Study On Degradation Performance And Mechanism Of Organic Pollutants Enhanced By Iron-based Compound Activated Persulfate Coupled Low-temperaturbe Plasma

Resource shortage and environmental pollution issues having restricted the sustainable development of China.Particularly,the problems of groundwater and soil pollution have become more and more serious as the process of urbanization proceeds.Driven by national policies,the groundwater and soil prevention and control industries have been developed rapidly whilst still lacks of technological innovations in groundwater and soil remediation toward high-quality development of the society.A wide variety of refractory organics,such as organic dyes,phenols and nitrochlorobenzene from printing and dyeing,medicine,petroleum and chemical industries have the characteristics of high toxicity,strong stability,difficult biodegradation and strong enrichment.These organic pollutants can seriously endanger the health of human beings and the ecological environment through various ways of migration and transformation.Recently,novel advanced oxidation technology based on sulfate radical(SO₄^·-)and low-temperature plasma has attracted more and more attention due to their high efficiency in degrading organics,fast reaction rate,and less secondary pollution.In this regard,to make full and effective use of their technical advantages,enhance the generation of active species,improve the degradation efficiency and total organic carbon（TOC）removal rate of refractory organic pollutants,and construct an efficient and stable refractory organic pollutant removal system,seems a good strategy to solve the problem of soil and water organic pollution.First,waste sulfonated polystyrene resin was used as a template,an in-situ ion exchange-calcination method was developed to prepare hollowα-Fe₂O₃microspheres（MS-Fe₂O₃）with higher catalytic activity and better stability than traditional iron oxide activated persulfate（PS）.The influences of main parameters（activator dosage,PS concentration,reaction temperature,initial p H,etc）on the degradation performance of typical dye organics in MS-Fe₂O₃activated PS system were investigated,based on which the structure-activity relationship between activator structure,physicochemical properties and activation performance was proposed,and the reaction mechanism of MS-Fe₂O₃activated PS to produce active free radicals was revealed.Moreover,through free radicals(SO₄^·-and·OH)mediated Rh B degradation intermediate products to deduce the possible reaction pathways of Rh B degradation in MS-Fe₂O₃/PS system.Next,in order to further reduce the loss of active components of activator and stabilize the cycle of Fe²⁺/Fe³⁺redox pairs,and thereby improve the degradation efficiency and TOC removal rate of refractory organic pollutants,core-shell Fe₂O₃-Co Fe₂O₄hybrid microspheres with rich oxygen vacancies were prepared by cobalt ion doping and directional design,and a heterogeneous Fenton-like catalytic system（Fe₂O₃-Co Fe₂O₄/PMS）was constructed.The degradation performance of various reaction systems to target pollutants（Rh B,phenol,p-chlorophenol and p-nitrochlorobenzene）was investigated,and the recyclability and structural stability of the activator Fe₂O₃-Co Fe₂O₄were explored.Through quenching experiment,EPR and electrochemical characteristics test,it was determined that there were four reactive oxygen species(SO₄^·-,·OH,O₂^·-,¹O₂)and electron transfer in Fe₂O₃-Co Fe₂O₄/PMS system,in which surface SO₄^·-played a dominant role.Combined with the calculation results of density functional theory（DFT）,the formation mechanism of reactive oxygen species（ROS）in the process of Fe₂O₃-Co Fe₂O₄activated PMS reaction was revealed from both aspects of bulk reaction and interface reaction.It was confirmed that the oxygen vacancy electron transfer process played an vital role in the formation of O₂^·-/¹O₂and the redox cycle of M²⁺/M³⁺（M:Fe,CO）,and trace metal ions could promote the activation of PMS to produce ROS.Further,in order to enhance the mineralization efficiency of refractory organics and reduce/avoid the use of oxidants,low-temperature plasma technology is also introduced.By using a self-designed,homemade"cross"underwater arc discharge plasma device,the effects of main discharge parameters（discharge atmosphere,discharge power,flow rate,different discharge systems,etc.）on the generation of active species were investigated.The role of microbubbles in promoting the internal circulation of main reaction liquid,mass transfer of active species and the generation and transmission of active species were explored.The synergistic effects and mechanisms of low-temperature plasma coupled activator-oxidant degradation of refractory organic pollutants（phenol,p-chlorophenol and p-nitrochlorobenzene）were revealed.The ion morphology and main reaction products in the reaction system were explored,based on which the possible degradation pathways of target pollutants and the reaction mechanism of active species were proposed.Finally,an integrated and optimized system（plasma/PMS/Fe₂O₃-Co Fe₂O₄）was developed and applied to the organic polluted soil environment.Typically,the disc-type dielectric barrier discharge plasma（DBDP）generator was designed and built,and the typical representatives of refractory organic pollutants（phenol,p-chlorophenol and p-nitrochlorobenzene）were selected as the modeling compounds to explore the degradation performance of DBDP/Fe₂O₃-Co Fe₂O₄/PMS system in simulated soil（the concentrations of phenol,p-chlorophenol and p-nitrochlorobenzene in simulated polluted soil were 500 mg/kg）and the effects of main factors（soil p H,natural organic matter（HA）,surfactant TW80,etc）on the degradation performance of the reaction system.On this basis,the main components of the collected actual organic polluted soil were analyzed by GC-MS and UHPLC-MS,and the degradation performance of DBDP/Fe₂O₃-Co Fe₂O₄/PMS system for organic pollutants in the actual polluted soil was explored,so as to explore the practical application potential of the research system.An efficient removal methodology for refractory organic pollutants in water and soil environment was developed,which provides theoretical inspirations for development of future technologies for remediation of actual organic pollution sites.