOS binder. The physico-chemical properties of the immobilized TiO2 layers were characterized using XRD, SEM and UV-Vis spectroscopic analysis. A 10-ppm solution of imidacloprid in water was recirculated through the reactor system. The efficiency of the immobilized photocatalytic layers was examined at different residence time and pH values. The intensity of UV-A and UV-B emitted from lamps was varied by changing the lamp distance from the reactor and measured using UV radiometer and corresponding UV-A and UV-B sensors. Samples were taken periodically and the concentration profiles of imidaclopride and main reaction byproducts were determined using HPLC and LC/Q-TOF analysis. According to the obtained results the corresponding kinetic and reactor model were proposed and the key parameters were estimated. The experimental results obtained under different reaction conditions were compared with the predictions resulting from the simulations. The successful validation confirms the scientific background of the model and its applicability for engineering purposes in the design and optimization of photocatalytic reactors.

photocatalysis, imidacloprid, flat-plate reactor

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