Search

The pulse current oxidation methods were used to degrade the malachite green (MG) using lead dioxide as anodes. The influences of operating parameters, including pulse frequency, pulse current density and pulse duty cycle, on the MG removal efficiency were investigated. The results indicate that MG removal efficiency can reach 99.6% after 90 min with the pulse frequency at 10 Hz, pulse current density at 30 mA cm−2 and pulse duty cycle at 0.6. The pulse degradation processes follow the pseudo-first-order kinetics. Comparison with direct current oxidisation methods, pulse oxidisation methods can enhance MG and COD removal efficiency and reduce the energy consumption. Moreover, pulse oxidisation methods can increase the amount of hydroxyl radicals generation and reduce side reactions (such as oxygen evolution) in the degradation process of MG. Finally, a possible degradation pathway of MG in pulse current modes was proposed based on the intermediate products identified by GC/MS. [ABSTRACT FROM AUTHOR]

In this work, Gd‐doped PbO2 electrodes were prepared by electrodeposition procedure. In the accelerated life test, the service life of Gd‐doped PbO2 electrodes are more stable and durable. Scanning electron microscope and x‐ray diffraction tests reveal that Gd‐doped PbO2 electrodes have more compact structure and finer grain size. Electrochemical measurements and fluorescence experiments show that Gd‐doped PbO2 electrodes have higher oxygen evolution overpotential, a larger electrochemically active surface area, and stronger ability to generate hydroxyl radicals. The electrocatalytic performance of the Gd‐doped PbO2 electrode for the electrochemical degradation of thiamethoxam was studied. The degradation process accorded with pseudo‐first‐order kinetics, with higher thiamethoxam and total organic carbon removal capabilities, as well as higher mineralization current efficiency and lower energy consumption. In the degradation process, it has favourable reusability. The experimental results demonstrate that Gd‐doped PbO2 electrodes have an excellent treatment effect and a wider application prospect in the field of pollutant degradation. [ABSTRACT FROM AUTHOR]

BACKGROUND Nitenpyram is a neonicotinoid insecticide widely used in agriculture and horticulture, which is stable and builds up in wastewater, causing serious environmental concerns. In this work, the process of advanced electrochemical oxidation for degrading nitenpyram was investigated in detail. The influences of operation parameters (including applied current density, initial nitenpyram concentration, Na2SO4 concentration and pH value) on the electrochemical removal of nitenpyram and its relative degradation mechanism were studied by a gadolinium‐doped lead dioxide (Gd‐PbO2) anode. RESULTS: The results demonstrated that the electrochemical oxidation of nitenpyram follows pseudo‐first‐order reaction kinetics under different operation conditions. After that, 95.44% of nitenpyram and 79.22% of COD could be eliminated from 0.15 mol L−1 Na2SO4 solution dissolving 75 mg L−1 nitenpyram under 70 mA cm−2 at pH = 5.0. Ultimately, high‐performance liquid chromatography (HPLC) and HPLC/mass spectroscopy (MS) were adopted to discover the degradation by‐products during the nitenpyram oxidization process, and up to 14 by‐products were successfully identified. Then a typical nitenpyram degradation pathway was proposed based on these by‐products, comprising two divided parallel sub‐routes. Indirect electrochemical oxidation was responsible for nitenpyram degradation by Gd‐PbO2 anode, and hydroxyl radicals were the main reactive oxygen species. CONCLUSION: The Gd‐PbO2 electrode presented remarkable performance in nitenpyram degradation. Therefore, the electrochemical oxidation method by Gd‐PbO2 anode is considered to be a very promising and practical mode of herbicide wastewater treatment. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]