Preparation Of Rare Earth Modified PbO₂ Electrodes And Electrocatalytic Of Neonicotinoid Insecticides

In this paper,three-dimensional porous PbO₂-CeO₂ composite electrodes（3D/PbO₂-CeO₂）and Yb-doped PbO₂ electrodes（Yb-PbO₂）were prepared by electrodeposition method,and were respectively applied to the electrocatalytic degradation of neonicotinoid insecticides（thiamethoxam and acetamiprid）.The main research contents are as follows:3D/PbO₂-CeO₂ electrodes were fabricated by composite electrodeposition method using oxygen bubbles as templateon,to eliminate neonicotinoid thiamethoxam in aqueous solution.Scanning electron microscope（SEM）,X-ray diffraction（XRD）and energy dispersive spectrometer（EDS）were used to characterize the surface morphology and composition of 3D/PbO₂-CeO₂ electrodes.Then the influence of the applied current density,the initial concentration of thiamethoxam,the concentration of supporting electrolyte,and initial p H value on the thiamethoxam removal ratio were also optimized.Through HPLC-MS analysis,Amount to twenty deductive intermediates of thiamethoxam degradation were identified,and the reaction of dechlorination,hydrogen abstraction,denitration,and hydroxylation in the electrochemical oxidation process of thiamethoxam was observed.On this basis,a hypothesized degradation mechanism was proposed.According to the different initial oxidation positions of thiamethoxam,thiamethoxam was divided into two parallel paths: chlorine atom on the thiazole ring and nitro group on the 1,3,5-oxadiazinane ring.Eventually all the intermediates were mineralized to H₂O and CO₂.The results showed that the electrochemical oxidation of thiamethoxam with 3D/PbO₂-CeO₂ electrodes could effectively remove thiamethoxam.The Yb-PbO₂ electrodes were fabricated by electrodeposition method.The results of SEM and XRD show that the adulteration of Yb can reduce the grain size and make the electrode structure more compact.Electrochemical measurements and electrolytic experiments show that Yb-PbO₂ electrodes has higher stability of oxygen evolution overpotential and acetamiprid removal ratio than pure PbO₂ electrodes.The effects of initial current density and p H on electrocatalytic degradation of acetamiprid were studied.The electrocatalytic oxidation of acetamiprid on Yb-PbO₂ electrodes were highly effective,which obeyed the pseudo-first-order kinetics model.The Yb-PbO₂ electrodes were used to analyze the intermediate and study the electrocatalytic degradation mechanism of acetamiprid,and the degradation pathways was divided into three different sub-routes,because acetamiprid was attacked by hydroxyl radical,had three functional groups.Finally,all the intermediates are oxidized to CO₂ and H₂O.The results show that Yb-PbO₂ electrodes has a good prospect in electrocatalytic degradation of refractory organic pollutants.