| Due to the extensive usage of neonicotinoid insecticides（NNIs）as thiacloprid（THIA）and the emission of NNIs into natural water through various pathways,NNIs are widely detected in surface water,groundwater and soil all over the world.However,because THIA possesses stable physical and chemical properties,traditional water treatment methods cannot achieve a good removal effect.Therefore,it is urgent to find a more efficient and effective method to degrade contaminated water containing THIA.In recent years,periodate has attracted some attention in advanced oxidation technology,which can convert oxidants into reactive radicals through specific reaction pathways and the reactive radicals can react with organic pollutants.A novel iron–manganese oxide loaded sludge biochar（Fe/Mn–SBC）catalyst was synthesized to assist periodate（PI）to degrade THIA in water.The specific research contents are as follows:（1）The effects of catalyst dosage,PI concentration and initial pH on the degradation process of THIA in Fe/Mn–SBC/PI system were investigated.It is found that with the increase of Fe/Mn–SBC dosage,the degradation efficiency of THIA was significantly enhanced;with the elevation of PI concentration,the degradation efficiency of THIA was only slightly enhanced;and more than 92%removal emoval rate of THIA in a wide pH range of 3–11 were achieved.The optimal reaction conditions of the experiment were as follows:the THIA concentration of 10 mg/L,the Fe/Mn–SBC concentration of 1 g/L,the PI concentration of 5 mmol/L and initial pH of 11,temperature of 25℃.The Fe/Mn–SBC catalyst exhibited good stability and can be reused at least 5 times.The leached concentration of iron ions was lower than the detection limit of atomic absorption spectrometer（0.03 mg/L）,while the leached concentration of manganese ions was 0.421 mg/L.（2）The effects of common inorganic anions(HCO3–,SO42–and Cl–)and natural organic humic acid（Humic acid,HA）in the environment on the degradation of THIA by Fe/Mn–SBC/PI system were investigated.The study found that the addition of high concentration of HCO3–had a significant inhibitory effect on the degradation process of THIA,while the introduction of Cl–and SO42–and HA had almost no effect on the degradation process of THIA in the Fe/Mn–SBC/PI system.（3）By comparing to investigate the surface morphology,functional groups,crystal structure,pore characteristics and surface metal valence of biomass carbon before or after the modification through various characterizations,it could be gained that the graphitic carbon structure（C–C）and surface functional groups（–OH,C=C,C=O and C–O,etc.）were involved in the process of activating PI to degrade THIA.The degradation mechanism of the system was proposed based on the results of free radical quenching experiment,the electron paramagnetic resonance experiment（EPR）and dissolved oxygen exclusion experiments,in which·OH and IO3·were considered as the main active species in the Fe/Mn–SBC/PI system.（4）In the Fe/Mn–SBC/PI system,LC–MS technology was used to identify THIA products,in which eleven possible intermediate products were detected.It was speculated that there were mainly three possible degradation pathways:（i）the hydroxylation processes occurring on THIA molecule;（ii）the oxidation process of THIA molecule by the attack of·OH and IO3·radicals;（iii）the direct degradation via cyano hydrolysis and chloropyridinyl dichlorination.Ecos AR software was used to evaluate the toxicity of THIA products,and the intermediate products were predicted to be less toxic than THIA.The second pathway was considered as the most fundamental degradation pathway,in which the intermediate products were the least toxic. |
