Preparation Of Sulfide Iron-based Nanomaterial And Its Degradation Effect And Mechanism For Triclosan

Chlorinated organic compounds are persistent organic pollutants,which have the characteristics of wide pollution,strong toxicity and difficult degradation.At present,the situation of organic chlorine pollution in the environment is still very serious.Therefore,it is imperative to develop an organic chlorine treatment technology with efficient degradation and dechlorination.Triclosan（TCS）is widely used in personal care products due to its antibacterial,antifungal and antiviral properties.As an emerging pollutant,TCS is frequently detected worldwide.Sulfide nano-zero-valent iron has strong reducibility and high catalytic performance,and has become a popular material for reductive dechlorination and activation of persulfate in recent years.In this paper,TCS was selected as the characteristic pollutant.Firstly,Sulfide nano-zero valent iron（S-nZVI）was prepared by liquid phase reduction method.The response mechanism of its reductive dechlorination performance to preparation conditions was elucidated by physicochemical properties characterization and degradation experiments,and the reductive dechlorination mechanism of TCS by S-nZVI under anoxic conditions was explored.Then,ball-milled sulfide nano-zero-valent iron(S-nZVI_mill)was prepared by dry ball milling and wet ball milling,and the material was optimized.The mechanism of S-nZVI_millactivating persulfate to degrade TCS was explored under aerobic conditions,.The conclusions are as follows:（1）The sulfidation method has significant effects on the apparent morphology,crystal structure and sulfur spatial distribution of S-nZVI.One-step synthesis method is more conducive to the formation of Fe_xS_ycompounds,and achieve internal uniform sulfidation.The sulfide reagent can regulate the morphology of S-nZVI,but does not affect its crystal structure.After sulfurization,the surface of S-nZVI is rough,which is conducive to dispersion.The surface and internal sulfur-iron species can effectively avoid the oxidation of Fe⁰and construct the electron transport channel from Fe⁰core to pollutants.（2）The S-nZVI materials with one-step synthesis combined with Na₂S as sulfur source showed the best degradation performance,and the degradation efficiency reached 90.72%when the molar ratio of S/Fe was 0.015.The uniform distribution of S₂^2-in S-nZVI is the key to improve the degradation performance of S-nZVI.S-nZVI has strong adaptability to the environment,and can maintain a high reaction activity under the severe acid-base environment and the interference of anions and cations.Moreover,S-nZVI has excellent selectivity and anti-aging ability.The Fe_xS_yin S-nZVI only acts as an electron transport channel to improve the reaction rate without participating in the reaction,ensuring the long-term effectiveness of the material.Through the identification of degradation products,it was found that TCS could achieve detoxification through dechlorination,hydroxylation,cyclization and ether bond cleavage.（3）Wet ball milling with EtOH as sulfur aid is beneficial to obtain lamellar materials with high specific surface area.With the increase of S/Fe,the roughness of the catalyst decreases,which is not conducive to its reactivity.EtOH helps to isolate oxygen during high-energy ball milling and prevent Fe⁰oxidation.XPS spectra showed that the sulfur in S-nZVI_millexisted in various forms,which proved that sulfur and iron were not simple physical mixing,but formed sulfur and iron compounds,the S-nZVI_millwas successfully synthesized.With Na₂S as sulfur source and EtOH as sulfur aid,the catalytic performance of S-nZVI_millwas the best when S/Fe=0.01,and the degradation efficiency of S-nZVI_millreached 96.09%within 10 min.In the S₃-nZVI_mill-EtOH@PDS system,S₃-nZVI_mill-EtOH has the best degradation performance on TCS when the dosage was 0.1 g/L and PDS is 1 m M.The system could adapt to a wide p H range,almost unaffected by anions（NO₃^-and Cl^-）and water matrix.In addition,it had excellent degradation ability for various chlorinated organic pollutants.（4）The characterization of the materials after the reaction showed that Fe₂（SO₄）₃was formed on the surface of S₃-nZVI_mill-EtOH,which was conducive to the continuous reaction of Fe⁰to Fe²⁺.Sulfuration can improve the catalytic performance by increasing the dissolution concentration of Fe²⁺and the ratio of Fe²⁺/Fe³⁺,and also improve the dechlorination capacity and the utilization rate of S₂O₈^2-.Combined with free radical identification,quenching experiments and degradation product analysis,it was concluded that·OH,SO₄^·-and ¹O₂were involved in the degradation of TCS,mainly SO₄^·-and ¹O₂.Under the joint action of·OH,SO₄^·-,¹O₂and e^-,TCS in S₃-nZVI_mill-EtOH@PDS system were rapidly degraded through cycloaddition,ether bond cleavage,ring opening and dechlorination,thus realizing the harmless of organic chlorine pollutants.