Photodegradation of Neonicotinoid Active Ingredients and Their Commercial Formulations in Water by Different Advanced Oxidation Processes

This contribution is concerned with the comparison of the efficiency of the removal of four pure neonicotinoid active ingredients (AIs) and their commercial formulations (CFs) from aqueous solutions by using different advanced oxidation processes at the pH 2.8. The AIs of thiamethoxam and imidacloprid, and their CFs (Actara and Confidor), having a nitroguanidine functional group, exhibited low persistence to photolysis. In contrast to them, thiacloprid and acetamiprid and their CFs (Calypso and Mospilan), containing a cyanoimine functional group, were stable during the UV irradiation period. As expected, the degradation rate of the studied neonicotinoids increased significantly in the combined action of UV radiation and H2O2. In the case of thiacloprid and acetamiprid and their CFs, the reaction of the OH radicals formed and molecules of these insecticides was the major destruction pathway. The increased photodegradation efficiency of the UV/7.2Fe/TiO2/H2O2 and vis/7.2Fe/TiO2/H2O2 processes was attributed to the surface photoreduction of Fe3+ to Fe2+, which produces new OH radicals in the reaction with H2O2. In the presence of visible light, the efficiency may be partly due to the formation of the H2O2-TiO2 complexes. For the 7.2Fe/TiO2/H2O2 process in the presence of UV or visible radiation, no significant influence on the efficiency of photodegradation was observed in dependence of the structural differences of selected neonicotinoids. These results strongly suggest that highly reactive hydroxyl radicals, generated on the catalyst's surface in the reaction involving H2O2, are responsible for this oxidation. In order to investigate degree of mineralization for all insecticides, TOC measurements were also conducted. Also, it was observed that the removal of pure AIs and their CFs by dark adsorption was almost negligible

Photodegradation of thiacloprid using Fe/TiO2 as a heterogeneous photo-Fenton catalyst

Three Fe/TiO2 photocatalysts with different content of Fe (1.9, 7.2 and 13.9%, w/w) were synthesized by a simple deposition-precipitation method and characterized by XRD, SEM, N-2 physisorption at 77K and Mossbauer spectroscopy. The characterization showed the presence of nano-sized Fe2O3 particles (less than 4 nm) on the TiO2 support. The photocatalytic efficiency of the catalysts was examined on the example of thiacloprid (TCL) degradation under UV light irradiation in aqueous suspension in the presence/absence of H2O2. Since the efficiency of TCL degradation in the presence of H2O2 (heterogeneous photo-Fenton process) was more than two times higher, all other investigations were conducted in the presence of H2O2. The photocatalyst with 7.2%, w/w Fe (denoted as 7.2Fe/TiO2) appeared to be most efficient. The photocatalytic degradation studied under different operating conditions indicated that 0.5 g L-1 of 7.2Fe/TiO2 was an optimal catalyst loading, and the optimal pH was 2.8. In the investigated range of initial concentrations of TCL (0.06-0.32 mM) the photocatalytic degradation in the first stage of the reaction followed approximately a pseudo-first order kinetics. The suspended Fe/TiO2 spontaneously precipitated once the stirring of the reaction mixture was terminated (>90% after 15 min). The results clearly demonstrated that 7.2Fe/TiO2 was stable and resistant to photocorrosion during the photocatalytic degradation of TCL The higher efficiency of 7.2Fe/TiO2 compared to Degussa P25 under the optimal experimental conditions of TCL photodegradation, spontaneous precipitation of the suspension, possibility of reusing the catalyst, as well as an insignificant increase in the iron concentration in water solution, all this indicates the possibility of the practical application of this photocatalyst for water treatment

Efficiency of neonicotinoids photocatalytic degradation by using annular slurry reactor

This article is concerned with the kinetics of the photocatalytic degradation of four neonicotinoids insecticides as active ingredients (AN) in their commercial formulations by using the annular slurry reactor (ASR). For all Als, more effective photodegradation was achieved by UVA than by visible light irradiation. The most efficient degradation was observed in the case of thiacloprid, which degraded completely after two hours of irradiation using UVA, and 59% using visible light irradiation. On the other hand, the most stable appeared to be acetamiprid, whereby during the same time of irradiation it was degraded 42% using UVA, and only 4% using visible light irradiation. Because of that the efficiency of a number of advanced oxidation processes was examined in the case of acetamiprid. It was found that the presence of H2O2 in ZnO, 7.8Fe/ZnO, and 7.2Fe/TiO2 systems using UVA did not bring significant changes in the efficiency of degradation. However, using visible light irradiation the presence of H2O2 in ZnO and 7.8Fe/ZnO systems significantly increases efficiency of acetamiprid degradation. Also, by adjusting pH to 2.80 in the system 7.2Fe/TiO2/H2O2 using both type of irradiation resulted in a significant increase of the degradation efficiency. For the first time, for ZnO/H2O2 system a general reaction mechanism in the dark, as well as in the presence of visible light irradiation was proposed. The electrical energy consumption of ASR was estimated for the most efficient visible light irradiation system using the figure-of-merit electrical energy per order and compared with batch and laminar falling film slurry reactor