Mechanistic Study On Degradation Of Imidacloprid By Hydroxyl Radical Induced By Soil Colloidal Minerals

Neonicotinoid insecticides represented by imidacloprid（IMD）are new organic pollutants emerging in the environment nowadays,which are increasingly detected as residues from soil media,and it is important to study the transformation process of IMD in soil to evaluate its potential ecological risk.However,most of the current studies only focus on the microbial transformation process of IMD in soil,there are few studies about the abiotic transformation of IMD in soil,especially the degradation of IMD transformation by soil colloidal mineral-mediated free radical processes.Indeed,soil colloidal minerals are important active components in soils and can participate extensively in redox processes in the soil environment,and single electron transfer-mediated free radical processes with oxygen have important effects on the transformation of organic pollutants in soils.Based on this,the paper focuses on the mechanism of·OH induced by soil colloidal mineral and its contribution and mechanism on IMD degradation,and examines the effect of small molecule organic acids,which are prevalent in the soil environment,on the·OH production and IMD degradation of mineral systems.The main findings are as follows:（1）The mechanism of ·OH generation by the soil mineral//H₂O₂ system and its contribution to the conversion degradation of IMD was revealed.Using H₂O₂（produced by plants,redox and other processes）and iron-oxygen minerals,which are commonly found in soils,the effects of·OH production by several different types of soil minerals,α-Fe OOH,hematite,ferrihydrite and clay minerals,on IMD degradation were investigated,and it was found thatα-Fe OOH has an important contribution to IMD degradation,and the degradation rate of IMD can reach more than 90%within 48 h.The effects of differentα-Fe OOH doses,p H and H₂O₂ concentrations on the degradation of IMD were further investigated,and the results showed that lowering the p H and increasing the H₂O₂ concentration both promoted the degradation of IMD,while too highα-Fe OOH dose inhibited the degradation of IMD;the free radicals of the system were identified using free radical quenching and electron paramagnetic resonance（EPR）,and it was found that tert-butanol(Finally,the degradation products of IMD were analyzed by liquid chromatography-mass spectrometry（LC-MS）,and 6-chloronicotinic acid was found to be the main degradation product of IMD.This indicates that·OH is the main active substance for IMD degradation,and the EPR experimental results further confirm the formation of·OH.The potential toxicity of IMD degradation intermediates was analyzed using ECOSR software,and it was found that the product toxicity of IMD varied with structure.（2）The mechanism of free radical degradation of IMD by the soil colloid/H₂O₂system was elucidated.Based on the study of mineral systems,the process of free radical formation for IMD transformation by three different types of soil colloids was further investigated,and XRD,TEM and XPS characterization revealed that all three colloids contained active components such as iron,aluminum and silicate.The experimental results showed that the yellow-brown soil colloids had the highest degradation efficiency of IMD,and the degradation efficiency of IMD could reach100%within 12 h.Further studies revealed that increasing the H₂O₂ concentration and acidic conditions were favorable to the degradation of IMD.The qualitative and quantitative analysis of·OH in the system using benzoic acid（BA）probe analysis and EPR revealed that different colloidal systems produced·OH at concentrations ranging from 2μM to 50μM,and the trend of·OH was consistent with the degradation of IMD,indicating that soil colloids can form Free radicals play an important role in the transformation of pollutants.（3）Effect of small-molecule organic acids on the formation of free radicals in soil colloidal mineral systems and their degradation of IMD.A large number of small-molecule organic acids exist in the soil environment,and they affect the redox reactions in the soil,so the effects of different kinds of small-molecule acids on the degradation of IMD in the soil colloidal mineral system were investigated,and it was found that ascorbic acid（AA）,a strong reducing organic acid,had a significant promotion effect on the degradation of IMD,and the degradation efficiency of IMD increased by 5 times within 48 hours;further The changes of·OH accumulation in the systems with different concentrations of AA,different reaction times and different concentrations of soil colloidal minerals were investigated.The p H of the system was also found to decrease with the increase of AA concentration,indicating that p H has a certain effect on the system,and it was found that increasing the concentrations of soil colloidal minerals and AA produced more·OH in the system.Figure[26]Table[4]Reference[144]...