| With the development of society economy and improvement of people’s living standards,various antibiotic drugs with different therapeutic effect have been developed and widely used in clinical therapy and animal husbandry.However,the problem of antibiotic contamination is becoming increasingly prominent.The antibiotics have been frequently detected in aquatic environment and have posed a potential threat to ecological environment and human healthy.Therefore,it is utmost importance to develop efficient technologies to control and reduce the concentration of antibiotics in aquatic environment.Over the past decades,ferrate(Fe(Ⅵ))as a green,powerful and environmentally friendly oxidant has attracted more and more attention,and has been extensively studied in the field of drinking water and wastewater treatment.Although Fe(Ⅵ)has a high redox potential and can remove a wide range of organic contaminants from water,degradation of some recalcitrant organic pollutants still requires a long time and higher dosage of Fe(Ⅵ).These limitations restrict the application of Fe(Ⅵ)in the drinking water and wastewater treatment.Therefore,developing more efficient and robust Fe(Ⅵ)oxidation process to accelerate the degradation of pollutants in water is necessary.Therefore,in this study,we explored various systems to enhance Fe(Ⅵ)oxidation capacity,and SMX was selected as the target pollutant to investigate the performance and mechanisms of different Fe(Ⅵ)oxidation system.The main work was as follows:(1)Firstly,the performance and reaction mechanism of Fe(Ⅵ)-GP system in the degradation of SMX was investigated.The results indicate that GP could effectively activate Fe(Ⅵ)to degrade SMX,and the degradation efficiency was higher than the Fe(Ⅵ)and GP system.The higher degradation efficiency of SMX in Fe(Ⅵ)-GP system main due to formed high-valent metal-oxo intermediates Fe(Ⅴ)and Fe(Ⅳ).The key operating parameters(i.e.,solution pH,Fe(Ⅵ)dosage,AB dosage and initial SMX concentration)could significantly affect the degradation efficiency of SMX in the Fe(Ⅵ)-GP system;Cl-,NO3-,HCO3-,Ca2+ and Mg2+ had little effect on the degradation of SMX,while HA,EDTA-2Na,NTA-3Na and TSPP could obviously inhibit the degradation of SMX in the Fe(Ⅵ)-GP system.The Fe(Ⅵ)-GP system exhibited satisfactory removal of SMX in real water.Besides,Fe(Ⅵ)-GP system could also effectively remove other recalcitrant organic pollutants(i.e.,BPA,2,4-DCP,PNP and CBZ).In addition,GP also exhibited high stability and recyclability for SMX degradation in the Fe(Ⅵ)-GP system.(2)Secondly,the performance and mechanism of carbon materials for catalyzing Fe(Ⅵ)to degrade SMX was investigated.The results suggest that multi-walled carbon nanotubes(CNTs),multilayer graphene oxide(GO),multilayer graphene(G),nanodiamond(ND),biochar(BC)and acetylene black(AB)all could activate Fe(Ⅵ)to degrade SMX,but the catalytic performance of carbon materials was different.Among the six carbon materials,AB exhibited the most excellent catalytic performance.In the process of six carbon materials catalyzing Fe(Ⅵ)for the degradation of pollutants,the main active oxidants were Fe(Ⅴ)and Fe(Ⅳ).In addition,it was found that the SMX degradation efficiency increased with the increase of Fe(Ⅵ)and AB dosage,decrease solution pH value and SMX initial concentration.Cl-,NO3-,HCO3-had little effect on the degradation efficiency of SMX,while HA could significantly inhibit the degradation efficiency of SMX.Fe(Ⅵ)-AB system also could effectively remove SMX in the actual water background.AB could remarkably accelerate Fe(Ⅵ)for the degradation of SMX mainly due to the C=O function group on the AB surface could interact with Fe(Ⅵ)to generate Fe(V)and Fe(IV),which have higher reactivity and could effectively degrade pollutants.In addition,the selfdecomposition products of Fe(Ⅵ)(i.e.,Fe(Ⅱ),Fe(Ⅲ)and H2O2)could also catalyze Fe(Ⅵ)for degrading SMX.Besides,the oxidation capability of Fe(Ⅵ)-AB system also was higher than Fe(Ⅵ)-Na2SO3 system and Mn(Ⅶ)-AB system.In addition,Fe(Ⅵ)-AB system also effectively degraded other recalcitrant organic pollutants,including 2,4-DCP,PNP,BPS and SIX.AB also exhibited high stability and recyclability for SMX degradation in the Fe(Ⅵ)-AB system.(3)Thirdly,the oxidation performance and mechanism of Fe(Ⅵ)-H2O2 system was investigated.It was found that addition of H2O2 could signally promote Fe(Ⅵ)to oxidize SMX at pH 8.0.Many lines of evidence including scavenging experiments,probe detection and electron paramagnetic resonance(EPR)tests verified that no hydroxyl radical(·OH)and superoxide radical(O2·-)generated in the Fe(Ⅵ)-H2O2 system.The better oxidation performance of Fe(Ⅵ)-H2O2 system was thoroughly attributed to high-valent iron intermediate(Fe(Ⅴ)and Fe(Ⅳ)).By revealing the oxidation properties and reactive species of peroxymonosulfate(PMS)and peroxydisulfate(PDS)for activating Fe(Ⅵ),it was illustrated that peroxides could reduce Fe(Ⅵ)via a two-electron transfer step rather than to form free-radicals.It was found that the degradation efficiency of SMX in the Fe(Ⅵ)-H2O2 system was greatly affected by the solution pH,the dosage of Fe(Ⅵ)and H2O2,and the initial concentration of SMX;Cl-,NO3-,SO42-,HCO3-have little effect on the degradation efficiency of SMX,while EDTA-2Na,NTA-3Na,TSPP and HA could significantly inhibit the degradation efficiency of SMX.Besides,the Fe(Ⅵ)-H2O2 system exhibited satisfactory removal of SMX in authentic water.The Fe(Ⅵ)-H2O2 system could also effectively remove other recalcitrant organic pollutants(i.e.,BPA,2,4-DCP,PNP and CBZ).(4)Fourthly,we also explore the oxidation performance of Fe(Ⅵ)-CaO2 system in the degradation of SMX.CaO2 as an agent which can slow-release H2O2,also could catalyze Fe(Ⅵ)for the degradation of SMX,and the Fe(Ⅴ)and Fe(Ⅳ)were the main active oxidants.The key operating parameters including solution pH,Fe(Ⅵ)dosage,CaO2 dosage and SMX concentration could significantly affect the degradation efficiency of SMX by the Fe(Ⅵ)-CaO2 system;Cl-,NO3-,SO42-,HCO3-,Ca2+ and Mg2+ have little effect on the degradation of SMX by Fe(Ⅵ)-CaO2 system,while HA,EDTA-2Na,NTA-3Na and TSPP could significantly inhibit the degradation of SMX in the Fe(Ⅵ)-CaO2 system.The oxidation performance of Fe(Ⅵ)-CaO2 system also was higher than Fe(Ⅵ)-Na2SO3 system,Fe(Ⅵ)-NaHSO3 system and Fe(Ⅵ)Na2S2O3 system.In addition,The Fe(Ⅵ)-H2O2 system exhibited satisfactory removal of SMX in real water.The Fe(Ⅵ)-H2O2 system could also effectively remove other recalcitrant organic pollutants(i.e.,ATZ、SIX、LVF、BPS).(5)Finally,the degradation products of SMX in enhance oxidation Fe(Ⅵ)system(i.e.,Fe(Ⅵ)-H2O2 system)were analyzed by UPLC-QTOF-MS/MS,and eleven intermediates were detected.Based on the detected intermediates,the degradation pathways of SMX were proposed comprehensively.The SMX in Fe(Ⅵ)-H2O2 system was degraded mainly through hydroxylation,aniline oxidation,N-radical coupling and N-S bond cleavage progresses.In this paper,a variety of ferrate(Fe(Ⅵ))oxidation systems were developed and exhibit strong oxidation capabilities to effectively degrade SMX.It put forward new strategies for promoting the practical application of Fe(Ⅵ)oxidation systems. |
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