Study On Dechlorination Degradation Of Atrazine Enhanced By Nanometer Zero-Valent Iron Sulfide Activated Persulfate

Atrazine is a typical triazine herbicide,and its long-term use has led to its residues in the environment.Although it has been banned in some countries and regions,it is still widely used in Northeast China.As a typical persistent organic pollutant,atrazine has the characteristics of moderate water solubility,difficult degradation and fast migration,which has caused serious harm to the environment and threatened human health.In recent years,the development of advanced oxidation technology based on nano zero-valent iron（nZVI）activated persulfate and its application in the field of organic pollution remediation have attracted much attention.However,nanometer zero-valent iron（nZVI）particles have some problems such as self-aggregation and poor stability,which limit its catalytic effect in practical application.The reactivity of nZVI can be effectively improved by vulcanization modification and loading of biochar（BC）.In this study,biochar was dispersed into Fe³⁺solution in N₂ atmosphere by one-step method,and then Na BH4 and Na₂S₂O₄solutions were added dropwise at a constant speed to synthesize biochar-loaded nano-scale zero-valent iron sulfide（S-nZVI@BC）.The activation mechanism of sodium persulfate（PS）was tested,and the oxidative degradation effect and enhanced dechlorination mechanism of atrazine in S-nZVI@BC-PS system were explored.The main conclusions of this study are as follows:（1）nZVI,S-nZVI and S-nZVI@BC were prepared.The catalyst materials were characterized by scanning electron microscope（SEM）,transmission electron microscope（TEM）,X-ray diffraction analysis（XRD）and X-ray photoelectron spectroscopy（XPS）.The main structural characteristics of S-nZVI@BC were identified,and the possible roles of different components of the composite in the oxidative degradation and dechlorination of atrazine were analyzed.T The core-shell structure of S-nZVI was clearly observed by SEM and TEM results.XRD results show that the main active substances in S-nZVI@BC are nZVI and Fe S;XPS results confirmed the core-shell structure of S-nZVI and the existing forms of different components.（2）A series of S-nZVI with different molar ratios of sulfur to iron were prepared,and their catalytic degradation effect on atrazine were compared.It was determined that S-nZVI had the best catalytic performance when the molar ratio of sulfur to iron was 0.15.The optimum dosage of S-nZVI@BC（0.1 g/L）and persulfate（PS,1 m M）was determined through a series of catalytic degradation experiments.In the optimum reaction system,the removal rate of atrazine could reach100%;The reusability of nZVI,S-nZVI and S-nZVI@BC was tested in the continuous cycle experiment.After three cycles,the removal rates of atrazine in nZVI-PS,S-nZVI-PS and S-nZVI@BC-PS systems remained at 55.5%,87.1%and 96.8%respectively;The leaching amount of iron ions in different reaction systems was detected.The leaching amount of iron ions in S-nZVI@BC-PS system was only 6 mg/L,which was significantly lower than that in nZVI-PS and S-nZVI-PS systems.It showed that S-nZVI@BC had good stability and still maintained high catalytic activity after the reaction.The effects of different reaction temperatures,different initial pH values,coexisting anions in solution and different water samples on the degradation of atrazine in S-nZVI@BC-PS system were studied.The results show that S-nZVI@BC-PS system is less affected by environmental factors,which can effectively reduce the activation energy of the reaction and promote the degradation of atrazine.（3）The main active substances in S-nZVI@BC-PS system were detected by electron spin resonance spectroscopy（ESR）,including Hydroxyl radical（˙OH）and Sulfate radical（SO₄˙^-）,Singlet oxygen（¹O₂）and Persistent free radical（PFRs）;The chloride ion concentration in the solution after the reaction was detected,which was about 1.65 mg/L.According to the law of conservation of chlorine,the chlorine element in atrazine molecule was completely removed,which indicated that the dechlorination of atrazine in S-nZVI@BC-PS system was complete.T The main metabolites of atrazine in S-nZVI@BC-PS system were analyzed by liquid chromatography-mass spectrometry（LC-MS）.It was found that atrazine degraded rapidly,with few intermediate products and thorough degradation.Based on the above research results,the main mechanism of oxidative degradation and enhanced dechlorination degradation of atrazine in S-nZVI@BC-PS system was put forward:S-nZVI releases Fe²⁺in the solution,Fe²⁺reacts with S₂O₈^2-to produce SO₄˙^-and SO₄^2-,SO₄^2-reacts with OH^-to produce˙OH,PFRs in BC provides electrons to O₂ to produce ¹O₂,S^2-loses electrons to promote the transformation of Fe³⁺to Fe²⁺,and Fe²⁺can react with S₂O₈^2-.The dechlorination and degradation of atrazine mainly went through Dechlorination,Alkyl oxidation,Dealkylation,Dehydrogenation and Olefinization.The results of this study have certain guiding significance for the development of efficient and stable persulfate activator,and put forward a deeper opinion on the reaction mechanism of oxidation and degradation of organic pollutants in S-nZVI@BC-PS system,which has important guiding significance for the remediation of organic polluted water bodies.