Preparation Of β-FeOOH@MnO₂ Core-Shell Structure Catalyst And Its Catalytic Degradation Mechanism Of Methylene Blue

Water resources are vital to human development and progress.In recent years,with the rapid development of urbanization and the improvement of people’s living standards,synthetic dyes have been commonly used in daily life,industrial manufacturing and other fields.However,most dyes are soluble in water,and the direct discharge of dye wastewater makes water bodies far beyond their self-purification capacity,leading to serious pollution and endangering human health.Advanced oxidation methods（AOPs）based on sulfate radicals are considered as an effective means of decomposing refractory organic matter due to their high oxidation capacity.Peroxymonosulfate（PMS）activation generates SO₄^·-a conventional method with high energy consumption,metal leaching,secondary pollution,etc.Therefore,it is crucial to design and study a new catalyst that can activate peroxymonosulfate（PMS）and treat organic wastewater efficiently under relatively mild and favorable environmental conditions.On this basis,ellipsoidalβ-FeOOH@MnO₂ core-shell catalysts were prepared in this thesis,and the performance and mechanism of the composite catalysts to activate peroxymonosulfate（PMS）for the degradation of methylene blue（MB）were investigated.The main contents and conclusions of the study are.（1）In this study,ellipsoidalβ-FeOOH@MnO₂ core-shell structure catalysts withβ-FeOOH as the core and low crystallinity MnO₂ nanosheets as the shell were synthesized by a two-step precipitation and hydrothermal method.The catalysts were characterized by X-ray powder diffractometer（XRD）,scanning electron microscope（SEM）,transmission electron microscope,high-resolution transmission electron microscopy（TEM and HRTEM）,X-ray photoelectron spectroscopy（XPS）and Brunauer–Emmett–Teller（BET）,and the catalytic oxidation performance ofβ-FeOOH@MnO₂ core-shell catalysts for methylene blue was investigated.The results showed that theβ-FeOOH@MnO₂ core-shell catalyst was successfully prepared,and theβ-FeOOH@MnO₂ core-shell catalyst showed an ellipsoidal core-shell structure similar to that of corn coating,and the low crystallinity MnO₂nanosheets were wrapped around the ellipsoidalβ-FeOOH surface.Theβ-FeOOH@MnO₂ core-shell catalyst prepared by precipitation-hydrothermal method has a large specific surface area(145.5 m² g^-1),thus exhibiting high performance in peroxymonosulfate（PMS）activation and methylene blue（MB）degradation.With its activation,the degradation rate of methylene blue（MB）was close to 99%within 60min.（2）Ellipsoidalβ-FeOOH@MnO₂ core-shell catalysts with different hydrothermal times,different hydrothermal temperatures and different Fe-Mn ratios were prepared by the same method described above,and the performance of the catalysts prepared under different synthesis conditions for the activation of peroxymonosulfate（PMS）for the degradation of methylene blue（MB）was investigated.The results showed that the preparedβ-FeOOH@MnO₂ core-shell catalysts under different conditions showed ellipsoidal morphology,and all of them exhibited good peroxymonosulfate（PMS）activation and methylene blue（MB）oxidative degradation performance.In addition,the ellipsoidalβ-FeOOH@MnO₂core-shell structure catalysts prepared at a hydrothermal time of 6 h,a hydrothermal temperature of 110°C,and an Fe:Mn of 4:3 were the most effective in activating peroxymonosulfate（PMS）to degrade methylene blue（MB）.（3）In this study,theβ-FeOOH@MnO₂ core-shell catalysts prepared at a hydrothermal time of 6 h,a hydrothermal temperature of 110℃and an Fe:Mn of 4:3were characterized by UV-visible spectroscopy（UV-vis）,liquid chromatography-mass spectrometry（LC-MS）,Fourier infrared spectroscopy（FT-IR）and X-ray photoelectron spectroscopy（XPS）,as well as free radical quenching.The degradation mechanism during the activation of peroxymonosulfate（PMS）degradation byβ-FeOOH@MnO₂ core-shell catalyst was analyzed in detail,and the possible methylene blue（MB）degradation pathways were given.It was shown that the synthesizedβ-FeOOH@MnO₂ core-shell catalyst itself has some adsorption and oxidation ability for methylene blue（MB）,and the catalyst exhibited better catalytic activity thanβ-FeOOH in activating peroxymonosulfate（PMS）to degrade methylene blue（MB）.This is due to the redox processes of Fe³⁺/Fe²⁺and Mn⁴⁺/Mn³⁺,and the synergistic effect of ¹O₂,O₂^·-,·OH and SO₄^·-generated by the catalyst activation of peroxymonosulfate（PMS）on the rapid degradation of methylene blue（MB）.More importantly,¹O₂ plays a dominant role in theβ-FeOOH@MnO₂/PMS/MB system.In addition,the catalytic degradation of methylene blue（MB）by the catalyst could still be maintained above 98%after four repeated catalytic experiments,which provides a basis for the application of the composite catalyst in practice.In summary,ellipsoidalβ-FeOOH@MnO₂ core-shell catalyst has great potential for the oxidative treatment of organic pollutants in industrial wastewater and sewage.In this thesis,an easy-to-operate and low-cost method is provided for the preparation of ellipsoidalβ-FeOOH@MnO₂ composite catalysts with core-shell structure.It also gives a more detailed mechanism for the methylene blue（MB）degradation process.