Preparation Of Complex FeS₂/MnFe₂O₄ And The Efficacy And Mechanism Of Activation Of PMS To Degrade 2,4 Dichlorophenol

2,4 Dichlorophenol（2,4-DCP）is widely used in many industries,such as pharmaceuticals,agriculture,textiles,paper,etc.However,large amounts of 2,4-DCP enter the natural environment due to production losses,accidental spills,industrial wastewater discharges,etc.Its physicochemical properties are very stable,bioconcentrating,and hard to degrade,leading to serious health problems such as cancer,deformation,and genetic mutation in humans,and also posing a serious threat to the natural ecological environment.It is difficult to degrade 2,4-DCP completely by conventional treatment methods,so it is important to study how to degrade 2,4-DCP efficiently to ensure the safety of water supply to the residents and the health of the ecological environment.Advanced oxidation based on peroxymonosulfate（PMS）is one of the most efficient methods for the removal of difficult to degrade organic pollutants,in which bimetallic oxide Mn Fe₂O₄ is an economical and green PMS activator.However,Fe（II）and Mn（II）are oxidized to Fe（III）and Mn（III）during the activation of PMS,but the activation effect of high-valent metal ions is poor,while the regeneration of low-valent metal ions is difficult,leading to the poor degradation performance of the system.Therefore,how to promote the conversion of Fe（Ⅲ）and Mn（Ⅲ）to Fe（Ⅱ）and Mn（Ⅱ）and accelerate the regeneration of low-valent metal ions is of great significance to enhance the degradation performance of the system.In this paper,we are devoted to investigating a PMS activation material based on Mn Fe₂O₄ to degrade 2,4-DCP with fast and efficient characteristics.Since sulfur is highly reductive and beneficial to promote the regeneration of low-valent metal ions,a novel nanocomposite,FeS₂/Mn Fe₂O₄,was prepared in this paper by a two-step hydrothermal method as a PMS activator for the degradation of 2,4-DCP.The optimization and characterization of the preparation conditions of the material,the evaluation of the catalytic performance,and the mechanistic performance of FeS₂/Mn Fe₂O₄ were investigated from three aspects:optimization of preparation conditions and characterization,evaluation of catalytic performance,and study of the mechanism.The main research results are as follows.（1）Three common methods for the preparation of sulfide complexes were selected for trial,and it was determined that the two-step hydrothermal method could successfully prepare FeS₂/Mn Fe₂O₄.four influencing factors in the hydrothermal synthesis process were selected to optimize the products,and finally determined:the optimal solvent was pure ethylene glycol,the metal salts were Fe Cl₃ and Mn（CH₃COOH）₂,the optimal hydrothermal temperature was 140°C,the optimal hydrothermal time was 9 h.The physical phase and elemental composition were analyzed by XRD and EDS mapping,and the FeS₂/Mn Fe₂O₄composites were proved to be successfully prepared.By SEM image analysis,FeS₂/Mn Fe₂O₄ has an irregularly shaped lamellar structure.By XPS,FT-IR,and Raman analysis,it was found that the characteristic peak shapes of sulfide and metal-oxygen did exist in FeS₂/Mn Fe₂O₄,which further clarified its structure.By electrochemical tests,it was found that FeS₂/Mn Fe₂O₄ has a larger electron transfer rate and stronger redox ability compared with Mn Fe₂O₄.（2）The degradation performance and influencing factors of the FeS₂/Mn Fe₂O₄/PMS system were investigated and found that the degradation rate of 2,4-DCP reached 90.4%at15 min for the system in this study,which was 48.4%higher than that of the system Mn Fe₂O₄/PMS.The k_obs was 0.1375 min^-1,which was 7.31 times higher than that of the system Mn Fe₂O₄/PMS(0.0188 min^-1),indicating that the performance of the catalyst was significantly improved after loading.Compared with other types of Fenton-type catalysts,the catalytic performance of FeS₂/Mn Fe₂O₄ has obvious advantages.When the FeS₂/Mn Fe₂O₄ concentration was 1.5 g/L,the concentration of 2,4-DCP was 100 mg/L,the concentration of PMS was 5 m M,and the initial p H of the solution was not adjusted,the degradation of 2,4-DCP by the FeS₂/Mn Fe₂O₄/PMS system under this condition was optimal.The degradation of 2,4-DCP by FeS₂/Mn Fe₂O₄ system can still reach 77.9%after three times of recovery.The results show that FeS₂/Mn Fe₂O₄ has excellent catalytic performance and exhibits good recyclability and environmental friendliness.（3）In the degradation of 2,4-DCP by FeS₂/Mn Fe₂O₄/PMS system,¹O₂ andO₂^·-and played the main role,SO₄^·-and OH and induced as the auxiliary degradation pathway.By monitoring the changes in TOC values of the solution during the reaction,it was found that the system showed good mineralization of 2,4-DCP,indicating that most of 2,4-DCP was mineralized to CO₂ and H₂O while being oxidized.The intermediates were analyzed and identified,three possible degradation pathways were proposed,the toxicity of the intermediates was predicted,and the overall toxicity was found to be less than that of 2,4-DCP.The results showed that the recycling of Fe（II）/Fe（III）and Mn（II）/Mn（III）was accelerated by the synergistic effect between Fe and Mn and the reducing ability of sulfur,and the loading of sulfide solved the problem of low valent metal ions in the catalysts.The loading of sulfide solves the problem of regeneration of low-valent metal ions in the catalyst and greatly improves the catalytic activity.