Activation Of Peroxymonosulfate By Silver Doped Metal Oxides For Degradation Of PPCPs In Water:Performances And Mechanisms

With the rapid development of medical treatment,animal husbandry and other fields,a large number of pharmaceuticals and personal care products（PPCPs）continue to enter the water environment.However,the traditional water treatment technology is difficult to effectively remove such refractory pollutants.Peroxymonosulfate（PMS）activation is a new advanced oxidation technology.Sulfate radical(SO₄^·-)produced by activating PMS can effectively degrade PPCPs in water.Metal oxides are the most widely used catalysts in PMS activators.Nevertheless,the performance of metal oxides in PMS activation is not ideal yet.In this paper,silver doping is used to increase the active sites of metal oxides,enhance the conductivity of materials,and then improve the activation performance of metal oxides,in order to provide more theoretical reference and application guidance for advanced oxidation technology based on PMS.In this paper,Ag-Fe₂O₃ and Ag-MnO₂ were prepared by precipitation calcination method and hydrothermal method,respectively.Scanning electron microscope（SEM）,transmission electron microscope（TEM）,X-ray photoelectron spectroscopy（XPS）and nitrogen adsorption-desorption instrument were used to analyze the morphology and structure of the catalyst.The degradation efficiency of sulfamethoxazole（SMX）via PMS activation by two catalysts was studied,and the effects of different factors on the degradation of SMX were systematically investigated.The activation mechanism was studied by free radical quenching experiment,XPS and electron spin resonance spectroscopy（EPR）.Finally,the degradation products and pathways were analyzed by the liquid chromatography-mass spectrometry（LC-MS）.The main conclusions are as follows:（1）Ag-Fe₂O₃ is distributed in a uniform needle shape and the specific surface area was81.8 m²·g^-1;Ag on the surface of the catalyst mainly existed in the form of Ag⁰ and Ag⁺.The degradation rate of SMX by Ag-Fe₂O₃ is 1.9 times ofα-Fe₂O₃.The degradation efficiency is the highest when the p H value of the system is 9.0.Quenching experiment and EPR test show that the main active species degrading SMX in Ag-Fe₂O₃/PMS system are SO₄^·-,O₂^·-and ¹O₂.On the one hand,silver doping can provide more active sites for the catalyst.On the other hand,it can improve the conductivity of the catalyst,accelerate the redox cycle of Fe³⁺/Fe²⁺and Ag⁺/Ag⁰,promote the generation of active species.After Ag-Fe₂O₃ was reused 3 times,the removal rate of SMX activated by PMS decreased by 47%.（2）Ag-MnO₂ has a spherical structure with specific surface area of 103.0 m²·g^-1.Ag on the surface of catalyst mainly existed in the form of Ag⁰ and Ag⁺.The degradation rate of SMX by Ag-MnO₂ is 9.7 times ofα-MnO₂.The degradation efficiency is the highest when the p H value of the system is 5.0.Quenching experiment and EPR test show that the main active species degrading SMX in Ag-MnO₂/PMS system are·OH、SO₄^·-、O₂^·-and ¹O₂.Silver doping also enriches the active sites and accelerates the redox cycle of Mn³⁺/Mn⁴⁺and Ag⁺/Ag⁰.After Ag-MnO₂ was reused 5 times,the removal rate of SMX activated by PMS decreased by 38%.