Molybdenum Disulfide Enhanced Efficacy And Mechanism Of Sulfamethoxazole Degradation By Homogeneous And Heterogeneous Iron Activated Peroxydisulfate System

Due to the widespread use of sulfanilamide antibiotics over the years,sulfonamides have been detected in aquatic environments in multiple locations.The long residual time and the possibility of inducing resistance genes posing a critical threat to the environment and human health.Advanced oxidation technology based on sulfate radicals(SO₄^·-)with excellent oxidation capacity,high treatment efficiency and wide applicability is a potential technology that can efficiently degrade sulfonamides.The Fe²⁺/PDS system has received a lot of attention from researchers because of its fast activation rate,simplicity,environmental friendliness,low price and no additional energy required.However,the low efficiency of Fe（Ⅲ）/Fe（Ⅱ）cycle and the slow regeneration of Fe²⁺limit the further application of the system in the water treatment.In this paper,a typical sulfonamide antibiotic,sulfamethoxazole（SMX）was selected as the target contaminant,and a method was proposed for the effective promotion of Fe（Ⅲ）/Fe（Ⅱ）cycle and efficient degradation of SMX by the reducing agent molybdenum disulfide（MoS₂）through enhanced homogeneous and non-homogeneous iron-activated PDS.The reaction mechanism was also clarified through characterization and validation experiments.The main research contents and results are as follows:Based on the Fe²⁺/PDS system,the Fe（Ⅲ）/Fe（Ⅱ）cycle was enhanced by the introduce of MoS₂,and the enhancing mechanism was revealed.The results showed that MoS₂ could effectively improve the degradation efficiency and mineralization of SMX.The degradation rate of SMX in the MoS₂/Fe²⁺/PDS system rose from 35.2%and 18.0%to 98.4%compared with the Fe²⁺/PDS and MoS₂/PDS systems,the TOC removal rates increased from 12.9%and 7.6%to 40.1%,and the reaction rate constants raised to 1.4 and 20.2 times,respectively.A comparative study with four other transition metal sulfides,WS₂,Fe S₂,Zn S and Cu S,showed that MoS₂ had the strongest enhancement effect on the Fe²⁺/PDS system,and the highest PDS stoichiometric efficiency and the best cycling stability.Free radical quenching experiments and EPR tests revealed that the main active species in the system were SO₄^·-and^·OH,which were mainly surface-bound.Instrumental characterization and validation experiments revealed that the five metal sulfides were not identical in their mechanism of co-catalytic effect on the Fe²⁺/PDS system.For MoS₂ and WS₂,Mo,W metal sites and S sites can effectively promote the reductive regeneration of Fe（Ⅱ）,and then accelerate the decomposition of PDS and the degradation of target pollutants;while for Fe S₂,Zn S and Cu S,the regeneration of Fe（Ⅱ）mainly comes from the reducing S sites.Considering the degradation efficiency of target pollutants,cycle stability and reaction stoichiometric efficiency of PDS,MoS₂/Fe²⁺/PDS system was selected for subsequent experiments to investigate the effects of different reaction conditions,coexistence of anions and humic acid on SMX degradation.The degradation efficiency of four sulfonamides antibiotics in MoS₂/Fe²⁺/PDS system was tested and it was found that the differences of degradation efficiency were mainly due to their structural characteristics.To further optimize the catalyst separation,the MoS₂/nZVI/PDS heterogeneous catalytic activation system was constructed using nano zero-valent iron（nZVI）as the iron source.The degradation efficiency of SMX in the MoS₂/nZVI/PDS system was improved by 37.2%and the reaction rate constant was increased to 15.6 times compared with the nZVI/PDS system.Radical quenching experiments and EPR tests showed that surface-bound SO₄^·-and^·OH were the main active species in the MoS₂/nZVI/PDS system.The characterization and verification experiments revealed that the Fe⁰ core,Mo（IV）and S sites could effectively promote the Fe（Ⅲ）/Fe（Ⅱ）cycle,continuously activate PDS to degrade SMX during the reaction process.The main degradation pathways of SMX in the MoS₂/Fe²⁺/PDS system were proposed based on the determination of intermediates.In order to alleviate the agglomeration of nZVI,expose more inner Fe⁰ core and reducing Mo（IV）active sites,fully utilize the reductive effect of nZVI and MoS₂,magnetic nZVI@MoS₂ composites were prepared to activate PDS and degrade SMX efficiently.The nZVI was loaded onto the surface of MoS₂ by mechanical ball-milling method,and the effects of ball-milling time,MoS₂/nZVI molar ratio were studied.The results showed that the specific surface area of the nZVI@MoS₂ composites gradually increased and the average pore size of the material gradually decreased with the increase of ball milling time.The degradation efficiency of SMX firstly increased and then decreased with the increase of MoS₂/nZVI molar ratio,and reached the The maximum is reached at a MoS₂/nZVI molar ratio of 0.5,i.e.,the composite was FM3.Therefore,the FM3/PDS system was constructed and the reaction rate constants are5.9,24.8 and 4.3 times higher than those of nZVI/PDS,MoS₂/PDS and MoS₂/nZVI/PDS systems,respectively.The results of radical trapping experiments and spectroscopic analysis indicated that the surface-bound SO₄^·-and^·OH played a major role in the degradation of SMX during the reaction of FM3/PDS system.The activation mechanism of the FM3/PDS system was proposed via instrumental characterization and validation experiments:the Fe⁰ core and Mo（IV）of the FM3composite could not only directly activate PDS,but also effectively promoted the Fe（Ⅲ）/Fe（Ⅱ）cycle.Meanwhile,the reducing S sites could effectively regenerated Fe（Ⅱ）and Mo（IV）,which could in turn promote the activation of PDS and the degradation of SMX.In addition,Four main degradation pathways of SMX in the FM3/PDS system were proposed based on the determination of SMX degradation intermediates.