Bimetallic Biochar Combined With 3D Electrofenton System For Neonicotinoid Pesticide Wastewater Degradation

Neonicotinoid insecticides（NEOs）have grown to be the most widely used class of insecticides in the world since their invention.Because it is highly neurotoxic to insects and may also cause organ and genetic lesions and even death in species such as bees and aquatic organisms.However,NEOs exhibit stability and persistence in aqueous solutions,it is difficult to degrade them by biological treatment processes in conventional wastewater plants.If NEOs were not untreated,which will pose a potential threat to human health and the environment.Electro-Fenton（EF）,as an advanced oxidation technology,has been demonstrated to efficiently degrade organic pollutants.But its practical application is limited due to expensive electrode materials,complicated electrode preparation process and short radical lifetimes(10^-6-10^-9s).Biochar has been popular in recent years due to its wide source and low price.It can be loaded on the cathode to enhance the removal rate of organic pollutants.Because the free radicals（PFRs）on the surface of biochar can activate hydrogen peroxide（H₂O₂）.At the same time,biochar can adsorb pollutants in water on the surface of the electrode,the Fenton reaction can occur at the small area.However,there were few reports on this topic.Therefore,this paper aims to:reveal the effectiveness of biochar in adsorption of NEOs;using biochar as a catalyst to construct a non-homogeneous EF system and loading biochar on the cathode surface reveal the degradation mechanisms and pathways of NEOs.The main conclusions are as follows:1.Nitenpyram（NIT）,the most water-soluble neonicotinoid,was considered a target pollutant.Biochar（BC）was prepared from pig manure and carboned for 2 h under the oxygen-limited（700°C）condition.Modified biochar（SBC）was obtained by treatment with 5%sulfuric acid and ultrasonic waves.Meanwhile,biochar loaded with nano-zero-valent iron（ZVI）and nano-zero-valent copper（ZVC）was prepared by liquid-phase reduction using SBC as precursors,marked as ZVI/ZVC@SBC.Scanning electron microscopy（SEM）coupled with Energy dispersive spectroscopy（EDS）,Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction spectrum（XRD）,Brunauer-Emmett-Teller（BET）and X-ray photoelectron spectroscopy（XPS）showed that the specific surface area and the number of functional groups of the modified biochar increased significantly.The results showed that ZVI/ZVC@SBC improved the adsorption capacity of NIT compared to BC.This adsorption process was a typical three-stage process,which was more consistent with the Elovich kinetic and Langmuir model.It showed that this process was determined by several mechanisms.Acidic conditions and the increase of biochar dosing would be more favorable for the removal of NIT.2.Then,this study compared the catalytic performance of iron nano-loaded biochar（ZVI@SBC）,copper nano-loaded biochar（ZVC@SBC）and ZVI/ZVC@SBC in the EF system.It explored the influence of environmental factors（p H,current intensity,aeration,electrolyte concentration）in the optimal degradation system and identified active species.Catalyst reuse performance and product in degradation process were explored by ultra performance liquid chromatography with triple quadrupole tandem mass spectrometry（UPLC-Q-TOF/MS）.The results showed that ZVI/ZVC@SBC was the most excellent catalyst in the EF system.The cathode loaded with ZVI/ZVC@SBC can improve the removal of NIT.The NIT removal rate was 79.24%at p H=7 after 120 min of reaction.Under the acidic condition,increasing the current and aeration were more favorable for the degradation of NIT.The effect of electrolyte concentration was not significant.·O₂^-and·OH were considered to be main active species,the catalytic performance of ZVI/ZVC@SBC decreased after 4 repetitions.The degradation pathways indicated that dechlorination,nitro substitution and double bond breaking were main mechanisms of NIT degradation.3.The reusability performance of ZVI/ZVC@SBC was poor,so it needed to enhance the catalytic performance of biochar and investigated whether it also had excellent removal performance for other NEOs.Imidacloprid（IMI）was the target pollutant due to its water solubility was weak.Straw-based biochar co-doped with ZVI and cobalt（Co）was prepared（ZVI/Co@SBC）by liquid-phase reduction.The performance of three-dimensional EF system constructed by ZVI/Co@SBC as a catalyst for IMI removal,environmental influencing factors and degradation mechanisms of IMI were studyed.The results illustrated that ZVI/Co@SBC can adsorb 36.03%of IMI within 120 min.This process was suitable for Elovich kinetic and Langmuir model.81.86%of IMI could be removed in 120 min under the neutral condition（p H=7）in EF system.Acidic condition,increasing current and aeration were all favorable for degradation of IMI.ZVI/Co@SBC can still remove 77.98%of IMI after being used 5 times.The degradation process was accompanied by nitro substitution,dechlorination and double bond breakage.