Enhanced Removal Performance Of Fe₃O₄-based Magnetic Materials For Pollutants In Water With Magnetic Field And Its Mechanism

The highly efficient degradation of pollutants in water can be achieved by coupling of magnetic materials’induced magnetic field generated by under applied magnetic field and paramagnetic particles,with the characteristics of simple,safe,cheap,green and eco-friendly.In this thesis,three kinds of Fe₃O₄-based magnetic composites prepared with Fe₃O₄ as catalyst or carrier were applied to Fenton-like degradation of tetracycline hydrochloride（TCH）,photocatalytic reduction of Cr（Ⅵ）and adsorption of Co（Ⅱ）respectively.The enhancement effect and mechanism of magnetic field on of Fe₃O₄-based magnetic materials were investigated.By delving into the mechanism of enhancing magnetic material performance under applied magnetic field,the impacts of magnetic field on reaction process involving paramagnetic particles and pollutant removal performance were revealed.This study is helpful to make full use of synergies between magnetic materials and applied magnetic field,which can provide references for the research on magnetic material design,synthesis and application under external magnetic field.It has important research value and broad application prospects.The main research contents of this thesis are as follows:（1）Enhanced performance and mechanism of TCH Fenton-like degradation by nano-Fe₃O₄under magnetic field.Nano-Fe₃O₄ particles were prepared by hydrothermal method and the morphology,structures and properties were characterized by SEM,XRD,VSM and other methods.The Fenton-like removal performance of nano-Fe₃O₄ on TCH（target pollutant）under applied magnetic field was investigated.A possible mechanism for the enhancement of Fenton-like degradation performance assisted by magnetic field was proposed based on the paramagnetism of Fe（II）and·OH.The experimental results show that the nano-Fe₃O₄ particles prepared by hydrothermal method have uniform size distribution of 25 nm and excellent magnetic properties.Under applied magnetic field,nano-Fe₃O₄ showed faster and more efficient degradation towards TCH.The mechanism study indicates that the promoted formation of·OH under magnetic field effectively improved the Fenton-like degradation performance of nano-Fe₃O₄ on TCH.（2）Enhanced performance and mechanism of Cr（Ⅵ）photocatalytic reduction by PoPD@Fe₃O₄under magnetic field.In this part,the loading of poly（o-phenylenediamine）（PoPD）on the surface of nano-Fe₃O₄ was achieved by photopolymerization method.The morphology,structures and properties were characterized by SEM,FTIR,XPS,VSM and other methods.The photocatalytic removal of Cr（Ⅵ）by nano-Fe₃O₄ and PoPD@Fe₃O₄ composites was tested and compared,followed by the investigation of effects that conditions such as applied magnetic field had on the photocatalytic reduction of Cr（Ⅵ）.The results show that the loading of POPD on the surface of nano-Fe₃O₄can promote the photocatalytic reduction of Cr（Ⅵ）,and the photocatalytic removal of Cr（Ⅵ）by PoPD@Fe₃O₄ can be significantly improved with the assistance of weak magnetic field.The experiment verified that Cr（III）could spontaneously migrate to the surface of PoPD@Fe₃O₄under the applied magnetic field.The mechanism of magnetic field enhanced photocatalytic reduction was interpreted as that the movement and adsorption of Cr（III）to the surface of the material under magnetic field reduced the concentration of Cr（III）in the solution,which accelerating the reduction reaction of Cr（Ⅵ）to Cr（III）.（3）Enhanced performance and mechanism of Co（Ⅱ）adsorption removal by CMC@MC under magnetic field.The CMC@MC was obtained by loading Fe₃O₄ on the surface of cotton with polyvinyl pyrrolidoneas（PVP）coupling agent and using sodium carboxymethyl cellulose（CMC）to modify the above material.SEM,BET,VSM and other methods to characterize the morphology,structure and properties of the samples.The improving effect of CMC@MC removal performance on Co（Ⅱ）under external magnetic field was investigated and the mechanism of magnetic field assists was interpreted.The results show that PVP as a coupling agent can achieve a large amount of Fe₃O₄ load on the cotton and CMC can significantly improve the adsorption performance of samples on Co（Ⅱ）.Through the ion migration experiments,the phenomenon that Co（Ⅱ）migrates to the region with stronger magnetic field under the applied magnetic field was verified.The magnetic field can enhance the CMC@MC removal performance on Co（Ⅱ）by may because the CMC@MC surface will produce stronger induced magnetic field in the applied of magnetic field which attract Co（Ⅱ）to migrate directionally toward the surface of materials.This behavior can realize the efficient adsorption performance of CMC@MC on Co（Ⅱ）.