Cobalt Ferrite Bimetallic Catalysts For Organic Pollutants Degradation Via Peroxymonosulfate Activation

Persulfate-based advanced oxidation process has attracted more attention owing to the advantages of simple operation,wide pH range of adaption and strong oxidation capacity.In this dissertation,the methods of PS activation were reviewed,besides,the progress of radical and non-radical pathway in PS activation was emphasized.To solve the problems of limited active sites,single degradation pathway and the high dissolution of Co ion in bimetallic catalysts,nitrogen and phosphorus co-doped cobalt ferrite with rich oxygen vacancy and nitrogen doped carbon coated cobalt ferrite nanoparticles with double sites were prepared for activating PS to degrade organic pollutants.The performance and mechanism of organic pollutants degradation via PS activation by bimetallic catalysts were systematically analyzed,and the mechanism of PS activation on different active sites was investigated.Moreover,structure-activity relationship and performance were clarified.The current results provide a new insight for the development of bimetallic catalysts and the regulation of PS activation pathways.The main innovations and conclusions of this study are as follows:（1）Oxygen vacancy-enriched N/P co-doped CoFe₂O₄（NPCFO-x）were synthesized using ionic liquid as N and P sources,which exhibited excellent catalytic performance in activating PMS to degrade organic pollutants,besides,the reaction mechanism and structure-activity relationship were further investigated.Oxygen vacancy could be effectively introduced into CoFe₂O₄by N/P co-doped,improving the catalytic capacity of CoFe₂O₄.In terms of PMS activation to degrade 4-CP,NPCFO-700 exhibited the higher catalytic capacity than pristine CFO,which could completely remove 4-CP in 30 min.Electron paramagnetic resonance and quenching experiments showed that radicals(·OH and SO₄^·-)and non-radicals（¹O₂）co-existed in the NPCFO-700/PMS system.Oxygen vacancy played a dual role in the PMS activation.On the one hand,it could accelerate the redox cycle of M²⁺/M³⁺（M=Co/Fe）for the generation of radical.On the other hand,oxygen vacancy could induce the generation of ¹O₂by PMS adsorption and successive capture.In addition,the contribution of radical and non-radical to 4-CP degradation was strongly depended on solution pH,radical was the major ROS in 4-CP degradation under acid and alkaline condition,while ¹O₂was involved in the degradation of 4-CP under neutral condition.The NPCFO-700/PMS system was highly resistant to background substances（eg.Cl^-、NO₃^-、HCO₃^-and HA）,and even,Cl^-and HCO₃^-exhibited certain facilitating effect on4-CP degradation.（2）Cobalt iron nanoparticles coated by nitrogen-doped carbon with different metal contents were synthesized by using metal-organic framework as precursors.The Me-Nx site and CoFe alloy were identified as the main active sites for the catalysts,and the mechanism of PS activation by different active sites in the materials was also revealed.The morphology and magnetic properties of catalysts were regulated by the control of metal content in the metal-organic framework,besides,the types of metal active sites were also adjusted.CoFe@NC-2 showed excellent performance in PMS activation to degrade PN,in which 98%phenol could be removed in 15 min,exhibited the higher catalytic capacity than CoFe-NC.EPR,electrochemical experiments,quenching test and the high valance metal capture experiments suggested that the high valance metal and singlet oxygen were main ROS in this system.CoFe-Nx site could catalyze PMS to produce the CoFe=O to degrade organic pollutants via PMS activation,and CoFe alloy could transfer elector to the lattice of carbon by M-O-C/M-N-C bond,which could directly catalyze PMS to produce ¹O₂to degrade organic pollutants.Moreover,this system exhibited great anti-interference performance owing to the non-radical pathway,so it had great application potential in real water.