Fe₃O₄-based Bimetal Synergistic Heterogeneous Activation PMS For Degradation Of Organic Pollutants

Advanced oxidation technology based on hydroxyl radical（HO?）and sulfate radical（SO₄^-?）has become a hot spot in water treatment,and the development of efficient and stable catalysts have also attracted more attention.In this paper,Fe-Mn and Fe-Cu bimetal catalysts based on Fe₃O₄ were prepared by a simple co-precipitation method.The catalyst was used to activate permonosulfate（PMS）to degrade rhodamine B（Rh B）and p-nitrophenol（PNP）respectively.This subject studied the performance of Fe-Mn and Fe-Cu bimetal catalysts,optimized the experimental conditions for degradation,identified the system free radicals,and explored the mechanism of bimetal synergy and heterogeneous activation mechanism.Fe₃O₄-MnO₂ nanocomposites were prepared by co-precipitation method,and the catalysts were characterized by TEM,XRD,VSM,XPS and Zeta potential.At natural p H,0.3 g/L Fe₃O₄-MnO₂ and 0.3 g/L PMS can completely degrade 20 mg/L Rh B in15min,and the mineralization rate reaches 91%.The system has no leaching of Fe and Mn ions,is an interface reaction,and has good catalytic performance.The catalyst can maintain a degradation rate of 94%after four cycles,and can effectively degrade Rh B in surface water and groundwater,indicating that it has excellent stability and certain practical application potential.The main reason for the p H change of Fe₃O₄-MnO₂/PMS system is the decomposition effect of PMS and the buffer capacity of the catalyst itself.There are SO₄^-?and HO?in the reaction system,both free radicals are present in the first stage（0-5 min）,and only HO?is present in the second stage（5 min～）.Combined with the degradation rate of TOC in different periods,SO₄^-?Contribution is higher.Rhodamine B（Rh B）is mainly mineralized by the deethylation process.There is a double-metal synergy between Fe and Mn.Manganese mainly provides reactive sites,and the presence of iron accelerates the reduction of high-valent manganese to a lower state,thereby further enhancing the redox cycle of the reaction system and providing magnetic properties.The Cu⁰@Fe₃O₄ magnetic core-shell material was also prepared by the co-precipitation method and characterized by TEM,SEM,XRD,VSM,and XPS.At the natural p H value（5.65）,the degradation rate of PNP of 200 mg/L Cu⁰@Fe₃O₄ and 0.5mmol/L PMS can reach 96%within 60min and the leaching of copper ions is almost negligible,which can be considered as the interface reaction.Through the degradation of different pollutants,it was found that the Cu⁰@Fe₃O₄/PMS system has certain degradation selectivity.The core-shell structure of Cu⁰@Fe₃O₄ changes the mechanism of pure Cu⁰ relying on acidic p H to release copper ions in the presence of PMS to generate active free radicals.It no longer follows the rule that the lower the p H value,the higher the degradation rate.In the Cu⁰@Fe₃O₄/PMS system,the coexistence of inorganic ions H2PO4^2-and SO4^2-has an inhibitory effect on the degradation of PNP,and the degree of inhibition is H₂PO₄^2->SO₄^2-,while HCO₃^-and Cl^-have a promotion effect on their degradation,the degree of promotion is HCO3^->Cl^-;The effects of metal ions Ca²⁺and Mg²⁺on the degradation of PNP are very small and can be ignored,Zn²⁺has an inhibitory effect on PNP degradation.Cu⁰@Fe₃O₄/PMS system has two kinds of active free radicals,SO₄^-?and HO?,which contribute 34%and 60%to the reaction system,so HO?is the dominant free radical.A bimetallic synergy exists between Fe and Cu,the presence of Cu（I）can promote the reduction of Fe（II）,thereby forming a good redox cycle and improving the durability of the reaction system.