Preparation And Mechanism Studies Of The Iron-based Composites Fenton Catalysts

Recently,iron-based materials used as Fenton catalysts have been widely employed in many fields such as environmental remediation and engineering applications.However,some artificial iron-based materials are difficult to scale up in practice due to the high cost and serious environmental pollution during its preparation process.By comparison,natural iron-based minerals are not only cheap and accessible but also have great potential for the degradation of organic pollutants.The previous works about pure iron-based materials were mainly focused on improving Fenton performance by regulating its crystal facet and synthesis methods,while less attention has been drawn to the influence mechanism of other associated components on the formation,transformation,and oxidation properties of iron-based minerals.Therefore,this thesis is aiming for demonstrating the influence mechanism of iron-based minerals on the Fenton system,such as the existing state（Chapter 2）,form transformation（Chapter 3）,and associated minerals（Chapter 4 and 5）.Based on the above purpose,this study conducts the following four aspects:（1）Effect of the existing state ofβ-FeOOH on the Palygorskite（PAL）in the Fenton system.The effects of Polydopamine（PDA）on the formation ofβ-FeOOH on palygorskite（PAL）and the degradation efficiency of metronidazole（MTZ）were investigated.The results confirmed that the introduction of PDA significantly improved the Fenton efficiency ofβ-FeOOH,and the degradation efficiency of MTZ increased by more than 4 times.·OH was confirmed to be the only reactive oxygen species by electron spin resonance（ESR）and·OH quenching experiments.Furthermore,the PDA biomineralizedβ-FeOOH has a faster surface Fe³⁺/Fe²⁺cycling rate by measuring the surface Fe²⁺/Fe³⁺ratio.Finally,acute toxicity tests and LC-MS demonstrated that PDA would not produce secondary pollution and biological toxicity.In conclusion,this Chapter confirmed that PDA had a significant effect on the formation and catalytic effect ofβ-FeOOH.（2）Mechanism of the form transformation ofβ-FeOOH on its Fenton properties.H-β-FeOOH/PAL composites were calcined at high temperatures to simulate the high-temperature conversion process of iron matrix composites.The effects of different calcination temperatures and Fe/C ratio onβ-FeOOH conversion and oxytetracycline（OTC）degradation efficiency were investigated.The results proved that catalysts with different phases and structures could be formed at different temperatures and Fe/C ratio.XRD,XPS,TEM,and other techniques were used to analyze the catalysts after high-temperature treatment.The results showed that H-β-FeOOH/PAL was transformed into Fe₃C@PAL structure at 750℃with a Fe/C ratio of 1:2.The determination of surface Fe²⁺proved that the surface Fe³⁺/Fe²⁺cycle efficiency of Fe₃C@PAL increased by 4.2%.The degradation experiments of OTC confirmed that the form transformation ofβ-FeOOH changed the decomposition path of H₂O₂,and most of the H₂O₂was decomposed into O₂.The results showed that the form transformation（β-FeOOH?Fe₃C）improved the Fe³⁺/Fe²⁺cycling efficiency on the catalyst surface and changes the decomposition path of H₂O₂,and 90%of the H₂O₂is decomposed into O₂through the surface oxygen defect mechanism.（3）The effects of associated minerals（Fe₃S₄）on the Fenton properties ofβ-FeOOH.In this chapter,β-FeOOH was modified by surface vulcanization and MTZ was taken as the target pollutant to explore the influence of surface vulcanization onβ-FeOOH and its Fenton effect and reaction mechanism during the transformation process.It was confirmed that surface vulcanization could significantly enhance the degradation capacity ofβ-FeOOH,and the degradation rate of MTZ was increased by40 times.The more existence of active SO₄^·-radicals in Fe₃S₄/β-FeOOH-H₂O₂system was confirmed by ESR and free radical quenching experiments,while O₂^·-/·O₂H was almost not observed.A new reaction mechanism was proposed in which the reduction of active Fe²⁺involved in the·OH formation was accomplished by S^2-,S⁰,and S_n^2-rather than by the Haber-Weiss mechanism(Fe³⁺+H₂O₂?Fe²⁺+·OOH+H⁺).In conclusion,the formation mechanism of PMS and SO₄^·-in the oxidation process was proposed by the ABTS method.（4）Influence mechanism of iron（hydrogen）oxide in natural Mackinawite on Fenton properties.Based on the discussion about the formation and transformation process of iron-based minerals and their influence on Fenton performance from Chapters 2 to 4,natural iron-based minerals（Mackinawite,Fe S）were selected as the research object in this chapter to explore the influence mechanism of iron oxide in Fe S on electron transfer at the oxidation interface of Fe S.Natural Fe S was characterized by Transmission electron microscope（TEM）,X-ray diffraction（XRD）and Mossbauer spectroscopy,and X-ray photoelectron spectroscopy（XPS）.The results showed that about 40%of Fe S was oxidized to iron（hydrogen）oxide.Comparing the oxidation efficiency of pure Fe S with natural Fe S on p-nitrobenzene powder（PNP）,the effect of iron（hydrogen）oxide on Fenton performance of Fe S was investigated.The experimental results revealed that the iron（hydrogen）oxides generated after natural oxidation participate in the Fenton reaction of Fe S and enhance Fenton activity of Fe S through interfacial electron transfer,and the degradation efficiency of PNP was increased by 21%.The electron transfer effect of iron（hydrogen）oxide in the degradation of PNP by Fe S was elucidated.