Efficiency And Mechanism Of Cobalt-based Twodimensional Nanosheets For PMS Degradation Of Phenolic EDCs

Recently,phenolic endocrine disruptors（EDCs）have attracted much attention due to their endocrine disrupting effects.They are widely applied in the manufacturing process of surfactants,plastics,antioxidants,flame retardants,wood treatment agents and organic solvents.Due to conventional wastewater treatment is difficult to achieve the complete removal of phenolic EDCs,the concentration of phenolic EDCs in the water environment is often kept within the detectable range.This not only has an unforeseeable negative impact on the ecological environment,but also poses a potential threat to human reproduction,development,and even nervous and immune systems after entering the human body through various ways such as the food chain.Therefore,the persulfate oxidation method using sulfate radicals as the main active substance in the system,with its successful application in the treatment of organic pollutants in the water environment,can not only provide a redox potential of 2.5～3.1 V and a redox potential of 30～40μs,but also SO₄^·-tends to attack nucleophiles through electron transfer reaction,which also enables it to selectively remove organics.In persulfate oxidation,cobalt-based catalyst is the best among transition metal catalysts,but it still has some problems such as complicated preparation process,poor stability and leakage risk.In view of these problems,this study designed and prepared efficient and stable two-dimensional ultra-thin cobalt-based nanosheets catalyst by combining various modification strategies,and then constructed a green and stable activated persulfate system,and finally realized efficient removal of phenolic EDCs pollutants in water.Firstly,a simple and rapid method for large-scale synthesis of amorphous Co O nanosheets（Co O-A）was designed in this study.Through various characterization analysis,it can be seen that the synergistic effect of the high specific surface area and amorphous structure of Co O-A generates more catalytic reactive sites,thus showing higher catalytic performance.At the same time,the system has a good degradation potential for 4-CP under the p H value of5.0-9.0.EPR and quenching experiments confirmed that SO₄^·-radical was the main ROS removing 4-CP,and^·OH radical contributed little.To further enhance the reliability of the material,two-dimensional ultra-thin porous Co₃O₄ nanosheets were synthesized by wet chemical method and calcination process,and it was determined that the catalyst prepared at 400℃had the best performance,that is,within30 min,the activation of 0.25 m M PMS by 0.05 g/L Co₃O₄ nanosheets degraded 98%of bisphenol A（BPA,10 mg/L）.This is attributed to the abundance of active centers in the two-dimensional porous structure and the strong electrostatic attraction between the PMS and the Co₃O₄ nanosheets.In addition,the degradation efficiency of PMS/Co₃O₄ nanosheets for BPA containing electron-donating groups（namely,-OH and CH₃）is up to 98%,while the degradation efficiency for organics containing electron-absorbing groups（such as-NO₂ and-COOH）is relatively low,and the degradation efficiency for organics with ionization potential over 9.39 eV is less than 20%.This also shows that the system can optimally oxidize the organics with electron-giving groups and low ionization potential.Then,in order to enhance the yield and efficiency,kaolin supported bimetallic oxide Mn Co₂O₄（CK-Mn）was synthesized by hydrothermal method for the first time on the basis of the preparation strategy of two-dimensional ultra-thin porous Co₃O₄ nanosheets.The degradation efficiency of BPA in this system was up to 98%within 15 min,and the metal ion leaching of the material was less.The high removal rate of total organic carbon was attributed to the abundant active sites in the stomatal structure of CK-Mn and the synergistic effect of bimetal and kaolin.In addition,a CK-Mn/PMS coupled ultrafiltration membrane system was constructed to evaluate its practical application value in surface water.The system not only has excellent water production capacity and effluent quality,but also has good performance in removing BPA,turbidity and humus from surface water,which also points to a novel way for the future practical application of PMS-AOP.